Studies of proliferative capabilities in isolated epidermal basal and differentiated cells.

In order to initiate studies to determine whether the restriction of mitosis to the basal layer in normal mammalian epidermis is a function of intrinsic changes in the cell or of environmental factors, a procedure which facilitates the isolation and separation of epidermal cells into suspensions of predominantly basal cells and of spinous and granular cells, respectively, was established. The comparatively high viability and good morphological preservation of the cells obtained by this method allowed us (1) to observe and describe morphological characteristics of keratinocytes in various stages of differentiation using phase contrast microscopy and (2) to study their respective proliferative capabilities in vitro using cell culture and metabolic tracer techniques. Over 200 successful primary cultures of basal cells have been performed to date but 56 attempts with suspensions composed of spinous and granular cells were unsuccessful. The incorporation of thymidine- 3 H, a specific precursor of DNA, into acid precipitable form after 8 hours incubation was nearly 100 fold greater in basal cell suspensions than in suspension of more differentiated cells. These observations suggest that the factors responsible for the absence of mitosis in cells from the upper epidermal layers are related to irreversible changes in the cell itself rather than to in situ environmental influence. Other evidence to support this tentative view is discussed.