Melanophores from tadpoles of Xenopus laevis (Daudin) were isolated by digestion of tail fins with acetyltrypsin and collagenase and maintained in primary culture for 6 weeks up to 3 months. Within 36 to 72 h the melanophores develop one to eight dendritic processes per cell; secondary and tertiary branchings of the processes were frequently observed. The melanophores in primary culture disperse under the influence of alpha-MSH or cyclic AMP; upon rinsing out these substances the cells aggregate. In darkness, about 40% of the cells disperse their pigment, whereas under illumination the pigment of the melanophores aggregates. To date, attempts to initiate cell division in melanophores have not been successful.

Pigment of tail-fin melanophores in periodic albino Xenopus laevis tadpoles is dispersed in response to darkness and to alpha-MSH in a manner similar to wild-type melanophores. However, periodic albino tadpoles lack the response to different background conditions and the melatonin-induced aggregation in darkness. The tyrosinase activity in cells of the latter type tadpoles is weak compared to the wild-type cells. Ultrastructural examination of melanophores from periodic albino mutants and cells from wild-type tadpoles shows similar organelles at corresponding sites. A morphological difference can be observed in the fine structure of the melanosomes, which in albinos resembles an earlier stage of development. It is postulated that periodic albino Xenopus laevis possess the cellular mechanism to disperse pigment in the melanophores, but that under physiological conditions the release of alpha-MSH appears to be absent or scarce.

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