Live-Cell Imaging Evidence for the Ciliary Transport of Rod Photoreceptor Opsin by Heterotrimeric Kinesin-2

Trivedi, Deepti; Colin, Emilie; Louie, Carrie M.; Williams, David S.

doi:10.1523/jneurosci.0015-12.2012

Cited by 61 publications

(49 citation statements)

References 63 publications

(95 reference statements)

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“…This indicates that at least the majority of rhodopsin is transported on the ciliary plasma membrane. Consistently, components of the intraflagellar transport complexes that link ciliary cargo to the microtubule cytoskeleton (20,21) and the anterograde motor, kinesin II (22,23), have been implicated in ciliary transport of rhodopsin.…”

Section: Discussionmentioning

confidence: 90%

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.

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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Section: Discussionmentioning

confidence: 90%

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.

103

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“…This led to the idea that kif3a may not be the only motor required to transport rhodopsin as well as other transmembrane proteins in rod photoreceptors and that rod degeneration is due to causes other than opsin mislocalization in this mutant line (Avasthi et al 2009). In contrast to these reports, a study of opsin-GFP trafficking in kif3a-deficient photoreceptor cells demonstrated a role for kif3a in opsin transport (Trivedi et al 2012).…”

Section: Kif3a Phenotypesmentioning

confidence: 94%

Unexpected Roles for Ciliary Kinesins and Intraflagellar Transport Proteins

Pooranachandran¹,

Malicki

2016

Genetics

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Transport of proteins in the ciliary shaft is driven by microtubule-dependent motors, kinesins. Prior studies suggested that the heterotrimeric ciliary kinesin may be dispensable for certain aspects of transport in specialized cilia of vertebrate photoreceptor cells. To test this possibility further, we analyzed the mutant phenotype of the zebrafish kif3a gene, which encodes the common motor subunit of heterotrimeric ciliary kinesins. Cilia are absent in all organs examined, leading to the conclusion that kif3a is indispensable for ciliogenesis in all cells, including photoreceptors. Unexpectedly, kif3a function precedes ciliogenesis as ciliary basal bodies are mispositioned in mutant photoreceptors. This phenotype is much less pronounced in intraflagellar transport (IFT) mutants and reveals that kif3a has a much broader role than previously assumed. Despite the severity of their basal body phenotype, kif3a mutant photoreceptors survive longer compared to those in IFT mutants, which display much weaker basal body mispositioning. This effect is absent in kif3a;IFT double mutants, indicating that IFT proteins have ciliary transport-independent roles, which add to the severity of their photoreceptor phenotype. kif3a is dispensable for basal body docking in otic vesicle sensory epithelia and, surprisingly, short cilia form in mechanosensory cristae even in the absence of kif3a. In contrast to Kif3a, the functions of the Kif3c-related protein, encoded by the kif3c-like (kif3cl) gene, and the homodimeric ciliary kinesin, kif17, are dispensable for photoreceptor morphogenesis. These studies demonstrate unexpected new roles for both ciliary heterotrimeric kinesins and IFT particle genes and clarify the function of kif17, the homodimeric ciliary kinesin gene.

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“…However, KIF3 and IFT88 were associated with rhodopsin trafficking in cultured hTert-RPE1 cells (56), and rhodopsin was pulled down by IFT88 together with GC1 as IFT cargo (21), suggesting the involvement of KIF3 in rhodopsin trafficking. To solve this apparent discrepancy, we deleted KIF3A in the adult mouse using a tamoxifen-inducible Cre/loxP recombination system, CAG-CreER (38) (Fig.…”

Section: Ift88mentioning

confidence: 99%

Heterotrimeric Kinesin-2 (KIF3) Mediates Transition Zone and Axoneme Formation of Mouse Photoreceptors

Jiang

Wei

Ronquillo

et al. 2015

Journal of Biological Chemistry

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Background: Heterotrimeric kinesin-2 (KIF3) has been implicated in intraflagellar trafficking of photoreceptor membrane proteins by IFT. Results: KIF3 and IFT88 are required for transition zone and axoneme formation, but are dispensable for rhodopsin trafficking. Conclusion: Transmembrane proteins, including rhodopsin, traffic to the OS even when IFT is disabled. Significance: KIF3 builds and maintains the photoreceptor transition zone and axoneme that are essential for photoreceptor integrity and vision.

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Live-Cell Imaging Evidence for the Ciliary Transport of Rod Photoreceptor Opsin by Heterotrimeric Kinesin-2

Cited by 61 publications

References 63 publications

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

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

Unexpected Roles for Ciliary Kinesins and Intraflagellar Transport Proteins

Heterotrimeric Kinesin-2 (KIF3) Mediates Transition Zone and Axoneme Formation of Mouse Photoreceptors

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