dMtmr6 and MTMR8 maintain endolysosomal homeostasis. (A) Representative image of fat body from fed L3 Drosophila larvae with control (GFP-negative) and clonal dMtmr6-knockdown cells (white dotted outline, green) stained with LysoTracker red to detect acidic vesicles and LysoTracker red only depicted in A′. (B) Quantification of LysoTracker red puncta number in WT versus dMtmr6-knockdown cells as represented in A. (C) Representative image of fat body from fed L3 Drosophila larvae with control (GFP-negative) and clonal dMtmr6-knockdown cells (white dotted outline, green) stained with Magic red to detect cathepsin B protease activity and Magic red only depicted in B′. (D) Quantification of Magic red puncta number in WT versus dMtmr6-knockdown cells as represented in C. (E) Representative Western blot of fat body cathepsin L protein levels from fed and starved fat body–specific knockdown larvae (L3) of the indicated genotype (CG-Gal4 > UAS-RNAi). (E′) Quantification of the ratio of procathepsin L to mature cathepsin L. Data are presented as mean ± minimum to maximum, n = 10 (C and D); and mean ± SEM, n = 6 animals for each genotype of three experimental replicates (E). Asterisks denote statistical significance (**, P < 0.01; ***, P < 0.001; ****, P < 0.0001), paired two-tailed t test (B and D) and one-way ANOVA (E). Scale bars, 20 µm (A and C). n.s., not significant.