Role of the Brg Bromodomain in BAF (mSWI/SNF) Chromatin Remodeling Complex Function and Genomic Targeting

Download or read book Role of the Brg Bromodomain in BAF (mSWI/SNF) Chromatin Remodeling Complex Function and Genomic Targeting written by Jehnna Lee Ronan and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The mammalian SWI/SNF, or BAF, complex is a polymorphic ATP-dependent chromatin remodeler that is mutated in approximately 20% of human cancers and is necessary for many stages of development. BAF (Brg/Brm-associated factors) complexes are enriched at around thirty thousand genomic sites that vary depending on cellular context. We found that in embryonic stem cells (ESCs), which are dependent on BAF complex function for self-renewal and pluripotency, the majority of BAF complex sites align with gene promoters and enhancers. BAF complex targeting and function may be influenced by several of its ~6-13 putative chromatin binding domains, but the in vivo role of these domains has not been explored. We created a mutant Brg bromodomain (N1507A) ESC line to investigate this putative chromatin binding domain's role in BAF complex function during development. Surprisingly, the Brg bromodomain is dispensible for ESC derivation and self-renewal, in contrast to the essential role of the Brg ATPase. In a cell culture model, we found that the Brg bromodomain is necessary for differentiation of neural progenitors into glutamatergic neurons. In vivo, however, the BrgN1507A mutation causes peri-implantation lethality (E4.5-E6.5). Based on successful blastocyst hatching and outgrowth, we hypothesize that the Brg bromodomain may be necessary for the survival of the early or late epiblast, from which the three embryonic germ layers are formed. From biochemical studies of the BrgN1507A-containing BAF complex, we determined that the composition, size, and stability of the BAF complex seem unaffected. Under steady-state conditions, the mobility of the BAF complex in live cells was also unaffected, although mutant complexes were partially resistant to a hyperacetylation-mediated reduction in mobility. In order to gain insight into the essential role of the Brg bromodomain in early embryonic development, we examined genome-wide BAF complex binding and gene expression in a cell culture model of epiblast formation. While a number of developmentally regulated genes are mis-expressed in the BrgN1507A model, BAF complex targeting is minimally affected. While these subtle targeting defects may be biologically relevant, we hypothesize that the main role of the Brg bromodomain is to regulate the BAF complex or its binding partners through allosteric mechanisms. We hope to continue studies of the Brg bromodomain in order to fully understand how it influences overall BAF complex function.