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ABSTRACT

Note to Readers: Human gene symbols are all uppercase italics (e.g., TYR); murine gene symbols are first letter uppercase, remainder lowercase italics (e.g., Tyr).

  • Melanocytes represent a relatively small subpopulation of cells, yet they are exclusively responsible for producing the melanin that accounts for virtually all visible pigmentation in the skin, hair, and eyes. Normal pigmentation requires a number of critical steps during development and a large number of genes have been shown to participate in those processes either directly or indirectly. Mutations in many of these genes produce clinical conditions of hypopigmentation, such as albinism and piebaldism.

  • Melanocytes in the skin interact with other types of cells either directly, as in the transfer of melanin granules to keratinocytes, or indirectly, as in the response to factors produced by other cells that influence the proliferation and/or pigmentation of melanocytes. Factors that regulate such melanocyte functions include environmental factors such as ultraviolet light, hormones, growth factors, cytokines, and a number of other modulators present in the milieu of the skin.

  • Tyrosinase is the critical enzyme to melanin production by virtue of its catalytic function in the hydroxylation of tyrosine, the rate-limiting reaction in the melanin biosynthetic pathway. However, there are a number of post-tyrosinase factors and enzymes that regulate the quality and quantity of melanins produced, and presumably their functional characteristics as well; included in that list are melanogenic inhibitors and other melanogenic enzymes that can modify the chemical and physical properties of melanins.

  • Two distinct types of melanins can be produced in melanocytes; these are termed eumelanins, which are black and/or brown, and pheomelanins, which are yellow and/or red. The chemical and physical characteristics, such as ultraviolet absorption, color, and solubility, of the two types of melanins are significantly different, although very little is known at present about determinants that modulate pheomelanogenesis within melanocytes.

  • The tyrosinase gene family currently contains three members: tyrosinase (TYR), tyrosinase-related protein 1 (TYRP1, also known as TRP1 and gp75), and tyrosinase-related protein 2 (dopachrome tautomerase, TRP2, Tyrp2 (DCT), also known as TRP2, TYRP2, and Tyrp2). All three genes encode proteins with similar amino acid sequences but bind different divalent metal cations, which provides them with their distinct catalytic properties. The protein products of these three loci are thought to be involved in the multicomponent melanogenic complex in the melanosome.

  • The tyrosinase locus (TYR) has been mapped to chromosome 11q14-21; the gene is more than 65 kb in length and has 5 exons. It is the human ortholog of the murine albino locus. The TYRP1 locus (orthologous to the murine brown locus) has been mapped to chromosome 9p23; TYRP1 has been shown to be important in stabilizing tyrosinase activities in human and murine melanosomes, and in mice, Tyrp1 functions as a DHICA oxidase. The DCT locus (orthologous to the murine slaty locus) has been mapped to chromosome 13q31-32, and functions as DOPAchrome tautomerase in humans and in mice.

  • The ...

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