Tumor-promoting phorbol esters promote melanogenesis and prevent expression of the adrenergic phenotype in quail neural crest cells.

Tumor-promoting phorbol esters were used to manipulate the in vitro development of neural crest cells. When plated at clonal density in secondary culture, quail neural crest cells from the trunk region gave rise to three types of colonies, pigmented, unpigmented, and mixed. Pigmented colonies consisted exclusively of melanocytes; up to 50% of the unpigmented mixed colonies contained adrenergic nerve cells which could be identified by a catecholamine-specific histofluorescence method. Addition of potent tumor promoters to the culture medium shortened the doubling time of neural crest cells and altered their morphologic appearance. It also delayed the onset of pigmentation, prevented the expression of the adrenergic phenotype, reduced the number of unpigmented and mixed colonies, and increased the number of pigmented colonies, most likely by directing progenitor cells preferentially to the melanogenic pathway. There was a clear correlation between the ability of phorbol esters to promote skin tumors in mice and their ability to interfere with the in vitro development of quail neural crest cells. The potent promoters 12-0-tetradecanoyl phorbol 13-acetate (TPA) and phorbol 12,13-didecanoate (PDD) were most effective, phorbol 12,13-diacetate (PDA) was considerably less effective, the nonpromoting analogues 4-0-methyl 12-0-tetradecanoyl phorbol 13-acetate (4-0-Me-TPA) and 4 alpha-phorbol 12,13-didecanoate (4alpha-PDD) and the parent alcohol phorbol (PHR) had little or no effect.