Keratinocyte stem cells of cornea, skin and hair follicle: common and distinguishing features

Tissues which undergo constant regeneration have developed a complex and tightly regulated system of replication and differentiation. The most primitive progenitor cells in these populations are termed stem cells. Much has been learned in recent years about the nature of stem cells and the dynamics of their replication, especially within hematopoietic tissues. This paper will define eight general features of stem cells, as they have been characterized in hematopoietic populations, and then review their presence in several keratinocyte populations, including corneal epithelium, interfollicular epidermis and hair follicle. Finally, this review will raise several important questions that remain unanswered about the nature of keratinocyte stem cells and hopefully will be the focus of future research.