Fig. 7. The human epidermis harbors a proliferative suprabasal population and a proposed model of mouse skin epidermal development.

a Immunostaining of Control (n = 7), psoriasis (PSO) (n = 3) and atopic dermatitis (AD) (n = 3) human skin samples for Ki67 (red) and K10 (green) (scale bar: 50 µm), and quantification of the percentage of Ki67-positive cells in the basal and suprabasal layers. *p < 0.05, **p < 0.01, ****p < 0.0001 (two-tailed student’s T-test). Bars represent mean  ± SD. b An illustration of the model for mouse skin epidermal development. The simple-like epithelium between E9.5–E12.5 undergoes its main stratification events during the first phase between E13.5–E15.5, where both basal and suprabasal keratinocytes have high proliferation/division rates and basal cells delaminate to fuel stratification. In the second phase between E15.5–E18.5, proliferation rates are slower, decreasing considerably in the suprabasal layer, delamination may be a dominant mechanism in maintaining stratification during tissue growth, and the angle of cell division orientation in the basal keratinocytes may be uncoupled from epidermal differentiation.