Disruption of microfilament organization and deregulation of disk membrane morphogenesis by cytochalasin D in rod and cone photoreceptors

Williams, David S.; Linberg, Kenneth A.; Vaughan, Dana K.; Fariss, Robert N.; Fisher, Steven K.

doi:10.1002/cne.902720202

Cited by 145 publications

(100 citation statements)

References 16 publications

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“…Topologically, the evagination process is akin to the lamellipod extension driven by actin polymerization (24), and inhibition of actin polymerization has been shown to cause the formation of a reduced number of enlarged OS discs (25)(26)(27)(28). However, the evaginations that lead to rod disk biogenesis have a depth of 11 nm, in contrast to a minimum of 100 nm for lamellipodia, which contain a network of multiple layers of actin filaments (each ∼10 nm in diameter), as well as a large number of cytoskeletal and signaling proteins (24,29).…”

Section: Discussionmentioning

confidence: 99%

“…Although most commonly associated with cell injury, blebbing is also part of physiological processes such as cytokinesis and motility (30). Destabilization of the membrane cortex with cytochalasin D has been shown to result in the formation of fewer, but larger, blebs in HeLa cells (31), reminiscent of the overgrown discs caused by cytochalasin treatment in the eye (25)(26)(27)(28). The accumulation of newly synthesized rhodopsin, but not a rod cGMP-gated plasma membrane channel, in the overgrown cytochalasin-induced discs, suggests F-actin may coordinate the postevagination phase of assembly of discrete discs separate from the plasma membrane (28).…”

Section: Discussionmentioning

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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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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 peripheral actin network at the base of the cilium plays a crucial role in the targeted delivery of ROS membranes and in photoreceptor morphogenesis (Chaitin, 1992;Williams et al, 1988). The capture of incoming Rab8-positive RTCs and their tethering at the fusion sites organized by PtdIns(4,5)P 2 is regulated by moesin and Rac1, through their cooperative regulation of the actin cytoskeleton (Deretic et al, 2004).…”

Section: Discussionmentioning

confidence: 99%

Syntaxin 3 and SNAP-25 pairing, regulated by omega-3 docosahexaenoic acid, controls the delivery of rhodopsin for the biogenesis of cilia-derived sensory organelles, the rod outer segments

Mazelova

Ransom

Astuto-Gribble

et al. 2009

Journal of Cell Science

118

108

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The biogenesis of cilia-derived sensory organelles, the photoreceptor rod outer segments (ROS), is mediated by rhodopsin transport carriers (RTCs). The small GTPase Rab8 regulates ciliary targeting of RTCs, but their specific fusion sites have not been characterized. Here, we report that the Sec6/8 complex, or exocyst, is a candidate effector for Rab8. We also show that the Qa-SNARE syntaxin 3 is present in the rod inner segment (RIS) plasma membrane at the base of the cilium and displays a microtubule-dependent concentration gradient, whereas the Qbc-SNARE SNAP-25 is uniformly distributed in the RIS plasma membrane and the synapse. Treatment with omega-3 docosahexaenoic acid [DHA, 22:6(n-3)] causes increased co-immunoprecipitation and colocalization of SNAP-25 and syntaxin 3 at the base of the cilium, which results in the increased delivery of membrane to the ROS. This is particularly evident in propranolol-treated retinas, in which the DHA-mediated increase in SNARE pairing overcomes the tethering block, including dissociation of Sec8 into the cytosol. Together, our data indicate that the Sec6/8 complex, syntaxin 3 and SNAP-25 regulate rhodopsin delivery, probably by mediating docking and fusion of RTCs. We show further that DHA, an essential polyunsaturated fatty acid of the ROS, increases pairing of syntaxin 3 and SNAP-25 to regulate expansion of the ciliary membrane and ROS biogenesis.

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“…Filamentous actin is concentrated in the distal connecting cilium of the outer segment (Chaitin et al, 1984;Wolfrum and Schmitt, 2000) and throughout the length of the ellipsoid, where it is laterally associated into longitudinal bundles that extend into microvillus-like calycal processes (CPs) that cup the base of the outer segment (Nagle et al, 1986;Arikawa and Williams, 1991). Disruption of actin filaments in Xenopus photoreceptors by cytochalasin led to the production of oversized outer-segment disks several times the normal diameter, suggesting that actin filaments are required for disk initiation but not for addition of new membrane to disks already initiated (Williams et al, 1988;.…”

Section: Introductionmentioning

confidence: 99%

Myo3A, One of Two Class III Myosin Genes Expressed in Vertebrate Retina, Is Localized to the Calycal Processes of Rod and Cone Photoreceptors and Is Expressed in the Sacculus

Dosé

Hillman

Wong

et al. 2003

MBoC

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The striped bass has two retina-expressed class III myosin genes, each composed of a kinase, motor, and tail domain. We report the cloning, sequence analysis, and expression patterns of the long (Myo3A) and short (Myo3B) class III myosins, as well as cellular localization and biochemical characterization of the long isoform, Myo3A. Myo3A (209 kDa) is expressed in the retina, brain, testis, and sacculus, and Myo3B (155 kDa) is expressed in the retina, intestine, and testis. The tails of these two isoforms contain two highly conserved domains, 3THDI and 3THDII. Whereas Myo3B has three IQ motifs, Myo3A has nine IQ motifs, four in its neck and five in its tail domain. Myo3A localizes to actin filament bundles of photoreceptors and is concentrated in the calycal processes. An anti-Myo3A antibody decorates the actin cytoskeleton of rod inner/outer segments, and this labeling is reduced by the presence of ATP. The ATP-sensitive actin association is a feature characteristic of myosin motors. The numerous IQ motifs may play a structural or signaling role in the Myo3A, and its localization to calycal processes indicates that this myosin mediates a local function at this site in vertebrate photoreceptors. INTRODUCTIONThe asymmetrical shapes of the rods and cones of the vertebrate retina are specialized to mediate photon detection and signal transmission. At the distal ends are the outer segments, which are composed of stacks of photopigmentbearing membranous disks surrounded by the plasma membrane. Progressively proximal to the outer segment are the mitochondrion-packed ellipsoid, the endoplasmic reticulum-and Golgi-rich myoid, the perinuclear region, the axon, and the synapse. The outer segment is connected to the rest of the cell by the narrow connecting cilium, through which metabolic fuels and newly synthesized proteins are transported. Although they maintain highly specialized shapes, photoreceptors are not static. Elaborately choreographed morphogenetic movements establish the specialized shapes of photoreceptors during development. Once formed, photoreceptors undergo outer segment turnover throughout life. This turnover is mediated by the daily addition of new disks to the base of the outer segment and the shedding of effete disks from the tip (Young, 1976). Disk addition requires transport of newly synthesized materials from the perinuclear and myoid regions to and through the connecting cilium. More dramatic photoreceptor motility occurs during retinomotor movements of lower vertebrates; light onset induces cone myoids to contract and rod myoids to elongate, whereas dark onset induces opposite movements (Burnside, 1978).Several observations suggest that the actin cytoskeleton plays an important role in photoreceptor motile processes. Photoreceptors are richly endowed with actin filaments deployed in distinct populations and likely to reflect specialized functional roles. Filamentous actin is concentrated in the distal connecting cilium of the outer segment (Chaitin et al., 1984;Wolfrum and Schmitt, 2000) and throu...

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Disruption of microfilament organization and deregulation of disk membrane morphogenesis by cytochalasin D in rod and cone photoreceptors

Cited by 145 publications

References 16 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

Syntaxin 3 and SNAP-25 pairing, regulated by omega-3 docosahexaenoic acid, controls the delivery of rhodopsin for the biogenesis of cilia-derived sensory organelles, the rod outer segments

Myo3A, One of Two Class III Myosin Genes Expressed in Vertebrate Retina, Is Localized to the Calycal Processes of Rod and Cone Photoreceptors and Is Expressed in the Sacculus

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