MLL Function in the Maintenance of the Blood Forming System

项目摘要 造血干细胞(HSCs)是目前研究最广泛、最灵活的组织干细胞之一。 在哺乳动物中，并在临床上对治疗先天性血液系统恶性肿瘤具有重要意义 骨髓综合征和其他恶性肿瘤。我们对分子途径的理解 自我更新与差异化决策的基础不足以让我们安全地 为了临床利益而操纵造血干细胞。我们的初步研究和发表的工作表明， 混合血统白血病(MLL)蛋白是维持HSCs发育和 动态平衡。我们已经开发并利用条件基因消融方法来定义 发展的窗口，在此期间，HSC变得依赖MLL进行扩张。此窗口 与骨髓中造血功能的建立不谋而合。我们还确定了一个 我们推测成人HSCs中的小而独特的基因网络是其直接转录靶点 MLL是其HSC维持功能的重要效应者。我们的总体目标是定义 MLL在胎儿和成人HSC中运行的遗传网络，因为HSC的关键特征 在这两个发育阶段，细胞的功能、增殖和自我更新是不同的。至 为了实现这一目标，我们将：1)鉴定小鼠胚胎HSC中MLL依赖的基因并进行比较 这些与我们的成人HSC数据相一致，2)利用人类 富含HSC的种群，3)确定生态位和发育阶段，定义了 MLL依赖的HSC扩张/内稳态，以及4)定义MLL依赖的转录 成年小鼠造血干细胞促进自我更新的网络和机制。完成 这些目标将导致对一条关键但未被充分研究的调控途径的重要新见解 HSC功能与自我更新。通过利用人类和老鼠模型系统的最佳功能，以及 将最先进的分子和基因组技术与严格的发育研究相结合， 我们希望找到安全有效的方法来操纵HSCs，使其临床受益。

Project Summary Hematopoietic stem cells (HSCs) represent one of the most flexible and well-studied tissue stem cells in mammals, and are clinically important for the treatment of hematologic malignancies, congenital bone marrow syndromes, and other malignancies. Our understanding of the molecular pathways that underlie the self-renewal versus differentiation decisions is insufficient to allow us to safely manipulate HSCs for clinical benefit. Our preliminary studies and published work demonstrates that the Mixed Lineage Leukemia (MLL) protein is essential for sustaining HSCs during development and homeostasis. We have developed and utilized conditional gene ablation approaches to define a window of development in which HSCs become dependent on MLL for their expansion. This window coincides with the establishment of hematopoiesis in the bone marrow. We have also identified a small, unique network of genes in adult HSCs that we hypothesize are direct transcriptional targets of MLL and are important effectors of its HSC maintenance function. Our overall objective is to define the genetic network within which MLL operates in fetal and adult HSCs, since key features of HSC function, proliferation and self-renewal are distinct between these two developmental periods. To achieve this objective, we will: 1) identify MLL-dependent genes in murine fetal HSCs and compare these to our adult HSC data, 2) determine the pattern of MLL binding in fetal HSCs using human HSC-enriched populations, 3) determine the niche and developmental stage defining the beginning of MLL dependent HSC expansion/homeostasis, and 4) define the MLL-dependent transcriptional network and mechanisms that operate in adult murine HSCs to promote self-renewal. Accomplishing these aims will result in important new insights into a critical but understudied pathway that regulates HSC function and self-renewal. By using the best features of human and mouse model systems, and combining state-of-the-art molecular and genomic techniques with rigorous developmental studies, we hope to discover safe and effective means to manipulate HSCs for clinical benefit.