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Letter

Nature Genetics 40, 921–926 (1 July 2008) | doi:10.1038/ng.173

Ras-MAPK signaling promotes trophectoderm formation from embryonic stem cells and mouse embryos

Chi-Wei Lu , Akiko Yabuuchi , Lingyi Chen , Srinivas Viswanathan , Kitai Kim & George Q Daley

In blastocyst chimeras, embryonic stem (ES) cells contribute to embryonic tissues but not extraembryonic trophectoderm. Conditional activation of HRas1Q61L in ES cells in vitro induces the trophectoderm marker Cdx2 and enables derivation of trophoblast stem (TS) cell lines that, when injected into blastocysts, chimerize placental tissues.