Human epidermal keratinocytes are born in a basal layer enriched in stem cells but gradually lose their replicative ability as they migrate towards the skin's surface. On page 1117, Dellambra et al. report that the evolution of the keratinocytes from stem to transient amplifying cells can be blocked by downregulating a single gene encoding 14-3-3σ. The new cell line avoids senescence and, thus far, has proven to be immortal. The 14-3-3 family of proteins has been implicated in multiple signal transduction pathways, so the direct biochemical consequence of the intervention is unknown.
In culture, normal keratinocyte stem cells go through 120–180 cell doublings before they senesce and stop dividing. During this period there is an increase in the number of larger transient amplifying cells, which form paraclones (aborted colonies with only terminally differentiated cells). Addition of an antisense...
