The role of a lincRNA in chromatin structure and hematopoiesis

 描述(由申请人提供)：HOX基因对维持造血干细胞(HSCs)自我更新和分化之间的平衡至关重要。虽然HOXB4基因在骨髓或胚胎干细胞(ESCs)中的异位表达导致了HSCs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的祖细胞和干细胞的轻微减少。相反，Hoxb3和HOXB4基因同时缺失的小鼠表现出严重的造血缺陷，HSC数量显著减少，这表明其他HoxB基因可能与HOXB4共同决定造血细胞的命运。重要的是要了解HoxB前基因被协同激活以决定HSC命运的潜在机制。HOX基因的表达受Polycomb(PcG)和TrxG(TrxG)组调节子表观遗传调控。我们发现hSET1A在HOXB4基因座上的招募调控其转录激活并促进HSC的命运。此外，我们还鉴定并克隆了一个HoxB基因座相关的长基因间非编码RNA(LincRNA)，HoxBlinc，它控制着中胚层来源的Flk1+血管母细胞的发育和规范。HoxBlinc与SETD1AHMT复合体结合，调节HoxB基因的染色质构象和前部HoxB基因的激活。因此，这些数据表明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图景和激活基因表达的造血谱系特异性程序。然而，目前尚不清楚HoxBlinc如何重新编程染色质状态以调节HoxB前部基因和造血特异性转录程序，以及HoxBlinc是否具有靶向组蛋白修饰酶以启动造血分化的作用。根据我们的初步数据，我们假设SETD1AHMT复合体选择性地募集到HoxB位点和协调HoxB的前部表达是由HoxBlinc介导的，以决定造血细胞的命运。在这项建议中，我们将研究HoxBlinc在重新编程染色质状态和调节HoxB基因前部转录中的作用。我们将研究HoxBlinc调节早期造血系承诺和分化的潜在表观遗传学机制。通过完成拟议的研究，我们希望能更好地理解lincRNA和表观遗传调节因子控制早期造血事件的分子机制。

 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.