Required for cytokinesis in both mitosis and meiosis. Has a role in actin cytoskeleton organization and is essential for many, if not all, actin-mediated events involving membrane invagination. May serve as a mediator between signaling molecules and actin organizers at specific phases of the cell cycle. Possible component of the contractile ring or may control its function. Localizes to the site where the metaphase furrow is anticipated to form, to the growing tip of cellularization furrows, and to contractile rings. 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.