CHANGES IN THE F-ACTIN CYTOSKELETON DURING NEUROSENSORY BRISTLE DEVELOPMENT IN DROSOPHILA - THE ROLE OF SINGED AND FORKED PROTEINS

Drosophila neurosensory bristle development provides an excellent mode l system to study the role of the actin-based cytoskeleton in polarize d cell growth. We used confocal fluorescence microscopy of isolated th oracic tissue to characterize changes in F-actin that occurred during macrochaete development in wild type flies and mutants that have aberr ant bristle morphology, At the earliest stages in wild type bristle de velopment, cortical patches of F-actin were present, but no bundles we re observed. Actin bundles began to form at 31% of pupal development a nd became more prominent as development progressed. The F-actin patche s gradually disappeared and were no longer present by 38% of pupal dev elopment. The distribution of F-actin in singed(3) mutant macrochaetae was indistinguishable from wild type bristles until 35% of developmen t when the actin bundles began to splay and appear ribbon-like. In for ked(36a) bristles, the mutant phenotype was evident at earlier stages of development than the singed(3) mutant. Wild type tissue stained wit h antibodies against the forked protein demonstrated that the forked p rotein colocalized with F-actin structures found in early and late sta ge developing macrochaetae. Antibodies against the singed protein show ed it appeared to localize with F-actin structures only at later stage s in development. These data suggested that the forked gene product wa s required for the initiation of fiber bundle formation and the singed gene product was required for the maintenance of fiber bundle morphol ogy during bristle development. Similar analyses of singed(3)/forked(3 6a) double mutants provided additional genetic evidence that the forke d gene product was required before the singed gene product. Further, t he analyses suggested that at least one additional crosslinking protei n was present in these bundles. (C) 1998 Wiley-Liss, Inc.