The Drosophila maternal-effect mutantcappuccino and its interactors

Abstract

cappuccino (capu) is a Drosophila melanogaster gene required for establishing the dorsal-ventral and anterior-posterior axes of the developing egg and embryo. Egg chambers mutant for capu exhibit cytoplasmic streaming during mid-oogenesis that does not normally occur until late oogenesis. All known capu alleles stream at the same speed. Since capu alleles do differ in their effects on the dorsal-ventral axis, it is unlikely that premature streaming is a cause of the dorsal-ventral defects. Premature streaming may, however, cause the posterior defects. Streaming occurs at the same speed if isolated egg chambers are treated with the actin depolymerizing drug cytochalasin D, which suggests that CAPU may act in the actin cytoskeleton. A screen for proteins which physically interact with CAPU identified profilin, a regulator of the actin cytoskeleton as a probable partner of CAPU. This again suggests that CAPU acts in the actin cytoskeleton. CAPU is a member of the formin homology (FH) family of proteins. Sequence analysis of this family makes it possible to multiply align all family members throughout their carboxy-terminal halves. This makes possible better predictions of secondary structure, phylogenetic analysis, and identification of novel regions of conserved sequence. Analysis of the amino-terminal halves suggests that significant alignment is also possible in these more highly divergent regions. Members of the rho family of small GTPases have been implicated in the regulation of the actin cytoskeleton. They physically associate with members of the FH family, including CAPU. All four rho-like proteins tested associate with CAPU in the Interaction Trap system. There are also indications of genetic interactions between capu and the rho-like genes dcdc42 and drac1.