β-catenin associated protein complex maintains ground state mouse embryonic stem cell by regulating lineage development

Mouse embryonic stem (ES) cells cultured in defined medium with MEK and GSK3 inhibitors (2i) resemble the pre-implantation epiblast in the ground state, with full development capacity including the somatic lineages and the germline. Although β-catenin is known to be crucial for naive pluripotency of ES cells, the mechanism is not fully understood. Here we showed that β-catenin interacted with a repressive protein complex to maintain the ground state of ES cells by fine-tuning their lineage development potential. Absence of β-catenin impaired ES cell self-renewal without affecting the core self-renewal circuitry of Oct4, Sox2 and Nanog as well as other pluripotency factors. However, β-catenin-deficient cells showed a primed state transcriptional signature with perturbed expression of germline and neuronal lineage genes. Knockdown of Tcf7l1, the repressor in canonical Wnt signaling pathway, did not completely rescue the β-catenin-deficient phenotype of ES cells. Mechanistically, β-catenin formed a novel biochemical complex with E2F6, HP1γ and HMGA2 to restrain ES cells from differentiation by co-occupying the promoters of germline and neuronal lineage regulators independent of TCF7L1. Overall, out work showed that β-catenin maintained ground state ES cells by orchestrating their development plasticity through a repressive protein complex with E2F6, HP1γ and HMGA2.