EXC-1 and EXC-9 promote RAB-mediated apical transport. (a and a’) mCherry::RME-1 is overexpressed in the excretory canals. Fluorescence micrograph of section of excretory canal expressing mCherry::rme-1 construct under an exc-9 promoter; endosomes are visible as bright puncta (a); measurement of fluorescence in boxed area of panel a, measured in direction of arrow along line in panel, with a width of 300 pixels (space between dotted lines; a’). (b–b’’) Expression of GFP::RAB-11 in worms also expressing mCherry::RME-1. Fluorescence micrograph (b); fluorescence of mCherry::RME-1; area measured is shown in box (b’); and fluorescence intensity of GFP::RAB-11 and mCherry::RME-1 (b’’). (c) Graph of average ratio of fluorescence of mCherry::RME-1 to autofluorescence within worm in area of canal. Left column: average ratio for animals expressing fluorescent mCherry::RME-1 alone; right column: for animals expressing GFP::RAB-11 in addition to mCherry::RME-1; n > 25 animals for each column. All data points are shown, including the mean ± SD. ***, P < 0.001 as calculated via one-way ANOVA test. (d) Length of excretory canals of exc mutant animals and same strain overexpressing rab-8; posterior canal lengths were measured. All data points are shown, including the mean ± SD. ***, P < 0.001; P value is calculated via one-way ANOVA test. (e and e’) Convoluted canal phenotype in exc-1 and exc-9 mutant animals with overexpression of rab-8. exc-1^−/− (e); exc-9^−/− (e’). Circled areas show regions of normal-diameter lumen coiled within shortened, swollen cytoplasm. (f) Measurement of frequency of canals showing convoluted tubules trapped within shortened basal surface; a convolution is defined as the lumen crossing itself at least once. Convolutions were counted in the progeny of animals microinjected with buffer (Mock) and for animals overexpressing rab-8. ***, P < 0.001; P value is calculated by one-way ANOVA test. n > 35 for all samples in d and f. OE, overexpressing.