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Distinctive roles for the chromatin remodeling ATPases Brg1 and Brm in early zebrafish embryos [RNA-seq]

ABSTRACT: Brg1 and Brm function as alternative core enzymatic ATPases of SWI/SNF complex in vertebrates, with clear homologs in zebrafish. Brg1 (but not Brm) is required for early cleavage-stage transcription in mice, but where and how Brg1 or Brm impact chromatin in early embryos remains unexplored. Here, we utilize zebrafish embryos to provide the first simultaneous genome-wide profiling of Brg1 and Brm occupancy in any organism/cell type, alongside our profiling of open chromatin and RNA polymerase II. We reveal shared and unique loci for Brg1 and Brm, their shared occupancy of open chromatin and particular developmental promoters, and higher transcription at co-occupied genes. Interestingly, only Brg1 is strongly associated with active histone modifications. Strikingly, only Brm commonly occupies gene bodies, overlapping precisely with Pol II. Functional experiments involving Pol II elongation inhibition alongside bioinformatic analyses suggest that Brm travels with Pol II into gene bodies, primarily at short, very highly-transcribed genes with few introns. Taken together, our results support roles for Brg1 primarily at promoters and enhancers, and for Brm in association with Pol II in elongation through chromatin within gene bodies during genome-wide transcriptional activation

ORGANISM(S): Danio rerio

PROVIDER: GSE175446 | GEO | 2024/05/24

REPOSITORIES: GEO

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Project description:The two catalytic subunits of the SWI/SNF chromatin remodeling complex - Brg1 and Brm - have been often implicated as essential components of common biological processes, suggesting a functional redundancy between these two proteins. For instance, earlier works indicated that both proteins are required for the activation of the myogenic program. However, their mutually exclusive pattern of incorporation in SWI/SNF complexes with variable composition and functional heterogeneity predicts that Brg1- and Brm-based SWI/SNF complexes execute specific functions to coordinate gene expression in multistep programs, such as skeletal myogenesis. We detected a distinct expression profile of Brg1 and Brm during the myogenic program, with Brm being upregulated in differentiating myocytes. Genetic knockdown of either Brg1 or Brm in skeletal myoblasts, followed by gene expression analysis, revealed discrete functions during myogenic differentiation. While Brm is required for the exit from the cell cycle at the early stages of differentiation, by repressing CyclinD1 transcription, Brg1 is required for the activation of muscle gene transcription. Interestingly, at later stages of differentiation Brg1 and Brm cooperate to the activation of a cluster of common target genes. Thus, Brg1 and Brm appear to coordinate activation and repression of distinct subsets of genes during initial phase myogenesis, and converge to cooperatively activate the expression of muscle genes at later stages. C2C12 myoblasts treated with siBRM or siBRG1 or siSCR in growth medium (GM) and differentiated by medium replacemnte (DM ). Celles were collected at 18h and 48h from the onset of DM for RNA extraction and microarray analysis. Arrays were used to generate 6 data sets in duplicate.To address the question of which genes were regulated by BRM and/or BRG1 the fold changes in gene expression were calculated between Scrambled siRNA and the BRM or BRG1 siRNA. The experiments were repeated at 2 different time points (18 hours and 48 hours) .

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Distinctive roles for the chromatin remodeling ATPases Brg1 and Brm in early zebrafish embryos [RNA-seq]

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