Project description:Substantial evidence supports the hypothesis that enhancers are critical regulators of cell-type determination, orchestrating both positive and negative transcriptional programs; however, the basic mechanisms by which enhancers orchestrate interactions with cognate promoters during activation and repression events remain incompletely understood. Here we report the required actions of LIM domain-binding protein 1 (LDB1)/cofactor of LIM homeodomain protein 2/nuclear LIM interactor, interacting with the enhancer-binding protein achaete-scute complex homolog 1, to mediate looping to target gene promoters and target gene regulation in corticotrope cells. LDB1-mediated enhancer:promoter looping appears to be required for both activation and repression of these target genes. Although LDB1-dependent activated genes are regulated at the level of transcriptional initiation, the LDB1-dependent repressed transcription units appear to be regulated primarily at the level of promoter pausing, with LDB1 regulating recruitment of metastasis-associated 1 family, member 2, a component of the nucleosome remodeling deacetylase complex, on these negative enhancers, required for the repressive enhancer function. These results indicate that LDB1-dependent looping events can deliver repressive cargo to cognate promoters to mediate promoter pausing events in a pituitary cell type.
Project description:Substantial evidence supports the hypothesis that enhancers are critical regulators of cell type determination, orchestrating both positive and negative transcriptional programs; however, the basic mechanisms by which enhancers orchestrate interactions with cognate promoters during activation and repression events remain incompletely understood. Here we report the required actions of the LIM domain binding protein, LDB1/CLIM2/NLI, interacting with the enhancer binding protein, ASCL1, to mediate looping to target gene promoters and target gene regulation in corticotrope cells. LDB1-mediated enhancer:promoter looping appears to be required for both activation and repression of these target target gene promoter genes. While LDB1-dependend activated genes are regulated at the level of transcriptional initiation, the LDB1-dependent repressed transcription units appear to be regulated primarily at the level of promoter pausing, with LDB1 regulating recruitment of MTA2, a component of the NuRD complex, on these negative enhancers, required for the repressive enhancer function. These results indicate that LDB1-dependent looping events can deliver repressive cargo to cognate promoters to mediate promoter pausing events in a pituitary cell type. ChIP assay followed by high throughput sequencing (ChIP-seq)
Project description:Substantial evidence supports the hypothesis that enhancers are critical regulators of cell type determination, orchestrating both positive and negative transcriptional programs; however, the basic mechanisms by which enhancers orchestrate interactions with cognate promoters during activation and repression events remain incompletely understood. Here we report the required actions of the LIM domain binding protein, LDB1/CLIM2/NLI, interacting with the enhancer binding protein, ASCL1, to mediate looping to target gene promoters and target gene regulation in corticotrope cells. LDB1-mediated enhancer:promoter looping appears to be required for both activation and repression of these target target gene promoter genes. While LDB1-dependend activated genes are regulated at the level of transcriptional initiation, the LDB1-dependent repressed transcription units appear to be regulated primarily at the level of promoter pausing, with LDB1 regulating recruitment of MTA2, a component of the NuRD complex, on these negative enhancers, required for the repressive enhancer function. These results indicate that LDB1-dependent looping events can deliver repressive cargo to cognate promoters to mediate promoter pausing events in a pituitary cell type. Global Run On (GRO) assay followed by high throughput sequencing (GRO-seq)
Project description:Substantial evidence supports the hypothesis that enhancers are critical regulators of cell type determination, orchestrating both positive and negative transcriptional programs; however, the basic mechanisms by which enhancers orchestrate interactions with cognate promoters during activation and repression events remain incompletely understood. Here we report the required actions of the LIM domain binding protein, LDB1/CLIM2/NLI, interacting with the enhancer binding protein, ASCL1, to mediate looping to target gene promoters and target gene regulation in corticotrope cells. LDB1-mediated enhancer:promoter looping appears to be required for both activation and repression of these target target gene promoter genes. While LDB1-dependend activated genes are regulated at the level of transcriptional initiation, the LDB1-dependent repressed transcription units appear to be regulated primarily at the level of promoter pausing, with LDB1 regulating recruitment of MTA2, a component of the NuRD complex, on these negative enhancers, required for the repressive enhancer function. These results indicate that LDB1-dependent looping events can deliver repressive cargo to cognate promoters to mediate promoter pausing events in a pituitary cell type.
Project description:Substantial evidence supports the hypothesis that enhancers are critical regulators of cell type determination, orchestrating both positive and negative transcriptional programs; however, the basic mechanisms by which enhancers orchestrate interactions with cognate promoters during activation and repression events remain incompletely understood. Here we report the required actions of the LIM domain binding protein, LDB1/CLIM2/NLI, interacting with the enhancer binding protein, ASCL1, to mediate looping to target gene promoters and target gene regulation in corticotrope cells. LDB1-mediated enhancer:promoter looping appears to be required for both activation and repression of these target target gene promoter genes. While LDB1-dependend activated genes are regulated at the level of transcriptional initiation, the LDB1-dependent repressed transcription units appear to be regulated primarily at the level of promoter pausing, with LDB1 regulating recruitment of MTA2, a component of the NuRD complex, on these negative enhancers, required for the repressive enhancer function. These results indicate that LDB1-dependent looping events can deliver repressive cargo to cognate promoters to mediate promoter pausing events in a pituitary cell type.
Project description:Enhancers establish proximity with distant target genes to regulate temporospatial gene expression and specify cell identity. Lim domain binding protein 1 (LDB1) is a conserved and widely expressed protein that functions as an enhancer looping factor. Previous studies in erythroid cells and neuronal cells showed that LDB1 forms protein complexes with different transcription factors to regulate cell-specific gene expression. Here, we show that LDB1 regulates expression of liver genes by occupying enhancer elements and cooperating with hepatic transcription factors HNF4A, FOXA1, TCF7 and GATA4. Using the glucose transporter SLC2A2 gene, encoding GLUT2, as an example, we find that LDB1 regulates gene expression by mediating enhancer-promoter interactions. In vivo, we find that LDB1 deficiency in primary mouse hepatocytes dysregulates metabolic gene expression and changes the enhancer landscape. Conditional deletion of LDB1 in adult mouse liver induces glucose intolerance. However, Ldb1 knockout hepatocytes show improved liver pathology under high-fat diet conditions associated with increased expression of genes related to liver fatty acid metabolic processes. Thus, LDB1 is linked to liver metabolic functions under normal and obesogenic conditions.
Project description:Promoter-proximal pausing of RNA polymerase II (Pol II) is a widespread transcriptional regulatory step across metazoans. Here we find that the nuclear exon junction complex (pre-EJC) is a critical and conserved regulator of this process. Depletion of pre-EJC subunits leads to a global decrease in Pol II pausing and to premature entry into elongation. This effect occurs, at least in part, via non-canonical recruitment of pre-EJC components at promoters. Failure to recruit the pre-EJC at promoters results in increased binding of the positive transcription elongation complex (P-TEFb) and in enhanced Pol II release. Notably, restoring pausing is sufficient to rescue exon skipping and the photoreceptor differentiation defect associated with depletion of pre-EJC components in vivo. We propose that the pre-EJC serves as an early transcriptional checkpoint to prevent premature entry into elongation, ensuring proper recruitment of RNA processing components that are necessary for exon definition.
Project description:Promoter-proximal pausing of RNA polymerase II (Pol II) is a major checkpoint in transcription. An unbiased search for new human proteins that could regulate paused Pol II at the HSPA1B gene identified TRIM28. In vitro analyses indicated HSF1-dependent attenuation of Pol II pausing upon TRIM28 depletion, whereas in vivo data revealed de novo expression of HSPA1B and other known genes regulated by paused Pol II upon TRIM28 knockdown. These results were supported by genome-wide ChIP-sequencing analyses of Pol II occupancy that revealed a global role for TRIM28 in regulating Pol II pausing and pause release. Furthermore, in vivo and in vitro mechanistic studies suggest that transcription-coupled phosphorylation regulates Pol II pause release by TRIM28. Collectively, our findings identify TRIM28 as a new factor that modulates Pol II pausing and transcriptional elongation at a large number of mammalian genes.