scholarly journals ARL2BP, a protein linked to retinitis pigmentosa, is needed for normal photoreceptor cilia doublets and outer segment structure

2018 ◽  
Vol 29 (13) ◽  
pp. 1590-1598 ◽  
Author(s):  
Abigail R. Moye ◽  
Ratnesh Singh ◽  
Victoria A. Kimler ◽  
Tanya L. Dilan ◽  
Daniella Munezero ◽  
...  
Keyword(s):  
Retinitis Pigmentosa ◽  
Outer Segment ◽  
Photoreceptor Cells ◽  
Visual Response ◽  
Photoreceptor Degeneration ◽  
Progressive Reduction ◽  
Ciliary Protein ◽  
Vertically Aligned ◽  
And Function

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.

scholarly journals Dysfunction of Heterotrimeric Kinesin-2 in Rod Photoreceptor Cells and the Role of Opsin Mislocalization in Rapid Cell Death

2010 ◽  
Vol 21 (23) ◽  
pp. 4076-4088 ◽  
Author(s):  
Vanda S. Lopes ◽  
David Jimeno ◽  
Kornnika Khanobdee ◽  
Xiaodan Song ◽  
Bryan Chen ◽  
...  
Keyword(s):  
Cell Death ◽  
Outer Segment ◽  
Photoreceptor Cell ◽  
Photoreceptor Cells ◽  
Cell Loss ◽  
Rod Photoreceptor ◽  
Retinal Degenerations ◽  
Cell Counts ◽  
And Function

Due to extensive elaboration of the photoreceptor cilium to form the outer segment, axonemal transport (IFT) in photoreceptors is extraordinarily busy, and retinal degeneration is a component of many ciliopathies. Functional loss of heterotrimeric kinesin-2, a major anterograde IFT motor, causes mislocalized opsin, followed by rapid cell death. Here, we have analyzed the nature of protein mislocalization and the requirements for the death of kinesin-2-mutant rod photoreceptors. Quantitative immuno EM showed that opsin accumulates initially within the inner segment, and then in the plasma membrane. The light-activated movement of arrestin to the outer segment is also impaired, but this defect likely results secondarily from binding to mislocalized opsin. Unlike some other retinal degenerations, neither opsin–arrestin complexes nor photoactivation were necessary for cell loss. In contrast, reduced rod opsin expression provided enhanced rod and cone photoreceptor survival and function, as measured by photoreceptor cell counts, apoptosis assays, and ERG analysis. The cell death incurred by loss of kinesin-2 function was almost completely negated by Rho−/−. Our results indicate that mislocalization of opsin is a major cause of photoreceptor cell death from kinesin-2 dysfunction and demonstrate the importance of accumulating mislocalized protein per se, rather than specific signaling properties of opsin, stemming from photoactivation or arrestin binding.

The role of splicing factors in retinitis pigmentosa: links to cilia

2021 ◽  
Author(s):  
Dale W. Maxwell ◽  
Raymond T. O'Keefe ◽  
Sudipto Roy ◽  
Kathryn E. Hentges
Keyword(s):  
Retinitis Pigmentosa ◽  
Primary Cilium ◽  
Photoreceptor Cells ◽  
Genetic Mutations ◽  
Splicing Factors ◽  
Sequence Variants ◽  
Biological Functions ◽  
Progressive Degeneration

Cilia are critical to numerous biological functions, both in development and everyday homeostatic processes. Diseases arising from genetic mutations that cause cilia dysfunction are termed ciliopathies. Several ubiquitously expressed splicing factors have been implicated in the condition Retinitis Pigmentosa (RP), a group of diseases characterised by the progressive degeneration of the retina. In many types of RP the disease affects the modified primary cilium of the photoreceptor cells and thus, these types of RP are considered ciliopathies. Here, we discuss sequence variants found within a number of these splicing factors, the resulting phenotypes, and the mechanisms underpinning disease pathology. Additionally, we discuss recent evidence investigating why RP patients with mutations in globally expressed splicing factors present with retina-specific phenotypes.

scholarly journals Sophisticated Gene Regulation for a Complex Physiological System: The Role of Non-coding RNAs in Photoreceptor Cells

2021 ◽  
Vol 8 ◽  
Author(s):  
Sabrina Carrella ◽  
Sandro Banfi ◽  
Marianthi Karali
Keyword(s):  
Molecular Mechanisms ◽  
Developmental Process ◽  
Photoreceptor Cells ◽  
Sensory Transduction ◽  
Circular Rnas ◽  
Therapeutic Implications ◽  
Physiological Processes ◽  
Non Coding Rnas ◽  
And Function

Photoreceptors (PRs) are specialized neuroepithelial cells of the retina responsible for sensory transduction of light stimuli. In the highly structured vertebrate retina, PRs have a highly polarized modular structure to accommodate the demanding processes of phototransduction and the visual cycle. Because of their function, PRs are exposed to continuous cellular stress. PRs are therefore under pressure to maintain their function in defiance of constant environmental perturbation, besides being part of a highly sophisticated developmental process. All this translates into the need for tightly regulated and responsive molecular mechanisms that can reinforce transcriptional programs. It is commonly accepted that regulatory non-coding RNAs (ncRNAs), and in particular microRNAs (miRNAs), are not only involved but indeed central in conferring robustness and accuracy to developmental and physiological processes. Here we integrate recent findings on the role of regulatory ncRNAs (e.g., miRNAs, lncRNAs, circular RNAs, and antisense RNAs), and of their contribution to PR pathophysiology. We also outline the therapeutic implications of translational studies that harness ncRNAs to prevent PR degeneration and promote their survival and function.

scholarly journals On the Wrong Track: Alterations of Ciliary Transport in Inherited Retinal Dystrophies

2021 ◽  
Vol 9 ◽  
Author(s):  
Laura Sánchez-Bellver ◽  
Vasileios Toulis ◽  
Gemma Marfany
Keyword(s):  
Retinal Degeneration ◽  
Outer Segment ◽  
Molecular Mechanisms ◽  
Photoreceptor Cells ◽  
Cellular Functions ◽  
Inherited Disorders ◽  
Inherited Retinal Dystrophies ◽  
Retinal Dystrophies ◽  
Elevated Protein ◽  
And Function

Ciliopathies are a group of heterogeneous inherited disorders associated with dysfunction of the cilium, a ubiquitous microtubule-based organelle involved in a broad range of cellular functions. Most ciliopathies are syndromic, since several organs whose cells produce a cilium, such as the retina, cochlea or kidney, are affected by mutations in ciliary-related genes. In the retina, photoreceptor cells present a highly specialized neurosensory cilium, the outer segment, stacked with membranous disks where photoreception and phototransduction occurs. The daily renewal of the more distal disks is a unique characteristic of photoreceptor outer segments, resulting in an elevated protein demand. All components necessary for outer segment formation, maintenance and function have to be transported from the photoreceptor inner segment, where synthesis occurs, to the cilium. Therefore, efficient transport of selected proteins is critical for photoreceptor ciliogenesis and function, and any alteration in either cargo delivery to the cilium or intraciliary trafficking compromises photoreceptor survival and leads to retinal degeneration. To date, mutations in more than 100 ciliary genes have been associated with retinal dystrophies, accounting for almost 25% of these inherited rare diseases. Interestingly, not all mutations in ciliary genes that cause retinal degeneration are also involved in pleiotropic pathologies in other ciliated organs. Depending on the mutation, the same gene can cause syndromic or non-syndromic retinopathies, thus emphasizing the highly refined specialization of the photoreceptor neurosensory cilia, and raising the possibility of photoreceptor-specific molecular mechanisms underlying common ciliary functions such as ciliary transport. In this review, we will focus on ciliary transport in photoreceptor cells and discuss the molecular complexity underpinning retinal ciliopathies, with a special emphasis on ciliary genes that, when mutated, cause either syndromic or non-syndromic retinal ciliopathies.

scholarly journals The connecting cilium inner scaffold provides a structural foundation to maintain photoreceptor integrity

2021 ◽  
Author(s):  
Olivier Mercey ◽  
Corinne Kostic ◽  
Eloïse Bertiaux ◽  
Alexia Giroud ◽  
Yashar Sadian ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Structural Foundation ◽  
Retinitis Pigmentosa ◽  
Molecular Mechanism ◽  
Outer Segment ◽  
Underlying Mechanism ◽  
Molecular Architecture ◽  
Photoreceptor Degeneration ◽  
Progressive Loss ◽  
Photoreceptor Development

AbstractRetinal degeneration is a leading cause of human blindness due to progressive loss of ciliated photoreceptors cells. While this degradation can be associated with cohesion defects of the microtubule-based connecting cilium (CC) structure, the underlying mechanism is not understood. Here, using expansion microscopy and electron microscopy, we reveal the molecular architecture of the CC and demonstrate that microtubules are linked together by a CC-inner scaffold (CC-IS) containing POC5, CENTRIN and FAM161A. Monitoring CC-IS assembly during photoreceptor development in mouse reveals that it acts as a structural zipper, progressively bridging microtubule doublets and straightening the CC. Consistently, Fam161a mutations lead to a specific CC-IS loss and trigger microtubule doublets spreading, prior to outer segment collapse and photoreceptor degeneration, providing a molecular mechanism for retinitis pigmentosa disease.One Sentence SummaryThe connecting cilium inner scaffold acts as a structural zipper granting photoreceptor integrity.

scholarly journals In silico analysis ofIDH3Agene revealed Novel mutations associated with Retinitis Pigmentosa

2019 ◽  
Author(s):  
Thwayba A. Mahmoud ◽  
Abdelrahman H. Abdelmoneim ◽  
Naseem S. Murshed ◽  
Zainab O. Mohammed ◽  
Dina T. Ahmed ◽  
...  
Keyword(s):  
Retinitis Pigmentosa ◽  
In Silico ◽  
In Silico Analysis ◽  
Photoreceptor Cells ◽  
Structure And Function ◽  
Novel Mutations ◽  
Inherited Disorders ◽  
Bioinformatics Tools ◽  
And Function ◽  
Silico Analysis

AbstractBackgroundRetinitis Pigmentosa (RP) refers to a group of inherited disorders characterized by the death of photoreceptor cells leading to blindness. The aim of this study is to identify the pathogenic SNPs in the IDH3A gene and their effect on the structure and function of the protein.Methodwe used different bioinformatics tools to predict the effect of each SNP on the structure and function of the protein.Result20 deleterious SNPs out of 178 were found to have a damaging effect on the protein structure and function.Conclusionthis is the first in silico analysis of IDH3A gene and 20 novel mutations were found using different bioinformatics tools, and they could be used as diagnostic markers for Retinitis Pigmentosa.

Disease mechanisms of X-linked retinitis pigmentosa due to RP2 and RPGR mutations

2016 ◽  
Vol 44 (5) ◽  
pp. 1235-1244 ◽  
Author(s):  
Rodanthi Lyraki ◽  
Roly Megaw ◽  
Toby Hurd
Keyword(s):  
Retinitis Pigmentosa ◽  
Cell Biology ◽  
Protein Delivery ◽  
Outer Segment ◽  
Protein Transport ◽  
Current Knowledge ◽  
Experimental Studies ◽  
Short Review ◽  
Retinal Cell ◽  
Photoreceptor Degeneration

Photoreceptor degeneration is the prominent characteristic of retinitis pigmentosa (RP), a heterogeneous group of inherited retinal dystrophies resulting in blindness. Although abnormalities in many pathways can cause photoreceptor degeneration, one of the most important causes is defective protein transport through the connecting cilium, the structure that connects the biosynthetic inner segment with the photosensitive outer segment of the photoreceptors. The majority of patients with X-linked RP have mutations in the retinitis pigmentosa GTPase regulator (RPGR) or RP2 genes, the protein products of which are both components of the connecting cilium and associated with distinct mechanisms of protein delivery to the outer segment. RP2 and RPGR proteins are associated with severe diseases ranging from classic RP to atypical forms. In this short review, we will summarise current knowledge generated by experimental studies and knockout animal models, compare and discuss the prominent hypotheses about the two proteins' functions in retinal cell biology.

scholarly journals Accumulation of non-outer segment proteins in the outer segment underlies photoreceptor degeneration in Bardet–Biedl syndrome

2015 ◽  
Vol 112 (32) ◽  
pp. E4400-E4409 ◽  
Author(s):  
Poppy Datta ◽  
Chantal Allamargot ◽  
Joseph S. Hudson ◽  
Emily K. Andersen ◽  
Sajag Bhattarai ◽  
...  
Keyword(s):  
Protein Trafficking ◽  
Outer Segment ◽  
Primary Cilia ◽  
Leucine Zipper ◽  
Photoreceptor Cells ◽  
Photoreceptor Degeneration ◽  
Photoreceptor Outer Segment ◽  
Bardet Biedl Syndrome ◽  
Major Function ◽  
Underlying Mechanisms

Compartmentalization and polarized protein trafficking are essential for many cellular functions. The photoreceptor outer segment (OS) is a sensory compartment specialized for phototransduction, and it shares many features with primary cilia. As expected, mutations disrupting protein trafficking to cilia often disrupt protein trafficking to the OS and cause photoreceptor degeneration. Bardet–Biedl syndrome (BBS) is one of the ciliopathies associated with defective ciliary trafficking and photoreceptor degeneration. However, precise roles of BBS proteins in photoreceptor cells and the underlying mechanisms of photoreceptor degeneration in BBS are not well understood. Here, we show that accumulation of non-OS proteins in the OS underlies photoreceptor degeneration in BBS. Using a newly developed BBS mouse model [Leucine zipper transcription factor-like 1 (Lztfl1)/Bbs17 mutant], isolated OSs, and quantitative proteomics, we determined 138 proteins that are enriched more than threefold in BBS mutant OS. In contrast, only eight proteins showed a more than threefold reduction. We found striking accumulation of Stx3 and Stxbp1/Munc18-1 and loss of polarized localization of Prom1 within the Lztfl1 and Bbs1 mutant OS. Ultrastructural analysis revealed that large vesicles are formed in the BBS OS, disrupting the lamellar structure of the OS. Our findings suggest that accumulation (and consequent sequestration) of non-OS proteins in the OS is likely the primary cause of photoreceptor degeneration in BBS. Our data also suggest that a major function of BBS proteins in photoreceptors is to transport proteins from the OS to the cell body or to prevent entry of non-OS proteins into the OS.

scholarly journals The Role of RPGR and Its Interacting Proteins in Ciliopathies

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Sarita Rani Patnaik ◽  
Rakesh Kotapati Raghupathy ◽  
Xun Zhang ◽  
David Mansfield ◽  
Xinhua Shu
Keyword(s):  
Retinitis Pigmentosa ◽  
Clinical Features ◽  
Protein Trafficking ◽  
Genetic Disorders ◽  
Interacting Proteins ◽  
Ciliary Protein ◽  
Retinal Disorders ◽  
Inherited Retinal Disorders ◽  
Insight Into

Ciliopathies encompass a group of genetic disorders characterized by defects in the formation, maintenance, or function of cilia. Retinitis pigmentosa (RP) is frequently one of the clinical features presented in diverse ciliopathies. RP is a heterogeneous group of inherited retinal disorders, characterized by the death of photoreceptors and affecting more than one million individuals worldwide. Theretinitis pigmentosa GTPase regulator(RPGR) gene is mutated in up to 20% of all RP patients. RPGR protein has different interacting partners to function in ciliary protein trafficking. In this review, we specifically focus on RPGR and its two interacting proteins: RPGRIP1 and RPGRIP1L. We summarize the function of the three proteins and highlight recent studies that provide insight into the cellular function of those proteins.

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