strategies for reprogramming of adult cells: from nuclear transfer to induction of pluripotency using specific transcription factors

clinical application of embryonic stem (es) cells faces difficulties regarding tissue rejection as well as ethical limitations. one solution for these issues is to reprogram somatic cells by the injection of their nucleus into an enucleated oocyte or zygote. however, technical complications and ethical considerations have impeded the therapeutic implications of this technology. an approach which is most recently developed is in vitro induction of reprogramming in adult cells. this was first achieved by using four transcription factors, including oct4, sox2, c-myc and klf4. subsequently, many ongoing efforts were performed for enhancing this method, also for making it compatible with clinical applications. however, there is still a long road ahead. in this paper we review strategies to reprogram somatic cells to embryonic state and discuss about the recent strategy and the relevant developments.