Functional analysis of the Drosophila Diaphanous FH protein in early embryonic development

The Drosophila Formin Homology (FH) protein Diaphanous has an essential rol e during cytokinesis. To gain insight into the function of Diaphanous durin g cytokinesis and explore its role in other processes, we generated embryos deficient for Diaphanous and analyzed three cell-cycle-regulated actin-med iated events during embryogenesis: formation of the metaphase furrow, cellu larization and formation of the pole cells. In dia embryos, all three proce sses are defective, Actin filaments do not organize properly to the metapha se and cellularization furrows and the actin ring is absent from the base o f the presumptive pole cells, Furthermore, plasma membrane invaginations th at initiate formation of the metaphase furrow and pole cells are missing. I mmunolocalization studies of wild-type embryos reveal that Diaphanous local izes to the site where the metaphase furrow is anticipated to form, to the growing tip of cellularization furrows, and to contractile rings. In additi on, the dia mutant phenotype reveals a role for Diaphanous in recruitment o f myosin II, anillin and Peanut to the cortical region between actin caps. Our findings thus indicate that Diaphanous has a role in actin cytoskeleton organization and is essential for many, if not all, actin-mediated events involving membrane imagination, Based on known biochemical functions of FB proteins, we propose that Diaphanous serves as a mediator between signaling molecules and actin organizers at specific phases of the cell cycle.