New regulatory factors for melanogenesis: developmental changes in neonatal mice of various genotypes.

The biosynthesis of melanin occurs through sequential steps known as the Mason-Raper pathway. The initial steps are the conversion of tyrosine to dihydroxyphenylalanine (dopa) and of dopa to dopaquinone by the enzyme tyrosinase (EC 1.10.3.1). Until recently it was assumed that once these first two conversions were completed, the subsequent reactions occurred spontaneously. However, studies with mouse melanoma cells in culture revealed that subsequent steps in the pathway are also regulated. In this report, we demonstrate that these steps are also regulated in skins of fetal and newborn mice. The specific activities of the regulatory factors change during the first week after birth and differ in mice of different genotypes. The findings provide new insights into genetic and developmental regulation of the pigmentary system in mammals.