Project description:3D-topology of DNA in the cell nucleus provides a level of transcription regulation beyond the sequence of the linear DNA. To study the relationship between transcriptional activity and spatial environment of a gene, we have used allele-specific 4C-technology to produce high-resolution topology maps of the active and inactive X-chromosomes in female cells. We found that loci on the active X form multiple long-range interactions, with spatial segregation of active and inactive chromatin. On the inactive X, silenced loci lack preferred interactions, suggesting a unique random organization inside the inactive territory. However, escapees, among which is Xist, are engaged in long-range contacts with each other, enabling identification of novel escapees. Deletion of Xist results in partial re-folding of the inactive X into a conformation resembling the active X, without affecting gene silencing or DNA methylation. Our data point to a role for Xist RNA in shaping the conformation of the inactive X-chromosome independently of transcription. Five or six 4C viewpoints were applied on the mouse female wild type active X-chromosome, the wild type inactive X-chromosome, the conditional Xist X-chromosome and the Xist knock out X-chromosome
Project description:3D-topology of DNA in the cell nucleus provides a level of transcription regulation beyond the sequence of the linear DNA. To study the relationship between transcriptional activity and spatial environment of a gene, we have used allele-specific 4C-technology to produce high-resolution topology maps of the active and inactive X-chromosomes in female cells. We found that loci on the active X form multiple long-range interactions, with spatial segregation of active and inactive chromatin. On the inactive X, silenced loci lack preferred interactions, suggesting a unique random organization inside the inactive territory. However, escapees, among which is Xist, are engaged in long-range contacts with each other, enabling identification of novel escapees. Deletion of Xist results in partial re-folding of the inactive X into a conformation resembling the active X, without affecting gene silencing or DNA methylation. Our data point to a role for Xist RNA in shaping the conformation of the inactive X-chromosome independently of transcription.
Project description:Recent epigenomic studies have predicted thousands of potential enhancers in the human genome. However, there has not been systematic characterization of target promoters for these potential enhancers. Using H3K4me2 as a mark for active enhancers, we identified genome-wide enhancer-promoter interactions in human CD4+ T cells. Among the 6,520 long-distance chromatin interactions, we identify 2,067 enhancers that interact with 1,619 promoters and enhance their expression. These enhancers exist in accessible chromatin regions and are associated with various histone modifications and Pol II binding. The promoters with interacting enhancers are expressed at higher levels than those without interacting enhancers and their expression levels are positively correlated with the number of interacting enhancers. Interestingly, interacting promoters are co-expressed in a tissue-specific manner. We also find that chromosomes are organized into multiple levels of interacting domains. Our results define a global view of enhancer-promoter interactions and provide a dataset to further understand mechanisms of enhancer targeting and long-range chromatin organization. Two biological replicates of ChIA-PET (Chromatin Interaction Analysis by Paired-End Tag Sequencing) experiment in CD4+ T cells
Project description:Transcriptional regulation in metazoans occurs through long range genomic contacts between enhancers and promoters, and most genes are transcribed in episodic ‘bursts’ of RNA synthesis. The relationship between these two phenomena and the dynamic regulation of genes in response to upstream signals is unknown. Here, we describe the use of live-cell RNA imaging coupled with Hi-C measurements to dissect the regulation of the estrogen-responsive TFF1 gene under endogenous regulation. Although this gene is highly induced, we observe short active periods and variable inactive periods ranging from minutes to days. The heterogeneity in inactive times gives rise to the widely-observed ‘noise’ in human gene expression and explains the distribution of protein levels in human tissue. We derive a mathematical model of regulation that relates transcription, chromosome structure, and the cell’s ability to ‘sense’ changes in estrogen and predicts that hypervariability is largely dynamic and does not reflect a stable biological state.
Project description:ChIP-seq was performed using Drosophila Kc167 cells using antibodies against H3K4me3 to identify active promoters and H3K4me1 to identify active enhancers. H3K27ac ChIPseq was performed to identify active promoters and enhancers. Once enhancers and promoters were identified, JIL-1 and histone phosphorylation, H3K9acS10ph and H3K27acS28ph, ChIP-seq was performed to look at binding trends. JIL-1 and phosphoacetlation is found at low levels at inactive enhancers and shows increase at active enhancers and promoters. Here we examine histone phosphorylation by JIL-1 and acetylation of H3K27ac by CBP at transcriptionally active vs. inactive promoters and enhancers. ChIP-seq is performed in Kc167 Drosophila cells using antibodies against JIL-1, H3K27acS28ph, H3K9acS10ph, H3K4me3, H3K4me1, and H3K27ac.
Project description:The impact of signal dependent transcription factors, such as glucocorticoid receptor (GR) and NFκB on the three-dimensional organization of chromatin remains a topic of discussion. The possible scenarios range from remodeling of higher order chromatin architecture by activated transcription factors to recruitment of activated transcription factors to pre-established long-range interactions. Using 4C-seq and high-resolution ChIA-PET analysis of P300 we observed agonist-induced changes in long-range chromatin interactions, and uncovered interconnected enhancer-enhancer hubs spanning up to one megabase. The vast majority of activated GR and NFκB appears to join pre-existing P300 enhancer hubs without affecting the chromatin conformation. In contrast, binding of the activated transcription factors to loci with their consensus response elements leads to increased formation of an active epigenetic state of enhancers and a significant increase in long-range interactions within pre-existing enhancer networks. De novo enhancers or ligand-responsive enhancer hubs preferentially interact with ligand-induced genes. We demonstrate that, at a subset of genomic loci, ligand-mediated induction leads to active enhancer formation and an increase in long-range interactions, facilitating efficient regulation of target genes. Therefore, our data suggest an active role of signal dependent transcription factors in chromatin and long-range interaction remodeling.