Dia 1 (also designated p140mDia) and Dia 2 (also designated p134mDia 2), mammalian homologs of Drosophila Diaphanous, belong to a family of formin-homology (FH) proteins, which are characterized by having tandemly aligned FH1 and FH2 domains in their carboxy terminal regions. The amino terminus of inactivated Dia 1 binds to the FH1 and FH2 domains, and is activated when GTP-bound Rho disrupts the intramolecular interaction of Dia 1 and converts it to an open conformation. Once activated, Dia 1 co-localizes with profilin and RhoA in dynamic plasma-membrane structures, and induces the formation of stress fibers in conjunction with the ROCK mediated signaling pathway. However, Dia 1 and ROCK activities antagonize each other in order to determine the thickness and density of the stress fibers formed. Dia 1 has also been implicated as the gene responsible for non-syndromic deafness.