Keratinocyte stem cells, label-retaining cells and possible genome protection mechanisms

Stem cells are the crucial cells upon which the entire tissue is dependent. Here we define and discuss what is meant by and known about keratinocyte stem cells. One way in which these cells have been studied is by their ability to retain radioactivity labelled thymidine for long periods of time (label retaining cells, LRCs). The underlying mechanism has been assumed in the past to be slow cycling but a more likely explanation is the selective segregation of old and new DNA strands (Cairns's hypothesis). Experiments in the small intestine indicate that the stem cells here are selectively sorting their DNA and becoming LRCs. A possible role for p53 in stem cell biology is presented.