SLC35D3 accumulates in melanosomes upon ectopic expression in wild-type but not muted (BLOC-1–deficient) melanocytes. Immortalized wild-type melan-Ink4a melanocytes (A-F) or BLOC-1–deficient melan-mu melanocytes (derived from muted mice; G-L) were infected with HA-SLC35D3 retrovirus, and then analyzed by IFM with Abs to the HA epitope (green; panels A, D, G, and J) and either the melanosome-resident protein TYRP1 (red; panels B and H) or the early endosomal SNARE protein STX13 (red; panels E and K) and appropriate secondary Abs. Images were deconvolved using OpenLab (A-C) or Volocity (D-L). Overlays of the 2 labels are shown in panels C, F, I, and L, and the boxed regions are magnified 5-fold (A-F) or 4-fold (G-L) in the insets. Note the extensive overlap of HA-SLC35D3 with TYRP1 on pigment granules (A-C) but not with STX13 (D-F) in wild-type melanocytes. In BLOC-1–deficient melan-mu cells, SLC35D3 also overlaps extensively with the mislocalized TYRP1 (G-I) on early endosomes marked by STX13 (J-L). Arrowheads in insets show examples of overlap. Scale bar indicates 10 μm.