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

细胞发育和分化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Tip60/Ep400复合物通过其Tip60亚基参与组蛋白乙酰化，并通过催化组蛋白H2A与组蛋白H2A的交换参与染色质重塑。通过它的Ep400亚基。Tip60/Ep400复合物的成功形成需要这两个亚基的存在。在上一个资助期内，我们使用了Ep400亚基的胶质特异性缺失来证明Tip60/Ep400复合物对小鼠髓鞘胶质细胞的正常发育很重要。特别是，我们已经记录了复合体在末梢分化和髓鞘形成中的重要作用，在周围神经系统的雪旺细胞和中枢神经系统的少突胶质细胞中。雪旺细胞主要需要Tip60/Ep400复合体来适当终止前体细胞程序，而少突胶质细胞则依赖该复合体来诱导分化程序，并在分化的脆弱阶段保护其基因组。在少突胶质细胞中，除Myrf基因外，尚未发现与Tip60/Ep400复合物功能相关的直接靶基因。少突胶质细胞中Tip60亚基的缺失导致分化过程中类似的干扰，正如之前在Ep400缺失后观察到的那样。然而，在祖细胞阶段，Tip60缺失会导致少突胶质发育的额外缺陷，这是由于Tip60作为染色质重塑复合体外的转录共激活因子的第二种功能。本文的目的是(i)通过比较Tip60和Ep400小鼠模型中的少突胶质特性和表达谱，结合Tip60和Ep400结合位点的全基因组定位方法以及诱导的染色质变化，全面了解Tip60和Ep400在少突胶质发育过程中的分子作用模式；（ii）鉴定功能相关的直接靶基因；（iii）将作为染色质重塑复合体一部分的Tip60和Ep400的共同功能与寡突胶质转录因子（如Sox10）的Tip60特异性共激活子功能分离开来。我们的工作不仅将对少突胶质发育和疾病相关干扰产生新的见解，而且还将有助于提高我们对染色质重塑物功能的认识，从通常研究的组织培养环境到体内复杂系统。

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.