51
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Yang X, Qian X, Ma R, Wang X, Yang J, Luo W, Chen P, Chi F, Ren D. Establishment of planar cell polarity is coupled to regional cell cycle exit and cell differentiation in the mouse utricle. Sci Rep 2017; 7:43021. [PMID: 28230212 PMCID: PMC5322371 DOI: 10.1038/srep43021] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2016] [Accepted: 01/18/2017] [Indexed: 01/16/2023] Open
Abstract
Sensory hair cells are coordinately oriented within each inner ear sensory organ to exhibit a particular form of planar cell polarity (PCP) necessary for mechanotransduction. However, the developmental events associated with establishing PCP in the vestibule are unclear, hindering data interpretation and employment of the vestibule for PCP studies. Herein, we investigated PCP of the mouse vestibular organs. We further characterised cell cycle exit, cell differentiation, and PCP establishment in the utricle. We found that hair cells formed first in the striolar and medial extrastriolar (MES) regions of the utricle at embryonic day 11.5 (E11.5), while cells in the lateral extrastriolar region (LES) mostly formed at E13.5. Cell differentiation was initiated in the striolar region, which expanded first toward the MES, then to the LES by E15.5. The polarity of hair cells was established at birth along a putative line of polarity reversal (LPR), lateral to the striolar region. Core PCP protein Vangl2 emerged in the cell boundaries since E11.5, while cell intrinsic polarity protein Gαi3 appeared at E12.5, then polarized to the bare zone of individual hair cell at E13.5. These findings provide a blueprint of the developmental events associated with establishing PCP in the utricle.
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Affiliation(s)
- Xiaoyu Yang
- Department of Otology and Skull Base Surgery, Eye &ENT Hospital of Fudan University, Shanghai 200031, China.,Shanghai Clinical Medical Center of Hearing Medicine, Eye &ENT Hospital of Fudan University, Shanghai 200031, China
| | - Xiaoqing Qian
- Department of Otology and Skull Base Surgery, Eye &ENT Hospital of Fudan University, Shanghai 200031, China.,Shanghai Clinical Medical Center of Hearing Medicine, Eye &ENT Hospital of Fudan University, Shanghai 200031, China
| | - Rui Ma
- Department of Otology and Skull Base Surgery, Eye &ENT Hospital of Fudan University, Shanghai 200031, China.,Shanghai Clinical Medical Center of Hearing Medicine, Eye &ENT Hospital of Fudan University, Shanghai 200031, China.,Department of Research Center, Eye &ENT Hospital of Fudan University, Shanghai 200031, China
| | - Xinwei Wang
- Department of Otology and Skull Base Surgery, Eye &ENT Hospital of Fudan University, Shanghai 200031, China.,Shanghai Clinical Medical Center of Hearing Medicine, Eye &ENT Hospital of Fudan University, Shanghai 200031, China
| | - Juanmei Yang
- Department of Otology and Skull Base Surgery, Eye &ENT Hospital of Fudan University, Shanghai 200031, China.,Shanghai Clinical Medical Center of Hearing Medicine, Eye &ENT Hospital of Fudan University, Shanghai 200031, China
| | - Wenwei Luo
- Department of Otology and Skull Base Surgery, Eye &ENT Hospital of Fudan University, Shanghai 200031, China.,Shanghai Clinical Medical Center of Hearing Medicine, Eye &ENT Hospital of Fudan University, Shanghai 200031, China
| | - Ping Chen
- Department of Cell Biology, Emory University, Atlanta, GA 30322, USA
| | - Fanglu Chi
- Department of Otology and Skull Base Surgery, Eye &ENT Hospital of Fudan University, Shanghai 200031, China.,Shanghai Clinical Medical Center of Hearing Medicine, Eye &ENT Hospital of Fudan University, Shanghai 200031, China
| | - Dongdong Ren
- Department of Otology and Skull Base Surgery, Eye &ENT Hospital of Fudan University, Shanghai 200031, China.,Shanghai Clinical Medical Center of Hearing Medicine, Eye &ENT Hospital of Fudan University, Shanghai 200031, China
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52
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Sultemeier DR, Choy KR, Schweizer FE, Hoffman LF. Spaceflight-induced synaptic modifications within hair cells of the mammalian utricle. J Neurophysiol 2017; 117:2163-2178. [PMID: 28228581 DOI: 10.1152/jn.00240.2016] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Revised: 02/21/2017] [Accepted: 02/21/2017] [Indexed: 02/08/2023] Open
Abstract
Exposure to the microgravity conditions of spaceflight alleviates the load normally imposed by the Earth's gravitational field on the inner ear utricular epithelia. Previous ultrastructural investigations have shown that spaceflight induces an increase in synapse density within hair cells of the rat utricle. However, the utricle exhibits broad physiological heterogeneity across different epithelial regions, and it is unknown whether capabilities for synaptic plasticity generalize to hair cells across its topography. To achieve systematic and broader sampling of the epithelium than was previously conducted, we used immunohistochemistry and volumetric image analyses to quantify synapse distributions across representative utricular regions in specimens from mice exposed to spaceflight (a 15-day mission of the space shuttle Discovery). These measures were compared with similarly sampled Earth-bound controls. Following paraformaldehyde fixation and microdissection, immunohistochemistry was performed on intact specimens to label presynaptic ribbons (anti-CtBP2) and postsynaptic receptor complexes (anti-Shank1A). Synapses were identified as closely apposed pre- and postsynaptic puncta. Epithelia from horizontal semicircular canal cristae served as "within-specimen" controls, whereas utricles and cristae from Earth-bound cohorts served as experimental controls. We found that synapse densities decreased in the medial extrastriolae of microgravity specimens compared with experimental controls, whereas they were unchanged in the striolae and horizontal cristae from the two conditions. These data demonstrate that structural plasticity was topographically localized to the utricular region that encodes very low frequency and static changes in linear acceleration, and illuminates the remarkable capabilities of utricular hair cells for synaptic plasticity in adapting to novel gravitational environments.NEW & NOTEWORTHY Spaceflight imposes a radically different sensory environment from that in which the inner ear utricle normally operates. We investigated synaptic modifications in utricles from mice flown aboard a space shuttle mission. Structural synaptic plasticity was detected in the medial extrastriola, a region associated with encoding static head position, as decreased synapse density. These results are remarkably congruent with a recent report of decreased utricular function in astronauts immediately after returning from the International Space Station.
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Affiliation(s)
- David R Sultemeier
- Department of Head & Neck Surgery, David Geffen School of Medicine, University of California, Los Angeles, California
| | - Kristel R Choy
- Department of Head & Neck Surgery, David Geffen School of Medicine, University of California, Los Angeles, California
| | - Felix E Schweizer
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California; and.,Brain Research Institute, David Geffen School of Medicine, University of California, Los Angeles, California
| | - Larry F Hoffman
- Department of Head & Neck Surgery, David Geffen School of Medicine, University of California, Los Angeles, California; .,Brain Research Institute, David Geffen School of Medicine, University of California, Los Angeles, California
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53
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Krey JF, Krystofiak ES, Dumont RA, Vijayakumar S, Choi D, Rivero F, Kachar B, Jones SM, Barr-Gillespie PG. Plastin 1 widens stereocilia by transforming actin filament packing from hexagonal to liquid. J Cell Biol 2016; 215:467-482. [PMID: 27811163 PMCID: PMC5119939 DOI: 10.1083/jcb.201606036] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Revised: 09/29/2016] [Accepted: 10/11/2016] [Indexed: 11/24/2022] Open
Abstract
With their essential role in inner ear function, stereocilia of sensory hair cells demonstrate the importance of cellular actin protrusions. Actin packing in stereocilia is mediated by cross-linkers of the plastin, fascin, and espin families. Although mice lacking espin (ESPN) have no vestibular or auditory function, we found that mice that either lacked plastin 1 (PLS1) or had nonfunctional fascin 2 (FSCN2) had reduced inner ear function, with double-mutant mice most strongly affected. Targeted mass spectrometry indicated that PLS1 was the most abundant cross-linker in vestibular stereocilia and the second most abundant protein overall; ESPN only accounted for ∼15% of the total cross-linkers in bundles. Mouse utricle stereocilia lacking PLS1 were shorter and thinner than wild-type stereocilia. Surprisingly, although wild-type stereocilia had random liquid packing of their actin filaments, stereocilia lacking PLS1 had orderly hexagonal packing. Although all three cross-linkers are required for stereocilia structure and function, PLS1 biases actin toward liquid packing, which allows stereocilia to grow to a greater diameter.
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Affiliation(s)
- Jocelyn F Krey
- Oregon Hearing Research Center, Oregon Health and Science University, Portland, OR 97239
- Vollum Institute, Oregon Health and Science University, Portland, OR 97239
| | - Evan S Krystofiak
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892
| | - Rachel A Dumont
- Oregon Hearing Research Center, Oregon Health and Science University, Portland, OR 97239
- Vollum Institute, Oregon Health and Science University, Portland, OR 97239
| | - Sarath Vijayakumar
- Department of Special Education and Communication Disorders, University of Nebraska-Lincoln, Lincoln, NE 68583
| | - Dongseok Choi
- Oregon Health and Science University-Portland State University School of Public Health, Oregon Health and Science University, Portland, OR 97239
- Graduate School of Dentistry, Kyung Hee University, Seoul 02447, Republic of Korea
| | - Francisco Rivero
- Centre for Cardiovascular and Metabolic Research, The Hull York Medical School, University of Hull, Hull HU6 7RX, England, UK
| | - Bechara Kachar
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892
| | - Sherri M Jones
- Department of Special Education and Communication Disorders, University of Nebraska-Lincoln, Lincoln, NE 68583
| | - Peter G Barr-Gillespie
- Oregon Hearing Research Center, Oregon Health and Science University, Portland, OR 97239
- Vollum Institute, Oregon Health and Science University, Portland, OR 97239
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54
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McLean WJ, McLean DT, Eatock RA, Edge ASB. Distinct capacity for differentiation to inner ear cell types by progenitor cells of the cochlea and vestibular organs. Development 2016; 143:4381-4393. [PMID: 27789624 DOI: 10.1242/dev.139840] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Accepted: 10/11/2016] [Indexed: 01/16/2023]
Abstract
Disorders of hearing and balance are most commonly associated with damage to cochlear and vestibular hair cells or neurons. Although these cells are not capable of spontaneous regeneration, progenitor cells in the hearing and balance organs of the neonatal mammalian inner ear have the capacity to generate new hair cells after damage. To investigate whether these cells are restricted in their differentiation capacity, we assessed the phenotypes of differentiated progenitor cells isolated from three compartments of the mouse inner ear - the vestibular and cochlear sensory epithelia and the spiral ganglion - by measuring electrophysiological properties and gene expression. Lgr5+ progenitor cells from the sensory epithelia gave rise to hair cell-like cells, but not neurons or glial cells. Newly created hair cell-like cells had hair bundle proteins, synaptic proteins and membrane proteins characteristic of the compartment of origin. PLP1+ glial cells from the spiral ganglion were identified as neural progenitors, which gave rise to neurons, astrocytes and oligodendrocytes, but not hair cells. Thus, distinct progenitor populations from the neonatal inner ear differentiate to cell types associated with their organ of origin.
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Affiliation(s)
- Will J McLean
- Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02114, USA.,Eaton-Peabody Laboratories of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA.,Program in Speech and Hearing Bioscience and Technology, Division of Health Sciences and Technology, Harvard & MIT, Cambridge, MA 02139, USA
| | - Dalton T McLean
- Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02114, USA.,Eaton-Peabody Laboratories of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA
| | - Ruth Anne Eatock
- Department of Neurobiology, University of Chicago, Chicago, IL 60637, USA
| | - Albert S B Edge
- Department of Otology and Laryngology, Harvard Medical School, Boston, MA 02114, USA .,Eaton-Peabody Laboratories of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA.,Program in Speech and Hearing Bioscience and Technology, Division of Health Sciences and Technology, Harvard & MIT, Cambridge, MA 02139, USA.,Harvard Stem Cell Institute, Cambridge, MA 02138, USA
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55
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Functional development of mechanosensitive hair cells in stem cell-derived organoids parallels native vestibular hair cells. Nat Commun 2016; 7:11508. [PMID: 27215798 PMCID: PMC4890183 DOI: 10.1038/ncomms11508] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Accepted: 04/05/2016] [Indexed: 12/28/2022] Open
Abstract
Inner ear sensory epithelia contain mechanosensitive hair cells that transmit information to the brain through innervation with bipolar neurons. Mammalian hair cells do not regenerate and are limited in number. Here we investigate the potential to generate mechanosensitive hair cells from mouse embryonic stem cells in a three-dimensional (3D) culture system. The system faithfully recapitulates mouse inner ear induction followed by self-guided development into organoids that morphologically resemble inner ear vestibular organs. We find that organoid hair cells acquire mechanosensitivity equivalent to functionally mature hair cells in postnatal mice. The organoid hair cells also progress through a similar dynamic developmental pattern of ion channel expression, reminiscent of two subtypes of native vestibular hair cells. We conclude that our 3D culture system can generate large numbers of fully functional sensory cells which could be used to investigate mechanisms of inner ear development and disease as well as regenerative mechanisms for inner ear repair. Sensory hair cells from the mammalian inner ear do not regenerate. Here, the authors induce direct hair cell formation from mouse embryonic stem cells using a three-dimensional culture system and observe differentiation of Type I and Type II vestibular hair cells and establishment of synapses with neurons.
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56
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Ebrahim S, Avenarius MR, Grati M, Krey JF, Windsor AM, Sousa AD, Ballesteros A, Cui R, Millis BA, Salles FT, Baird MA, Davidson MW, Jones SM, Choi D, Dong L, Raval MH, Yengo CM, Barr-Gillespie PG, Kachar B. Stereocilia-staircase spacing is influenced by myosin III motors and their cargos espin-1 and espin-like. Nat Commun 2016; 7:10833. [PMID: 26926603 PMCID: PMC4773517 DOI: 10.1038/ncomms10833] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Accepted: 01/25/2016] [Indexed: 12/12/2022] Open
Abstract
Hair cells tightly control the dimensions of their stereocilia, which are actin-rich protrusions with graded heights that mediate mechanotransduction in the inner ear. Two members of the myosin-III family, MYO3A and MYO3B, are thought to regulate stereocilia length by transporting cargos that control actin polymerization at stereocilia tips. We show that eliminating espin-1 (ESPN-1), an isoform of ESPN and a myosin-III cargo, dramatically alters the slope of the stereocilia staircase in a subset of hair cells. Furthermore, we show that espin-like (ESPNL), primarily present in developing stereocilia, is also a myosin-III cargo and is essential for normal hearing. ESPN-1 and ESPNL each bind MYO3A and MYO3B, but differentially influence how the two motors function. Consequently, functional properties of different motor-cargo combinations differentially affect molecular transport and the length of actin protrusions. This mechanism is used by hair cells to establish the required range of stereocilia lengths within a single cell.
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Affiliation(s)
- Seham Ebrahim
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Matthew R Avenarius
- Oregon Hearing Research Center and Vollum Institute, Oregon Health &Science University, Portland, Oregon 97239, USA
| | - M'hamed Grati
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Jocelyn F Krey
- Oregon Hearing Research Center and Vollum Institute, Oregon Health &Science University, Portland, Oregon 97239, USA
| | - Alanna M Windsor
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Aurea D Sousa
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Angela Ballesteros
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Runjia Cui
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Bryan A Millis
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Felipe T Salles
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Michelle A Baird
- National High Magnetic Field Laboratory and Department of Biological Science, Florida State University, Tallahassee, Florida 32310, USA
| | - Michael W Davidson
- National High Magnetic Field Laboratory and Department of Biological Science, Florida State University, Tallahassee, Florida 32310, USA
| | - Sherri M Jones
- Department of Special Education and Communication Disorders, University of Nebraska-Lincoln, Lincoln, Nebraska 68583, USA
| | - Dongseok Choi
- Department of Public Health and Preventive Medicine, Oregon Health and Science University, Portland, Oregon 97239, USA
| | - Lijin Dong
- Genetic Engineering Core, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Manmeet H Raval
- Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, Pennsylvania 17033, USA
| | - Christopher M Yengo
- Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, Pennsylvania 17033, USA
| | - Peter G Barr-Gillespie
- Oregon Hearing Research Center and Vollum Institute, Oregon Health &Science University, Portland, Oregon 97239, USA
| | - Bechara Kachar
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA
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57
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Lim R, Brichta AM. Anatomical and physiological development of the human inner ear. Hear Res 2016; 338:9-21. [PMID: 26900072 DOI: 10.1016/j.heares.2016.02.004] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Revised: 01/20/2016] [Accepted: 02/12/2016] [Indexed: 01/05/2023]
Abstract
We describe the development of the human inner ear with the invagination of the otic vesicle at 4 weeks gestation (WG), the growth of the semicircular canals from 5 WG, and the elongation and coiling of the cochlea at 10 WG. As the membranous labyrinth takes shape, there is a concomitant development of the sensory neuroepithelia and their associated structures within. This review details the growth and differentiation of the vestibular and auditory neuroepithelia, including synaptogenesis, the expression of stereocilia and kinocilia, and innervation of hair cells by afferent and efferent nerve fibres. Along with development of essential sensory structures we outline the formation of crucial accessory structures of the vestibular system - the cupula and otolithic membrane and otoconia as well as the three cochlea compartments and the tectorial membrane. Recent molecular studies have elaborated on classical anatomical studies to characterize the development of prosensory and sensory regions of the fetal human cochlea using the transcription factors, PAX2, MAF-B, SOX2, and SOX9. Further advances are being made with recent physiological studies that are beginning to describe when hair cells become functionally active during human gestation. This article is part of a Special Issue entitled <Annual Reviews 2016>.
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Affiliation(s)
- Rebecca Lim
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, The University of Newcastle, NSW, Australia.
| | - Alan M Brichta
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, The University of Newcastle, NSW, Australia
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58
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Mathur PD, Vijayakumar S, Vashist D, Jones SM, Jones TA, Yang J. A study of whirlin isoforms in the mouse vestibular system suggests potential vestibular dysfunction in DFNB31-deficient patients. Hum Mol Genet 2015; 24:7017-30. [PMID: 26420843 DOI: 10.1093/hmg/ddv403] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Accepted: 09/21/2015] [Indexed: 11/12/2022] Open
Abstract
The DFNB31 gene plays an indispensable role in the cochlea and retina. Mutations in this gene disrupt its various isoforms and lead to non-syndromic deafness, blindness and deaf-blindness. However, the known expression of Dfnb31, the mouse ortholog of DFNB31, in vestibular organs and the potential vestibular-deficient phenotype observed in one Dfnb31 mutant mouse (Dfnb31(wi/wi)) suggest that DFNB31 may also be important for vestibular function. In this study, we find that full-length (FL-) and C-terminal (C-) whirlin isoforms are expressed in the vestibular organs, where their stereociliary localizations are similar to those of developing cochlear inner hair cells. No whirlin is detected in Dfnb31(wi/wi) vestibular organs, while only C-whirlin is expressed in Dfnb31(neo/neo) vestibular organs. Both FL- and C-whirlin isoforms are required for normal vestibular stereociliary growth, although they may play slightly different roles in the central and peripheral zones of the crista ampullaris. Vestibular sensory-evoked potentials demonstrate severe to profound vestibular deficits in Dfnb31(neo/neo) and Dfnb31(wi/wi) mice. Swimming and rotarod tests demonstrate that the two Dfnb31 mutants have balance problems, with Dfnb31(wi/wi) mice being more affected than Dfnb31(neo/neo) mice. Because Dfnb31(wi/wi) and Dfnb31(neo/neo) mice faithfully recapitulate hearing and vision symptoms in patients, our findings of vestibular dysfunction in these Dfnb31 mutants raise the question of whether DFNB31-deficient patients may acquire vestibular as well as hearing and vision loss.
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Affiliation(s)
- Pranav Dinesh Mathur
- Department of Ophthalmology and Visual Sciences, Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT 84132, USA, Department of Neurobiology and Anatomy, University of Utah, 20 North 1900 East, Salt Lake City, UT 84132, USA
| | - Sarath Vijayakumar
- Department of Special Education and Communication Disorders, University of Nebraska-Lincoln, 304 Barkley Memorial Center, Lincoln, NE 68583, USA and
| | - Deepti Vashist
- Department of Ophthalmology and Visual Sciences, Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT 84132, USA
| | - Sherri M Jones
- Department of Special Education and Communication Disorders, University of Nebraska-Lincoln, 304 Barkley Memorial Center, Lincoln, NE 68583, USA and
| | - Timothy A Jones
- Department of Special Education and Communication Disorders, University of Nebraska-Lincoln, 304 Barkley Memorial Center, Lincoln, NE 68583, USA and
| | - Jun Yang
- Department of Ophthalmology and Visual Sciences, Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT 84132, USA, Department of Neurobiology and Anatomy, University of Utah, 20 North 1900 East, Salt Lake City, UT 84132, USA, Division of Otolaryngology, Department of Surgery, University of Utah, 50 North Medical Drive, Salt Lake City, UT 84132, USA
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59
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Falk N, Lösl M, Schröder N, Gießl A. Specialized Cilia in Mammalian Sensory Systems. Cells 2015; 4:500-19. [PMID: 26378583 PMCID: PMC4588048 DOI: 10.3390/cells4030500] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Revised: 08/04/2015] [Accepted: 09/09/2015] [Indexed: 02/01/2023] Open
Abstract
Cilia and flagella are highly conserved and important microtubule-based organelles that project from the surface of eukaryotic cells and act as antennae to sense extracellular signals. Moreover, cilia have emerged as key players in numerous physiological, developmental, and sensory processes such as hearing, olfaction, and photoreception. Genetic defects in ciliary proteins responsible for cilia formation, maintenance, or function underlie a wide array of human diseases like deafness, anosmia, and retinal degeneration in sensory systems. Impairment of more than one sensory organ results in numerous syndromic ciliary disorders like the autosomal recessive genetic diseases Bardet-Biedl and Usher syndrome. Here we describe the structure and distinct functional roles of cilia in sensory organs like the inner ear, the olfactory epithelium, and the retina of the mouse. The spectrum of ciliary function in fundamental cellular processes highlights the importance of elucidating ciliopathy-related proteins in order to find novel potential therapies.
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Affiliation(s)
- Nathalie Falk
- Department of Biology, Animal Physiology, University of Erlangen-Nuremberg, 91058 Erlangen, Germany.
| | - Marlene Lösl
- Department of Biology, Animal Physiology, University of Erlangen-Nuremberg, 91058 Erlangen, Germany.
| | - Nadja Schröder
- Department of Biology, Animal Physiology, University of Erlangen-Nuremberg, 91058 Erlangen, Germany.
| | - Andreas Gießl
- Department of Biology, Animal Physiology, University of Erlangen-Nuremberg, 91058 Erlangen, Germany.
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60
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Meredith FL, Kirk ME, Rennie KJ. Kv1 channels and neural processing in vestibular calyx afferents. Front Syst Neurosci 2015; 9:85. [PMID: 26082693 PMCID: PMC4451359 DOI: 10.3389/fnsys.2015.00085] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2015] [Accepted: 05/18/2015] [Indexed: 11/13/2022] Open
Abstract
Potassium-selective ion channels are important for accurate transmission of signals from auditory and vestibular sensory end organs to their targets in the central nervous system. During different gravity conditions, astronauts experience altered input signals from the peripheral vestibular system resulting in sensorimotor dysfunction. Adaptation to altered sensory input occurs, but it is not explicitly known whether this involves synaptic modifications within the vestibular epithelia. Future investigations of such potential plasticity require a better understanding of the electrophysiological mechanisms underlying the known heterogeneity of afferent discharge under normal conditions. This study advances this understanding by examining the role of the Kv1 potassium channel family in mediating action potentials in specialized vestibular afferent calyx endings in the gerbil crista and utricle. Pharmacological agents selective for different sub-types of Kv1 channels were tested on membrane responses in whole cell recordings in the crista. Kv1 channels sensitive to α-dendrotoxin and dendrotoxin-K were found to prevail in the central regions, whereas K(+) channels sensitive to margatoxin, which blocks Kv1.3 and 1.6 channels, were more prominent in peripheral regions. Margatoxin-sensitive currents showed voltage-dependent inactivation. Dendrotoxin-sensitive currents showed no inactivation and dampened excitability in calyces in central neuroepithelial regions. The differential distribution of Kv1 potassium channels in vestibular afferents supports their importance in accurately relaying gravitational and head movement signals through specialized lines to the central nervous system. Pharmacological modulation of specific groups of K(+) channels could help alleviate vestibular dysfunction on earth and in space.
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Affiliation(s)
- Frances L Meredith
- Department of Otolaryngology, University of Colorado School of Medicine Aurora, Colorado, USA
| | - Matthew E Kirk
- Department of Otolaryngology, University of Colorado School of Medicine Aurora, Colorado, USA
| | - Katherine J Rennie
- Department of Otolaryngology, University of Colorado School of Medicine Aurora, Colorado, USA ; Department of Physiology and Biophysics, University of Colorado School of Medicine Aurora, Colorado, USA
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61
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Huwe JA, Logan GJ, Williams B, Rowe MH, Peterson EH. Utricular afferents: morphology of peripheral terminals. J Neurophysiol 2015; 113:2420-33. [PMID: 25632074 DOI: 10.1152/jn.00481.2014] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Accepted: 01/23/2015] [Indexed: 11/22/2022] Open
Abstract
The utricle provides critical information about spatiotemporal properties of head movement. It comprises multiple subdivisions whose functional roles are poorly understood. We previously identified four subdivisions in turtle utricle, based on hair bundle structure and mechanics, otoconial membrane structure and hair bundle coupling, and immunoreactivity to calcium-binding proteins. Here we ask whether these macular subdivisions are innervated by distinctive populations of afferents to help us understand the role each subdivision plays in signaling head movements. We quantified the morphology of 173 afferents and identified six afferent classes, which differ in structure and macular locus. Calyceal and dimorphic afferents innervate one striolar band. Bouton afferents innervate a second striolar band; they have elongated terminals and the thickest processes and axons of all bouton units. Bouton afferents in lateral (LES) and medial (MES) extrastriolae have small-diameter axons but differ in collecting area, bouton number, and hair cell contacts (LES >> MES). A fourth, distinctive population of bouton afferents supplies the juxtastriola. These results, combined with our earlier findings on utricular hair cells and the otoconial membrane, suggest the hypotheses that MES and calyceal afferents encode head movement direction with high spatial resolution and that MES afferents are well suited to signal three-dimensional head orientation and striolar afferents to signal head movement onset.
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Affiliation(s)
- J A Huwe
- Department of Biological Sciences and Neuroscience Program, Ohio University, Athens, Ohio
| | - G J Logan
- Department of Biological Sciences and Neuroscience Program, Ohio University, Athens, Ohio
| | - B Williams
- Department of Biological Sciences and Neuroscience Program, Ohio University, Athens, Ohio
| | - M H Rowe
- Department of Biological Sciences and Neuroscience Program, Ohio University, Athens, Ohio
| | - E H Peterson
- Department of Biological Sciences and Neuroscience Program, Ohio University, Athens, Ohio
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Davis JL, Grant JW. Turtle utricle dynamic behavior using a combined anatomically accurate model and experimentally measured hair bundle stiffness. Hear Res 2014; 318:37-44. [PMID: 25445820 DOI: 10.1016/j.heares.2014.10.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Revised: 08/11/2014] [Accepted: 10/21/2014] [Indexed: 11/27/2022]
Abstract
Anatomically correct turtle utricle geometry was incorporated into two finite element models. The geometrically accurate model included appropriately shaped macular surface and otoconial layer, compact gel and column filament (or shear) layer thicknesses and thickness distributions. The first model included a shear layer where the effects of hair bundle stiffness was included as part of the shear layer modulus. This solid model's undamped natural frequency was matched to an experimentally measured value. This frequency match established a realistic value of the effective shear layer Young's modulus of 16 Pa. We feel this is the most accurate prediction of this shear layer modulus and fits with other estimates (Kondrachuk, 2001b). The second model incorporated only beam elements in the shear layer to represent hair cell bundle stiffness. The beam element stiffness's were further distributed to represent their location on the neuroepithelial surface. Experimentally measured striola hair cell bundles mean stiffness values were used in the striolar region and the mean extrastriola hair cell bundles stiffness values were used in this region. The results from this second model indicated that hair cell bundle stiffness contributes approximately 40% to the overall stiffness of the shear layer-hair cell bundle complex. This analysis shows that high mass saccules, in general, achieve high gain at the sacrifice of frequency bandwidth. We propose the mechanism by which this can be achieved is through increase the otoconial layer mass. The theoretical difference in gain (deflection per acceleration) is shown for saccules with large otoconial layer mass relative to saccules and utricles with small otoconial layer mass. Also discussed is the necessity of these high mass saccules to increase their overall system shear layer stiffness. Undamped natural frequencies and mode shapes for these sensors are shown.
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Affiliation(s)
- J L Davis
- Department of Engineering, University of Southern Indiana, 8600 University Blvd., Evansville, IN 47712, USA.
| | - J W Grant
- Department of Biomedical Engineering and Mechanics, Blacksburg, VA 24061, USA
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63
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Pujol R, Pickett SB, Nguyen TB, Stone JS. Large basolateral processes on type II hair cells are novel processing units in mammalian vestibular organs. J Comp Neurol 2014; 522:3141-59. [PMID: 24825750 DOI: 10.1002/cne.23625] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Revised: 05/05/2014] [Accepted: 05/06/2014] [Indexed: 12/29/2022]
Abstract
Sensory receptors in the vestibular system (hair cells) encode head movements and drive central motor reflexes that control gaze, body movements, and body orientation. In mammals, type I and II vestibular hair cells are defined by their shape, contacts with vestibular afferent nerves, and membrane conductance. Here we describe unique morphological features of type II vestibular hair cells in mature rodents (mice and gerbils) and bats. These features are cytoplasmic processes that extend laterally from the hair cell base and project under type I hair cells. Closer analysis of adult mouse utricles demonstrated that the basolateral processes of type II hair cells vary in shape, size, and branching, with the longest processes extending three to four hair cell widths. The hair cell basolateral processes synapse upon vestibular afferent nerves and receive inputs from vestibular efferent nerves. Furthermore, some basolateral processes make physical contacts with the processes of other type II hair cells, forming some sort of network among type II hair cells. Basolateral processes are rare in perinatal mice and do not attain their mature form until 3-6 weeks of age. These observations demonstrate that basolateral processes are significant signaling regions of type II vestibular hair cells and suggest that type II hair cells may directly communicate with each other, which has not been described in vertebrates.
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Affiliation(s)
- Rémy Pujol
- The Virginia Merrill Bloedel Hearing Research Center, and the Department of Otolaryngology-Head and Neck Surgery, University of Washington, Seattle, Washington, 98195-7923; INSERM Unit 1051, Institute of Neuroscience, 34091, Montpellier, France
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64
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Koehler KR, Hashino E. 3D mouse embryonic stem cell culture for generating inner ear organoids. Nat Protoc 2014; 9:1229-44. [PMID: 24784820 DOI: 10.1038/nprot.2014.100] [Citation(s) in RCA: 98] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
This protocol describes a culture system in which inner-ear sensory tissue is produced from mouse embryonic stem (ES) cells under chemically defined conditions. This model is amenable to basic and translational investigations into inner ear biology and regeneration. In this protocol, mouse ES cells are aggregated in 96-well plates in medium containing extracellular matrix proteins to promote epithelialization. During the first 14 d, a series of precisely timed protein and small-molecule treatments sequentially induce epithelia that represent the mouse embryonic non-neural ectoderm, preplacodal ectoderm and otic vesicle epithelia. Ultimately, these tissues develop into cysts with a pseudostratified epithelium containing inner ear hair cells and supporting cells after 16-20 d. Concurrently, sensory-like neurons generate synapse-like structures with the derived hair cells. We have designated the stem cell-derived epithelia harboring hair cells, supporting cells and sensory-like neurons as inner ear organoids. This method provides a reproducible and scalable means to generate inner ear sensory tissue in vitro.
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Affiliation(s)
- Karl R Koehler
- 1] Medical Neuroscience Graduate Program, Indiana University School of Medicine, Indianapolis, Indiana, USA. [2] Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana, USA. [3] Department of Otolaryngology-Head and Neck Surgery, Indiana University School of Medicine, Indianapolis, Indiana, USA
| | - Eri Hashino
- 1] Medical Neuroscience Graduate Program, Indiana University School of Medicine, Indianapolis, Indiana, USA. [2] Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana, USA. [3] Department of Otolaryngology-Head and Neck Surgery, Indiana University School of Medicine, Indianapolis, Indiana, USA
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65
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Tropitzsch A, Arnold H, Bassiouni M, Müller A, Eckhard A, Müller M, Löwenheim H. Assessing cisplatin-induced ototoxicity and otoprotection in whole organ culture of the mouse inner ear in simulated microgravity. Toxicol Lett 2014; 227:203-12. [PMID: 24709139 DOI: 10.1016/j.toxlet.2014.03.022] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Revised: 03/25/2014] [Accepted: 03/27/2014] [Indexed: 12/20/2022]
Abstract
Cisplatin is a widely used anti-cancer drug. Ototoxicity is a major dose-limiting side-effect. A reproducible mammalian in-vitro model of cisplatin ototoxicity is required to screen and validate otoprotective drug candidates. We utilized a whole organ culture system of the postnatal mouse inner ear in a rotating wall vessel bioreactor under "simulated microgravity" culture conditions. As previously described this system allows whole organ culture of the inner ear and quantitative assessment of ototoxic effects of aminoglycoside induced hair cell loss. Here we demonstrate that this model is also applicable to the assessment of cisplatin induced ototoxicity. In this model cisplatin induced hair cell loss was dose and time dependent. Increasing exposure time of cisplatin led to decreasing EC50 concentrations. Outer hair cells were more susceptible than inner hair cells, and hair cells in the cochlear base were more susceptible than hair cells in the cochlear apex. Initial cisplatin dose determined the final extent of hair cell loss irrespective if the drug was withdrawn or continued. Dose dependant otoprotection was demonstrated by co-administration of the antioxidant agent N-acetyl l-cysteine. The results support the use of this inner ear organ culture system as an in vitro assay and validation platform for inner ear toxicology and the search for otoprotective compounds.
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Affiliation(s)
- Anke Tropitzsch
- University of Tübingen Medical School, Department of Otorhinolaryngology - Head & Neck Surgery, Hearing Research Center, Elfriede-Aulhorn-Straße 5, D-72076 Tübingen, Germany.
| | - Heinz Arnold
- University of Tübingen Medical School, Department of Otorhinolaryngology - Head & Neck Surgery, Hearing Research Center, Elfriede-Aulhorn-Straße 5, D-72076 Tübingen, Germany.
| | - Mohamed Bassiouni
- University of Tübingen Medical School, Department of Otorhinolaryngology - Head & Neck Surgery, Hearing Research Center, Elfriede-Aulhorn-Straße 5, D-72076 Tübingen, Germany.
| | - Andrea Müller
- University of Tübingen Medical School, Department of Otorhinolaryngology - Head & Neck Surgery, Hearing Research Center, Elfriede-Aulhorn-Straße 5, D-72076 Tübingen, Germany.
| | - Andreas Eckhard
- University of Tübingen Medical School, Department of Otorhinolaryngology - Head & Neck Surgery, Hearing Research Center, Elfriede-Aulhorn-Straße 5, D-72076 Tübingen, Germany.
| | - Marcus Müller
- University of Tübingen Medical School, Department of Otorhinolaryngology - Head & Neck Surgery, Hearing Research Center, Elfriede-Aulhorn-Straße 5, D-72076 Tübingen, Germany.
| | - Hubert Löwenheim
- University of Tübingen Medical School, Department of Otorhinolaryngology - Head & Neck Surgery, Hearing Research Center, Elfriede-Aulhorn-Straße 5, D-72076 Tübingen, Germany.
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66
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Zheng L, Beeler DM, Bartles JR. Characterization and regulation of an additional actin-filament-binding site in large isoforms of the stereocilia actin-bundling protein espin. J Cell Sci 2014; 127:1306-17. [PMID: 24424026 PMCID: PMC3953818 DOI: 10.1242/jcs.143255] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The espin actin-bundling proteins, which are produced as isoforms of different sizes from a single gene, are required for the growth of hair cell stereocilia. We have characterized an additional actin-filament-binding site present in the extended amino-termini of large espin isoforms. Constitutively active in espin 2, the site increased the size of actin bundles formed in vitro and inhibited actin fluorescence recovery in microvilli. In espin 1, which has an N-terminal ankyrin repeat domain, the site was autoinhibited by binding between the ankyrin repeat domain and a peptide near the actin-binding site. Deletion of this peptide from espin 1 activated its actin-binding site. The peptide resembled tail homology domain I of myosin III, a ligand of the ankyrin repeat domain localized with espin 1 at the tip of stereocilia. A myosin III tail homology domain I peptide, but not scrambled control peptides, inhibited internal binding of the ankyrin repeat domain and released the espin 1 actin-binding site from autoinhibition. Thus, this regulation could result in local activation of the additional actin-binding site of espin 1 by myosin III in stereocilia.
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Affiliation(s)
- Lili Zheng
- Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611 USA
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67
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Generation of inner ear sensory epithelia from pluripotent stem cells in 3D culture. Nature 2013; 500:217-21. [PMID: 23842490 PMCID: PMC3739998 DOI: 10.1038/nature12298] [Citation(s) in RCA: 270] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2012] [Accepted: 05/13/2013] [Indexed: 02/06/2023]
Abstract
The inner ear contains sensory epithelia that detect head movements, gravity and sound. It is unclear how to derive these sensory epithelia from pluripotent stem cells, a process which will be critical for modeling inner ear disorders or developing cell-based therapies for profound hearing loss and balance disorders1,2. To date, attempts to derive inner ear mechanosensitive hair cells and sensory neurons have resulted in inefficient or incomplete phenotypic conversion of stem cells into inner ear-like cells3–7. A key insight lacking from these previous studies is the importance of the non-neural and pre-placodal ectoderm, two critical precursors during inner ear development8–11. Here we report the step-wise differentiation of inner ear sensory epithelia from mouse embryonic stem cells (ESCs) in three-dimensional culture12,13. We show that by recapitulating in vivo development with precise temporal control of BMP, TGFβ and FGF signaling, ESC aggregates transform sequentially into non-neural, pre-placodal and otic placode-like epithelia. Remarkably, in a self-organized process that mimics normal development, vesicles containing prosensory cells emerge from the presumptive otic placodes and give rise to hair cells bearing stereocilia bundles and a kinocilium. Moreover, these stem cell-derived hair cells exhibit functional properties of native mechanosensitive hair cells and form specialized synapses with sensory neurons that have also arisen from ESCs in the culture. Finally, we demonstrate how these vesicles are structurally and biochemically comparable to developing vestibular end organs. Our data thus establish a novel in vitro model of inner ear differentiation that can be used to gain deeper insight into inner ear development and disorder.
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Abstract
Afferent nerve fibers in the central zones of vestibular epithelia form calyceal endings around type I hair cells and have phasic response properties that emphasize fast head motions. We investigated how stages from hair-cell transduction to calyceal spiking contribute tuning and timing to central (striolar)-zone afferents of the rat saccular epithelium. In an excised preparation, we deflected individual hair bundles with rigid probes driven with steps and sinusoids (0.5-500 Hz) and recorded whole-cell responses from hair cells and calyces at room temperature and body temperature. In immature hair cells and calyces (postnatal days (P)1-P4), tuning sharpened at each stage. Transducer adaptation and membrane-charging time produced bandpass filtering of the receptor potential with best frequencies of 10-30 Hz and phase leads below 10 Hz. For small stimuli, electrical resonances sharply tuned the hair-cell membrane in the frequency range of 5-40 Hz. The synaptic delay of quantal transmission added a phase lag at frequencies above 10 Hz. The influence of spike thresholds at the calyceal spike initiation stage sharpened tuning and advanced response phase. Two additional mechanisms strongly advanced response phase above 10 Hz when present: (1) maturing (P7-P9) type I hair cells acquired low-voltage-activated channels that shortened the rise time of the receptor potential and (2) some calyces had nonquantal transmission with little synaptic delay. By reducing response time, the identified inner-ear mechanisms (transducer adaptation, low-voltage-activated channels, nonquantal transmission, and spike triggering) may compensate for transmission delays in vestibular reflex pathways and help stabilize posture and gaze during rapid head motions.
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69
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Dimiccoli M, Girard B, Berthoz A, Bennequin D. Striola magica. A functional explanation of otolith geometry. J Comput Neurosci 2013; 35:125-54. [DOI: 10.1007/s10827-013-0444-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2011] [Revised: 01/22/2013] [Accepted: 01/27/2013] [Indexed: 10/27/2022]
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Hair cell replacement in adult mouse utricles after targeted ablation of hair cells with diphtheria toxin. J Neurosci 2013; 32:15093-105. [PMID: 23100430 DOI: 10.1523/jneurosci.1709-12.2012] [Citation(s) in RCA: 134] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
We developed a transgenic mouse to permit conditional and selective ablation of hair cells in the adult mouse utricle by inserting the human diphtheria toxin receptor (DTR) gene into the Pou4f3 gene, which encodes a hair cell-specific transcription factor. In adult wild-type mice, administration of diphtheria toxin (DT) caused no significant hair cell loss. In adult Pou4f3(+/DTR) mice, DT treatment reduced hair cell numbers to 6% of normal by 14 days post-DT. Remaining hair cells were located primarily in the lateral extrastriola. Over time, hair cell numbers increased in these regions, reaching 17% of untreated Pou4f3(+/DTR) mice by 60 days post-DT. Replacement hair cells were morphologically distinct, with multiple cytoplasmic processes, and displayed evidence for active mechanotransduction channels and synapses characteristic of type II hair cells. Three lines of evidence suggest replacement hair cells were derived via direct (nonmitotic) transdifferentiation of supporting cells: new hair cells did not incorporate BrdU, supporting cells upregulated the pro-hair cell gene Atoh1, and supporting cell numbers decreased over time. This study introduces a new method for efficient conditional hair cell ablation in adult mouse utricles and demonstrates that hair cells are spontaneously regenerated in vivo in regions where there may be ongoing hair cell turnover.
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71
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A mutation in the Srrm4 gene causes alternative splicing defects and deafness in the Bronx waltzer mouse. PLoS Genet 2012; 8:e1002966. [PMID: 23055939 PMCID: PMC3464207 DOI: 10.1371/journal.pgen.1002966] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2012] [Accepted: 08/08/2012] [Indexed: 11/19/2022] Open
Abstract
Sensory hair cells are essential for hearing and balance. Their development from epithelial precursors has been extensively characterized with respect to transcriptional regulation, but not in terms of posttranscriptional influences. Here we report on the identification and functional characterization of an alternative-splicing regulator whose inactivation is responsible for defective hair-cell development, deafness, and impaired balance in the spontaneous mutant Bronx waltzer (bv) mouse. We used positional cloning and transgenic rescue to locate the bv mutation to the splicing factor-encoding gene Ser/Arg repetitive matrix 4 (Srrm4). Transcriptome-wide analysis of pre–mRNA splicing in the sensory patches of embryonic inner ears revealed that specific alternative exons were skipped at abnormally high rates in the bv mice. Minigene experiments in a heterologous expression system confirmed that these skipped exons require Srrm4 for inclusion into the mature mRNA. Sequence analysis and mutagenesis experiments showed that the affected transcripts share a novel motif that is necessary for the Srrm4-dependent alternative splicing. Functional annotations and protein–protein interaction data indicated that the encoded proteins cluster in the secretion and neurotransmission pathways. In addition, the splicing of a few transcriptional regulators was found to be Srrm4 dependent, and several of the genes known to be targeted by these regulators were expressed at reduced levels in the bv mice. Although Srrm4 expression was detected in neural tissues as well as hair cells, analyses of the bv mouse cerebellum and neocortex failed to detect splicing defects. Our data suggest that Srrm4 function is critical in the hearing and balance organs, but not in all neural tissues. Srrm4 is the first alternative-splicing regulator to be associated with hearing, and the analysis of bv mice provides exon-level insights into hair-cell development. The identification of novel deafness-causing mutations has been instrumental in revealing unexpected mechanisms that are required for development of the sound- and gravity-sensing hair cells of the inner ear. The Bronx waltzer (bv) mouse is characterized by defects in hair-cell development, as well as by deafness and impaired balance. Here, we report on our identification of a mutation in the Ser/Arg repetitive matrix 4 (Srrm4) gene as the source of these defects. The encoded protein, Srrm4, belongs to a family of RNA splicing factors that regulate the inclusion of certain genetic information (i.e. alternative exons) into the transcribed RNA. We analyzed the molecular function of Srrm4 by comparing the exon composition of RNAs in the inner ear of bv and control mice. This approach revealed that, in the bv mice, specific alternative exons were omitted from protein-encoding RNAs. The affected transcripts shared two features: they contained a short sequence motif that was required for Srrm4-dependent splicing, and they encoded proteins that were related predominantly to secretion and neurotransmission. In addition, RNAs of a few gene expression regulators contained Srrm4-regulated exons. Our data suggest that Srrm4-dependent alternative splicing has a profound effect on the developmental program of hair cells.
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72
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Burns JC, On D, Baker W, Collado MS, Corwin JT. Over half the hair cells in the mouse utricle first appear after birth, with significant numbers originating from early postnatal mitotic production in peripheral and striolar growth zones. J Assoc Res Otolaryngol 2012; 13:609-27. [PMID: 22752453 DOI: 10.1007/s10162-012-0337-0] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2012] [Accepted: 05/25/2012] [Indexed: 12/22/2022] Open
Abstract
Many non-mammalian vertebrates produce hair cells throughout life and recover from hearing and balance deficits through regeneration. In contrast, embryonic production of hair cells declines sharply in mammals where deficits from hair cell losses are typically permanent. Hair cell density estimates recently suggested that the vestibular organs of mice continue to add hair cells after birth, so we undertook comprehensive counting in murine utricles at different ages. The counts show that 51% of the hair cells in adults arise during the 2 weeks after birth. Immature hair cells are most common near the neonatal macula's peripheral edge and striola, where anti-Ki-67 labels cycling nuclei in zones that appear to contain niches for supporting-cell-like stem cells. In vivo lineage tracing in a novel reporter mouse where tamoxifen-inducible supporting cell-specific Cre expression switched tdTomato fluorescence to eGFP fluorescence showed that proteolipid-protein-1-expressing supporting cells are an important source of the new hair cells. To assess the contributions of postnatal cell divisions, we gave mice an injection of BrdU or EdU on the day of birth. The labels were restricted to supporting cells 1 day later, but by 12 days, 31% of the labeled nuclei were in myosin-VIIA-positive hair cells. Thus, hair cell populations in neonatal mouse utricles grow appreciably through two processes: the progressive differentiation of cells generated before birth and the differentiation of new cells arising from divisions of progenitors that progress through S phase soon after birth. Subsequent declines in these processes coincide with maturational changes that appear unique to mammalian supporting cells.
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Affiliation(s)
- Joseph C Burns
- Department of Neuroscience, University of Virginia School of Medicine, 409 Lane Rd, Charlottesville, VA 22908, USA.
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73
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Hair bundle defects and loss of function in the vestibular end organs of mice lacking the receptor-like inositol lipid phosphatase PTPRQ. J Neurosci 2012; 32:2762-72. [PMID: 22357859 DOI: 10.1523/jneurosci.3635-11.2012] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Recent studies have shown that mutations in PTPRQ, a gene encoding a receptor-like inositol lipid phosphatase, cause recessive, nonsyndromic, hereditary hearing loss with associated vestibular dysfunction. Although null mutations in Ptprq cause the loss of high-frequency auditory hair cells and deafness in mice, a loss of vestibular hair cells and overt behavioral defects characteristic of vestibular dysfunction have not been described. Hair bundle structure and vestibular function were therefore examined in Ptprq mutant mice. Between postnatal days 5 and 16, hair bundles in the extrastriolar regions of the utricle in Ptprq(-/-) mice become significantly longer than those in heterozygous controls. This increase in length (up to 50%) is accompanied by the loss and fusion of stereocilia. Loss and fusion of stereocilia also occurs in the striolar region of the utricle in Ptprq(-/-) mice, but is not accompanied by hair bundle elongation. These abnormalities persist until 12 months of age but are not accompanied by significant hair cell loss. Hair bundle defects are also observed in the saccule and ampullae of Ptprq(-/-) mice. At ∼3 months of age, vestibular evoked potentials were absent from the majority (12 of 15) of Ptprq(-/-) mice examined, and could only be detected at high stimulus levels in the other 3 mutants. Subtle but distinct defects in swimming behavior were detected in most (seven of eight) mutants tested. The results reveal a distinct phenotype in the vestibular system of Ptprq(-/-) mice and suggest similar hair bundle defects may underlie the vestibular dysfunction reported in humans with mutations in PTPRQ.
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74
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Levin ME, Holt JR. The function and molecular identity of inward rectifier channels in vestibular hair cells of the mouse inner ear. J Neurophysiol 2012; 108:175-86. [PMID: 22496522 DOI: 10.1152/jn.00098.2012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Inner ear hair cells respond to mechanical stimuli with graded receptor potentials. These graded responses are modulated by a host of voltage-dependent currents that flow across the basolateral membrane. Here, we examine the molecular identity and the function of a class of voltage-dependent ion channels that carries the potassium-selective inward rectifier current known as I(K1). I(K1) has been identified in vestibular hair cells of various species, but its molecular composition and functional contributions remain obscure. We used quantitative RT-PCR to show that the inward rectifier gene, Kir2.1, is highly expressed in mouse utricle between embryonic day 15 and adulthood. We confirmed Kir2.1 protein expression in hair cells by immunolocalization. To examine the molecular composition of I(K1), we recorded voltage-dependent currents from type II hair cells in response to 50-ms steps from -124 to -54 in 10-mV increments. Wild-type cells had rapidly activating inward currents with reversal potentials close to the K(+) equilibrium potential and a whole-cell conductance of 4.8 ± 1.5 nS (n = 46). In utricle hair cells from Kir2.1-deficient (Kir2.1(-/-)) mice, I(K1) was absent at all stages examined. To identify the functional contribution of Kir2.1, we recorded membrane responses in current-clamp mode. Hair cells from Kir2.1(-/-) mice had significantly (P < 0.001) more depolarized resting potentials and larger, slower membrane responses than those of wild-type cells. These data suggest that Kir2.1 is required for I(K1) in type II utricle hair cells and contributes to hyperpolarized resting potentials and fast, small amplitude receptor potentials in response to current inputs, such as those evoked by hair bundle deflections.
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Affiliation(s)
- Michaela E Levin
- Department of Neuroscience, University of Virginia School of Medicine, Charlottesville, Virginia, USA
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75
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Zakir M, Wu LQ, Dickman JD. Morphology and innervation of the vestibular lagena in pigeons. Neuroscience 2012; 209:97-107. [PMID: 22387112 DOI: 10.1016/j.neuroscience.2012.02.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Revised: 02/05/2012] [Accepted: 02/08/2012] [Indexed: 11/26/2022]
Abstract
The morphological characteristics of the pigeon lagena were examined using histology, scanning electron microscopy, and biotinylated dextran amine (BDA) neural tracers. The lagena epithelium was observed to lie partially in a parasagittal plane, but was also U-shaped with orthogonal (lateral) directed tips. Hair cell planar polarities were oriented away from a central reversal line that ran nearly the length of the epithelium. Similar to the vertebrate utricle and saccule, three afferent classes were observed based upon their terminal innervation pattern, which include calyx, dimorph, and bouton fibers. Calyx and dimorph afferents innervated the striola region of the lagena, whereas bouton afferents innervated the extrastriola and a small region of the central striola known as the type II band. Calyx units had large calyceal terminal structures that innervated only type I hair cells. Dimorph afferents innervated both type I and II hair cells, with calyx and bouton terminals. Bouton afferents had the largest most complex innervation patterns and the greatest terminal areas contacting many hair cells.
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Affiliation(s)
- M Zakir
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
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76
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Inhibition of Notch activity promotes nonmitotic regeneration of hair cells in the adult mouse utricles. J Neurosci 2011; 31:15329-39. [PMID: 22031879 DOI: 10.1523/jneurosci.2057-11.2011] [Citation(s) in RCA: 127] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The capacity of adult mammals to regenerate sensory hair cells is not well defined. To explore early steps in this process, we examined reactivation of a transiently expressed developmental gene, Atoh1, in adult mouse utricles after neomycin-induced hair cell death in culture. Using an adenoviral reporter for Atoh1 enhancer, we found that Atoh1 transcription is activated in some hair cell progenitors (supporting cells) 3 d after neomycin treatment. By 18 d after neomycin, the number of cells with Atoh1 transcriptional activity increased significantly, but few cells acquired hair cell features (i.e., accumulated ATOH1 or myosin VIIa protein or developed stereocilia). Treatment with DAPT, an inhibitor of γ-secretase, reduced notch pathway activity, enhanced Atoh1 transcriptional activity, and dramatically increased the number of Atoh1-expressing cells with hair cell features, but only in the striolar/juxtastriolar region. Similar effects were seen with TAPI-1, an inhibitor of another enzyme required for notch activity (TACE). Division of supporting cells was rare in any control or DAPT-treated utricles. This study shows that mature mammals have a natural capacity to initiate vestibular hair cell regeneration and suggests that regional notch activity is a significant inhibitor of direct transdifferentiation of supporting cells into hair cells following damage.
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77
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Eatock RA, Songer JE. Vestibular hair cells and afferents: two channels for head motion signals. Annu Rev Neurosci 2011; 34:501-34. [PMID: 21469959 DOI: 10.1146/annurev-neuro-061010-113710] [Citation(s) in RCA: 158] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Vestibular epithelia of the inner ear detect head motions over a wide range of amplitudes and frequencies. In mammals, afferent nerve fibers from central and peripheral zones of vestibular epithelia form distinct populations with different response dynamics and spike timing. Central-zone afferents are large, fast conduits for phasic signals encoded in irregular spike trains. The finer afferents from peripheral zones conduct more slowly and encode more tonic, linear signals in highly regular spike trains. The hair cells are also of two types, I and II, but the two types do not correspond directly to the two afferent populations. Zonal differences in afferent response dynamics may arise at multiple stages, including mechanoelectrical transduction, voltage-gated channels in hair cells and afferents, afferent transmission at calyceal and bouton synapses, and spike generation in regular and irregular afferents. In contrast, zonal differences in spike timing may depend more simply on the selective expression of low-voltage-activated ion channels by irregular afferents.
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Affiliation(s)
- Ruth Anne Eatock
- Department of Otology and Laryngology, Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02114, USA.
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78
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The postnatal accumulation of junctional E-cadherin is inversely correlated with the capacity for supporting cells to convert directly into sensory hair cells in mammalian balance organs. J Neurosci 2011; 31:11855-66. [PMID: 21849546 DOI: 10.1523/jneurosci.2525-11.2011] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Mammals experience permanent impairments from hair cell (HC) losses, but birds and other non-mammals quickly recover hearing and balance senses after supporting cells (SCs) give rise to replacement HCs. Avian HC epithelia express little or no E-cadherin, and differences in the thickness of F-actin belts at SC junctions strongly correlate with different species' capacities for HC replacement, so we investigated junctional cadherins in human and murine ears. We found strong E-cadherin expression at SC-SC junctions that increases more than sixfold postnatally in mice. When we cultured utricles from young mice with γ-secretase inhibitors (GSIs), striolar SCs completely internalized their E-cadherin, without affecting N-cadherin. Hes and Hey expression also decreased and the SCs began to express Atoh1. After 48 h, those SCs expressed myosins VI and VIIA, and by 72 h, they developed hair bundles. However, some scattered striolar SCs retained E-cadherin and the SC phenotype. In extrastriolar regions, the vast majority of SCs also retained E-cadherin and failed to convert into HCs even after long GSI treatments. Microscopic measurements revealed that the junctions between extrastriolar SCs were more developed than those between striolar SCs. In GSI-treated utricles as old as P12, differentiated striolar SCs converted into HCs, but such responses declined with age and ceased by P16. Thus, temporal and spatial differences in postnatal SC-to-HC phenotype conversion capacity are linked to the structural attributes of E-cadherin containing SC junctions in mammals, which differ substantially from their counterparts in non-mammalian vertebrates that readily recover from hearing and balance deficits through hair cell regeneration.
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79
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Spoon C, Moravec WJ, Rowe MH, Grant JW, Peterson EH. Steady-state stiffness of utricular hair cells depends on macular location and hair bundle structure. J Neurophysiol 2011; 106:2950-63. [PMID: 21918003 DOI: 10.1152/jn.00469.2011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Spatial and temporal properties of head movement are encoded by vestibular hair cells in the inner ear. One of the most striking features of these receptors is the orderly structural variation in their mechanoreceptive hair bundles, but the functional significance of this diversity is poorly understood. We tested the hypothesis that hair bundle structure is a significant contributor to hair bundle mechanics by comparing structure and steady-state stiffness of 73 hair bundles at varying locations on the utricular macula. Our first major finding is that stiffness of utricular hair bundles varies systematically with macular locus. Stiffness values are highest in the striola, near the line of hair bundle polarity reversal, and decline exponentially toward the medial extrastriola. Striolar bundles are significantly more stiff than those in medial (median: 8.9 μN/m) and lateral (2.0 μN/m) extrastriolae. Within the striola, bundle stiffness is greatest in zone 2 (106.4 μN/m), a band of type II hair cells, and significantly less in zone 3 (30.6 μN/m), which contains the only type I hair cells in the macula. Bathing bundles in media that break interciliary links produced changes in bundle stiffness with predictable time course and magnitude, suggesting that links were intact in our standard media and contributed normally to bundle stiffness during measurements. Our second major finding is that bundle structure is a significant predictor of steady-state stiffness: the heights of kinocilia and the tallest stereocilia are the most important determinants of bundle stiffness. Our results suggest 1) a functional interpretation of bundle height variability in vertebrate vestibular organs, 2) a role for the striola in detecting onset of head movement, and 3) the hypothesis that differences in bundle stiffness contribute to diversity in afferent response dynamics.
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Affiliation(s)
- Corrie Spoon
- Department of Engineering Science and Mechanics, Virginia Tech, Blacksburg, Virginia, USA
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80
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Sekerková G, Richter CP, Bartles JR. Roles of the espin actin-bundling proteins in the morphogenesis and stabilization of hair cell stereocilia revealed in CBA/CaJ congenic jerker mice. PLoS Genet 2011; 7:e1002032. [PMID: 21455486 PMCID: PMC3063760 DOI: 10.1371/journal.pgen.1002032] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Accepted: 02/02/2011] [Indexed: 01/19/2023] Open
Abstract
Hearing and vestibular function depend on mechanosensory staircase collections of hair cell stereocilia, which are produced from microvillus-like precursors as their parallel actin bundle scaffolds increase in diameter and elongate or shorten. Hair cell stereocilia contain multiple classes of actin-bundling protein, but little is known about what each class contributes. To investigate the roles of the espin class of actin-bundling protein, we used a genetic approach that benefited from a judicious selection of mouse background strain and an examination of the effects of heterozygosity. A congenic jerker mouse line was prepared by repeated backcrossing into the inbred CBA/CaJ strain, which is known for excellent hearing and minimal age-related hearing loss. We compared stereocilia in wild-type CBA/CaJ mice, jerker homozygotes that lack espin proteins owing to a frameshift mutation in the espin gene, and jerker heterozygotes that contain reduced espin levels. The lack of espins radically impaired stereociliary morphogenesis, resulting in stereocilia that were abnormally thin and short, with reduced differential elongation to form a staircase. Mean stereociliary diameter did not increase beyond ∼0.10–0.14 µm, making stereocilia ∼30%–60% thinner than wild type and suggesting that they contained ∼50%–85% fewer actin filaments. These characteristics indicate a requirement for espins in the appositional growth and differential elongation of the stereociliary parallel actin bundle and fit the known biological activities of espins in vitro and in transfected cells. The stereocilia of jerker heterozygotes showed a transient proximal-distal tapering suggestive of haploinsufficiency and a slowing of morphogenesis that revealed previously unrecognized assembly steps and intermediates. The lack of espins also led to a region-dependent degeneration of stereocilia involving shortening and collapse. We conclude that the espin actin-bundling proteins are required for the assembly and stabilization of the stereociliary parallel actin bundle. Stereocilia are the fingerlike projections of inner ear hair cells that detect sound and motion. Stereocilia grow to specific lengths and diameters and form staircase-like arrays. The changes in size appear to be driven by matching alterations in the dimensions of an underlying molecular scaffold consisting of a bundle of actin filaments cross-linked by actin-bundling proteins. To elucidate the roles of the espin actin-bundling proteins in hair cell stereocilia, we carry out an in-depth accounting of stereociliary size and shape in the jerker mutant mouse, which lacks the espin proteins because of a mutation in the espin gene. We examine a new and improved jerker mouse with a genetic background known for high-quality lifelong hearing. We find that, in the absence of espins, stereocilia do not increase in diameter or complete their elongation, but instead bend, shorten, and disappear. Although the specifics vary according to inner ear region, the stereociliary defects are profound and can readily account for the deafness and balance problems of jerker mice and humans with certain espin gene mutations. Even reducing espin levels by one-half leads to temporary defects in stereociliary diameter. Thus, espins play crucial roles in the formation and maintenance of hair cell stereocilia.
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Affiliation(s)
- Gabriella Sekerková
- Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States of America
| | - Claus-Peter Richter
- Department of Otolaryngology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States of America
- Hugh Knowles Center for Clinical and Basic Science in Hearing and Its Disorders, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States of America
| | - James R. Bartles
- Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States of America
- Hugh Knowles Center for Clinical and Basic Science in Hearing and Its Disorders, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States of America
- * E-mail:
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81
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Simmons DD, Tong B, Schrader AD, Hornak AJ. Oncomodulin identifies different hair cell types in the mammalian inner ear. J Comp Neurol 2010; 518:3785-802. [PMID: 20653034 DOI: 10.1002/cne.22424] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The tight regulation of Ca(2+) is essential for inner ear function, and yet the role of Ca(2+) binding proteins (CaBPs) remains elusive. By using immunofluorescence and reverse transcriptase-polymerase chain reaction (RT-PCR), we investigated the expression of oncomodulin (Ocm), a member of the parvalbumin family, relative to other EF-hand CaBPs in cochlear and vestibular organs in the mouse. In the mouse cochlea, Ocm is found only in outer hair cells and is localized preferentially to the basolateral outer hair cell membrane and to the base of the hair bundle. Developmentally, Ocm immunoreactivity begins as early as postnatal day (P) 2 and shows preferential localization to the basolateral membrane and hair bundle after P8. Unlike the cochlea, Ocm expression is substantially reduced in vestibular tissues at older adult ages. In vestibular organs, Ocm is found in type I striolar or central hair cells, and has a more diffuse subcellular localization throughout the hair cell body. Additionally, Ocm immunoreactivity in vestibular hair cells is present as early as E18 and is not obviously affected by mutations that cause a disruption of hair bundle polarity. We also find Ocm expression in striolar hair cells across mammalian species. These data suggest that Ocm may have distinct functional roles in cochlear and vestibular hair cells.
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Affiliation(s)
- Dwayne D Simmons
- Department of Integrative Biology and Physiology and the Brain Research Institute, University of California Los Angeles, Los Angeles, California 90095, USA.
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82
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Huss D, Navaluri R, Faulkner KF, Dickman JD. Development of otolith receptors in Japanese quail. Dev Neurobiol 2010; 70:436-55. [PMID: 20155736 DOI: 10.1002/dneu.20787] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
This study examined the morphological development of the otolith vestibular receptors in quail. Here, we describe epithelial growth, hair cell density, stereocilia polarization, and afferent nerve innervation during development. The otolith maculae epithelial areas increased exponentially throughout embryonic development reaching asymptotic values near posthatch day P7. Increases in hair cell density were dependent upon macular location; striolar hair cells developed first followed by hair cells in extrastriola regions. Stereocilia polarization was initiated early, with defining reversal zones forming at E8. Less than half of all immature hair cells observed had nonpolarized internal kinocilia with the remaining exhibiting planar polarity. Immunohistochemistry and neural tracing techniques were employed to examine the shape and location of the striolar regions. Initial innervation of the maculae was by small fibers with terminal growth cones at E6, followed by collateral branches with apparent bouton terminals at E8. Calyceal terminal formation began at E10; however, no mature calyces were observed until E12, when all fibers appeared to be dimorphs. Calyx afferents innervating only Type I hair cells did not develop until E14. Finally, the topographic organization of afferent macular innervation in the adult quail utricle was quantified. Calyx and dimorph afferents were primarily confined to the striolar regions, while bouton fibers were located in the extrastriola and Type II band. Calyx fibers were the least complex, followed by dimorph units. Bouton fibers had large innervation fields, with arborous branches and many terminal boutons.
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Affiliation(s)
- David Huss
- Department of Biology, California Institute of Technology, Pasadena, California 91125, USA
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83
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Targeting of the hair cell proteins cadherin 23, harmonin, myosin XVa, espin, and prestin in an epithelial cell model. J Neurosci 2010; 30:7187-201. [PMID: 20505086 DOI: 10.1523/jneurosci.0852-10.2010] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
We have developed an advantageous epithelial cell transfection model for examining the targeting, interactions, and mutations of hair cell proteins. When expressed in LLC-PK1-CL4 epithelial cells (CL4 cells), the outer hair cell protein prestin showed faithful domain-specific targeting to the basolateral plasma membrane. We examined the consequences of mutations affecting prestin activity and assigned a targeting role to the cytoplasmic tail. The stereociliary link protein cadherin 23 (Cdh23) was targeted to the plasma membrane of CL4 cell microvilli, the topological equivalent of stereocilia. In cells coexpressing the Cdh23 cytoplasmic binding protein harmonin, a large fraction of harmonin became colocalized with Cdh23 in microvilli. Using this assay and in vitro protein binding assays, we formulated an alternative model for Cdh23-harmonin binding, in which the primary interaction is between the harmonin N-domain and a 35-residue internal peptide in the Cdh23 cytoplasmic tail. Contrary to a previous model, we found no role for the Cdh23 C-terminal PDZ (PSD-95/Dlg/ZO-1)-binding motif and observed that Cdh23 bound similar levels of harmonin with or without the exon 68 peptide. We also examined two proteins involved in stereocilium elongation. The stereociliary actin-bundling protein espin was targeted to CL4 cell microvilli and caused microvillar elongation, whereas espin with the c.2469delGTCA or c.1988delAGAG human deafness mutation showed defects in microvillar targeting and elongation. The unconventional myosin motor myosin XVa accumulated at the tips of espin-elongated microvilli, by analogy to its location in stereocilia, whereas myosin XVa with the c.4351G>A or c.4669A>G human deafness mutation did not, revealing functional deficits in motor activity.
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84
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Maklad A, Kamel S, Wong E, Fritzsch B. Development and organization of polarity-specific segregation of primary vestibular afferent fibers in mice. Cell Tissue Res 2010; 340:303-21. [PMID: 20424840 PMCID: PMC2953634 DOI: 10.1007/s00441-010-0944-1] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Accepted: 02/04/2010] [Indexed: 12/19/2022]
Abstract
A striking feature of vestibular hair cells is the polarized arrangement of their stereocilia as the basis for their directional sensitivity. In mammals, each of the vestibular end organs is characterized by a distinct distribution of these polarized cells. We utilized the technique of post-fixation transganglionic neuronal tracing with fluorescent lipid soluble dyes in embryonic and postnatal mice to investigate whether these polarity characteristics correlate with the pattern of connections between the endorgans and their central targets; the vestibular nuclei and cerebellum. We found that the cerebellar and brainstem projections develop independently from each other and have a non-overlapping distribution of neurons and afferents from E11.5 on. In addition, we show that the vestibular fibers projecting to the cerebellum originate preferentially from the lateral half of the utricular macula and the medial half of the saccular macula. In contrast, the brainstem vestibular afferents originate primarily from the medial half of the utricular macula and the lateral half of the saccular macula. This indicates that the line of hair cell polarity reversal within the striola region segregates almost mutually exclusive central projections. A possible interpretation of this feature is that this macular organization provides an inhibitory side-loop through the cerebellum to produce synergistic tuning effects in the vestibular nuclei. The canal cristae project to the brainstem vestibular nuclei and cerebellum, but the projection to the vestibulocerebellum originates preferentially from the superior half of each of the cristae. The reason for this pattern is not clear, but it may compensate for unequal activation of crista hair cells or may be an evolutionary atavism reflecting a different polarity organization in ancestral vertebrate ears.
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Affiliation(s)
- Adel Maklad
- Department of Anatomy, University of Mississippi Medical Center, Jackson, MS 39216, USA.
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85
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Delta/notch-like EGF-related receptor (DNER) is expressed in hair cells and neurons in the developing and adult mouse inner ear. J Assoc Res Otolaryngol 2010; 11:187-201. [PMID: 20058045 DOI: 10.1007/s10162-009-0203-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2009] [Accepted: 12/01/2009] [Indexed: 10/20/2022] Open
Abstract
The Notch signaling pathway is known to play important roles in inner ear development. Previous studies have shown that the Notch1 receptor and ligands in the Delta and Jagged families are important for cellular differentiation and patterning of the organ of Corti. Delta/notch-like epidermal growth factor (EGF)-related receptor (DNER) is a novel Notch ligand expressed in developing and adult CNS neurons known to promote maturation of glia through activation of Notch. Here we use in situ hybridization and an antibody against DNER to carry out expression studies of the mouse cochlea and vestibule. We find that DNER is expressed in spiral ganglion neuron cell bodies and peripheral processes during embryonic development of the cochlea and expression in these cells is maintained in adults. DNER becomes strongly expressed in auditory hair cells during postnatal maturation in the mouse cochlea and immunoreactivity for this protein is strong in hair cells and afferent and efferent peripheral nerve endings in the adult organ of Corti. In the vestibular system, we find that DNER is expressed in hair cells and vestibular ganglion neurons during development and in adults. To investigate whether DNER plays a functional role in the inner ear, perhaps similar to its described role in glial maturation, we examined cochleae of DNER-/- mice using immunohistochemical markers of mature glia and supporting cells as well as neurons and hair cells. We found no defects in expression of markers of supporting cells and glia or myelin, and no abnormalities in hair cells or neurons, suggesting that DNER plays a redundant role with other Notch ligands in cochlear development.
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86
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Schweizer FE, Savin D, Luu C, Sultemeier DR, Hoffman LF. Distribution of high-conductance calcium-activated potassium channels in rat vestibular epithelia. J Comp Neurol 2009; 517:134-45. [PMID: 19731297 DOI: 10.1002/cne.22148] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Voltage- and calcium-activated potassium channels (BK) are important regulators of neuronal excitability. BK channels seem to be crucial for frequency tuning in nonmammalian vestibular and auditory hair cells. However, there are a paucity of data concerning BK expression in mammalian vestibular hair cells. We therefore investigated the localization of BK channels in mammalian vestibular hair cells, specifically in rat vestibular neuroepithelia. We find that only a subset of hair cells in the utricle and the crista ampullaris express BK channels. BK-positive hair cells are located mainly in the medial striolar region of the utricle, where they constitute at most 12% of hair cells, and in the central zone of the horizontal crista. A majority of BK-positive hair cells are encapsulated by a calretinin-positive calyx defining them as type I cells. The remainder are either type I cells encapsulated by a calretinin-negative calyx or type II hair cells. Surprisingly, the number of BK-positive hair cells in the utricle peaks in juvenile rats and declines in early adulthood. BK channels were not found in vestibular afferent dendrites or somata. Our data indicate that BK channel expression in the mammalian vestibular system differs from the expression pattern in the mammalian auditory and the nonmammalian vestibular system. The molecular diversity of vestibular hair cells indicates a functional diversity that has not yet been fully characterized. The predominance of BK-positive hair cells within the medial striola of juvenile animals suggests that they contribute to a scheme of highly lateralized coding of linear head movements during late development.
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Affiliation(s)
- Felix E Schweizer
- Department of Neurobiology, David Geffen School of Medicine at UCLA, Los Angeles, California 90095, USA.
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87
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Lysakowski A, Goldberg JM. Ultrastructural analysis of the cristae ampullares in the squirrel monkey (Saimiri sciureus). J Comp Neurol 2008; 511:47-64. [PMID: 18729176 DOI: 10.1002/cne.21827] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Type I hair cells outnumber type II hair cells (HCs) in squirrel monkey (Saimiri sciureus) cristae by a nearly 3:1 ratio. Associated with this type I HC preponderance, calyx fibers make up a much larger fraction of the afferent innervation than in rodents (Fernández et al. [1995] J. Neurophysiol. 73:1253-1269). To study how this affects synaptic architecture, we used disector methods to estimate various features associated with type I and type II HCs in central (CZ) and peripheral (PZ) zones of monkey cristae. Each type I HC makes, on average, 5-10 ribbon synapses with the inner face of a calyx ending. Inner-face synapses outnumber those on calyx outer faces by a 40:1 ratio. Expressed per afferent, there are, on average, 15 inner-face ribbon synapses, 0.38 outer-face ribbons, and 2.6 efferent boutons on calyx-bearing endings. Calyceal invaginations per type I HC range from 19 in CZ to 3 in PZ. For type II HCs, there are many more ribbons and afferent boutons in PZ than in CZ, whereas efferent innervation is relatively uniform throughout the neuroepithelium. Despite outer-face ribbons being more numerous in chinchilla than in squirrel monkey, afferent discharge properties are similar (Lysakowski et al. [1995] J. Neurophysiol. 73:1270-1281), reinforcing the importance of inner-face ribbons in synaptic transmission. Comparisons across mammalian species suggest that the prevalence of type I HCs is a primate characteristic, rather than an arboreal life-style adaptation. Unlike cristae, type II HCs predominate in monkey maculae. Differences in hair-cell counts may reflect the stimulus magnitudes handled by semicircular canals and otolith organs.
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Affiliation(s)
- Anna Lysakowski
- Department of Anatomy and Cell Biology, University of Illinois at Chicago, Illinois 60612, USA.
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88
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Dynamic length regulation of sensory stereocilia. Semin Cell Dev Biol 2008; 19:502-10. [PMID: 18692583 DOI: 10.1016/j.semcdb.2008.07.006] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2008] [Accepted: 07/15/2008] [Indexed: 01/02/2023]
Abstract
Stereocilia, the mechanosensory organelles of hair cells, are a distinctive class of actin-based cellular protrusions with an unparalleled ability to regulate their lengths over time. Studies on actin turnover in stereocilia, as well as the identification of several deafness-related proteins essential for proper stereocilia structure and function, provide new insights into the mechanisms and molecules involved in stereocilia length regulation and long-term maintenance. Comparisons of ongoing investigations on stereocilia with studies on other actin protrusions offer new opportunities to further understand common principles for length regulation, the diversity of its mechanisms, and how the specific needs of each cell are met.
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89
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Eatock RA, Xue J, Kalluri R. Ion channels in mammalian vestibular afferents may set regularity of firing. J Exp Biol 2008; 211:1764-74. [PMID: 18490392 PMCID: PMC3311106 DOI: 10.1242/jeb.017350] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Rodent vestibular afferent neurons offer several advantages as a model system for investigating the significance and origins of regularity in neuronal firing interval. Their regularity has a bimodal distribution that defines regular and irregular afferent classes. Factors likely to be involved in setting firing regularity include the morphology and physiology of the afferents' contacts with hair cells, which may influence the averaging of synaptic noise and the afferents' intrinsic electrical properties. In vitro patch clamp studies on the cell bodies of primary vestibular afferents reveal a rich diversity of ion channels, with indications of at least two neuronal populations. Here we suggest that firing patterns of isolated vestibular ganglion somata reflect intrinsic ion channel properties, which in vivo combine with hair cell synaptic drive to produce regular and irregular firing.
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Affiliation(s)
- Ruth Anne Eatock
- Otology and Laryngology, Harvard Medical School, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114, USA.
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