Characteristics of rp/rp mice. Wild-type (B6) data are shown in the left panels and rp/rp in the right. (A) Coat color dilution in rp/rp mice. (B) Lack of platelet dense bodies (arrows) in rp/rp platelets. Magnification × 14 000. (C) Morphology and pigmentation of wild-type (B6, melan-a) and rp/rp immortal mouse melanocytes (bright-field images). Note decreased melanin pigmentation in rp/rp cells. Bar represents 50 μM. (D) Electron microscopy. Melanosomes of rp/rp melanocytes are less numerous than in wild-type melanocytes. All stages of melanosome development are found, as in wild type, but immature stages are more frequent (arrows), and some clustering of melanosomes is seen (not shown). Bar represents 0.5 μM. (E) Tyrosinase localization shown by L-DOPA staining (bright-field microscopy). Tyrosinase accumulates in the perinuclear region in rp/rp melanocytes (arrow) but is well distributed across the cell in wild-type melanocytes. Bar represents 50 μM. (F) Electron microscopy of l-DOPA–stained melanocytes. Mutant melanocytes show DOPA-positive tubular structures (arrow) not seen in wild-type cells. Bar represents 1.0 μM.