The induction of typical epidermis from the chick chorionic epithelium (CE) was studied with the following methods: (a) Grafting of 15-day scale dermis (tarsometatarsal dermis) directly onto 9-day host-chorioallantoic membrane (CAM). (b) Grafting of a recombinant composed of 9-day CE and 15-day scale dermis onto 9-day host-CAM. (c) Grafting of a recombinant composed of 9-day CE and 15-day scale dermis inside a Millipore filter chamber placed on top of host-CAM and (d) Organ culture of 9-day CE in contact with 15-day scale dermis on a liquid culture medium.
Examination of the explants resulting from the four different explantation methods mentioned above has shown that the CE is highly plastic and is readily transformed into typical scale epidermis. There is no epidermal induction when a non-dermal tissue (muscle) is placed in contact with 9-day CE. These observations together with other results obtained in the control series, support the idea that a specific dermal influence is involved in the metaplasia of the CE to epidermis.
Metaplastic changes of the CE leading to epidermal differentiation are described. Evidence is presented indicating that the sole origin of the induced epidermis is from the homogeneous cell population belonging to the inner, basal cells of 9-day CE. Environmental conditions in which CE metaplasia proceeds influence the degree of normality of the induced epidermis. The limitations and the advantages of each transplantation method and its possible application to a more general problem concerning epithelial metaplasia and tissue interactions in skin development are discussed.