TET family members enzymes Factor Xa convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) in DNA. Here, we display that Tet1 and Tet2 are Oct4-regulated enzymes that with each other sustain 5hmC in mouse embryonic stem cells (ESCs) and are induced concomitantly with 5hmC all through reprogramming of fibroblasts selleck inhibitor to induced pluripotent stem cells. ESCs depleted of Tet1 by RNAi show diminished expression from the Nodal antagonist Lefty1 and show hyperactive Nodal signaling and skewed differentiation into the endoderm-mesoderm lineage in embryoid bodies in vitro. In Fgf4- and heparin-supplemented culture conditions, Tet1-depleted ESCs activate the trophoblast stem cell lineage determinant Elf5 and may colonize the placenta in midgestation embryo chimeras. Constant with these findings, Tet1-depleted ESCs type aggressive hemorrhagic teratomas with elevated endoderm, diminished neuroectoderm, and ectopic appearance of trophoblastic giant cells. So, 5hmC is definitely an epigenetic modification related to the pluripotent state, and Tet1 functions to regulate the lineage differentiation likely of ESCs.