The differentiation of epidermis:I. The interrelationship of epidermis and dermis in embryonic chicken skin

Abstract

ABSTRACT Experiments were made on the tarso-metatarsal skin of 12-day chicken embryos to determine the relative importance of different dermal constituents for the continued growth and differentiation of the epidermis. The two tissues were separated after exposure to Versene and the isolated epidermis was either recombined with the dermis which had previously been subjected to various treatments, or explanted on different gels, including acetic acid-extracted collagen. After growth in organ culture on natural medium, the explants were examined histologically. The isolated epidermis did not survive in culture when laid directly on a plasma-embryo extract clot, but it grew and keratinized when placed with the basal surface downwards on dermis killed by freezing and thawing or on a gel of collagen; when frozen-killed dermis was trypsinized, the epidermis differentiated at first, but then degenerated. The epidermis did not survive on heat-killed dermis, on agar, alginate, or fibrin gels, nor on Gelfilm. The epidermis survived on Millipore filter only in the presence of an increased concentration of embryo extract, when it differentiated to form a s. corneum. A periodic acid-Schiff-reactive basement membrane was formed in the absence of living dermal cells. It is concluded that, under the conditions of the experiments, the survival of embryonic chicken epidermis as an organized, keratinizing tissue depends on the contact of the basal surface with a suitable substratum, but not on the presence of living dermal cells. In the normal substratum provided by the dermis, both collagen and trypsin-labile ground substance are required by the epidermis, yet a gel of collagen can provide a suitable surface on which the epidermis is capable of normal differentiation in vitro. It has been suggested therefore that the epidermis reacts to the flat surface of collagen gels in the same way as to the extracellular moiety of the dermis.