Project description:CTCF binding polarity determines chromatin looping CTCF ChIPseq was performed in E14 embryonic stem cells and neural precursor cells
Project description:CCCTC-binding factor (CTCF) is an architectural protein involved in the three-dimensional organization of chromatin. In this study, we systematically assayed the 3D genomic contact profiles of hundreds of CTCF binding sites in multiple tissues with high-resolution 4C-seq. We find both developmentally stable and dynamic chromatin loops. As recently reported, our data also suggest that chromatin loops preferentially form between CTCF binding sites oriented in a convergent manner. To directly test this, we used CRISPR-Cas9 genome editing to delete core CTCF binding sites in three loci, including the CTCF site in the Sox2 super-enhancer. In all instances, CTCF and cohesin recruitment were lost, and chromatin loops with distal CTCF sites were disrupted or destabilized. Re-insertion of oppositely oriented CTCF recognition sequences restored CTCF and cohesin recruitment, but did not re-establish chromatin loops. We conclude that CTCF binding polarity plays a functional role in the formation of higher order chromatin structure. 4C-seq was performed on a large number of viewpoints in E14 embryonic stem cells, neural precursor cells and primary fetal liver cells
Project description:Current models propose that boundaries of mammalian topologically associating domains (TADs) arise from the ability of the CTCF protein to stop extrusion of chromatin loops by cohesin. While the orientation of CTCF motifs determines which pairs of CTCF sites preferentially stabilize loops, the molecular basis of this polarity remains mysterious. Here we report that CTCF positions cohesin but does not control its overall binding dynamics on chromatin by single molecule live imaging. Using an inducible complementation system, we found that CTCF mutants lacking the N-terminus cannot insulate TADs properly. Cohesin remained at CTCF sites in this mutant, albeit with reduced enrichment. Given that the orientation of the CTCF motif presents the CTCF N-terminus towards cohesin as it translocates from the interior of TADs, these observations explain how the orientation of CTCF binding sites determines the genomic distribution of chromatin loops.
Project description:CCCTC-binding factor (CTCF) is an architectural protein involved in the three-dimensional organization of chromatin. In this study, we systematically assayed the 3D genomic contact profiles of hundreds of CTCF binding sites in multiple tissues with high-resolution 4C-seq. We find both developmentally stable and dynamic chromatin loops. As recently reported, our data also suggest that chromatin loops preferentially form between CTCF binding sites oriented in a convergent manner. To directly test this, we used CRISPR-Cas9 genome editing to delete core CTCF binding sites in three loci, including the CTCF site in the Sox2 super-enhancer. In all instances, CTCF and cohesin recruitment were lost, and chromatin loops with distal CTCF sites were disrupted or destabilized. Re-insertion of oppositely oriented CTCF recognition sequences restored CTCF and cohesin recruitment, but did not re-establish chromatin loops. We conclude that CTCF binding polarity plays a functional role in the formation of higher order chromatin structure.
Project description:Sequencing files provided here include 4C-seq experiments for a total of 6 viewpoints neighboring 5 highly sex-biased genes in mouse liver. These files are part of a larger study ("CTCF and Cohesin link sex-biased distal regulatory elements to sex-biased gene expression in mouse liver"), where we compare CTCF and cohesin binding in male and female mouse liver as well as differences in chromatin conformation (DNA looping).
Project description:Mammalian circadian rhythm is established by the negative feedback loops consisting of a set of clock genes, which lead to the circadian expression of thousands of downstream genes. As genome-wide transcription is organized under the high-order chromosome structure, it is unclear how circadian gene expression is influenced by chromosome structure. In this study, we focus on the function of chromatin structure proteins cohesin as well as CTCF (CCCTC-binding factor) in circadian rhythm. We analyzed the interactome of a Bmal1-bound enhancer upstream of a clock gene, Nr1d1, by 4C-seq and observed that cohesin binding sites are enriched in the interactome. Integrating circadian transcriptome data and cistrome data, we found that cohesin-CTCF co-binding sites tend to insulate the phases of circadian oscillating genes while cohesin-non-CTCF sites facilitate the interaction between circadian enhancer and promoter. A coarse-grained model integrating the long-range effect of cohesin and CTCF markedly improved our mechanistic understanding of circadian gene expression. This model is subsequently supported by our RNA-seq data from cohesin knockout cells. Cohesin is required at least in part for driving the circadian gene expression by facilitating the enhancer-promoter looping. Taken together, our study provided a novel insight into the relationship between circadian transcriptome and the high-order chromosome structure. 4C-seq of a Bmal1 enhancer in mouse liver
Project description:Chromatin looping mediated by the CCCTC binding factor CTCF regulates V(D)J recombination at antigen receptor loci. CTCF-mediated looping can influence recombination signal sequence accessibility by regulating enhancer activation of germline promoters. CTCF-mediated looping has also been shown to limit directional tracking of the RAG recombinase along chromatin, and to regulate through-space interactions between recombination signal sequences, independent of the RAG recombinase. However, in all prior instances in which CTCF-mediated looping was shown to influence V(D)J recombination, it was not possible to fully resolve the relative contributions to the V(D)J recombination phenotype of changes in accessibility, RAG-tracking, and RAG-independent long-distance interactions. Here, to assess mechanisms by which CTCF-mediated looping can impact V(D)J recombination, we introduced an ectopic CTCF binding element (CBE) immediately downstream of Eδ in the murine Tcra-Tcrd locus. The ectopic CBE impaired inversional rearrangement of Trdv5 in the absence of measurable effects on Trdv5 transcription and chromatin accessibility. Moreover, although the ectopic CBE limited directional RAG tracking from the Tcrd recombination center, such tracking cannot account for Trdv5-to-Trdd2 inversional rearrangement. Rather, the defect in Trdv5 rearrangement could only be attributed to a reconfigured chromatin loop organization that limited RAG-independent through-space interactions between the Trdv5 and Trdd2 RSSs. We conclude that CTCF can regulate V(D)J recombination by segregating RSSs into distinct loop domains and inhibiting RSS synapsis, independent of any effects on transcription, RSS accessibility and RAG tracking. RAG-initiatd Tcrd D segment rearrangements in developing thymocytes were generated by deep sequencing using illumine Miseq