Nuclear reprogramming by xenopus oocytes.

The aim of this contribution is to relate amphibian nuclear transplantation work to prospects for stem cell creation and hence to the long-term aim of cell replacement in humans. The methods used include the transplantation of single somatic cell nuclei to enudeated unfertilized eggs of Xenopus, and also the transfer of multiple somatic cell nuclei to the nucleus (germinal vesicle) of a growing ovarian oocyte. A key difference between these types of recipient cell is that eggs immediately induce DNA replication in transplanted nuclei, whereas an oocyte induces no DNA replication, but directly reprograms an injected nucleus to a new pattern of transcriptional activity. We summarize the extent and success of past and current nuclear reprogramming in experiments with enucleated frog eggs, and also those carried out with growing oocytes. We discuss possible mechanisms of nuclear reprogramming, and the possible contribution of such knowledge for stem cell creation and cell replacement in humans.