多梳蛋白复合体组分EED在小脑发育中的功能研究

The cerebellum is critically important in normal development of central nervous system. The developmental defects of the cerebellum can result in motor, autism and higher cognitive dysfunctions. However, the molecular and cellular mechanisms underlying neurodevelopment have remained elusive. Recent studies have shown a link between aberrant histone modification and neurodevelopmental disorders. This proposed project will focus on the functions of histone methyltransferase PRC2 (Polycomb Repressive Complex 2). EED (embryonic ectoderm development) is a core component of PRC2 which catalyzes histone H3 lysine 27 trimethylation(H3K27me3). Trimethylated H3K27 (H3K27me3) can mediates the process of gene silencing and chromatin condensation. Although previous studies indicate that EED is required for self-renewal, proliferation and differentiation of ESCs, its function in mammalian nervous system especially in control of cerebellum development has remained unclear. We used a conditional knockout of EED mice for model, demonstrating that loss of EED in the brain led to striking abnormalities of motor and cerebellar hypoplasia. Finally, we will identify key downstream targets of EED in the development of cerebellum. This project will provide new evidence to understand the mechanisms of EED mutations that lead to cerebellum defects and Weaver's syndrome with autism disorders.

小脑在神经系统发育中发挥重要作用。小脑发育缺陷导致运动功能障碍，自闭症以及高阶认知行为缺陷，但其背后的分子调控机理，尤其表观遗传调控机制待深入揭示。研究发现，组蛋白修饰异常与这些神经发育疾病密切相关。本课题将以组蛋白甲基转移酶PRC2为研究对象。其中EED作为PRC2的一个核心组分，能够催化H3K27me3使其水平升高，压缩染色质发挥转录抑制功能。前期报道EED在胚胎干细胞的自我更新，增殖和分化中起作用，但是其在哺乳动物神经系统尤其是小脑发育中，EED的功能目前没有发现。我们利用EED条件性敲除小鼠为模型，初步分析表明EED缺失后小鼠运动功能障碍，小脑发育不全。因此，我们拟进一步筛选鉴定分析EED作用的下游信号通路，探索EED在小脑发育中的关键作用靶点，为理解EED缺失导致的小脑发育不全以及EED突变导致的weaver综合症伴发自闭症的发病机制，提供一个新思路。

EED是多梳蛋白复合物 2 (PRC2) 的核心亚基，可感知组蛋白H3赖氨酸27(H3K27) 的三甲基化。新出现的证据表明，EED 在胚胎干/祖细胞的自我更新、增殖和分化过程中起着重要作用。然而，其在小脑发育中的生物学功能仍然未知。在这里，我们表明，从神经干细胞 (NSC) 或小脑颗粒细胞祖细胞 (GCP) 中敲除 EED 会导致小鼠 GCP 增殖延迟、细胞死亡、小脑发育不全和运动缺陷减少。小脑颗粒细胞的 RNA-seq 和 ChIP-Seq 联合分析表明，EED 调节参与小脑发育的相关基因表达。重要的是，NSC 和 GCP 中的 EED 敲除表现出TGF-β信号通路的增强。TGF-β信号的过度激活是导致小鼠运动缺陷的原因。因此，我们的研究表明，EED 通过 H3K27me3 依赖性抑制TGF-β信号传导对小脑形态和控制小脑发育起着至关重要的作用。