Different distribution of epidermal basal cells in the anuran larval skin correlates with the skin's region‐specific fate at metamorphosis

The epidermis of the body skin in anurans undergoes a metamorphic fate different from that of the tail skin. The former survives metamorphosis and is transformed into the adult type, while the latter is subject to apoptosis. In a search for an explanation for this regional specificity at the cellular level, the epidermis of tadpoles of the bullfrog, Rana catesbeiana, was characterized histologically and immunohistochemically during metamorphosis and was compared between the body and the tail. No histological difference in the epidermis was apparent between the two tissues at stages I and II defined by Taylor and Kollros (Anatomical Record94:7–23, 1946). A clear difference was first noticed at late stage III with respect to basal cells, which are thought to be the progenitor cells of the germinative basal cells of the adult‐type epidermis: basal cells appeared at this stage in the body but not in the tail. At stage X, about 22% of epidermal cells were basal cells in the body, whereas there were still no basal cells in the tail. However, we present histological evidence for the presence of adult‐type cells in the tail at the late stages of climax. Weak but consistent expression of adult antigens in the tail skin was also demonstrated immunohistochemically with antibodies against human blood group A antigen, which cross‐react with an epitope present in adult‐type epidermal cells. We conclude that even the tail epidermis, a larva‐specific tissue, contains a population of cells that can differentiate into adult‐type cells. The different distribution of basal cells between the body and the tail epidermis closely correlates with the difference in metamorphic fate between the two tissues.