Project description:Histone H3K4me1/2 methyltransferases MLL3/MLL4 and H3K27 acetyltransferases CBP/p300 are major enhancer epigenomic writers. To understand how these epigenomic writers orchestrate enhancer landscapes during cell differentiation, we have profiled genomic binding of MLL4, CBP, lineage-determining transcription factors, as well as transcriptome and epigenome during adipogenesis of immortalized preadipocytes derived from mouse brown adipose tissue (BAT). We show that MLL4 and CBP drive the dynamic enhancer epigenome, which correlates with the dynamic transcriptome. MLL3/MLL4 are required for CBP/p300 binding on enhancers activated during adipogenesis. Further, we show that MLL4 and CBP identify super-enhancers of adipogenesis and that MLL3/MLL4 are required for the formation of super-enhancers. Finally, in brown adipocytes differentiated in culture, MLL4 identifies primed super-enhancers of genes fully activated in BAT such as the thermogenic Ucp1. Comparison of MLL4-defined super-enhancers in brown and white adipogenesis predicted a list of brown-specific super-enhancers SEs associated genes that are likely to be important to BAT functions. These results establish MLL3/MLL4 and CBP/p300 as master enhancer epigenomic writers and suggest that enhancer-priming by MLL3/MLL4 followed by enhancer-activation by CBP/p300 sequentially shape dynamic enhancer landscapes during cell differentiation. Our data also provide a rich resource for understanding epigenomic regulation of brown adipogenesis.
Project description:Insulin action initiates a series of phosphorylation events regulating cellular differentiation, growth and metabolism. We have previously discovered, in a mass spectrometry-based phosphoproteomic study, that insulin/IGF-1 signaling induces phosphorylation of retinoid x receptor alpha (RXRα) at S22 in mouse brown pre-adipocytes. Here, we show that insulin induces the phosphorylation of RXRα at S22 in both brown precursor and mature adipocytes through a pathway involving ERK, downstream of IRS-1 and -2. We also found that RXRα S22 phosphorylation is promoted by insulin and upon re-feeding in brown adipose tissue in vivo, and that insulin-stimulated S22 phosphorylation of RXRα is dampened by diet-induced obesity. We used Rxra knockout cells re-expressing wild type (WT) or S22A non-phosphorylatable forms of RXRα to further characterize the role of S22 in brown adipocytes. Knockout of Rxra in brown pre-adipocytes resulted in decreased lipid accumulation and adipogenic gene expression during differentiation, and re-expression of RxraWT alleviated these effects. However, we observed no significant difference in cells re-expressing the RxraS22A mutant as compared with the cells re-expressing RxraWT. Furthermore, comparison of gene expression during adipogenesis in the WT and S22A re-expressing cells by RNA sequencing revealed similar transcriptomic profiles. Thus, our data propose a dispensable role for RXRα S22 phosphorylation in adipogenesis and transcription in differentiating brown pre-adipocytes.
Project description:Increasing energy expenditure by promoting the thermogenic program in brown adipocytes is a promising approach to combat human obesity. To fully exploit the potential of this approach a comprehensive understanding of the gene regulatory network that controls both lineage commitment and differentiation of brown cells is necessary. Here, we systematically examine the transcriptomic and epigenomic transitions from mesenchymal stem cells to brown adipocytes (BA) and we perform a comparative analysis with differentiating white adipocytes (WA). We identify coding genes, lncRNA genes, and microRNA genes that are differentially regulated upon BA differentiation. In addition, we generate genome wide reference maps for several chromatin marks throughout brown adipogenesis. We identify putative (super-)enhancers, super-enhancers controlled genes in brown and white adipocytes, as well as target genes of the brown lineage-committing factor BMP7. Finally we show that overexpression and knockdown of four putative novel adipogenic regulators (the kinase Pim1, and the transcription factors Six1, Rreb1, and Sox13), indeed affects BA differentiation, suggesting an important role in brown adipogenesis.
Project description:Enhancers play a central role in cell-type-specific gene expression and are marked by H3K4me1/2. Active enhancers are further marked by H3K27ac. However, the methyltransferases responsible for the deposition of H3K4me1/2 on enhancers remain elusive. Furthermore, the functions of these methyltransferases on enhancers and associated cell-type-specific gene expression are poorly understood. Here, we identify MLL4 (KMT2D) as a major H3K4 mono- and di-methyltransferase in mammalian cells. Using adipogenesis and myogenesis as model systems, we show that MLL4 exhibits cell-type- and differentiation-stage-specific genomic binding and is predominantly localized on enhancers. MLL4 co-localizes with lineage-determining transcription factors (TFs) on active enhancers during differentiation. Deletion of MLL4 dramatically decreases H3K4me1/2 and H3K27ac on enhancers and leads to severe defects in cell-type-specific gene expression and cell differentiation. Finally, we provide evidence that lineage-determining TFs recruit and require MLL4 to establish enhancers critical for cell-type-specific gene expression. Together, these results identify MLL4 as an H3K4 mono-/di-methyltransferase required for enhancer activation during cell differentiation. RNA-Seq analyses of mRNA profiles at D0 (day 0) and D2 (day 2) of adipogenesis in WT (MLL3-/-) and MLL4 KO (MLL3-/-;MLL4-/-) brown preadipocytes.
Project description:Brown and beige fats generate heat via uncoupled respiration to defend against cold, mechanistically, through the action of a network of transcription factors and cofactors. Here we globally profiled long noncoding RNAs (lncRNAs) gene expression during thermogenic adipocyte formation and identified Brown fat lncRNA 1 (Blnc1) as a novel nuclear lncRNA that promotes brown and beige adipocyte differentiation and function by forming a feedforward regulatory loop with EBF2 to drive adipogenesis toward thermogenic phenotype. LncRNAs expression were measured in BAT and WAT from mice injected saline/CL and during brown adipocyte differentiation with two replicates using Arraystar Mouse LncRNA microarray V2.0
Project description:Brown and beige fats generate heat via uncoupled respiration to defend against cold, mechanistically, through the action of a network of transcription factors and cofactors. Here we globally profiled long noncoding RNAs (lncRNAs) gene expression during thermogenic adipocyte formation and identified Brown fat lncRNA 1 (Blnc1) as a novel nuclear lncRNA that promotes brown and beige adipocyte differentiation and function by forming a feedforward regulatory loop with EBF2 to drive adipogenesis toward thermogenic phenotype.