Role of formins during Drosophila embryonic myogenesis. Su Deng¹, Ingo Bothe², Mary Baylies². 1) Weill Cornell Medical College, New York, NY; 2) Memorial Sloan-Kettering Cancer Center.

   Cell-cell fusion is a highly regulated process that is critical for various events, such as fertilization, bone remodeling, and the generation of skeletal muscle. In our lab we use Drosophila embryonic body wall muscle as a model system to study myoblast fusion. Current research has revealed that Arp2/3, which nucleates branched actin filaments, and its regulators, Scar/WAVE and WASp, are required for the actin rearrangements necessary for myoblast fusion. However, whether the generation of unbranched actin filaments is involved in cell fusion is unknown. Formins are a family of proteins that nucleate unbranched actin filaments. We screened known formin mutant alleles in Drosophila and assayed for muscle phenotypes during embryogenesis. We find that both loss and gain of function of the Drosophila formin, Diaphanous (Dia), generate muscle phenotypes, including fusion and muscle attachment defects. Consistent with the loss and gain of function phenotypes, Dia is present in myoblasts and is enriched at the fusion site. At later stages of development, Dia is expressed at muscle attachment sites. Together, these data suggest that Dia may be required for myoblast fusion and myotendinous junction formation and/or stability. Further studies of how Dia is involved during muscle differentiation are in progress.