ULTRASTRUCTURAL-CHANGES OF THE MICROVILLAR CYTOSKELETON IN THE PHOTORECEPTOR OF THE CRAYFISH ORCONECTES-LIMOSUS RELATED TO DIFFERENT ADAPTATION CONDITIONS
W. Hevers et H. Stieve, ULTRASTRUCTURAL-CHANGES OF THE MICROVILLAR CYTOSKELETON IN THE PHOTORECEPTOR OF THE CRAYFISH ORCONECTES-LIMOSUS RELATED TO DIFFERENT ADAPTATION CONDITIONS, Tissue & cell, 27(4), 1995, pp. 405-419
In the retina of crayfish microvilli of seven of the eight photorecept
or cells build highly organized structures, the rhabdoms. Cytoskeletal
elements inside the microvilli were investigated in conventional and
slightly extracted electron microscopical preparations. In conventiona
l preparations the ultrastructure of these cytoskeletal elements depen
ded on the adaptational state of the animal. They appeared as central
filament-like structures inside each microvillus when dark-adapted ret
inae were prepared and fixed at night in the absence of calcium. Chang
es of these conditions (light, daytime, or calcium concentration) impa
ired the detectability of these central filaments; in light-adapted ey
es prepared at midday they were rarely seen. Nevertheless, single micr
ovillar filaments were present in light-adapted retinae after mild cel
l permeabilization with the saponin beta-escin. They appeared as a reg
ular structure in each microvillus, often attached to the membrane. Th
eir fine structure was consistent with the ultrastructure of single ac
tin filaments as indicated by fast-fourier-analysis and further suppor
ted by the presence of anti-actin immunoreactivity in electron microsc
opical and immunocytochemical preparations. These results indicate tha
t microvillar filaments are not necessarily destroyed by light as prev
iously described; we suggest that their appearance inside the microvil
lus might be altered by the properties of associated, maybe sidearm-li
ke proteins.