Dermo-epidermal interactions between birds and mammals: differentiation of cutaneous appendages.

1. The capacity of skin constituents to participate in feather and hair morphogenesis has been analysed in chick and mouse embryos. 2. Reconstituted homoand heterospecific skin explants, consisting of epidermis and dermis from both species, were cultured for 8 days on the chorioallantoic membrane of the chick. 3. Recombinants of dorsal 11-5and 125-day mouse epidermis and dorsal 7-day or tarsometatarsal 12-day chick dermis gave rise to stage 2 abnormally elongated hair prepapillae. Associations of plantar 14-5-day mouse epidermis with dorsal 7-day chick dermis formed stage 3 hair papillae. 4. The reverse combinations of dorsal 5and 6-day chick epidermis and dorsal 11-5to 14-5-day mouse dermis gave rise to arrested feather buds (with 11-5and 12-5-day dermis) and to short and aberrant feather filaments (with 12-5-, 13-5and 14-5-day dermis). These short filaments were characterized by the differentiation of easily recognizable but chaotically arranged barb-ridges. The same type of feather differentiation was obtained in recombinants of normally glabrous epidermis from the comb, midventral apterium, or tarsometatarsum from 10-day chick embryos and 13-5and 14-5-day dorsal mouse dermis. 5. Control homospecific recombinations formed typical well organized feather filaments or stage 4-5 hair cone follicles. Heterospecific associations of featheror hair-forming epidermis with dermis from glabrous regions did not differentiate any kind of cutaneous appendages. 6. When distribution of feather filaments was compared in recombinants of chick epidermis with either dorsal pelage hair dermis or upper-lip vibrissal dermis, it was found that the feather pattern conformed with the regional origin of the mouse dermis. 7. It was concluded that, during feather and hair development, the dermis transmits two kinds of morphogenetic messages: one that is apparently non-specific and can therefore be understood and expressed by a foreign epidermis from another zoological class, leading to the formation of feather or hair buds, in conformity with the origin of the epidermis; the other message contains specific cues necessary for specific morphological organization of feather and hair.