1
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Lipovsek M. Comparative biology of the amniote vestibular utricle. Hear Res 2024; 448:109035. [PMID: 38763033 DOI: 10.1016/j.heares.2024.109035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/31/2024] [Revised: 05/09/2024] [Accepted: 05/13/2024] [Indexed: 05/21/2024]
Abstract
The sensory epithelia of the auditory and vestibular systems of vertebrates have shared developmental and evolutionary histories. However, while the auditory epithelia show great variation across vertebrates, the vestibular sensory epithelia appear seemingly more conserved. An exploration of the current knowledge of the comparative biology of the amniote utricle, a vestibular sensory epithelium that senses linear acceleration, shows interesting instances of variability between birds and mammals. The distribution of sensory hair cell types, the position of the line of hair bundle polarity reversal and the properties of supporting cells show marked differences, likely impacting vestibular function and hair cell regeneration potential.
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Affiliation(s)
- Marcela Lipovsek
- Ear Institute, Faculty of Brain Sciences, University College London, London, UK.
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2
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Goodrich EJ, Deans MR. Emx2 lineage tracing reveals antecedent patterns of planar polarity in the mouse inner ear. Development 2024; 151:dev202425. [PMID: 38804528 DOI: 10.1242/dev.202425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Accepted: 04/18/2024] [Indexed: 05/01/2024]
Abstract
The planar polarized organization of hair cells in the vestibular maculae is unique because these sensory organs contain two groups of cells with oppositely oriented stereociliary bundles that meet at a line of polarity reversal (LPR). EMX2 is a transcription factor expressed by one hair cell group that reverses the orientation of their bundles, thereby forming the LPR. We generated Emx2-CreERt2 transgenic mice for genetic lineage tracing and demonstrate Emx2 expression before hair cell specification when the nascent utricle and saccule constitute a continuous prosensory domain. Precursors labeled by Emx2-CreERt2 at this stage give rise to hair cells located along one side of the LPR in the mature utricle or saccule, indicating that this boundary is first established in the prosensory domain. Consistent with this, Emx2-CreERt2 lineage tracing in Dreher mutants, where the utricle and saccule fail to segregate, labels a continuous field of cells along one side of a fused utriculo-saccular-cochlear organ. These observations reveal that LPR positioning is pre-determined in the developing prosensory domain, and that EMX2 expression defines lineages of hair cells with oppositely oriented stereociliary bundles.
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Affiliation(s)
- Ellison J Goodrich
- Department of Neurobiology, Spencer Fox Eccles School of Medicine at the University of Utah, Salt Lake City, UT 84112, USA
| | - Michael R Deans
- Department of Neurobiology, Spencer Fox Eccles School of Medicine at the University of Utah, Salt Lake City, UT 84112, USA
- Department of Otolaryngology - Head and Neck Surgery, Spencer Fox Eccles School of Medicine at the University of Utah, Salt Lake City, UT 84132, USA
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3
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Moreno JA, Dudchenko O, Feigin CY, Mereby SA, Chen Z, Ramos R, Almet AA, Sen H, Brack BJ, Johnson MR, Li S, Wang W, Gaska JM, Ploss A, Weisz D, Omer AD, Yao W, Colaric Z, Kaur P, Leger JS, Nie Q, Mena A, Flanagan JP, Keller G, Sanger T, Ostrow B, Plikus MV, Kvon EZ, Aiden EL, Mallarino R. Emx2 underlies the development and evolution of marsupial gliding membranes. Nature 2024; 629:127-135. [PMID: 38658750 PMCID: PMC11062917 DOI: 10.1038/s41586-024-07305-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Accepted: 03/13/2024] [Indexed: 04/26/2024]
Abstract
Phenotypic variation among species is a product of evolutionary changes to developmental programs1,2. However, how these changes generate novel morphological traits remains largely unclear. Here we studied the genomic and developmental basis of the mammalian gliding membrane, or patagium-an adaptative trait that has repeatedly evolved in different lineages, including in closely related marsupial species. Through comparative genomic analysis of 15 marsupial genomes, both from gliding and non-gliding species, we find that the Emx2 locus experienced lineage-specific patterns of accelerated cis-regulatory evolution in gliding species. By combining epigenomics, transcriptomics and in-pouch marsupial transgenics, we show that Emx2 is a critical upstream regulator of patagium development. Moreover, we identify different cis-regulatory elements that may be responsible for driving increased Emx2 expression levels in gliding species. Lastly, using mouse functional experiments, we find evidence that Emx2 expression patterns in gliders may have been modified from a pre-existing program found in all mammals. Together, our results suggest that patagia repeatedly originated through a process of convergent genomic evolution, whereby regulation of Emx2 was altered by distinct cis-regulatory elements in independently evolved species. Thus, different regulatory elements targeting the same key developmental gene may constitute an effective strategy by which natural selection has harnessed regulatory evolution in marsupial genomes to generate phenotypic novelty.
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Affiliation(s)
- Jorge A Moreno
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
- Stowers Institute for Medical Research, Kansas City, MO, USA
| | - Olga Dudchenko
- The Center for Genome Architecture, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
- The Center for Theoretical Biological Physics, Rice University, Houston, TX, USA
| | - Charles Y Feigin
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
- School of BioSciences, The University of Melbourne, Parkville, Victoria, Australia
- Department of Environment and Genetics, La Trobe University, Bundoora, Victoria, Australia
| | - Sarah A Mereby
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Zhuoxin Chen
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, USA
| | - Raul Ramos
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, USA
| | - Axel A Almet
- Department of Mathematics, University of California, Irvine, Irvine, CA, USA
- NSF-Simons Center for Multiscale Cell Fate Research, University of California, Irvine, Irvine, CA, USA
| | - Harsha Sen
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Benjamin J Brack
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Matthew R Johnson
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Sha Li
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Wei Wang
- Lewis Sigler Center for Integrative Genomics, Princeton University, Princeton, NJ, USA
| | - Jenna M Gaska
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Alexander Ploss
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - David Weisz
- The Center for Genome Architecture, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Arina D Omer
- The Center for Genome Architecture, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Weijie Yao
- The Center for Genome Architecture, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Zane Colaric
- The Center for Genome Architecture, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Parwinder Kaur
- The University of Western Australia, Crawley, Western Australia, Australia
| | - Judy St Leger
- Cornell University College of Veterinary Medicine, Ithaca, NY, USA
| | - Qing Nie
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, USA
- Department of Mathematics, University of California, Irvine, Irvine, CA, USA
- NSF-Simons Center for Multiscale Cell Fate Research, University of California, Irvine, Irvine, CA, USA
- Center for Complex Biological Systems, University of California, Irvine, Irvine, CA, USA
| | | | | | - Greta Keller
- Department of Biology, Loyola University, Chicago, IL, USA
| | - Thomas Sanger
- Department of Biology, Loyola University, Chicago, IL, USA
| | - Bruce Ostrow
- Department of Biology, Grand Valley State University, Allendale, MI, USA
| | - Maksim V Plikus
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, USA
| | - Evgeny Z Kvon
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, USA
| | - Erez Lieberman Aiden
- The Center for Genome Architecture, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA.
- The Center for Theoretical Biological Physics, Rice University, Houston, TX, USA.
| | - Ricardo Mallarino
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA.
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4
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Jarysta A, Tadenev ALD, Day M, Krawchuk B, Low BE, Wiles MV, Tarchini B. Inhibitory G proteins play multiple roles to polarize sensory hair cell morphogenesis. eLife 2024; 12:RP88186. [PMID: 38651641 PMCID: PMC11037916 DOI: 10.7554/elife.88186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2024] Open
Abstract
Inhibitory G alpha (GNAI or Gαi) proteins are critical for the polarized morphogenesis of sensory hair cells and for hearing. The extent and nature of their actual contributions remains unclear, however, as previous studies did not investigate all GNAI proteins and included non-physiological approaches. Pertussis toxin can downregulate functionally redundant GNAI1, GNAI2, GNAI3, and GNAO proteins, but may also induce unrelated defects. Here, we directly and systematically determine the role(s) of each individual GNAI protein in mouse auditory hair cells. GNAI2 and GNAI3 are similarly polarized at the hair cell apex with their binding partner G protein signaling modulator 2 (GPSM2), whereas GNAI1 and GNAO are not detected. In Gnai3 mutants, GNAI2 progressively fails to fully occupy the sub-cellular compartments where GNAI3 is missing. In contrast, GNAI3 can fully compensate for the loss of GNAI2 and is essential for hair bundle morphogenesis and auditory function. Simultaneous inactivation of Gnai2 and Gnai3 recapitulates for the first time two distinct types of defects only observed so far with pertussis toxin: (1) a delay or failure of the basal body to migrate off-center in prospective hair cells, and (2) a reversal in the orientation of some hair cell types. We conclude that GNAI proteins are critical for hair cells to break planar symmetry and to orient properly before GNAI2/3 regulate hair bundle morphogenesis with GPSM2.
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Affiliation(s)
| | | | - Matthew Day
- The Jackson LaboratoryBar HarborUnited States
| | | | | | | | - Basile Tarchini
- The Jackson LaboratoryBar HarborUnited States
- Tufts University School of MedicineBostonUnited States
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5
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Beaulieu MO, Thomas ED, Raible DW. Transdifferentiation is uncoupled from progenitor pool expansion during hair cell regeneration in the zebrafish inner ear. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.09.588777. [PMID: 38645220 PMCID: PMC11030336 DOI: 10.1101/2024.04.09.588777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
Death of mechanosensory hair cells in the inner ear is a common cause of auditory and vestibular impairment in mammals, which have a limited ability to regrow these cells after damage. In contrast, non-mammalian vertebrates including zebrafish can robustly regenerate hair cells following severe organ damage. The zebrafish inner ear provides an understudied model system for understanding hair cell regeneration in organs that are highly conserved with their mammalian counterparts. Here we quantitatively examine hair cell addition during growth and regeneration of the larval zebrafish inner ear. We used a genetically encoded ablation method to induce hair cell death and observed gradual regeneration with correct spatial patterning over two weeks following ablation. Supporting cells, which surround and are a source of new hair cells, divide in response to hair cell ablation, expanding the possible progenitor pool. In parallel, nascent hair cells arise from direct transdifferentiation of progenitor pool cells uncoupled from progenitor division. These findings reveal a previously unrecognized mechanism of hair cell regeneration with implications for how hair cells may be encouraged to regenerate in the mammalian ear.
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Affiliation(s)
- Marielle O. Beaulieu
- Molecular and Cellular Biology Graduate Program, Seattle, WA
- Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology - Head and Neck Surgery, Seattle, WA
| | - Eric D. Thomas
- Neuroscience Graduate Program, Seattle, WA
- Department of Biological Structure University of Washington, Seattle, WA
| | - David W. Raible
- Molecular and Cellular Biology Graduate Program, Seattle, WA
- Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology - Head and Neck Surgery, Seattle, WA
- Neuroscience Graduate Program, Seattle, WA
- Department of Biological Structure University of Washington, Seattle, WA
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6
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Ratzan EM, Lee J, Madison MA, Zhu H, Zhou W, Géléoc GSG, Holt JR. TMC function, dysfunction, and restoration in mouse vestibular organs. Front Neurol 2024; 15:1356614. [PMID: 38638308 PMCID: PMC11024474 DOI: 10.3389/fneur.2024.1356614] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Accepted: 03/18/2024] [Indexed: 04/20/2024] Open
Abstract
Tmc1 and Tmc2 are essential pore-forming subunits of mechanosensory transduction channels localized to the tips of stereovilli in auditory and vestibular hair cells of the inner ear. To investigate expression and function of Tmc1 and Tmc2 in vestibular organs, we used quantitative polymerase chain reaction (qPCR), fluorescence in situ hybridization - hairpin chain reaction (FISH-HCR), immunostaining, FM1-43 uptake and we measured vestibular evoked potentials (VsEPs) and vestibular ocular reflexes (VORs). We found that Tmc1 and Tmc2 showed dynamic developmental changes, differences in regional expression patterns, and overall expression levels which differed between the utricle and saccule. These underlying changes contributed to unanticipated phenotypic loss of VsEPs and VORs in Tmc1 KO mice. In contrast, Tmc2 KO mice retained VsEPs despite the loss of the calcium buffering protein calretinin, a characteristic biomarker of mature striolar calyx-only afferents. Lastly, we found that neonatal Tmc1 gene replacement therapy is sufficient to restore VsEP in Tmc1 KO mice for up to six months post-injection.
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Affiliation(s)
- Evan M. Ratzan
- Department of Otolaryngology, F.M. Kirby Neurobiology Center, Boston Children’s Hospital and Harvard Medical School, Boston, MA, United States
| | - John Lee
- Department of Otolaryngology, F.M. Kirby Neurobiology Center, Boston Children’s Hospital and Harvard Medical School, Boston, MA, United States
| | - Margot A. Madison
- Department of Otolaryngology, F.M. Kirby Neurobiology Center, Boston Children’s Hospital and Harvard Medical School, Boston, MA, United States
| | - Hong Zhu
- Department of Otolaryngology - Head and Neck Surgery, University of Mississippi Medical Center, Jackson, MS, United States
| | - Wu Zhou
- Department of Otolaryngology - Head and Neck Surgery, University of Mississippi Medical Center, Jackson, MS, United States
| | - Gwenaëlle S. G. Géléoc
- Department of Otolaryngology, F.M. Kirby Neurobiology Center, Boston Children’s Hospital and Harvard Medical School, Boston, MA, United States
| | - Jeffrey R. Holt
- Department of Otolaryngology, F.M. Kirby Neurobiology Center, Boston Children’s Hospital and Harvard Medical School, Boston, MA, United States
- Department of Neurology, Boston Children’s Hospital and Harvard Medical School, Boston, MA, United States
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7
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Jukic A, Lei Z, Cebul ER, Pinter K, Mosqueda N, David S, Tarchini B, Kindt K. Presynaptic Nrxn3 is essential for ribbon-synapse assembly in hair cells. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.14.580267. [PMID: 38410471 PMCID: PMC10896334 DOI: 10.1101/2024.02.14.580267] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/28/2024]
Abstract
Hair cells of the inner ear rely on specialized ribbon synapses to transmit sensory information to the central nervous system. The molecules required to assemble these synapses are not fully understood. We show that Nrxn3, a presynaptic adhesion molecule, is critical for ribbon-synapse assembly in hair cells. In both mouse and zebrafish models, loss of Nrxn3 results in significantly fewer intact ribbon synapses. In zebrafish we demonstrate that a 60% loss of synapses in nrxn3 mutants dramatically reduces both presynaptic responses in hair cells and postsynaptic responses in afferent neurons. Despite a reduction in synapse function in this model, we find no deficits in the acoustic startle response, a behavior reliant on these synapses. Overall, this work demonstrates that Nrxn3 is a critical and conserved molecule required to assemble ribbon synapses. Understanding how ribbon synapses assemble is a key step towards generating novel therapies to treat forms of age-related and noise-induced hearing loss that occur due to loss of ribbon synapses.
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Affiliation(s)
- Alma Jukic
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, Bethesda, MD, 20892, USA
| | - Zhengchang Lei
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, Bethesda, MD, 20892, USA
| | - Elizabeth R Cebul
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, Bethesda, MD, 20892, USA
| | - Katherine Pinter
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, Bethesda, MD, 20892, USA
| | - Natalie Mosqueda
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, Bethesda, MD, 20892, USA
| | - Sandeep David
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, Bethesda, MD, 20892, USA
| | | | - Katie Kindt
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, Bethesda, MD, 20892, USA
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8
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Hewitt MN, Cruz IA, Raible DW. Spherical harmonics analysis reveals cell shape-fate relationships in zebrafish lateral line neuromasts. Development 2024; 151:dev202251. [PMID: 38276966 PMCID: PMC10905750 DOI: 10.1242/dev.202251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Accepted: 12/28/2023] [Indexed: 01/16/2024]
Abstract
Cell shape is a powerful readout of cell state, fate and function. We describe a custom workflow to perform semi-automated, 3D cell and nucleus segmentation, and spherical harmonics and principal components analysis to distill cell and nuclear shape variation into discrete biologically meaningful parameters. We apply these methods to analyze shape in the neuromast cells of the zebrafish lateral line system, finding that shapes vary with cell location and identity. The distinction between hair cells and support cells accounted for much of the variation, which allowed us to train classifiers to predict cell identity from shape features. Using transgenic markers for support cell subpopulations, we found that subtypes had different shapes from each other. To investigate how loss of a neuromast cell type altered cell shape distributions, we examined atoh1a mutants that lack hair cells. We found that mutant neuromasts lacked the cell shape phenotype associated with hair cells, but did not exhibit a mutant-specific cell shape. Our results demonstrate the utility of using 3D cell shape features to characterize, compare and classify cells in a living developing organism.
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Affiliation(s)
- Madeleine N. Hewitt
- Molecular and Cellular Biology Graduate Program, University of Washington School of Medicine, Seattle, WA 98195, USA
- Department of Otolaryngology-HNS, University of Washington School of Medicine, Seattle, WA 98195, USA
| | - Iván A. Cruz
- Department of Biological Structure, University of Washington School of Medicine, Seattle, WA 98195, USA
| | - David W. Raible
- Molecular and Cellular Biology Graduate Program, University of Washington School of Medicine, Seattle, WA 98195, USA
- Department of Otolaryngology-HNS, University of Washington School of Medicine, Seattle, WA 98195, USA
- Department of Biological Structure, University of Washington School of Medicine, Seattle, WA 98195, USA
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9
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Jarysta A, Tadenev ALD, Day M, Krawchuk B, Low BE, Wiles MV, Tarchini B. Inhibitory G proteins play multiple roles to polarize sensory hair cell morphogenesis. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.05.25.542257. [PMID: 37292807 PMCID: PMC10245865 DOI: 10.1101/2023.05.25.542257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Inhibitory G alpha (GNAI or Gαi) proteins are critical for the polarized morphogenesis of sensory hair cells and for hearing. The extent and nature of their actual contributions remains unclear, however, as previous studies did not investigate all GNAI proteins and included non-physiological approaches. Pertussis toxin can downregulate functionally redundant GNAI1, GNAI2, GNAI3 and GNAO proteins, but may also induce unrelated defects. Here we directly and systematically determine the role(s) of each individual GNAI protein in mouse auditory hair cells. GNAI2 and GNAI3 are similarly polarized at the hair cell apex with their binding partner GPSM2, whereas GNAI1 and GNAO are not detected. In Gnai3 mutants, GNAI2 progressively fails to fully occupy the subcellular compartments where GNAI3 is missing. In contrast, GNAI3 can fully compensate for the loss of GNAI2 and is essential for hair bundle morphogenesis and auditory function. Simultaneous inactivation of Gnai2 and Gnai3 recapitulates for the first time two distinct types of defects only observed so far with pertussis toxin: 1) a delay or failure of the basal body to migrate off-center in prospective hair cells, and 2) a reversal in the orientation of some hair cell types. We conclude that GNAI proteins are critical for hair cells to break planar symmetry and to orient properly before GNAI2/3 regulate hair bundle morphogenesis with GPSM2.
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10
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Li X, Ren M, Gu Y, Zhu T, Zhang Y, Li J, Li C, Wang G, Song L, Bi Z, Liu Z. In situ regeneration of inner hair cells in the damaged cochlea by temporally regulated co-expression of Atoh1 and Tbx2. Development 2023; 150:dev201888. [PMID: 38078650 DOI: 10.1242/dev.201888] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 11/02/2023] [Indexed: 12/18/2023]
Abstract
Cochlear inner hair cells (IHCs) are primary sound receptors, and are therefore a target for developing treatments for hearing impairment. IHC regeneration in vivo has been widely attempted, although not yet in the IHC-damaged cochlea. Moreover, the extent to which new IHCs resemble wild-type IHCs remains unclear, as is the ability of new IHCs to improve hearing. Here, we have developed an in vivo mouse model wherein wild-type IHCs were pre-damaged and nonsensory supporting cells were transformed into IHCs by ectopically expressing Atoh1 transiently and Tbx2 permanently. Notably, the new IHCs expressed the functional marker vGlut3 and presented similar transcriptomic and electrophysiological properties to wild-type IHCs. Furthermore, the formation efficiency and maturity of new IHCs were higher than those previously reported, although marked hearing improvement was not achieved, at least partly due to defective mechanoelectrical transduction (MET) in new IHCs. Thus, we have successfully regenerated new IHCs resembling wild-type IHCs in many respects in the damaged cochlea. Our findings suggest that the defective MET is a critical barrier that prevents the restoration of hearing capacity and should thus facilitate future IHC regeneration studies.
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Affiliation(s)
- Xiang Li
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai 200031, China
| | - Minhui Ren
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai 200031, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yunpeng Gu
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai 200031, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Tong Zhu
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai 200031, China
| | - Yu Zhang
- Department of Otolaryngology-Head and Neck Surgery, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China
- Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China
| | - Jie Li
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai 200031, China
| | - Chao Li
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai 200031, China
| | - Guangqin Wang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai 200031, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Lei Song
- Department of Otolaryngology-Head and Neck Surgery, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China
- Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China
| | - Zhenghong Bi
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai 200031, China
| | - Zhiyong Liu
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai 200031, China
- University of Chinese Academy of Sciences, Beijing 100049, China
- Shanghai Center for Brain Science and Brain-Inspired Intelligence Technology, Shanghai 201210, China
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11
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Liu Z, Bagnall MW. Organization of vestibular circuits for postural control in zebrafish. Curr Opin Neurobiol 2023; 82:102776. [PMID: 37634321 DOI: 10.1016/j.conb.2023.102776] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2023] [Revised: 07/28/2023] [Accepted: 08/01/2023] [Indexed: 08/29/2023]
Abstract
Most animals begin controlling their posture, or orientation with respect to gravity, at an early stage in life. Posture is vital for locomotor function. Even animals like fish, which are capable of swimming upside-down, must actively control their orientation to coordinate behaviors such as capturing prey near the water's surface. Here we review recent research from multiple laboratories investigating the organization and function of the vestibular circuits underlying postural control in zebrafish. Some findings in zebrafish strongly align with prior observations in mammals, reinforcing our understanding of homologies between systems. In other instances, the unique transparency and accessibility of zebrafish has enabled new analyses of several neural circuit components that remain challenging to study in mammalian systems. These new results demonstrate topographical and circuit features in postural control.
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Affiliation(s)
- Zhikai Liu
- Department of Neuroscience, Washington University in St. Louis, 660 S. Euclid Ave., St. Louis MO 63108, USA; Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA. https://twitter.com/zhikai_liu
| | - Martha W Bagnall
- Department of Neuroscience, Washington University in St. Louis, 660 S. Euclid Ave., St. Louis MO 63108, USA.
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12
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Cetera M, Sharan R, Hayward-Lara G, Phillips B, Biswas A, Halley M, Beall E, vonHoldt B, Devenport D. Region-specific reversal of epidermal planar polarity in the rosette fancy mouse. Development 2023; 150:dev202078. [PMID: 37622728 PMCID: PMC10499026 DOI: 10.1242/dev.202078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Accepted: 08/21/2023] [Indexed: 08/26/2023]
Abstract
The planar cell polarity (PCP) pathway collectively orients cells with respect to a body axis. Hair follicles of the murine epidermis provide a striking readout of PCP activity in their uniform alignment across the skin. Here, we characterize, from the molecular to tissue-scale, PCP establishment in the rosette fancy mouse, a natural variant with posterior-specific whorls in its fur, to understand how epidermal polarity is coordinated across the tissue. We find that rosette hair follicles emerge with reversed orientations specifically in the posterior region, creating a mirror image of epidermal polarity. The rosette trait is associated with a missense mutation in the core PCP gene Fzd6, which alters a consensus site for N-linked glycosylation, inhibiting its membrane localization. Unexpectedly, the Fzd6 trafficking defect does not block asymmetric localization of the other PCP proteins. Rather, the normally uniform axis of PCP asymmetry rotates where the PCP-directed cell movements that orient follicles are reversed, suggesting the PCP axis rotates 180°. Collectively, our multiscale analysis of epidermal polarity reveals PCP patterning can be regionally decoupled to produce posterior whorls in the rosette fancy mouse.
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Affiliation(s)
- Maureen Cetera
- Department of Genetics, Cell Biology and Development, University of Minnesota Twin Cities, Minneapolis, MN 55455, USA
| | - Rishabh Sharan
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08540, USA
| | | | - Brooke Phillips
- Department of Molecular Biology, Princeton University, Princeton, NJ 08540, USA
| | - Abhishek Biswas
- Department of Molecular Biology, Princeton University, Princeton, NJ 08540, USA
- Research Computing, Office of Information Technology, Princeton University, Princeton, NJ 08540, USA
| | - Madalene Halley
- Department of Genetics, Cell Biology and Development, University of Minnesota Twin Cities, Minneapolis, MN 55455, USA
| | - Evalyn Beall
- Department of Genetics, Cell Biology and Development, University of Minnesota Twin Cities, Minneapolis, MN 55455, USA
| | - Bridgett vonHoldt
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08540, USA
| | - Danelle Devenport
- Department of Molecular Biology, Princeton University, Princeton, NJ 08540, USA
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13
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Jia S, Ratzan EM, Goodrich EJ, Abrar R, Heiland L, Tarchini B, Deans MR. The dark kinase STK32A regulates hair cell planar polarity opposite of EMX2 in the developing mouse inner ear. eLife 2023; 12:e84910. [PMID: 37144879 PMCID: PMC10202454 DOI: 10.7554/elife.84910] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Accepted: 05/03/2023] [Indexed: 05/06/2023] Open
Abstract
The vestibular maculae of the inner ear contain sensory receptor hair cells that detect linear acceleration and contribute to equilibrioception to coordinate posture and ambulatory movements. These hair cells are divided between two groups, separated by a line of polarity reversal (LPR), with oppositely oriented planar-polarized stereociliary bundles that detect motion in opposite directions. The transcription factor EMX2 is known to establish this planar polarized organization in mouse by regulating the distribution of the transmembrane receptor GPR156 at hair cell boundaries in one group of cells. However, the genes regulated by EMX2 in this context were previously not known. Using mouse as a model, we have identified the serine threonine kinase STK32A as a downstream effector negatively regulated by EMX2. Stk32a is expressed in hair cells on one side of the LPR in a pattern complementary to Emx2 expression in hair cells on the opposite side. Stk32a is necessary to align the intrinsic polarity of the bundle with the core planar cell polarity (PCP) proteins in EMX2-negative regions, and is sufficient to reorient bundles when ectopically expressed in neighboring EMX2-positive regions. We demonstrate that STK32A reinforces LPR formation by regulating the apical localization of GPR156. These observations support a model in which bundle orientation is determined through separate mechanisms in hair cells on opposite sides of the maculae, with EMX2-mediated repression of Stk32a determining the final position of the LPR.
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Affiliation(s)
- Shihai Jia
- Department of Neurobiology, Spencer Fox Eccles School of Medicine at the University of UtahSalt Lake CityUnited States
| | - Evan M Ratzan
- Interdepartmental Program in Neuroscience, Spencer Fox Eccles School of Medicine at the University of UtahSalt Lake CityUnited States
- Departments of Otolaryngology and Neurology, Boston Children’s Hospital and Harvard Medical SchoolBostonUnited States
| | - Ellison J Goodrich
- Department of Neurobiology, Spencer Fox Eccles School of Medicine at the University of UtahSalt Lake CityUnited States
| | - Raisa Abrar
- Department of Neurobiology, Spencer Fox Eccles School of Medicine at the University of UtahSalt Lake CityUnited States
| | - Luke Heiland
- Department of Otolaryngology, Spencer Fox Eccles School of Medicine at the University of UtahSalt Lake CityUnited States
| | - Basile Tarchini
- The Jackson LaboratoryBar HarborUnited States
- Tufts University School of MedicineBostonUnited States
| | - Michael R Deans
- Department of Neurobiology, Spencer Fox Eccles School of Medicine at the University of UtahSalt Lake CityUnited States
- Department of Otolaryngology, Spencer Fox Eccles School of Medicine at the University of UtahSalt Lake CityUnited States
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14
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Baeza-Loya S, Raible DW. Vestibular physiology and function in zebrafish. Front Cell Dev Biol 2023; 11:1172933. [PMID: 37143895 PMCID: PMC10151581 DOI: 10.3389/fcell.2023.1172933] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Accepted: 04/06/2023] [Indexed: 05/06/2023] Open
Abstract
The vestibular system of the inner ear provides information about head motion and spatial orientation relative to gravity to ensure gaze stability, balance, and postural control. Zebrafish, like humans, have five sensory patches per ear that serve as peripheral vestibular organs, with the addition of the lagena and macula neglecta. The zebrafish inner ear can be easily studied due to its accessible location, the transparent tissue of larval fish, and the early development of vestibular behaviors. Thus, zebrafish are an excellent model for studying the development, physiology, and function of the vestibular system. Recent work has made great strides to elucidate vestibular neural circuitry in fish, tracing sensory transmission from receptors in the periphery to central computational circuits driving vestibular reflexes. Here we highlight recent work that illuminates the functional organization of vestibular sensory epithelia, innervating first-order afferent neurons, and second-order neuronal targets in the hindbrain. Using a combination of genetic, anatomical, electrophysiological, and optical techniques, these studies have probed the roles of vestibular sensory signals in fish gaze, postural, and swimming behaviors. We discuss remaining questions in vestibular development and organization that are tractable in the zebrafish model.
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Affiliation(s)
| | - David W. Raible
- Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology-HNS and Biological Structure, University of Washington, Seattle, WA, United States
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15
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Kindig K, Stepanyan R, Kindt KS, McDermott BM. Asymmetric mechanotransduction by hair cells of the zebrafish lateral line. Curr Biol 2023; 33:1295-1307.e3. [PMID: 36905930 DOI: 10.1016/j.cub.2023.02.033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Revised: 11/22/2022] [Accepted: 02/09/2023] [Indexed: 03/12/2023]
Abstract
In the lateral line system, water motion is detected by neuromast organs, fundamental units that are arrayed on a fish's surface. Each neuromast contains hair cells, specialized mechanoreceptors that convert mechanical stimuli, in the form of water movement, into electrical signals. The orientation of hair cells' mechanosensitive structures ensures that the opening of mechanically gated channels is maximal when deflected in a single direction. In each neuromast organ, hair cells have two opposing orientations, enabling bi-directional detection of water movement. Interestingly, Tmc2b and Tmc2a proteins, which constitute the mechanotransduction channels in neuromasts, distribute asymmetrically so that Tmc2a is expressed in hair cells of only one orientation. Here, using both in vivo recording of extracellular potentials and calcium imaging of neuromasts, we demonstrate that hair cells of one orientation have larger mechanosensitive responses. The associated afferent neuron processes that innervate neuromast hair cells faithfully preserve this functional difference. Moreover, Emx2, a transcription factor required for the formation of hair cells with opposing orientations, is necessary to establish this functional asymmetry within neuromasts. Remarkably, loss of Tmc2a does not impact hair cell orientation but abolishes the functional asymmetry as measured by recording extracellular potentials and calcium imaging. Overall, our work indicates that oppositely oriented hair cells within a neuromast employ different proteins to alter mechanotransduction to sense the direction of water motion.
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Affiliation(s)
- Kayla Kindig
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA; Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Ruben Stepanyan
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA; Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
| | - Katie S Kindt
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, Bethesda, MD 20892, USA.
| | - Brian M McDermott
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA; Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA; Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA; Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
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16
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Fritzsch B, Kersigo J, Rejent K, Gherman W, Frank PW, Giovannucci DR, Maklad A. Hair cell morphological patterns and polarity organization in the sea lamprey vestibular cristae. Anat Rec (Hoboken) 2023. [PMID: 36651665 DOI: 10.1002/ar.25164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 12/19/2022] [Accepted: 12/23/2022] [Indexed: 01/19/2023]
Abstract
The inner ear of the sea lamprey was examined by scanning electron microscopy, antibody labeling with tubulin, Myo7a, Spectrin, and Phalloidin stain to elucidate the canal cristae organization and the morphology and polarity of the hair cells. We characterized the hair cell stereocilia bundles and their morphological polarity with respect to the kinocilia. We identified three types of hair cells. In Type 1 hair cells, the kinocilia were slightly longer than the tallest stereocilia. This type was located along the medial bank of the crista and their polarity, based on kinocilia location, was uniformly pointed ampullipetally. Type 2 hair cells that had kinocilia that were much longer than the stereocilia, were most abundant in the central region of the crista. This type of hair cell displayed variable polarity. Type 3 hair cells had extremely long kinocilia (~40-50 μm long) and with extremely short stereocilia. They were mostly located in the lateral zone crista and displayed ampullipetal polarity. Myo7a and tubulin antibodies revealed that hair cells and vestibular afferents are distributed across the canal cristae in the lamprey, covering the area of cruciate eminence; a feature that is absent in more derived vertebrates. Spectrin shows hair cells of varying polarities in the central zone. In this zone, some cells followed the main polarity vector (lateral) like those in medial and lateral zones, whereas other cells displayed polarities that carried up to 40° from the main polarity vector.
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Affiliation(s)
- Bernd Fritzsch
- Department of Biology, College of Liberal Arts and Sciences, University of Iowa, Iowa City, Iowa, USA
| | - Jennifer Kersigo
- Department of Biology, College of Liberal Arts and Sciences, University of Iowa, Iowa City, Iowa, USA
| | - Kassidy Rejent
- Department of Neurosciences, College of Medicine and Life Sciences, University of Toledo, Toledo, Ohio, USA
| | - Wesley Gherman
- Department of Neurosciences, College of Medicine and Life Sciences, University of Toledo, Toledo, Ohio, USA
| | - Patrick W Frank
- Department of Neurosciences, College of Medicine and Life Sciences, University of Toledo, Toledo, Ohio, USA.,Department of Medical Education, College of Medicine and Life Sciences, University of Toledo, Toledo, Ohio, USA
| | - David R Giovannucci
- Department of Neurosciences, College of Medicine and Life Sciences, University of Toledo, Toledo, Ohio, USA.,Department of Medical Education, College of Medicine and Life Sciences, University of Toledo, Toledo, Ohio, USA
| | - Adel Maklad
- Department of Neurosciences, College of Medicine and Life Sciences, University of Toledo, Toledo, Ohio, USA.,Department of Medical Education, College of Medicine and Life Sciences, University of Toledo, Toledo, Ohio, USA
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17
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Tanimoto M, Watakabe I, Higashijima SI. Tiltable objective microscope visualizes selectivity for head motion direction and dynamics in zebrafish vestibular system. Nat Commun 2022; 13:7622. [PMID: 36543769 PMCID: PMC9772181 DOI: 10.1038/s41467-022-35190-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Accepted: 11/16/2022] [Indexed: 12/24/2022] Open
Abstract
Spatio-temporal information about head orientation and movement is fundamental to the sense of balance and motion. Hair cells (HCs) in otolith organs of the vestibular system transduce linear acceleration, including head tilt and vibration. Here, we build a tiltable objective microscope in which an objective lens and specimen tilt together. With in vivo Ca2+ imaging of all utricular HCs and ganglion neurons during 360° static tilt and vibration in pitch and roll axes, we reveal the direction- and static/dynamic stimulus-selective topographic responses in larval zebrafish. We find that head vibration is preferentially received by striolar HCs, whereas static tilt is preferentially transduced by extrastriolar HCs. Spatially ordered direction preference in HCs is consistent with hair-bundle polarity and is preserved in ganglion neurons through topographic innervation. Together, these results demonstrate topographically organized selectivity for direction and dynamics of head orientation/movement in the vestibular periphery.
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Affiliation(s)
- Masashi Tanimoto
- grid.419396.00000 0004 0618 8593Division of Behavioral Neurobiology, National Institute for Basic Biology, Okazaki, Aichi 444-8787 Japan ,grid.250358.90000 0000 9137 6732Neuronal Networks Research Group, Exploratory Research Center on Life and Living Systems (ExCELLS), Okazaki, Aichi 444-8787 Japan
| | - Ikuko Watakabe
- grid.419396.00000 0004 0618 8593Division of Behavioral Neurobiology, National Institute for Basic Biology, Okazaki, Aichi 444-8787 Japan ,grid.250358.90000 0000 9137 6732Neuronal Networks Research Group, Exploratory Research Center on Life and Living Systems (ExCELLS), Okazaki, Aichi 444-8787 Japan
| | - Shin-ichi Higashijima
- grid.419396.00000 0004 0618 8593Division of Behavioral Neurobiology, National Institute for Basic Biology, Okazaki, Aichi 444-8787 Japan ,grid.250358.90000 0000 9137 6732Neuronal Networks Research Group, Exploratory Research Center on Life and Living Systems (ExCELLS), Okazaki, Aichi 444-8787 Japan
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18
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Ji YR, Tona Y, Wafa T, Christman ME, Tourney ED, Jiang T, Ohta S, Cheng H, Fitzgerald T, Fritzsch B, Jones SM, Cullen KE, Wu DK. Function of bidirectional sensitivity in the otolith organs established by transcription factor Emx2. Nat Commun 2022; 13:6330. [PMID: 36280667 PMCID: PMC9592604 DOI: 10.1038/s41467-022-33819-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2022] [Accepted: 10/04/2022] [Indexed: 12/25/2022] Open
Abstract
Otolith organs of the inner ear are innervated by two parallel afferent projections to the brainstem and cerebellum. These innervations were proposed to segregate across the line of polarity reversal (LPR) within each otolith organ, which divides the organ into two regions of hair cells (HC) with opposite stereociliary orientation. The relationship and functional significance of these anatomical features are not known. Here, we show regional expression of Emx2 in otolith organs, which establishes LPR, mediates the neuronal segregation across LPR and constitutes the bidirectional sensitivity function. Conditional knockout (cKO) of Emx2 in HCs lacks LPR. Tmie cKO, in which mechanotransduction was abolished selectively in HCs within the Emx2 expression domain also lacks bidirectional sensitivity. Analyses of both mutants indicate that LPR is specifically required for mice to swim comfortably and to traverse a balance beam efficiently, but LPR is not required for mice to stay on a rotating rod.
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Affiliation(s)
- Young Rae Ji
- Section on Sensory Cell Regeneration and Development, Laboratory of Molecular Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, 20892, USA
- Sensory & Motor Systems Research Group, Korea Brain Research Institute (KBRI), 61 Cheomdan-ro, Dong-gu, Daegu, 41062, Republic of Korea
| | - Yosuke Tona
- Section on Sensory Cell Regeneration and Development, Laboratory of Molecular Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, 20892, USA
- Otolaryngology/Head and Neck Surgery, Kyoto University Hospital, 54 Shogoin-kawahara-cho, Sakyo-ku, Kyoto City, Kyoto, 606-8507, Japan
| | - Talah Wafa
- Mouse Auditory Testing Core Facility, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Matthew E Christman
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
| | - Edward D Tourney
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
| | - Tao Jiang
- Section on Sensory Cell Regeneration and Development, Laboratory of Molecular Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, 20892, USA
- ENT Institute and Otorhinolaryngology Department of Eye & ENT Hospital, Fudan University, Shanghai, 200031, China
| | - Sho Ohta
- Section on Sensory Cell Regeneration and Development, Laboratory of Molecular Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Hui Cheng
- Bioinformatics and Biostatistics Collaboration Core, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Tracy Fitzgerald
- Mouse Auditory Testing Core Facility, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Bernd Fritzsch
- Department of Biology & Department of Otolaryngology, University of Iowa, Iowa City, IA, 52242, USA
| | - Sherri M Jones
- Department of Special Education and Communication Disorders, 301 Barkley Memorial Center, University of Nebraska-Lincoln, Lincoln, NE, 68583, USA
| | - Kathleen E Cullen
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
| | - Doris K Wu
- Section on Sensory Cell Regeneration and Development, Laboratory of Molecular Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, 20892, USA.
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19
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Glover JC, Fritzsch B. Molecular mechanisms governing development of the hindbrain choroid plexus and auditory projection: A validation of the seminal observations of Wilhelm His. IBRO Neurosci Rep 2022; 13:306-313. [PMID: 36247525 PMCID: PMC9561746 DOI: 10.1016/j.ibneur.2022.09.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Revised: 09/29/2022] [Accepted: 09/29/2022] [Indexed: 11/05/2022] Open
Abstract
Studies by His from 1868 to 1904 delineated the critical role of the dorsal roof plate in the development of the hindbrain choroid plexus, and of the rhombic lips in the development of hindbrain auditory centers. Modern molecular studies have confirmed these observations and placed them in a mechanistic context. Expression of the transcription factor Lmx1a/b is crucial to the development of the hindbrain choroid plexus, and also regulates the expression of Atoh1, a transcription factor that is essential for the formation of the cochlear hair cells and auditory nuclei. By contrast, development of the vestibular hair cells, vestibular ganglion and vestibular nuclei does not depend on Lmx1a/b. These findings demonstrate a common dependence on a specific gene for the hindbrain choroid plexus and the primary auditory projection from hair cells to sensory neurons to hindbrain nuclei. Thus, His' conclusions regarding the origins of specific hindbrain structures are borne out by molecular genetic experiments conducted more than a hundred years later.
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Affiliation(s)
- Joel C. Glover
- Department of Molecular Medicine, University of Oslo, Oslo, Norway
- Norwegian Center for Stem Cell Research, Oslo University Hospital, Oslo, Norway
- Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, Norway
- Corresponding author at: Department of Molecular Medicine, University of Oslo, Oslo, Norway.
| | - Bernd Fritzsch
- Department of Biology, University of Iowa, Iowa, IA 52242, USA
- Corresponding author.
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20
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Fritzsch B, Elliott KL, Yamoah EN. Neurosensory development of the four brainstem-projecting sensory systems and their integration in the telencephalon. Front Neural Circuits 2022; 16:913480. [PMID: 36213204 PMCID: PMC9539932 DOI: 10.3389/fncir.2022.913480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Accepted: 08/23/2022] [Indexed: 11/18/2022] Open
Abstract
Somatosensory, taste, vestibular, and auditory information is first processed in the brainstem. From the brainstem, the respective information is relayed to specific regions within the cortex, where these inputs are further processed and integrated with other sensory systems to provide a comprehensive sensory experience. We provide the organization, genetics, and various neuronal connections of four sensory systems: trigeminal, taste, vestibular, and auditory systems. The development of trigeminal fibers is comparable to many sensory systems, for they project mostly contralaterally from the brainstem or spinal cord to the telencephalon. Taste bud information is primarily projected ipsilaterally through the thalamus to reach the insula. The vestibular fibers develop bilateral connections that eventually reach multiple areas of the cortex to provide a complex map. The auditory fibers project in a tonotopic contour to the auditory cortex. The spatial and tonotopic organization of trigeminal and auditory neuron projections are distinct from the taste and vestibular systems. The individual sensory projections within the cortex provide multi-sensory integration in the telencephalon that depends on context-dependent tertiary connections to integrate other cortical sensory systems across the four modalities.
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Affiliation(s)
- Bernd Fritzsch
- Department of Biology, The University of Iowa, Iowa City, IA, United States
- Department of Otolaryngology, The University of Iowa, Iowa City, IA, United States
- *Correspondence: Bernd Fritzsch,
| | - Karen L. Elliott
- Department of Biology, The University of Iowa, Iowa City, IA, United States
| | - Ebenezer N. Yamoah
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, Reno, NV, United States
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21
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Dorrego-Rivas A, Ezan J, Moreau MM, Poirault-Chassac S, Aubailly N, De Neve J, Blanchard C, Castets F, Fréal A, Battefeld A, Sans N, Montcouquiol M. The core PCP protein Prickle2 regulates axon number and AIS maturation by binding to AnkG and modulating microtubule bundling. SCIENCE ADVANCES 2022; 8:eabo6333. [PMID: 36083912 PMCID: PMC9462691 DOI: 10.1126/sciadv.abo6333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Accepted: 07/25/2022] [Indexed: 06/15/2023]
Abstract
Core planar cell polarity (PCP) genes, which are involved in various neurodevelopmental disorders such as neural tube closure, epilepsy, and autism spectrum disorder, have poorly defined molecular signatures in neurons, mostly synapse-centric. Here, we show that the core PCP protein Prickle-like protein 2 (Prickle2) controls neuronal polarity and is a previously unidentified member of the axonal initial segment (AIS) proteome. We found that Prickle2 is present and colocalizes with AnkG480, the AIS master organizer, in the earliest stages of axonal specification and AIS formation. Furthermore, by binding to and regulating AnkG480, Prickle2 modulates its ability to bundle microtubules, a crucial mechanism for establishing neuronal polarity and AIS formation. Prickle2 depletion alters cytoskeleton organization, and Prickle2 levels determine both axon number and AIS maturation. Last, early Prickle2 depletion produces impaired action potential firing.
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Affiliation(s)
- Ana Dorrego-Rivas
- Univ. Bordeaux, INSERM, Magendie, U1215, F-33077 Bordeaux, France
- Corresponding author.
| | - Jerome Ezan
- Univ. Bordeaux, INSERM, Magendie, U1215, F-33077 Bordeaux, France
| | - Maïté M Moreau
- Univ. Bordeaux, INSERM, Magendie, U1215, F-33077 Bordeaux, France
| | | | | | - Julie De Neve
- Univ. Bordeaux, INSERM, Magendie, U1215, F-33077 Bordeaux, France
| | | | - Francis Castets
- Aix-Marseille Université, CNRS, Institut de Biologie du Développement de Marseille, UMR 7288, Case 907, 13288 Marseille Cedex 09, France
| | - Amélie Fréal
- Department of Functional Genomics, Vrije Universiteit (VU), Amsterdam, Netherlands
| | - Arne Battefeld
- Univ. Bordeaux, CNRS, IMN, UMR 5293, F-33000 Bordeaux, France
| | - Nathalie Sans
- Univ. Bordeaux, INSERM, Magendie, U1215, F-33077 Bordeaux, France
- Corresponding author.
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22
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Lukasz D, Beirl A, Kindt K. Chronic neurotransmission increases the susceptibility of lateral-line hair cells to ototoxic insults. eLife 2022; 11:77775. [PMID: 36047587 PMCID: PMC9473691 DOI: 10.7554/elife.77775] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Accepted: 08/30/2022] [Indexed: 11/27/2022] Open
Abstract
Sensory hair cells receive near constant stimulation by omnipresent auditory and vestibular stimuli. To detect and encode these stimuli, hair cells require steady ATP production, which can be accompanied by a buildup of mitochondrial byproducts called reactive oxygen species (ROS). ROS buildup is thought to sensitize hair cells to ototoxic insults, including the antibiotic neomycin. Work in neurons has shown that neurotransmission is a major driver of ATP production and ROS buildup. Therefore, we tested whether neurotransmission is a significant contributor to ROS buildup in hair cells. Using genetics and pharmacology, we disrupted two key aspects of neurotransmission in zebrafish hair cells: presynaptic calcium influx and the fusion of synaptic vesicles. We find that chronic block of neurotransmission enhances hair-cell survival when challenged with the ototoxin neomycin. This reduction in ototoxin susceptibility is accompanied by reduced mitochondrial activity, likely due to a reduced ATP demand. In addition, we show that mitochondrial oxidation and ROS buildup are reduced when neurotransmission is blocked. Mechanistically, we find that it is the synaptic vesicle cycle rather than presynaptic- or mitochondrial-calcium influx that contributes most significantly to this metabolic stress. Our results comprehensively indicate that, over time, neurotransmission causes ROS buildup that increases the susceptibility of hair cells to ototoxins.
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Affiliation(s)
- Daria Lukasz
- Section on Sensory Cell Development and Function, National Institutes of Health, Bethesda, United States
| | - Alisha Beirl
- Section on Sensory Cell Development and Function, National Institutes of Health, Bethesda, United States
| | - Katie Kindt
- Section on Sensory Cell Development and Function, National Institutes of Health, Bethesda, United States
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23
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Abstract
Motor circuits develop in sequence from those governing fast movements to those governing slow. Here we examine whether upstream sensory circuits are organized by similar principles. Using serial-section electron microscopy in larval zebrafish, we generated a complete map of the gravity-sensing (utricular) system spanning from the inner ear to the brainstem. We find that both sensory tuning and developmental sequence are organizing principles of vestibular topography. Patterned rostrocaudal innervation from hair cells to afferents creates an anatomically inferred directional tuning map in the utricular ganglion, forming segregated pathways for rostral and caudal tilt. Furthermore, the mediolateral axis of the ganglion is linked to both developmental sequence and neuronal temporal dynamics. Early-born pathways carrying phasic information preferentially excite fast escape circuits, whereas later-born pathways carrying tonic signals excite slower postural and oculomotor circuits. These results demonstrate that vestibular circuits are organized by tuning direction and dynamics, aligning them with downstream motor circuits and behaviors. How sensory systems are organized during development remains unclear. Here, the authors used electron microscopy to examine the gravity-sensing system in zebrafish, finding that directional tuning and developmental age are organizing principles of the transformation from vestibular sensation to motor control.
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Zhang Q, Kindt KS. Using Light-Sheet Microscopy to Study Spontaneous Activity in the Developing Lateral-Line System. Front Cell Dev Biol 2022; 10:819612. [PMID: 35592245 PMCID: PMC9112283 DOI: 10.3389/fcell.2022.819612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2021] [Accepted: 01/18/2022] [Indexed: 11/13/2022] Open
Abstract
Hair cells are the sensory receptors in the auditory and vestibular systems of all vertebrates, and in the lateral-line system of aquatic vertebrates. The purpose of this work is to explore the zebrafish lateral-line system as a model to study and understand spontaneous activity in vivo. Our work applies genetically encoded calcium indicators along with light-sheet fluorescence microscopy to visualize spontaneous calcium activity in the developing lateral-line system. Consistent with our previous work, we show that spontaneous calcium activity is present in developing lateral-line hair cells. We now show that supporting cells that surround hair cells, and cholinergic efferent terminals that directly contact hair cells are also spontaneously active. Using two-color functional imaging we demonstrate that spontaneous activity in hair cells does not correlate with activity in either supporting cells or cholinergic terminals. We find that during lateral-line development, hair cells autonomously generate spontaneous events. Using localized calcium indicators, we show that within hair cells, spontaneous calcium activity occurs in two distinct domains—the mechanosensory bundle and the presynapse. Further, spontaneous activity in the mechanosensory bundle ultimately drives spontaneous calcium influx at the presynapse. Comprehensively, our results indicate that in developing lateral-line hair cells, autonomously generated spontaneous activity originates with spontaneous mechanosensory events.
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25
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Deans MR. Conserved and Divergent Principles of Planar Polarity Revealed by Hair Cell Development and Function. Front Neurosci 2021; 15:742391. [PMID: 34733133 PMCID: PMC8558554 DOI: 10.3389/fnins.2021.742391] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Accepted: 09/28/2021] [Indexed: 11/13/2022] Open
Abstract
Planar polarity describes the organization and orientation of polarized cells or cellular structures within the plane of an epithelium. The sensory receptor hair cells of the vertebrate inner ear have been recognized as a preeminent vertebrate model system for studying planar polarity and its development. This is principally because planar polarity in the inner ear is structurally and molecularly apparent and therefore easy to visualize. Inner ear planar polarity is also functionally significant because hair cells are mechanosensors stimulated by sound or motion and planar polarity underlies the mechanosensory mechanism, thereby facilitating the auditory and vestibular functions of the ear. Structurally, hair cell planar polarity is evident in the organization of a polarized bundle of actin-based protrusions from the apical surface called stereocilia that is necessary for mechanosensation and when stereociliary bundle is disrupted auditory and vestibular behavioral deficits emerge. Hair cells are distributed between six sensory epithelia within the inner ear that have evolved unique patterns of planar polarity that facilitate auditory or vestibular function. Thus, specialized adaptations of planar polarity have occurred that distinguish auditory and vestibular hair cells and will be described throughout this review. There are also three levels of planar polarity organization that can be visualized within the vertebrate inner ear. These are the intrinsic polarity of individual hair cells, the planar cell polarity or coordinated orientation of cells within the epithelia, and planar bipolarity; an organization unique to a subset of vestibular hair cells in which the stereociliary bundles are oriented in opposite directions but remain aligned along a common polarity axis. The inner ear with its complement of auditory and vestibular sensory epithelia allows these levels, and the inter-relationships between them, to be studied using a single model organism. The purpose of this review is to introduce the functional significance of planar polarity in the auditory and vestibular systems and our contemporary understanding of the developmental mechanisms associated with organizing planar polarity at these three cellular levels.
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Affiliation(s)
- Michael R Deans
- Department of Surgery, Division of Otolaryngology, University of Utah School of Medicine, Salt Lake City, UT, United States.,Department of Neurobiology, University of Utah School of Medicine, Salt Lake City, UT, United States
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Plazas PV, Elgoyhen AB. The Cholinergic Lateral Line Efferent Synapse: Structural, Functional and Molecular Similarities With Those of the Cochlea. Front Cell Neurosci 2021; 15:765083. [PMID: 34712122 PMCID: PMC8545859 DOI: 10.3389/fncel.2021.765083] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 09/21/2021] [Indexed: 11/25/2022] Open
Abstract
Vertebrate hair cell (HC) systems are innervated by efferent fibers that modulate their response to external stimuli. In mammals, the best studied efferent-HC synapse, the cholinergic medial olivocochlear (MOC) efferent system, makes direct synaptic contacts with HCs. The net effect of MOC activity is to hyperpolarize HCs through the activation of α9α10 nicotinic cholinergic receptors (nAChRs) and the subsequent activation of Ca2+-dependent SK2 potassium channels. A serious obstacle in research on many mammalian sensory systems in their native context is that their constituent neurons are difficult to access even in newborn animals, hampering circuit observation, mapping, or controlled manipulation. By contrast, fishes and amphibians have a superficial and accessible mechanosensory system, the lateral line (LL), which circumvents many of these problems. LL responsiveness is modulated by efferent neurons which aid to distinguish between external and self-generated stimuli. One component of the LL efferent system is cholinergic and its activation inhibits LL afferent activity, similar to what has been described for MOC efferents. The zebrafish (Danio rerio) has emerged as a powerful model system for studying human hearing and balance disorders, since LL HC are structurally and functionally analogous to cochlear HCs, but are optically and pharmacologically accessible within an intact specimen. Complementing mammalian studies, zebrafish have been used to gain significant insights into many facets of HC biology, including mechanotransduction and synaptic physiology as well as mechanisms of both hereditary and acquired HC dysfunction. With the rise of the zebrafish LL as a model in which to study auditory system function and disease, there has been an increased interest in studying its efferent system and evaluate the similarity between mammalian and piscine efferent synapses. Advances derived from studies in zebrafish include understanding the effect of the LL efferent system on HC and afferent activity, and revealing that an α9-containing nAChR, functionally coupled to SK channels, operates at the LL efferent synapse. In this review, we discuss the tools and findings of these recent investigations into zebrafish efferent-HC synapse, their commonalities with the mammalian counterpart and discuss several emerging areas for future studies.
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Affiliation(s)
- Paola V Plazas
- Instituto de Farmacología, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
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Tarchini B. A Reversal in Hair Cell Orientation Organizes Both the Auditory and Vestibular Organs. Front Neurosci 2021; 15:695914. [PMID: 34646115 PMCID: PMC8502876 DOI: 10.3389/fnins.2021.695914] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Accepted: 09/03/2021] [Indexed: 01/17/2023] Open
Abstract
Sensory hair cells detect mechanical stimuli with their hair bundle, an asymmetrical brush of actin-based membrane protrusions, or stereocilia. At the single cell level, stereocilia are organized in rows of graded heights that confer the hair bundle with intrinsic directional sensitivity. At the organ level, each hair cell is precisely oriented so that its intrinsic directional sensitivity matches the direction of mechanical stimuli reaching the sensory epithelium. Coordinated orientation among neighboring hair cells usually ensures the delivery of a coherent local group response. Accordingly, hair cell orientation is locally uniform in the auditory and vestibular cristae epithelia in birds and mammals. However, an exception to this rule is found in the vestibular macular organs, and in fish lateral line neuromasts, where two hair cell populations show opposing orientations. This mirror-image hair cell organization confers bidirectional sensitivity at the organ level. Here I review our current understanding of the molecular machinery that produces mirror-image organization through a regional reversal of hair cell orientation. Interestingly, recent evidence suggests that auditory hair cells adopt their normal uniform orientation through a global reversal mechanism similar to the one at work regionally in macular and neuromast organs. Macular and auditory organs thus appear to be patterned more similarly than previously appreciated during inner ear development.
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Affiliation(s)
- Basile Tarchini
- The Jackson Laboratory, Bar Harbor, ME, United States.,Department of Medicine, Tufts University, Boston, MA, United States.,Graduate School of Biomedical Science and Engineering (GSBSE), University of Maine, Orono, ME, United States
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Evaluation on Effectiveness of a New System as well as Analysis on Optimal Horizontal Eye Position for Vertical Video Head Impulse Test. Curr Med Sci 2021; 41:705-711. [PMID: 34403095 DOI: 10.1007/s11596-021-2415-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Accepted: 07/16/2021] [Indexed: 10/20/2022]
Abstract
OBJECTIVE To compare the performances among three different systems for video head impulse test (vHIT), and to identify an optimal target angle for precisely evaluating the function of vertical semicircular canals in vHIT. METHODS A two-center prospective study was done. Participants were sit 1.2 m away from the wall in a noise-proved room that dedicated for vHIT experiments. During the comparison experiments, similar settings were ensured in both hospitals, with the same distance to wall and angle of staring. For each equipment, the procedures followed the developers' recommendations. The same examiner performed the comparison between two systems in one location. For the eye-position projects, targets were placed on the wall sequentially at the pre-marked lines for different angles. For the comparison projects, 9 and 13 participants were recruited, respectively. Any participant with otologic or vestibular disorders was excluded. A total of 26 healthy participants were recruited in the eye-position experiments, 16 of which were further involved in inter-examiner tests. RESULTS Our evaluations of three different systems showed that a new vHIT system, VertiGoggles® ZT-VNG-I (VG) performed as good as the long-tested Otometrics® ICS impulse (Oto) and EyeSeeCam® (ESC). During the comparison, we validated 25-degree, instead of right ahead at 0 degree, is a better place to set the targets when torsion was applied at vertical semicircular canal planes. CONCLUSION The new VG system is good for clinical practices. Furthermore, we proposed a new protocol to set the targets 25 degrees from right ahead after tilting head 45 degrees to evaluate vertical canals during vHIT.
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An Integrated Perspective of Evolution and Development: From Genes to Function to Ear, Lateral Line and Electroreception. DIVERSITY 2021; 13. [PMID: 35505776 PMCID: PMC9060560 DOI: 10.3390/d13080364] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Four sensory systems (vestibular, lateral line, electroreception, auditory) are unique and project exclusively to the brainstem of vertebrates. All sensory neurons depend on a common set of genes (Eya1, Sox2, Neurog1, Neurod1) that project to a dorsal nucleus and an intermediate nucleus, which differentiate into the vestibular ear, lateral line and electroreception in vertebrates. In tetrapods, a loss of two sensory systems (lateral line, electroreception) leads to the development of a unique ear and auditory system in amniotes. Lmx1a/b, Gdf7, Wnt1/3a, BMP4/7 and Atoh1 define the lateral line, electroreception and auditory nuclei. In contrast, vestibular nuclei depend on Neurog1/2, Ascl1, Ptf1a and Olig3, among others, to develop an independent origin of the vestibular nuclei. A common origin of hair cells depends on Eya1, Sox2 and Atoh1, which generate the mechanosensory cells. Several proteins define the polarity of hair cells in the ear and lateral line. A unique connection of stereocilia requires CDH23 and PCDH15 for connections and TMC1/2 proteins to perceive mechanosensory input. Electroreception has no polarity, and a different system is used to drive electroreceptors. All hair cells function by excitation via ribbons to activate neurons that innervate the distinct target areas. An integrated perspective is presented to understand the gain and loss of different sensory systems.
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30
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Kindt KS, Akturk A, Jarysta A, Day M, Beirl A, Flonard M, Tarchini B. EMX2-GPR156-Gαi reverses hair cell orientation in mechanosensory epithelia. Nat Commun 2021; 12:2861. [PMID: 34001891 PMCID: PMC8129141 DOI: 10.1038/s41467-021-22997-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Accepted: 04/10/2021] [Indexed: 12/21/2022] Open
Abstract
Hair cells detect sound, head position or water movements when their mechanosensory hair bundle is deflected. Each hair bundle has an asymmetric architecture that restricts stimulus detection to a single axis. Coordinated hair cell orientations within sensory epithelia further tune stimulus detection at the organ level. Here, we identify GPR156, an orphan GPCR of unknown function, as a critical regulator of hair cell orientation. We demonstrate that the transcription factor EMX2 polarizes GPR156 distribution, enabling it to signal through Gαi and trigger a 180° reversal in hair cell orientation. GPR156-Gαi mediated reversal is essential to establish hair cells with mirror-image orientations in mouse otolith organs in the vestibular system and in zebrafish lateral line. Remarkably, GPR156-Gαi also instructs hair cell reversal in the auditory epithelium, despite a lack of mirror-image organization. Overall, our work demonstrates that conserved GPR156-Gαi signaling is integral to the framework that builds directional responses into mechanosensory epithelia.
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MESH Headings
- Animals
- Cell Polarity/genetics
- Epithelium/metabolism
- Female
- GTP-Binding Protein alpha Subunits, Gi-Go/genetics
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- Hair Cells, Auditory/cytology
- Hair Cells, Auditory/metabolism
- Homeodomain Proteins/genetics
- Homeodomain Proteins/metabolism
- Male
- Mice, Inbred C57BL
- Mice, Knockout
- Mice, Transgenic
- Microscopy, Confocal/methods
- Receptors, G-Protein-Coupled/genetics
- Receptors, G-Protein-Coupled/metabolism
- Transcription Factors/genetics
- Transcription Factors/metabolism
- Zebrafish/metabolism
- Mice
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Affiliation(s)
- Katie S Kindt
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA
| | | | | | | | - Alisha Beirl
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA
| | | | - Basile Tarchini
- The Jackson Laboratory, Bar Harbor, ME, USA.
- Department of Medicine, Tufts University, Boston, MA, USA.
- Graduate School of Biomedical Science and Engineering (GSBSE), University of Maine, Orono, ME, USA.
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31
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Ballesteros A, Fitzgerald TS, Swartz KJ. Expression of a membrane-targeted fluorescent reporter disrupts auditory hair cell mechanoelectrical transduction and causes profound deafness. Hear Res 2021; 404:108212. [PMID: 33667877 PMCID: PMC8035305 DOI: 10.1016/j.heares.2021.108212] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Revised: 02/11/2021] [Accepted: 02/13/2021] [Indexed: 11/22/2022]
Abstract
The reporter mT/mG mice expressing a membrane-targeted fluorescent protein are becoming widely used to study the auditory and vestibular system due to its versatility. Here we show that high expression levels of the fluorescent mtdTomato reporter affect the function of the sensory hair cells and the auditory performance of mT/mG transgenic mice. Auditory brainstem responses and distortion product otoacoustic emissions revealed that adult mT/mG homozygous mice are profoundly deaf, whereas heterozygous mice present high frequency loss. We explore whether this line would be useful for studying and visualizing the membrane of auditory hair cells by airyscan super-resolution confocal microscopy. Membrane localization of the reporter was observed in hair cells of the cochlea, facilitating imaging of both cell bodies and stereocilia bundles without altering cellular architecture or the expression of the integral membrane motor protein prestin. Remarkably, hair cells from mT/mG homozygous mice failed to uptake the FM1-43 dye and to locate TMC1 at the stereocilia, indicating defective mechanotransduction machinery. Our work emphasizes that precautions must be considered when working with reporter mice and highlights the potential role of the cellular membrane in maintaining functional hair cells and ensuring proper hearing.
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Affiliation(s)
- Angela Ballesteros
- Molecular Physiology and Biophysics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, United States.
| | - Tracy S Fitzgerald
- Mouse Auditory Testing Core, National Institute on Deafness and other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, United States
| | - Kenton J Swartz
- Molecular Physiology and Biophysics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, United States.
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32
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Iyer AA, Groves AK. Transcription Factor Reprogramming in the Inner Ear: Turning on Cell Fate Switches to Regenerate Sensory Hair Cells. Front Cell Neurosci 2021; 15:660748. [PMID: 33854418 PMCID: PMC8039129 DOI: 10.3389/fncel.2021.660748] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Accepted: 03/08/2021] [Indexed: 12/15/2022] Open
Abstract
Non-mammalian vertebrates can restore their auditory and vestibular hair cells naturally by triggering the regeneration of adjacent supporting cells. The transcription factor ATOH1 is a key regulator of hair cell development and regeneration in the inner ear. Following the death of hair cells, supporting cells upregulate ATOH1 and give rise to new hair cells. However, in the mature mammalian cochlea, such natural regeneration of hair cells is largely absent. Transcription factor reprogramming has been used in many tissues to convert one cell type into another, with the long-term hope of achieving tissue regeneration. Reprogramming transcription factors work by altering the transcriptomic and epigenetic landscapes in a target cell, resulting in a fate change to the desired cell type. Several studies have shown that ATOH1 is capable of reprogramming cochlear non-sensory tissue into cells resembling hair cells in young animals. However, the reprogramming ability of ATOH1 is lost with age, implying that the potency of individual hair cell-specific transcription factors may be reduced or lost over time by mechanisms that are still not clear. To circumvent this, combinations of key hair cell transcription factors have been used to promote hair cell regeneration in older animals. In this review, we summarize recent findings that have identified and studied these reprogramming factor combinations for hair cell regeneration. Finally, we discuss the important questions that emerge from these findings, particularly the feasibility of therapeutic strategies using reprogramming factors to restore human hearing in the future.
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Affiliation(s)
- Amrita A. Iyer
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
- Program in Genetics & Genomics, Houston, TX, United States
| | - Andrew K. Groves
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
- Program in Genetics & Genomics, Houston, TX, United States
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, United States
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33
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Holmgren M, Sheets L. Using the Zebrafish Lateral Line to Understand the Roles of Mitochondria in Sensorineural Hearing Loss. Front Cell Dev Biol 2021; 8:628712. [PMID: 33614633 PMCID: PMC7892962 DOI: 10.3389/fcell.2020.628712] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Accepted: 12/23/2020] [Indexed: 01/05/2023] Open
Abstract
Hair cells are the mechanosensory receptors of the inner ear and can be damaged by noise, aging, and ototoxic drugs. This damage often results in permanent sensorineural hearing loss. Hair cells have high energy demands and rely on mitochondria to produce ATP as well as contribute to intracellular calcium homeostasis. In addition to generating ATP, mitochondria produce reactive oxygen species, which can lead to oxidative stress, and regulate cell death pathways. Zebrafish lateral-line hair cells are structurally and functionally analogous to cochlear hair cells but are optically and pharmacologically accessible within an intact specimen, making the zebrafish a good model in which to study hair-cell mitochondrial activity. Moreover, the ease of genetic manipulation of zebrafish embryos allows for the study of mutations implicated in human deafness, as well as the generation of transgenic models to visualize mitochondrial calcium transients and mitochondrial activity in live organisms. Studies of the zebrafish lateral line have shown that variations in mitochondrial activity can predict hair-cell susceptibility to damage by aminoglycosides or noise exposure. In addition, antioxidants have been shown to protect against noise trauma and ototoxic drug–induced hair-cell death. In this review, we discuss the tools and findings of recent investigations into zebrafish hair-cell mitochondria and their involvement in cellular processes, both under homeostatic conditions and in response to noise or ototoxic drugs. The zebrafish lateral line is a valuable model in which to study the roles of mitochondria in hair-cell pathologies and to develop therapeutic strategies to prevent sensorineural hearing loss in humans.
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Affiliation(s)
- Melanie Holmgren
- Department of Otolaryngology, Washington University School of Medicine, St. Louis, MO, United States
| | - Lavinia Sheets
- Department of Otolaryngology, Washington University School of Medicine, St. Louis, MO, United States.,Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO, United States
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Jiang T, Zhao L, Yin Y, Yu H, Li Q. Evaluation of Middle Ear Function by Tympanometry and the Influence of Lower Barometric Pressure at High Altitude. High Alt Med Biol 2021; 22:70-76. [PMID: 33395350 DOI: 10.1089/ham.2020.0042] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Jiang, Tao, Liping Zhao, Yanbo Yin, Huiqian Yu, and Qingzhong Li. Evaluation of middle ear function by tympanometry and the influence of lower barometric pressure at high altitude. High Alt Med Biol. 22:70-76, 2021. Objective: To evaluate middle ear function in residents of high-altitude areas in comparison to sea-level participants. Design: Prospective observational study. Setting: All experiments were performed by experienced audiologists with a calibrated tympanometry machine. Participants: Young adults between the age of 17 and 23 were recruited. Seventy-five participants from Shanghai (altitude 4 m) and 133 participants from the Shigatse area (altitude 4,040 m) were recruited. Any participant with any otological disorder was excluded. Main Outcome Measure: Four indexes of the tympanogram were evaluated in the two groups from different altitudes. Results: Our results showed that the peak of static compliance for the participants in Shigatse was smaller, but the absolute compliance of tympanic membrane remained the same. Similarly, the ear canal volume (ECV) from tympanometry was also affected by the elevated altitude in Tibet. In addition, the tympanometric peak pressure was decreased in high-altitude residents, which suggests a slightly declined function of the Eustachian tube at lower barometric pressure. However, no difference was found in the tympanometric width (TW). Conclusion: Our results indicate that tympanograms were affected by decreased atmospheric pressure at high altitude. Therefore, other than pressure-related indexes, TW is better for evaluating the function of the middle ear in high-altitude regions.
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Affiliation(s)
- Tao Jiang
- ENT Institute and Otorhinolaryngology Department of Eye & ENT Hospital, State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Fudan University, Shanghai, P.R. China
- NHC Key Laboratory of Hearing Medicine (Fudan University), Shanghai, P.R. China
| | - Liping Zhao
- ENT Institute and Otorhinolaryngology Department of Eye & ENT Hospital, State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Fudan University, Shanghai, P.R. China
- NHC Key Laboratory of Hearing Medicine (Fudan University), Shanghai, P.R. China
| | - Yanbo Yin
- ENT Institute and Otorhinolaryngology Department of Eye & ENT Hospital, State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Fudan University, Shanghai, P.R. China
- NHC Key Laboratory of Hearing Medicine (Fudan University), Shanghai, P.R. China
| | - Huiqian Yu
- ENT Institute and Otorhinolaryngology Department of Eye & ENT Hospital, State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Fudan University, Shanghai, P.R. China
- NHC Key Laboratory of Hearing Medicine (Fudan University), Shanghai, P.R. China
| | - Qingzhong Li
- ENT Institute and Otorhinolaryngology Department of Eye & ENT Hospital, State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Fudan University, Shanghai, P.R. China
- NHC Key Laboratory of Hearing Medicine (Fudan University), Shanghai, P.R. China
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35
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Ohta S, Ji YR, Martin D, Wu DK. Emx2 regulates hair cell rearrangement but not positional identity within neuromasts. eLife 2020; 9:e60432. [PMID: 33377867 PMCID: PMC7806267 DOI: 10.7554/elife.60432] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 12/29/2020] [Indexed: 11/13/2022] Open
Abstract
Each hair cell (HC) precursor of zebrafish neuromasts divides to form two daughter HCs of opposite hair bundle orientations. Previously, we showed that transcription factor Emx2, expressed in only one of the daughter HCs, generates this bidirectional HC pattern (Jiang et al., 2017). Here, we asked whether Emx2 mediates this effect by changing location of hair bundle establishment or positions of HCs since daughter HCs are known to switch positions with each other. We showed this HC rearrangement, redefined as two processes named Rock and Roll, is required for positional acquisition of HCs. Apical protrusion formation of nascent HCs and planar polarity signaling are both important for the Rock and Roll. Emx2 facilitates Rock and Roll by delaying apical protrusion of its nascent HCs but it does not determine HCs' ultimate positions, indicating that Emx2 mediates bidirectional HC pattern by changing the location where hair bundle is established in HCs.
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Affiliation(s)
- Sho Ohta
- National Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Young Rae Ji
- National Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Daniel Martin
- Genomics and Computational Biology Core, National Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Doris K Wu
- National Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
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36
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Ratzan EM, Moon AM, Deans MR. Fgf8 genetic labeling reveals the early specification of vestibular hair cell type in mouse utricle. Development 2020; 147:dev.192849. [PMID: 33046506 DOI: 10.1242/dev.192849] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 10/07/2020] [Indexed: 01/16/2023]
Abstract
FGF8 signaling plays diverse roles in inner ear development, acting at multiple stages from otic placode induction to cellular differentiation in the organ of Corti. As a secreted morphogen with diverse functions, Fgf8 expression is likely to be spatially restricted and temporally dynamic throughout inner ear development. We evaluated these characteristics using genetic labeling mediated by Fgf8 mcm gene-targeted mice and determined that Fgf8 expression is a specific and early marker of Type-I vestibular hair cell identity. Fgf8 mcm expression initiates at E11.5 in the future striolar region of the utricle, labeling hair cells following EdU birthdating, and demonstrates that sub-type identity is determined shortly after terminal mitosis. This early fate specification is not apparent using markers or morphological criteria that are not present before birth in the mouse. Although analyses of Fgf8 conditional knockout mice did not reveal developmental phenotypes, the restricted pattern of Fgf8 expression suggests that functionally redundant FGF ligands may contribute to vestibular hair cell differentiation and supports a developmental model in which Type-I and Type-II hair cells develop in parallel rather than from an intermediate precursor.
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Affiliation(s)
- Evan M Ratzan
- Department of Neurobiology and Anatomy, University of Utah School of Medicine, Salt Lake City, UT 84112, USA.,Interdepartmental Program in Neuroscience, University of Utah School of Medicine, Salt Lake City, UT 84112, USA
| | - Anne M Moon
- Departments of Molecular and Functional Genomics and Pediatrics, Weis Center for Research, Geisinger Clinic and Geisinger Commonwealth School of Medicine, Danville, PA 17822, USA.,Departments of Pediatrics and Human Genetics, University of Utah, Salt Lake City, UT 84112 USA
| | - Michael R Deans
- Department of Neurobiology and Anatomy, University of Utah School of Medicine, Salt Lake City, UT 84112, USA .,Department of Surgery, Division of Otolaryngology, University of Utah School of Medicine, Salt Lake City, UT 84132, USA
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Tona Y, Wu DK. Live imaging of hair bundle polarity acquisition demonstrates a critical timeline for transcription factor Emx2. eLife 2020; 9:e59282. [PMID: 32965215 PMCID: PMC7535933 DOI: 10.7554/elife.59282] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Accepted: 09/17/2020] [Indexed: 12/22/2022] Open
Abstract
Directional sensitivity of hair cells (HCs) is conferred by the aymmetric apical hair bundle, comprised of a kinocilium and stereocilia staircase. The mother centriole (MC) forms the base of the kinocilium and the stereocilia develop adjacent to it. Previously, we showed that transcription factor Emx2 reverses hair bundle orientation and its expression in the mouse vestibular utricle is restricted, resulting in two regions of opposite bundle orientation (Jiang et al., 2017). Here, we investigated establishment of opposite bundle orientation in embryonic utricles by live-imaging GFP-labeled centrioles in HCs. The daughter centriole invariably migrated ahead of the MC from the center to their respective peripheral locations in HCs. Comparing HCs between utricular regions, centriole trajectories were similar but they migrated toward opposite directions, suggesting that Emx2 pre-patterned HCs prior to centriole migration. Ectopic Emx2, however, reversed centriole trajectory within hours during a critical time-window when centriole trajectory was responsive to Emx2.
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Affiliation(s)
- Yosuke Tona
- National Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Doris K Wu
- National Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
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38
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Erzberger A, Jacobo A, Dasgupta A, Hudspeth AJ. Mechanochemical symmetry breaking during morphogenesis of lateral-line sensory organs. NATURE PHYSICS 2020; 16:949-957. [PMID: 33790985 PMCID: PMC8009062 DOI: 10.1038/s41567-020-0894-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Actively regulated symmetry breaking, which is ubiquitous in biological cells, underlies phenomena such as directed cellular movement and morphological polarization. Here we investigate how an organ-level polarity pattern emerges through symmetry breaking at the cellular level during the formation of a mechanosensory organ. Combining theory, genetic perturbations, and in vivo imaging, we study the development and regeneration of the fluid-motion sensors in the zebrafish's lateral line. We find that two interacting symmetry-breaking events - one mediated by biochemical signaling and the other by cellular mechanics - give rise to precise rotations of cell pairs, which produce a mirror-symmetric polarity pattern in the receptor organ.
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Affiliation(s)
- A. Erzberger
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, NY 10065 USA
- These authors contributed equally
- ;
| | - A. Jacobo
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, NY 10065 USA
- These authors contributed equally
| | - A. Dasgupta
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, NY 10065 USA
| | - A. J. Hudspeth
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, NY 10065 USA
- ;
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39
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Ono K, Sandell LL, Trainor PA, Wu DK. Retinoic acid synthesis and autoregulation mediate zonal patterning of vestibular organs and inner ear morphogenesis. Development 2020; 147:dev.192070. [PMID: 32665247 DOI: 10.1242/dev.192070] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Accepted: 07/01/2020] [Indexed: 12/13/2022]
Abstract
Retinoic acid (RA), a vitamin A (retinol) derivative, has pleiotropic functions during embryonic development. The synthesis of RA requires two enzymatic reactions: oxidation of retinol into retinaldehyde by alcohol dehydrogenases (ADHs) or retinol dehydrogenases (RDHs); and oxidation of retinaldehyde into RA by aldehyde dehydrogenases family 1, subfamily A (ALDH1as), such as ALDH1a1, ALDH1a2 and ALDH1a3. Levels of RA in tissues are regulated by spatiotemporal expression patterns of genes encoding RA-synthesizing and -degrading enzymes, such as cytochrome P450 26 (Cyp26 genes). Here, we show that RDH10 is important for both sensory and non-sensory formation of the vestibule of the inner ear. Mice deficient in Rdh10 exhibit failure of utricle-saccule separation, otoconial formation and zonal patterning of vestibular sensory organs. These phenotypes are similar to those of Aldh1a3 knockouts, and the sensory phenotype is complementary to that of Cyp26b1 knockouts. Together, these results demonstrate that RDH10 and ALDH1a3 are the key RA-synthesis enzymes involved in vestibular development. Furthermore, we discovered that RA induces Cyp26b1 expression in the developing vestibular sensory organs, which generates the differential RA signaling required for zonal patterning.
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Affiliation(s)
- Kazuya Ono
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA
| | - Lisa L Sandell
- Department of Oral Immunology and Infectious Diseases, School of Dentistry, University of Louisville, Louisville, KY 40201, USA
| | - Paul A Trainor
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA.,Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Doris K Wu
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA
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40
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Abstract
The cochlea, a coiled structure located in the ventral region of the inner ear, acts as the primary structure for the perception of sound. Along the length of the cochlear spiral is the organ of Corti, a highly derived and rigorously patterned sensory epithelium that acts to convert auditory stimuli into neural impulses. The development of the organ of Corti requires a series of inductive events that specify unique cellular characteristics and axial identities along its three major axes. Here, we review recent studies of the cellular and molecular processes regulating several aspects of cochlear development, such as axial patterning, cochlear outgrowth and cellular differentiation. We highlight how the precise coordination of multiple signaling pathways is required for the successful formation of a complete organ of Corti.
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Affiliation(s)
- Elizabeth Carroll Driver
- Laboratory of Cochlear Development, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA
| | - Matthew W Kelley
- Laboratory of Cochlear Development, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA
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41
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Prins TJ, Myers ZA, Saldate JJ, Hoffman LF. Calbindin expression in adult vestibular epithelia. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2020; 206:623-637. [PMID: 32350587 DOI: 10.1007/s00359-020-01418-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2019] [Revised: 03/28/2020] [Accepted: 04/01/2020] [Indexed: 01/11/2023]
Abstract
The mammalian vestibular epithelia exhibit a remarkably stereotyped organization featuring cellular characteristics under planar cell polarity (PCP) control. PCP mechanisms are responsible for the organization of hair cell morphologic polarization vectors, and are thought to be responsible for the postsynaptic expression of the calcium-binding protein calretinin that defines the utricular striola and cristae central zone. However, recent analyses revealed that subtle differences in the topographic expression of oncomodulin, another calcium-binding protein, reflects heterogeneous factors driving the subtle variations in expression. Calbindin represents a third calcium-binding protein that has been previously described to be expressed in both hair cells and afferent calyces in proximity to the utricular striola and crista central zone. The objective of the present investigation was to determine calbindin's topographic pattern of expression to further elucidate the extent to which PCP mechanisms might exert control over the organization of vestibular neuroepithelia. The findings revealed that calbindin exhibited an expression pattern strikingly similar to oncomodulin. However, within calyces of the central zone calbindin was colocalized with calretinin. These results indicate that organizational features of vestibular epithelia are governed by a suite of factors that include PCP mechanisms as well others yet to be defined.
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Affiliation(s)
- Terry J Prins
- Department of Head and Neck Surgery, David Geffen School of Medicine at UCLA, Box 951624, Los Angeles, CA, 90095-1624, USA.,Department of Integrative Biology and Physiology, UCLA, Los Angeles, CA, 90095, USA
| | - Zachary A Myers
- Department of Head and Neck Surgery, David Geffen School of Medicine at UCLA, Box 951624, Los Angeles, CA, 90095-1624, USA
| | - Johnny J Saldate
- Department of Head and Neck Surgery, David Geffen School of Medicine at UCLA, Box 951624, Los Angeles, CA, 90095-1624, USA
| | - Larry F Hoffman
- Department of Head and Neck Surgery, David Geffen School of Medicine at UCLA, Box 951624, Los Angeles, CA, 90095-1624, USA. .,Brain Research Institute, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
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42
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Kozak EL, Palit S, Miranda-Rodríguez JR, Janjic A, Böttcher A, Lickert H, Enard W, Theis FJ, López-Schier H. Epithelial Planar Bipolarity Emerges from Notch-Mediated Asymmetric Inhibition of Emx2. Curr Biol 2020; 30:1142-1151.e6. [PMID: 32109392 DOI: 10.1016/j.cub.2020.01.027] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 11/28/2019] [Accepted: 01/08/2020] [Indexed: 12/24/2022]
Abstract
Most plane-polarized tissues are formed by identically oriented cells [1, 2]. A notable exception occurs in the vertebrate vestibular system and lateral-line neuromasts, where mechanosensory hair cells orient along a single axis but in opposite directions to generate bipolar epithelia [3-5]. In zebrafish neuromasts, pairs of hair cells arise from the division of a non-sensory progenitor [6, 7] and acquire opposing planar polarity via the asymmetric expression of the polarity-determinant transcription factor Emx2 [8-11]. Here, we reveal the initial symmetry-breaking step by decrypting the developmental trajectory of hair cells using single-cell RNA sequencing (scRNA-seq), diffusion pseudotime analysis, lineage tracing, and mutagenesis. We show that Emx2 is absent in non-sensory epithelial cells, begins expression in hair-cell progenitors, and is downregulated in one of the sibling hair cells via signaling through the Notch1a receptor. Analysis of Emx2-deficient specimens, in which every hair cell adopts an identical direction, indicates that Emx2 asymmetry does not result from auto-regulatory feedback. These data reveal a two-tiered mechanism by which the symmetric monodirectional ground state of the epithelium is inverted by deterministic initiation of Emx2 expression in hair-cell progenitors and a subsequent stochastic repression of Emx2 in one of the sibling hair cells breaks directional symmetry to establish planar bipolarity.
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Affiliation(s)
- Eva L Kozak
- Research Unit of Sensory Biology & Organogenesis, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany
| | - Subarna Palit
- Institute of Computational Biology, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany
| | - Jerónimo R Miranda-Rodríguez
- Research Unit of Sensory Biology & Organogenesis, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany
| | - Aleksandar Janjic
- Department Biology II, Anthropology and Human Genomics, Ludwig Maximilians University of Munich, Großhaderner Straße 2, 82152 Martinsried, Germany
| | - Anika Böttcher
- Institute of Diabetes and Regeneration Research, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany; German Center for Diabetes Research, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany; Institute of Stem Cell Research, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany
| | - Heiko Lickert
- Institute of Diabetes and Regeneration Research, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany; German Center for Diabetes Research, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany; Institute of Stem Cell Research, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany; School of Medicine, Technical University of Munich, Ismaninger Straße 22, 81675 Munich, Germany
| | - Wolfgang Enard
- Department Biology II, Anthropology and Human Genomics, Ludwig Maximilians University of Munich, Großhaderner Straße 2, 82152 Martinsried, Germany
| | - Fabian J Theis
- Institute of Computational Biology, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany; School of Life Sciences Weihenstephan, Technical University of Munich, Alte Akademie, 85354 Freising, Germany; Department of Mathematics, Technical University of Munich, Boltzmannstraße 3, 85748 Garching, Germany
| | - Hernán López-Schier
- Research Unit of Sensory Biology & Organogenesis, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany.
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43
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Ono K, Keller J, López Ramírez O, González Garrido A, Zobeiri OA, Chang HHV, Vijayakumar S, Ayiotis A, Duester G, Della Santina CC, Jones SM, Cullen KE, Eatock RA, Wu DK. Retinoic acid degradation shapes zonal development of vestibular organs and sensitivity to transient linear accelerations. Nat Commun 2020; 11:63. [PMID: 31896743 PMCID: PMC6940366 DOI: 10.1038/s41467-019-13710-4] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Accepted: 11/21/2019] [Indexed: 01/18/2023] Open
Abstract
Each vestibular sensory epithelium in the inner ear is divided morphologically and physiologically into two zones, called the striola and extrastriola in otolith organ maculae, and the central and peripheral zones in semicircular canal cristae. We found that formation of striolar/central zones during embryogenesis requires Cytochrome P450 26b1 (Cyp26b1)-mediated degradation of retinoic acid (RA). In Cyp26b1 conditional knockout mice, formation of striolar/central zones is compromised, such that they resemble extrastriolar/peripheral zones in multiple features. Mutants have deficient vestibular evoked potential (VsEP) responses to jerk stimuli, head tremor and deficits in balance beam tests that are consistent with abnormal vestibular input, but normal vestibulo-ocular reflexes and apparently normal motor performance during swimming. Thus, degradation of RA during embryogenesis is required for formation of highly specialized regions of the vestibular sensory epithelia with specific functions in detecting head motions.
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Affiliation(s)
- Kazuya Ono
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, 20892, USA
| | - James Keller
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, 20892, USA
- Qiagen Sciences Inc., Germantown, MD, 20874, USA
| | - Omar López Ramírez
- Department of Neurobiology, University of Chicago, Chicago, IL, 60637, USA
| | | | - Omid A Zobeiri
- Department of Physiology McGill University, Montreal, QC, Canada, H3G 1Y6
| | | | - Sarath Vijayakumar
- Department of Special Education and Communication Disorders, 301 Barkley Memorial Center, University of Nebraska-Lincoln, Lincoln, NE, 68583-0738, USA
| | - Andrianna Ayiotis
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
| | - Gregg Duester
- Neuroscience and Aging Research Center, Stanford Burnham Prebys Medical Discovery Institutes, Stanford, CA, 92037, USA
| | - Charles C Della Santina
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
- Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
| | - Sherri M Jones
- Department of Special Education and Communication Disorders, 301 Barkley Memorial Center, University of Nebraska-Lincoln, Lincoln, NE, 68583-0738, USA
| | - Kathleen E Cullen
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
| | - Ruth Anne Eatock
- Department of Neurobiology, University of Chicago, Chicago, IL, 60637, USA
| | - Doris K Wu
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, 20892, USA.
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44
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Jacobo A, Dasgupta A, Erzberger A, Siletti K, Hudspeth A. Notch-Mediated Determination of Hair-Bundle Polarity in Mechanosensory Hair Cells of the Zebrafish Lateral Line. Curr Biol 2019; 29:3579-3587.e7. [DOI: 10.1016/j.cub.2019.08.060] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2019] [Revised: 07/05/2019] [Accepted: 08/22/2019] [Indexed: 10/25/2022]
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45
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Wong HTC, Zhang Q, Beirl AJ, Petralia RS, Wang YX, Kindt K. Synaptic mitochondria regulate hair-cell synapse size and function. eLife 2019; 8:e48914. [PMID: 31609202 PMCID: PMC6879205 DOI: 10.7554/elife.48914] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Accepted: 10/13/2019] [Indexed: 11/21/2022] Open
Abstract
Sensory hair cells in the ear utilize specialized ribbon synapses. These synapses are defined by electron-dense presynaptic structures called ribbons, composed primarily of the structural protein Ribeye. Previous work has shown that voltage-gated influx of Ca2+ through CaV1.3 channels is critical for hair-cell synapse function and can impede ribbon formation. We show that in mature zebrafish hair cells, evoked presynaptic-Ca2+ influx through CaV1.3 channels initiates mitochondrial-Ca2+ (mito-Ca2+) uptake adjacent to ribbons. Block of mito-Ca2+ uptake in mature cells depresses presynaptic-Ca2+ influx and impacts synapse integrity. In developing zebrafish hair cells, mito-Ca2+ uptake coincides with spontaneous rises in presynaptic-Ca2+ influx. Spontaneous mito-Ca2+ loading lowers cellular NAD+/NADH redox and downregulates ribbon size. Direct application of NAD+ or NADH increases or decreases ribbon size respectively, possibly acting through the NAD(H)-binding domain on Ribeye. Our results present a mechanism where presynaptic- and mito-Ca2+ couple to confer proper presynaptic function and formation.
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MESH Headings
- 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/pharmacology
- Animals
- Animals, Genetically Modified
- Calcium/metabolism
- Calcium Channel Agonists/pharmacology
- Calcium Channel Blockers/pharmacology
- Calcium Channels, L-Type/genetics
- Calcium Channels, L-Type/metabolism
- Calcium Signaling
- Cell Size
- Embryo, Nonmammalian
- Evoked Potentials, Auditory/physiology
- Eye Proteins/chemistry
- Eye Proteins/genetics
- Eye Proteins/metabolism
- Gene Expression
- Hair Cells, Auditory/cytology
- Hair Cells, Auditory/drug effects
- Hair Cells, Auditory/metabolism
- Isradipine/pharmacology
- Mitochondria/drug effects
- Mitochondria/metabolism
- Mitochondria/ultrastructure
- NAD/metabolism
- Oxidation-Reduction
- Protein Binding
- Protein Interaction Domains and Motifs
- Ruthenium Compounds/pharmacology
- Synapses/drug effects
- Synapses/metabolism
- Synapses/ultrastructure
- Synaptic Transmission
- Zebrafish
- Zebrafish Proteins/agonists
- Zebrafish Proteins/antagonists & inhibitors
- Zebrafish Proteins/chemistry
- Zebrafish Proteins/genetics
- Zebrafish Proteins/metabolism
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Affiliation(s)
- Hiu-tung C Wong
- Section on Sensory Cell Development and FunctionNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
- National Institutes of Health-Johns Hopkins University Graduate Partnership ProgramNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Qiuxiang Zhang
- Section on Sensory Cell Development and FunctionNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Alisha J Beirl
- Section on Sensory Cell Development and FunctionNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Ronald S Petralia
- Advanced Imaging CoreNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Ya-Xian Wang
- Advanced Imaging CoreNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Katie Kindt
- Section on Sensory Cell Development and FunctionNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
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46
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Climer LK, Cox AM, Reynolds TJ, Simmons DD. Oncomodulin: The Enigmatic Parvalbumin Protein. Front Mol Neurosci 2019; 12:235. [PMID: 31649505 PMCID: PMC6794386 DOI: 10.3389/fnmol.2019.00235] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2019] [Accepted: 09/13/2019] [Indexed: 01/21/2023] Open
Abstract
EF-hand Ca2+-binding protein family members, α- and β-parvalbumins have been studied for decades. Yet, considerable information is lacking distinguishing functional differences between mammalian α-parvalbumin (PVALB) and oncomodulin (OCM), a branded β-parvalbumin. Herein, we provide an overview detailing the current body of work centered around OCM as an EF-Hand Ca2+-binding protein and describe potential mechanisms of OCM function within the inner ear and immune cells. Additionally, we posit that OCM is evolutionarily distinct from PVALB and most other β-parvalbumins. This review summarizes recent studies pertaining to the function of OCM and emphasizes OCM as a parvalbumin possessing a unique cell and tissue distribution, Ca2+ buffering capacity and phylogenetic origin.
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Affiliation(s)
- Leslie K Climer
- Department of Biology, Baylor University, Waco, TX, United States.,Department of Psychology and Neuroscience, Baylor University, Waco, TX, United States
| | - Andrew M Cox
- Department of Biology, Baylor University, Waco, TX, United States.,Department of Psychology and Neuroscience, Baylor University, Waco, TX, United States
| | | | - Dwayne D Simmons
- Department of Biology, Baylor University, Waco, TX, United States.,Department of Psychology and Neuroscience, Baylor University, Waco, TX, United States.,Biomedical Sciences Program, Baylor University, Waco, TX, United States
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47
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Denans N, Baek S, Piotrowski T. Comparing Sensory Organs to Define the Path for Hair Cell Regeneration. Annu Rev Cell Dev Biol 2019; 35:567-589. [PMID: 31553635 DOI: 10.1146/annurev-cellbio-100818-125503] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Deafness or hearing deficits are debilitating conditions. They are often caused by loss of sensory hair cells or defects in their function. In contrast to mammals, nonmammalian vertebrates robustly regenerate hair cells after injury. Studying the molecular and cellular basis of nonmammalian vertebrate hair cell regeneration provides valuable insights into developing cures for human deafness. In this review, we discuss the current literature on hair cell regeneration in the context of other models for sensory cell regeneration, such as the retina and the olfactory epithelium. This comparison reveals commonalities with, as well as differences between, the different regenerating systems, which begin to define a cellular and molecular blueprint of regeneration. In addition, we propose how new technical advances can address outstanding questions in the field.
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Affiliation(s)
- Nicolas Denans
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA;
| | - Sungmin Baek
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA;
| | - Tatjana Piotrowski
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA;
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48
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Tarchini B, Lu X. New insights into regulation and function of planar polarity in the inner ear. Neurosci Lett 2019; 709:134373. [PMID: 31295539 PMCID: PMC6732021 DOI: 10.1016/j.neulet.2019.134373] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2019] [Revised: 07/02/2019] [Accepted: 07/06/2019] [Indexed: 12/18/2022]
Abstract
Acquisition of cell polarity generates signaling and cytoskeletal asymmetry and thus underpins polarized cell behaviors during tissue morphogenesis. In epithelial tissues, both apical-basal polarity and planar polarity, which refers to cell polarization along an axis orthogonal to the apical-basal axis, are essential for epithelial morphogenesis and function. A prime example of epithelial planar polarity can be found in the auditory sensory epithelium (or organ of Corti, OC). Sensory hair cells, the sound receptors, acquire a planar polarized apical cytoskeleton which is uniformely oriented along an axis orthogonal to the longitudinal axis of the cochlear duct. Both cell-intrinsic and tissue-level planar polarity are necessary for proper perception of sound. Here we review recent insights into the novel roles and mechanisms of planar polarity signaling gained from genetic analysis in mice, focusing mainly on the OC but also with some discussions on the vestibular sensory epithelia.
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Affiliation(s)
- Basile Tarchini
- The Jackson Laboratory, Bar Harbor, ME, 04609, USA; Department of Medicine, Tufts University, Boston, 02111, MA, USA; Graduate School of Biomedical Science and Engineering (GSBSE), University of Maine, Orono, 04469, ME, USA.
| | - Xiaowei Lu
- Department of Cell Biology, University of Virginia Health System, Charlottesville, VA, 22908, USA.
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49
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PCP and Wnt pathway components act in parallel during zebrafish mechanosensory hair cell orientation. Nat Commun 2019; 10:3993. [PMID: 31488837 PMCID: PMC6728366 DOI: 10.1038/s41467-019-12005-y] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2019] [Accepted: 08/05/2019] [Indexed: 12/03/2022] Open
Abstract
Planar cell polarity (PCP) plays crucial roles in developmental processes such as gastrulation, neural tube closure and hearing. Wnt pathway mutants are often classified as PCP mutants due to similarities between their phenotypes. Here, we show that in the zebrafish lateral line, disruptions of the PCP and Wnt pathways have differential effects on hair cell orientations. While mutations in the PCP genes vangl2 and scrib cause random orientations of hair cells, mutations in wnt11f1, gpc4 and fzd7a/b induce hair cells to adopt a concentric pattern. This concentric pattern is not caused by defects in PCP but is due to misaligned support cells. The molecular basis of the support cell defect is unknown but we demonstrate that the PCP and Wnt pathways work in parallel to establish proper hair cell orientation. Consequently, hair cell orientation defects are not solely explained by defects in PCP signaling, and some hair cell phenotypes warrant re-evaluation. Planar cell polarity (PCP) regulates hair cell orientation in the zebrafish lateral line. Here, the authors show that mutating Wnt pathway genes (wnt11f1, fzd7a/b, and gpc4) causes concentric hair cell patterns not regulated by PCP, thus showing PCP/Wnt pathway genes have different consequences on hair cell orientation.
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Schmidt H, Fritzsch B. Npr2 null mutants show initial overshooting followed by reduction of spiral ganglion axon projections combined with near-normal cochleotopic projection. Cell Tissue Res 2019; 378:15-32. [PMID: 31201541 DOI: 10.1007/s00441-019-03050-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Accepted: 05/20/2019] [Indexed: 12/19/2022]
Abstract
Npr2 (natriuretic peptide receptor 2) affects bifurcation of neural crest or placode-derived afferents upon entering the brain stem/spinal cord, leading to a lack of either rostral or caudal branches. Previous work has shown that early embryonic growth of cochlear and vestibular afferents is equally affected in this mutant but later work on postnatal Npr2 point mutations suggested some additional effects on the topology of afferent projections and mild functional defects. Using multicolor lipophilic dye tracing, we show that absence of Npr2 has little to no effect on the initial patterning of inner ear afferents with respect to their dorsoventral cochleotopic-specific projections. However, in contrast to control animals, we found a variable degree of embryonic extension of auditory afferents beyond the boundaries of the anterior cochlear nucleus into the cerebellum that emanates only from apical spiral ganglion neurons. Such expansion has previously only been reported for Hox gene mutants and implies an unclear interaction of Hox codes with Npr2-mediated afferent projection patterning to define boundaries. Some vestibular ganglion neurons expand their projections to reach the cochlear apex and the cochlear nuclei, comparable to previous findings in Neurod1 mutant mice. Before birth, such expansions are reduced or lost leading to truncated projections to the anteroventral cochlear nucleus and expansion of low-frequency fibers of the apex to the posteroventral cochlear nucleus.
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Affiliation(s)
- Hannes Schmidt
- Interfaculty Institute of Biochemistry, University of Tübingen, Tübingen, Germany
| | - Bernd Fritzsch
- Department of Biology & Department of Otolaryngology, CLAS, University of Iowa, 128 Jefferson Avenue, Iowa City, IA, 52242, USA.
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