Identification and Immunolocalization of Actin Cytoskeletal Components in Light- and Dark-adapted Octopus Retinas

Velasco, Begona de; Martinez, Juana M; Ochoa, Gina H; Miller, Aria M.; Clark, Ying Mei; Matsumoto, Brian; Robles, Laura J.

doi:10.1006/exer.1999.0654

Cited by 10 publications

(9 citation statements)

References 86 publications

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“…1D–E, see inset on 1E). The membrane of each rhabdomere microvillus contains rhodopsin and signal transduction proteins necessary to process the visual signal after light absorption by rhodopsin as well as a core of actin filaments and accessory proteins (Robles et al 1995, De Velasco et al 1999). As mentioned, the rhabdoms increase in size in the dark, by the addition and lengthening of the rhabdomere microvilli, and decrease in the light by the disassembly and shortening of the same microvilli (Torres et al 1997).…”

Section: Resultsmentioning

confidence: 99%

Rho Signaling Mediates Cytoskeletal Re-arrangements in Octopus Photoreceptors*

Gray¹,

Kelly²,

Robles³

2008

American Malacological Bulletin

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Light sensitive rhabdoms in the octopus retina increase in cross-sectional area in the dark and shrink in the light. Growth in the dark is due to the formation of microvilli in an avillar region of the photoreceptor cell membrane and lengthening of rhabdomere microvilli already present. Diminution in the light is the result of the disassembly and shortening of the same microvilli. Each microvillus contains an actin filament core that must be assembled or disassembled in the dark or light, respectively. To understand the regulation of the construction and breakdown of rhabdomere microvilli in the light and dark, we used centrifugation to separate the rhabdom membranes followed by Western blotting and Rho pull-down assays to investigate the role of Rho GTPases in this process. Western blotting showed a difference in the distribution of Rho in rhabdom membrane and supernatant fractions. In the light, Rho was mostly present in the supernatant but in the dark it was found in the fraction enriched with rhabdom membranes. Complementing these results, pull-down assays showed that Rho is activated in the dark but in the light, Rho is mostly inactive. We believe that in the dark, activated Rho binds to the rhabdom membrane and initiates signaling pathways, leading to growth of rhabdomere microvilli. In the light, Rho is present in the soluble fraction, is inactivated, and is likely bound to a Rho GDI. Receptors involved in the activation of Rho in the dark are undetermined and may involve rhodopsin or another membrane protein.

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Section: Resultsmentioning

confidence: 99%

Rho Signaling Mediates Cytoskeletal Re-arrangements in Octopus Photoreceptors*

Gray¹,

Kelly²,

Robles³

2008

American Malacological Bulletin

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“…3c!. Based on past observations using electron microscopy~unpublished!, we believe these structures are internalized membrane~de Velasco et al, 1999!, and it is therefore likely that Rho participates in signaling pathways related to light-induced membrane shedding. The association of Rho with actin in the rhabdomeres suggests that this signaling protein is in close proximity to rhodopsin and can therefore be activated by light absorption.…”

Section: Discussionmentioning

confidence: 91%

“…from which project two opposing sets of microvilli, or rhabdomeres. Rhabdomeres from four adjacent cells form the rhabdom~Wells, 1978; Robles et al, 1995;Torres et al, 1997;de Velasco et al, 1999!. The outer segment tips are ensheathed in an inner limiting membrane that separates the neural retina from the vitreous body.…”

Section: Immunocytochemistry Octopus Retinal Structurementioning

confidence: 99%

Rho GTPases regulate rhabdom morphology in octopus photoreceptors

et al. 2005

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In the cephalopod retina, light/dark adaptation is accompanied by a decrease/increase in rhabdom size and redistribution of rhodopsin and retinochrome. Rearrangements in the actin cytoskeleton probably govern changes in rhabdom size by regulating the degradation/formation of rhabdomere microvilli. Photopigment movements may be directed by microtubules present in the outer segment core cytoplasm. We believe that rhodopsin activation by light stimulates Rho and Rac signaling pathways, affecting these cytoskeletal systems and their possible functions in controlling rhabdom morphology and protein movements. In this study, we localized cytoskeletal and signaling proteins in octopus photoreceptors to determine their concurrence between the lighting conditions. We used toxin B from Clostridium difficile to inhibit the activity of Rho/Rac and observed its effect on the location of signaling proteins and actin and tubulin. In both lighting conditions, we found Rho in specific sets of juxtaposed rhabdomeres in embryonic and adult retinas. In the light, Rho and actin were localized along the length of the rhabdomere, but, in the dark, both proteins were absent from a space beneath the inner limiting membrane. Rac colocalized with tubulin in the outer segment core cytoplasm and, like Rho, the two proteins were also absent beneath the inner limiting membrane in the dark. The distribution of actin and Rho was affected by toxin B and, in dark-adapted retinas, actin and Rho distribution was similar to that observed in the light. Our results suggest that the Rho/Rac GTPases are candidates for the regulation of rhabdomere size and protein movements in light-dark-adapted octopus photoreceptors.

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“…Torres et al (1997) demonstrated that subsets of rhabdomere microvilli are formed in the dark and degraded in the light. Since cephalopod rhabdomere microvilli contain an actin core (Saibil, 1982;Saibil & Hewat, 1987;Tsukita et al, 1988;Blest & Stowe, 1990) and actin-binding proteins (De Velasco et al, 1999), we suggested that actin cytoskeletal rearrangements drive the formation and degradation of rhabdomere microvilli subsets that occurs between the two lighting conditions.…”

Section: Introductionmentioning

confidence: 90%

Distribution of tubulin, kinesin, and dynein in light- and dark-adapted octopus retinas

et al. 2000

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Cephalopod retinas exhibit several responses to light and dark adaptation, including rhabdom size changes, photopigment movements, and pigment granule migration. Light- and dark-directed rearrangements of microfilament and microtubule cytoskeletal transport pathways could drive these changes. Recently, we localized actin-binding proteins in light-/dark-adapted octopus rhabdoms and suggested that actin cytoskeletal rearrangements bring about the formation and degradation of rhabdomere microvilli subsets. To determine if the microtubule cytoskeleton and associated motor proteins control the other light/dark changes, we used immunoblotting and immunocytochemical procedures to map the distribution of tubulin, kinesin, and dynein in dorsal and ventral halves of light- and dark-adapted octopus retinas. Immunoblots detected alpha- and beta-tubulin, dynein intermediate chain, and kinesin heavy chain in extracts of whole retinas. Epifluorescence and confocal microscopy showed that the tubulin proteins were distributed throughout the retina with more immunoreactivity in retinas exposed to light. Kinesin localization was heavy in the pigment layer of light- and dark-adapted ventral retinas but was less prominent in the dorsal region. Dynein distribution also varied in dorsal and ventral retinas with more immunoreactivity in light- and dark-adapted ventral retinas and confocal microscopy emphasized the granular nature of this labeling. We suggest that light may regulate the distribution of microtubule cytoskeletal proteins in the octopus retina and that position, dorsal versus ventral, also influences the distribution of motor proteins. The microtubule cytoskeleton is most likely involved in pigment granule migration in the light and dark and with the movement of transport vesicles from the photoreceptor inner segments to the rhabdoms.

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Identification and Immunolocalization of Actin Cytoskeletal Components in Light- and Dark-adapted Octopus Retinas

Cited by 10 publications

References 86 publications

Rho Signaling Mediates Cytoskeletal Re-arrangements in Octopus Photoreceptors*

Rho Signaling Mediates Cytoskeletal Re-arrangements in Octopus Photoreceptors*

Rho GTPases regulate rhabdom morphology in octopus photoreceptors

Distribution of tubulin, kinesin, and dynein in light- and dark-adapted octopus retinas

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