A putative GDP-GTP exchange factor is required for development of the excretory cell in Caenorhabditis elegans

The Caenorhabditis elegans excretory cell extends tubular processes, called canals, along the basolateral surface of the epidermis. Mutations in the e xc-5 gene cause tubulocystic defects in this canal. Ultrastructural analysi s suggests that exc-5 is required for the proper placement of cytoskeletal elements at the apical epithelial surface. exc-5 encodes a protein homologo us to guanine nucleotide exchange factors and contains motif architecture s imilar to that of FGD1, which is responsible for faciogenital dysplasia. ex c-5 interacts genetically with mig-2 which encodes Rho GTPase. These result s suggest that EXC-5 controls the structural organization of the excretory canal by regulating Rho family GTPase activities.