Formins play an important role in the nucleation of actin and the formation of linear actin filaments. Important for cell migration and formation, elongation and maintenance of filopodia. Specifically controls filopodial dynamics by regulating actin turnover at the barbed ends of actin filaments. Interacts with vasP, proB/profilin-2 and rac1A. Interacts (via GBD/FH3 domain) with activated Rho-GTPases. Enriched at the tips of filopodia. The N-terminus of the protein targets the protein to the cell cortex and the FH1/FH2 region refines the localization specifically to filopodial tips. Expression is kept at constant levels after the onset of development. During sexual development, displays a significant increase in fusion competent cells. The DAD domain regulates activation via by an autoinhibitory interaction with the GBD/FH3 domain. This autoinhibition is released upon competitive binding of an activated GTPase. The release of DAD allows the FH2 domain to then nucleate and elongate nonbranched actin filaments (By similarity). Belongs to the formin homology family. Diaphanous subfamily.