V100 is predominantly an early endosomal protein in addition to its localization to synaptic vesicles. (A) Schematic of intracellular localization of markers and compartments in WT. (B) WT colocalization of 16 markers with V100 in developing photoreceptor terminals at ∼P + 25%. (C and D) Double labeling of a developing optic lobe for Syx7/Avl (purple) and V100 (green). (D) High resolution section of the developing lamina. Arrows in C indicate increased labeling of the lamina, which is shown at a higher resolution in D. (C’–D’’) Single channels from C and D are shown. (E) Triple labeling of a developing eye–brain section. Green, photoreceptor-specific expression of Rab5-GFP; blue, V100; red, Sunglasses/CD63. Note that V100 and Rab5-GFP colocalize at the developing photoreceptor terminals (lamina plexus), whereas Rab5-GFP is also enriched at the developing rhabdomeres in the cell bodies (eye disc). Blue arrows show colocalization of GFP-Rab5 and V100 at synapses, green arrowheads indicate absence of colocalization of GFP-Rab5 and V100 at the rhabdomeres, and red arrowheads indicate absence of colocalization of Sun and V100. (E’’’) In contrast to V100, the lysosomal marker Sunglasses marks different compartments, mostly in the cell bodies. EE, early endosome; MVB, multivesicular body/late endosome; Ly, Lysosome; SV, synaptic vesicle; RE, recycling endosome; RV, recycling vesicle. Error bars indicate SEM. Bars: (C) 10 µm; (D) 1 µm; (E) 5 µm.