1. ¹Department of Anatomy and Cell Biology, Caver College of Medicine, The University of Iowa, Iowa City, Iowa, USA
2. ²Department of Dermatology, Caver College of Medicine, The University of Iowa, Iowa City, Iowa, USA

Correspondence: Dr Jackie R. Bickenbach, Department of Anatomy and Cell Biology, Caver College of Medicine, The University of Iowa, 1-457 BSB, 51 Newton Road, Iowa City, Iowa 52240, USA. E-mail: jackie-bickenbach@uiowa.edu

Received 12 January 2006; Revised 10 March 2006; Accepted 13 March 2006.

Abstract

Homeostasis of continuously renewing tissues, such as the epidermis, is maintained by somatic undifferentiated, self-renewing stem cells, which are thought to persist throughout life. Through a series of labeling experiments, we previously showed that stem cells from mouse skin did not divide often, but they did divide at a steady rate in vivo. Using our recently redefined sorting method, we isolated epidermal stem and transit amplifying (TA) cells from mouse skin. When injected into a developing blastocyst or into damaged tissues, the stem cells, but not the TA cells, could participate in the formation of new tissues. We hypothesize that all tissues contain reserved undifferentiated stem cells that are primed to react if needed. These reserve stem cells could restore the tissue in which they reside or they could be called upon to help restore another tissue that was severely damage.