TY - JOUR T1 - Endogenous epitope-tagging of <em>Tet1</em>, <em>Tet2</em> and <em>Tet3</em> identifies TET2 as a naïve pluripotency marker JF - Life Science Alliance JO - Life Sci. Alliance DO - 10.26508/lsa.201900516 VL - 2 IS - 5 SP - e201900516 AU - Raphaël Pantier AU - Tülin Tatar AU - Douglas Colby AU - Ian Chambers Y1 - 2019/10/01 UR - https://www.life-science-alliance.org/content/2/5/e201900516.abstract N2 - Tet1, Tet2, and Tet3 encode DNA demethylases that play critical roles during stem cell differentiation and reprogramming to pluripotency. Although all three genes are transcribed in pluripotent cells, little is known about the expression of the corresponding proteins. Here, we tagged all the endogenous Tet family alleles using CRISPR/Cas9, and characterised TET protein expression in distinct pluripotent cell culture conditions. Whereas TET1 is abundantly expressed in both naïve and primed pluripotent cells, TET2 expression is restricted to the naïve state. Moreover, TET2 is expressed heterogeneously in embryonic stem cells (ESCs) cultured in serum/leukemia inhibitory factor, with expression correlating with naïve pluripotency markers. FACS-sorting of ESCs carrying a Tet2Flag-IRES-EGFP reporter demonstrated that TET2-negative cells have lost the ability to form undifferentiated ESC colonies. We further show that TET2 binds to the transcription factor NANOG. We hypothesize that TET2 and NANOG co-localise on chromatin to regulate enhancers associated with naïve pluripotency genes. ER -