ABSTRACT
Two series of experiments were made to determine the possible alteration of paths of differentiation of the epidermis from the metatarsal region of 12-day chicken embryos. The epidermis, separated from dermis after Versene treatment of the skin, either was cultivated in isolation for various periods, then recombined with dermis and cultivated further (series 1), or was placed on gels of collagen and grown in culture in the presence of excess of vitamin A (series 2). All explants were examined histologically.
When epidermis isolated for 24 h was recombined with dermis, the upper cells degenerated as though still in isolation, but the basal cells, although they had become flattened while isolated, regenerated a viable, keratinizing epidermis; this ability was lost after 30–36 h of isolation. A basement membrane was re-formed against epidermis, following recombination, after isolation for 36–42 h. Thus the basal cells of isolated epidermis can survive for several hours in the absence of a basement membrane; the changes that they undergo are reversible for 24–30 h, but there is then a gradual loss of their potentialities.
Epidermis grown on collagen gels on control medium formed a stratum corneum, but in the presence of excess of vitamin A no keratin appeared, the epithelium became thin, and mucous cells developed. The effect resembled that on epidermis of whole skin. The results demonstrate that the effect of the vitamin on the epidermis is direct and is not mediated by the dermis.
