The role of a lincRNA in chromatin structure and hematopoiesis

 描述（申请人提供）：Hox基因对于维持造血干细胞（HSC）自我更新和分化之间的平衡至关重要。尽管HoxB4基因在骨髓或胚胎干细胞（ESC）中的异位表达导致HSC的显著扩增和长期植入潜力，但HoxB4缺陷小鼠仅表现出胎肝和骨髓中祖细胞和干细胞的轻度减少。相反，HoxB3和HoxB4基因缺陷的小鼠表现出严重的造血缺陷，HSC数量显著减少，表明其他前部HoxB基因可能与HoxB4合作来指定造血细胞的命运。重要的是要了解潜在的机制，其中前HoxB基因协同激活，赋予HSC的命运。Hox基因的表达在表观遗传学上受多梳（polycomb，PcG）和三胸（trithorax，TrxG）组调节因子的调控。我们发现，募集hSET1A的HoxB4基因座控制其转录激活和促进HSC的命运。此外，我们已经确定并克隆了一个HoxB基因座相关的长基因间非编码RNA（lincRNA），HoxBlinc，它控制中胚层来源的Flk 1+成血管细胞的发展和规范。HoxBlinc与Setd1a HMT复合物相关，以调节HoxB基因座染色质构象和前HoxB基因激活。因此，数据表明，HoxBlinc RNA可能在早期造血中发挥重要作用，可能是通过塑造组蛋白修饰景观并激活基因表达的造血谱系特异性程序。然而，HoxBlinc如何重编程染色质状态以调节前部HoxB基因和造血特异性转录程序以及HoxBlinc是否在靶向组蛋白修饰酶至这些基因以启动造血分化中发挥作用仍然是未知的。基于我们的初步数据，我们假设选择性募集Setd1a HMT复合物的HoxB基因座和协调前HoxB的表达是由HoxBlinc介导的，以指定造血细胞的命运。在这个提议中，我们将研究HoxBlinc在重编程染色质状态和调节前HoxB基因转录中的作用。我们将研究HoxBlinc调控早期造血谱系定型和分化的潜在表观遗传机制。通过完成拟议的研究，我们期望更好地了解lincRNA和表观遗传调节因子控制造血早期事件的分子机制。

 DESCRIPTION (provided by applicant): Hox genes are critical for maintaining the balance between self-renewal and differentiation of hematopoietic stem cells (HSCs). Although ectopic expression of the HoxB4 gene in bone marrow or embryonic stem cells (ESCs) leads to a dramatic expansion and long-term engraftment potential of HSCs, HoxB4 deficient mice exhibit only a mild reduction in progenitors and stem cells in fetal liver and bone marrow. In contrast, mice deficient in both HoxB3 and HoxB4 genes display severe hematopoietic defects with a marked decrease in HSC population indicating that other anterior HoxB genes may cooperate with HoxB4 to specify hematopoietic cell fate. It is important to understand underlying mechanisms by which the anterior HoxB genes are coordinately activated to confer HSC fate. The expression of Hox genes is regulated epigenetically by polycomb (PcG) and trithorax (TrxG) group regulators. We showed that recruitment of hSET1A to the HoxB4 locus governs its transcription activation and promotes HSC fate. Furthermore, we have identified and cloned a HoxB locus associated long intergenic noncoding RNA (lincRNA), HoxBlinc, which controls the development and specification of mesoderm-derived Flk1+ hemangioblasts. HoxBlinc associates with the Setd1a HMT complex to modulate HoxB locus chromatin conformation and anterior HoxB gene activation. Thus, the data suggest that HoxBlinc RNA may play an important role in early hematopoiesis, perhaps by shaping the histone modification landscape and activate hematopoietic lineage specific program of gene expression. However, it remains unknown how HoxBlinc reprograms chromatin state to regulate anterior HoxB genes and hematopoietic specific transcription program and whether HoxBlinc plays a role in targeting histone modifying enzymes to these genes to initiate hematopoietic differentiation. Based on our preliminary data, we hypothesize that selective recruitment of the Setd1a HMT complex to the HoxB locus and coordination of anterior HoxB expression are mediated by HoxBlinc to specify the hematopoietic cell fate. In this proposal, we will examine the role of HoxBlinc in reprograming chromatin state and modulating anterior HoxB gene transcription. We will investigate underlying epigenetic mechanism by which HoxBlinc regulates early hematopoietic lineage commitment and differentiation. By finishing the proposed research, we expect a better understanding of molecular mechanism by which lincRNA and epigenetic regulators control early events of hematopoiesis.