MLL Function in the Maintenance of the Blood Forming System

项目摘要 造血干细胞（HSCs）是最灵活和研究最多的组织干细胞之一 在哺乳动物中，并且对于治疗血液恶性肿瘤、先天性 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 操纵HSC以获得临床益处。我们的初步研究和发表的工作表明， 混合谱系白血病（MLL）蛋白对于在发育期间维持HSC是必需的， 体内平衡我们已经开发并利用条件性基因切除方法来定义一种 HSC依赖于MLL进行扩增的发育窗口。此窗口 与骨髓中造血的建立相吻合。我们还发现了一个 我们假设成年HSC中的小的、独特的基因网络是 MLL和MLL是其HSC维持功能的重要效应子。我们的总体目标是定义 MLL在胎儿和成人HSC中运作的遗传网络，因为HSC的关键特征 功能、增殖和自我更新在这两个发育阶段之间是不同的。到 为了实现这一目标，我们将：1）鉴定小鼠胎儿HSC中的MLL依赖性基因，并比较 2）使用人造血干细胞测定MLL在胎儿HSC中的结合模式， HSC富集群体，3）确定生态位和发展阶段，定义开始 MLL依赖性HSC扩增/稳态，以及4）定义MLL依赖性转录调控因子， 在成年鼠HSC中运作以促进自我更新的网络和机制。完成 这些目标将导致对一个关键但研究不足的途径的重要新见解， HSC的功能和自我更新。通过使用人类和小鼠模型系统的最佳功能， 将最先进的分子和基因组技术与严格的发育研究相结合， 我们希望发现安全有效的方法来操纵HSC以获得临床益处。

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.