The proliferation of epidermal cells in mouse ear organ culture

Mouse ear fragments were cultured for up to 1 day in a chemically defined fluid medium and for 2-3 days in a solid Agar medium. Within 24 h of incubation, the epidermal cells were found to migrate towards the cut edges, a process which led to an epithelialization of the denuded surface. Concomitantly, the epidermal cell proliferation was enhanced: an entry of increasing numbers of interfollicular cells into S phase occurred after 7-10 h of incubation and was maximal around the 20th h. Correspondingly, the mitotic rate rose after 20 h. During an incubation period of 48-72 h in solid medium, the mitotic activity of the proliferating tissues in mouse ear skin continued, and the interfollicular epidermis in the proximity of the cut edges became hyperplastic. Thus, mouse ear epidermis kept in this organ culture seems to resemble a wounded epidermis in vivo. Epidermal cell proliferation was studied by determining (a) the mitotic rate and (b) the incorporation of tritiated thymidine by means of liquid scintillation spectrometry and autoradiography. Various factors affecting the incorporation of tritiated thymidine were investigated, and it was concluded that liquid scintillation spectrometry proves to be a rapid and suitable method for determining the effects of both growth-promoting and growth-inhibiting agents on epidermal cell proliferation.