Involvement of follicular stem cells in forming not only the follicle but also the epidermis

The location of follicular and epidermal stem cells in mammalian skin is a crucial issue in cutaneous biology. We demonstrate that hair follicular ste m cells, located in the bulge region, can give rise to several cell types o f the hair follicle as well as upper follicular cells. Moreover, we devised a double-label technique to show that upper follicular keratinocytes emigr ate into the epidermis in normal newborn mouse skin, and in adult mouse ski n in response to a penetrating wound. These findings indicate that the hair follicle represents a major repository of keratinocyte stem cells in mouse skin, and that follicular bulge stem cells are potentially bipotent as the y can give rise to not only the hair follicle, but also the epidermis.