Abstract
The epidermal cell suspensions of the neonatal dorsal skin derived from wild type mouse at the pink‐eyed dilution (p) locus (black, C57BL/10JHir‐P/P) and their congenic mutant mouse (pink‐eyed dilution, C57BL/10JHir‐p/p) were cultured with a serum‐free melanocyte growth medium supplemented with additional L‐tyrosine (Tyr) from initiation of the primary culture. L‐Tyr inhibited the proliferation of P/P melanocytes in a dose‐dependent manner, whereas L‐Tyr stimulated the proliferation of p/p melanoblasts and melanocytes regardless of dose. On the other hand, L‐Tyr stimulated (P/P) or induced (p/p) the differentiation of epidermal melanocytes in a dose‐dependent manner. In both P/P and p/p melanoblasts and melanocytes cultured with 2.0 mM L‐Tyr for 14 days, slight increases in contents of eumelanin marker, pyrrole‐2,3,5‐tricarboxylic acid (PTCA) and pheomelanin marker, aminohydroxyphenylalanine (AHP) were observed. The average number of total melanosomes (stages I, II, III, and IV) per P/P melanocyte was not changed by L‐Tyr treatment, but the proportion of stage IV melanosomes in the total melanosomes was increased. On the contrary, in p/p melanoblasts and melanocytes L‐Tyr increased dramatically the number of stage II, III, and IV melanosomes as well as the proportion of stage III melanosomes. Contents of PTCA and eumelanin precursor, 5,6‐dihydroxyindole‐2‐carboxylic acid (DHICA) of cultured media in p/p melanocytes were much more greatly increased than in P/P melanocytes. However, contents of AHP and pheomelanin precursor, 5‐S‐cysteinyldopa (5‐S‐CD) of cultured media in p/p melanocytes were increased in a similar tendency to P/P melanocytes. These results suggest that p/p melanocytes in the primary culture are induced to synthesize eumelanin by excess L‐Tyr, but difficult to accumulate them in melanosomes. J. Cell. Physiol. 191: 162–172, 2002. © 2002 Wiley‐Liss, Inc.