Three-Dimensional Architecture of the Rod Sensory Cilium and Its Disruption in Retinal Neurodegeneration

Gilliam, Jared C.; Chang, Juan; Sandoval, Ivette M.; Zhang, Youwen; Li, Tiansen; Pittler, Steven J.; Chiu, Wah; Wensel, Theodore G.

doi:10.1016/j.cell.2012.10.038

Cited by 157 publications

(234 citation statements)

References 51 publications

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“…An insufficient supply of Stx3 and Stxbp1 in the IS may result in a delay or failure of vesicle fusion at the IS/OS interface. Although we were not able to quantify it in our micrographs, accumulation of vesicles was observed near the base of connecting cilium of Bbs4 mutant photoreceptors (38). This phenotype could be a result of the deficiency of Stx3 and Stxbp1 in the IS.…”

Section: Discussionmentioning

confidence: 60%

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

Datta

Allamargot

Hudson

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

136

128

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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.photoreceptor degeneration | trafficking | primary cilia | outer segment | retinitis pigmentosa

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Section: Discussionmentioning

confidence: 60%

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

Datta

Allamargot

Hudson

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

136

128

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“…Our tomographic reconstructions also show that successive ciliary plasma membrane evaginations fuse to form discrete discs. This progressive disk closure from the axoneme could lead to the nascent discs appearing to be enclosed by plasma membrane, as previously described in both frozen and chemically fixed preparations (13,15), depending upon the position of the axoneme within the section plane and the section orientation.…”

Section: Discussionmentioning

confidence: 99%

“…A recent study reported the existence of rhodopsin-bearing vesicles and tubules within the connecting cilium and at the base of the OS (13), but others have reported that most rhodopsin is transported on the ciliary plasma membrane (14). Furthermore, cryoelectron tomography failed to identify vesicles within the connecting cilium, but also presented data suggesting that nascent discs were enclosed within plasma membrane, which cannot be fully explained by either model (15).In this manuscript, we show by immuno-EM that rhodopsin is transported primarily on the ciliary plasma membrane. By conventional EM and tomography, we demonstrate fusion of the open ends of adjacent nascent OS discs that have been formed by evaginations of the ciliary plasma membrane.…”

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confidence: 84%

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confidence: 99%

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Rod disc renewal occurs by evagination of the ciliary plasma membrane that makes cadherin-based contacts with the inner segment

Burgoyne

Meschede

Burden

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

105

103

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The outer segments of vertebrate rod photoreceptors are renewed every 10 d. Outer segment components are transported from the site of synthesis in the inner segment through the connecting cilium, followed by assembly of the highly ordered discs. Two models of assembly of discrete discs involving either successive fusion events between intracellular rhodopsin-bearing vesicles or the evagination of the plasma membrane followed by fusion of adjacent evaginations have been proposed. Here we use immuno-electron microscopy and electron tomography to show that rhodopsin is transported from the inner to the outer segment via the ciliary plasma membrane, subsequently forming successive evaginations that "zipper" up proximally, but at their leading edges are free to make junctions containing the protocadherin, PCDH21, with the inner segment plasma membrane. Given the physical dimensions of the evaginations, coupled with likely instability of the membrane cortex at the distal end of the connecting cilium, we propose that the evagination occurs via a process akin to blebbing and is not driven by actin polymerization. Disassembly of these junctions is accompanied by fusion of the leading edges of successive evaginations to form discrete discs. This fusion is topologically different to that mediated by the membrane fusion proteins, SNAREs, as initial fusion is between exoplasmic leaflets, and is accompanied by gain of the tetraspanin rim protein, peripherin.rod photoreceptors | disc renewal | rhodopsin | protocadherin R od photoreceptors are specialized neurons of the vertebrate retina responsible for vision in dim light. The cylindrical outer segment (OS) contains ∼1,000 stacked discontinuous membranous discs packed with the light-sensitive pigment rhodopsin. This contrasts with the cone OS, which consists of a series of evaginations of the plasma membrane that remain exposed to the extracellular space (1). OS constituents are synthesized in the inner segment (IS) and then transported to the OS via a nonmotile cilium (connecting cilium) that resembles the transition zone of the primary cilium. Because of the high metabolic demand of phototransduction, OS discs undergo daily renewal, whereby the tip (distal end) is shed and phagocytosed by the retinal pigment epithelium while new discs are formed at the base (proximal end) of the OS (2, 3). How these discs are generated and rhodopsin incorporated remains controversial. The evagination model proposes that the ciliary plasma membrane evaginates to form discs that are initially exposed to the extracellular space and then pinch off to form fully closed discs (4). In contrast, the fusion model proposes that discs originate from rhodopsincontaining vesicles, which undergo homotypic fusion to form new discs (5, 6). Conventional electron microscopic (EM) analyses of chemically fixed specimens have clearly shown discs open to the extracellular space at the base of the OS, supporting the evagination model (4,7,8). Furthermore, studies in amphibians have demonstrated that membrane imper...

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“…In photoreceptors, the sensory cilium forms a narrow isthmus that connects the metabolically active inner segment (IS) to the outer segment (OS). Membrane and soluble proteins essential for phototransduction and critical for maintenance of the OS traffic through the photoreceptor cilium (6,7).…”

Section: Introductionmentioning

confidence: 99%

Overlap of abnormal photoreceptor development and progressive degeneration in Leber congenital amaurosis caused byNPHP5mutation

et al. 2016

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Ciliary defects can result in severe disorders called ciliopathies. Mutations in NPHP5 cause a ciliopathy characterized by severe childhood onset retinal blindness, Leber congenital amaurosis (LCA), and renal disease. Using the canine NPHP5-LCA model we compared human and canine retinal phenotypes, and examined the early stages of photoreceptor development and degeneration, the kinetics of photoreceptor loss, the progression of degeneration and the expression profiles of selected genes. NPHP5-mutant dogs recapitulate the human phenotype of very early loss of rods, and relative retention of the central retinal cone photoreceptors that lack function. In mutant dogs, rod and cone photoreceptors have a sensory cilium, but develop and function abnormally and then rapidly degenerate; L/M cones are more severely affected than S-cones. The lack of outer segments in mutant cones indicates a ciliary dysfunction. Genes expressed in mutant rod or both rod and cone photoreceptors show significant downregulation, while those expressed only in cones are unchanged. Many genes in celldeath and -survival pathways also are downregulated. The canine disease is a non-syndromic LCA-ciliopathy, with normal renal structures and no CNS abnormalities. Our results identify the critical time points in the pathogenesis of the photoreceptor disease, and bring us closer to defining a potential time window for testing novel therapies for translation to patients. †

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Three-Dimensional Architecture of the Rod Sensory Cilium and Its Disruption in Retinal Neurodegeneration

Cited by 157 publications

References 51 publications

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

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

Rod disc renewal occurs by evagination of the ciliary plasma membrane that makes cadherin-based contacts with the inner segment

Overlap of abnormal photoreceptor development and progressive degeneration in Leber congenital amaurosis caused byNPHP5mutation

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