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Project description:The architectural protein CTCF is a mediator of chromatin conformation, but how CTCF binding to DNA is orchestrated to maintain long-range gene expression is poorly understood. Here we perform RNAi knockdown to reduce CTCF levels and reveal a shared subset of CTCF-bound sites are robustly resistant to protein depletion. The 'persistent' CTCF sites are enriched at domain boundaries and chromatin loops constitutive to all cell types. CRISPR-Cas9 deletion of 2 persistent CTCF sites at the boundary between a long-range epigenetically active (LREA) and silenced (LRES) region, within the Kallikrein (KLK) locus, results in concordant activation of all 8 KLK genes within the LRES region. CTCF genome-wide depletion results in alteration in Topologically Associating Domain (TAD) structure, including the merging of TADs, whereas TAD boundaries are not altered where persistent sites are maintained. We propose that the subset of essential CTCF sites are involved in cell-type constitutive, higher order chromatin architecture.
| S-EPMC6946690 | biostudies-literature
Project description:Constitutively bound CTCF sites maintain 3D chromatin architecture and long-range epigenetically regulated domains
| PRJNA517606 | ENA
Project description:BackgroundCTCF binding contributes to the establishment of a higher-order genome structure by demarcating the boundaries of large-scale topologically associating domains (TADs). However, despite the importance and conservation of TADs, the role of CTCF binding in their evolution and stability remains elusive.ResultsWe carry out an experimental and computational study that exploits the natural genetic variation across five closely related species to assess how CTCF binding patterns stably fixed by evolution in each species contribute to the establishment and evolutionary dynamics of TAD boundaries. We perform CTCF ChIP-seq in multiple mouse species to create genome-wide binding profiles and associate them with TAD boundaries. Our analyses reveal that CTCF binding is maintained at TAD boundaries by a balance of selective constraints and dynamic evolutionary processes. Regardless of their conservation across species, CTCF binding sites at TAD boundaries are subject to stronger sequence and functional constraints compared to other CTCF sites. TAD boundaries frequently harbor dynamically evolving clusters containing both evolutionarily old and young CTCF sites as a result of the repeated acquisition of new species-specific sites close to conserved ones. The overwhelming majority of clustered CTCF sites colocalize with cohesin and are significantly closer to gene transcription start sites than nonclustered CTCF sites, suggesting that CTCF clusters particularly contribute to cohesin stabilization and transcriptional regulation.ConclusionsDynamic conservation of CTCF site clusters is an apparently important feature of CTCF binding evolution that is critical to the functional stability of a higher-order chromatin structure.
| S-EPMC6945661 | biostudies-literature
Project description:Spatial genome organization and its effect on transcription remains a fundamental question. We applied an advanced chromatin interaction analysis by paired-end tag sequencing (ChIA-PET) strategy to comprehensively map higher-order chromosome folding and specific chromatin interactions mediated by CCCTC-binding factor (CTCF) and RNA polymerase II (RNAPII) with haplotype specificity and nucleotide resolution in different human cell lineages. We find that CTCF/cohesin-mediated interaction anchors serve as structural foci for spatial organization of constitutive genes concordant with CTCF-motif orientation, whereas RNAPII interacts within these structures by selectively drawing cell-type-specific genes toward CTCF foci for coordinated transcription. Furthermore, we show that haplotype variants and allelic interactions have differential effects on chromosome configuration, influencing gene expression, and may provide mechanistic insights into functions associated with disease susceptibility. 3D genome simulation suggests a model of chromatin folding around chromosomal axes, where CTCF is involved in defining the interface between condensed and open compartments for structural regulation. Our 3D genome strategy thus provides unique insights in the topological mechanism of human variations and diseases.
| S-EPMC4734140 | biostudies-literature
Project description:CTCF, a conserved 3D genome architecture protein, determines proper genome-wide chromatin looping interactions through directional binding to specific sequence elements of four modules within numerous CTCF-binding sites (CBSs) by its 11 zinc fingers (ZFs). Here, we report four crystal structures of human CTCF in complex with CBSs of the protocadherin (Pcdh) clusters. We show that directional CTCF binding to cognate CBSs of the Pcdh enhancers and promoters is achieved through inserting its ZF3, ZFs 4-7, and ZFs 9-11 into the major groove along CBSs, resulting in a sequence-specific recognition of module 4, modules 3 and 2, and module 1, respectively; and ZF8 serves as a spacer element for variable distances between modules 1 and 2. In addition, the base contact with the asymmetric "A" in the central position of modules 2-3, is essential for directional recognition of the CBSs with symmetric core sequences but lacking module 1. Furthermore, CTCF tolerates base changes at specific positions within the degenerated CBS sequences, permitting genome-wide CTCF binding to a diverse range of CBSs. Together, these complex structures provide important insights into the molecular mechanisms for the directionality, diversity, flexibility, dynamics, and conservation of multivalent CTCF binding to its cognate sites across the entire human genome.
| S-EPMC5674162 | biostudies-literature
Project description:BackgroundTumor suppressor gene (TSG) RASSF1A and candidate TSG BLU are two tandem head-to-tail genes located at 3p21.3. We hypothesized that there may be a concordance on their gene expression and promoter methylation status. If not, then there may be an insulator located between RASSF1A and BLU genes that provides a barrier activity.Methodology/principal findingsWe first identified potential transcriptionally important CpG sites using the methylation-specific oligonucleotide array in relation to mRNA expression of RASSF1A and BLU genes in primary lung tumors. We demonstrated that E2F1 bound to the potential transcriptionally important CpG sites in RASSF1A gene of a normal lung cell line expressing RASSF1A transcripts, whereas loss of E2F1 binding to RASSF1A in A549 cancer cell line was the result of DNA methylation. Both RASSF1A and BLU genes had their own potential transcriptionally important CpG regions. However, there was no correlation of methylation status between RASSF1A and BLU. Using gel shift assay and chromatin immunoprecipitation-PCR (ChIP-PCR), we found that CCCTC-binding factor (CTCF) bound to insulator sequences located between these two genes. Bisulfite sequencing and ChIP-PCR revealed distinct methylation and chromatin boundaries separated by the CTCF binding domains in normal cells, whereas such distinct epigenetic domains were not observed in cancer cells. Note that demethylation reagent and histone deacetylase inhibitor treatments led to CTCF binding and recovery of barrier effect for RASSF1A and BLU genes in cancer cells.Conclusions/significanceOur study dissects the potential transcriptionally important CpG sites for RASSF1A and BLU genes at the sequence level and demonstrates that CTCF binding to the insulator of BLU gene provides a barrier activity within separate epigenetic domains of the juxtaposed BLU and RASSF1A loci in the 3p21.3 gene cluster region.
| S-EPMC2942851 | biostudies-literature
Project description:Increasing evidence in the last years indicates that the vast amount of regulatory information contained in mammalian genomes is organized in precise 3D chromatin structures. However, the impact of this spatial chromatin organization on gene expression and its degree of evolutionary conservation is still poorly understood. The Six homeobox genes are essential developmental regulators organized in gene clusters conserved during evolution. Here, we reveal that the Six clusters share a deeply evolutionarily conserved 3D chromatin organization that predates the Cambrian explosion. This chromatin architecture generates two largely independent regulatory landscapes (RLs) contained in two adjacent topological associating domains (TADs). By disrupting the conserved TAD border in one of the zebrafish Six clusters, we demonstrate that this border is critical for preventing competition between promoters and enhancers located in separated RLs, thereby generating different expression patterns in genes located in close genomic proximity. Moreover, evolutionary comparison of Six-associated TAD borders reveals the presence of CCCTC-binding factor (CTCF) sites with diverging orientations in all studied deuterostomes. Genome-wide examination of mammalian HiC data reveals that this conserved CTCF configuration is a general signature of TAD borders, underscoring that common organizational principles underlie TAD compartmentalization in deuterostome evolution.
| S-EPMC4475986 | biostudies-literature
Project description:SATB1, a nuclear matrix-associated protein, has long been proposed to function as a global chromatin loop organizer in T cells. However, the precise roles of SATB1 in chromatin organization remain elusive. Here we show that the depletion of SATB1 in immortalized T cells led to pronounced changes in gene expression, particularly for genes involved in cell proliferation and T cell activation, as well as 3D genome architecture at multiple scales, including the A/B compartment, topologically associating domains (TADs), and loops. Importantly, SATB1 extensively colocalizes with CTCF throughout the genome. Depletion of SATB1 led to increased association among the SATB1/CTCF co-occupied sites, as well as increased chromatin contacts across these sites, thereby altering the genome-wide chromatin loop landscape. SATB1 does not regulate genome architecture by modulating CTCF occupancy. Rather, the topological effects imposed by SATB1 may be attributed to SATB1-dependent anchoring of CTCF to the salt extraction-resistant nuclear matrix. Together, our findings suggest that the functional interplay between nuclear matrix and CTCF plays a critical role in orchestrating 3D genome organization.
2023-03-05 | GSE199006 | GEO
Project description:SATB1, a nuclear matrix-associated protein, has long been proposed to function as a global chromatin loop organizer in T cells. However, the precise roles of SATB1 in chromatin organization remain elusive. Here we show that the depletion of SATB1 in immortalized T cells led to pronounced changes in gene expression, particularly for genes involved in cell proliferation and T cell activation, as well as 3D genome architecture at multiple scales, including the A/B compartment, topologically associating domains (TADs), and loops. Importantly, SATB1 extensively colocalizes with CTCF throughout the genome. Depletion of SATB1 led to increased association among the SATB1/CTCF co-occupied sites, as well as increased chromatin contacts across these sites, thereby altering the genome-wide chromatin loop landscape. SATB1 does not regulate genome architecture by modulating CTCF occupancy. Rather, the topological effects imposed by SATB1 may be attributed to SATB1-dependent anchoring of CTCF to the salt extraction-resistant nuclear matrix. Together, our findings suggest that the functional interplay between nuclear matrix and CTCF plays a critical role in orchestrating 3D genome organization.
2023-03-05 | GSE199007 | GEO
Project description:Pervasive usage of alternative promoters leads to deregulation of gene expression in carcinogenesis and may drive the emergence of new genes in spermatogenesis. However, little is known regarding the mechanisms underpinning the activation of alternative promoters. In our present study, we uncovered a novel mechanism by which alternative cancer-testis-specific transcription is activated from the intergenic and intronic clustered CTCF binding sites, which are transcriptionally inert in normal somatic cells. BORIS/CTCFL, a paralog of CTCF with cancer-testis-specific expression forms a heterodimer with CTCF at the clustered binding sites thus triggering epigenetic reprogramming of these sites into units of active transcription. BORIS binding to CTCF sites leads to the recruitment of chromatin-remodeling factor SRCAP, with subsequent replacement of H2A histone with H2A.Z, therefore creating a more relaxed chromatin state in the nucleosomes flanking the clustered binding sites. This facilitates opening of chromatin beyond CTCF/BORIS binding sites and paves the way to the recruitment of multiple additional transcription factors, thereby activating transcription from a given binding site. We demonstrate that the CTCF binding sites, epigenetically reprogrammed by ectopic BORIS expression can drive the expression of cancer-testis genes, long-noncoding RNAs, retro-pseudogenes, and dormant transposable elements harbored by activated long transcripts. Taking together, our results reveal that BORIS functions as a transcription factor that epigenetically reprograms clustered CTCF binding sites into transcriptional start sites, promoting transcription from alternative promoters in both germ cells and cancer cells.
2024-01-03 | GSE207058 | GEO