Immuno-electron microscopy confirms that the scolopale, a characteristically prominent cytoskeletal element of insect scolopidia, is composed mainly of actin filaments. Immunohistochemistry reveals that these filaments are co-localized with tropomyosin. Myosin S1-decoration shows that their polarity is unidirectional. Antibodies to α-actinin do not bind within the scolopale. The association of these actin filaments with tropomyosin in the absence of myosin, together with their uniform polarity, strongly suggests that, in the scolopale, they have a stabilizing rather than contractile function. Filament elasticity would appear to be important for stimulation. The degree of elasticity may well be governed by the extent of tropomyosin binding
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