Effects of genic substitution at the pink‐eyed dilution locus on the proliferation and differentiation of mouse epidermal melanocytes in vivo and in vitro

Abstract

Cells positive to the dopa reaction (melanocytes) as well as to the combined dopa-premelanin reaction (melanoblasts and melanocytes) in the epidermis of C57BL/10JHir-p/p (pink-eyed dilution) mice were fewer and less reactive than in C57BL/10JHir (black, P/P) mice, suggesting that the proliferation and differentiation of p/p melanocytes are inhibited. To confirm the inhibitory effects of p gene on the proliferation and differentiation of epidermal melanocytes, we cultured epidermal cell suspensions of neonatal skins from P/P and p/p in a serum-free medium. The proliferation and differentiation of p/p melanoblasts/melanocytes in primary culture were greatly inhibited as compared to P/P melanoblasts/melanocytes. The morphology of p/p melanoblasts/melanocytes cultured in melanocyte growth medium, though non-pigmented, was similar to P/P melanocytes; namely, dendritic, polygonal, or epithelioid. About 8% of p/p cells cultured in melanocyte growth medium were positive to the dopa reaction, and about 25% were reactive to the combined dopa-premelanin reaction. Eumelanin content in p/p was extremely reduced compared to P/P. The immunocytochemical staining of p/p melanoblasts/melanocytes revealed that they are negative to tyrosinase, but reactive to tyrosinase-related protein (TRP)-1, TRP-2, and c-kit. However, the reactivities in p/p were lower than in P/P. Although the differentiation of p/p melanoblasts was not induced by endothelin (ET)-1, ET-2, and ET-3, the proliferation of p/p melanoblasts was stimulated by them. These results suggest for the first time that p gene exerts its influence on the proliferative activities of mouse epidermal melanoblasts by affecting the regulatory mechanisms dependent on the function of ETs.

Allele variations in the OCA2 gene (pink-eyed-dilution locus) are associated with genetic susceptibility to melanoma

“…17 The eumelanin content, the proliferation, and the differentiation of melanoblasts and melanocytes are all greatly reduced p mutant mice. 17 It therefore seems quite reasonable to assume that the quantity and/or quality of melanin, that determines part of the risk of skin cancer, is strongly influenced by the OCA2 protein.…”

“…17 The eumelanin content, the proliferation, and the differentiation of melanoblasts and melanocytes are all greatly reduced p mutant mice. 17 It therefore seems quite reasonable to assume that the quantity and/or quality of melanin, that determines part of the risk of skin cancer, is strongly influenced by the OCA2 protein. In fact, a decrease of eumelanin in OCA2-variant melanocytes could contribute to mutagenesis and confer susceptibility to MM and nonmelanoma skin cancer by enhancing toxicity of free radicals following ultraviolet exposure.…”

Variants of theMATP/SLC45A2gene are protective for melanoma in the French population

“…The OCA2 gene maps to chromosome 15q11.2-q12, is highly polymorphic [Lee et al, 1995], and encodes an 838-amino acid melanosomal protein resembling a channel or a transporter [Gardner et al, 1992;Ramsay et al, 1992;Rinchik et al, 1993;Rosemblat et al, 1998;Staleva et al, 2002]. OCA2 plays an important role in controlling the eumelanin content of melanocytes [Hirobe et al, 2002;Lamoreux et al, 1995;Orlow and Brilliant, 1999;Ozeki et al, 1995;Tamate et al, 1989] via the processing of tyrosinase and the regulation of the melanosomal pH [Chen et al, 2002;Toyofuku et al, 2002]. It has recently been shown that three OCA2 intronic variants (rs7495174, rs4778241, and rs4778138) were closely associated with normal phenotypic variations in human eye color [Duffy et al, 2007].…”

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

“…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).…”