| Summary: | Summary: Embryonic stem cells (ESCs) cultured in leukemia inhibitory factor (LIF) plus fetal bovine serum (FBS) exhibit heterogeneity in the expression of naive and primed transcription factors. This heterogeneity reflects the dynamic condition of ESCs and their versatility to promptly respond to signaling effectors promoting naive or primed pluripotency. Here, we report that ESCs lacking Nanog or overexpressing Otx2 exhibit an early primed identity in LIF + FBS and fail to convert into 2i-induced naive state. Conversely, Otx2-null ESCs possess naive identity features in LIF + FBS similar to Nanog-overexpressing ESCs and convert poorly into FGF-induced early primed state. When both Nanog and Otx2 are inactivated, ESCs cultured in LIF + FBS exhibit primed identity and weakened ability to convert into naive state. These data suggest that, through mutual antagonism, NANOG and OTX2 specify the heterogeneous identity of ESCs cultured in LIF + FBS and individually predispose them for optimal response to naive or primed inducing factors. : In this article, Simeone and colleagues study the molecular mechanism controlling the heterogeneous and flexible identity of ESCs cultured in LIF + FBS. They analyze a series of ESC lines carrying different dosages of OTX2 and/or NANOG. They find that synergism between the OTX2 and NANOG antagonistic regulatory networks specifies the identity of ESCs in LIF + FBS. Keywords: embryonic stem cell heterogeneity, OTX2, NANOG, LIF signaling, pluripotency
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