STEM-CELL PATTERNING AND FATE IN HUMAN EPIDERMIS

Within human epidermis there are two types of proliferating keratinocy te: stem cells, which have high proliferative potential, and transit-a mplifying cells, which are destined to undergo terminal differentiatio n after a few rounds of division. We show that, in vivo, stem cells ex press higher levels of the alpha(2) beta(1) and alpha(3) beta(1) integ rins than transit-amplifying cells and that this can be used both to d etermine the location of stem cells within the epidermis and to isolat e them directly from the tissue. The distribution of stem cells and tr ansit-amplifying cells is not random: patches of integrin-bright and i ntegrin-dull cells have a specific location with respect to the epider mal-dermal junction that varies between body sites and that correlates with the distribution of S phase cells. Stem cell patterning can be r ecreated in culture, in the absence of dermis, and appears to be subje ct to autoregulation.