A Single Type of Progenitor Cell Maintains Normal Epidermis

In the 2007 study by Clayton et al., it was demonstrated that normal epidermis in mouse tail skin might be maintained by a single type of progenitor cell, challenging the then-current model that proposed two distinct populations (stem cells and transit amplifying cells) were responsible for skin tissue homeostasis. The researchers used inducible genetic labeling to track progenitor cells at single-cell resolution over time intervals up to one year, finding that the clone-size distributions supported a model where these progenitor cells could undergo both symmetric and asymmetric divisions to ensure epidermal homeostasis. However, the study noted that it was unclear if this model would apply to other skin areas or if a small, quiescent stem cell population might also exist and become active under special conditions, such as wound healing.