Behavioral differences between donor site-matched adult and neonatal melanocytes in culture

Little is known about the biologic behaviors of cultured melanocytes ill re lation to donor age. To investigate age-dependent differences, neonatal and adult melanocytes were isolated from the same anatomical site, the foreski n, and cultured in the same growth medium supplemented with cAMP inducers ( choleratoxin and 3-isobutyl-methylxanthine). The morphology, melanin conten t, pattern of melanosome distribution, and growth rate were then compared. Neonatal melanocytes were bipolar in appearance, whereas adult melanocytes were highly dendritic in appearance. Image analysis showed that adult melan ocytes were larger and longer, and had a greater number of dendrites than n eonatal melanocytes. When the growth medium was replaced by a medium withou t cAMP inducers, adult melanocytes showed a change in their morphology from dendritic to spindle-shaped, while the morphology of neonatal melanocytes remained unchanged. Melanosomes of adult melanocytes were distributed singl y along the dendrites, and extracellular secretion of melanosomes was also found. In contrast, melanosomes of neonatal melanocytes were aggregated nea r the nuclei. No age-dependent differences ill melanin content and growth r ate were noted in the donor site-matched cultured melanocytes. These result s suggest that donor age is one of the factors involved in determining mela nocyte dendricity and melanosome distribution, and that increased dendricit y of adult melanocytes is due to increased sensitivity to cAMP inducers. In addition, the adult melanocytes established in our culture system, which r esembled dendritic melanocytes in vivo, could be considered a desirable mod el for studying the mechanisms of adult-onset hyperpigmentary disorders and melanogenesis.