UAS regulatory sequences drive expression of a FRET-based genetically encoded 'activation bioprobe' (A-probe.1) that can be used to monitor activation patterns of Cdc42 in vivo. The bioprobe consists of two fluorophores (CFP and YFP) separated by Cdc42 fused to the Cdc42 binding domain (CBD) of WASp. When Cdc42 protein is activated, it binds to the WASp CBD, resulting in a change in protein conformation that allows FRET (fluorescence resonance energy transfer) to occur between the donor (CFP) and acceptor (YFP) fluorescent proteins.