胚胎干细胞具有体外培养无限增殖，同时保持特定条件下定向分化为个体几乎所有的细胞类型的特点。因此，它为再生医学打开了机会之门。然而，胚胎干细胞维持自我更新的具体分子机制至今仍知之甚少。利用基于CRISPR/Cas9的基因编辑技术，我们在胚胎干细胞中逐个完全剔除多梳蛋白超家族的已知成员，结果显示Pcgf6及其所在非经典PRC1.6复合物在胚胎干细胞的自我更新维持中起关键作用。蛋白组学和免疫沉淀技术进一步揭示,PRC1.6复合物还包括DREAM复合物的核心成员，而DREAM复合物是细胞周期调控的中心环节。本课题研究的目的是运用多学科技术手段，深入探讨PRC1.6及其所包含DREAM复合物的主要成员Lin54在胚胎干细胞自我更新中的作用及其分子机制。本课题的顺利开展不仅能进一步揭示干细胞自我更新的分子机制，而且能为干细胞技术向临床应用的转化奠定理论基础。

Embryonic stem cells (ESCs) have an indefinitely unlimited capacity for self-renewal and can differentiate into virtually all of the cell types building our body, which holds significant promise for applications in regenerative medicine. However, the underlying genetic and epigenetic mechanisms that control self-renewal are largely unknown. Polycomb Group (PcG) proteins are best known for their role in maintaining the pluripotent state of ESCs, but their potential functions in self-renewal remain elusive. To address the role of PcG family in ESCs, we used an independently designed CRISPR-Cas9-based screening to identify genes from this family that are essential for the self-renewal of ES cells. We find that Pcgf6 is the only member of the Pcgf family which is critical for the maintenance of the self-renewal state of ES cells. Furthermore, deletion of L3mbtl2, Max and MGA, other core components of Pcgf6-mediated PRC1.6 (Polycomb Repressive Complex1.6), results in compromised proliferation of ESCs. The overall objective of this study is to comprehensively define the role of Pcgf6-containing PRC1.6 complex as well as Lin54, a core component of DREAM complex, in ESCs to determine their function at the molecular mechanistic level. To address these questions, we take advantage of a multidisciplinary approach, which included genetic, molecular, biochemical and cellular probes. The proposed study will not only reveal the molecular mechanism governing stem cell self-renewal but also offer basic knowledge that is required for realizing the potential of stem cell-based therapies.