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 α- and β-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.