The dermal-epidermal junction during the development of skin and cutaneous appendages in the chick embryo.

The ultrastructure of the junction zone between dermis and epidermis was examined in the chick embryo during the development of feather-forming, scale-forming and glabrous skin. Direct contacts between dermal and epidermal cells were extremely rare and seen sporadically in feather-forming skin only, in connection with anchor filaments. Everywhere else, the basement membrane (BM) comprised an uninterrupted lamina densa. In feather-forming skin, zones of close parallel apposition (CPA) of dermal cell processes against the BM lamina densa were frequent at the margin of feather buds and at the base of feather filaments, and scarce in interplumar skin. In scale-forming skin, the density of CPA was lower, at 10 days, in the interplacode region than within the scale primordium, and, at 11 and 12 days, at the apex of the scale than at its base. At 11 days, dermal cells in scale primordia were equipped with long and thin tubular processes oriented predominantly at right angle with respect to the basal-apical axis of the scale. In the midventral apterium, CPA of dermal cell processes against the BM was very rare at 12 days, and non-existent at later stages, when a complex collagenous matrix was laid down in orthogonal ply-wood fashion underneath the BM lamina densa. Thus, it appeared that the heterogeneity of the distribution of dermal cell processes beneath the basement membrane might represent part of the morphogenetic message that the dermis is known to transmit to the epidermis during the formation of the appendages.