Expression of the 53 kD forked protein rescues F-actin bundle formation and mutant bristle phenotypes in Drosophila

forked mutations affect bristle development in Drosophila pupae, resulting in short, thick, gnarled bristles in the adult. The forked proteins are components of 200-300-microm-long actin fiber bundles that are present transiently during pupal development [Petersen et al., 1994: Genetics 136:173-182]. These bundles are composed of segments of 3-10 microm long, and forked protein is localized along the actin fiber bundle segments and accumulates at the junctions connecting them longitudinally. In the forked mutants, f(36a) and f(hd), F-actin bundles are greatly reduced in number and size, and bundle segmentation is absent. The p-element, P[w(+), falter] contains a 5.3-kb fragment of the forked gene that encodes the 53-kD forked protein [Lankenau et al., 1996: Mol Cell Biol 16:3535-3544]. Expression of only the 53-kD forked protein is sufficient to rescue the actin bundle and bristle phenotypes of f(36a) and f(hd) mutant flies. The 5.3-kb forked sequence, although smaller than the 13-kb region previously shown to rescue forked mutants [Petersen et al., 1994: Genetics 136:173-182], does contain the core forked sequence that encodes actin binding and bundling domains in cultured mammalian cells [Grieshaber and Petersen, 1999: J Cell Sci 112:2203-2211]. These data show that the 53-kD forked protein is sufficient for normal bristle development and that the domains shown previously to be important for actin bundling in cell culture may be all that are required for normal actin bundle formation in developing Drosophila bristles.