Pluripotency in mouse embryonic stem cells (mESCs) is controlled by a transcriptional network regulated by three core transcription factors: Nanog, Oct4, and Sox2 (reviewed in Silva an d Smith, 2008; Nichols and Smith, 2009; Wray and Hartmann, 2012). Extrinsic signaling molecules including leukemia inhibitory factor (LIF) and Wnts influence the balance between pluripotency and differentiation in a context-dependent manner (Okita and Yamanaka, 2006; Loh et al., 2015). The primary consequence of Wnt stimulus is stabilization of β-catenin, a nuclear effector that activates transcription of target genes together with the lymphoid enhancer factor/T cell factor (TCF) family of transcription factors (Valenta et al., 2012). In addition to its nuclear functions, much of the cellular β-catenin is membrane localized at adherens junctions, where it interacts with E-cadherin and α-catenin (Valenta et al., 2012). The Wnt/β-catenin pathway is important for early embryonic development of metazoans, particularly in the specification of the body axis and patterning of mesendoderm and neural lineages (Nusse and Varmus, 2012; Oates et al., 2012; Park and Shen, 2012). Exogenous addition of Wnt proteins to mESCs has been shown to activate TCF target genes while promoting self-renewal and inhibiting differentiation (Sato et al., 2004; Ogawa et al., 2006; Singla et al., 2006; Ying et al., 2008; Wagner et al., 2010; ten Berge et al., 2011). By contrast, studies have also suggested that Wnt activity is low in self-renewing embryonic stem cells (ESCs) and is activated during differentiation (Davidson et al., 2012; Marks et al., 2012; Faunes et al., 2013), raising the question of whether TCF-mediated transcription is required for pluripotency. The primary evidence for direct regulation of the pluripotency transcriptional network (PTN) by Wnt/β-catenin pathway comes from studies involving TCF3 (TCF7L1), a transcriptional repressor of Wnt target genes (Cole et al., 2008; Zhang et al., 2013) that promotes differentiation by directly inhibiting the PTN (Wray et al., 2011; Yi et al., 2011). It is thought that β-catenin alleviates TCF3’s repressive function by binding to TCF3 and removing it from the DNA, thereby promoting self-renewal (Wray et al., 2011; Shy et al., 2013). Although β-catenin has been implicated in influencing PTN activity (Merrill, 2012), the precise interactions by which

The ability of mouse embryonic stem cells (mESCs) to self-renew or differentiate into various cell lineages is regulated by signaling pathways and a core pluripotency transcriptional network (PTN) comprising Nanog, Oct4, and Sox2. The Wnt/β-catenin pathway promotes pluripotency by alleviating T cell factor TCF3-mediated repression of the PTN. However, it has remained unclear how β-catenin’s function as a transcriptional activator with TCF1 influences mESC fate. Here, we show that TCF1-mediated transcription is up-regulated in differentiating mESCs and that chemical inhibition of β-catenin/TCF1 interaction improves long-term self-renewal and enhances functional pluripotency. Genetic loss of TCF1 inhibited differentiation by delaying exit from pluripotency and conferred a transcriptional profile strikingly reminiscent of self-renewing mESCs with high Nanog expression. Together, our data suggest that β-catenin’s function in regulating mESCs is highly context specific and that its interaction with TCF1 promotes differentiation, further highlighting the need for understanding how its individual protein–protein interactions drive stem cell fate.