THE DERMAL-EPIDERMAL JUNCTION DURING THE DEVELOPMENT OF SKIN AND CUTANEOUS APPENDAGES IN THE CHICK-EMBRYO

Abstract

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 nonexistent at later stages, when a complex collagenous matrix was laid down in orthogonal plywood fashion underneath the BM lamina densa. The heterogeneity of the distribution of dermal cell processes beneath the BM might represent part of the morphogenetic message that the dermis transmits to the epidermis during the formation of the appendages.