Twinfilin is required for actin-dependent developmental processes in Drosophila

The actin cytoskeleton is essential for cellular remodeling and many develo pmental and morphological processes. Twinfilin is a ubiquitous actin monome r-binding protein whose biological function has remained unclear. We discov ered and cloned the Drosophila twinfilin homologue, and show that this prot ein is ubiquitously expressed in different tissues and developmental stages . A mutation in the twf gene leads to a number of developmental defects, in cluding aberrant bristle morphology. This results from uncontrolled polymer ization of actin filaments and misori-entation of actin bundles in developi ng bristles. In wildtype bristles, twinfilin localizes diffusively to cytop lasm and to the ends of actin bundles, and may therefore be involved in loc alization of actin monomers in cells. We also show that twinfilin and the A DF/cofilin encoding gene twinstar interact genetically in bristle morphogen esis. These results demonstrate that the accurate regulation of size and dy namics of the actin monomer pool by twinfilin is essential for a number of actin-dependent developmental processes in multicellular eukaryotes.