Stem cell patterning and fate in human epidermis.

Within human epidermis there are two types of proliferating keratinocyte: stem cells, which have high proliferative potential, and transit-amplifying cells, which are destined to undergo terminal differentiation after a few rounds of division. We show that, in vivo, stem cells express higher levels of the alpha 2 beta 1 and alpha 3 beta 1 integrins than transit-amplifying cells and that this can be used both to determine the location of stem cells within the epidermis and to isolate them directly from the tissue. The distribution of stem cells and transit-amplifying cells is not random: patches of integrin-bright and integrin-dull cells have a specific location with respect to the epidermal-dermal junction that varies between body sites and that correlates with the distribution of S phase cells. Stem cell patterning can be recreated in culture, in the absence of dermis, and appears to be subject to autoregulation.