Project description:MED1 often serves as a surrogate of the general transcription coactivator complex Mediator for identifying active enhancers. MED1 is required for phenotypic conversion of fibroblasts to adipocytes in vitro but its role in adipose development and expansion in vivo has not been reported. Here we show that MED1 is not generally required for transcription during adipogenesis in culture and that MED1 is dispensable for adipose development in mice. Instead, MED1 is required for postnatal adipose expansion and the induction of fatty acid and triglyceride synthesis genes after pups switch diet from high-fat maternal milk to carbohydrate-based chow. During adipogenesis, MED1 is dispensable for induction of lineage-determining transcription factors (TFs) PPARγ and C/EBPα but is required for lipid accumulation in the late phase of differentiation. Mechanistically, MED1 controls the induction of lipogenesis genes by facilitating lipogenic TF ChREBP- and SREBP1a-dependent recruitment of Mediator to active enhancers. Together, our findings identify a cell- and gene-specific regulatory role of MED1 as a lipogenesis coactivator required for postnatal adipose expansion.
Project description:Fate and behaviour of neural progenitor cells is tightly regulated during mammalian brain development. Metabolic pathways, such as glycolysis and oxidative phosphorylation, that are required for supplying energy and providing molecular building blocks to generate cells, govern progenitor function. However, the role of de novo lipogenesis, which is the conversion of glucose into fatty acids through the multi-enzyme protein fatty acid synthase (FASN), for brain development remains unknown. Using Emx1Cre-mediated, tissue-specific deletion of Fasn in the mouse embryonic telencephalon, we show that loss of FASN causes severe microcephaly, largely due to altered polarity of apical, radial glia progenitors (APs) and reduced progenitor proliferation. Further, genetic deletion and pharmacological inhibition of FASN in human embryonic stem cell (ESC)-derived forebrain organoids identifies a conserved role of FASN-dependent lipogenesis for radial glia cell polarity and progenitor expansion in the developing human forebrain. Thus, our data establish a role of de novo lipogenesis for mouse and human brain development and identify a link between progenitor cell polarity and lipid metabolism.
Project description:Med1 overexpression leads to induction of a wide spectrum of genes. Adenovirally-driven overexpression of Med1 in mouse liver stimulates hepatocyte DNA synthesis with enhanced expression of DNA replication, cell cycle control and liver specific genes as observed at day 3 and day 5 post injection. Med1 gene is amplified in a number of cancers so in this study we tested the hypothesis that Med1 by itself has the capacity to induce cell proliferation. Analysis of the Med1- induced gene expression showed a robust induction of a wide spectrum of genes involved in hepatocellular proliferation. Med1 floxed mice (Med1fl/fl) were injected with Ad-His-Med1 (adenovirus expressing Med1 gene) via tail vein and killed 3 or 5 days after injection. Ad-LacZ (adenovirus expression beta-galactosidase gene) injected mouse liver served as control. Total RNA were isolated from the liver and subjected to the microarray.
Project description:Med1 overexpression leads to induction of a wide spectrum of genes. Adenovirally-driven overexpression of Med1 in mouse liver stimulates hepatocyte DNA synthesis with enhanced expression of DNA replication, cell cycle control and liver specific genes as observed at day 3 and day 5 post injection. Med1 gene is amplified in a number of cancers so in this study we tested the hypothesis that Med1 by itself has the capacity to induce cell proliferation. Analysis of the Med1- induced gene expression showed a robust induction of a wide spectrum of genes involved in hepatocellular proliferation.
Project description:The Mediator co-activator complex directs gene specific expression by binding distal enhancer-bound transcription factors through its Med1 subunit while bridging to RNA Polymerase-II (Pol-II) at gene promoters. In addition, Mediator scaffolds epigenetic modifying enzymes that determine local DNA accessibility. We previously found that deletion of Med1 in cardiomyocytes deregulates more than 5000 genes and promotes acute heart failure and hypothesize Med1 deficiency disrupts enhancer-promoter coupling. Using ChIP-seq, we find Pol-II pausing index is increased in Med1 knockout versus floxed control hearts primarily from decreased Pol-II occupancy at the majority of transcriptional start sites. Med1-dependent gene expression correlates strongly with histone H3 K27 acetylation while H3 K27 tri-methylated levels are increased and inversely correlate with absolute expression levels. Furthermore, Med1 deletion leads to dynamic changes in acetyl-K27 associated super-enhancer regions and their enriched transcription factor binding motifs that are consistent with altered gene expression. Our findings suggest that Med1 is important in establishing enhancer-promoter coupling in the heart by facilitating the recruitment of Pol-II to gene promoters, determining chromatin accessibility within genes and enhancer regions and altering transcription factor binding motifs that are likely important in directing gene-specific expression.
Project description:Effector CD8+ T cells are crucial in adaptive immunity for effective protection against infectious pathogens. The regulatory mechanisms underlying CD8+ effector T cell development are incompletely understood. Here, we defined a critical role of mediator complex subunit 1 (Med1) in controlling effector CD8+ T cell differentiation and survival during acute infections. Mice with Med1 deletion in CD8+ T cells exhibited a significantly impaired effector cell expansion with large reduction of KLRG1+ terminally differentiated and Ly6c+ effector cell populations. Med1 deficiency led to enhanced cell apoptosis and expression of exhausted T cell associated inhibitory receptors (PD-1, Tim3, Lag3 and TIGHT). RNA-Seq analysis revealed the defects of T-bet and Zeb2 mediated transcriptional programs in effector differentiation. Overexpression of T-bet could rescue the Med1-deficient CD8+ effector T cell differentiation and survival. Mechanistically, transcription factor C/EBPβ promoted T-bet expression through interacting with Med1 in effector T cells. Collectively, our findings revealed a novel role of Med1 in regulating effector CD8+ T cell differentiation and survival during immune response.
Project description:We performed RNA-seq and ChIP-seq in three prostate cell lines (VCaP, LNCaP and DU145) to ascertain the role of the mediator complex MED1 in AR signaling. Upon androgen stimulation, MED1 undergoes phosphorylation by CDK7 and physically engages with AR at super-enhancer sites, which is essential for AR-mediated transcription. The CDK7 specific inhibitor THZ1 blunts AR-dependent neoplastic growth by preventing the co-recruitment of AR/MED1 in a genome-wide fashion, and reverts the enzalutamide resistance characterized by hyper-phosphorylated MED1. The effect of THZ1 phenocopies that for MED1 and CDK7 knockdown.
Project description:CRISPR/Cas9 system was used to generate mediator complex subunit 1 (MED1) knockout human pre-B ALL cell line 697. ChIP-seq was performed to identify genomic regions responsible for recruitment of MED1 and RUNX1.
Project description:Mammalian RNA polymerase II (Pol II) initiation, elongation, termination and reinitiation are well studied, but how Pol II dynamically recycles after the transcription cycle remains unclear. By establishing in vitro and in vivo transcription recycling systems, we find that human Mediator 1 (MED1), when phosphorylated at the mammal-specific threonine 1032 by cyclin-dependent kinase 9, dynamically travels with Pol II throughout the transcribed genes to drive Pol II recycling. Mechanistically, MED1 phosphorylation leads to an increase of recycled Pol II via the molecular bridge of MED31, enhancing mRNA output during the transcription recycling process. Importantly, MED1 phosphorylation increases during prostate cancer progression to the lethal phase, and pharmacological inhibition of CDK9 decreases prostate tumor growth through decreasing MED1 phosphorylation and Pol II recycling. Our findings reveal essential mechanisms underlying Pol II recycling and suggest a neglected, yet fundamental Pol II transcription process for therapeutic intervention.