BAF complexes in T cell development

描述（由申请人提供）：哺乳动物Swi/ snf相关BAF复合物是普遍表达的，是典型的“atp依赖性染色质重塑复合物”，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，但对BAF复合物的生理功能了解甚少。我们的长期目标是利用T细胞发育作为模型系统来识别BAF复合物的生理靶基因，剖析BAF复合物调节这些基因的机制，并了解BAF复合物如何响应信号通路。我们发现，删除atp酶亚基Brg会在T细胞发育过程中产生多种缺陷，其中一些缺陷会通过HMG-box蛋白BAF57的突变重现。矛盾的是，BAF57以及BAF复合物的许多其他亚基对于经典的brg催化的体外atp依赖性重塑是必不可少的。我们假设“不可缺少的”亚基可以通过独立于brg介导的染色质重塑的新机制调节基因表达，并通过刺激靶基因在其自然染色质背景下的重塑。我们将采用遗传和生化相结合的方法，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，并探讨其功能的分子基础，最终确定BAF57是否可以帮助Brg重塑内源性靶基因。这些研究将增强我们对T细胞发育的理解，并且具有普遍的兴趣：它们承担了染色质领域的主要挑战，即解决染色质重塑者的体内功能，特别是那些由其不可缺少的亚基介导的功能。此外，鉴于BAF复合物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.