Together with Cdc42, involved in establishment of planar cell polarity in the developing compound eye by contributing to ommatidial rotation. Together with DAAM and Cdc42, has a role in neuronal development of mushroom bodies. Self-associates. Interacts (via GBD/FH3 domain) with Cdc42; the interaction is stronger with the GTP bound form of Cdc42. 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. Lethal; shows planar cell polarity defects with abnormal ommatidial orientation. RNAi-mediated knockdown in the eye results in planar cell polarity defects with ommatidia showing defective rotation. Belongs to the formin homology family.