EXC-1/IRG is localized exclusively at the apical surface of canals. (a) Scale diagram of the GTPase domains within the EXC-1 protein. (b–b’’) Collocation of (CRISPR/Cas9–generated endogenous) EXC-1::GFP and mKate2::EXC-9 at the canal apical surface. EXC-1 fluorescence (b); EXC-9 fluorescence (b’); and merge (b’’). (b’’’) Fluorescence intensity profiles of mKate2::EXC-9 (red) and EXC-1::GFP (green) along the white line of b’’. (b’’’’) Comparison of average canal length of wild-type and exc-1::gfp animals. For fluorescence studies, n = 20 animals examined; for canal length, n = 50 animals examined. (c–c’’) EXC-1::GFP remains at the apical surface in a homozygous null exc-9(qp130) cystic mutant. EXC-1 fluorescence (c); DIC image of fluid-filled cysts (c’); and merge (c’’); n = 25 animals examined. (d) EXC-1 is retained at the surface of canals in a homozygous exc-2(qp110) cystic mutant. EXC-1 fluorescence (d); DIC image of fluid-filled cysts (d’); and merge (d’’); n = 25 animals examined. All scale bars, 5 µm.