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Induced pluripotency requires the expression of defined factors and culture conditions that support the self-renewal of embryonic stem (ES) cells 1Takahashi K. Yamanaka S. Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors.Cell. 2006; 126: 663-676Abstract Full Text Full Text PDF PubMed Scopus (18861) Google Scholar. Small molecule inhibition of MAP kinase (MEK) and glycogen synthase kinase 3 (GSK3) with LIF (2i/LIF) provides an optimal culture environment for mouse ES cells 2Ying Q.L. Wray J. Nichols J. Batlle-Morera L. Doble B. Woodgett J. Cohen P. Smith A. The ground state of embryonic stem cell self-renewal.Nature. 2008; 453: 519-523Crossref PubMed Scopus (2534) Google Scholar and promotes transition to naive pluripotency in partially reprogrammed (pre-iPS) cells 3Silva J. Barrandon O. Nichols J. Kawaguchi J. Theunissen T.W. Smith A. Promotion of reprogramming to ground state pluripotency by signal inhibition.PLoS Biol. 2008; 6: e253Crossref PubMed Scopus (651) Google Scholar. Here we show that 2i/LIF treatment in clonal lines of pre-iPS cells results in the activation of endogenous Nanog and rapid downregulation of retroviral Oct4 expression. Nanog enables somatic cell reprogramming in serum-free medium supplemented with LIF, a culture condition which does not support induced pluripotency or the self-renewal of ES cells, and is sufficient to reprogram epiblast-derived stem cells to naive pluripotency in serum-free medium alone. Nanog also enhances reprogramming in cooperation with kinase inhibition or 5-aza-cytidine, a small molecule inhibitor of DNA methylation. These results highlight the capacity of Nanog to overcome multiple barriers to reprogramming and reveal a synergy between Nanog and chemical inhibitors that promote reprogramming. We conclude that Nanog induces pluripotency in minimal conditions. This provides a strategy for imposing naive pluripotency in mammalian cells independently of species-specific culture requirements.
Theunissen et al. (2010) studied this question.