The Role of the De-condensed Structure of Nascent Chromatin During T Cell Differentiation

项目总结： 在细胞分化过程中，转录程序会发生变化，然后必须维持在 转弯。基于染色质的表观遗传机制是维持和切换的核心 转录程序。表观标记的性质和表观遗传标记的基本问题 在分化过程中切换这种标记的机制仍然不清楚，因为缺乏相关的 实验方法。我们开发了新的实验范式，允许研究 在单细胞和基因特异性水平上DNA复制过程中染色质的结构。使用我们的新产品 技术，我们发现在分化过程中染色质的结构有显著的差异。 多能人类胚胎干细胞(HESC)和抗原缺乏经验(幼稚)的T细胞。在.期间 诱导hESCs分化为多巴胺神经元谱系后的最初几个小时，或T细胞向 不同的T细胞亚群，H3K27me3在新生DNA上的积累明显延迟。自.以来 基因组中H3K27me3的出现与核小体的致密结构相吻合，这 提示在新生DNA上存在暂时解聚的核小体结构 诱导细胞分化后。我们的初步数据表明，去凝聚的‘开放’结构 染色质可能是谱系特异性转录因子(TF)重新聚集到DNA中所必需的 这是在细胞分化过程中诱导转录程序变化所必需的。因此，我们的 结果从分子上解释了如何激活被抑制的基因组的大片区域。 在细胞分化过程中。该提案的目标是使用不同的方法测试两个独特的假设 多能hESCs和特化T细胞向不同谱系分化的模型：1) 检查早期分化细胞中复制后染色质开放的时间是否是 几个组蛋白修饰蛋白活性的复杂相互作用；和2)检查这是否 开放的复制后染色质为血统的高度可及性创造了一个机会之窗-- 指定在细胞分化过程中改变转录程序所需的转录因子。 检验这些独特的假设可能会提供一种普遍的基于染色质的分子机制 细胞的生物可塑性。

Project Summary: During cell differentiation, transcriptional programs are changed, and then must be maintained in turn. Chromatin-based epigenetic mechanisms are at the core of maintenance and switching of transcriptional programs. The fundamental issues of the nature of epigenetic marking and of the mechanisms that switch this marking during differentiation remain unclear due to lack of relevant experimental approaches. We developed new experimental paradigms that allow investigating the structure of chromatin during DNA replication at a single-cell and at a gene-specific levels. Using our new techniques, we found striking differences in the structure of chromatin during differentiation of the pluripotent human embryonic stem cells (hESC) and the antigen-inexperienced (naïve) T cells. During the first several hours after induction of differentiation of hESCs to dopamine neuron lineage, or T cells to different T cell subsets, accumulation of H3K27me3 is significantly delayed on nascent DNA. Since the occurrence of H3K27me3 in the genome coincides with the dense structure of nucleosomes, this suggests the existence of a temporarily de-condensed structure of nucleosomes on nascent DNA shortly after induction of cell differentiation. Our preliminary data indicate that the de-condensed, `open' structure of chromatin may be essential for recruitment to DNA of the lineage-specific transcription factors (TFs) that are essential to induce changes in transcriptional programs during cell differentiation. Thus, our results present a molecular explanation of how the vast areas of the repressed genome can be activated during cell differentiation. The goals of this proposal are to test two unique hypotheses using different models of differentiation to various lineages for pluripotent hESCs and for specialized T cells: 1) To examine whether the period of `open' post-replicative chromatin in early differentiating cells is a result of complex interplay of activities of several histone-modifying proteins; and 2) To examine whether this open post-replicative chromatin creates a `window of opportunity' for high accessibility of lineage- specifying TFs that are required to change the transcriptional program during cell differentiation. Examining these unique hypotheses may provide a universal chromatin-based molecular mechanism for biological plasticity of the cell.