Chromatin Organization Regulates Osteogenesis

摘要 这个新的 R01 建立在 R37 时期（2008-2018）的发现之上，这些发现建立了表观遗传机制 （miRNA、组蛋白修饰）调节成骨细胞分化。我们首次表征了 特定组蛋白修饰的“签名”，与基因表达的动态变化相关 成骨的时间进展。这些组蛋白修饰也预测了“增强子”，即 有助于局部基因表达的关键顺式调控元件。我们现在建议审查最近 公认的“超级增强子”结构域 (SED)，其中包含多个转录因子的调控元件 已成为细胞表型的关键调节因子。 SED 通过远距离在染色质组织中发挥作用 染色体内和染色体间的相互作用，协调负责谱系的基因群的控制 规格和独特的细胞身份。我们的初步研究已经确定了 SED 的一个子集，我们现在 提出的是假定的“骨必需超级增强剂”和重要决策阶段的候选者 MSC 致力于成骨。我们假设超级增强子域是不同的 从未分化的MSC激活到成骨细胞定型阶段，并发挥建立成骨细胞的功能 通过协调调节基因网络并促进高阶染色质来形成成骨表型 支持细胞身份的组织。我们的研究将： 目标 1 - 分析优先 SED 的功能效果 我们通过定向抑制和鉴定与成骨细胞生成和成熟骨活性相关 在 MSC 中使用 CRISPR/Cas9 激活 SED；目标 2-确定相互作用的染色体结构域 使用 SED 来控制多个基因和网络，通过这些基因和网络将 MSC 转变成成骨细胞表型 染色质组织；目标 3 - 在小鼠模型中证明使用 CRISPR 激活 MSC 中的 SED 会刺激骨骼形成。 影响：这些研究开创了 MSC 谱系对成骨作用的基因调控新水平， 基于对其他组织中 SED 功能的新认识，但在骨骼中的研究很少。 通过表征 MSC 中与染色质组织和稳定相关的 SED 机制，我们将发现 转录中枢和蛋白质复合物多维坐标控制的新机制 SED 负责建立对成骨细胞表型的承诺。重要的是，知识 稳定成骨表型的染色质组织对未来新型治疗策略的影响 用于骨骼疾病。

SUMMARY This new R01 builds on discoveries during the R37 period (2008-2018) that established epigenetic mechanisms (miRNAs, histone modifications) regulating osteoblast differentiation. We characterized for the first time a “signature” of specific histone modifications that are associated with dynamic changes in gene expression during the temporal progression of osteogenesis. These histone modifications also predicted “enhancers”, which are critical cis-regulatory elements that contribute to local gene expression. We now propose to examine the recently recognized “super enhancer” domains (SEDs) that include regulatory elements for multiple transcription factors that have emerged as key regulators of cell phenotypes. SEDs function in chromatin organization via long range intra- and inter-chromosomal interactions that coordinate control of gene cohorts responsible for lineage specification and distinct cell identity. Our preliminary studies have identified a subset of SEDs that we now propose are putative “bone-essential super-enhancers” and candidates for the important decision stage of commitment to osteogenesis from MSCs. We hypothesize that super-enhancer domains are differentially activated from the undifferentiated MSC to the osteoblast commitment stage, and function to establish the osteogenic phenotype by coordinately regulating gene networks and contributing to higher order chromatin organization that supports cell identity. Our studies will in: Aim1- analyze the functional effects of prioritized SEDs we have identified related to osteoblastogenesis and mature bone activities through directed inhibition and activation of SEDs using CRISPR/Cas9 in MSCs; Aim 2- determine the chromosomal domains that interact with SEDs to control multiple genes and networks that commit MSCs to the osteoblast phenotype through chromatin organization; and Aim 3- demonstrate in mouse models that using CRISPR activated SEDs in MSCs will stimulate bone formation. Impact: These studies pioneer a new level of gene regulation for MSC lineage commitment to osteogenesis, based on an emerging understanding of SED functions in other tissues but have been minimally studied in bone. By characterizing SED mechanisms related to chromatin organization and stabilization in MSCs, we will discover novel mechanisms of multi-dimensional coordinate control of transcriptional hubs and protein complexes within an SED that is responsible for establishing commitment to the osteoblast phenotype. Importantly, knowledge of the chromatin organization that stabilizes the osteogenic phenotype impacts on future novel treatment strategies for skeletal disorders.