Calmodulin-binding protein that acts as a guanine exchange factor for Rab10 and Rab11 (PubMed:9813038, PubMed:23369713, PubMed:23226104). Essential for maintenance of adult photoreceptor cells (PubMed:23226104). Upon light stimulation, required for trafficking of newly synthesized ninaE (Rh1) from the trans-Golgi network to rhabdomere membranes via Rab11-dependent vesicular transport (PubMed:23226104). During egg development, essential for establishing and maintaining epithelial cell polarity by regulating the correct polarized deposition of basal membrane (BM) proteins in follicular epithelial (FE) cells (PubMed:18331716, PubMed:23369713, PubMed:24828534). Functions by targeting Rab10 to the basal cytoplasm, where it restricts the secretion of BM proteins such as trol/Pcan and vkg/Coll IV to the basal surface (PubMed:18331716, PubMed:23369713, PubMed:24828534). Appears to be involved in regulating the levels and distribution of the guanine nucleotide exchange factor strat, however the two proteins appear to have independent roles in regulating polarized BM protein secretion in the FE (PubMed:28228250). Interacts with Cam (PubMed:18331716, PubMed:9813038). Interacts with Rab10 (PubMed:23369713). Interacts (via the DENN domains) with Rab11 (PubMed:23226104). In follicle cells (FC), accumulates at the plasma membrane and in both early and recycling endosomes. In FCs, detected at the lateral and apical cell cortex during early stages of oogenesis. At later stages, mostly expressed at the lateral cortex but some expression is still detected at the apical surface (PubMed:18331716). Colocalizes with Rab10 near the FC basal surface (PubMed:23369713). In photoreceptor cells, colocalizes with Rab11 in punctate structures (PubMed:23226104). Expressed in the adult head and body. Expressed in the follicle epithelial cells throughout their development (PubMed:18331716). Not detected until the adult stage (PubMed:9813038).