Although much of our understanding of telomerase in degenerative conditions and cancers has been rooted in studies of telomerase knockout mice and focused on its telomere capping function, there is emerging evidence of a role for telomerase in stem-cell biology that does not involve its telomere maintenance function. In a series of transgenic studies, enforced TERT expression in the skin was shown to activate quiescent hair-follicle stem cells and stimulate hair growth. This TERT-induced stem-cell activation effect is not related to TERT’s classic telo mere synthesis activities, as it can occur on a telomerase-deficient background (Terc−/−) or with an enzymatically inactive TERT transgene68. These observations point to telomere-independent function of TERT in tissue stem-cell homeostasis, an area that gains added significance in light of the ability of human TERT to bind the RNA component (RMRP) of the ribonucleoprotein endoribonuclease (the RNase MRP complex)69. In the context of our model, this report is intriguing because the RNase MRP complex is involved in diverse cellular and mitochondrial functions; moreover, patients with mutations in RMRP develop cartilage–hair hypoplasia syndrome that is characterized by
