A perspective on in vitro clonogenic keratinocytes: A window into the regulation of the progenitor cell compartment of the cutaneous epithelium

Although there have been some recent advances toward the prospective identification of keratinocyte stem cells (KSCs), particularly those of the hair follicle (1–4), stem cells in the cutaneous epithelium have usually been identified by their functions, such as retention of [3H]thymidine label, in vitro colony formation, and the ability to reconstitute a graft. We will discuss here the functional properties of in vitro clonogenic keratinocytes from mice and will show how they provide a window into the regulation of the stemcell compartment.