Stimulation of the proliferation and differentiation of mouse pink‐eyed dilution epidermal melanocytes by excess tyrosine in serum‐free primary culture

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/Pmelanocytes 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/Pmelanocytes. 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.

A Potential Benefit of Albinism in Astyanax Cavefish: Downregulation of the oca2 Gene Increases Tyrosine and Catecholamine Levels as an Alternative to Melanin Synthesis

“…Our conclusion that L-tyrosine is a driver of CAT synthesis is supported by studies in other vertebrates showing that the rate of CAT synthesis is highly sensitive to local concentrations of L-tyrosine [45]. Alternatively, the amount of L-tyrosine substrate is also known to control melanin synthesis [55,56]. Therefore, we propose a relationship between the two pathways in which CAT synthesis can be enhanced at the expense of melanin synthesis.…”

“…Our results suggest that disruption of melanin synthesis by oca2 loss of function can provide additional L-tyrosine substrate to enhance the CAT pathway. The role of L-tyrosine as a driver of both pathways is established [45,55,56], but to our knowledge the results described here are the first to provide evidence for a reciprocal relationship between the two pathways, a situation that could be involved in the evolution of cavefish albinism.…”

Quantitative Analysis of Eumelanin and Pheomelanin in Humans, Mice, and Other Animals: a Comparative Review

“…Hirobe et al. (41) then examined the effects of l ‐tyrosine on the melanin contents in pink‐eyed dilution epidermal melanocytes (data not shown). Graham et al.…”

Changes in the Proliferation and Differentiation of Neonatal Mouse Pink‐Eyed Dilution Melanocytes in the Presence of Excess Tyrosine

“…Bipolar, tripolar, dendritic, polygonal or epithelioid cells, as seen by phase contrast, which contained brown or black pigment granules, as observed by bright‐field microscopy, were scored as differentiated melanocytes. In p/p melanocytes, some unpigmented cells were detected as dopa‐positive melanocytes by dopa cytochemistry (9, 22). In P/P melanocytes, the number of pigmented cells was comparable with that of dopa‐positive melanocytes.…”

“…In addition to the reduction in the amount of eumelanin deposited (12, 13), melanin granules within the hair shafts of p/p mice are smaller than those in P/P mice (14). The p/p melanocytes contain smaller and rounder (15, 16) immature (17–19) melanosomes, and the number of stage III and IV melanosomes are much fewer than in P/P melanocytes (20–22). Levels of tyrosinase, the rate‐limiting enzyme in melanin synthesis, are decreased in melanocytes of p/p mice (23–26).…”