Dermo--epidermal adhesion and its effect on epidermal structure in the mouse.

Evidence is presented that dermo--epidermal adhesion is low in mouse ear. Consequently the pressure caused by mitotic activity in the basal epidermal layer is readily relieved by cell extrusion distally and the number of basal cells per unit skin area remains low. The rule then is that the number of distal cells per unit skin area must be equally low, and the epidermis is therefore thin. Conversely, dermo--epidermal adhesion is high in mouse sole-of-foot epidermis, and the mitotic pressure leads through cell crowding to a columnar basal epithelium. Furthermore, in the footpad centre, where adhesion is evidently highest, the baseline folds. With basal cell crowding and baseline folding there are more basal cells, and therefore more distal cells, per unit skin area. The epidermis is thick. Epidermal cells are regarded as equipotential. The different epidermal characteristics of the different body regions are determined by the combined actions of the local mitotic rate and the local strength of the dermal grip.