Electron microscopic study of leaf frog melanophore differentiation in culture, with special reference to allopurinol effect on pterorhodin formation.

Melanophores in the skin from metamorphic climax tadpoles can produce pterorhodin autonomously in culture. Thyroxine neither accelerated synthesis nor increased the amount of pterorhodin deposited. Cytoplasmic events attendant to the transformation of the larval melanosome in vitro were like those that occur in vivo. These include the uplifting of the melanosomal limiting membrane, the presence of many small cytoplasmic vesicles that can fuse with the limiting membrane, and the gradual deposition of pterorhodin flocculations on the melanin surface starting at age 25, the completion of metamorphic climax. Allopurinol inhibits pterohodin synthesis in melanophores in skin culture. It is proposed that the autonomous transformation of larval melanosomes to the pterorhodin-containing adult type is based upon a preprogramming that occurs near the onset of metamorphic climax. This preprogramming involves the uptake of elements necessary for pterorhodin biosynthesis and implicates current theory concerning the origin of pigment cells.