DROSOPHILA FASCIN MUTANTS ARE RESCUED BY OVEREXPRESSION OF THE VILLIN-LIKE PROTEIN, QUAIL

Actin bundle assembly in specialized structures such as microvilli on intestinal epithelia and Drosophila bristles requires two actin bundli ng proteins. In these systems, the distinct biochemical properties and temporal localization of actin bundling proteins suggest that these p roteins are not redundant, During Drosophila oogenesis, the formation of cytoplasmic actin bundles in nurse cells requires two actin bundlin g proteins, fascin encoded by the singed gene and a villin-like protei n encoded by the quail gene, singed and quail mutations are fully rece ssive and each mutation disrupts nurse cell cytoplasmic actin bundle f ormation, We used P-element mediated germline transformation to overex press quail in singed mutants and test whether these proteins have red undant functions in vivo, Overexpression of quail protein in a sterile singed background restores actin bundle formation in egg chambers, Th e degree of rescue by quail depends on the level of quail protein over expression, as well as residual levels of fascin function, In nurse ce lls that contain excess quail but no fascin, the cytoplasmic actin net work initially appears wild type hut then becomes disorganized in the final stages of nurse cell cytoplasm transport, The ability of quail o verexpression to compensate for the absence of fascin demonstrates tha t fascin is partially redundant with quail in the Drosophila germline, Quail appears to function as a bundle initiator while fascin provides bundle organization.