Diameter equilibration of the extending canal lumen requires IF-dependent spacing of aquaporin-rich canalicular vesicles at the lumenal membrane. (a and b) ifb-1 larval RNAi clusters AQP-8::GFP-bearing canalicular vesicles around varicosity cysts. Compare multiple, small, homogenously distributed canalicular puncta (arrow in a; see Fig. 5, e–g, for contrasting sparse, large, irregularly distributed endosomal vesicles) to canalicular aggregates in multicystic varicosities (arrows in b). (c–j) Loss of AQP-8/aquaporin and disruption of its water-channel activity by mercury suppresses ifb-1(larvalRNAi) and ifa-4(ok1734) cysts and reextends canals. Note premature canal truncation in the aqp-8(ok2800) null allele (e) and large (d) versus small (f) cystic varicosities in ifb-1(larvalRNAi) versus aqp-8(ok2800) ifb-1(larvalRNAi) canal arm sections. (g–j) Quantification of suppression. (k–n) AQP-8 overexpression enhances ifb-1(RNAi) cysts and lethality. (k–l′) Representative images of AQP-8–overexpressing transgenic line (AQP::GFP[++]) and AQP-8::GFP[++] ifb-1(RNAi) cysts are shown. (m and n) Quantification of enhancement. Scale bars represent 10 µM (in a for a–f) and 15 µM (in k for k–l′).