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Jellinger KA. Pathomechanisms of behavioral abnormalities in Huntington disease: an update. J Neural Transm (Vienna) 2024:10.1007/s00702-024-02794-y. [PMID: 38874766 DOI: 10.1007/s00702-024-02794-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2024] [Accepted: 06/05/2024] [Indexed: 06/15/2024]
Abstract
Huntington disease (HD), a devastating autosomal-dominant neurodegenerative disease caused by an expanded CAG trinucleotide repeat, is clinically characterized by a triad of symptoms including involuntary motions, behavior problems and cognitive deficits. Behavioral symptoms with anxiety, irritability, obsessive-compulsive behaviors, apathy and other neuropsychiatric symptoms, occurring in over 50% of HD patients are important features of this disease and contribute to impairment of quality of life, but their pathophysiology is poorly understood. Behavior problems, more frequent than depression, can be manifest before obvious motor symptoms and occur across all HD stages, usually correlated with duration of illness. While specific neuropathological data are missing, the relations between gene expression and behavior have been elucidated in transgenic models of HD. Disruption of interneuronal communications, with involvement of prefronto-striato-thalamic networks and hippocampal dysfunctions produce deficits in multiple behavioral domains. These changes that have been confirmed by multistructural neuroimaging studies are due to a causal cascade linking molecular pathologies (glutamate-mediated excitotoxicity, mitochondrial dysfunctions inducing multiple biochemical and structural alterations) and deficits in multiple behavioral domains. The disruption of large-scale connectivities may explain the variability of behavior profiles and is useful in understanding the biological backgrounds of functional decline in HD. Such findings offer new avenues for targeted treatments in terms of minimizing neurobehavioral impairment in HD.
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Affiliation(s)
- Kurt A Jellinger
- Institute of Clinical Neurobiology, Alberichgasse 5/13, Vienna, A-1150, Austria.
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2
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Masek M, Bachmann-Gagescu R. Control of protein and lipid composition of photoreceptor outer segments-Implications for retinal disease. Curr Top Dev Biol 2023; 155:165-225. [PMID: 38043951 DOI: 10.1016/bs.ctdb.2023.09.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2023]
Abstract
Vision is arguably our most important sense, and its loss brings substantial limitations to daily life for affected individuals. Light is perceived in retinal photoreceptors (PRs), which are highly specialized neurons subdivided into several compartments with distinct functions. The outer segments (OSs) of photoreceptors represent highly specialized primary ciliary compartments hosting the phototransduction cascade, which transforms incoming light into a neuronal signal. Retinal disease can result from various pathomechanisms originating in distinct subcompartments of the PR cell, or in the retinal pigment epithelium which supports the PRs. Dysfunction of primary cilia causes human disorders known as "ciliopathies", in which retinal disease is a common feature. This chapter focuses on PR OSs, discussing the mechanisms controlling their complex structure and composition. A sequence of tightly regulated sorting and trafficking events, both upstream of and within this ciliary compartment, ensures the establishment and maintenance of the adequate proteome and lipidome required for signaling in response to light. We discuss in particular our current understanding of the role of ciliopathy proteins involved in multi-protein complexes at the ciliary transition zone (CC2D2A) or BBSome (BBS1) and how their dysfunction causes retinal disease. While the loss of CC2D2A prevents the fusion of vesicles and delivery of the photopigment rhodopsin to the ciliary base, leading to early OS ultrastructural defects, BBS1 deficiency results in precocious accumulation of cholesterol in mutant OSs and decreased visual function preceding morphological changes. These distinct pathomechanisms underscore the central role of ciliary proteins involved in multiple processes controlling OS protein and lipid composition.
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Affiliation(s)
- Markus Masek
- Institute of Medical Genetics, University of Zurich, Zurich, Switzerland; Department of Molecular Life Sciences, University of Zurich, Zurich, Switzerland
| | - Ruxandra Bachmann-Gagescu
- Institute of Medical Genetics, University of Zurich, Zurich, Switzerland; Department of Molecular Life Sciences, University of Zurich, Zurich, Switzerland; University Research Priority Program AdaBD, University of Zurich, Zurich, Switzerland.
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3
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Sangermano R, Galdikaité-Braziené E, Bujakowska KM. Non-syndromic Retinal Degeneration Caused by Pathogenic Variants in Joubert Syndrome Genes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1415:173-182. [PMID: 37440031 DOI: 10.1007/978-3-031-27681-1_26] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/14/2023]
Abstract
Inherited retinal degenerations (IRDs) are a group of genetic disorders characterized by progressive dysfunction and loss of photoreceptors. IRDs are classified as non-syndromic or syndromic, depending on whether retinal degeneration manifests alone or in combination with other associated symptoms. Joubert syndrome (JBTS) is a genetically and clinically heterogeneous disorder affecting the central nervous system and other organs and tissues, including the neuroretina. To date, 39 genes have been associated with JBTS, a majority of which encode structural or functional components of the primary cilium, a specialized sensory organelle present in most post-mitotic cells, including photoreceptors. The use of whole exome and IRD panel next-generation sequencing in routine diagnostics of non-syndromic IRD cases led to the discovery of pathogenic variants in JBTS genes that cause photoreceptor loss without other syndromic features. Here, we recapitulate these findings, describing the JBTS gene defects leading to non-syndromic IRDs.
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Affiliation(s)
- Riccardo Sangermano
- Ocular Genomics Institute, Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
| | - Egle Galdikaité-Braziené
- Ocular Genomics Institute, Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
| | - Kinga M Bujakowska
- Ocular Genomics Institute, Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, Boston, MA, USA.
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4
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Travis AM, Pearring JN. Human Mutations in Arl3, a Small GTPase Involved in Lipidated Cargo Delivery to the Cilia, Cause Retinal Dystrophy. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1415:283-288. [PMID: 37440046 DOI: 10.1007/978-3-031-27681-1_41] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/14/2023]
Abstract
Photoreceptors are highly polarized sensory neurons. Precise localization of signaling molecules within the ciliary outer segment is critical for photoreceptor function and viability. The small GTPase Arl3 plays a particularly important role in photoreceptors as it regulates outer segment enrichment of lipidated proteins essential for the visual response: transducin-α, transducin-γ, PDEα, PDE β, and Grk1. Recently, mutations in Arl3 have been identified in human patients with nonsyndromic autosomal recessive and dominant inherited retinal degenerations as well as syndromic Joubert syndrome including retinal dystrophy.
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Affiliation(s)
- Amanda M Travis
- Department of Ophthalmology and Visual Science, University of Michigan, Ann Arbor, MI, USA
| | - Jillian N Pearring
- Department of Ophthalmology and Visual Science, University of Michigan, Ann Arbor, MI, USA.
- Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, MI, USA.
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5
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Travis AM, Manocha S, Willer JR, Wessler TS, Skiba NP, Pearring JN. Disrupting the ciliary gradient of active Arl3 affects rod photoreceptor nuclear migration. eLife 2023; 12:80533. [PMID: 36598133 PMCID: PMC9831603 DOI: 10.7554/elife.80533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Accepted: 01/03/2023] [Indexed: 01/05/2023] Open
Abstract
The small GTPase Arl3 is important for the enrichment of lipidated proteins to primary cilia, including the outer segment of photoreceptors. Human mutations in the small GTPase Arl3 cause both autosomal recessive and dominant inherited retinal dystrophies. We discovered that dominant mutations result in increased active G-protein-Arl3-D67V has constitutive activity and Arl3-Y90C is fast cycling-and their expression in mouse rods resulted in a displaced nuclear phenotype due to an aberrant Arl3-GTP gradient. Using multiple strategies, we go on to show that removing or restoring the Arl3-GTP gradient within the cilium is sufficient to rescue the nuclear migration defect. Together, our results reveal that an Arl3 ciliary gradient is involved in proper positioning of photoreceptor nuclei during retinal development.
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Affiliation(s)
- Amanda M Travis
- Department of Ophthalmology and Visual Science, University of Michigan-Ann ArborAnn ArborUnited States
| | - Samiya Manocha
- Department of Ophthalmology and Visual Science, University of Michigan-Ann ArborAnn ArborUnited States
| | - Jason R Willer
- Department of Ophthalmology and Visual Science, University of Michigan-Ann ArborAnn ArborUnited States
| | - Timothy S Wessler
- Department of Mathematics, University of North Carolina at Chapel HillChapel HillUnited States
| | - Nikolai P Skiba
- Department of Ophthalmology, Duke UniversityDurhamUnited States
| | - Jillian N Pearring
- Department of Ophthalmology and Visual Science, University of Michigan-Ann ArborAnn ArborUnited States,Department of Cell and Developmental Biology, University of Michigan–Ann ArborAnn ArborUnited States
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6
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Wang L, Sun L, Wan QH, Fang SG. Comparative Genomics Provides Insights into Adaptive Evolution in Tactile-Foraging Birds. Genes (Basel) 2022; 13:genes13040678. [PMID: 35456484 PMCID: PMC9028243 DOI: 10.3390/genes13040678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 04/07/2022] [Accepted: 04/11/2022] [Indexed: 11/28/2022] Open
Abstract
Tactile-foraging birds have evolved an enlarged principal sensory nucleus (PrV) but smaller brain regions related to the visual system, which reflects the difference in sensory dependence. The “trade-off” may exist between different senses in tactile foragers, as well as between corresponding sensory-processing areas in the brain. We explored the mechanism underlying the adaptive evolution of sensory systems in three tactile foragers (kiwi, mallard, and crested ibis). The results showed that olfaction-related genes in kiwi and mallard and hearing-related genes in crested ibis were expanded, indicating they may also have sensitive olfaction or hearing, respectively. However, some genes required for visual development were positively selected or had convergent amino acid substitutions in all three tactile branches, and it seems to show the possibility of visual degradation. In addition, we may provide a new visual-degradation candidate gene PDLIM1 who suffered dense convergent amino acid substitutions within the ZM domain. At last, two genes responsible for regulating the proliferation and differentiation of neuronal progenitor cells may play roles in determining the relative sizes of sensory areas in brain. This exploration offers insight into the relationship between specialized tactile-forging behavior and the evolution of sensory abilities and brain structures.
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Turn RE, Hu Y, Dewees SI, Devi N, East MP, Hardin KR, Khatib T, Linnert J, Wolfrum U, Lim MJ, Casanova JE, Caspary T, Kahn RA. The ARF GAPs ELMOD1 and ELMOD3 act at the Golgi and cilia to regulate ciliogenesis and ciliary protein traffic. Mol Biol Cell 2022; 33:ar13. [PMID: 34818063 PMCID: PMC9236152 DOI: 10.1091/mbc.e21-09-0443] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 11/16/2021] [Accepted: 11/19/2021] [Indexed: 11/11/2022] Open
Abstract
ELMODs are a family of three mammalian paralogues that display GTPase-activating protein (GAP) activity toward a uniquely broad array of ADP-ribosylation factor (ARF) family GTPases that includes ARF-like (ARL) proteins. ELMODs are ubiquitously expressed in mammalian tissues, highly conserved across eukaryotes, and ancient in origin, being present in the last eukaryotic common ancestor. We described functions of ELMOD2 in immortalized mouse embryonic fibroblasts (MEFs) in the regulation of cell division, microtubules, ciliogenesis, and mitochondrial fusion. Here, using similar strategies with the paralogues ELMOD1 and ELMOD3, we identify novel functions and locations of these cell regulators and compare them to those of ELMOD2, allowing the determination of functional redundancy among the family members. We found strong similarities in phenotypes resulting from deletion of either Elmod1 or Elmod3 and marked differences from those arising in Elmod2 deletion lines. Deletion of either Elmod1 or Elmod3 results in the decreased ability of cells to form primary cilia, loss of a subset of proteins from cilia, and accumulation of some ciliary proteins at the Golgi, predicted to result from compromised traffic from the Golgi to cilia. These phenotypes are reversed upon activating mutant expression of either ARL3 or ARL16, linking their roles to ELMOD1/3 actions.
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Affiliation(s)
- Rachel E. Turn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
- Biochemistry, Cell & Developmental Biology Graduate Program, Emory University, Atlanta, GA 30322
- Department of Microbiology and Immunology, Stanford University, Palo Alto, CA 94305
| | - Yihan Hu
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
- Department of Otolaryngology, Xiangya Hospital, Central South University, Changsha, 410008 Hunan, China
| | - Skylar I. Dewees
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
- Biochemistry, Cell & Developmental Biology Graduate Program, Emory University, Atlanta, GA 30322
| | - Narra Devi
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
| | - Michael P. East
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Katherine R. Hardin
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322
- Biochemistry, Cell & Developmental Biology Graduate Program, Emory University, Atlanta, GA 30322
| | - Tala Khatib
- Department of Hematology and Medical Oncology, Emory University School of Medicine, Atlanta, GA 30322
- Biochemistry, Cell & Developmental Biology Graduate Program, Emory University, Atlanta, GA 30322
| | - Joshua Linnert
- Institute of Molecular Physiology, Johannes Gutenberg University, Mainz 55128, Germany
| | - Uwe Wolfrum
- Institute of Molecular Physiology, Johannes Gutenberg University, Mainz 55128, Germany
| | - Michael J. Lim
- Department of Cell Biology, University of Virginia, Charlottesville, VA 22908
| | - James E. Casanova
- Department of Cell Biology, University of Virginia, Charlottesville, VA 22908
| | - Tamara Caspary
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322
| | - Richard A. Kahn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
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8
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Ratnapriya R, Jacobson SG, Cideciyan AV, English MA, Roman AJ, Sumaroka A, Sheplock R, Swaroop A. A Novel ARL3 Gene Mutation Associated With Autosomal Dominant Retinal Degeneration. Front Cell Dev Biol 2021; 9:720782. [PMID: 34485303 PMCID: PMC8416110 DOI: 10.3389/fcell.2021.720782] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2021] [Accepted: 07/07/2021] [Indexed: 12/18/2022] Open
Abstract
Despite major progress in the discovery of causative genes, many individuals and families with inherited retinal degenerations (IRDs) remain without a molecular diagnosis. We applied whole exome sequencing to identify the genetic cause in a family with an autosomal dominant IRD. Eye examinations were performed and affected patients were studied with electroretinography and kinetic and chromatic static perimetry. Sequence variants were analyzed in genes (n = 271) associated with IRDs listed on the RetNet database. We applied a stepwise filtering process involving the allele frequency in the control population, in silico prediction tools for pathogenicity, and evolutionary conservation to prioritize the potential causal variant(s). Sanger sequencing and segregation analysis were performed on the proband and other family members. The IRD in this family is expressed as a widespread progressive retinal degeneration with maculopathy. A novel heterozygous variant (c.200A > T) was identified in the ARL3 gene, leading to the substitution of aspartic acid to valine at position 67. The Asp67 residue is evolutionary conserved, and the change p.Asp67Val is predicted to be pathogenic. This variant was segregated in affected members of the family and was absent from an unaffected individual. Two previous reports of a de novo missense mutation in the ARL3 gene, each describing a family with two affected generations, are the only examples to date of autosomal dominant IRD associated with this photoreceptor gene. Our results, identifying a novel pathogenic variant in ARL3 in a four-generation family with a dominant IRD, augment the evidence that the ARL3 gene is another cause of non-syndromic retinal degeneration.
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Affiliation(s)
- Rinki Ratnapriya
- Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD, United States.,Department of Ophthalmology, Baylor College of Medicine, Houston, TX, United States
| | - Samuel G Jacobson
- Department of Ophthalmology, Perelman School of Medicine, Scheie Eye Institute, University of Pennsylvania, Philadelphia, PA, United States
| | - Artur V Cideciyan
- Department of Ophthalmology, Perelman School of Medicine, Scheie Eye Institute, University of Pennsylvania, Philadelphia, PA, United States
| | - Milton A English
- Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
| | - Alejandro J Roman
- Department of Ophthalmology, Perelman School of Medicine, Scheie Eye Institute, University of Pennsylvania, Philadelphia, PA, United States
| | - Alexander Sumaroka
- Department of Ophthalmology, Perelman School of Medicine, Scheie Eye Institute, University of Pennsylvania, Philadelphia, PA, United States
| | - Rebecca Sheplock
- Department of Ophthalmology, Perelman School of Medicine, Scheie Eye Institute, University of Pennsylvania, Philadelphia, PA, United States
| | - Anand Swaroop
- Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
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9
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Functional compartmentalization of photoreceptor neurons. Pflugers Arch 2021; 473:1493-1516. [PMID: 33880652 DOI: 10.1007/s00424-021-02558-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 03/15/2021] [Accepted: 03/22/2021] [Indexed: 12/16/2022]
Abstract
Retinal photoreceptors are neurons that convert dynamically changing patterns of light into electrical signals that are processed by retinal interneurons and ultimately transmitted to vision centers in the brain. They represent the essential first step in seeing without which the remainder of the visual system is rendered moot. To support this role, the major functions of photoreceptors are segregated into three main specialized compartments-the outer segment, the inner segment, and the pre-synaptic terminal. This compartmentalization is crucial for photoreceptor function-disruption leads to devastating blinding diseases for which therapies remain elusive. In this review, we examine the current understanding of the molecular and physical mechanisms underlying photoreceptor functional compartmentalization and highlight areas where significant knowledge gaps remain.
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10
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Turn RE, Linnert J, Gigante ED, Wolfrum U, Caspary T, Kahn RA. Roles for ELMOD2 and Rootletin in ciliogenesis. Mol Biol Cell 2021; 32:800-822. [PMID: 33596093 PMCID: PMC8108518 DOI: 10.1091/mbc.e20-10-0635] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
ELMOD2 is a GTPase-activating protein with uniquely broad specificity for ARF family GTPases. We previously showed that it acts with ARL2 in mitochondrial fusion and microtubule stability and with ARF6 during cytokinesis. Mouse embryonic fibroblasts deleted for ELMOD2 also displayed changes in cilia-related processes including increased ciliation, multiciliation, ciliary morphology, ciliary signaling, centrin accumulation inside cilia, and loss of rootlets at centrosomes with loss of centrosome cohesion. Increasing ARL2 activity or overexpressing Rootletin reversed these defects, revealing close functional links between the three proteins. This was further supported by the findings that deletion of Rootletin yielded similar phenotypes, which were rescued upon increasing ARL2 activity but not ELMOD2 overexpression. Thus, we propose that ARL2, ELMOD2, and Rootletin all act in a common pathway that suppresses spurious ciliation and maintains centrosome cohesion. Screening a number of markers of steps in the ciliation pathway supports a model in which ELMOD2, Rootletin, and ARL2 act downstream of TTBK2 and upstream of CP110 to prevent spurious release of CP110 and to regulate ciliary vesicle docking. These data thus provide evidence supporting roles for ELMOD2, Rootletin, and ARL2 in the regulation of ciliary licensing.
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Affiliation(s)
- Rachel E Turn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.,Biochemistry, Cell & Developmental Biology Graduate Program, Emory University, Atlanta, GA 30322
| | - Joshua Linnert
- Institut für Molekulare Physiologie, Johannes Gutenberg-Universität, Mainz 655099, Germany
| | - Eduardo D Gigante
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322.,Neuroscience Graduate Program, Emory University, Atlanta, GA 30322
| | - Uwe Wolfrum
- Institut für Molekulare Physiologie, Johannes Gutenberg-Universität, Mainz 655099, Germany
| | - Tamara Caspary
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322
| | - Richard A Kahn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322
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11
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Barnes CL, Malhotra H, Calvert PD. Compartmentalization of Photoreceptor Sensory Cilia. Front Cell Dev Biol 2021; 9:636737. [PMID: 33614665 PMCID: PMC7889997 DOI: 10.3389/fcell.2021.636737] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Accepted: 01/07/2021] [Indexed: 12/12/2022] Open
Abstract
Functional compartmentalization of cells is a universal strategy for segregating processes that require specific components, undergo regulation by modulating concentrations of those components, or that would be detrimental to other processes. Primary cilia are hair-like organelles that project from the apical plasma membranes of epithelial cells where they serve as exclusive compartments for sensing physical and chemical signals in the environment. As such, molecules involved in signal transduction are enriched within cilia and regulating their ciliary concentrations allows adaptation to the environmental stimuli. The highly efficient organization of primary cilia has been co-opted by major sensory neurons, olfactory cells and the photoreceptor neurons that underlie vision. The mechanisms underlying compartmentalization of cilia are an area of intense current research. Recent findings have revealed similarities and differences in molecular mechanisms of ciliary protein enrichment and its regulation among primary cilia and sensory cilia. Here we discuss the physiological demands on photoreceptors that have driven their evolution into neurons that rely on a highly specialized cilium for signaling changes in light intensity. We explore what is known and what is not known about how that specialization appears to have driven unique mechanisms for photoreceptor protein and membrane compartmentalization.
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Affiliation(s)
| | | | - Peter D. Calvert
- Department of Ophthalmology and Visual Sciences, Center for Vision Research, SUNY Upstate Medical University, Syracuse, NY, United States
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12
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Sundar J, Matalkah F, Jeong B, Stoilov P, Ramamurthy V. The Musashi proteins MSI1 and MSI2 are required for photoreceptor morphogenesis and vision in mice. J Biol Chem 2021; 296:100048. [PMID: 33168629 PMCID: PMC7948980 DOI: 10.1074/jbc.ra120.015714] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Revised: 10/30/2020] [Accepted: 11/09/2020] [Indexed: 12/11/2022] Open
Abstract
The Musashi family of RNA-binding proteins is known for its role in stem-cell renewal and is a negative regulator of cell differentiation. Interestingly, in the retina, the Musashi proteins MSI1 and MSI2 are differentially expressed throughout the cycle of retinal development, with MSI2 protein displaying robust expression in the adult retinal tissue. In this study, we investigated the importance of Musashi proteins in the development and function of photoreceptor neurons in the retina. We generated a pan-retinal and rod photoreceptor neuron-specific conditional KO mouse lacking MSI1 and MSI2. Independent of the sex, photoreceptor neurons with simultaneous deletion of Msi1 and Msi2 were unable to respond to light and displayed severely disrupted photoreceptor outer segment morphology and ciliary defects. Mice lacking MSI1 and MSI2 in the retina exhibited neuronal degeneration, with complete loss of photoreceptors within 6 months. In concordance with our earlier studies that proposed a role for Musashi proteins in regulating alternative splicing, the loss of MSI1 and MSI2 prevented the use of photoreceptor-specific exons in transcripts critical for outer segment morphogenesis, ciliogenesis, and synaptic transmission. Overall, we demonstrate a critical role for Musashi proteins in the morphogenesis of terminally differentiated photoreceptor neurons. This role is in stark contrast with the canonical function of these two proteins in the maintenance and renewal of stem cells.
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Affiliation(s)
- Jesse Sundar
- Department of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA
| | - Fatimah Matalkah
- Department of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA
| | - Bohye Jeong
- Department of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA
| | - Peter Stoilov
- Department of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA.
| | - Visvanathan Ramamurthy
- Department of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA; Department of Ophthalmology and Visual Sciences, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA; Department of Neuroscience, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA.
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13
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Collin GB, Gogna N, Chang B, Damkham N, Pinkney J, Hyde LF, Stone L, Naggert JK, Nishina PM, Krebs MP. Mouse Models of Inherited Retinal Degeneration with Photoreceptor Cell Loss. Cells 2020; 9:cells9040931. [PMID: 32290105 PMCID: PMC7227028 DOI: 10.3390/cells9040931] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Revised: 04/05/2020] [Accepted: 04/07/2020] [Indexed: 12/12/2022] Open
Abstract
Inherited retinal degeneration (RD) leads to the impairment or loss of vision in millions of individuals worldwide, most frequently due to the loss of photoreceptor (PR) cells. Animal models, particularly the laboratory mouse, have been used to understand the pathogenic mechanisms that underlie PR cell loss and to explore therapies that may prevent, delay, or reverse RD. Here, we reviewed entries in the Mouse Genome Informatics and PubMed databases to compile a comprehensive list of monogenic mouse models in which PR cell loss is demonstrated. The progression of PR cell loss with postnatal age was documented in mutant alleles of genes grouped by biological function. As anticipated, a wide range in the onset and rate of cell loss was observed among the reported models. The analysis underscored relationships between RD genes and ciliary function, transcription-coupled DNA damage repair, and cellular chloride homeostasis. Comparing the mouse gene list to human RD genes identified in the RetNet database revealed that mouse models are available for 40% of the known human diseases, suggesting opportunities for future research. This work may provide insight into the molecular players and pathways through which PR degenerative disease occurs and may be useful for planning translational studies.
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Affiliation(s)
- Gayle B. Collin
- The Jackson Laboratory, Bar Harbor, Maine, ME 04609, USA; (G.B.C.); (N.G.); (B.C.); (N.D.); (J.P.); (L.F.H.); (L.S.); (J.K.N.)
| | - Navdeep Gogna
- The Jackson Laboratory, Bar Harbor, Maine, ME 04609, USA; (G.B.C.); (N.G.); (B.C.); (N.D.); (J.P.); (L.F.H.); (L.S.); (J.K.N.)
| | - Bo Chang
- The Jackson Laboratory, Bar Harbor, Maine, ME 04609, USA; (G.B.C.); (N.G.); (B.C.); (N.D.); (J.P.); (L.F.H.); (L.S.); (J.K.N.)
| | - Nattaya Damkham
- The Jackson Laboratory, Bar Harbor, Maine, ME 04609, USA; (G.B.C.); (N.G.); (B.C.); (N.D.); (J.P.); (L.F.H.); (L.S.); (J.K.N.)
- Department of Immunology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
- Siriraj Center of Excellence for Stem Cell Research, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
| | - Jai Pinkney
- The Jackson Laboratory, Bar Harbor, Maine, ME 04609, USA; (G.B.C.); (N.G.); (B.C.); (N.D.); (J.P.); (L.F.H.); (L.S.); (J.K.N.)
| | - Lillian F. Hyde
- The Jackson Laboratory, Bar Harbor, Maine, ME 04609, USA; (G.B.C.); (N.G.); (B.C.); (N.D.); (J.P.); (L.F.H.); (L.S.); (J.K.N.)
| | - Lisa Stone
- The Jackson Laboratory, Bar Harbor, Maine, ME 04609, USA; (G.B.C.); (N.G.); (B.C.); (N.D.); (J.P.); (L.F.H.); (L.S.); (J.K.N.)
| | - Jürgen K. Naggert
- The Jackson Laboratory, Bar Harbor, Maine, ME 04609, USA; (G.B.C.); (N.G.); (B.C.); (N.D.); (J.P.); (L.F.H.); (L.S.); (J.K.N.)
| | - Patsy M. Nishina
- The Jackson Laboratory, Bar Harbor, Maine, ME 04609, USA; (G.B.C.); (N.G.); (B.C.); (N.D.); (J.P.); (L.F.H.); (L.S.); (J.K.N.)
- Correspondence: (P.M.N.); (M.P.K.); Tel.: +1-207-2886-383 (P.M.N.); +1-207-2886-000 (M.P.K.)
| | - Mark P. Krebs
- The Jackson Laboratory, Bar Harbor, Maine, ME 04609, USA; (G.B.C.); (N.G.); (B.C.); (N.D.); (J.P.); (L.F.H.); (L.S.); (J.K.N.)
- Correspondence: (P.M.N.); (M.P.K.); Tel.: +1-207-2886-383 (P.M.N.); +1-207-2886-000 (M.P.K.)
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14
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Yang D, Yao Q, Li Y, Xu Y, Wang J, Zhao H, Liu F, Zhang Z, Liu Y, Bie X, Wang Y, Xu L, Luan Y, Yang S, Yang G, He Y. A c.544_618del75bp mutation in the splicing factor gene PRPF31 is involved in non-syndromic retinitis pigmentosa by reducing the level of mRNA expression. Ophthalmic Physiol Opt 2020; 40:289-299. [PMID: 32031697 DOI: 10.1111/opo.12672] [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] [Received: 09/28/2019] [Accepted: 01/02/2020] [Indexed: 01/08/2023]
Abstract
PURPOSE A previous study reported a novel c.544_618del75bp mutation in exon 7 of the PRPF31 gene in a Chinese family with autosomal dominant retinal pigmentosa (ADRP). However, the selected pedigree was a small part of the whole family and the function of the c.544_618del75bp mutation was not explored deeply. The aim of the present study was to validate the previous results and explore the functional significance of the c.544_618del75bp mutation. METHODS We extended the size of the ADRP pedigree and sequenced DNA and cDNA of the PRPF31 gene for all members of the family and 100 healthy controls. Real-time quantitative polymerase chain reaction (PCR) analysis was performed on the cDNA of patients in the family and cell culture, plasmids transfection and western blot analysis were done to evaluate the functional effect of the mutation in vitro. RESULTS Sanger sequencing showed that the mutation was present in all patients and absent in all normal individuals, except for participant III-9. Bioinformatics analysis revealed that the c.544_618del75bp mutation caused a 25 amino acid deletion in the PRPF31 protein. In addition, the mRNA expression assay revealed that the mRNA expression level of the PRPF31 and RP9 genes were significantly lower in RP patients than controls (p < 0.05). Finally, the in vitro transfection assay demonstrated that the mRNA expression level of the mutant transfection group was significantly lower than the wild-type transfection group (p < 0.05). CONCLUSIONS Our study suggested that the c.544_618del75bp mutation in the PRPF31 gene was a causative mutation in this ADRP family and affected the expression of RP9 gene by influencing the formation of U4/U6-U5 tri-snRNP, eventually leading to the occurrence of RP.
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Affiliation(s)
- Dongzhi Yang
- School of Life Sciences, Zhengzhou University, Zhengzhou, China
| | - Qihui Yao
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Ya Li
- Henan Eye Institute, Henan Provincial People's Hospital, Zhengzhou, China
| | - Yan Xu
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Jun Wang
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Huiling Zhao
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Fuyong Liu
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Zhaojing Zhang
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Yang Liu
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Xiaoshuai Bie
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Yuanli Wang
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Liyan Xu
- Henan Eye Institute, Henan Provincial People's Hospital, Zhengzhou, China
| | - Yingying Luan
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Shangdong Yang
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
| | - Ge Yang
- Department of Ophthalmology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Ying He
- Department of Medical Genetics & Cell Biology, School of Basic Medical Sciences, Zhengzhou University, Zhengzhou, China
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15
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Sundar JC, Munezero D, Bryan-Haring C, Saravanan T, Jacques A, Ramamurthy V. Rhodopsin signaling mediates light-induced photoreceptor cell death in rd10 mice through a transducin-independent mechanism. Hum Mol Genet 2020; 29:394-406. [PMID: 31925423 PMCID: PMC7015845 DOI: 10.1093/hmg/ddz299] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Revised: 11/22/2019] [Accepted: 12/02/2019] [Indexed: 01/08/2023] Open
Abstract
Retinitis pigmentosa (RP) is a debilitating blinding disease affecting over 1.5 million people worldwide, but the mechanisms underlying this disease are not well understood. One of the common models used to study RP is the retinal degeneration-10 (rd10) mouse, which has a mutation in Phosphodiesterase-6b (Pde6b) that causes a phenotype mimicking the human disease. In rd10 mice, photoreceptor cell death occurs with exposure to normal light conditions, but as demonstrated in this study, rearing these mice in dark preserves their retinal function. We found that inactivating rhodopsin signaling protected photoreceptors from degeneration suggesting that the pathway activated by this G-protein-coupled receptor is causing light-induced photoreceptor cell death in rd10 mice. However, inhibition of transducin signaling did not prevent the loss of photoreceptors in rd10 mice reared under normal light conditions implying that the degeneration caused by rhodopsin signaling is not mediated through its canonical G-protein transducin. Inexplicably, loss of transducin in rd10 mice also led to photoreceptor cell death in darkness. Furthermore, we found that the rd10 mutation in Pde6b led to a reduction in the assembled PDE6αβγ2 complex, which was corroborated by our data showing mislocalization of the γ subunit. Based on our findings and previous studies, we propose a model where light activates a non-canonical pathway mediated by rhodopsin but independent of transducin that sensitizes cyclic nucleotide gated channels to cGMP and causes photoreceptor cell death. These results generate exciting possibilities for treatment of RP patients without affecting their vision or the canonical phototransduction cascade.
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Affiliation(s)
- Jesse C Sundar
- Departments of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26505, USA
| | - Daniella Munezero
- Departments of Ophthalmology and Visual Sciences, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26505, USA
| | - Caitlyn Bryan-Haring
- Departments of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26505, USA
| | - Thamaraiselvi Saravanan
- Departments of Ophthalmology and Visual Sciences, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26505, USA
| | - Angelica Jacques
- Departments of Ophthalmology and Visual Sciences, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26505, USA
| | - Visvanathan Ramamurthy
- Departments of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26505, USA
- Departments of Ophthalmology and Visual Sciences, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26505, USA
- Departments of Neuroscience, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26505, USA
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16
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Sheikh SA, Sisk RA, Schiavon CR, Waryah YM, Usmani MA, Steel DH, Sayer JA, Narsani AK, Hufnagel RB, Riazuddin S, Kahn RA, Waryah AM, Ahmed ZM. Homozygous Variant in ARL3 Causes Autosomal Recessive Cone Rod Dystrophy. Invest Ophthalmol Vis Sci 2020; 60:4811-4819. [PMID: 31743939 PMCID: PMC6944245 DOI: 10.1167/iovs.19-27263] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Purpose Cone rod dystrophy (CRD) is a group of inherited retinopathies characterized by the loss of cone and rod photoreceptor cells, which results in poor vision. This study aims to clinically and genetically characterize the segregating CRD phenotype in two large, consanguineous Pakistani families. Methods Funduscopy, optical coherence tomography (OCT), electroretinography (ERG), color vision, and visual acuity assessments were performed to evaluate the retinal structure and function of the affected individuals. Exome sequencing was performed to identify the genetic cause of CRD. Furthermore, the mutation's effect was evaluated using purified, bacterially expressed ADP-ribosylation factor-like protein 3 (ARL3) and mammalian cells. Results Fundus photography and OCT imaging demonstrated features that were consistent with CRD, including bull's eye macular lesions, macular atrophy, and central photoreceptor thinning. ERG analysis demonstrated moderate to severe reduction primarily of photopic responses in all affected individuals, and scotopic responses show reduction in two affected individuals. The exome sequencing revealed a novel homozygous variant (c.296G>T) in ARL3, which is predicted to substitute an evolutionarily conserved arginine with isoleucine within the encoded protein GTP-binding domain (R99I). The functional studies on the bacterial and heterologous mammalian cells revealed that the arginine at position 99 is essential for the stability of ARL3. Conclusions Our study uncovers an additional CRD gene and assigns the CRD phenotype to a variant of ARL3. The results imply that cargo transportation in photoreceptors as mediated by the ARL3 pathway is essential for cone and rod cell survival and vision in humans.
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Affiliation(s)
- Shakeel A Sheikh
- Department of Otorhinolaryngology-Head and Neck Surgery, School of Medicine University of Maryland, Baltimore, Maryland, United States.,Molecular Biology & Genetics Department, Liaquat University of Medical & Health Sciences, Jamshoro, Pakistan
| | - Robert A Sisk
- Abrahamson Pediatric Eye Institute, Cincinnati Children's Hospital, Cincinnati, Ohio, United States.,Cincinnati Eye Institute, Cincinnati, Ohio, United States
| | - Cara R Schiavon
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia, United States
| | - Yar M Waryah
- Molecular Biology & Genetics Department, Liaquat University of Medical & Health Sciences, Jamshoro, Pakistan
| | - Muhammad A Usmani
- Department of Otorhinolaryngology-Head and Neck Surgery, School of Medicine University of Maryland, Baltimore, Maryland, United States
| | - David H Steel
- Institute of Genetic Medicine, Newcastle University, International Centre for Life, Newcastle upon Tyne, United Kingdom
| | - John A Sayer
- Institute of Genetic Medicine, Newcastle University, International Centre for Life, Newcastle upon Tyne, United Kingdom
| | - Ashok K Narsani
- Institute of Ophthalmology, Liaquat University of Medical & Health Sciences, Jamshoro, Pakistan
| | - Robert B Hufnagel
- National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Saima Riazuddin
- Department of Otorhinolaryngology-Head and Neck Surgery, School of Medicine University of Maryland, Baltimore, Maryland, United States
| | - Richard A Kahn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia, United States
| | - Ali M Waryah
- Molecular Biology & Genetics Department, Liaquat University of Medical & Health Sciences, Jamshoro, Pakistan
| | - Zubair M Ahmed
- Department of Otorhinolaryngology-Head and Neck Surgery, School of Medicine University of Maryland, Baltimore, Maryland, United States
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17
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AY O, OI O, FO Y, AM A, IO A, OJ O. Oral Monosodium Glutamate Differentially Affects Open-Field Behaviours, Behavioural Despair and Place Preference in Male and Female Mice. ACTA ACUST UNITED AC 2019. [DOI: 10.2174/2211556008666181213160527] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Background:
Monosodium glutamate (MSG) is a flavour enhancer which induces
behavioural changes in animals. However the influence of sex on the behavioural response
to MSG has not been investigated.
Objective:
The sex-differential effects of MSG on open-field behaviours, anxiety-related
behaviour, behavioural despair, place-preference, and plasma/brain glutamate levels in
adult mice were assessed.
Methods:
Mice were assigned to three groups (1-3), based on the models used to assess
behaviours. Animals in group 1 were for the elevated-plus maze and tail-suspension paradigms,
group 2 for the open-field and forced-swim paradigms, while mice in group 3 were
for observation in the conditioned place preference paradigm. Mice in all groups were further
assigned into five subgroups (10 males and 10 females), and administered vehicle (distilled
water at 10 ml/kg) or one of four doses of MSG (20, 40, 80 and 160 mg/kg) daily for
6 weeks, following which they were exposed to the behavioural paradigms. At the end of
the behavioural tests, the animals were sacrificed, and blood was taken for estimation of
glutamate levels. The brains were also homogenised for estimation of glutamate levels.
Results:
MSG was associated with a reduction in locomotion in males and females (except
at 160 mg/kg, male), an anxiolytic response in females, an anxiogenic response in males,
and decreased behavioural despair in both sexes (females more responsive). Postconditioning
MSG-associated place-preference was significantly higher in females. Plasma/
brain glutamate was not significantly different between sexes.
Conclusion:
Repeated MSG administration alters a range of behaviours in a sex-dependent
manner in mice.
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Affiliation(s)
- Onaolapo AY
- Behavioural Neuroscience/Neurobiology Unit, Department of Anatomy, Ladoke Akintola University of Technology, Ogbomosho, Oyo State, Nigeria
| | - Olawore OI
- Behavioural Neuroscience/Neurobiology Unit, Department of Anatomy, Ladoke Akintola University of Technology, Ogbomosho, Oyo State, Nigeria
| | - Yusuf FO
- Behavioural Neuroscience/Neurobiology Unit, Department of Anatomy, Ladoke Akintola University of Technology, Ogbomosho, Oyo State, Nigeria
| | - Adeyemo AM
- Behavioural Neuroscience/Neurobiology Unit, Department of Anatomy, Ladoke Akintola University of Technology, Ogbomosho, Oyo State, Nigeria
| | - Adewole IO
- Behavioural Neuroscience/Neuropharmacology Unit, Department of Pharmacology, Ladoke Akintola University of Technology, Osogbo, Osun State, Nigeria
| | - Onaolapo OJ
- Behavioural Neuroscience/Neuropharmacology Unit, Department of Pharmacology, Ladoke Akintola University of Technology, Osogbo, Osun State, Nigeria
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18
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Maza NA, Schiesser WE, Calvert PD. An intrinsic compartmentalization code for peripheral membrane proteins in photoreceptor neurons. J Cell Biol 2019; 218:3753-3772. [PMID: 31594805 PMCID: PMC6829649 DOI: 10.1083/jcb.201906024] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 08/01/2019] [Accepted: 08/29/2019] [Indexed: 12/22/2022] Open
Abstract
In neurons, peripheral membrane proteins are enriched in subcellular compartments, where they play key roles, including transducing and transmitting information. However, little is known about the mechanisms underlying their compartmentalization. To explore the roles of hydrophobic and electrostatic interactions, we engineered probes consisting of lipidation motifs attached to fluorescent proteins by variously charged linkers and expressed them in Xenopus rod photoreceptors. Quantitative live cell imaging showed dramatic differences in distributions and dynamics of the probes, including presynapse and ciliary OS enrichment, depending on lipid moiety and protein surface charge. Opposing extant models of ciliary enrichment, most probes were weakly membrane bound and diffused through the connecting cilium without lipid binding chaperone protein interactions. A diffusion-binding-transport model showed that ciliary enrichment of a rhodopsin kinase probe occurs via recycling as it perpetually leaks out of the ciliary OS. The model accounts for weak membrane binding of peripheral membrane proteins and a leaky connecting cilium diffusion barrier.
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Affiliation(s)
- Nycole A Maza
- Center for Vision Research, Department of Ophthalmology and Visual Sciences, State University of New York Upstate Medical University, Syracuse, NY.,Department of Neuroscience and Physiology, State University of New York Upstate Medical University, Syracuse, NY
| | - William E Schiesser
- Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, PA
| | - Peter D Calvert
- Center for Vision Research, Department of Ophthalmology and Visual Sciences, State University of New York Upstate Medical University, Syracuse, NY .,Department of Neuroscience and Physiology, State University of New York Upstate Medical University, Syracuse, NY
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19
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Blond F, Léveillard T. Functional Genomics of the Retina to Elucidate its Construction and Deconstruction. Int J Mol Sci 2019; 20:E4922. [PMID: 31590277 PMCID: PMC6801968 DOI: 10.3390/ijms20194922] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Accepted: 10/01/2019] [Indexed: 12/20/2022] Open
Abstract
The retina is the light sensitive part of the eye and nervous tissue that have been used extensively to characterize the function of the central nervous system. The retina has a central position both in fundamental biology and in the physiopathology of neurodegenerative diseases. We address the contribution of functional genomics to the understanding of retinal biology by reviewing key events in their historical perspective as an introduction to major findings that were obtained through the study of the retina using genomics, transcriptomics and proteomics. We illustrate our purpose by showing that most of the genes of interest for retinal development and those involved in inherited retinal degenerations have a restricted expression to the retina and most particularly to photoreceptors cells. We show that the exponential growth of data generated by functional genomics is a future challenge not only in terms of storage but also in terms of accessibility to the scientific community of retinal biologists in the future. Finally, we emphasize on novel perspectives that emerge from the development of redox-proteomics, the new frontier in retinal biology.
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Affiliation(s)
- Frédéric Blond
- Department of Genetics, Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012 Paris, France.
| | - Thierry Léveillard
- Department of Genetics, Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012 Paris, France.
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20
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Bhattarai SR, Begum S, Popow R, Ezratty EJ. The ciliary GTPase Arl3 maintains tissue architecture by directing planar spindle orientation during epidermal morphogenesis. Development 2019; 146:dev.161885. [PMID: 30952667 DOI: 10.1242/dev.161885] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Accepted: 03/08/2019] [Indexed: 12/17/2022]
Abstract
Arl/ARF GTPases regulate ciliary trafficking, but their tissue-specific functions are unclear. Here, we demonstrate that ciliary GTPase Arl3 is required for mitotic spindle orientation of mouse basal stem cells during skin development. Arl3 loss diminished cell divisions within the plane of the epithelium, leading to increased perpendicular divisions, expansion of progenitor cells and loss of epithelial integrity. These observations suggest that an Arl3-dependent mechanism maintains cell division polarity along the tissue axis, and disruption of planar spindle orientation has detrimental consequences for epidermal architecture. Defects in planar cell polarity (PCP) can disrupt spindle positioning during tissue morphogenesis. Upon Arl3 loss, the PCP signaling molecules Celsr1 and Vangl2 failed to maintain planar polarized distributions, resulting in defective hair follicle angling, a hallmark of disrupted PCP. In the absence of Celsr1 polarity, frizzled 6 lost its asymmetrical distribution and abnormally segregated to the apical cortex of basal cells. We propose that Arl3 regulates polarized endosomal trafficking of PCP components to compartmentalized membrane domains. Cell-cell communication via ciliary GTPase signaling directs mitotic spindle orientation and PCP signaling, processes that are crucial for the maintenance of epithelial architecture.
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Affiliation(s)
- Samip R Bhattarai
- Department of Pathology and Cell Biology, Columbia University Medical Center, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
| | - Salma Begum
- Department of Pathology and Cell Biology, Columbia University Medical Center, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
| | - Rachel Popow
- Department of Pathology and Cell Biology, Columbia University Medical Center, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
| | - Ellen J Ezratty
- Department of Pathology and Cell Biology, Columbia University Medical Center, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
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21
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Dilan TL, Moye AR, Salido EM, Saravanan T, Kolandaivelu S, Goldberg AFX, Ramamurthy V. ARL13B, a Joubert Syndrome-Associated Protein, Is Critical for Retinogenesis and Elaboration of Mouse Photoreceptor Outer Segments. J Neurosci 2019; 39:1347-1364. [PMID: 30573647 PMCID: PMC6381253 DOI: 10.1523/jneurosci.1761-18.2018] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2018] [Revised: 11/16/2018] [Accepted: 12/12/2018] [Indexed: 11/21/2022] Open
Abstract
Mutations in the Joubert syndrome-associated small GTPase ARL13B are linked to photoreceptor impairment and vision loss. To determine the role of ARL13B in the development, function, and maintenance of ciliated photoreceptors, we generated a pan-retina knock-out (Six3-Cre) and a rod photoreceptor-specific inducible conditional knock-out (Pde6g-CreERT2) of ARL13B using murine models. Embryonic deletion of ARL13B led to defects in retinal development with reduced cell proliferation. In the absence of ARL13B, photoreceptors failed to develop outer segment (OS) membranous discs and axonemes, resulting in loss of function and rapid degeneration. Additionally, the majority of photoreceptor basal bodies did not dock properly at the apical edge of the inner segments. The removal of ARL13B in adult rod photoreceptor cells after maturation of OS resulted in loss of photoresponse and vesiculation in the OS. Before changes in photoresponse, removal of ARL13B led to mislocalization of rhodopsin, prenylated phosphodiesterase-6 (PDE6), and intraflagellar transport protein-88 (IFT88). Our findings show that ARL13B is required at multiple stages of retinogenesis, including early postnatal proliferation of retinal progenitor cells, development of photoreceptor cilia, and morphogenesis of photoreceptor OS discs regardless of sex. Last, our results establish a need for ARL13B in photoreceptor maintenance and protein trafficking.SIGNIFICANCE STATEMENT The normal development of photoreceptor cilia is essential to create functional, organized outer segments with stacked membrane discs that house the phototransduction proteins necessary for sight. Our study identifies a complex role for ARL13B, a small GTPase linked to Joubert syndrome and visual impairment, at various stages of photoreceptor development. Loss of ARL13B led to defects in retinal proliferation, altered placement of basal bodies crucial for components of the cilium (transition zone) to emanate, and absence of photoreceptor-stacked discs. These defects led to extinguished visual response and dysregulated protein trafficking. Our findings show the complex role ARL13B plays in photoreceptor development, viability, and function. Our study accounts for the severe retinal impairment observed in ARL13B-linked Joubert syndrome patients.
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Affiliation(s)
- Tanya L Dilan
- Department of Ophthalmology and Neuroscience
- Department of Biochemistry
| | - Abigail R Moye
- Department of Ophthalmology and Neuroscience
- Department of Biochemistry
| | | | | | | | | | - Visvanathan Ramamurthy
- Department of Ophthalmology and Neuroscience,
- Department of Biochemistry
- WVU Rockefeller Neuroscience Institute, West Virginia University, Morgantown, West Virginia 26506, and
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22
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Essa MM, Moghadas M, Ba-Omar T, Walid Qoronfleh M, Guillemin GJ, Manivasagam T, Justin-Thenmozhi A, Ray B, Bhat A, Chidambaram SB, Fernandes AJ, Song BJ, Akbar M. Protective Effects of Antioxidants in Huntington’s Disease: an Extensive Review. Neurotox Res 2019; 35:739-774. [DOI: 10.1007/s12640-018-9989-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2018] [Revised: 12/09/2018] [Accepted: 12/11/2018] [Indexed: 01/18/2023]
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23
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Dilan TL, Singh RK, Saravanan T, Moye A, Goldberg AFX, Stoilov P, Ramamurthy V. Bardet-Biedl syndrome-8 (BBS8) protein is crucial for the development of outer segments in photoreceptor neurons. Hum Mol Genet 2019; 27:283-294. [PMID: 29126234 DOI: 10.1093/hmg/ddx399] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Accepted: 11/06/2017] [Indexed: 11/15/2022] Open
Abstract
Bardet-Biedl syndrome (BBS) is an autosomal recessive ciliopathy characterized by developmental abnormalities and vision loss. To date, mutations in 21 genes have been linked to BBS. The products of eight of these BBS genes form a stable octameric complex termed the BBSome. Mutations in BBS8, a component of the BBSome, cause early vision loss, but the role of BBS8 in supporting vision is not known. To understand the mechanisms by which BBS8 supports rod and cone photoreceptor function, we generated animal models lacking BBS8. The loss of BBS8 protein led to concomitant decrease in the levels of BBSome subunits, BBS2 and BBS5 and increase in the levels of the BBS1 and BBS4 subunits. BBS8 ablation was associated with severe reduction of rod and cone photoreceptor function and progressive degeneration of each photoreceptor subtype. We observed disorganized and shortened photoreceptor outer segments (OS) at post-natal day 10 as the OS elaborates. Interestingly, loss of BBS8 led to changes in the distribution of photoreceptor axonemal proteins and hyper-acetylation of ciliary microtubules. In contrast to properly localized phototransduction machinery, we observed OS accumulation of syntaxin3, a protein normally found in the cytoplasm and the synaptic termini. In conclusion, our studies demonstrate the requirement for BBS8 in early development and elaboration of ciliated photoreceptor OS, explaining the need for BBS8 in normal vision. The findings from our study also imply that early targeting of both rods and cones in BBS8 patients is crucial for successful restoration of vision.
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Affiliation(s)
- Tanya L Dilan
- Departments of Ophthalmology, West Virginia University, Morgantown, WA 26506, USA.,Biochemistry, West Virginia University, Morgantown, WA 26506, USA
| | - Ratnesh K Singh
- Departments of Ophthalmology, West Virginia University, Morgantown, WA 26506, USA.,Biochemistry, West Virginia University, Morgantown, WA 26506, USA
| | | | - Abigail Moye
- Departments of Ophthalmology, West Virginia University, Morgantown, WA 26506, USA.,Biochemistry, West Virginia University, Morgantown, WA 26506, USA
| | | | - Peter Stoilov
- Biochemistry, West Virginia University, Morgantown, WA 26506, USA
| | - Visvanathan Ramamurthy
- Departments of Ophthalmology, West Virginia University, Morgantown, WA 26506, USA.,Biochemistry, West Virginia University, Morgantown, WA 26506, USA.,Rockefeller Neurosciences Institute, West Virginia University, Morgantown, WA 26506, USA
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24
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Dilan T, Ramamurthy V. The Dynamic and Complex Role of the Joubert Syndrome-Associated Ciliary Protein, ADP-Ribosylation Factor-Like GTPase 13B (ARL13B) in Photoreceptor Development and Maintenance. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1185:501-505. [PMID: 31884661 DOI: 10.1007/978-3-030-27378-1_82] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Photoreceptor neurons are modified primary cilia with an extended ciliary compartment known as the outer segment (OS). The mechanism behind the elaboration of photoreceptor cilia and OS morphogenesis remains poorly understood. In this review, we discuss the role of ADP-ribosylation factor-like GTPase 13B (ARL13B), a small GTPase in OS morphogenesis and its impact on photoreceptor health and biology.
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Affiliation(s)
- Tanya Dilan
- Departments of Ophthalmology, West Virginia University, Morgantown, WV, USA
| | - Visvanathan Ramamurthy
- Departments of Ophthalmology, West Virginia University, Morgantown, WV, USA.
- Departments of Biochemistry, West Virginia University, Morgantown, WV, USA.
- Eye Institute, One Medical Center Drive, West Virginia University, Morgantown, WV, USA.
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25
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Baehr W, Hanke-Gogokhia C, Sharif A, Reed M, Dahl T, Frederick JM, Ying G. Insights into photoreceptor ciliogenesis revealed by animal models. Prog Retin Eye Res 2018; 71:26-56. [PMID: 30590118 DOI: 10.1016/j.preteyeres.2018.12.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Revised: 12/10/2018] [Accepted: 12/18/2018] [Indexed: 12/11/2022]
Abstract
Photoreceptors are polarized neurons, with very specific subcellular compartmentalization and unique requirements for protein expression and trafficking. Each photoreceptor contains an outer segment, the site of photon capture that initiates vision, an inner segment that houses the biosynthetic machinery and a synaptic terminal for signal transmission to downstream neurons. Outer segments and inner segments are connected by a connecting cilium (CC), the equivalent of a transition zone (TZ) of primary cilia. The connecting cilium is part of the basal body/axoneme backbone that stabilizes the outer segment. This report will update the reader on late developments in photoreceptor ciliogenesis and transition zone formation, specifically in mouse photoreceptors, focusing on early events in photoreceptor ciliogenesis. The connecting cilium, an elongated and narrow structure through which all outer segment proteins and membrane components must traffic, functions as a gate that controls access to the outer segment. Here we will review genes and their protein products essential for basal body maturation and for CC/TZ genesis, sorted by phenotype. Emphasis is given to naturally occurring mouse mutants and gene knockouts that interfere with CC/TZ formation and ciliogenesis.
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Affiliation(s)
- Wolfgang Baehr
- Department of Ophthalmology and Visual Sciences, University of Utah Health Sciences, Salt Lake City, UT, 84132, USA.
| | - Christin Hanke-Gogokhia
- Department of Ophthalmology and Visual Sciences, University of Utah Health Sciences, Salt Lake City, UT, 84132, USA
| | - Ali Sharif
- Department of Ophthalmology and Visual Sciences, University of Utah Health Sciences, Salt Lake City, UT, 84132, USA
| | - Michelle Reed
- Department of Ophthalmology and Visual Sciences, University of Utah Health Sciences, Salt Lake City, UT, 84132, USA
| | - Tiffanie Dahl
- Department of Ophthalmology and Visual Sciences, University of Utah Health Sciences, Salt Lake City, UT, 84132, USA
| | - Jeanne M Frederick
- Department of Ophthalmology and Visual Sciences, University of Utah Health Sciences, Salt Lake City, UT, 84132, USA
| | - Guoxin Ying
- Department of Ophthalmology and Visual Sciences, University of Utah Health Sciences, Salt Lake City, UT, 84132, USA
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26
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Sokolov M, Yadav RP, Brooks C, Artemyev NO. Chaperones and retinal disorders. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2018; 114:85-117. [PMID: 30635087 DOI: 10.1016/bs.apcsb.2018.09.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Defects in protein folding and trafficking are a common cause of photoreceptor degeneration, causing blindness. Photoreceptor cells present an unusual challenge to the protein folding and transport machinery due to the high rate of protein synthesis, trafficking and the renewal of the outer segment, a primary cilium that has been modified into a specialized light-sensing compartment. Phototransduction components, such as rhodopsin and cGMP-phosphodiesterase, and multimeric ciliary transport complexes, such as the BBSome, are hotspots for mutations that disrupt proteostasis and lead to the death of photoreceptors. In this chapter, we review recent studies that advance our understanding of the chaperone and transport machinery of phototransduction proteins.
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Affiliation(s)
- Maxim Sokolov
- Department of Ophthalmology, West Virginia University, Morgantown, WV, United States
| | - Ravi P Yadav
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, IA, United States
| | - Celine Brooks
- Department of Ophthalmology, West Virginia University, Morgantown, WV, United States
| | - Nikolai O Artemyev
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, IA, United States; Department of Ophthalmology and Visual Sciences, The University of Iowa Carver College of Medicine, Iowa City, IA, United States.
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27
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Wright ZC, Loskutov Y, Murphy D, Stoilov P, Pugacheva E, Goldberg AFX, Ramamurthy V. ADP-Ribosylation Factor-Like 2 (ARL2) regulates cilia stability and development of outer segments in rod photoreceptor neurons. Sci Rep 2018; 8:16967. [PMID: 30446707 PMCID: PMC6240099 DOI: 10.1038/s41598-018-35395-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Accepted: 10/28/2018] [Indexed: 01/31/2023] Open
Abstract
Photoreceptor cells are specialized neurons with a sensory cilium carrying an elaborate membrane structure, the outer segment (OS). Inherited mutations in genes involved in ciliogenesis frequently result in OS malformation and blindness. ADP-ribosylation factor-like 2 (ARL2) has recently been implicated in OS formation through its association with Binder of ARL2 (BART or ARL2BP), a protein linked to inherited blinding disease. To test the role of ARL2 in vision we created a transgenic mouse model expressing a tagged-dominant active form of human ARL2 (ARL2-Q70L) under a rod-specific promoter. Transgenic ARL2-Q70L animals exhibit reduced photoreceptor cell function as early as post-natal day 16 and progressive rod degeneration. We attribute loss of photoreceptor function to the defective OS morphogenesis in the ARL2-Q70L transgenic model. ARL2-Q70L expression results in shortened inner and outer segments, shortened and mislocalized axonemes and cytoplasmic accumulation of rhodopsin. In conclusion, we show that ARL2-Q70L is crucial for photoreceptor neuron sensory cilium development. Future research will expand upon our hypothesis that ARL2-Q70L mutant interferes with microtubule maintenance and tubulin regulation resulting in impaired growth of the axoneme and elaboration of the photoreceptor outer segment.
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Affiliation(s)
- Zachary C Wright
- Departments of Ophthalmology, West Virginia University, Morgantown, West Virginia, 26506, USA
| | - Yuriy Loskutov
- Departments of Biochemistry, West Virginia University, Morgantown, West Virginia, 26506, USA
| | - Daniel Murphy
- Departments of Biochemistry, West Virginia University, Morgantown, West Virginia, 26506, USA
| | - Peter Stoilov
- Departments of Biochemistry, West Virginia University, Morgantown, West Virginia, 26506, USA
| | - Elena Pugacheva
- Departments of Biochemistry, West Virginia University, Morgantown, West Virginia, 26506, USA
| | | | - Visvanathan Ramamurthy
- Departments of Ophthalmology, West Virginia University, Morgantown, West Virginia, 26506, USA. .,Departments of Biochemistry, West Virginia University, Morgantown, West Virginia, 26506, USA. .,Center for Neuroscience, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, 26506, USA.
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28
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Zaneveld SA, Eblimit A, Liang Q, Bertrand R, Wu N, Liu H, Nguyen Q, Zaneveld J, Wang K, Li Y, Chen R. Gene Therapy Rescues Retinal Degeneration in Receptor Expression-Enhancing Protein 6 Mutant Mice. Hum Gene Ther 2018; 30:302-315. [PMID: 30101608 PMCID: PMC6437630 DOI: 10.1089/hum.2018.078] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Hereditary retinal dystrophy is clinically defined as a broad group of chronic and progressive disorders that affect visual function by causing photoreceptor degeneration. Previously, we identified mutations in the gene encoding receptor expression-enhancing protein 6 (REEP6), in individuals with autosomal recessive retinitis pigmentosa (RP), the most common form of inherited retinal dystrophy. One individual was molecularly diagnosed with biallelic REEP6 mutations, a missense mutation over a frameshift mutation. In this study, we generated Reep6 compound heterozygous mice, Reep6L135P/-, which mimic the patient genotype and recapitulate the early-onset retinal degeneration phenotypes observed in the individual with RP. To determine the feasibility of rescuing the Reep6 mutant phenotype via gene replacement therapy, we delivered Reep6.1, the mouse retina-specific isoform of REEP6, to photoreceptors of Reep6 mutant mice on postnatal day 20. Evaluation of the therapeutic effects 2 months posttreatment showed improvements in the photoresponse as well as preservation of photoreceptor cells. Importantly, guanylyl cyclase 1 (GC1) expression was also restored to the outer segment after treatment. Furthermore, rAAV8-Reep6.1 single treatment in Reep6 mutant mice 1 year postinjection showed significant improvements in retinal function and morphology, suggesting that the treatment is effective even after a prolonged period. Findings from this study show that gene replacement therapy in the retina with rAAV overexpressing Reep6 is effective, preserving photoreceptor function in Reep6 mutant mice. These findings provide evidence that rAAV8-based gene therapy can prolong survival of photoreceptors in vivo and can be potentially used as a therapeutic modality for treatment of patients with RP.
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Affiliation(s)
- Smriti Agrawal Zaneveld
- 1 Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX.,2 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX
| | - Aiden Eblimit
- 1 Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX.,2 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX
| | - Qingnan Liang
- 1 Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX.,3 Department of Biochemistry, Baylor College of Medicine, Houston, TX
| | - Renae Bertrand
- 1 Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX.,3 Department of Biochemistry, Baylor College of Medicine, Houston, TX
| | - Nathaniel Wu
- 1 Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX.,2 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX
| | - Hehe Liu
- 1 Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX.,2 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX
| | - Quynh Nguyen
- 3 Department of Biochemistry, Baylor College of Medicine, Houston, TX
| | - Jacques Zaneveld
- 1 Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX.,2 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX
| | - Keqing Wang
- 1 Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX.,2 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX
| | - Yumei Li
- 1 Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX.,2 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX
| | - Rui Chen
- 1 Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX.,2 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX
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29
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Song P, Perkins BD. Developmental expression of the zebrafish Arf-like small GTPase paralogs arl13a and arl13b. Gene Expr Patterns 2018; 29:82-87. [PMID: 30009987 DOI: 10.1016/j.gep.2018.07.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2018] [Revised: 07/10/2018] [Accepted: 07/12/2018] [Indexed: 12/13/2022]
Abstract
Members of the Arf-like (Arl) family of small GTP-binding proteins regulate a number of cellular functions and play important roles in cilia structure and signaling. The small GTPase Arl13a is a close paralog to Arl13b, a small GTPase required for normal cilia formation that causes Joubert Syndrome when mutated. As mutation of arl13b causes a slow retinal degeneration in zebrafish (Song et al., 2016), we hypothesized that expression of arl13a may provide functional redundancy. We determined the expression domains of arl13a and arl13b during zebrafish development and examined subcellular localization by expression of fluorescence fusion proteins. Both genes are widely expressed during early cell division and gastrulation and Arl13a and Arl13b both localize to microtubules in ciliated and dividing cells of the early zebrafish embryo. Between 2 and 5 days post fertilization (dpf), arl13b is expressed in neural tissues while expression of arl13a is downregulated by 2 dpf and restricted to craniofacial structures. These results indicate that arl13a and arl13b have evolved different roles and that arl13a does not function in the zebrafish retina.
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Affiliation(s)
- Ping Song
- Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, OH, 44195, USA
| | - Brian D Perkins
- Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, OH, 44195, USA.
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30
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Moye AR, Singh R, Kimler VA, Dilan TL, Munezero D, Saravanan T, Goldberg AFX, Ramamurthy V. ARL2BP, a protein linked to retinitis pigmentosa, is needed for normal photoreceptor cilia doublets and outer segment structure. Mol Biol Cell 2018; 29:1590-1598. [PMID: 29718757 PMCID: PMC6080659 DOI: 10.1091/mbc.e18-01-0040] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The outer segment (OS) of photoreceptor cells is an elaboration of a primary cilium with organized stacks of membranous disks that contain the proteins needed for phototransduction and vision. Though ciliary formation and function has been well characterized, little is known about the role of cilia in the development of photoreceptor OS. Nevertheless, progress has been made by studying mutations in ciliary proteins, which often result in malformed OSs and lead to blinding diseases. To investigate how ciliary proteins contribute to OS formation, we generated a knockout (KO) mouse model for ARL2BP, a ciliary protein linked to retinitis pigmentosa. The KO mice display an early and progressive reduction in visual response. Before photoreceptor degeneration, we observed disorganization of the photoreceptor OS, with vertically aligned disks and shortened axonemes. Interestingly, ciliary doublet microtubule (MT) structure was also impaired, displaying open B-tubule doublets, paired with loss of singlet MTs. On the basis of results from this study, we conclude that ARL2BP is necessary for photoreceptor ciliary doublet formation and axoneme elongation, which is required for OS morphogenesis and vision.
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Affiliation(s)
- Abigail R Moye
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506.,Department of Biochemistry, West Virginia University, Morgantown, WV 26506
| | - Ratnesh Singh
- Department of Biochemistry, West Virginia University, Morgantown, WV 26506
| | | | - Tanya L Dilan
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506.,Department of Biochemistry, West Virginia University, Morgantown, WV 26506
| | - Daniella Munezero
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506.,Department of Biochemistry, West Virginia University, Morgantown, WV 26506
| | | | | | - Visvanathan Ramamurthy
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506.,Department of Biochemistry, West Virginia University, Morgantown, WV 26506.,Rockefeller Neurosciences Institute, West Virginia University, Morgantown, WV 26506
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31
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Saavedra A, García-Díaz Barriga G, Pérez-Navarro E, Alberch J. Huntington's disease: novel therapeutic perspectives hanging in the balance. Expert Opin Ther Targets 2018; 22:385-399. [PMID: 29671352 DOI: 10.1080/14728222.2018.1465930] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
INTRODUCTION Huntington's disease (HD), an autosomal dominant neurodegenerative disorder caused by an expansion of CAG repeats in the huntingtin gene, has long been characterized by the presence of motor symptoms due to the loss of striatal projection neurons. Cognitive dysfunction and neuropsychiatric symptoms are also present and they occur in the absence of cell death in most mouse models, pointing to neuronal dysfunction and abnormal synaptic plasticity as causative mechanisms. Areas covered: Here, we focus on those common mechanisms altered by the presence of mutant huntingtin affecting corticostriatal and hippocampal function as therapeutic targets that could prove beneficial to ameliorate both cognitive and motor function in HD. Specifically, we discuss the importance of reestablishing the balance in (1) synaptic/extrasynaptic N-methyl-D-aspartate receptor signaling, (2) mitochondrial dynamics/trafficking, (3) TrkB/p75NTR signaling, and (4) transcriptional activity. Expert opinion: Mutant huntingtin has a broad impact on multiple cellular processes, which makes it very challenging to design a curative therapeutic strategy. As we point out here, novel therapeutic interventions should look for multi-purpose drugs targeting common and early affected processes leading to corticostriatal and hippocampal dysfunction that additionally operate in a feedforward vicious cycle downstream the activation of extrasynaptic N-methyl-D-aspartate receptor.
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Affiliation(s)
- Ana Saavedra
- a Departament de Biomedicina, Facultat de Medicina i Ciències de la Salut, Institut de Neurociències , Universitat de Barcelona , Barcelona , Spain.,b Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS) , Barcelona , Spain.,c Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED) , Spain
| | - Gerardo García-Díaz Barriga
- a Departament de Biomedicina, Facultat de Medicina i Ciències de la Salut, Institut de Neurociències , Universitat de Barcelona , Barcelona , Spain.,b Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS) , Barcelona , Spain.,c Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED) , Spain
| | - Esther Pérez-Navarro
- a Departament de Biomedicina, Facultat de Medicina i Ciències de la Salut, Institut de Neurociències , Universitat de Barcelona , Barcelona , Spain.,b Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS) , Barcelona , Spain.,c Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED) , Spain
| | - Jordi Alberch
- a Departament de Biomedicina, Facultat de Medicina i Ciències de la Salut, Institut de Neurociències , Universitat de Barcelona , Barcelona , Spain.,b Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS) , Barcelona , Spain.,c Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED) , Spain
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32
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Lyraki R, Lokaj M, Soares DC, Little A, Vermeren M, Marsh JA, Wittinghofer A, Hurd T. Characterization of a novel RP2-OSTF1 interaction and its implication for actin remodelling. J Cell Sci 2018; 131:jcs.211748. [PMID: 29361551 DOI: 10.1242/jcs.211748] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 12/21/2017] [Indexed: 11/20/2022] Open
Abstract
Retinitis pigmentosa 2 (RP2) is the causative gene for a form of X-linked retinal degeneration. RP2 was previously shown to have GTPase-activating protein (GAP) activity towards the small GTPase ARL3 via its N-terminus, but the function of the C-terminus remains elusive. Here, we report a novel interaction between RP2 and osteoclast-stimulating factor 1 (OSTF1), an intracellular protein that indirectly enhances osteoclast formation and activity and is a negative regulator of cell motility. Moreover, this interaction is abolished by a human pathogenic mutation in RP2. We utilized a structure-based approach to pinpoint the binding interface to a strictly conserved cluster of residues on the surface of RP2 that spans both the C- and N-terminal domains of the protein, and which is structurally distinct from the ARL3-binding site. In addition, we show that RP2 is a positive regulator of cell motility in vitro, recruiting OSTF1 to the cell membrane and preventing its interaction with the migration regulator Myo1E.
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Affiliation(s)
- Rodanthi Lyraki
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK
| | - Mandy Lokaj
- Structural Biology Group, Max-Planck Institut für Molekulare Physiologie, Abteilung Strukturelle Biologie, Otto-Hahn-Str. 11, 44227 Dortmund, Germany
| | - Dinesh C Soares
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK
| | - Abigail Little
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK
| | - Matthieu Vermeren
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK.,MRC Centre for Inflammation Research, The Queen's Medical Research Institute, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
| | - Joseph A Marsh
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK
| | - Alfred Wittinghofer
- Structural Biology Group, Max-Planck Institut für Molekulare Physiologie, Abteilung Strukturelle Biologie, Otto-Hahn-Str. 11, 44227 Dortmund, Germany
| | - Toby Hurd
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK
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33
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Seo S, Datta P. Photoreceptor outer segment as a sink for membrane proteins: hypothesis and implications in retinal ciliopathies. Hum Mol Genet 2017; 26:R75-R82. [PMID: 28453661 DOI: 10.1093/hmg/ddx163] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2017] [Accepted: 04/24/2017] [Indexed: 12/28/2022] Open
Abstract
The photoreceptor outer segment (OS) is a unique modification of the primary cilium, specialized for light perception. Being homologous organelles, the primary cilium and the OS share common building blocks and molecular machinery to construct and maintain them. The OS, however, has several unique structural features that are not seen in primary cilia. Although these unique features of the OS have been well documented, their implications in protein localization have been under-appreciated. In this review, we compare the structural properties of the primary cilium and the OS, and propose a hypothesis that the OS can act as a sink for membrane proteins. We further discuss the implications of this hypothesis in polarized protein localization in photoreceptors and mechanisms of photoreceptor degeneration in retinal ciliopathies.
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Affiliation(s)
- Seongjin Seo
- Department of Ophthalmology and Visual Sciences, Wynn Institute for Vision Research, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
| | - Poppy Datta
- Department of Ophthalmology and Visual Sciences, Wynn Institute for Vision Research, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
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34
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Hanke-Gogokhia C, Wu Z, Sharif A, Yazigi H, Frederick JM, Baehr W. The guanine nucleotide exchange factor Arf-like protein 13b is essential for assembly of the mouse photoreceptor transition zone and outer segment. J Biol Chem 2017; 292:21442-21456. [PMID: 29089384 DOI: 10.1074/jbc.ra117.000141] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2017] [Revised: 10/24/2017] [Indexed: 01/17/2023] Open
Abstract
Arf-like protein 13b (ARL13b) is a small GTPase that functions as a guanosine nucleotide exchange factor (GEF) for ARL3-GDP. ARL13b is located exclusively in photoreceptor outer segments (OS) presumably anchored to discs by palmitoylation, whereas ARL3 is an inner segment cytoplasmic protein. Hypomorphic mutations affecting the ARL13b G-domain inactivate GEF activity and lead to Joubert syndrome (JS) in humans. However, the molecular mechanisms in ARL13b mutation-induced Joubert syndrome, particularly the function of primary cilia, are still incompletely understood. Because Arl13b germline knockouts in mouse are lethal, we generated retina-specific deletions of ARL13b in which ARL3-GTP formation is impaired. In mouse retArl13b-/- central retina at postnatal day 6 (P6) and older, outer segments were absent, thereby preventing trafficking of outer segment proteins to their destination. Ultrastructure of postnatal day 10 (P10) central retArl13b-/- photoreceptors revealed docking of basal bodies to cell membranes, but mature transition zones and disc structures were absent. Deletion of ARL13b in adult mice via tamoxifen-induced Cre/loxP recombination indicated that axonemes gradually shorten and outer segments progressively degenerate. IFT88, essential for anterograde intraflagellar transport (IFT), was significantly reduced at tamArl13b-/- basal bodies, suggesting impairment of intraflagellar transport. AAV2/8 vector-mediated ARL13b expression in the retArl13b-/- retina rescued ciliogenesis.
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Affiliation(s)
- Christin Hanke-Gogokhia
- From the Department of Ophthalmology, John A. Moran Eye Center, University of Utah Health Science Center, Salt Lake City, Utah 84132
| | - Zhijian Wu
- NEI, National Institutes of Health, Bethesda, Maryland 20892
| | - Ali Sharif
- From the Department of Ophthalmology, John A. Moran Eye Center, University of Utah Health Science Center, Salt Lake City, Utah 84132
| | - Hussein Yazigi
- From the Department of Ophthalmology, John A. Moran Eye Center, University of Utah Health Science Center, Salt Lake City, Utah 84132
| | - Jeanne M Frederick
- From the Department of Ophthalmology, John A. Moran Eye Center, University of Utah Health Science Center, Salt Lake City, Utah 84132
| | - Wolfgang Baehr
- From the Department of Ophthalmology, John A. Moran Eye Center, University of Utah Health Science Center, Salt Lake City, Utah 84132, .,Department of Neurobiology and Anatomy, University of Utah Health Science Center, Salt Lake City, Utah 84132, and.,Department of Biology, University of Utah, Salt Lake City, Utah 84112
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35
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Liu F, Qin Y, Yu S, Soares DC, Yang L, Weng J, Li C, Gao M, Lu Z, Hu X, Liu X, Jiang T, Liu JY, Shu X, Tang Z, Liu M. Pathogenic mutations in retinitis pigmentosa 2 predominantly result in loss of RP2 protein stability in humans and zebrafish. J Biol Chem 2017; 292:6225-6239. [PMID: 28209709 PMCID: PMC5391753 DOI: 10.1074/jbc.m116.760314] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2016] [Revised: 02/14/2017] [Indexed: 12/20/2022] Open
Abstract
Mutations in retinitis pigmentosa 2 (RP2) account for 10-20% of X-linked retinitis pigmentosa (RP) cases. The encoded RP2 protein is implicated in ciliary trafficking of myristoylated and prenylated proteins in photoreceptor cells. To date >70 mutations in RP2 have been identified. How these mutations disrupt the function of RP2 is not fully understood. Here we report a novel in-frame 12-bp deletion (c.357_368del, p.Pro120_Gly123del) in zebrafish rp2 The mutant zebrafish shows reduced rod phototransduction proteins and progressive retinal degeneration. Interestingly, the protein level of mutant Rp2 is almost undetectable, whereas its mRNA level is near normal, indicating a possible post-translational effect of the mutation. Consistent with this hypothesis, the equivalent 12-bp deletion in human RP2 markedly impairs RP2 protein stability and reduces its protein level. Furthermore, we found that a majority of the RP2 pathogenic mutations (including missense, single-residue deletion, and C-terminal truncation mutations) severely destabilize the RP2 protein. The destabilized RP2 mutant proteins are degraded via the proteasome pathway, resulting in dramatically decreased protein levels. The remaining non-destabilizing mutations T87I, R118H/R118G/R118L/R118C, E138G, and R211H/R211L are suggested to impair the interaction between RP2 and its protein partners (such as ARL3) or with as yet unknown partners. By utilizing a combination of in silico, in vitro, and in vivo approaches, our work comprehensively indicates that loss of RP2 protein structural stability is the predominating pathogenic consequence for most RP2 mutations. Our study also reveals a role of the C-terminal domain of RP2 in maintaining the overall protein stability.
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Affiliation(s)
- Fei Liu
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Yayun Qin
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Shanshan Yu
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Dinesh C Soares
- MRC Human Genetics Unit/Centre for Genomic and Experimental Medicine, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XU, United Kingdom, and
| | - Lifang Yang
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Jun Weng
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Chang Li
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Meng Gao
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Zhaojing Lu
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Xuebin Hu
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Xiliang Liu
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Tao Jiang
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Jing Yu Liu
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Xinhua Shu
- Department of Life Sciences, Glasgow Caledonian University, Glasgow G4 0BA, United Kingdom
| | - Zhaohui Tang
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Mugen Liu
- From the Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Genetics and Developmental Biology, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China,
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Abstract
Arl2 and Arl3 are Arf-like small GTP-binding proteins of the Arf subfamily of the Ras superfamily. Despite their structural similarity and sharing of many interacting partners, Arl2 and Arl3 have different biochemical properties and biological functions. Growing evidence suggest that Arl2 and Arl3 play a fundamental role as regulators of trafficking of lipid modified proteins between different compartments. Here we highlight the similarities and differences between these 2 homologous proteins and discuss the sorting mechanism of lipidated cargo into the ciliary compartment through the carriers PDE6δ and Unc119 and the release factors Arl2 and Arl3.
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Affiliation(s)
- Eyad K Fansa
- a Max Planck Institute of Molecular Physiology , Dortmund , Germany
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Dutta N, Seo S. RPGR, a prenylated retinal ciliopathy protein, is targeted to cilia in a prenylation- and PDE6D-dependent manner. Biol Open 2016; 5:1283-9. [PMID: 27493202 PMCID: PMC5051646 DOI: 10.1242/bio.020461] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
RPGR (retinitis pigmentosa GTPase regulator) is a ciliary protein associated with several forms of inherited retinal degenerative diseases. PDE6D is a ubiquitously expressed prenyl-binding protein and involved in ciliary targeting of prenylated proteins. The current working model for the RPGR function depicts that RPGR acts as a scaffold protein to recruit cargo-loaded PDE6D to primary cilia. Here, we present evidence demonstrating an alternative relationship between RPGR and PDE6D, in which RPGR is a cargo of PDE6D for ciliary targeting. We found that the constitutive isoform of RPGR, which is prenylated, requires prenylation for its ciliary localization. We also found that there are at least two independent ciliary targeting signals in RPGR: one within the N-terminal region that contains the RCC1-like domain and the other near the prenylation site at the C-terminus. Ablation of PDE6D blocked ciliary targeting of RPGR. Our study indicates that prenylated RPGR is one of the cargos of PDE6D for ciliary trafficking and provides insight into the mechanisms by which RPGR is targeted to cilia. Summary: RPGR is a ciliary protein that functions as a scaffold to recruit cargo-loaded PDE6D to cilia. Our study shows that RPGR is also a cargo of PDE6D.
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Affiliation(s)
- Nirmal Dutta
- Department of Ophthalmology and Visual Sciences, University of Iowa College of Medicine, Iowa City, IA 52242, USA
| | - Seongjin Seo
- Department of Ophthalmology and Visual Sciences, University of Iowa College of Medicine, Iowa City, IA 52242, USA
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