Role of MLL1 chromatin remodeling factor in neural stem cells

描述（由申请人提供）： 神经干细胞（NSC）有望用于治疗神经系统疾病，了解NSC神经发生和胶质细胞发生的分子机制是释放其治疗潜力的关键。成年人的大脑-包括人类的大脑-在脑室下区（SVZ）中含有一群NSC。神经干细胞如何“忘记”其干细胞身份的表观遗传记忆，并“学习”神经发生和胶质细胞发生的发育程序是知之甚少。Mll 1（Mixed lineage leukemia-1）是一种与三胸果蝇（Drosophila Trithorax）相关的染色质重塑因子，它可以通过介导细胞的应用来调节细胞的身份。 或去除特定的染色质修饰。我们先前表明，Mll 1是来自出生后SVZ NSC的神经元而不是神经胶质细胞的发生所需的（Nature 2009，458：529- 33）。新兴的研究表明，不同的染色质签名在DNA调控元件称为增强子决定特定基因启动子的转录活性，但很少有人知道如何在增强子的染色质状态进行调节。在初步研究中，我们表明MLL 1通过调节基因间增强子元件促进神经原性基因Dlx 2和Dlx 5的表达（手稿提交给Nature Cell Bio）。我们的染色质分析支持一个模型，其中MLL 1保持增强子处于“平衡”状态，以促进神经元分化过程中的快速基因激活。此外，我们发现MLL 1是定位JMJD 3所必需的，JMJD 3是一种组蛋白去甲基化酶，能够去除组蛋白3在赖氨酸27（H3 K27 me 3）处的抑制性三甲基化。为了研究JMJD 3在成人神经发生中的作用，我们在体内和体外用条件性敲除和shRNA介导的敲除研究了JMJD 3功能丧失。事实上，JMJD 3缺陷型SVZ神经干细胞在神经发生方面有缺陷，但在胶质细胞生成方面没有缺陷。基于这些新数据，我们假设MLL 1通过靶向特异性增强子元件协调多能NSC的神经元分化，使其能够通过JMJD 3的作用快速激活。在本申请中，我们提出了测试这种调节模型的特定目标，该模型对一般发育具有广泛的影响，并进一步确定MLL 1在神经发育中的作用。

DESCRIPTION (provided by applicant): Neural stem cells (NSCs) hold promise for the treatment of neurological disorders, and understanding the molecular mechanisms of NSC neurogenesis and gliogenesis is key to unlocking their therapeutic potential. The adult brain - including that of humans - harbors a population of NSCs in the subventricular zone (SVZ). How NSCs 'forget' the epigenetic memory of their stem cell identity and 'learn' the developmental programs for neurogenesis and gliogenesis is poorly understood. Mll1 (Mixed lineage leukemia-1), a chromatin-remodeling factor related to Drosophila Trithorax, can regulate cellular identity by mediating the application or removal of specific chromatin modifications. We previously showed that Mll1 is required for the genesis of neurons - but not glial cells - from postnatal SVZ NSCs (Nature 2009, 458:529- 33). Emerging studies indicate that distinct chromatin signatures at DNA regulatory elements called enhancers determine the transcriptional activity of specific gene promoters, but little is known about how the chromatin-state at enhancers is regulated. In Preliminary Studies, we show that MLL1 promotes the expression of neurogenic genes Dlx2 and Dlx5 by regulating intergenic enhancer elements (manuscript submitted to Nature Cell Bio). Our chromatin analysis supports a model in which MLL1 maintains enhancers in a 'poised' state to facilitate rapid gene activation during neuronal differentiation. Furthermore, we found that MLL1 is required for the localization of JMJD3, a histone demethylase capable of removing repressive trimethylation of histone 3 at lysine 27 (H3K27me3) at poised enhancer elements. To investigate the role of JMJD3 in adult neurogenesis, we studied JMJD3-loss of function in vivo and in vitro with conditional knockout and shRNA-mediate knockdown. Indeed, JMJD3-deficient SVZ NSCs were defective for neurogenesis, but not gliogenesis. Based on these new data, we hypothesize that MLL1 coordinates neuronal differentiation from multipotent NSCs by targeting specific enhancer elements, enabling their rapid activation by the action of JMJD3. In this application, we propose Specific Aims that test this regulatory model, which has broad implications for development in general, and further determine the role of MLL1 in neural development.