Probing the coordination of cell cycle progression and differentiation in hematopoietic stem cells

摘要 造血干细胞（HSC）在成人中产生所有成熟的血细胞。他们保持沉默， 但当需要时，可以重新进入细胞周期，以自我更新或分化和补充细胞周期。 造血系统虽然调控HSC自我更新的途径刚刚被发现， 说明HSC分化在很大程度上仍然是难以捉摸的。最近的研究表明，居住在离散阶段， 细胞周期的变化增强了不同来源的胚胎干细胞和成体干细胞的分化。但 细胞周期驻留对HSC分化的影响还没有被直接研究。在这里，我们报告 在染色质修饰剂Sin3B的遗传失活后引起的造血表型。Sin3B作为 一种支架蛋白，通过与序列特异性 转录因子和组蛋白修饰剂。通过其调节细胞周期基因转录的能力 Sin3B通过细胞周期的早期阶段限制进展。Sin3B缺失的HSC保留了它们的自我- 更新能力，但它们无法正确区分。血统的恰当表达 特异性转录因子表明，染色质景观的改变可能决定了 Sin3B-/-HSC的分化缺陷。因此，Sin3B失活提供了一个独特的机会，研究 将细胞周期进程与允许转录的转录环境的产生联系起来的过程， HSC分化。我们的中心假设是，HSC的分化能力仅限于一个离散的细胞周期。 在细胞周期的早期阶段的窗口。我们将测试Sin3B的丢失诱导伪 通过细胞周期的早期阶段的进展，这与适当的HSC分化不相容，由于 染色质景观的改变。我们在这里建议：建立是否Sin3B依赖性限制的 细胞周期进展使得HSC分化成为可能（目的1）。使用细胞周期报告，谱系追踪工具和 单细胞转录组学分析，我们将利用Sin3B失活引起的表型， 确定HSC中细胞周期进展和分化之间的功能关系;以及 确定HSC中Sin3B依赖性分化的分子基础（目的2）。 可及性分析和组蛋白标记的全基因组定位，我们将确定 使HSC能够在细胞周期进程中对促分化刺激作出反应。根据我们初步的 数据，我们将测试我们在Sin3B-/-HSC中发现的特定信号通路改变的假设，包括 紧张性干扰素反应，调节HSC分化的能力。我们提出的工作将确定一个 细胞周期进程和造血分化之间的分子联系尚未充分研究，指出 用于治疗目的的调节HSC扩增和分化的潜在方法。

ABSTRACT Hematopoietic stem cells (HSCs) generate all mature blood cells in adults. They remain quiescent at homeostasis but when needed, can reenter the cell cycle to either self-renew or differentiate and replenish the hematopoietic system. While the pathways governing HSC self-renewal are just being uncovered, what dictates HSC differentiation remains largely elusive. Recent studies indicate that residence in discrete phases of the cell cycle potentiates differentiation in embryonic and adult stem cells of different origins. However, the impact of cell cycle residence on HSC differentiation has not been directly explored. Here, we report the hematopoietic phenotypes elicited upon genetic inactivation of the chromatin modifier Sin3B. Sin3B serves as a scaffold protein that tethers repressive activities to discrete loci by interacting with sequence-specific transcription factors and histone modifiers. Through its ability to modulate transcription of cell cycle genes Sin3B restricts progression through the early phases of the cell cycle. Sin3B-deleted HSCs retain their self- renewal capacities, but they are unable to properly differentiate. The appropriate expression of lineage specification transcription factors suggests that alterations of the chromatin landscape likely dictate the defective differentiation in Sin3B-/- HSCs. Thus, Sin3B inactivation provides a unique opportunity to study the processes linking cell cycle progression with the generation of a transcriptional environment permissive for HSC differentiation. Our central hypothesis is that the ability of HSCs to differentiate is restricted to a discrete window within the early phase of the cell cycle. We will test the possibility that loss of Sin3B induces spurious progression through early stages of the cell cycle, which is incompatible with proper HSC differentiation, due to alterations in the chromatin landscape. We propose here to: Establish whether Sin3B-dependent restriction of cell cycle progression enables HSC differentiation (aim 1). Using cell cycle reporters, lineage tracing tools and single cell transcriptomic analyses, we will leverage the phenotypes elicited upon Sin3B inactivation to determine the functional relationship between cell cycle progression and differentiation in HSCs; and Determine the molecular bases for Sin3B-dependent differentiation in HSCs (aim 2).Through chromatin accessibility assays and genome-wide mapping of histone marks, we will determine the chromatin features that enable HSCs to respond to pro-differentiation stimuli during cell cycle progression. Based on our preliminary data, we will test the hypothesis that specific signaling pathways we found altered in Sin3B-/- HSCs, including the tonic interferon response, modulate the ability of HSCs to differentiate. Our proposed work will define an understudied molecular link between cell cycle progression and hematopoietic differentiation, pointing to potential approaches to modulate HSC expansion and differentiation for therapeutic purposes.