Physiological regulation of epidermal cell growth.

According to the negative feedback theory, epidermal growth is regulated in vivo (at least in part) by the combined action of two inhibitors upon the basal cell proliferative pool. One blocks 85% of basal cells in G1 the other blocks 5--10% in G2. When isolating and culturing in vitro populations of basal cells from adult guinea pig skin, it has been possible to confirm that these cells are sensitive to both G1 and G2 inhibitions. However, only a small fraction (10% or less) of the G1 blocked cell population would be governed by G1 inhibitory messages released by suprabasal, maturing keratinocytes. As regards the G2 block in vitro experiments confirm that basal cells produce a G2 blocker to which about 9% or less are susceptible. The relatively good correspondence between in vitro and in vivo experimental data point to the interest of adult isolated epidermal basal cell cultures as a model for the study of epidermal growth regulatory mechanisms.