F-Actin Bundles Are Derivatives of Microvilli: What Does This Tell US about How Bundles Might Form?

Fruit fly bristles have us tearing out our few remaining hairs. The puzzle is, in forming long bristles, how and why do flies assemble long actin bundles by gluing shorter bundles end-to-end? Fruit fly bristles extend posteriorly in a gentle curve over the fly's back like the hair on a well-groomed individual from the 60's. These bristles, which are cellular extensions of 70 μm in the microchaete and 400 μm in the macrochaete, are supported by a ring of 7–11 cross-linked, membrane-attached actin bundles that run the length of the extension. To generate such an extension and yet to allow curvature of the bristle, the bundles are composed of units or modules, which bend at their junction points (Tilney et al. 1996, Tilney et al. 1998). Fig. 1, a light micrograph of a macrochaete, reveals...