Role of MLL 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。NSC的命运由许多平行表达的基因的集体作用控制，并且染色质重塑是协调基因组的激活和抑制的表观遗传机制。该提案的重点是Mll（混合谱系白血病），一种与果蝇三胸相关的染色质重塑因子。三胸组（trxG）和多梳（PcG）基因产物是进化上保守的染色质重塑系统的一部分，其分别选择性地维持和沉默基因表达。PcG成员Bmi 1是NSC自我更新所必需的; trxG成员Mll在神经发育中的作用尚不清楚。我们的初步研究表明，MII缺陷的神经干细胞在出生后的大脑脑室下区（SVZ）可以生存，增殖，并有效地分化成胶质细胞谱系，然而，神经元分化严重受损。因此，Mll似乎维持特异性指导神经发生而非胶质细胞发生的转录程序。我们假设Mll在特定神经元谱系的神经发育中广泛需要。为了检验这一假设并定义MII在神经谱系特化中所起的作用，我们将利用我们的条件性敲除小鼠模型追求三个具体目标。在目标1中，我们将进一步鉴定和表征来自SVZ的MII依赖性谱系，SVZ是成年哺乳动物脑中最大的神经干细胞库。在目的2中，我们将研究Mll在齿状回颗粒下层（SGL）的神经干细胞中的作用，SGL是另一个出生后/成年的神经干细胞群体。在目标3中，我们将通过将Mll缺失靶向更广泛和更早的NSC群体来发现Mll在胚胎神经发育中发挥的作用。总之，这些目标的数据奠定了基础，为当前和未来的调查不同的神经谱系是如何通过特定的染色质重塑因子表观遗传“编程”。 公共卫生相关性： 神经干细胞（NSC）有望用于治疗神经系统疾病，了解NSC分化为神经元和神经胶质细胞的分子机制是释放其治疗潜力的关键。我们的研究项目旨在确定调节神经干细胞（NSC）自我更新和分化的分子机制。对于神经干细胞制造神经元，子细胞需要表达某些基因，同时抑制其他基因。这种谱系特异性转录程序的维持部分受染色质结构的调节-DNA与组蛋白的“包装”状态。目前在我的实验室的工作表明，MLL染色质重塑因子是从神经干细胞的神经元分化所必需的;胶质细胞分化正常发生没有MLL，这表明MLL保持一个转录程序的神经发生特异性。我们已经开始确定MLL的遗传靶点。我们计划使用细胞生物学和分子方法来研究MLL如何维持神经发生特异性的转录程序。这些信息将有助于突出的努力，“程序”特定的神经元谱系从神经干细胞用于治疗目的，如那些来自胚胎干细胞。因此，来自这些拟议研究的数据为开发基于细胞的治疗方法奠定了基础，这些治疗方法用于我们退伍军人群体中的服务相关损伤以及神经退行性疾病。

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. NSC fate is controlled by the collective action of many genes expressed in parallel, and chromatin remodeling is an epigenetic mechanism that coordinates the activation and repression of sets of genes. This proposal focuses on Mll (Mixed lineage leukemia), a chromatin remodeling factor related to Drosophila Trithorax. The trithorax group (trxG) and Polycomb (PcG) gene products are part of an evolutionarily conserved chromatin remodeling system that selectively maintain and silence gene expression, respectively. PcG member Bmi1 is required for NSC self-renewal; roles for trxG member Mll in neural development are unknown. Our Preliminary Studies indicate that Mll-deficient NSCs in the postnatal brain subventricular zone (SVZ) can survive, proliferate, and efficiently differentiate into glial lineages; however, neuronal differentiation is severely impaired. Thus, Mll appears to maintain a transcriptional program that specifically instructs neurogenesis and not gliogenesis. We hypothesize that Mll is broadly required in neural development for specific neuronal lineages. To test this hypothesis and to define the roles that Mll plays in neural lineage specification, we will pursue three specific aims utilizing our conditional knockout mouse model. In Aim 1, we will further identify and characterize the Mll-dependent lineages from the SVZ, the largest repository of NSCs in the adult mammalian brain. In Aim 2, we will investigate the role that Mll plays in the NSCs of the dentate gyrus subgranular layer (SGL), the other postnatal/adult NSC population. In Aim 3, we will discover the roles that Mll plays in embryonic neural development by targeting Mll deletion to a broader and earlier population of NSCs. Together, data from these Aims lay the groundwork for current and future investigations of how distinct neural lineages are epigenetically "programmed" by specific chromatin remodeling factors. PUBLIC HEALTH RELEVANCE: Neural stem cells (NSCs) hold promise for the treatment of neurological disorders, and understanding the molecular mechanisms by which NSCs differentiate into neurons and glia is key to unlocking their therapeutic potential. Our research projects are aimed at determining the molecular mechanisms that regulate neural stem cell (NSC) self-renewal and differentiation. For NSCs to make neurons, daughter cells need to express certain sets of genes while repressing others. The maintenance of such lineage-specific transcriptional programs is in part regulated by chromatin structure - the "packaged" state of DNA with histone proteins. Current work in my lab demonstrates that the MLL chromatin remodeling factor is required for neuronal differentiation from NSCs; glial differentiation occurs normally without MLL, suggesting that MLL maintains a transcriptional program specific for neurogenesis. We have begun to identify the genetic targets of MLL. We plan to use both cell biology and molecular approaches to investigate how MLL maintains a transcriptional program specific for neurogenesis. Such information will contribute prominently to the efforts to "program" specific neuronal lineages from NSCs intended for therapeutic purposes, such as those derived from embryonic stem cells. Thus data from these proposed studies lay the groundwork for the development of cell-based therapies for both service-related injuries as well as neurodegenerative diseases in our veteran population.