Cell proliferative activity of epidermal keratinocytes in hair discs

To clarify the differences in epidermal keratinocyte proliferative activity and in postnatal developmental changes of this activity between the hair discs and the interfollicular epidermis, the incorporation of 3H-thymidine into the nuclei of the basal cells was measured by autoradiography, and the percentages of basal cells thus labelled were calculated. This percentage was higher in hair discs than in interfollicular epidermis at all stages examined. The percentage of labelled basal cells in the hair discs was 10% up to 15 days after birth, decreasing to about 6% from 20 days postnatally. These results suggest that the degree of cell proliferation in the hair disc epidermis differs from that in the surrounding epidermis and that changes in proliferative activity during the postnatal developmental stages are well correlated with the morphogenesis of the hair discs.