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Torten G, Fisher SK, Linberg KA, Luna G, Perkins G, Ellisman MH, Williams DS. Three-Dimensional Ultrastructure of the Normal Rod Photoreceptor Synapse and Degenerative Changes Induced by Retinal Detachment. J Neurosci 2023; 43:5468-5482. [PMID: 37414561 PMCID: PMC10376940 DOI: 10.1523/jneurosci.2267-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 05/08/2023] [Accepted: 06/19/2023] [Indexed: 07/08/2023] Open
Abstract
The rod photoreceptor synapse is the first synapse of dim-light vision and one of the most complex in the mammalian CNS. The components of its unique structure, a presynaptic ribbon and a single synaptic invagination enclosing several postsynaptic processes, have been identified, but disagreements about their organization remain. Here, we have used EM tomography to generate high-resolution images of 3-D volumes of the rod synapse from the female domestic cat. We have resolved the synaptic ribbon as a single structure, with a single arciform density, indicating the presence of one long site of transmitter release. The organization of the postsynaptic processes, which has been difficult to resolve with past methods, appears as a tetrad arrangement of two horizontal cell and two rod bipolar cell processes. Retinal detachment severely disrupts this organization. After 7 d, EM tomography reveals withdrawal of rod bipolar dendrites from most spherules; fragmentation of synaptic ribbons, which lose their tight association with the presynaptic membrane; and loss of the highly branched telodendria of the horizontal cell axon terminals. After detachment, the hilus, the opening through which postsynaptic processes enter the invagination, enlarges, exposing the normally sequestered environment within the invagination to the extracellular space of the outer plexiform layer. Our use of EM tomography provides the most accurate description to date of the complex rod synapse and details changes it undergoes during outer segment degeneration. These changes would be expected to disrupt the flow of information in the rod pathway.SIGNIFICANCE STATEMENT Ribbon-type synapses transmit the first electrical signals of vision and hearing. Despite their crucial role in sensory physiology, the three-dimensional ultrastructure of these synapses, especially the complex organization of the rod photoreceptor synapse, is not well understood. We used EM tomography to obtain 3-D imaging at nanoscale resolution to help resolve the organization of rod synapses in normal and detached retinas. This approach has enabled us to show that in the normal retina a single ribbon and arciform density oppose a tetrad of postsynaptic processes. In addition, it enabled us to provide a 3-D perspective of the ultrastructural changes that occur in response to retinal detachment.
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Affiliation(s)
- Gil Torten
- Departments of Ophthalmology and Neurobiology, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095
| | - Steven K Fisher
- Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, California 93117
- Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California 93117
| | - Kenneth A Linberg
- Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, California 93117
| | - Gabriel Luna
- Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, California 93117
| | - Guy Perkins
- National Center for Microscopy and Imaging Research and Department of Neurosciences, University of California, San Diego, La Jolla, California 92093
| | - Mark H Ellisman
- National Center for Microscopy and Imaging Research and Department of Neurosciences, University of California, San Diego, La Jolla, California 92093
| | - David S Williams
- Departments of Ophthalmology and Neurobiology, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095
- Molecular Biology Institute, University of California, Los Angeles, Los Angeles, California 90095
- Brain Research Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095
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Hall JC, Paull D, Pébay A, Lidgerwood GE. Human pluripotent stem cells for the modelling of retinal pigment epithelium homeostasis and disease: A review. Clin Exp Ophthalmol 2022; 50:667-677. [PMID: 35739648 PMCID: PMC9546239 DOI: 10.1111/ceo.14128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Revised: 06/06/2022] [Accepted: 06/19/2022] [Indexed: 12/05/2022]
Abstract
Human pluripotent stem cells (hPSCs), which include induced pluripotent stem cells and embryonic stem cells, are powerful tools for studying human development, physiology and disease, including those affecting the retina. Cells from selected individuals, or specific genetic backgrounds, can be differentiated into distinct cell types allowing the modelling of diseases in a dish for therapeutic development. hPSC‐derived retinal cultures have already been used to successfully model retinal pigment epithelium (RPE) degeneration for various retinal diseases including monogenic conditions and complex disease such as age‐related macular degeneration. Here, we will review the current knowledge gained in understanding the molecular events involved in retinal disease using hPSC‐derived retinal models, in particular RPE models. We will provide examples of various conditions to illustrate the scope of applications associated with the use of hPSC‐derived RPE models.
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Affiliation(s)
- Jenna C Hall
- Department of Anatomy and Physiology The University of Melbourne Parkville Victoria Australia
| | - Daniel Paull
- The New York Stem Cell Foundation Research Institute New York New York USA
| | - Alice Pébay
- Department of Anatomy and Physiology The University of Melbourne Parkville Victoria Australia
- Department of Surgery, Royal Melbourne Hospital The University of Melbourne Parkville Victoria Australia
| | - Grace E. Lidgerwood
- Department of Anatomy and Physiology The University of Melbourne Parkville Victoria Australia
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Whole Genome Sequencing, Focused Assays and Functional Studies Increasing Understanding in Cryptic Inherited Retinal Dystrophies. Int J Mol Sci 2022; 23:ijms23073905. [PMID: 35409265 PMCID: PMC8999823 DOI: 10.3390/ijms23073905] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 03/24/2022] [Accepted: 03/30/2022] [Indexed: 12/15/2022] Open
Abstract
The inherited retinal dystrophies (IRDs) are a clinically and genetically complex group of disorders primarily affecting the rod and cone photoreceptors or other retinal neuronal layers, with emerging therapies heralding the need for accurate molecular diagnosis. Targeted capture and panel-based strategies examining the partial or full exome deliver molecular diagnoses in many IRD families tested. However, approximately one in three families remain unsolved and unable to obtain personalised recurrence risk or access to new clinical trials or therapy. In this study, we investigated whole genome sequencing (WGS), focused assays and functional studies to assist with unsolved IRD cases and facilitate integration of these approaches to a broad molecular diagnostic clinical service. The WGS approach identified variants not covered or underinvestigated by targeted capture panel-based clinical testing strategies in six families. This included structural variants, with notable benefit of the WGS approach in repetitive regions demonstrated by a family with a hybrid gene and hemizygous missense variant involving the opsin genes, OPN1LW and OPN1MW. There was also benefit in investigation of the repetitive GC-rich ORF15 region of RPGR. Further molecular investigations were facilitated by focused assays in these regions. Deep intronic variants were identified in IQCB1 and ABCA4, with functional RNA based studies of the IQCB1 variant revealing activation of a cryptic splice acceptor site. While targeted capture panel-based methods are successful in achieving an efficient molecular diagnosis in a proportion of cases, this study highlights the additional benefit and clinical value that may be derived from WGS, focused assays and functional genomics in the highly heterogeneous IRDs.
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Chahine Karam F, Loi TH, Ma A, Nash BM, Grigg JR, Parekh D, Riley LG, Farnsworth E, Bennetts B, Gonzalez-Cordero A, Jamieson RV. Human iPSC-Derived Retinal Organoids and Retinal Pigment Epithelium for Novel Intronic RPGR Variant Assessment for Therapy Suitability. J Pers Med 2022; 12:jpm12030502. [PMID: 35330501 PMCID: PMC8951517 DOI: 10.3390/jpm12030502] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 03/16/2022] [Accepted: 03/17/2022] [Indexed: 02/04/2023] Open
Abstract
The RPGR gene encodes Retinitis Pigmentosa GTPase Regulator, a known interactor with ciliary proteins, which is involved in maintaining healthy photoreceptor cells. Variants in RPGR are the main contributor to X-linked rod-cone dystrophy (RCD), and RPGR gene therapy approaches are in clinical trials. Hence, elucidation of the pathogenicity of novel RPGR variants is important for a patient therapy opportunity. Here, we describe a novel intronic RPGR variant, c.1415 − 9A>G, in a patient with RCD, which was classified as a variant of uncertain significance according to current clinical diagnostic criteria. The variant lay several base pairs intronic to the canonical splice acceptor site, raising suspicion of an RPGR RNA splicing abnormality and consequent protein dysfunction. To investigate disease causation in an appropriate disease model, induced pluripotent stem cells were generated from patient fibroblasts and differentiated to retinal pigment epithelium (iPSC-RPE) and retinal organoids (iPSC-RO). Abnormal RNA splicing of RPGR was demonstrated in patient fibroblasts, iPSC-RPE and iPSC-ROs, leading to a predicted frameshift and premature stop codon. Decreased RPGR expression was demonstrated in these cell types, with a striking loss of RPGR localization at the ciliary transitional zone, critically in the photoreceptor cilium of the patient iPSC-ROs. Mislocalisation of rhodopsin staining was present in the patient’s iPSC-RO rod photoreceptor cells, along with an abnormality of L/M opsin staining affecting cone photoreceptor cells and increased photoreceptor apoptosis. Additionally, patient iPSC-ROs displayed an increase in F-actin expression that was consistent with an abnormal actin regulation phenotype. Collectively, these studies indicate that the splicing abnormality caused by the c.1415 − 9A>G variant has an impact on RPGR function. This work has enabled the reclassification of this variant to pathogenic, allowing the consideration of patients with this variant having access to gene therapy clinical trials. In addition, we have identified biomarkers of disease suitable for the interrogation of other RPGR variants of uncertain significance.
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Affiliation(s)
- Fidelle Chahine Karam
- Eye Genetics Research Unit, Children’s Medical Research Institute, Sydney Children’s Hospitals Network, Save Sight Institute, University of Sydney, Westmead, Sydney 2145, Australia; (F.C.K.); (T.H.L.); (A.M.); (B.M.N.); (J.R.G.)
| | - To Ha Loi
- Eye Genetics Research Unit, Children’s Medical Research Institute, Sydney Children’s Hospitals Network, Save Sight Institute, University of Sydney, Westmead, Sydney 2145, Australia; (F.C.K.); (T.H.L.); (A.M.); (B.M.N.); (J.R.G.)
| | - Alan Ma
- Eye Genetics Research Unit, Children’s Medical Research Institute, Sydney Children’s Hospitals Network, Save Sight Institute, University of Sydney, Westmead, Sydney 2145, Australia; (F.C.K.); (T.H.L.); (A.M.); (B.M.N.); (J.R.G.)
- Department of Clinical Genetics, Western Sydney Genetics Program, Sydney Children’s Hospitals Network, Westmead, Sydney 2145, Australia
- Specialty of Genomic Medicine, Faculty of Medicine and Health, University of Sydney, Westmead, Sydney 2145, Australia; (E.F.); (B.B.)
| | - Benjamin M. Nash
- Eye Genetics Research Unit, Children’s Medical Research Institute, Sydney Children’s Hospitals Network, Save Sight Institute, University of Sydney, Westmead, Sydney 2145, Australia; (F.C.K.); (T.H.L.); (A.M.); (B.M.N.); (J.R.G.)
- Specialty of Genomic Medicine, Faculty of Medicine and Health, University of Sydney, Westmead, Sydney 2145, Australia; (E.F.); (B.B.)
- Sydney Genome Diagnostics, Western Sydney Genetics Program, Sydney Children’s Hospitals Network, Westmead, Sydney 2145, Australia
| | - John R. Grigg
- Eye Genetics Research Unit, Children’s Medical Research Institute, Sydney Children’s Hospitals Network, Save Sight Institute, University of Sydney, Westmead, Sydney 2145, Australia; (F.C.K.); (T.H.L.); (A.M.); (B.M.N.); (J.R.G.)
- Specialty of Ophthalmology, Faculty of Medicine and Health, University of Sydney, Sydney 2006, Australia
| | - Darshan Parekh
- Rare Diseases Functional Genomics Laboratory, Sydney Children’s Hospitals Network and Children’s Medical Research Institute, Westmead, Sydney 2145, Australia; (D.P.); (L.G.R.)
| | - Lisa G. Riley
- Rare Diseases Functional Genomics Laboratory, Sydney Children’s Hospitals Network and Children’s Medical Research Institute, Westmead, Sydney 2145, Australia; (D.P.); (L.G.R.)
- Specialty of Child and Adolescent Health, University of Sydney, Westmead, Sydney 2145, Australia
| | - Elizabeth Farnsworth
- Specialty of Genomic Medicine, Faculty of Medicine and Health, University of Sydney, Westmead, Sydney 2145, Australia; (E.F.); (B.B.)
- Sydney Genome Diagnostics, Western Sydney Genetics Program, Sydney Children’s Hospitals Network, Westmead, Sydney 2145, Australia
| | - Bruce Bennetts
- Specialty of Genomic Medicine, Faculty of Medicine and Health, University of Sydney, Westmead, Sydney 2145, Australia; (E.F.); (B.B.)
- Sydney Genome Diagnostics, Western Sydney Genetics Program, Sydney Children’s Hospitals Network, Westmead, Sydney 2145, Australia
| | - Anai Gonzalez-Cordero
- Stem Cell Medicine Group, Children’s Medical Research Institute, University of Sydney, Westmead, Sydney 2145, Australia;
- School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Sydney 2006, Australia
| | - Robyn V. Jamieson
- Eye Genetics Research Unit, Children’s Medical Research Institute, Sydney Children’s Hospitals Network, Save Sight Institute, University of Sydney, Westmead, Sydney 2145, Australia; (F.C.K.); (T.H.L.); (A.M.); (B.M.N.); (J.R.G.)
- Department of Clinical Genetics, Western Sydney Genetics Program, Sydney Children’s Hospitals Network, Westmead, Sydney 2145, Australia
- Specialty of Genomic Medicine, Faculty of Medicine and Health, University of Sydney, Westmead, Sydney 2145, Australia; (E.F.); (B.B.)
- Correspondence: ; Tel.: +61-2-9687-2800; Fax: +61-2-9687-2120
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