Mechanisms that Regulate Self-renewal and Proliferation in Hematopoietic Stem Cells

造血干细胞（HSC）分化率和自体造血干细胞（自体造血干细胞）分化率是至关重要的。 更新是仔细调节和保持平衡，因为严重的疾病状态出现时， 平衡被打破了。不幸的是，人们对维持这种平衡的机制知之甚少， 这种缺乏了解是研究进展的主要障碍， 限制了基于HSC的治疗干预的临床潜力。研究的目标 本文旨在阐明调控HSC静止、自我更新和 分化，重点是关键的HSC调节因子，阴阳1（YY 1）。YY 1是一个无处不在的 锌指转录因子是小鼠HSC发育所必需的。我们最近的出版物 结果表明，YY1缺陷型HSC不能自我更新，不能维持静止状态。此外，委员会认为， 干细胞因子（SCF）/c-Kit信号传导是HSC发育的关键调控途径， 在YY1缺陷型HSC中显著下调。YY1占据远端增强子和启动子 在Kit基因座上的序列，并促进HSC中Kit基因的表达。因此，我们令人信服的数据 提示SCF/c-Kit通路是YY1调节HSC自身免疫的关键下游介质。 更新和静止。我们的初步数据也提供了强有力的证据， 抑制染色体结构维持（SMC）1和3，粘附素的核心成分 复合物，对于其在HSC中建立静止的能力至关重要。重要的是，有缺陷的HSC 在Yy 1缺失小鼠中的静止完全被Smc 3处的杂合性拯救。总的来说，我们的结果 支持YY 1调节HSC自我更新和静止的机制， 包括通过控制Kit基因座处的染色体结构变化来激活SCF/c-Kit信号传导， 和抑制粘附素。为了研究这一假设，我们用一种N-末端截短的YY1突变体， 缺乏YY1的转录激活和共激活因子募集功能，但保留了 YY1的转录抑制和DNA成环功能，将在骨髓中表达， YY 1-/-条件性敲除小鼠，其允许用以下评价YY 1作用机制： 在SCF/c-Kit信号传导、cohesin表达、HSC自我更新和增殖方面。另外还有按 将使用独特的YY 1-/-SMC 3 +/-条件性敲除小鼠品系研究机制 YY 1-调节粘附素的机制及其在决定HSC自我更新和分化中的重要性。 拟议的研究将阐明尚未充分表征的机制和途径， YY1参与以及其对HSC细胞命运的影响是如何介导的。这些机制可能 包括对染色质可及性YY 1依赖性效应、高级染色质/染色体 结构和/或激活/抑制靶基因，包括Kit和Smc 3。

It is of critical importance that the rates of hematopoietic stem cell (HSC) differentiation and self- renewal are carefully regulated and kept in balance, because severe disease states arise when this balance is disrupted. Unfortunately, the mechanisms that maintain this balance are poorly understood, and this lack of understanding represents a major impediment to research progress, while also severely restricting the clinical potential of HSC-based therapeutic interventions. The goal of the research proposed here is to elucidate mechanisms that regulate HSC quiescence, self-renewal and differentiation, with a focus on the critical HSC regulatory factor, Yin Yang 1 (YY1). YY1 is a ubiquitous zinc finger transcription factor that is essential for HSC development in mice. Our recent publication showed that YY1-deficient HSCs fail to self-renew and fail to maintain a quiescent state. Furthermore, Stem Cell Factor (SCF)/c-Kit signaling, a critical regulatory pathway in HSC development, is significantly downregulated in YY1-deficient HSCs. YY1 occupies the distal enhancer and promoter sequences at the Kit locus and promotes Kit gene expression in HSCs. Thus, our compelling data implicates the SCF/c-Kit pathway as a critical downstream mediator for YY1 in regulating HSC self- renewal and quiescence. Our preliminary data also provide strong evidence that YY1-dependent repression of Structural Maintenance of Chromosomes (SMC) 1 and 3, core components of the cohesin complex, are critical to its ability to establish quiescence in HSCs. Importantly, defective HSC quiescence in Yy1 null mice is completely rescued by heterozygosity at Smc3. Collectively, our results support the hypothesis that YY1 regulates HSC self-renewal and quiescence by mechanisms that include activation of SCF/c-Kit signaling by controlling chromosome structural change at the Kit locus, and repression of cohesin. To investigate the hypothesis, an N-terminally truncated YY1 mutant, which lacks the transcriptional activation and co-activator recruitment functions of YY1, but which retains transcriptional repression and DNA looping functions of YY1, will be expressed in the bone marrow of Yy1-/- conditional knockout mice, which allows the YY1 mechanism of action to be evaluated with respect to SCF/c-Kit signaling, cohesin expression, HSC self-renewal and proliferation. In addition, a unique Yy1-/- SMC3+/- conditional knockout mouse strain will be used to investigate the mechanism(s) by which YY1-regulates cohesin and its importance in determining HSC self-renewal and differentiation. The proposed studies will elucidate as yet poorly characterized mechanisms and pathways in which YY1 participates and how its effects on HSC cell fate are mediated. These mechanisms are likely to include YY1-dependent effects on chromatin accessibility, higher-order chromatin/chromosome structure and/or activation/repression of target genes including Kit and Smc3.