EXC-4/CLIC, Gα, and Rho/Rac signaling regulate tubulogenesis in C. elegans

The Rho-family of small GTPases, which play crucial roles in development and disease, are regulated by many signal-transduction cascades, including G-protein-coupled receptor (GPCR)-heterotrimeric G-protein (G/{beta}/{gamma}) pathways. Using genetic approaches in C. elegans we identified a new role for G and Rho/Rac signaling in cell outgrowth during tubulogenesis and show that the Chloride Intracellular Channel (CLIC) protein EXC-4 is an evolutionarily-conserved player in this pathway. The gene exc-4 was identified by its role in tubulogenesis of the excretory canal (ExCa) cell--a unicellular tube required for osmoregulation and fluid clearance. We identified an exc-4 loss-of-function allele that affects an evolutionarily conserved residue in the C-terminus. Using this mutant we identified genetic interactions between exc-4, G, and Rho-family GTPases, defining novel roles for G-encoding genes (gpa-12/G12/13, gpa-7/Gi, egl-30/Gq, gsa-1/Gs) and the Rho-family members ced-10/Rac and mig-2/RhoG in ExCa outgrowth. EXC-4 and human CLICs have conserved functions in tubulogenesis, and CLICs and G-Rho/Rac signaling regulate tubulogenesis during blood vessel development. Therefore, our work defines a primordial role for EXC-4/CLICs in G-Rho/Rac-signaling during tubulogenesis. One Sentence SummaryG and Rho/Rac signaling regulates EXC-4/CLIC-mediated cell outgrowth during tubulogenesis in C. elegans, linking elements of G-protein signaling to the enigmatic CLIC family of proteins.