MLL Function in the Maintenance of the Blood Forming System

描述(申请人提供)：造血干细胞(HSCs)是哺乳动物中最灵活和研究最充分的组织干细胞之一，在治疗血液系统恶性肿瘤、先天性骨髓综合征和其他恶性肿瘤方面具有重要的临床意义。我们对自我更新与分化决策背后的分子途径的了解不足以让我们安全地操纵造血干细胞用于临床。 利益。我们的初步研究和发表的工作表明，混合血统白血病(MLL)蛋白对于维持HSCs的发育和动态平衡是必不可少的。我们已经开发和利用了有条件的基因消融方法来定义一个发育窗口，在这个窗口中，造血干细胞变得依赖MLL进行扩张。这一窗口与骨髓中造血的建立不谋而合。我们还在成人HSC中发现了一个小的、独特的基因网络，我们假设它是MLL的直接转录靶点，并且是其HSC维持功能的重要效应者。我们的总体目标是确定MLL在胎儿和成人HSCs中运行的遗传网络，因为这两个发育时期HSC功能、增殖和自我更新的关键特征是不同的。为了实现这一目标，我们将：1)在小鼠胎儿HSC中识别MLL依赖的基因，并将这些基因与我们的成人HSC数据进行比较；2)利用人类HSC丰富的群体来确定胎儿HSC中MLL结合的模式；3)确定定义MLL依赖的HSC扩增/动态平衡的开始的生态位和发育阶段；以及4)确定在成年小鼠HSC中运行以促进自我更新的MLL依赖的转录网络和机制。实现这些目标将为调节HSC功能和自我更新的关键但未被研究的途径带来重要的新见解。通过利用人类和小鼠模型系统的最佳特征，并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。 与公共健康相关：在成年哺乳动物的一生中，造血或造血系统必须不断地再生所有类型的血细胞。这种再生最终是由一小群独特的被称为造血干细胞(HSCs)的细胞来推动的。这种细胞类型是骨髓移植成功的基础，骨髓移植是治疗白血病和其他血液疾病的一种方法。我们建议研究由混合血统白血病(MLL)基因调控的分子途径，因为该基因对于维持小鼠的HSCs和整个造血系统是必不可少的，我们假设也是在人类。我们将使用最先进的基因组方法和基因工程动物模型来确定成人和胎儿造血干细胞中MLL控制的分子通路。通过了解这些通路是如何调控的，我们将揭示扩大造血干细胞的方法的基本新见解，以及对白血病启动机制的见解。

DESCRIPTION (provided by applicant): 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. PUBLIC HEALTH RELEVANCE: The hematopoietic or blood-forming system must continuously regenerate all blood cell types throughout the lifetime of adult mammals. This regeneration is ultimately fueled by a small and unique population of cells termed hematopoietic stem cells (HSCs). This cell type underlies the success of bone marrow transplantation, which is a treatment for leukemia and other blood disorders. We propose to investigate the molecular pathways that are regulated by the Mixed Lineage Leukemia (MLL) gene, because this gene is essential for sustaining HSCs and the entire hematopoietic system in mice and, we hypothesize, in humans. We will determine the molecular pathways controlled by MLL in adult and fetal hematopoietic stem cells using state-of- the art genomic approaches coupled with genetically engineered animal models. By understanding how these pathways are regulated, we will reveal fundamental new insights into methods to expand HSCs and insights into the mechanisms by which leukemia is initiated.