CYTOSKELETAL ELEMENTS IN INSECT SENSILLA

Insect sensilla have evolved prominent cytoskeletal elements as part o f their functional specialization. The cytoskeleton present in sensory cells as well as in auxiliary cells may play an important role in sen silla function. The scolopale, the characteristic cytoskeletal compone nt in the innermost auxiliary cell of mechanosensitive scolopidia and thermo-/hygrosensitive sensilla, is mainly composed of bundles of 10nm filaments. Cytochemical approaches for light and electron microscopy identified these structures as actin filaments that exhibited a unique filament orientation and uniform filament polarity. None of these app roaches has provided evidence for the presence of myo sins in the scol opale. In contrast, tropomyosin and the microtubule-associated protein 2 are associated with the actin filament bundles in the scolopale of scolopidia. All data taken together suggest that the actin filaments o f scolopale have a stabilizing rather than a contractile function. In scolopidia, in addition to cellular stabilization, filament elasticity would appear to be important during stimulation. Owing to the high nu mber of microtubules, the scolopale in thermo-/hygrosensitive sensilla seems more rigid than in scolopidia and may protect sensory dendrites from mechanical forces. In sensory cells of scolopidia, regularly cro ss-striated ciliary rootlets are additional prominent cytoskeletal str uctures. Immunohistochemistry reveals that these rootlets contain the Ca2+-binding protein centrin, which forms contractile filaments in oth er systems, e.g., unicellular green algae. Accordingly, contractions o f ciliary rootlets may also be part of the filament. function in insec t sensilla. (C) 1997 Elsevier Science Ltd. All rights reserved.