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Singh RK, Winkler PA, Binette F, Petersen-Jones SM, Nasonkin IO. Comparison of Developmental Dynamics in Human Fetal Retina and Human Pluripotent Stem Cell-Derived Retinal Tissue. Stem Cells Dev 2021; 30:399-417. [PMID: 33677999 DOI: 10.1089/scd.2020.0085] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Progressive vision loss, caused by retinal degenerative (RD) diseases such as age-related macular degeneration, retinitis pigmentosa, and Leber congenital amaurosis, severely impacts quality of life and affects millions of people. Finding efficient treatment for blinding diseases is among the greatest unmet clinical needs. The evagination of optic vesicles from developing pluripotent stem cell-derived neuroepithelium and self-organization, lamination, and differentiation of retinal tissue in a dish generated considerable optimism for developing innovative approaches for treating RD diseases, which previously were not feasible. Retinal organoids may be a limitless source of multipotential retinal progenitors, photoreceptors (PRs), and the whole retinal tissue, which are productive approaches for developing RD disease therapies. In this study we compared the distribution and expression level of molecular markers (genetic and epigenetic) in human fetal retina (age 8-16 weeks) and human embryonic stem cell (hESC)-derived retinal tissue (organoids) by immunohistochemistry, RNA-seq, flow cytometry, and mass-spectrometry (to measure methylated and hydroxymethylated cytosine level), with a focus on PRs to evaluate the clinical application of hESC-retinal tissue for vision restoration. Our results revealed high correlation in gene expression profiles and histological profiles between human fetal retina (age 8-13 weeks) and hESC-derived retinal tissue (10-12 weeks). The transcriptome signature of hESC-derived retinal tissue from retinal organoids maintained for 24 weeks in culture resembled the transcriptome of human fetal retina of more advanced developmental stages. The histological profiles of 24 week-old hESC-derived retinal tissue displayed mature PR immunophenotypes and presence of developing inner and outer segments. Collectively, our work highlights the similarity of hESC-derived retinal tissue at early stages of development (10 weeks), and human fetal retina (age 8-13 weeks) and it supports the development of regenerative medicine therapies aimed at using tissue from hESC-derived retinal organoids (hESC-retinal implants) for mitigating vision loss.
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Affiliation(s)
| | - Paige A Winkler
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA
| | | | - Simon M Petersen-Jones
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA
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2
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Marino V, Dal Cortivo G, Maltese PE, Placidi G, De Siena E, Falsini B, Bertelli M, Dell’Orco D. Impaired Ca 2+ Sensitivity of a Novel GCAP1 Variant Causes Cone Dystrophy and Leads to Abnormal Synaptic Transmission Between Photoreceptors and Bipolar Cells. Int J Mol Sci 2021; 22:ijms22084030. [PMID: 33919796 PMCID: PMC8070792 DOI: 10.3390/ijms22084030] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Revised: 04/06/2021] [Accepted: 04/09/2021] [Indexed: 01/23/2023] Open
Abstract
Guanylate cyclase-activating protein 1 (GCAP1) is involved in the shutdown of the phototransduction cascade by regulating the enzymatic activity of retinal guanylate cyclase via a Ca2+/cGMP negative feedback. While the phototransduction-associated role of GCAP1 in the photoreceptor outer segment is widely established, its implication in synaptic transmission to downstream neurons remains to be clarified. Here, we present clinical and biochemical data on a novel isolate GCAP1 variant leading to a double amino acid substitution (p.N104K and p.G105R) and associated with cone dystrophy (COD) with an unusual phenotype. Severe alterations of the electroretinogram were observed under both scotopic and photopic conditions, with a negative pattern and abnormally attenuated b-wave component. The biochemical and biophysical analysis of the heterologously expressed N104K-G105R variant corroborated by molecular dynamics simulations highlighted a severely compromised Ca2+-sensitivity, accompanied by minor structural and stability alterations. Such differences reflected on the dysregulation of both guanylate cyclase isoforms (RetGC1 and RetGC2), resulting in the constitutive activation of both enzymes at physiological levels of Ca2+. As observed with other GCAP1-associated COD, perturbation of the homeostasis of Ca2+ and cGMP may lead to the toxic accumulation of second messengers, ultimately triggering cell death. However, the abnormal electroretinogram recorded in this patient also suggested that the dysregulation of the GCAP1–cyclase complex further propagates to the synaptic terminal, thereby altering the ON-pathway related to the b-wave generation. In conclusion, the pathological phenotype may rise from a combination of second messengers’ accumulation and dysfunctional synaptic communication with bipolar cells, whose molecular mechanisms remain to be clarified.
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Affiliation(s)
- Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37129 Verona, Italy; (V.M.); (G.D.C.)
| | - Giuditta Dal Cortivo
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37129 Verona, Italy; (V.M.); (G.D.C.)
| | | | - Giorgio Placidi
- Fondazione Policlinico Universitario “A. Gemelli”, IRCCS, 00168 Rome, Italy; (G.P.); (E.D.S.)
- Università Cattolica del Sacro Cuore, 00168 Rome, Italy
| | - Elisa De Siena
- Fondazione Policlinico Universitario “A. Gemelli”, IRCCS, 00168 Rome, Italy; (G.P.); (E.D.S.)
- Università Cattolica del Sacro Cuore, 00168 Rome, Italy
| | - Benedetto Falsini
- Fondazione Policlinico Universitario “A. Gemelli”, IRCCS, 00168 Rome, Italy; (G.P.); (E.D.S.)
- Università Cattolica del Sacro Cuore, 00168 Rome, Italy
- Correspondence: (B.F.); (D.D.); Tel.: +39-06-3015-6344 (B.F.); +39-045-802-7637 (D.D.)
| | - Matteo Bertelli
- MAGI’S Lab S.R.L., 38068 Rovereto, Italy; (P.E.M.); (M.B.)
- MAGI Euregio, 39100 Bolzano, Italy
| | - Daniele Dell’Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, 37129 Verona, Italy; (V.M.); (G.D.C.)
- Correspondence: (B.F.); (D.D.); Tel.: +39-06-3015-6344 (B.F.); +39-045-802-7637 (D.D.)
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3
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Avesani A, Marino V, Zanzoni S, Koch KW, Dell'Orco D. Molecular properties of human guanylate cyclase-activating protein 2 (GCAP2) and its retinal dystrophy-associated variant G157R. J Biol Chem 2021; 296:100619. [PMID: 33812995 PMCID: PMC8113879 DOI: 10.1016/j.jbc.2021.100619] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Revised: 03/25/2021] [Accepted: 03/30/2021] [Indexed: 12/31/2022] Open
Abstract
In murine and bovine photoreceptors, guanylate cyclase-activating protein 2 (GCAP2) activates retinal guanylate cyclases (GCs) at low Ca2+ levels, thus contributing to the Ca2+/cGMP negative feedback on the cyclase together with its paralog guanylate cyclase-activating protein 1, which has the same function but different Ca2+ sensitivity. In humans, a GCAP2 missense mutation (G157R) has been associated with inherited retinal degeneration (IRD) via an unknown molecular mechanism. Here, we characterized the biochemical properties of human GCAP2 and the G157R variant, focusing on its dimerization and the Ca2+/Mg2+-binding processes in the presence or absence of N-terminal myristoylation. We found that human GCAP2 and its bovine/murine orthologs significantly differ in terms of oligomeric properties, cation binding, and GC regulation. Myristoylated GCAP2 endothermically binds up to 3 Mg2+ with high affinity and forms a compact dimer that may reversibly dissociate in the presence of Ca2+. Conversely, nonmyristoylated GCAP2 does not bind Mg2+ over the physiological range and remains as a monomer in the absence of Ca2+. Both myristoylated and nonmyristoylated GCAP2 bind Ca2+ with high affinity. At odds with guanylate cyclase-activating protein 1 and independently of myristoylation, human GCAP2 does not significantly activate retinal GC1 in a Ca2+-dependent fashion. The IRD-associated G157R variant is characterized by a partly misfolded, molten globule-like conformation with reduced affinity for cations and prone to form aggregates, likely mediated by hydrophobic interactions. Our findings suggest that GCAP2 might be mostly implicated in processes other than phototransduction in human photoreceptors and suggest a possible molecular mechanism for G157R-associated IRD.
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Affiliation(s)
- Anna Avesani
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy
| | - Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy
| | - Serena Zanzoni
- Centro Piattaforme Tecnologiche, University of Verona, Verona, Italy
| | - Karl-Wilhelm Koch
- Department of Neuroscience, Division of Biochemistry, University of Oldenburg, Oldenburg, Germany
| | - Daniele Dell'Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy.
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4
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Zang J, Neuhauss SCF. Biochemistry and physiology of zebrafish photoreceptors. Pflugers Arch 2021; 473:1569-1585. [PMID: 33598728 PMCID: PMC8370914 DOI: 10.1007/s00424-021-02528-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Revised: 01/25/2021] [Accepted: 01/28/2021] [Indexed: 02/06/2023]
Abstract
All vertebrates share a canonical retina with light-sensitive photoreceptors in the outer retina. These photoreceptors are of two kinds: rods and cones, adapted to low and bright light conditions, respectively. They both show a peculiar morphology, with long outer segments, comprised of ordered stacks of disc-shaped membranes. These discs host numerous proteins, many of which contribute to the visual transduction cascade. This pathway converts the light stimulus into a biological signal, ultimately modulating synaptic transmission. Recently, the zebrafish (Danio rerio) has gained popularity for studying the function of vertebrate photoreceptors. In this review, we introduce this model system and its contribution to our understanding of photoreception with a focus on the cone visual transduction cascade.
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Affiliation(s)
- Jingjing Zang
- Department of Molecular Life Sciences, University of Zurich, Winterthurerstrase 190, CH - 8057, Zürich, Switzerland
| | - Stephan C F Neuhauss
- Department of Molecular Life Sciences, University of Zurich, Winterthurerstrase 190, CH - 8057, Zürich, Switzerland.
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5
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Maddox JW, Randall KL, Yadav RP, Williams B, Hagen J, Derr PJ, Kerov V, Della Santina L, Baker SA, Artemyev N, Hoon M, Lee A. A dual role for Ca v1.4 Ca 2+ channels in the molecular and structural organization of the rod photoreceptor synapse. eLife 2020; 9:e62184. [PMID: 32940604 PMCID: PMC7561352 DOI: 10.7554/elife.62184] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Accepted: 09/09/2020] [Indexed: 02/06/2023] Open
Abstract
Synapses are fundamental information processing units that rely on voltage-gated Ca2+ (Cav) channels to trigger Ca2+-dependent neurotransmitter release. Cav channels also play Ca2+-independent roles in other biological contexts, but whether they do so in axon terminals is unknown. Here, we addressed this unknown with respect to the requirement for Cav1.4 L-type channels for the formation of rod photoreceptor synapses in the retina. Using a mouse strain expressing a non-conducting mutant form of Cav1.4, we report that the Cav1.4 protein, but not its Ca2+ conductance, is required for the molecular assembly of rod synapses; however, Cav1.4 Ca2+ signals are needed for the appropriate recruitment of postsynaptic partners. Our results support a model in which presynaptic Cav channels serve both as organizers of synaptic building blocks and as sources of Ca2+ ions in building the first synapse of the visual pathway and perhaps more broadly in the nervous system.
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Affiliation(s)
- J Wesley Maddox
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Pappajohn Biomedical Institute, University of IowaIowa CityUnited States
| | - Kate L Randall
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Pappajohn Biomedical Institute, University of IowaIowa CityUnited States
| | - Ravi P Yadav
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
| | - Brittany Williams
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Pappajohn Biomedical Institute, University of IowaIowa CityUnited States
| | - Jussara Hagen
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Pappajohn Biomedical Institute, University of IowaIowa CityUnited States
| | - Paul J Derr
- Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
| | - Vasily Kerov
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
| | - Luca Della Santina
- Department of Ophthalmology, University of California, San FranciscoSan FranciscoUnited States
| | - Sheila A Baker
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Department of Biochemistry, University of IowaIowa CityUnited States
- Department of OphthalmologyIowa CityUnited States
| | - Nikolai Artemyev
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Department of OphthalmologyIowa CityUnited States
| | - Mrinalini Hoon
- Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
- Department of Ophthalmology and Visual Science, University of Wisconsin-MadisonMadisonUnited States
| | - Amy Lee
- Department of Molecular Physiology and Biophysics, University of IowaIowa CityUnited States
- Iowa Neuroscience Institute, University of IowaIowa CityUnited States
- Pappajohn Biomedical Institute, University of IowaIowa CityUnited States
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Pfeiffer RL, Anderson JR, Dahal J, Garcia JC, Yang JH, Sigulinsky CL, Rapp K, Emrich DP, Watt CB, Johnstun HA, Houser AR, Marc RE, Jones BW. A pathoconnectome of early neurodegeneration: Network changes in retinal degeneration. Exp Eye Res 2020; 199:108196. [PMID: 32810483 DOI: 10.1016/j.exer.2020.108196] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Revised: 07/27/2020] [Accepted: 08/11/2020] [Indexed: 10/23/2022]
Abstract
Connectomics has demonstrated that synaptic networks and their topologies are precise and directly correlate with physiology and behavior. The next extension of connectomics is pathoconnectomics: to map neural network synaptology and circuit topologies corrupted by neurological disease in order to identify robust targets for therapeutics. In this report, we characterize a pathoconnectome of early retinal degeneration. This pathoconnectome was generated using serial section transmission electron microscopy to achieve an ultrastructural connectome with 2.18nm/px resolution for accurate identification of all chemical and gap junctional synapses. We observe aberrant connectivity in the rod-network pathway and novel synaptic connections deriving from neurite sprouting. These observations reveal principles of neuron responses to the loss of network components and can be extended to other neurodegenerative diseases.
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Affiliation(s)
- Rebecca L Pfeiffer
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA.
| | - James R Anderson
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA
| | - Jeebika Dahal
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA
| | - Jessica C Garcia
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA
| | - Jia-Hui Yang
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA
| | | | - Kevin Rapp
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA
| | - Daniel P Emrich
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA
| | - Carl B Watt
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA
| | - Hope Ab Johnstun
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA
| | - Alexis R Houser
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA
| | - Robert E Marc
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA; Signature Immunologics, Torrey, UT, USA
| | - Bryan W Jones
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA.
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Forward genetic analysis using OCT screening identifies Sfxn3 mutations leading to progressive outer retinal degeneration in mice. Proc Natl Acad Sci U S A 2020; 117:12931-12942. [PMID: 32457148 DOI: 10.1073/pnas.1921224117] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Retinal disease and loss of vision can result from any disruption of the complex pathways controlling retinal development and homeostasis. Forward genetics provides an excellent tool to find, in an unbiased manner, genes that are essential to these processes. Using N-ethyl-N-nitrosourea mutagenesis in mice in combination with a screening protocol using optical coherence tomography (OCT) and automated meiotic mapping, we identified 11 mutations presumably causative of retinal phenotypes in genes previously known to be essential for retinal integrity. In addition, we found multiple statistically significant gene-phenotype associations that have not been reported previously and decided to target one of these genes, Sfxn3 (encoding sideroflexin-3), using CRISPR/Cas9 technology. We demonstrate, using OCT, light microscopy, and electroretinography, that two Sfxn3 -/- mouse lines developed progressive and severe outer retinal degeneration. Electron microscopy showed thinning of the retinal pigment epithelium and disruption of the external limiting membrane. Using single-cell RNA sequencing of retinal cells isolated from C57BL/6J mice, we demonstrate that Sfxn3 is expressed in several bipolar cell subtypes, retinal ganglion cells, and some amacrine cell subtypes but not significantly in Müller cells or photoreceptors. In situ hybridization confirmed these findings. Furthermore, pathway analysis suggests that Sfxn3 may be associated with synaptic homeostasis. Importantly, electron microscopy analysis showed disruption of synapses and synaptic ribbons in the outer plexiform layer of Sfxn3 -/- mice. Our work describes a previously unknown requirement for Sfxn3 in retinal function.
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Moser T, Grabner CP, Schmitz F. Sensory Processing at Ribbon Synapses in the Retina and the Cochlea. Physiol Rev 2020; 100:103-144. [DOI: 10.1152/physrev.00026.2018] [Citation(s) in RCA: 80] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In recent years, sensory neuroscientists have made major efforts to dissect the structure and function of ribbon synapses which process sensory information in the eye and ear. This review aims to summarize our current understanding of two key aspects of ribbon synapses: 1) their mechanisms of exocytosis and endocytosis and 2) their molecular anatomy and physiology. Our comparison of ribbon synapses in the cochlea and the retina reveals convergent signaling mechanisms, as well as divergent strategies in different sensory systems.
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Affiliation(s)
- Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, Göttingen, Germany; Synaptic Nanophysiology Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; and Institute for Anatomy and Cell Biology, Department of Neuroanatomy, Medical School, Saarland University, Homburg, Germany
| | - Chad P. Grabner
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, Göttingen, Germany; Synaptic Nanophysiology Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; and Institute for Anatomy and Cell Biology, Department of Neuroanatomy, Medical School, Saarland University, Homburg, Germany
| | - Frank Schmitz
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, Göttingen, Germany; Synaptic Nanophysiology Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; and Institute for Anatomy and Cell Biology, Department of Neuroanatomy, Medical School, Saarland University, Homburg, Germany
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9
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Pregnancy-Associated Plasma Protein-aa Regulates Photoreceptor Synaptic Development to Mediate Visually Guided Behavior. J Neurosci 2018; 38:5220-5236. [PMID: 29739870 DOI: 10.1523/jneurosci.0061-18.2018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Revised: 04/04/2018] [Accepted: 04/30/2018] [Indexed: 02/08/2023] Open
Abstract
To guide behavior, sensory systems detect the onset and offset of stimuli and process these distinct inputs via parallel pathways. In the retina, this strategy is implemented by splitting neural signals for light onset and offset via synapses connecting photoreceptors to ON and OFF bipolar cells, respectively. It remains poorly understood which molecular cues establish the architecture of this synaptic configuration to split light-onset and light-offset signals. A mutant with reduced synapses between photoreceptors and one bipolar cell type, but not the other, could reveal a critical cue. From this approach, we report a novel synaptic role for pregnancy-associated plasma protein aa (pappaa) in promoting the structure and function of cone synapses that transmit light-offset information. Electrophysiological and behavioral analyses indicated pappaa mutant zebrafish have dysfunctional cone-to-OFF bipolar cell synapses and impaired responses to light offset, but intact cone-to-ON bipolar cell synapses and light-onset responses. Ultrastructural analyses of pappaa mutant cones showed a lack of presynaptic domains at synapses with OFF bipolar cells. pappaa is expressed postsynaptically to the cones during retinal synaptogenesis and encodes a secreted metalloprotease known to stimulate insulin-like growth factor 1 (IGF1) signaling. Induction of dominant-negative IGF1 receptor expression during synaptogenesis reduced light-offset responses. Conversely, stimulating IGF1 signaling at this time improved pappaa mutants' light-offset responses and cone presynaptic structures. Together, our results indicate Pappaa-regulated IGF1 signaling as a novel pathway that establishes how cone synapses convey light-offset signals to guide behavior.SIGNIFICANCE STATEMENT Distinct sensory inputs, like stimulus onset and offset, are often split at distinct synapses into parallel circuits for processing. In the retina, photoreceptors and ON and OFF bipolar cells form discrete synapses to split neural signals coding light onset and offset, respectively. The molecular cues that establish this synaptic configuration to specifically convey light onset or offset remain unclear. Our work reveals a novel cue: pregnancy-associated plasma protein aa (pappaa), which regulates photoreceptor synaptic structure and function to specifically transmit light-offset information. Pappaa is a metalloprotease that stimulates local insulin-like growth factor 1 (IGF1) signaling. IGF1 promotes various aspects of synaptic development and function and is broadly expressed, thus requiring local regulators, like Pappaa, to govern its specificity.
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10
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Efficient stimulus-secretion coupling at ribbon synapses requires RIM-binding protein tethering of L-type Ca 2+ channels. Proc Natl Acad Sci U S A 2017; 114:E8081-E8090. [PMID: 28874522 DOI: 10.1073/pnas.1702991114] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Fast neurotransmitter release from ribbon synapses via Ca2+-triggered exocytosis requires tight coupling of L-type Ca2+ channels to release-ready synaptic vesicles at the presynaptic active zone, which is localized at the base of the ribbon. Here, we used genetic, electrophysiological, and ultrastructural analyses to probe the architecture of ribbon synapses by perturbing the function of RIM-binding proteins (RBPs) as central active-zone scaffolding molecules. We found that genetic deletion of RBP1 and RBP2 did not impair synapse ultrastructure of ribbon-type synapses formed between rod bipolar cells (RBCs) and amacrine type-2 (AII) cells in the mouse retina but dramatically reduced the density of presynaptic Ca2+ channels, decreased and desynchronized evoked neurotransmitter release, and rendered evoked and spontaneous neurotransmitter release sensitive to the slow Ca2+ buffer EGTA. These findings suggest that RBPs tether L-type Ca2+ channels to the active zones of ribbon synapses, thereby synchronizing vesicle exocytosis and promoting high-fidelity information transfer in retinal circuits.
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11
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In Vivo Ribbon Mobility and Turnover of Ribeye at Zebrafish Hair Cell Synapses. Sci Rep 2017; 7:7467. [PMID: 28785118 PMCID: PMC5547071 DOI: 10.1038/s41598-017-07940-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 07/03/2017] [Indexed: 11/08/2022] Open
Abstract
Ribbons are presynaptic structures that mediate synaptic vesicle release in some sensory cells of the auditory and visual systems. Although composed predominately of the protein Ribeye, very little is known about the structural dynamics of ribbons. Here we describe the in vivo mobility and turnover of Ribeye at hair cell ribbon synapses by monitoring fluorescence recovery after photobleaching (FRAP) in transgenic zebrafish with GFP-tagged Ribeye. We show that Ribeye can exchange between halves of a ribbon within ~1 minute in a manner that is consistent with a simple diffusion mechanism. In contrast, exchange of Ribeye between other ribbons via the cell's cytoplasm takes several hours.
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12
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Haumann I, Junghans D, Anstötz M, Frotscher M. Presynaptic localization of GluK5 in rod photoreceptors suggests a novel function of high affinity glutamate receptors in the mammalian retina. PLoS One 2017; 12:e0172967. [PMID: 28235022 PMCID: PMC5325551 DOI: 10.1371/journal.pone.0172967] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 02/13/2017] [Indexed: 01/04/2023] Open
Abstract
Kainate receptors mediate glutamatergic signaling through both pre- and presynaptic receptors. Here, we studied the expression of the high affinity kainate receptor GluK5 in the mouse retina. Double-immunofluoresence labeling and electron microscopic analysis revealed a presynaptic localization of GluK5 in the outer plexiform layer. Unexpectedly, we found GluK5 almost exclusively localized to the presynaptic ribbon of photoreceptor terminals. Moreover, in GluK5-deficient mutant mice the structural integrity of synaptic ribbons was severely altered pointing to a novel function of GluK5 in organizing synaptic ribbons in the presynaptic terminals of rod photoreceptors.
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Affiliation(s)
- Iris Haumann
- Institute of Neuroanatomy, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
- * E-mail: (MF); (IH)
| | - Dirk Junghans
- Institute of Embryology and Stem Cell Biology, Department of Biomedicine, University of Basel, Basel, Switzerland
| | - Max Anstötz
- Institute of Neuroanatomy, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Michael Frotscher
- Institute for Structural Neurobiology, Center for Molecular Neurobiology Hamburg (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
- * E-mail: (MF); (IH)
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13
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Mitochondria Maintain Distinct Ca 2+ Pools in Cone Photoreceptors. J Neurosci 2017; 37:2061-2072. [PMID: 28115482 DOI: 10.1523/jneurosci.2689-16.2017] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Revised: 01/10/2017] [Accepted: 01/12/2017] [Indexed: 01/01/2023] Open
Abstract
Ca2+ ions have distinct roles in the outer segment, cell body, and synaptic terminal of photoreceptors. We tested the hypothesis that distinct Ca2+ domains are maintained by Ca2+ uptake into mitochondria. Serial block face scanning electron microscopy of zebrafish cones revealed that nearly 100 mitochondria cluster at the apical side of the inner segment, directly below the outer segment. The endoplasmic reticulum surrounds the basal and lateral surfaces of this cluster, but does not reach the apical surface or penetrate into the cluster. Using genetically encoded Ca2+ sensors, we found that mitochondria take up Ca2+ when it accumulates either in the cone cell body or outer segment. Blocking mitochondrial Ca2+ uniporter activity compromises the ability of mitochondria to maintain distinct Ca2+ domains. Together, our findings indicate that mitochondria can modulate subcellular functional specialization in photoreceptors.SIGNIFICANCE STATEMENT Ca2+ homeostasis is essential for the survival and function of retinal photoreceptors. Separate pools of Ca2+ regulate phototransduction in the outer segment, metabolism in the cell body, and neurotransmitter release at the synaptic terminal. We investigated the role of mitochondria in compartmentalization of Ca2+ We found that mitochondria form a dense cluster that acts as a diffusion barrier between the outer segment and cell body. The cluster is surprisingly only partially surrounded by the endoplasmic reticulum, a key mediator of mitochondrial Ca2+ uptake. Blocking the uptake of Ca2+ by mitochondria causes redistribution of Ca2+ throughout the cell. Our results show that mitochondrial Ca2+ uptake in photoreceptors is complex and plays an essential role in normal function.
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Brockerhoff SE. Genome Editing to Study Ca 2+ Homeostasis in Zebrafish Cone Photoreceptors. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1016:91-100. [PMID: 29130155 DOI: 10.1007/978-3-319-63904-8_5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Photoreceptors are specialized sensory neurons with unique biological features. Phototransduction is well understood due in part to the exclusive expression and function of the molecular components of this cascade. Many other processes are less well understood, but also extremely important for understanding photoreceptor function and for treating disease. One example is the role of Ca2+ in the cell body and overall compartmentalization and regulation of Ca2+ within the cell. The recent development of CRISPR/Cas9 genome editing techniques has made it possible to rapidly and cheaply alter specific genes. This will help to define the biological function of elusive processes that have been more challenging to study. CRISPR/Cas9 has been optimized in many systems including zebrafish, which already has some distinct advantages for studying photoreceptor biology and function. These new genome editing technologies and the continued use of the zebrafish model system will help advance our understanding of important understudied aspects of photoreceptor biology.
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Affiliation(s)
- Susan E Brockerhoff
- Departments of Biochemistry and Ophthalmology, University of Washington, UW Medicine, 750 Republican St, Box 358058, Seattle, WA, 98109, USA.
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15
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Cochlear Synaptopathy and Noise-Induced Hidden Hearing Loss. Neural Plast 2016; 2016:6143164. [PMID: 27738526 PMCID: PMC5050381 DOI: 10.1155/2016/6143164] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Revised: 08/09/2016] [Accepted: 08/21/2016] [Indexed: 11/18/2022] Open
Abstract
Recent studies on animal models have shown that noise exposure that does not lead to permanent threshold shift (PTS) can cause considerable damage around the synapses between inner hair cells (IHCs) and type-I afferent auditory nerve fibers (ANFs). Disruption of these synapses not only disables the innervated ANFs but also results in the slow degeneration of spiral ganglion neurons if the synapses are not reestablished. Such a loss of ANFs should result in signal coding deficits, which are exacerbated by the bias of the damage toward synapses connecting low-spontaneous-rate (SR) ANFs, which are known to be vital for signal coding in noisy background. As there is no PTS, these functional deficits cannot be detected using routine audiological evaluations and may be unknown to subjects who have them. Such functional deficits in hearing without changes in sensitivity are generally called “noise-induced hidden hearing loss (NIHHL).” Here, we provide a brief review to address several critical issues related to NIHHL: (1) the mechanism of noise induced synaptic damage, (2) reversibility of the synaptic damage, (3) the functional deficits as the nature of NIHHL in animal studies, (4) evidence of NIHHL in human subjects, and (5) peripheral and central contribution of NIHHL.
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16
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Kulkarni M, Trifunović D, Schubert T, Euler T, Paquet-Durand F. Calcium dynamics change in degenerating cone photoreceptors. Hum Mol Genet 2016; 25:3729-3740. [PMID: 27402880 DOI: 10.1093/hmg/ddw219] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Revised: 06/24/2016] [Accepted: 06/25/2016] [Indexed: 11/14/2022] Open
Abstract
Cone photoreceptors (cones) are essential for high-resolution daylight vision and colour perception. Loss of cones in hereditary retinal diseases has a dramatic impact on human vision. The mechanisms underlying cone death are poorly understood, and consequently, there are no treatments available. Previous studies suggest a central role for calcium (Ca2+) homeostasis deficits in photoreceptor degeneration; however, direct evidence for this is scarce and physiological measurements of Ca2+ in degenerating mammalian cones are lacking.Here, we took advantage of the transgenic HR2.1:TN-XL mouse line that expresses a genetically encoded Ca2+ biosensor exclusively in cones. We cross-bred this line with mouse models for primary ("cone photoreceptor function loss-1", cpfl1) and secondary ("retinal degeneration-1", rd1) cone degeneration, respectively, and assessed resting Ca2+ levels and light-evoked Ca2+ responses in cones using two-photon imaging. We found that Ca2+ dynamics were altered in cpfl1 cones, showing higher noise and variable Ca2+ levels, with significantly wider distribution than for wild-type and rd1 cones. Unexpectedly, up to 21% of cpfl1 cones still displayed light-evoked Ca2+ responses, which were larger and slower than wild-type responses. In contrast, genetically intact rd1 cones were characterized by lower noise and complete lack of visual function.Our study demonstrates alterations in cone Ca2+ dynamics in both primary and secondary cone degeneration. Our results are consistent with the view that higher (fluctuating) cone Ca2+ levels are involved in photoreceptor cell death in primary (cpfl1) but not in secondary (rd1) cone degeneration. These findings may guide the future development of therapies targeting photoreceptor Ca2+ homeostasis.
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Affiliation(s)
- Manoj Kulkarni
- Institute for Ophthalmic Research.,Werner Reichardt Centre for Integrative Neuroscience.,Graduate School of Cellular & Molecular Neuroscience
| | | | - Timm Schubert
- Institute for Ophthalmic Research.,Werner Reichardt Centre for Integrative Neuroscience
| | - Thomas Euler
- Institute for Ophthalmic Research (F.P-D.) (T.E.).,Werner Reichardt Centre for Integrative Neuroscience.,Bernstein Centre for Computational Neuroscience, University of Tübingen, Tübingen, Germany
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17
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The Disease Protein Tulp1 Is Essential for Periactive Zone Endocytosis in Photoreceptor Ribbon Synapses. J Neurosci 2016; 36:2473-93. [PMID: 26911694 DOI: 10.1523/jneurosci.2275-15.2016] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Mutations in the Tulp1 gene cause severe, early-onset retinitis pigmentosa (RP14) in humans. In the retina, Tulp1 is mainly expressed in photoreceptors that use ribbon synapses to communicate with the inner retina. In the present study, we demonstrate that Tulp1 is highly enriched in the periactive zone of photoreceptor presynaptic terminals where Tulp1 colocalizes with major endocytic proteins close to the synaptic ribbon. Analyses of Tulp1 knock-out mice demonstrate that Tulp1 is essential to keep endocytic proteins enriched at the periactive zone and to maintain high levels of endocytic activity close to the synaptic ribbon. Moreover, we have discovered a novel interaction between Tulp1 and the synaptic ribbon protein RIBEYE, which is important to maintain synaptic ribbon integrity. The current findings suggest a new model for Tulp1-mediated localization of the endocytic machinery at the periactive zone of ribbon synapses and offer a new rationale and mechanism for vision loss associated with genetic defects in Tulp1.
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18
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Abstract
The first synapses transmitting visual information contain an unusual organelle, the ribbon, which is involved in the transport and priming of vesicles to be released at the active zone. The ribbon is one of many design features that allow efficient refilling of the active zone, which in turn enables graded changes in membrane potential to be transmitted using a continuous mode of neurotransmitter release. The ribbon also plays a key role in supplying vesicles for rapid and transient bursts of release that signal fast changes, such as the onset of light. We increasingly understand how the physiological properties of ribbon synapses determine basic transformations of the visual signal and, in particular, how the process of refilling the active zone regulates the gain and adaptive properties of the retinal circuit. The molecular basis of ribbon function is, however, far from clear.
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Affiliation(s)
- Leon Lagnado
- School of Life Sciences, University of Sussex, Brighton BN1 9QG, United Kingdom;
| | - Frank Schmitz
- Department of Neuroanatomy, Institute for Anatomy and Cell Biology, Medical School Saarland University, Homburg/Saar, Germany;
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19
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Caputo A, Piano I, Demontis GC, Bacchi N, Casarosa S, Della Santina L, Gargini C. TMEM16A is associated with voltage-gated calcium channels in mouse retina and its function is disrupted upon mutation of the auxiliary α2δ4 subunit. Front Cell Neurosci 2015; 9:422. [PMID: 26557056 PMCID: PMC4617175 DOI: 10.3389/fncel.2015.00422] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Accepted: 10/04/2015] [Indexed: 02/02/2023] Open
Abstract
Photoreceptors rely upon highly specialized synapses to efficiently transmit signals to multiple postsynaptic targets. Calcium influx in the presynaptic terminal is mediated by voltage-gated calcium channels (VGCC). This event triggers neurotransmitter release, but also gates calcium-activated chloride channels (TMEM), which in turn regulate VGCC activity. In order to investigate the relationship between VGCC and TMEM channels, we analyzed the retina of wild type (WT) and Cacna2d4 mutant mice, in which the VGCC auxiliary α2δ4 subunit carries a nonsense mutation, disrupting the normal channel function. Synaptic terminals of mutant photoreceptors are disarranged and synaptic proteins as well as TMEM16A channels lose their characteristic localization. In parallel, calcium-activated chloride currents are impaired in rods, despite unaltered TMEM16A protein levels. Co-immunoprecipitation revealed the interaction between VGCC and TMEM16A channels in the retina. Heterologous expression of these channels in tsA-201 cells showed that TMEM16A associates with the CaV1.4 subunit, and the association persists upon expression of the mutant α2δ4 subunit. Collectively, our experiments show association between TMEM16A and the α1 subunit of VGCC. Close proximity of these channels allows optimal function of the photoreceptor synaptic terminal under physiological conditions, but also makes TMEM16A channels susceptible to changes occurring to calcium channels.
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Affiliation(s)
| | - Ilaria Piano
- Department of Pharmacy, University of Pisa Pisa, Italy
| | | | - Niccolò Bacchi
- Centre for Integrative Biology, University of Trento Trento, Italy
| | - Simona Casarosa
- Centre for Integrative Biology, University of Trento Trento, Italy
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20
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Ackermann F, Waites CL, Garner CC. Presynaptic active zones in invertebrates and vertebrates. EMBO Rep 2015; 16:923-38. [PMID: 26160654 DOI: 10.15252/embr.201540434] [Citation(s) in RCA: 92] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2015] [Accepted: 06/19/2015] [Indexed: 11/09/2022] Open
Abstract
The regulated release of neurotransmitter occurs via the fusion of synaptic vesicles (SVs) at specialized regions of the presynaptic membrane called active zones (AZs). These regions are defined by a cytoskeletal matrix assembled at AZs (CAZ), which functions to direct SVs toward docking and fusion sites and supports their maturation into the readily releasable pool. In addition, CAZ proteins localize voltage-gated Ca(2+) channels at SV release sites, bringing the fusion machinery in close proximity to the calcium source. Proteins of the CAZ therefore ensure that vesicle fusion is temporally and spatially organized, allowing for the precise and reliable release of neurotransmitter. Importantly, AZs are highly dynamic structures, supporting presynaptic remodeling, changes in neurotransmitter release efficacy, and thus presynaptic forms of plasticity. In this review, we discuss recent advances in the study of active zones, highlighting how the CAZ molecularly defines sites of neurotransmitter release, endocytic zones, and the integrity of synapses.
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Affiliation(s)
- Frauke Ackermann
- German Center for Neurodegenerative Disease, Charité Medical University, Berlin, Germany
| | - Clarissa L Waites
- Department of Pathology and Cell Biology, Columbia University, New York, NY, USA
| | - Craig C Garner
- German Center for Neurodegenerative Disease, Charité Medical University, Berlin, Germany
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21
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Mavlyutov TA, Epstein M, Guo LW. Subcellular localization of the sigma-1 receptor in retinal neurons - an electron microscopy study. Sci Rep 2015; 5:10689. [PMID: 26033680 PMCID: PMC4649997 DOI: 10.1038/srep10689] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Accepted: 04/27/2015] [Indexed: 11/09/2022] Open
Abstract
The Sigma-1 receptor (S1R) is known to play a protective role in the central nervous system including the retina. A major barrier for understanding the underlying mechanism is an ambiguity of S1R subcellular localizations. We thus conducted the first electron microscopy (EM) study of S1R subcellular distribution in the mouse retina. Immuno-EM imaging showed previously under-appreciated S1R presence in photoreceptor cells. Unlike in other cell types in previous reports, in photoreceptor cells S1R was found in the nuclear envelope but not localized in the endoplasmic reticulum (ER), raising a possibility of S1R-mediated modulatory mechanisms different than conventionally thought. While in bipolar cells S1R was detected only in the nuclear envelope, in ganglion cells S1R was identified predominantly in the nuclear envelope and found in the ER as well. A predominant localization of S1R in the nuclear envelope in all three retinal neurons implicates a potential role of S1R in modulating nuclear activities. Moreover, its absence in the plasma membrane and presence in the subsurface ER cisternae that are juxtaposed to the plasma membrane in ganglion cells may lend mechanistic insights generally important for frequently reported S1R modulations of ion channels in neurons.
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Affiliation(s)
- Timur A. Mavlyutov
- Department of Surgery, University of Wisconsin School of Medicine and Public Health, 5151 Wisconsin Institute for Medical Research, 1111 Highland Ave, Madison, WI 53705, USA
- McPherson Eye Research Institute, University of Wisconsin School of Medicine and Public Health, 5151 Wisconsin Institute for Medical Research, 1111 Highland Ave, Madison, WI 53705, USA
| | - Miles Epstein
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, 41 Bardeen Medical Laboratory, 470 N Charter Street, Madison, WI 53706, USA
| | - Lian-Wang Guo
- Department of Surgery, University of Wisconsin School of Medicine and Public Health, 5151 Wisconsin Institute for Medical Research, 1111 Highland Ave, Madison, WI 53705, USA
- McPherson Eye Research Institute, University of Wisconsin School of Medicine and Public Health, 5151 Wisconsin Institute for Medical Research, 1111 Highland Ave, Madison, WI 53705, USA
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22
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Sharma RK, Baehr W, Makino CL, Duda T. Ca(2+) and Ca(2+)-interlocked membrane guanylate cyclase signal modulation of neuronal and cardiovascular signal transduction. Front Mol Neurosci 2015; 8:7. [PMID: 25798085 PMCID: PMC4351612 DOI: 10.3389/fnmol.2015.00007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 02/16/2015] [Indexed: 12/29/2022] Open
Affiliation(s)
- Rameshwar K Sharma
- Research Divisions of Biochemistry and Molecular Biology, The Unit of Regulatory and Molecular Biology, Salus University Elkins Park, PA, USA
| | - Wolfgang Baehr
- School of Medicine, Department of Ophthalmology and Visual Sciences, University of Utah Salt Lake City, UT, USA
| | - Clint L Makino
- Massachusetts Eye and Ear Infirmary and Harvard Medical School Boston, MA, USA
| | - Teresa Duda
- Research Divisions of Biochemistry and Molecular Biology, The Unit of Regulatory and Molecular Biology, Salus University Elkins Park, PA, USA
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23
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Anjum R, Ayoubian H, Schmitz F. Differential synaptic distribution of the scaffold proteins Cask and Caskin1 in the bovine retina. Mol Cell Neurosci 2014; 62:19-29. [DOI: 10.1016/j.mcn.2014.08.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Revised: 07/24/2014] [Accepted: 08/10/2014] [Indexed: 11/26/2022] Open
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Romero-Pozuelo J, Dason JS, Mansilla A, Baños-Mateos S, Sardina JL, Chaves-Sanjuán A, Jurado-Gómez J, Santana E, Atwood HL, Hernández-Hernández Á, Sánchez-Barrena MJ, Ferrús A. The guanine-exchange factor Ric8a binds to the Ca²⁺ sensor NCS-1 to regulate synapse number and neurotransmitter release. J Cell Sci 2014; 127:4246-59. [PMID: 25074811 DOI: 10.1242/jcs.152603] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The conserved Ca(2+)-binding protein Frequenin (homolog of the mammalian NCS-1, neural calcium sensor) is involved in pathologies that result from abnormal synapse number and probability of neurotransmitter release per synapse. Both synaptic features are likely to be co-regulated but the intervening mechanisms remain poorly understood. We show here that Drosophila Ric8a (a homolog of mammalian synembryn, which is also known as Ric8a), a receptor-independent activator of G protein complexes, binds to Frq2 but not to the virtually identical homolog Frq1. Based on crystallographic data on Frq2 and site-directed mutagenesis on Frq1, the differential amino acids R94 and T138 account for this specificity. Human NCS-1 and Ric8a reproduce the binding and maintain the structural requirements at these key positions. Drosophila Ric8a and Gαs regulate synapse number and neurotransmitter release, and both are functionally linked to Frq2. Frq2 negatively regulates Ric8a to control synapse number. However, the regulation of neurotransmitter release by Ric8a is independent of Frq2 binding. Thus, the antagonistic regulation of these two synaptic properties shares a common pathway, Frq2-Ric8a-Gαs, which diverges downstream. These mechanisms expose the Frq2-Ric8a interacting surface as a potential pharmacological target for NCS-1-related diseases and provide key data towards the corresponding drug design.
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Affiliation(s)
- Jesús Romero-Pozuelo
- Department of Molecular, Cellular and Developmental Neurobiology, Institute Cajal, CSIC, Avenida Dr. Arce 37, Madrid 28002, Spain
| | - Jeffrey S Dason
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Alicia Mansilla
- Department of Molecular, Cellular and Developmental Neurobiology, Institute Cajal, CSIC, Avenida Dr. Arce 37, Madrid 28002, Spain
| | - Soledad Baños-Mateos
- Department of Crystallography and Structural Biology, Institute of Physical-Chemistry 'Rocasolano', CSIC, Serrano 119, Madrid 28006, Spain
| | - José L Sardina
- Department of Biochemistry and Molecular Biology, University of Salamanca, Salamanca 37007, Spain
| | - Antonio Chaves-Sanjuán
- Department of Crystallography and Structural Biology, Institute of Physical-Chemistry 'Rocasolano', CSIC, Serrano 119, Madrid 28006, Spain
| | - Jaime Jurado-Gómez
- Department of Molecular, Cellular and Developmental Neurobiology, Institute Cajal, CSIC, Avenida Dr. Arce 37, Madrid 28002, Spain
| | - Elena Santana
- Department of Molecular, Cellular and Developmental Neurobiology, Institute Cajal, CSIC, Avenida Dr. Arce 37, Madrid 28002, Spain
| | - Harold L Atwood
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Ángel Hernández-Hernández
- Department of Molecular, Cellular and Developmental Neurobiology, Institute Cajal, CSIC, Avenida Dr. Arce 37, Madrid 28002, Spain Department of Biochemistry and Molecular Biology, University of Salamanca, Salamanca 37007, Spain Institute for Biomedical Research (IBSAL), Salamanca 37007, Spain
| | - María-José Sánchez-Barrena
- Department of Crystallography and Structural Biology, Institute of Physical-Chemistry 'Rocasolano', CSIC, Serrano 119, Madrid 28006, Spain
| | - Alberto Ferrús
- Department of Molecular, Cellular and Developmental Neurobiology, Institute Cajal, CSIC, Avenida Dr. Arce 37, Madrid 28002, Spain
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Wen XH, Dizhoor AM, Makino CL. Membrane guanylyl cyclase complexes shape the photoresponses of retinal rods and cones. Front Mol Neurosci 2014; 7:45. [PMID: 24917784 PMCID: PMC4040495 DOI: 10.3389/fnmol.2014.00045] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Accepted: 05/01/2014] [Indexed: 12/02/2022] Open
Abstract
In vertebrate rods and cones, photon capture by rhodopsin leads to the destruction of cyclic GMP (cGMP) and the subsequent closure of cyclic nucleotide gated ion channels in the outer segment plasma membrane. Replenishment of cGMP and reopening of the channels limit the growth of the photon response and are requisite for its recovery. In different vertebrate retinas, there may be as many as four types of membrane guanylyl cyclases (GCs) for cGMP synthesis. Ten neuronal Ca2+ sensor proteins could potentially modulate their activities. The mouse is proving to be an effective model for characterizing the roles of individual components because its relative simplicity can be reduced further by genetic engineering. There are two types of GC activating proteins (GCAPs) and two types of GCs in mouse rods, whereas cones express one type of GCAP and one type of GC. Mutant mouse rods and cones bereft of both GCAPs have large, long lasting photon responses. Thus, GCAPs normally mediate negative feedback tied to the light-induced decline in intracellular Ca2+ that accelerates GC activity to curtail the growth and duration of the photon response. Rods from other mutant mice that express a single GCAP type reveal how the two GCAPs normally work together as a team. Because of its lower Ca2+ affinity, GCAP1 is the first responder that senses the initial decrease in Ca2+ following photon absorption and acts to limit response amplitude. GCAP2, with a higher Ca2+ affinity, is recruited later during the course of the photon response as Ca2+ levels continue to decline further. The main role of GCAP2 is to provide for a timely response recovery and it is particularly important after exposure to very bright light. The multiplicity of GC isozymes and GCAP homologs in the retinas of other vertebrates confers greater flexibility in shaping the photon responses in order to tune visual sensitivity, dynamic range and frequency response.
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Affiliation(s)
- Xiao-Hong Wen
- Department of Ophthalmology, Massachusetts Eye and Ear Infirmary and Harvard Medical School Boston, MA, USA
| | - Alexander M Dizhoor
- Department of Basic Sciences Research and Pennsylvania College of Optometry, Salus University Elkins Park, PA, USA
| | - Clint L Makino
- Department of Ophthalmology, Massachusetts Eye and Ear Infirmary and Harvard Medical School Boston, MA, USA
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