The epidermal stem cell compartment: variation in expression levels of E-cadherin and catenins within the basal layer of human epidermis.

The basal layer of the epidermis contains two types of proliferating keratinocyte: stem cells, with high proliferative potential, and transit amplifying cells, which are destined to undergo terminal differentiation after a few rounds of division. It has been shown previously that two- to three-fold differences in the average staining intensity of fluorescein-conjugated antibodies to beta 1 integrin subunits reflect profound differences in the proliferative potential of keratinocytes, with integrin-bright populations being enriched for stem cells. In the search for additional stem cell markers, we have stained sections of normal human epidermis with antibodies to proteins involved in intercellular adhesion and quantitated the fluorescence of individual cell-cell borders. In the basal layer, patches of brightly labeled cells were detected with antibodies to E-cadherin, beta-catenin, and gamma-catenin, but not with antibodies to P-cadherin, alpha-catenin, or with pan-desmocollin and pan-desmoglein antibodies. In the body sites examined, palm and foreskin, integrin-bright regions were strongly labeled for gamma-catenin and weakly labeled for E-cadherin and beta-catenin. Our data suggest that there are gradients of both cell-cell and cell-extracellular matrix adhesiveness within the epidermal basal layer and that the levels of E-cadherin and of beta- and gamma-catenin may provide markers for the stem cell compartment, stem cells expressing relatively higher levels of gamma-catenin and lower levels of E-cadherin and beta-catenin than other basal keratinocytes.