RETROVIRAL TRANSDUCTION OF MURINE EPIDERMAL STEM-CELLS DEMONSTRATES CLONAL UNITS OF EPIDERMAL STRUCTURE

It has been suggested that the number and position of epidermal stem c ells are related to the units of columnar structure in the upper epide rmal strata and that the cells of each unit are derived from a single stem cell. Studies of cell lineage in developing tissues have been fac ilitated by the use of retroviral transduction to provide inherited ex pression of a histochemically demonstrable foreign gene product. To pr ovide direct evidence about the clonal nature of epidermal units, muri ne epidermal keratinocytes were transduced with a replication-deficien t retroviral vector carrying the beta-galactosidase gene. Subepidermal injection of virus in vivo led to infrequent transduction with only t ransient presence of beta-galstaining keratinocytes within the epiderm is. Transduction of keratinocytes in vitro and transplantation back to in vivo sites permitted demonstration of the transduced gene in clust ers of cells within the reformed epidermis throughout a 12-wk period. The epidermis redeveloped an ordered columnar structure with restricti on of transduced cells to individual columnar units. This clonal appea rance is compatible with derivation of each epidermal unit from a sing le stem cell but is not compatible with a random pattern of cell proli feration. Transduced epidermal sheets that were recombined with oral m ucosal connective tissue also redeveloped normal columnar structure wi th restriction of beta-gal staining to individual columnar units, Thes e data suggest that the establishment of an epidermal stem cell patter n related to units of structure is an intrinsic property of the epithe lium and is not dependent on regionally-specific connective tissue inf luences.