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

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 mi crotubule cytoskeletal transport pathways could drive these changes. Recent ly, we localized actin-binding proteins in light-/dark-adapted octopus rhab doms and suggested that actin cytoskeletal rearrangements bring about the f ormation and degradation of rhabdomere microvilli subsets. To determine if the microtubule cytoskeleton and associated motor proteins control the othe r light/dark changes, we used immunoblotting and immunocytochemical procedu res to map the distribution of tubulin, kinesin, and dynein in dorsal and v entral halves of light- and dark-adapted octopus retinas. Immunoblots detec ted alpha and beta-tubulin, dynein intermediate chain, and kinesin heavy ch ain in extracts of whole retinas. Epifluorescence and confocal microscopy s howed that the tubulin proteins were distributed throughout the retina with more immunoreactivity in retinas exposed to light. Kinesin localization wa s heavy in the pigment layer of light- and dark-adapted ventral retinas but was less prominent in the dorsal region. Dynein distribution also varied i n dorsal and ventral retinas with more immunoreactivity in light- and dark- adapted ventral retinas and confocal microscopy emphasized the granular nat ure of this labeling. We suggest that light may regulate the distribution o f 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 m igration in the light and dark and with the movement of transport vesicles from the photoreceptor inner segments to the rhabdoms.