Yang, J. et al. Nature 550, 393–397 (2017).

Early in mammalian development, cells that will form embryonic tissues distinguish themselves from those that will form extraembryonic tissues. Existing culture methods cannot typically maintain cells in the high state of pluripotency that exists prior to this split, but Yang et al. have found a way to generate mouse stem cells with expanded potential. The researchers derived cell lines by culturing single cells from embryos in either the four-cell or eight-cell stage in a medium that blocks blastomere development using small-molecule inhibitors of mitogen-activated protein kinases (MAPKs), Src and Hippo pathways. The extended pluripotent stem cell (EPSC) lines contributed to both inner cell mass (embryonic) and trophectoderm (extraembryonic) tissue and could differentiate into any blastomere lineage. In addition, the culture medium could even induce greater extraembryonic potential in existing pluripotent stem cell lines.