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 (Gα/β/γ) pathways. Using genetic approaches in C. elegans we identified a new role for Gα 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 , Gα, and Rho-family GTPases, defining novel roles for Gα-encoding genes ( gpa-12/ Gα _12/13 , gpa-7/ Gα _i , egl-30 /Gα _q , gsa-1 /Gα _s ) 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 Gα-Rho/Rac signaling regulate tubulogenesis during blood vessel development. Therefore, our work defines a primordial role for EXC-4/CLICs in Gα-Rho/Rac-signaling during tubulogenesis.