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Morikawa R, Rodrigues TM, Schreyer HM, Cowan CS, Nadeau S, Graff-Meyer A, Patino-Alvarez CP, Khani MH, Jüttner J, Roska B. The sodium-bicarbonate cotransporter Slc4a5 mediates feedback at the first synapse of vision. Neuron 2024:S0896-6273(24)00639-1. [PMID: 39317184 DOI: 10.1016/j.neuron.2024.08.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Revised: 07/22/2024] [Accepted: 08/27/2024] [Indexed: 09/26/2024]
Abstract
Feedback at the photoreceptor synapse is the first neuronal circuit computation in vision, which influences downstream activity patterns within the visual system. Yet, the identity of the feedback signal and the mechanism of synaptic transmission are still not well understood. Here, we combined perturbations of cell-type-specific genes of mouse horizontal cells with two-photon imaging of the result of light-induced feedback in cones and showed that the electrogenic bicarbonate transporter Slc4a5, but not the electroneutral bicarbonate transporter Slc4a3, both expressed specifically in horizontal cells, is necessary for horizontal cell-to-cone feedback. Pharmacological blockage of bicarbonate transporters and buffering pH also abolished the feedback but blocking sodium-proton exchangers and GABA receptors did not. Our work suggests an unconventional mechanism of feedback at the first visual synapse: changes in horizontal cell voltage modulate bicarbonate transport to the cell, via Slc4a5, which leads to the modulation of feedback to cones.
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Affiliation(s)
- Rei Morikawa
- Institute of Molecular and Clinical Ophthalmology Basel, 4031 Basel, Switzerland
| | - Tiago M Rodrigues
- Institute of Molecular and Clinical Ophthalmology Basel, 4031 Basel, Switzerland; Department of Ophthalmology, University of Basel, 4031 Basel, Switzerland
| | | | - Cameron S Cowan
- Institute of Molecular and Clinical Ophthalmology Basel, 4031 Basel, Switzerland
| | - Sarah Nadeau
- Institute of Molecular and Clinical Ophthalmology Basel, 4031 Basel, Switzerland
| | - Alexandra Graff-Meyer
- Facility for Advanced Imaging and Microscopy, Friedrich Miescher Institute for Biomedical Research, 4056 Basel, Switzerland
| | | | | | - Josephine Jüttner
- Institute of Molecular and Clinical Ophthalmology Basel, 4031 Basel, Switzerland
| | - Botond Roska
- Institute of Molecular and Clinical Ophthalmology Basel, 4031 Basel, Switzerland; Department of Ophthalmology, University of Basel, 4031 Basel, Switzerland.
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Lanzetti S, Di Biase V. Small Molecules as Modulators of Voltage-Gated Calcium Channels in Neurological Disorders: State of the Art and Perspectives. Molecules 2022; 27:1312. [PMID: 35209100 PMCID: PMC8879281 DOI: 10.3390/molecules27041312] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2022] [Revised: 02/11/2022] [Accepted: 02/11/2022] [Indexed: 01/03/2023] Open
Abstract
Voltage-gated calcium channels (VGCCs) are widely expressed in the brain, heart and vessels, smooth and skeletal muscle, as well as in endocrine cells. VGCCs mediate gene transcription, synaptic and neuronal structural plasticity, muscle contraction, the release of hormones and neurotransmitters, and membrane excitability. Therefore, it is not surprising that VGCC dysfunction results in severe pathologies, such as cardiovascular conditions, neurological and psychiatric disorders, altered glycemic levels, and abnormal smooth muscle tone. The latest research findings and clinical evidence increasingly show the critical role played by VGCCs in autism spectrum disorders, Parkinson's disease, drug addiction, pain, and epilepsy. These findings outline the importance of developing selective calcium channel inhibitors and modulators to treat such prevailing conditions of the central nervous system. Several small molecules inhibiting calcium channels are currently used in clinical practice to successfully treat pain and cardiovascular conditions. However, the limited palette of molecules available and the emerging extent of VGCC pathophysiology require the development of additional drugs targeting these channels. Here, we provide an overview of the role of calcium channels in neurological disorders and discuss possible strategies to generate novel therapeutics.
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Affiliation(s)
| | - Valentina Di Biase
- Institute of Pharmacology, Department of Medical Statistics, Informatics and Health Economics, Medical University of Innsbruck, Peter-Mayr Strasse 1, A-6020 Innsbruck, Austria;
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Banderali U, Jain M, Thakur S, Jayanthan A, Belke DD, Giles WR, Narendran A. The T-type Calcium Channel Cav3.1 in Y79 Retinoblastoma Cells is Regulated by the Epidermal Growth Factor Receptor via the MAPK Signaling Pathway. Curr Eye Res 2021; 47:426-435. [PMID: 34674590 DOI: 10.1080/02713683.2021.1988982] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
PURPOSE Retinoblastoma is the most frequent intraocular cancer in children. It is also one of the most common causes for enucleation and carries a significant morbidity rate in affected individuals. Hence, studies on its pathophysiological and growth regulatory mechanisms are urgently needed to identify more effective novel therapeutics. METHODS Using the Y79 retinoblastoma cell line, we investigated the electrophysiological and functional activities of the T-type voltage-gated calcium channel Cav3.1, that is constitutively expressed in these cells. We also analyzed the Akt and MAPK signaling pathways downstream of the epidermal growth factor receptor (EGFR) to understand the mechanism responsible for the inhibition of Cav3.1. RESULTS We demonstrate that the EGFR inhibitor Afatinib significantly reduced cell viability and Cav3.1 mRNA expression and electrophysiological activity. At low concentrations (1 µM), Afatinib reduced the amplitude of Cav3.1 current density, whereas at a high concentration (10 µM), it completely abolished the voltage-gated calcium current. Our results show that inhibition of the MAPK pathway by a specific inhibitor VX-11e affected the Cav3.1 current in a dose-dependent manner. VX-11e (50 nM-1 µM) treatment reduced Cav3.1 current densities in Y79 cells, with complete abolishment of Cav3.1 current at higher concentrations (5 µM). We also demonstrate that the specific inhibition of the Akt kinase (using MK-2206) had no effect on the Cav3.1 currents. CONCLUSION Our study provides a functional relationship between the MAPK pathway and EGFR signaling and indicates that the MAPK signaling pathway mediates the control of Cav3.1 by EGFR in retinoblastoma.
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Affiliation(s)
- Umberto Banderali
- Human Health Therapeutics Research Centre, National Research Council of Canada, Ottawa, Canada
| | - Mohit Jain
- POETIC Laboratory for Pre-Clinical Studies and the Division of Pediatric Oncology, Alberta Children's Hospital, Faculty of Medicine, University of Calgary, Calgary, AB, Canada
| | - Satbir Thakur
- POETIC Laboratory for Pre-Clinical Studies and the Division of Pediatric Oncology, Alberta Children's Hospital, Faculty of Medicine, University of Calgary, Calgary, AB, Canada
| | - Aarthi Jayanthan
- POETIC Laboratory for Pre-Clinical Studies and the Division of Pediatric Oncology, Alberta Children's Hospital, Faculty of Medicine, University of Calgary, Calgary, AB, Canada
| | - Darrell D Belke
- Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada
| | - Wayne R Giles
- Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada
| | - Aru Narendran
- POETIC Laboratory for Pre-Clinical Studies and the Division of Pediatric Oncology, Alberta Children's Hospital, Faculty of Medicine, University of Calgary, Calgary, AB, Canada
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4
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Kessi M, Chen B, Peng J, Yan F, Yang L, Yin F. Calcium channelopathies and intellectual disability: a systematic review. Orphanet J Rare Dis 2021; 16:219. [PMID: 33985586 PMCID: PMC8120735 DOI: 10.1186/s13023-021-01850-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Accepted: 05/04/2021] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND Calcium ions are involved in several human cellular processes including corticogenesis, transcription, and synaptogenesis. Nevertheless, the relationship between calcium channelopathies (CCs) and intellectual disability (ID)/global developmental delay (GDD) has been poorly investigated. We hypothesised that CCs play a major role in the development of ID/GDD and that both gain- and loss-of-function variants of calcium channel genes can induce ID/GDD. As a result, we performed a systematic review to investigate the contribution of CCs, potential mechanisms underlying their involvement in ID/GDD, advancements in cell and animal models, treatments, brain anomalies in patients with CCs, and the existing gaps in the knowledge. We performed a systematic search in PubMed, Embase, ClinVar, OMIM, ClinGen, Gene Reviews, DECIPHER and LOVD databases to search for articles/records published before March 2021. The following search strategies were employed: ID and calcium channel, mental retardation and calcium channel, GDD and calcium channel, developmental delay and calcium channel. MAIN BODY A total of 59 reports describing 159 cases were found in PubMed, Embase, ClinVar, and LOVD databases. Variations in ten calcium channel genes including CACNA1A, CACNA1C, CACNA1I, CACNA1H, CACNA1D, CACNA2D1, CACNA2D2, CACNA1E, CACNA1F, and CACNA1G were found to be associated with ID/GDD. Most variants exhibited gain-of-function effect. Severe to profound ID/GDD was observed more for the cases with gain-of-function variants as compared to those with loss-of-function. CACNA1E, CACNA1G, CACNA1F, CACNA2D2 and CACNA1A associated with more severe phenotype. Furthermore, 157 copy number variations (CNVs) spanning calcium genes were identified in DECIPHER database. The leading genes included CACNA1C, CACNA1A, and CACNA1E. Overall, the underlying mechanisms included gain- and/ or loss-of-function, alteration in kinetics (activation, inactivation) and dominant-negative effects of truncated forms of alpha1 subunits. Forty of the identified cases featured cerebellar atrophy. We identified only a few cell and animal studies that focused on the mechanisms of ID/GDD in relation to CCs. There is a scarcity of studies on treatment options for ID/GDD both in vivo and in vitro. CONCLUSION Our results suggest that CCs play a major role in ID/GDD. While both gain- and loss-of-function variants are associated with ID/GDD, the mechanisms underlying their involvement need further scrutiny.
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Affiliation(s)
- Miriam Kessi
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China
- Kilimanjaro Christian Medical University College, Moshi, Tanzania
- Mawenzi Regional Referral Hospital, Moshi, Tanzania
| | - Baiyu Chen
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China
| | - Jing Peng
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China
| | - Fangling Yan
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China
| | - Lifen Yang
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China
| | - Fei Yin
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China.
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China.
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5
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Waldner DM, Ito K, Chen LL, Nguyen L, Chow RL, Lee A, Rancourt DE, Tremblay F, Stell WK, Bech-Hansen NT. Transgenic Expression of Cacna1f Rescues Vision and Retinal Morphology in a Mouse Model of Congenital Stationary Night Blindness 2A (CSNB2A). Transl Vis Sci Technol 2020; 9:19. [PMID: 33117610 PMCID: PMC7571326 DOI: 10.1167/tvst.9.11.19] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2020] [Accepted: 09/17/2020] [Indexed: 12/20/2022] Open
Abstract
Purpose Congenital stationary night blindness 2A (CSNB2A) is a genetic retinal disorder characterized by poor visual acuity, nystagmus, strabismus, and other signs of retinal dysfunction resulting from mutations in Cacna1f -the gene coding for the pore-forming subunit of the calcium channel CaV1.4. Mouse models of CSNB2A have shown that mutations causing the disease deleteriously affect photoreceptors and their synapses with second-order neurons. This study was undertaken to evaluate whether transgenic expression of Cacna1f could rescue morphology and visual function in a Cacna1f-KO model of CSNB2A. Methods Strategic creation, breeding and use of transgenic mouse lines allowed for Cre-driven retina-specific expression of Cacna1f in a CSNB2A model. Transgene expression and retinal morphology were investigated with immunohistochemistry in retinal wholemounts or cross-sections. Visual function was assessed by optokinetic response (OKR) analysis and electroretinography (ERG). Results Mosaic, prenatal expression of Cacna1f in the otherwise Cacna1f-KO retina was sufficient to rescue some visual function. Immunohistochemical analyses demonstrated wild-type-like photoreceptor and synaptic morphology in sections with transgenic expression of Cacna1f. Conclusions This report describes a novel system for Cre-inducible expression of Cacna1f in a Cacna1f-KO mouse model of CSNB2A and provides preclinical evidence for the potential use of gene therapy in the treatment of CSNB2A. Translational Relevance These data have relevance in the treatment of CSNB2A and in understanding how photoreceptor integration might be achieved in retinas in which photoreceptors have been lost, such as retinitis pigmentosa, age-related macular degeneration, and other degenerative conditions.
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Affiliation(s)
- Derek M Waldner
- Graduate Department of Neuroscience, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
| | - Kenichi Ito
- Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, AB, Canada
| | - Li-Li Chen
- Department of Biology, University of Victoria, Victoria, BC, Canada
| | - Lisa Nguyen
- Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
| | - Robert L Chow
- Department of Biology, University of Victoria, Victoria, BC, Canada
| | - Amy Lee
- Department of Molecular Physiology and Biophysics, Department of Otolaryngology Head-Neck Surgery and Department of Neurology, University of Iowa, Iowa City, IA, USA
| | - Derrick E Rancourt
- Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, AB, Canada
| | - Francois Tremblay
- Department of Ophthalmology and Visual Sciences, Faculty of Medicine, and Clinical Vision Sciences Program, Faculty of Health Dalhousie University, NS, Canada
| | - William K Stell
- Department of Cell Biology and Anatomy and Department of Surgery, Hotchkiss Brain Institute, and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
| | - N Torben Bech-Hansen
- Department of Medical Genetics, and Department of Surgery, Alberta Children's Hospital Research Institute, and Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
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6
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Sensing through Non-Sensing Ocular Ion Channels. Int J Mol Sci 2020; 21:ijms21186925. [PMID: 32967234 PMCID: PMC7554890 DOI: 10.3390/ijms21186925] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Revised: 09/17/2020] [Accepted: 09/18/2020] [Indexed: 12/12/2022] Open
Abstract
Ion channels are membrane-spanning integral proteins expressed in multiple organs, including the eye. In the eye, ion channels are involved in various physiological processes, like signal transmission and visual processing. A wide range of mutations have been reported in the corresponding genes and their interacting subunit coding genes, which contribute significantly to an array of blindness, termed ocular channelopathies. These mutations result in either a loss- or gain-of channel functions affecting the structure, assembly, trafficking, and localization of channel proteins. A dominant-negative effect is caused in a few channels formed by the assembly of several subunits that exist as homo- or heteromeric proteins. Here, we review the role of different mutations in switching a “sensing” ion channel to “non-sensing,” leading to ocular channelopathies like Leber’s congenital amaurosis 16 (LCA16), cone dystrophy, congenital stationary night blindness (CSNB), achromatopsia, bestrophinopathies, retinitis pigmentosa, etc. We also discuss the various in vitro and in vivo disease models available to investigate the impact of mutations on channel properties, to dissect the disease mechanism, and understand the pathophysiology. Innovating the potential pharmacological and therapeutic approaches and their efficient delivery to the eye for reversing a “non-sensing” channel to “sensing” would be life-changing.
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7
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Three cases of acute-onset bilateral photophobia. Jpn J Ophthalmol 2019; 63:172-180. [DOI: 10.1007/s10384-018-00649-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2018] [Accepted: 11/15/2018] [Indexed: 12/26/2022]
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8
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Dai X, Pang S, Wang J, FitzMaurice B, Pang J, Chang B. Photoreceptor degeneration in a new Cacna1f mutant mouse model. Exp Eye Res 2018; 179:106-114. [PMID: 30445045 DOI: 10.1016/j.exer.2018.11.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Revised: 10/17/2018] [Accepted: 11/12/2018] [Indexed: 02/06/2023]
Abstract
The Cacna1f gene encodes the α1F subunit of an L-type voltage-gated calcium channel, Cav1.4. In photoreceptor synaptic terminals, Cav1.4 channels mediate glutamate release and postsynaptic responses associated with visual signal transmission. We have discovered a new Cacna1f mutation in nob9 mice, which display more severe phenotypes than do nob2 mice. To characterize the nob9 phenotype at different ages, we examined the murine fundus, applied retinal optical coherence tomography, measured flash electroretinograms (ERGs) in vivo, and analyzed the retinal histology in vitro. After identifying the X-linked recessive inheritance trait, we sequenced Cacna1f as the candidate gene. Mutations in this gene were detected by polymerase chain reaction (PCR) and confirmed by restriction fragment length polymorphism. Morphologically, an early-onset of retinal disorder was detected, and the degeneration of the outer plexiform layers progressed rapidly. Moreover, the mutant mice showed drastically reduced scotopic ERGs with increasing age. In 14-month-old nob9 retinas, immunostaining of cone opsins demonstrated a reduction in the number of short-wavelength opsins (S-opsins) to 54% of wild-type levels, and almost no middle-wavelength opsins (M-opsins) were observed. No cone ERGs could be detected from residual cones, in which S-opsins abnormally migrated to inner segments of the photoreceptors. The mutations of the Cacna1f gene in nob9 mice involved both a single nucleotide G to A transition and a 10-nucleotide insertion, the latter resulting in a frame-shift mutation in exon 14.
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Affiliation(s)
- Xufeng Dai
- School of Ophthalmology and Optometry, The Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, 325027, China; Department of Ophthalmology, University of Florida, Gainesville, FL, 32610, USA
| | - Shiyi Pang
- The Jackson Laboratory, Bar Harbor, ME, 04609, USA; College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Jieping Wang
- The Jackson Laboratory, Bar Harbor, ME, 04609, USA
| | | | - Jijing Pang
- School of Ophthalmology and Optometry, The Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, 325027, China; Department of Ophthalmology, University of Florida, Gainesville, FL, 32610, USA; College of Medicine, University of Florida, Gainesville, FL, 32610, USA; Eye Research Institute, Xiamen Eye Center of Xiamen University, Xiamen, 361001, China.
| | - Bo Chang
- The Jackson Laboratory, Bar Harbor, ME, 04609, USA.
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Waldner DM, Bech-Hansen NT, Stell WK. Channeling Vision: Ca V1.4-A Critical Link in Retinal Signal Transmission. BIOMED RESEARCH INTERNATIONAL 2018; 2018:7272630. [PMID: 29854783 PMCID: PMC5966690 DOI: 10.1155/2018/7272630] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 02/15/2018] [Indexed: 01/09/2023]
Abstract
Voltage-gated calcium channels (VGCC) are key to many biological functions. Entry of Ca2+ into cells is essential for initiating or modulating important processes such as secretion, cell motility, and gene transcription. In the retina and other neural tissues, one of the major roles of Ca2+-entry is to stimulate or regulate exocytosis of synaptic vesicles, without which synaptic transmission is impaired. This review will address the special properties of one L-type VGCC, CaV1.4, with particular emphasis on its role in transmission of visual signals from rod and cone photoreceptors (hereafter called "photoreceptors," to the exclusion of intrinsically photoreceptive retinal ganglion cells) to the second-order retinal neurons, and the pathological effects of mutations in the CACNA1F gene which codes for the pore-forming α1F subunit of CaV1.4.
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Affiliation(s)
- D. M. Waldner
- Department of Neuroscience, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
| | - N. T. Bech-Hansen
- Department of Medical Genetics and Department of Surgery, Alberta Children's Hospital Research Institute, and Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
| | - W. K. Stell
- Department of Cell Biology and Anatomy and Department of Surgery, Hotchkiss Brain Institute, and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
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10
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Waldner DM, Giraldo Sierra NC, Bonfield S, Nguyen L, Dimopoulos IS, Sauvé Y, Stell WK, Bech-Hansen NT. Cone dystrophy and ectopic synaptogenesis in a Cacna1f loss of function model of congenital stationary night blindness (CSNB2A). Channels (Austin) 2018; 12:17-33. [PMID: 29179637 PMCID: PMC5972796 DOI: 10.1080/19336950.2017.1401688] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Revised: 10/22/2017] [Accepted: 10/31/2017] [Indexed: 01/05/2023] Open
Abstract
Congenital stationary night blindness 2A (CSNB2A) is an X-linked retinal disorder, characterized by phenotypically variable signs and symptoms of impaired vision. CSNB2A is due to mutations in CACNA1F, which codes for the pore-forming α1F subunit of a L-type voltage-gated calcium channel, Cav1.4. Mouse models of CSNB2A, used for characterizing the effects of various Cacna1f mutations, have revealed greater severity of defects than in human CSNB2A. Specifically, Cacna1f-knockout mice show an apparent lack of visual function, gradual retinal degeneration, and disruption of photoreceptor synaptic terminals. Several reports have also noted cone-specific disruptions, including axonal abnormalities, dystrophy, and cell death. We have explored further the involvement of cones in our 'G305X' mouse model of CSNB2A, which has a premature truncation, loss-of-function mutation in Cacna1f. We show that the expression of genes for several phototransduction-related cone markers is down-regulated, while that of several cellular stress- and damage-related markers is up-regulated; and that cone photoreceptor structure and photopic visual function - measured by immunohistochemistry, optokinetic response and electroretinography - deteriorate progressively with age. We also find that dystrophic cone axons establish synapse-like contacts with rod bipolar cell dendrites, which they normally do not contact in wild-type retinas - ectopically, among rod cell bodies in the outer nuclear layer. These data support a role for Cav1.4 in cone synaptic development, cell viability, and synaptic transmission of cone-dependent visual signals. Although our novel finding of cone-to-rod-bipolar cell contacts in this mouse model of a retinal channelopathy may challenge current views of the role of Cav1.4 in photopic vision, it also suggests a potential new target for restorative therapy.
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Affiliation(s)
- D. M. Waldner
- Department of Neuroscience, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - N. C. Giraldo Sierra
- Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - S. Bonfield
- Department of Neuroscience, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - L. Nguyen
- Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - I. S. Dimopoulos
- Department of Ophthalmology and Visual Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Y. Sauvé
- Department of Ophthalmology and Visual Sciences, University of Alberta, Edmonton, Alberta, Canada
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada
| | - W. K. Stell
- Department of Cell Biology and Anatomy and Department of Surgery, Hotchkiss Brain Institute, and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - N. T. Bech-Hansen
- Department of Medical Genetics, and Department of Surgery, Alberta Children's Hospital Research Institute, and Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
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11
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Zamponi GW. Targeting voltage-gated calcium channels in neurological and psychiatric diseases. Nat Rev Drug Discov 2015; 15:19-34. [DOI: 10.1038/nrd.2015.5] [Citation(s) in RCA: 254] [Impact Index Per Article: 28.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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12
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Deming JD, Pak JS, Brown BM, Kim MK, Aung MH, Eom YS, Shin JA, Lee EJ, Pardue MT, Craft CM. Visual Cone Arrestin 4 Contributes to Visual Function and Cone Health. Invest Ophthalmol Vis Sci 2015; 56:5407-16. [PMID: 26284544 DOI: 10.1167/iovs.15-16647] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
PURPOSE Visual arrestins (ARR) play a critical role in shutoff of rod and cone phototransduction. When electrophysiological responses are measured for a single mouse cone photoreceptor, ARR1 expression can substitute for ARR4 in cone pigment desensitization; however, each arrestin may also contribute its own, unique role to modulate other cellular functions. METHODS A combination of ERG, optokinetic tracking, immunohistochemistry, and immunoblot analysis was used to investigate the retinal phenotypes of Arr4 null mice (Arr4-/-) compared with age-matched control, wild-type mice. RESULTS When 2-month-old Arr4-/- mice were compared with wild-type mice, they had diminished visual acuity and contrast sensitivity, yet enhanced ERG flicker response and higher photopic ERG b-wave amplitudes. In contrast, in older Arr4-/- mice, all ERG amplitudes were significantly reduced in magnitude compared with age-matched controls. Furthermore, in older Arr4-/- mice, the total cone numbers decreased and cone opsin protein immunoreactive expression levels were significantly reduced, while overall photoreceptor outer nuclear layer thickness was unchanged. CONCLUSIONS Our study demonstrates that Arr4-/- mice display distinct phenotypic differences when compared to controls, suggesting that ARR4 modulates essential functions in high acuity vision and downstream cellular signaling pathways that are not fulfilled or substituted by the coexpression of ARR1, despite its high expression levels in all mouse cones. Without normal ARR4 expression levels, cones slowly degenerate with increasing age, making this a new model to study age-related cone dystrophy.
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Affiliation(s)
- Janise D Deming
- Mary D. Allen Laboratory for Vision Research, USC Eye Institute, Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States
| | - Joseph S Pak
- Mary D. Allen Laboratory for Vision Research, USC Eye Institute, Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States
| | - Bruce M Brown
- Mary D. Allen Laboratory for Vision Research, USC Eye Institute, Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States
| | - Moon K Kim
- Rehabilitation Research & Development Center of Excellence, Atlanta VA Medical Center, Decatur, Georgia, United States
| | - Moe H Aung
- Neuroscience/Ophthalmology, Emory University, Atlanta, Georgia, United States
| | - Yun Sung Eom
- Mary D. Allen Laboratory for Vision Research, USC Eye Institute, Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States 4Dornsife College of Letters, Arts and Sciences, Univers
| | - Jung-A Shin
- Mary D. Allen Laboratory for Vision Research, USC Eye Institute, Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States 5Department of Anatomy, School of Medicine, Ewha Womans
| | - Eun-Jin Lee
- Mary D. Allen Laboratory for Vision Research, USC Eye Institute, Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States 6Department of Biomedical Engineering, University of Sou
| | - Machelle T Pardue
- Rehabilitation Research & Development Center of Excellence, Atlanta VA Medical Center, Decatur, Georgia, United States 3Neuroscience/Ophthalmology, Emory University, Atlanta, Georgia, United States
| | - Cheryl Mae Craft
- Mary D. Allen Laboratory for Vision Research, USC Eye Institute, Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States 7Department of Cell & Neurobiology, Keck School of Medic
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13
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Psychophysical testing in rodent models of glaucomatous optic neuropathy. Exp Eye Res 2015; 141:154-63. [PMID: 26144667 DOI: 10.1016/j.exer.2015.06.025] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Revised: 06/08/2015] [Accepted: 06/29/2015] [Indexed: 12/14/2022]
Abstract
Processing of visual information begins in the retina, with photoreceptors converting light stimuli into neural signals. Ultimately, signals are transmitted to the brain through signaling networks formed by interneurons, namely bipolar, horizontal and amacrine cells providing input to retinal ganglion cells (RGCs), which form the optic nerve with their axons. As part of the chronic nature of glaucomatous optic neuropathy, the increasing and irreversible damage and ultimately loss of neurons, RGCs in particular, occurs following progressive damage to the optic nerve head (ONH), eventually resulting in visual impairment and visual field loss. There are two behavioral assays that are typically used to assess visual deficits in glaucoma rodent models, the visual water task and the optokinetic drum. The visual water task can assess an animal's ability to distinguish grating patterns that are associated with an escape from water. The optokinetic drum relies on the optomotor response, a reflex turning of the head and neck in the direction of the visual stimuli, which usually consists of rotating black and white gratings. This reflex is a physiological response critical for keeping the image stable on the retina. Driven initially by the neuronal input from direction-selective RGCs, this reflex is comprised of a number of critical sensory and motor elements. In the presence of repeatable and defined stimuli, this reflex is extremely well suited to analyze subtle changes in the circuitry and performance of retinal neurons. Increasing the cycles of these alternating gratings per degree, or gradually reducing the contrast of the visual stimuli, threshold levels can be determined at which the animal is no longer tracking the stimuli, and thereby visual function of the animal can be determined non-invasively. Integrating these assays into an array of outcome measures that determine multiple aspects of visual function is a central goal in vision research and can be realized, for example, by the combination of measuring optomotor reflex function with electroretinograms (ERGs) and optical coherence tomography (OCT) of the retina. These structure-function correlations in vivo are urgently needed to identify disease mechanisms as potential new targets for drug development. Such a combination of the experimental assessment of the optokinetic reflex (OKR) or optomotor response (OMR) with other measures of retinal structure and function is especially valuable for research on GON. The chronic progression of the disease is characterized by a gradual decrease in function accompanied by a concomitant increase in structural damage to the retina, therefore the assessment of subtle changes is key to determining the success of novel intervention strategies.
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Park S, Li C, Haeseleer F, Palczewski K, Ames JB. Structural insights into activation of the retinal L-type Ca²⁺ channel (Cav1.4) by Ca²⁺-binding protein 4 (CaBP4). J Biol Chem 2014; 289:31262-73. [PMID: 25258313 DOI: 10.1074/jbc.m114.604439] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
CaBP4 modulates Ca(2+)-dependent activity of L-type voltage-gated Ca(2+) channels (Cav1.4) in retinal photoreceptor cells. Mg(2+) binds to the first and third EF-hands (EF1 and EF3), and Ca(2+) binds to EF1, EF3, and EF4 of CaBP4. Here we present NMR structures of CaBP4 in both Mg(2+)-bound and Ca(2+)-bound states and model the CaBP4 structural interaction with Cav1.4. CaBP4 contains an unstructured N-terminal region (residues 1-99) and four EF-hands in two separate lobes. The N-lobe consists of EF1 and EF2 in a closed conformation with either Mg(2+) or Ca(2+) bound at EF1. The C-lobe binds Ca(2+) at EF3 and EF4 and exhibits a Ca(2+)-induced closed-to-open transition like that of calmodulin. Exposed residues in Ca(2+)-bound CaBP4 (Phe(137), Glu(168), Leu(207), Phe(214), Met(251), Phe(264), and Leu(268)) make contacts with the IQ motif in Cav1.4, and the Cav1.4 mutant Y1595E strongly impairs binding to CaBP4. We conclude that CaBP4 forms a collapsed structure around the IQ motif in Cav1.4 that we suggest may promote channel activation by disrupting an interaction between IQ and the inhibitor of Ca(2+)-dependent inactivation domain.
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Affiliation(s)
- Saebomi Park
- From the Department of Chemistry, University of California, Davis, California 95616
| | - Congmin Li
- From the Department of Chemistry, University of California, Davis, California 95616
| | - Françoise Haeseleer
- the Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195, and
| | - Krzysztof Palczewski
- the Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965
| | - James B Ames
- From the Department of Chemistry, University of California, Davis, California 95616,
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15
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Simms BA, Zamponi GW. Neuronal voltage-gated calcium channels: structure, function, and dysfunction. Neuron 2014; 82:24-45. [PMID: 24698266 DOI: 10.1016/j.neuron.2014.03.016] [Citation(s) in RCA: 420] [Impact Index Per Article: 42.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Voltage-gated calcium channels are the primary mediators of depolarization-induced calcium entry into neurons. There is great diversity of calcium channel subtypes due to multiple genes that encode calcium channel α1 subunits, coassembly with a variety of ancillary calcium channel subunits, and alternative splicing. This allows these channels to fulfill highly specialized roles in specific neuronal subtypes and at particular subcellular loci. While calcium channels are of critical importance to brain function, their inappropriate expression or dysfunction gives rise to a variety of neurological disorders, including, pain, epilepsy, migraine, and ataxia. This Review discusses salient aspects of voltage-gated calcium channel function, physiology, and pathophysiology.
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Affiliation(s)
- Brett A Simms
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, AB T2N 4N1, Canada
| | - Gerald W Zamponi
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, AB T2N 4N1, Canada.
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16
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Schmitz F. Presynaptic [Ca(2+)] and GCAPs: aspects on the structure and function of photoreceptor ribbon synapses. Front Mol Neurosci 2014; 7:3. [PMID: 24567702 PMCID: PMC3915146 DOI: 10.3389/fnmol.2014.00003] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Accepted: 01/15/2014] [Indexed: 12/21/2022] Open
Abstract
Changes in intracellular calcium ions [Ca2+] play important roles in photoreceptor signaling. Consequently, intracellular [Ca2+] levels need to be tightly controlled. In the light-sensitive outer segments (OS) of photoreceptors, Ca2+ regulates the activity of retinal guanylate cyclases thus playing a central role in phototransduction and light-adaptation by restoring light-induced decreases in cGMP. In the synaptic terminals, changes of intracellular Ca2+ trigger various aspects of neurotransmission. Photoreceptors employ tonically active ribbon synapses that encode light-induced, graded changes of membrane potential into modulation of continuous synaptic vesicle exocytosis. The active zones of ribbon synapses contain large electron-dense structures, synaptic ribbons, that are associated with large numbers of synaptic vesicles. Synaptic coding at ribbon synapses differs from synaptic coding at conventional (phasic) synapses. Recent studies revealed new insights how synaptic ribbons are involved in this process. This review focuses on the regulation of [Ca2+] in presynaptic photoreceptor terminals and on the function of a particular Ca2+-regulated protein, the neuronal calcium sensor protein GCAP2 (guanylate cyclase-activating protein-2) in the photoreceptor ribbon synapse. GCAP2, an EF-hand-containing protein plays multiple roles in the OS and in the photoreceptor synapse. In the OS, GCAP2 works as a Ca2+-sensor within a Ca2+-regulated feedback loop that adjusts cGMP levels. In the photoreceptor synapse, GCAP2 binds to RIBEYE, a component of synaptic ribbons, and mediates Ca2+-dependent plasticity at that site. Possible mechanisms are discussed.
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Affiliation(s)
- Frank Schmitz
- Department of Neuroanatomy, Institute for Anatomy and Cell Biology, Medical School Homburg/Saar, Saarland University Saarland, Germany
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17
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De Sevilla Müller LP, Liu J, Solomon A, Rodriguez A, Brecha NC. Expression of voltage-gated calcium channel α(2)δ(4) subunits in the mouse and rat retina. J Comp Neurol 2014; 521:2486-501. [PMID: 23296739 DOI: 10.1002/cne.23294] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2012] [Revised: 12/12/2012] [Accepted: 12/27/2012] [Indexed: 01/18/2023]
Abstract
High-voltage activated Ca channels participate in multiple cellular functions, including transmitter release, excitation, and gene transcription. Ca channels are heteromeric proteins consisting of a pore-forming α(1) subunit and auxiliary α(2)δ and β subunits. Although there are reports of α(2)δ(4) subunit mRNA in the mouse retina and localization of the α(2)δ(4) subunit immunoreactivity to salamander photoreceptor terminals, there is a limited overall understanding of its expression and localization in the retina. α(2)δ(4) subunit expression and distribution in the mouse and rat retina were evaluated by using reverse transcriptase polymerase chain reaction, western blot, and immunohistochemistry with specific primers and a well-characterized antibody to the α(2)δ(4) subunit. α(2)δ(4) subunit mRNA and protein are present in mouse and rat retina, brain, and liver homogenates. Immunostaining for the α(2)δ(4) subunit is mainly localized to Müller cell processes and endfeet, photoreceptor terminals, and photoreceptor outer segments. This subunit is also expressed in a few displaced ganglion cells and bipolar cell dendrites. These findings suggest that the α(2)δ(4) subunit participates in the modulation of L-type Ca(2+) current regulating neurotransmitter release from photoreceptor terminals and Ca(2+)-dependent signaling pathways in bipolar and Müller cells.
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Affiliation(s)
- Luis Pérez De Sevilla Müller
- Department of Neurobiology, David Geffen School of Medicine at UCLA, University of California, Los Angeles, California 90095, USA.
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18
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Jia S, Muto A, Orisme W, Henson HE, Parupalli C, Ju B, Baier H, Taylor MR. Zebrafish Cacna1fa is required for cone photoreceptor function and synaptic ribbon formation. Hum Mol Genet 2014; 23:2981-94. [PMID: 24419318 DOI: 10.1093/hmg/ddu009] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Mutations in the human CACNA1F gene cause incomplete congenital stationary night blindness type 2 (CSNB2), a non-progressive, clinically heterogeneous retinal disorder. However, the molecular mechanisms underlying CSNB2 have not been fully explored. Here, we describe the positional cloning of a blind zebrafish mutant, wait until dark (wud), which encodes a zebrafish homolog of human CACNA1F. We identified two zebrafish cacna1f paralogs and showed that the cacna1fa transcript (the gene mutated in wud) is expressed exclusively in the photoreceptor layer. We demonstrated that Cacna1fa localizes at the photoreceptor synapse and is absent from wud mutants. Electroretinograms revealed abnormal cone photoreceptor responses from wud mutants, indicating a defect in synaptic transmission. Although there are no obvious morphological differences, we found that wud mutants lacked synaptic ribbons and that wud is essential for the development of synaptic ribbons. We found that Ribeye, the most prominent synaptic ribbon protein, was less abundant and mislocalized in adult wud mutants. In addition to cloning wud, we identified synaptojanin 1 (synj1) as the defective gene in slacker (slak), a blind mutant with floating synaptic ribbons. We determined that Cacna1fa was expressed in slak photoreceptors and that Synj1 was initially expressed wud photoreceptors, but was absent by 5 days postfertilization. Collectively, our data demonstrate that Cacna1fa is essential for cone photoreceptor function and synaptic ribbon formation and reveal a previously unknown yet critical role of L-type voltage-dependent calcium channels in the expression and/or distribution of synaptic ribbon proteins, providing a new model to study the clinical variability in human CSNB2 patients.
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Affiliation(s)
- Sujuan Jia
- Department of Chemical Biology and Therapeutics, St Jude Children's Research Hospital, Memphis, TN 38105, USA
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19
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A novel large in-frame deletion within the CACNA1F gene associates with a cone-rod dystrophy 3-like phenotype. PLoS One 2013; 8:e76414. [PMID: 24124559 PMCID: PMC3790679 DOI: 10.1371/journal.pone.0076414] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 08/25/2013] [Indexed: 01/18/2023] Open
Abstract
Cone-rod dystrophies (CORDs) represent a heterogeneous group of monogenic diseases leading to early impairment of vision. The majority of CORD entities show autosomal modes of inheritance and X-linked traits are comparably rare. So far, three X-chromosomal entities were reported (CORDX1, -X2 and -X3). In this study, we analysed a large family of German origin with solely affected males over three generations showing a CORDX-like phenotype. Due to the heterogeneity of cone-rod dystrophies, we performed a combined linkage and X-exome sequencing approach and identified a novel large intragenic in-frame deletion encompassing exons 18 to 26 within the CACNA1F gene. CACNA1F is described causative for CORDX3 in a single family originating from Finland and alterations in this gene have not yet been reported in other CORDX pedigrees. Our data independently confirm CACNA1F as the causative gene for CORDX3-like phenotypes and detailed clinical characterization of the family expands the knowledge about the phenotypic spectrum of deleterious CACNA1F alterations.
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20
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Shi Q, Stell WK. Die Fledermaus: regarding optokinetic contrast sensitivity and light-adaptation, chicks are mice with wings. PLoS One 2013; 8:e75375. [PMID: 24098693 PMCID: PMC3787091 DOI: 10.1371/journal.pone.0075375] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2013] [Accepted: 08/14/2013] [Indexed: 01/27/2023] Open
Abstract
BACKGROUND Through adaptation, animals can function visually under an extremely broad range of light intensities. Light adaptation starts in the retina, through shifts in photoreceptor sensitivity and kinetics plus modulation of visual processing in retinal circuits. Although considerable research has been conducted on retinal adaptation in nocturnal species with rod-dominated retinas, such as the mouse, little is known about how cone-dominated avian retinas adapt to changes in mean light intensity. METHODOLOGY/PRINCIPAL FINDINGS We used the optokinetic response to characterize contrast sensitivity (CS) in the chick retina as a function of spatial frequency and temporal frequency at different mean light intensities. We found that: 1) daytime, cone-driven CS was tuned to spatial frequency; 2) nighttime, presumably rod-driven CS was tuned to temporal frequency and spatial frequency; 3) daytime, presumably cone-driven CS at threshold intensity was invariant with temporal and spatial frequency; and 4) daytime photopic CS was invariant with clock time. CONCLUSION/SIGNIFICANCE Light- and dark-adaptational changes in CS were investigated comprehensively for the first time in the cone-dominated retina of an avian, diurnal species. The chick retina, like the mouse retina, adapts by using a "day/night" or "cone/rod" switch in tuning preference during changes in lighting conditions. The chick optokinetic response is an attractive model for noninvasive, behavioral studies of adaptation in retinal circuitry in health and disease.
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Affiliation(s)
- Qing Shi
- Neuroscience Graduate Program, University of Calgary Faculty of Medicine, Calgary, Alberta, Canada
| | - William K. Stell
- Department of Cell Biology and Anatomy, and Department of Surgery, and Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute; University of Calgary Faculty of Medicine, Calgary, Alberta, Canada
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21
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Zabouri N, Haverkamp S. Calcium channel-dependent molecular maturation of photoreceptor synapses. PLoS One 2013; 8:e63853. [PMID: 23675510 PMCID: PMC3652833 DOI: 10.1371/journal.pone.0063853] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Accepted: 04/08/2013] [Indexed: 01/08/2023] Open
Abstract
Several studies have shown the importance of calcium channels in the development and/or maturation of synapses. The CaV1.4(α1F) knockout mouse is a unique model to study the role of calcium channels in photoreceptor synapse formation. It features abnormal ribbon synapses and aberrant cone morphology. We investigated the expression and targeting of several key elements of ribbon synapses and analyzed the cone morphology in the CaV1.4(α1F) knockout retina. Our data demonstrate that most abnormalities occur after eye opening. Indeed, scaffolding proteins such as Bassoon and RIM2 are properly targeted at first, but their expression and localization are not maintained in adulthood. This indicates that either calcium or the CaV1.4 channel, or both are necessary for the maintenance of their normal expression and distribution in photoreceptors. Other proteins, such as Veli3 and PSD-95, also display abnormal expression in rods prior to eye opening. Conversely, vesicle related proteins appear normal. Our data demonstrate that the CaV1.4 channel is important for maintaining scaffolding proteins in the ribbon synapse but less vital for proteins related to vesicular release. This study also confirms that in adult retinae, cones show developmental features such as sprouting and synaptogenesis. Overall we present evidence that in the absence of the CaV1.4 channel, photoreceptor synapses remain immature and are unable to stabilize.
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Affiliation(s)
- Nawal Zabouri
- Neuroanatomy, Max-Planck-Institute for Brain Research, Frankfurt am Main, Germany.
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22
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Filamin and phospholipase C-ε are required for calcium signaling in the Caenorhabditis elegans spermatheca. PLoS Genet 2013; 9:e1003510. [PMID: 23671426 PMCID: PMC3650001 DOI: 10.1371/journal.pgen.1003510] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Accepted: 03/30/2013] [Indexed: 12/05/2022] Open
Abstract
The Caenorhabditis elegans spermatheca is a myoepithelial tube that stores sperm and undergoes cycles of stretching and constriction as oocytes enter, are fertilized, and exit into the uterus. FLN-1/filamin, a stretch-sensitive structural and signaling scaffold, and PLC-1/phospholipase C-ε, an enzyme that generates the second messenger IP3, are required for embryos to exit normally after fertilization. Using GCaMP, a genetically encoded calcium indicator, we show that entry of an oocyte into the spermatheca initiates a distinctive series of IP3-dependent calcium oscillations that propagate across the tissue via gap junctions and lead to constriction of the spermatheca. PLC-1 is required for the calcium release mechanism triggered by oocyte entry, and FLN-1 is required for timely initiation of the calcium oscillations. INX-12, a gap junction subunit, coordinates propagation of the calcium transients across the spermatheca. Gain-of-function mutations in ITR-1/IP3R, an IP3-dependent calcium channel, and loss-of-function mutations in LFE-2, a negative regulator of IP3 signaling, increase calcium release and suppress the exit defect in filamin-deficient animals. We further demonstrate that a regulatory cassette consisting of MEL-11/myosin phosphatase and NMY-1/non-muscle myosin is required for coordinated contraction of the spermatheca. In summary, this study answers long-standing questions concerning calcium signaling dynamics in the C. elegans spermatheca and suggests FLN-1 is needed in response to oocyte entry to trigger calcium release and coordinated contraction of the spermathecal tissue. During organism development and normal physiological function cells sense, integrate, and respond to a variety of cues or signals including biochemical and mechanical stimuli. In this study we used Caenorhabditis elegans, a small transparent worm, to study filamin (FLN-1), a structural protein that may act as a molecular strain gauge. The C. elegans spermatheca is a contractile tube that is stretched during normal function, making it an ideal candidate for study of how cells respond to stretch. Oocytes are ovulated into the spermatheca, fertilized, and then pushed into the uterus by constriction of the spermatheca. The ability of the spermatheca to constrict depends on inositol 1,4,5-triphosphate (IP3), a signaling molecule produced by the enzyme phospholipase C (PLC-1) that triggers calcium release within cells. In animals with mutated FLN-1 or PLC-1 the spermathecal cells fail to constrict. Using genetic analysis and a calcium-sensitive fluorescent protein, we show that FLN-1 functions with PLC-1 to regulate IP3 production, calcium release, and contraction of the spermatheca. Filamin may function to sense stretch caused by entering oocytes and to trigger constriction. These findings establish a link between filamin and calcium signaling that may apply to similar signaling pathways in other systems.
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Abstract
Photoreceptors are exquisitely adapted to transform light stimuli into electrical signals that modulate neurotransmitter release. These cells are organized into several compartments including the unique outer segment (OS). Its whole function is to absorb light and transduce this signal into a change of membrane potential. Another compartment is the inner segment where much of metabolism and regulation of membrane potential takes place and that connects the OS and synapse. The synapse is the compartment where changes in membrane potentials are relayed to other neurons in the retina via release of neurotransmitter. The composition of the plasma membrane surrounding these compartments varies to accommodate their specific functions. In this chapter, we discuss the organization of the plasma membrane emphasizing the protein composition of each region as it relates to visual signaling. We also point out examples where mutations in these proteins cause visual impairment.
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Affiliation(s)
- Sheila A Baker
- Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA.
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Trafficking of presynaptic PMCA signaling complexes in mouse photoreceptors requires Cav1.4 α1 subunits. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012. [PMID: 22183401 DOI: 10.1007/978-1-4614-0631-0_94] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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25
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Nejatbakhsh N, Feng ZP. Calcium binding protein-mediated regulation of voltage-gated calcium channels linked to human diseases. Acta Pharmacol Sin 2011; 32:741-8. [PMID: 21642945 DOI: 10.1038/aps.2011.64] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Calcium ion entry through voltage-gated calcium channels is essential for cellular signalling in a wide variety of cells and multiple physiological processes. Perturbations of voltage-gated calcium channel function can lead to pathophysiological consequences. Calcium binding proteins serve as calcium sensors and regulate the calcium channel properties via feedback mechanisms. This review highlights the current evidences of calcium binding protein-mediated channel regulation in human diseases.
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Fletcher EL, Jobling AI, Vessey KA, Luu C, Guymer RH, Baird PN. Animal models of retinal disease. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2011; 100:211-86. [PMID: 21377628 DOI: 10.1016/b978-0-12-384878-9.00006-6] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
Diseases of the retina are the leading causes of blindness in the industrialized world. The recognition that animals develop retinal diseases with similar traits to humans has led to not only a dramatic improvement in our understanding of the pathogenesis of retinal disease but also provided a means for testing possible treatment regimes and successful gene therapy trials. With the advent of genetic and molecular biological tools, the association between specific gene mutations and retinal signs has been made. Animals carrying natural mutations usually in one gene now provide well-established models for a host of inherited retinal diseases, including retinitis pigmentosa, Leber congenital amaurosis, inherited macular degeneration, and optic nerve diseases. In addition, the development of transgenic technologies has provided a means by which to study the effects of these and novel induced mutations on retinal structure and function. Despite these advances, there is a paucity of suitable animal models for complex diseases, including age-related macular degeneration (AMD) and diabetic retinopathy, largely because these diseases are not caused by single gene defects, but involve complex genetics and/or exacerbation through environmental factors, epigenetic, or other modes of genetic influence. In this review, we outline in detail the available animal models for inherited retinal diseases and how this information has furthered our understanding of retinal diseases. We also examine how transgenic technologies have helped to develop our understanding of the role of isolated genes or pathways in complex diseases like AMD, diabetes, and glaucoma.
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Affiliation(s)
- Erica L Fletcher
- Department of Anatomy and Cell Biology, The University of Melbourne, Parkville, Victoria, Australia
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