Acts redundantly with hlh-1 to promote body wall muscle cell and coelomocyte specification in postembryonic mesoderm progenitors, probably through suppression of sem-2. Transiently expressed in all mesoderm derived progenitor body wall muscle cells before they differentiate. Expressed in sex myoblasts at the 16-M cell and 18-M cell stages of mesoderm development in hermaphrodite larvae. Double RNAi-mediated knockdown with sem-2 results in no sex myoblast production. Belongs to the formin homology family.