A comparative ultrastructural and physiological study on melanophores of wild-type and periodic albino mutants of Xenopus laevis.

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.