甲基化酶Setd1a调控Oct4转录活性及其在干细胞特性维持和体细胞重编程中的作用和机制研究

Embryonic stem (ES) cells are pluripotent cell lines which can contribute differentiated progeny to all adult tissues. The pluripotent identity of ES cells is governed by a coordinated regulatory network consisting of signaling pathways, key transcriptional factors (e.g. Oct4, Sox2, Klf4 and c-Myc) and epigenetic regulatory factors. While much progress has been made in identification and characterization of the signaling pathways and transcriptional factors important for ES cell pluripotency, less is known for epigenetic regulatory factors involved, and their functional selectivity and specificity. We have carried out a systemic protein-protein interaction analysis examining the interaction of a large number of epigenetic regulatory factors with Oct4, Sox2, Klf4 and c-Myc and uncovered a specific interaction between Setd1a and Oct4. In this proposal, we will investigate the role of Setd1a in transcriptional program regulated by Oct4 and the underlying mechanism. A genome wide transcription and localization study will be carried to determine the transcriptional program and target genes regulated by Setd1a and the functional relationship between Setd1a and Oct4. In addition, we will determine the role of Setd1a in maintenance of ES pluripotency and reprogramming of somatic cells to induced pluripotency cells (iPS). This study will provide new insight into how the specific functional interplay between a transcription factor and epigenetic regulator contributes to regulation of pluripotency.

胚胎干细胞（ES）是一种具有全能性的干细胞，在特定条件下能特化成各种功能细胞，从而构成机体各种复杂的组织器官。研究表明ES细胞的全能性维持受细胞信号通路，核心转录因子(如Oct4, Sox2, Klf4和c-Myc)和表观调控因子等组成的网络协同调控，但表观调控因子的选择性和特异性目前还研究较少。通过系统分析表观调控因子和核心转录因子Oct4, Sox2, Klf4和c-Myc的相互作用，本课题前期工作发现组蛋白甲基化酶Setd1a能特异与Oct4相互作用。在此基础上，本课题拟重点研究Setd1a这一组蛋白H3K4甲基化酶在Oct4的转录调控中的作用，在基因组水平上研究确定Setd1a与Oct4靶基因的相关性，研究确定Setd1a在ES细胞干性维持和细胞重编程中的功能和作用机制。本项目的顺利实施将促进对干细胞核心转录因子与表观调控因子如何协同调控和维持干细胞命运的深入了解。

目前研究表明有限的几个核心转录因子和转录共调控因子在胚胎干细胞的转录调控及干性维持中起着重要作用，但核心转录因子与共调控因子之间如何相互作用及功能协同则还不清楚。我们较系统的分析了胚胎干细胞四个核心转录因子Oct4, Sox2, Klf4 和Myc (简称OSKM）与一系列共调控因子的相互作用，发现两者之间存在共同及特异的相互作用。我们发现在SET1/MLL家族H3K4甲基化酶中，Set1a特异地与Oct4相互作用并且这种相互作用不依赖于Wdr5。我们发现Set1a被Oct4招募至Oct4靶基因并且为Oct4靶基因启动子H3K4甲基化所必须。此外，我们发现Set1a为胚胎干细胞干性维持所必须并且促进体细胞向胚胎干细胞的重编程。基因表达谱式分析及基因组染色质免疫共沉淀分析发现Set1a广泛参与Oct4转录调控并且富集于基因启动子。基因敲除实验证明Set1a不仅为小鼠早期胚胎发育所必须，而且为产生表达Oct4的胚胎细胞所必须。我们的研究工作为OSKM与转录共调控因子的相互作用提供了有价值的信息并且为Set1a在胚胎干细胞及胚胎发育中的重要性提供了分子机制解释。