DESCRIPTION (provided by applicant): Stem cells are natural units of tissue repair and homeostasis. Recent studies suggest that stem cells may be more versatile than previously appreciated. This property holds promise for tissue regeneration, particularly for less controversial adult stem cells. Our global objective is to develop strategies for the isolation, purification and characterization of multipotent adult skin stem cells and their transitamplifying progeny. While skin keratinocytes are one of the few adult stem cells that can be maintained and propagated in vitro, their identification and isolation have been hampered by the lack of reliable markers that distinguish stem cells from their progeny. Without this information, the stress of removing stem cells from their niche make it impossible to assess at what point these cells might cease to function as multipotent stem cells. Here, we propose a novel strategy for purification of multipotent adult murine skin stem cells from their natural niche, by taking advantage of the slow-cycling properties and the few known markers preferentially expressed in these cells. We also devise strategies for purifying three different transit-amplifying progeny of these cells. We will determine and compare the global expression patterns of these cell populations and employ these and known markers to examine how skin stem cells change programs of gene expression during both embryonic development, and postnatally, in natural homeostasis, with the hair cycle, in response to injury or tumorigenesis, and when placed in culture. Finally, we will use this information to explore the functional consequences of altering the expression programs of key genes, which distinguish skin stem cells from their non-stem lineages. Taken together, these studies are expected to provide new and important insights into understanding how skin stem cells possess and maintain their unique self-renewing properties, and how they adopt different fates, including epidermal and hair follicle differentiation. This research is a fundamental prerequisite to ascertaining the potential of skin stem cells for therapeutic purposes that go beyond their present use in providing long-term engraftment on burn patients.