Regulates mbt kinase activity and is also required to recruit mbt to adherens junctions (PubMed:12490550). Together with mbt and Frl, regulates photoreceptor cell morphogenesis (PubMed:12490550, PubMed:26801180). Together with Frl, has a role in the neuronal development of mushroom bodies (PubMed:26801180). GTP + H2O = GDP + H(+) + phosphate Interacts with Frl (via GBD/FH3 domain); the interaction is stronger with the GTP bound form of Cdc42 (PubMed:26801180). The GTP-bound but not the GDP-bound form interacts with mbt and gek (PubMed:9371783, PubMed:12490550). When GTP-bound, interacts with Pak (PubMed:8628256). Adherens junctions of developing photoreceptor cells. Belongs to the small GTPase superfamily. Rho family. CDC42 subfamily.