Introduction

Abstract

As cells proceed in normal development from embryonic and fetal stages to an adult state, they become increasingly committed to their differentiated state. Hardly ever do cells reverse this process and go back from a differentiated state to an embryonic one. Nevertheless, there are experimental procedures by which this reversal of differentiation can be induced. These include somatic cell nuclear transfer to eggs and oocytes and the fusion of adult with embryonic cells as was shown over 50 years ago. Nevertheless, the field of nuclear reprogramming received an enormous stimulus when it was shown by Takahashi and Yamanaka in 2006 that some fully differentiated cells could be induced by transcription factor overexpression (iPS) to form multipotential ES cells. These can then be directed into a wide range of differentiated states unrelated to that of the original cells. Although changes in cell differentiation by overexpression of particular transcription factors had been shown many years before, the sucess with which the reversal to an iPS state took place was a surprise to everyone. The iPS-derived embryonic stem cells have the ability to proliferate indefinitely as embryonic stem cells but are then able to differentiate into many different somatic cell types as well as germ cells.