Fig. 5. Ultrastructure of primary melanocytes established from wild-type and from uw-mutant mice. (A) Wild-type melanocytes showing numerous stage III and IV melanosomes. (B) uw-mutant melanocytes displaying primarily stage I and II melanosomes. (C) uw-mutant melanocytes incubated with DOPA show a dark staining in stage I and II melanosomes (arrows), which proves the presence of active tyrosinase. (D) Secreted vesicle fraction from uw-mutant melanocytes where stage I and II melanosomes, similar to those found in (B), are identified clearly. Bar, 20 µm.