COMMENTARY Colour genes, oncogenes and melanocyte differentiation

Pigmentation has long been a favourite and easily used marker in the genetics of diverse organisms. Mammalian integumental pigments are melanins, synthesized by melanocytes in the epidermis and hair bulbs. Our understanding of mammalian pigmentation genes has been advanced significantly in the last few years (Hearing and Jim6nez, 1989), partly by the advent of methods for the culture and immortalization of melanocytes. In cultured melanocytes, homozygous recessive germline mutations can be visibly expressed, complemented or even revert spontaneously, as will be discussed. In the mouse there are over 130 mutations that affect coat colour, mapping to well over 50 loci (Silvers, 1979). For the sake of brevity, most of this commentary will be concerned with the recent molecular characterization of mutations at just four of these loci, two of which encode developmentally controlled, melanocyte-specific products while the other two play a part in melanocyte development.