Role of the chromatin remodeling Tip60/ Ep400 complex in myelin-forming glia

细胞发育和分化的过程通常与染色质的实质性变化有关，这些变化是由组蛋白修饰酶和染色质重塑复合物引起的。多亚基Tip 60/Ep 400复合物通过其Tip 60亚基参与组蛋白乙酰化，以及通过其Ep 400亚基催化组蛋白H2 A与组蛋白H2A.Z的交换参与染色质重塑。Tip 60/Ep 400复合物的成功形成需要两个亚基的存在。在上一个资助期，我们使用胶质细胞特异性缺失Ep 400亚基来表明Tip 60/Ep 400复合物对于小鼠髓鞘形成胶质细胞的正常发育是重要的。特别是，我们已经证明了在外周神经系统的雪旺细胞以及中枢神经系统的少突胶质细胞中的终末分化和髓鞘形成的复合物的重要作用。而施万细胞主要需要Tip 60/Ep 400复合物的前体细胞程序的适当终止，少突胶质细胞依赖于复合物的诱导分化程序和保护其基因组在脆弱的分化阶段。除了Myrf基因，功能相关的直接靶基因尚未被确定为少突胶质细胞中的Tip 60/Ep 400复合物。少突胶质细胞中Tip 60亚基的缺失导致与先前在Ep 400缺失后观察到的分化过程类似的干扰。然而，Tip 60缺失导致在祖细胞阶段的少突胶质细胞发育中的额外缺陷，这可归因于Tip 60作为染色质重塑复合物外的转录共激活剂的第二功能。本提案的目的是（i）通过比较Tip 60和Ep 400小鼠模型中的少突胶质细胞特性和表达谱，结合Tip 60和Ep 400结合位点的全基因组作图方法以及诱导的染色质变化，获得Tip 60和Ep 400在少突胶质细胞发育背景下的分子作用模式的完整图像，（ii）鉴定功能相关的直接靶基因和（iii）将作为染色质重塑复合物一部分的Tip 60和Ep 400的共同功能与少突胶质细胞转录因子如Sox 10的Tip 60特异性共激活因子功能分开。我们的工作不仅将产生新的见解少突胶质细胞的发展和疾病相关的干扰，但也将有助于推进我们的知识染色质重塑的功能，从通常研究的组织培养设置复杂的系统在体内。

Processes of cellular development and differentiation are frequently linked to substantial changes in chromatin that are brought about by histone-modifying enzymes and chromatin-remodeling complexes. The multisubunit Tip60/Ep400 complex is involved in histone acetylation via its Tip60 subunit, as well as in chromatin remodeling by catalyzing the exchange of histone H2A against histone H2A.Z via its Ep400 subunit. Successful formation of the Tip60/Ep400 complex requires the presence of both subunits. In the last funding period, we have used glia-specific deletion of the Ep400 subunit to show that the Tip60/Ep400 complex is important for proper development of myelinating glia in mice. In particular we have documented essential roles of the complex for terminal differentiation and myelin formation in Schwann cells of the peripheral nervous system as well as in oligodendrocytes of the central nervous system. Whereas Schwann cells primarily require the Tip60/Ep400 complex for proper termination of the precursor cell program, oligodendrocytes rely on the complex for induction of the differentiation program and for protection of their genome during the vulnerable phase of differentiation. Apart from the Myrf gene, functionally relevant direct target genes have not yet been identified for the Tip60/Ep400 complex in oligodendroglial cells. Deletion of the Tip60 subunit in oligodendrocytes leads to similar disturbances in the differentiation process as previously observed after Ep400 deletion. However, Tip60 deletion causes additional defects in oligodendroglial development at the progenitor cell stage that are attributable to a second function of Tip60 as a transcriptional co-activator outside the chromatin remodeling complex. It is the aim of the current proposal (i) to obtain a complete picture of the molecular mode of action of Tip60 and Ep400 in the context of oligodendroglial development by comparing oligodendroglial properties and expression profiles in Tip60 and Ep400 mouse models in combination with genome-wide mapping approaches for binding sites of Tip60 and Ep400 as well as induced chromatin changes, (ii) to identify functionally relevant direct target genes and (iii) to separate common functions of Tip60 and Ep400 as part of the chromatin remodeling complex from Tip60-specific co-activator functions for oligodendroglial transcription factors such as Sox10. Our work will not only yield new insights into oligodendroglial development und disease-relevant disturbances, but will also be instrumental in advancing our knowledge on the function of chromatin remodelers from the commonly studied tissue culture settings to complex systems in vivo.