Analysis of the "de novo" chromatin opening induced by C/EBPß

在真核细胞中，DNA与组蛋白相关，并以致密结构染色质的形式存在。基因的激活伴随着染色质结构的局部改变，使得调控蛋白可以进入基因的调控区域。染色质重塑的机制已经得到了详细的研究，然而，在基因激活过程中打开致密染色质结构的第一步目前还知之甚少。所谓的“先锋因子”被认为以某种方式识别致密染色质中的相关区域，但它们如何启动致密染色质结构的打开尚未得到详细研究，因为这类因子很少被确定。变异组蛋白H3.3目前也引起了人们的广泛关注，因为它被特异性地整合到活性染色质区域，并在表观遗传机制中发挥重要作用，如表观遗传记忆。我们最近的工作为我们提供了一个实验系统来研究这两个过程，初始染色质重塑和H3.3沉积，并建立它们之间的因果关系。利用鸡的mim-1基因作为模型系统，我们已经证明转录因子C/EBPβ可以作为一个先锋因子，在髓细胞特异性增强子处启动沉默染色质的“从头”重塑。此外，我们已经观察到C/EBPβ与H3.3特异性组蛋白伴侣Hira相互作用，并诱导H3.3沉积在m-1增强子上，提出了这两种事件相关的有趣可能性。在本课题中，我们将详细研究C/EBPβ在染色质打开和H3.3沉积中的新功能，以了解这两个过程的机制基础和因果关系。我们期望这不仅将扩展我们对C/EBPβ功能的认识，而且还将通过提供对沉默染色质中启动染色质重塑的机制以及组蛋白H3.3在这一过程中的作用的新见解而具有普遍意义。

In eukaryotic cells DNA is associated with histones and exists as a compact structure, the chromatin. The activation of a gene is accompanied by local alterations of the chromatin structure making regulatory regions of the gene accessible for regulatory proteins. The mechanisms of the chromatin-remodeling have been studied in great detail, however, the initial step of opening compacted chromatin structures during the activation of a gene is only poorly understood at present. So-called “pioneer-factors” are assumed to somehow recognize the relevant regions in compact chromatin but how they initiate the opening of the compact chromatin structure has not been studied in much detail because of few of such factors have been identified. The variant histone H3.3 has currently also attracted a lot of attention because it is specifically incorporated into active chromatin regions and appears to play an important role in epigenetic mechanisms, such as epigenetic memory. Our recent work has provided us with an experimental system to study both of these processes, initial chromatin remodelling and H3.3 deposition, and establish the causal relationship between them. Using the chicken mim-1 gene as a model system we have shown that the transcription factor C/EBPβ can act as a pioneer factor and initiate „de novo“ remodelling of silent chromatin at a myeloid-specific enhancer. Furthermore, we have observed that C/EBPβ interacts with the H3.3-specific histone chaperone Hira and induces H3.3 deposition at the mim-1 enhancer, raising the intriguing possibility that both events are linked. In this research project we would like to investigate the novel functions of C/EBPβ in chromatin opening and H3.3 deposition in detail, in order to understand the mechanistic basis and causal relationship of both processes. We expect that this will not only extend our knowledge of the function of C/EBPβ but will also be of general relevance by providing novel insight into the mechanisms that are responsible for initiating chromatin remodelling in silent chromatin and into the role histone H3.3 in this process.