EGFP-STX13 labels recycling endosomal-derived transport intermediates in melanocytic cells. (a–d) Ultrathin cryosections of fixed human MNT-1 melanoma cells that stably express EGFP-STX13 were labeled with anti-GFP antibody and protein A conjugated to 10-nm gold particles (PAG10) and then analyzed by electron microscopy. Arrowheads point to vesicular structures associated with melanosomes (M; a and d) or endosomes (E; b); arrows (c and d) point to tubules that are continuous with endosomes or melanosomes; triangles (b) point to a bilayered clathrin coat on a vacuolar endosome. Bars, 200 nm. (e–l). WT melan-Ink4a mouse melanocytes were transiently transfected with mCh-STX13 and either GFP-RAB5A (e–h) or GFP-RAB11A (i–l) and analyzed 24 h later by spinning-disk confocal microscopy. (e and i) Single frames of representative cells showing overlap of mCh-STX13 with RAB5A-labeled vesicles (e) or RAB11A-labeled tubules (i). Bars, 10 µm. Image sequences from the boxed region in e and i are shown magnified 3× in f–h and j–l, respectively, with each label shown individually in black and white (f, g, j, and k) and merged images shown in color (h and l); elapsed time in seconds is indicated at bottom right. In f–h, an mCh-STX13–labeled tubule (yellow arrows) emerges from a GFP-RAB5–labeled punctate structure (white arrowheads). In j–l, a tubule (yellow arrows) is labeled for both mCh-STX13 and GFP-RAB11A. Bars, 2 µm.