The role of chromatin structure in differentiation of hematopoietic stem cells

 描述(由申请人提供)：基因转录状态的表观遗传依赖于在细胞增殖过程中细胞周期阶段染色质结构的保守。在细胞分化的早期阶段，染色质的表观遗传信息和结构发生了变化；这导致了新的基因表达程序的激活，这些程序是由增殖的祖细胞繁殖的。多能祖细胞分化为髓系或红系祖细胞诱导新的转录程序，这些程序由新激活的C/EBPDNA、PU.1和GATA-1转录因子以序列特异性的方式与α结合。然而，染色质的结构是否在这些转录因子与DNA的最初结合中发挥作用尚不清楚。利用新的实验方法研究DNA复制后蛋白质的表观遗传标记和重组，我们发现，与细胞因子处理的细胞相比，多潜能CD34+祖细胞(MPP)的特征是DNA复制后染色质的延迟成熟。基于我们的初步数据，我们认为这创造了一种独特的开放的染色质复制后结构，可以解释多能造血祖细胞的生物可塑性。在分子水平上，这种可塑性可能反映了在谱系承诺的初始阶段，关键转录因子如C/EBPCD34+细胞中的C/EBPα、PU.1和GATA-1与新生DNA的联系。相比之下，富含干细胞的CD34+细胞具有更紧密的染色质构象，这表明染色质成熟的变化可能对造血干细胞(HSCs)的分化至关重要。我们建议通过以下研究来检验这一模型：i)在细胞因子处理的干细胞和多潜能CD34+造血细胞中转录因子的诱导和DNA结合的动力学；ii)干细胞丰富和多潜能的CD34+细胞在细胞因子依赖的分化过程中染色质的成熟和重新组装；iii)在复制的早期阶段染色质构象在干细胞丰富和多潜能的CD34+细胞的分化和谱系选择过程中对转录因子的结合的作用。如果所提出的HSC分化过程中的染色质构象“动力学”模型和MPPs的谱系承诺模型是正确的，这些研究将对理解正常细胞的HSC分化和谱系选择过程，甚至白血病细胞的异常分化具有重要的意义。

 DESCRIPTION (provided by applicant): Epigenetic inheritance of the state of gene transcription relies on the conservation of the structure of chromatin through cell cycle stages during cell proliferation. Epigenetic information and structure of chromatin change during early stages of cell differentiation; this results in the activation of novel gene expression programs tht are propagated by proliferating progenitor cells. Differentiation of multipotent progenitors into myeloid or erythroid lineage-committed progenitors induces new transcriptional programs that are triggered by newly activated C/EBPα, PU.1 and GATA-1 transcription factors that bind to DNA in a sequence-specific manner. However, it is unknown whether the structure of chromatin plays a role in the initial association of these transcription factors with DNA. Using new experimental approaches to study epigenetic marking and re- assembly of proteins after DNA replication, we discovered that, compared to cytokine-treated cells, multipotent CD34+ progenitors (MPPs) are characterized by delayed maturation of chromatin following DNA replication. Based on our preliminary data, we propose that this creates a uniquely open post-replicative structure of chromatin that may explain the biological plasticity of multipotent hematopoietic progenitors. Molecularly, this plasticity may reflect facilitated association of key transcription factors, like C/EBPα, PU.1 and GATA-1 in multipotent CD34+ cells, to nascent DNA during initial stages of lineage commitment. By contrast, stem cell- enriched CD34+ cells have a more compact chromatin conformation, suggesting a model whereby changes in chromatin maturation may be essential for differentiation of hematopoietic stem cells (HSCs). We propose to test this model by investigating: i) the kinetics of induction and DNA association of transcription factors in cytokine-treated stem cell-enriched and multipotent CD34+ hematopoietic cells; ii) maturation and re- assembly of chromatin during cytokine-dependent differentiation of stem cell-enriched and multipotent CD34+ cells; iii) the role of chromatin conformation at early stages of replication for the association of transcription factors during differentiation and lineage choice of stem cell-enriched and multipotent CD34+ cells. If the proposed model of chromatin conformation `dynamics' during differentiation of HSCs and lineage commitment of MPPs is correct, these studies will have important implications for understanding the process of HSC differentiation and lineage choice in normal cells, and, perhaps, the aberrant differentiation of leukemic cells.