Pluripotent stem cells
Embryonic stem cells (ES cells) are active during early development and give rise to all cell types of the organism. Nuclear reprogramming – whereby the nucleus from a differentiated somatic cell is reprogrammed to a pluripotent, embryonic-like state – was first achieved by nuclear transfer (injection of the nucleus of a differentiated cell into an undifferentiated cell, such as an oocyte) or by the fusion of somatic cells with ES cells. In 2006, Takahashi and Yamanaka reported that it is possible to reprogramme adult somatic cells to a pluripotent state by ectopically expressing four transcription factors and culturing the cells under ES cell-like conditions. The resulting cells were named 'induced pluripotent stem cells' (iPSCs).
The discovery of iPSCs has revolutionized the stem cell field, as it circumvents some of the technical challenges and ethical issues associated with the earlier nuclear reprogramming approaches. Reprogramming to iPSCs has enabled the detailed study of the intricate signalling pathways and molecular mechanisms that regulate pluripotency, cell fate specification and the stability of such states. Moreover, it has opened new therapeutic prospects, such as modelling and studying diseases, screening drugs and regenerating tissues. This specially commissioned Focus issue highlights the progress that has been made in understanding the molecular mechanisms underlying reprogramming and changes in cell fate, the properties of pluripotent stem cells (ES cells and iPSCs) and how they can be derived and maintained in culture. The articles also look at achievements, limitations and future challenges for the translation of stem cell research to the clinic.
