UASt regulatory sequences drive expression of a photoactivatable, constitutively active form of Cdc42 (carries amino acid substitutions Q79L, E91H and N92H) that is tagged at the N-terminal end with mCherry. The Cdc42 protein has been rendered photoactivatable by being tagged with Tag:AsLOV2; in response to blue light illumination, the conformation of the Tag:AsLOV2 is altered, releasing the active site of the constitutively active Cdc42 protein.