Bundles of parallel actin filaments can impart strength and permanence to structures such as microvilli, stereocilia of the inner ear, and bristles. Large actin bundles can form in Drosophila bristles in less than an hour. But fascin, one of the bundling proteins present in the bristle, yields only a small bundle over several days in vitro. One reason for the difference appears to be the presence of multiple bundling proteins in the bristle.
Tilney et al. (page ) examine various Drosophila mutants by electron microscopy to determine the role of the two bundling proteins, forked and fascin, in bristle development. The initial bundling events require forked. Fascin is then needed for ordering the large bundles into a hexagonal array, an arrangement that allows maximal cross-linking of the helical filaments and results in straight and rigid bristles.
The system is sensitive to the level of forked. Too much forked results...
