Dopa reaction of fetal melanocytes before and after skin transplantation on to nude mice

We have previously demonstrated that human fetal epidermal melanocytes are dopa-negative. The present study was conducted to test the hypothesis that human fetal melanocytes can be activated to produce melanin under conditions differing from their natural in utero environment. To address this question, dopa staining activity of fetal epidermal sheets, obtained from seven aborted fetuses with estimated gestational ages of 13-20 weeks, was evaluated before and after engraftment on to nude mice. Dopa staining became positive 7 days post-engraftment. The intensity of the dopa reaction and the mean number of melanocytes increased by day 14 post-engraftment, and these changes were even greater by day 30. These observations indicate that human fetal melanocytes, potentially capable of synthesizing melanin under conditions differing from their normal in utero environment, are either inhibited, or not stimulated to do so.