Developmental Gene Regulation Via Chromatin Remodeling

描述(由申请人提供)：发育阶段的进展需要转录因子和调控元件的复杂相互作用，以实现必要基因表达的正确的时间和空间模式。生化和遗传学研究表明，染色质结构的表观遗传修饰是基因转录调控的重要机制。基因调控元件中核小体构象和/或位置的改变(称为染色质重塑)通过调节反式作用转录因子的可及性来促进或限制基因的表达。从机制上讲，局部染色质结构的修饰部分是通过多亚单位蛋白质复合体的活性实现的，这些复合体利用ATP水解的能量来破坏核小体的构象和位置。哺乳动物中一类重要的依赖于ATP的核小体重构体是SWI/SNF相关家族的核小体重构体，它由利用Brahma(BRM)或Brahma相关基因1(BRG1)作为催化亚基的大型多蛋白复合体组成。对人SWI-SNF相关复合体和酵母复合体的生化研究表明，这些复合体能够破坏组蛋白与DNA的接触，并以依赖于ATP的方式重新定位核小体。因此，SWI/SNF复合体家族的功能是使核小体DNA更容易被转录因子和限制性内切酶所利用。哺乳动物SWI/SNF复合体可分为两个亚家族，BAF(Brahma相关基因1(BRG1)相关因子)和PBAF(多溴相关BAF)。虽然BAF/PBAF复合体有许多共同的亚基，但它们是通过存在四个独特的亚基来区分的。尽管在小鼠中的基因打靶研究表明SWI/SNF相关的复合体参与了发育过程，但还没有研究区分这些复合体亚家族之间的体内功能差异。为了验证这一假设，即独特的亚基对于以基因或细胞类型特异性的方式在染色质上的特定位置调节不同的BAF/PBAF辅因子活性是必不可少的，提出了一系列新颖的遗传学实验，通过检测发育过程中不同时间和不同组织类型的表型来区分复杂的功能。 公共卫生相关性：染色质重塑复合体的生化研究已经证明它们有能力破坏组蛋白-DNA接触和重新定位核小体。因此，这些复合体在调节全球基因表达方面至关重要。基因实验是为了阐明这些复合体的生物学特异性，以及当表达不当时导致疾病状态的异常结果。

DESCRIPTION (provided by applicant): Progression through developmental stages requires complex interactions of transcription factors and regulatory elements to achieve correct temporal and spatial patterns of requisite gene expression. Biochemical and genetic studies have implicated epigenetic modifications of chromatin structure as an important mechanism in regulation of gene transcription. Alteration of nucleosome conformation and/or position (termed chromatin remodeling) within gene regulatory elements serves to promote or restrict gene expression through regulating accessibility of trans-acting transcription factors. Mechanistically, modification of local chromatin structure is achieved, in part, through the activity of multi-subunit protein complexes that utilize the energy of ATP hydrolysis to disrupt nucleosome conformation and position. One important class of mammalian ATP- dependent nucleosome remodelers is that of the SWI/SNF-related family, which consists of large, multi-protein complexes that utilize either brahma (BRM) or brahma-related gene 1 (BRG1) as the catalytic subunit. Biochemical studies on the human SWI-SNF-related complexes and its yeast counterpart have demonstrated the ability of these complexes to disrupt histone-DNA contacts and reposition nucleosomes in an ATP-dependent manner. Consequently, the SWI/SNF family of complexes functions to render nucleosomal DNA more accessible to transcription factors and restriction enzymes. Mammalian SWI/SNF complexes can be grouped into two major subfamilies, BAF (Brahma-related-gene 1 (BRG1)-associated factor) and PBAF (polybromo- associated BAF). Although the BAF/PBAF complexes share many common subunits; they are distinguishable by the presence of four unique subunits. Although gene-targeting studies in the mouse have implicated SWI/SNF-related complexes in developmental processes, no studies have been done to distinguish the in vivo functional differences between the subfamilies of complexes. To test the hypothesis that the unique subunits are essential for mediating distinct BAF/PBAF cofactor activities at select sites on chromatin in a gene- or cell type-specific manner, a series of novel genetic experiments in mouse are proposed to distinguish complex function by examining phenotype at different times and in various tissue types during development. Public Health Relevance: Biochemical studies on chromatin remodeling complexes have demonstrated their ability to disrupt histone- DNA contacts and reposition nucleosomes. Consequently, these complexes are critical in regulating global gene expression. Genetic experiments are proposed to elucidate the biological specificity of these complexes and the abnormal outcomes that lead to disease states when inappropriately expressed.