Chapter 4 - Induced pluripotency and intrinsic reprogramming factors: adult stem cells versus somatic cells

Abstract

Induced pluripotency has indeed revolutionized the field of pluripotent stem cell biology for one and a half decades. However, embryonic stem cells (ESCs) have been finding their research application since the early eighties. Moreover, cell therapy applications using human ESCs had significant concerns such as ethical issues due to the destruction of the embryos and teratoma-forming potential. The former has been, however, sorted out with the advent of induced pluripotent stem cells (iPSCs), although the latter issue is similar in both ESC and iPSC differentiated cell types. As a rule of thumb, any somatic cell devoid of intrinsic pluripotency factors such as Oct3/4, Nanog, Sox2, Klf4, c-Myc, Lin28 will need at least four of the reprogramming factors to convert such somatic cells into iPSCs. However, depending on the intrinsic expression of one or two or sometimes more of the reprogramming factors, that is mostly seen in progenitor or adult stem cells, the reprogramming process requires not all the factors. Here, we have reviewed various cell types having an endogenous expression of reprogramming factors and their conversion into iPSC. Along-with, we have also reviewed various mechanisms-genetic or epigenetic that enables such cell types with endogenous expression of reprogramming factors for conversion into iPSCs.