BAF complexes in T cell development

描述(申请人提供)：哺乳动物SWI/SNF相关的BAF复合体普遍表达，典型的“依赖于ATP的染色质重塑复合体”可以利用能量来操纵核小体结构以响应外部信号。BAF突变与多种人类肿瘤有关，但BAF复合体的生理功能知之甚少。我们的长期目标是利用T细胞发育作为模型系统，以确定BAF复合体的生理靶基因，剖析BAF复合体调控这些基因的机制，并了解BAF复合体如何响应信号通路。我们已经发现，缺失ATPase亚单位Brg会在T细胞发育中产生多种缺陷，其中一些缺陷是由HMG-box蛋白BAF57的突变概括的。矛盾的是，BAF57和BAF复合体的许多其他亚基对于经典的Brg催化的、依赖于ATP的体外重塑是必不可少的。我们假设，“不必要的”亚基可以通过独立于Brg介导的染色质重塑的新机制，以及通过刺激目标基因在其自然染色质环境中的重塑来调节基因的表达。我们将结合遗传学和生物化学的方法，试图确定在T细胞发育过程中推测的不依赖于ATP的BAF在基因调控中的功能，并探讨这些功能的分子基础，最终确定BAF57是否能够帮助Brg重塑内源性靶基因。这些研究将加深我们对T细胞发育的理解，并具有普遍的意义：它们在染色质领域面临着一个重大挑战，即解决染色质重构体的体内功能，特别是由其非必要亚基介导的功能。此外，鉴于BAF复合体在肿瘤发生中的作用，我们的研究具有实用价值。

DESCRIPTION (provided by applicant): Mammalian Swi/Snf-related BAF complexes are ubiquitously expressed, prototypical "ATP-dependent chromatin remodeling complexes" that can use energy to manipulate nucleosome structure in response to external signals. BAF mutations are linked to multiple human tumors, but the physiological functions of BAF complexes are poorly understood. Our long-term goals are to use T cell development as model systems to identify physiological target genes of BAF complexes, to dissect the mechanisms by which BAF complexes regulate these genes, and to understand how BAF complexes respond to signaling pathways. We have found that deleting the ATPase subunit Brg produces multiple defects in T cell development, some of which are recapitulated by mutations in BAF57, an HMG-box protein. Paradoxically, BAF57 as well as many other subunits of BAF complexes are dispensable for the classical Brg-catalyzed, ATP-dependent remodeling in vitro. We hypothesize that the "dispensable" subunits can regulate gene expression by novel mechanisms independent of Brg-mediated chromatin remodeling, and by stimulating remodeling of the target genes in their natural chromatin contexts. Using a combination of genetic and biochemical methods, we will attempt to identify the putative ATP-independent BAF functions in gene regulation during T cell development, to probe the molecular basis of such functions, and finally to determine whether BAF57 can help Brg to remodel endogenous target genes. These studies will enhance our understanding of T cell development, and are of general interest: they take on a major challenge in the chromatin field, which is to address the in vivo functions of chromatin remodelers especially those mediated by their dispensable subunits. In addition, our studies are of practical value, given the roles of BAF complexes in tumorigenesis.