Severs actin filaments and accelerates their polymerization and depolymerization. Phosphate inhibits both the depolymerization and severing activities. Interacts with profilin and actin at the FH1 and FH2 domains respectively. Interacts with DAAM2 (By similarity). The WH2 domain acts as the DAD (diaphanous autoregulatory) domain and binds to actin monomers. Regulated by autoinhibition due to intramolecular GBD-DAD binding. The severing activity is dependent on covalent attachment of the FH2 domain to the C-terminus. Belongs to the formin homology family. Extended N-terminus. Truncated N-terminus.