The spatial relationship between stem cells and their progeny in the basallayer of human epidermis: a new view based on whole-mount labelling and lineage analysis

In order to examine the spatial organisation of stem cells and their progen y in human epidermis, we developed a method for whole-mount epidermal immun ofluorescence labelling using high surface beta 1 integrin expression as a stem cell marker. We confirmed that there are clusters of high beta 1 integ rin-expressing cells at the tips of the dermal papillae in epidermis from s everal body sites, whereas alpha 6 integrin expression is more uniform. The majority of actively cycling cells detected by Ki67 or bromodeoxyuridine l abelling were found in the beta 1 integrin-dull, transit amplifying populat ion and integrin-negative, keratin 10-positive cells left the basal layer e xclusively from this compartment. When we examined p53-positive clones in s un-exposed epidermis, we found two types of clone that differed in size and position in a way that was consistent with the founder cell being a stem o r transit amplifying cell. The patterning of the basal layer implies that t ransit amplifying cells migrate over the basement membrane away from the st em cell clusters. In support of this, isolated beta 1 integrin-dull keratin ocytes were more motile on type IV collagen than beta 1 integrin-bright ker atinocytes and EGFP-labelled stem cell clones in confluent cultured sheets were compact, whereas transit amplifying clones were dispersed. The combina tion of whole-mount labelling and lineage marking thus reveals features of epidermal organisation that were previously unrecognised.