Migration of epidermal melanophores to the dermis through the basement membrane during metamorphosis in the frog, Rana japonica.

The number of epidermal melanophores of the skin decreases dramatically during metamorphosis in the frog, Rana japonica. This decrease may represent an adaptation for rapid color change, a property which the animal acquires after metamorphosis. We concluded that the decrease was due to the migration of epidermal melanophores to the dermis. Epidermal melanophores and epidermal cells are tightly associated with each other in the young tadpole. The association becomes looser at the metamorphic stage and, occasionally, small breaks in the basement membrane are seen. These breaks may facilitate the migration. The migration was observed exclusively at the metamorphic stage, in spite of careful observation of other stages under the electron microscope. The migration of epidermal melanophores was induced by treatment with thyroxine of cultured skin from tadpoles at stage 15, and this hormone may act directly on epidermal melanophores. Until now, the increase in the number of dermal melanophores during metamorphosis has been explained by the differentiation of dermal melanophores from melanoblasts and by their mitotic division. Our results show that the migration of epidermal melanophores to the dermis may be a factor which accounts for the increase in the number of dermal melanophores.