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细胞增殖期间细胞周期阶段染色质结构的保守性。在细胞分化的早期阶段，表观遗传信息和染色质结构发生变化;这导致新基因表达程序的激活，这些程序由增殖的祖细胞繁殖。多能祖细胞分化为髓系或红系定向祖细胞诱导新的转录程序，这些程序由新激活的C/EBPα、PU. 1和加塔-1转录因子触发，这些转录因子以序列特异性方式与DNA结合。然而，目前尚不清楚染色质的结构是否在这些转录因子与DNA的初始结合中起作用。使用新的实验方法来研究DNA复制后蛋白质的表观遗传标记和重新组装，我们发现，与苦参碱处理的细胞相比，多能CD 34+祖细胞（MPP）的特征在于DNA复制后染色质的延迟成熟。基于我们的初步数据，我们提出，这创造了一个独特的开放的复制后结构的染色质，可以解释多能造血祖细胞的生物可塑性。分子上，这种可塑性可能反映了在谱系定型的初始阶段，多能CD 34+细胞中关键转录因子如C/EBPα、PU. 1和加塔-1与新生DNA的易化关联。相比之下，干细胞富集的CD 34+细胞具有更紧凑的染色质构象，表明染色质成熟的变化可能是造血干细胞（HSC）分化所必需的模型。我们建议通过研究以下来测试该模型：i）在富含干细胞和多能CD 34+造血细胞中，经苦参碱处理的转录因子的诱导和DNA结合的动力学; ii）在富含干细胞和多能CD 34+细胞的苦参碱依赖性分化期间，染色质的成熟和重新组装; iii）在干细胞富集和多能性CD 34+细胞的分化和谱系选择过程中，复制早期阶段染色质构象对于转录因子相关性的作用。如果所提出的模型的染色质构象动态分化的HSC和MPP的谱系承诺是正确的，这些研究将有重要的意义，了解过程中的HSC分化和谱系选择在正常细胞，也许，异常分化的白血病细胞。

 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.