Project description:Bacterial artificial chromosomes establish replication timing and sub-nuclear compartment de novo as extra-chromosomal vectors [repli-seq]
Project description:The role of DNA sequence in determining replication timing (RT) and chromatin higher order organization remains elusive. To address this question, we have developed an extra-chromosomal replication system consisting of ~200kb human bacteria artificial chromosomes (BACs) modified with Epstein-Barr virus (EBV) replication origin elements (E-BACs). E-BACs were stably maintained as autonomous mini-chromosomes in both HeLa and human induced pluripotent stem cells (hiPSCs) and established their RT de novo. We applied 4C-seq to evaluate E-BACs' sub-nuclear compartment.
Project description:The role of DNA sequence in determining replication timing (RT) and chromatin higher order organization remains elusive. To address this question, we have developed an extra-chromosomal replication system consisting of ~200kb human bacteria artificial chromosomes (BACs) modified with Epstein-Barr virus (EBV) replication origin elements (E-BACs). E-BACs were stably maintained as autonomous mini-chromosomes in both HeLa and human induced pluripotent stem cells (hiPSCs) and established their RT de novo. We applied repli-seq to evaluate E-BACs' replication timing.
Project description:X chromosome dosage compensation in Drosophila requires chromosome-wide coordination of gene activation. The male-specific-lethal dosage compensation complex (DCC) identifies X chromosomal High Affinity Sites (HAS) from which it reaches out to boost transcription. A recently discovered sub-class of HAS, PionX sites, represent first contacts on the X. We explored the chromosomal interactions of representative PionX sites by high-resolution 4C methodology and determined the overall chromosome conformation by Hi-C in sex-sorted embryos. X chromosomes from male and female cells display similar nuclear architecture, concordant with clustered, constitutively active genes. PionX sites, like HAS, are evenly distributed in the active compartment and engage in short- and long-range interactions beyond compartment boundaries. De novo induction of DCC in female cells allowed monitoring the reach of activation surrounding PionX sites. Remarkably, DCC not only activates genes in linear proximity, but also at megabase distance if close in space, suggesting that dosage compensation profits from chromosome folding.
Project description:Detailed genomic contact maps have revealed that chromosomes are composed of developmentally stable topologically associated domains (TADs) and more flexible sub-TADs. These domains reside in active and inactive nuclear compartments, but cause and consequence of compartmentalization are largely unknown. Here, we combined lacO/lacR binding platforms with allele-specific 4C technologies to track their precise position in the three-dimensional genome upon recruitment of NANOG, SUV39H1 or EZH2. We observed locked genomic loci resistant to spatial repositioning and unlocked loci that could be repositioned to different nuclear sub-compartments with distinct chromatin signatures. Focal protein recruitment caused the entire sub- TAD, but not surrounding regions, to engage in new genomic contacts. Compartment switching was uncoupled from gene expression changes and enzymatically modifying histones per se was insufficient for repositioning. Collectively this suggests that transassociated factors determine three-dimensional compartmentalization independent of their cis-effect on local chromatin composition and activity. 4C-seq was performed on a range of viewpoints in 129/Sv;C57BL/6 embryonic stem cells carying a lacO array in chromosome 8 and 11.
Project description:Background: The packaging of long chromatin fibres in the nucleus poses a major challenge, as it must fulfil both physical and functional requirements. Until recently, insight into the chromosomal architecture of plants was mainly provided by cytogenetic studies. Complementary to these analyses, chromosome conformation technologies promise to refine and improve our view on chromosomal architecture and to provide a more generalised description of nuclear organization. Results: Employing circular chromosome conformation capture (4C), this study describes chromosomal architecture in Arabidopsis nuclei from a genome-wide perspective. Surprisingly, the linear organisation of chromosomes is reflected in the genome-wide interactome. In addition, we studied the interplay of the interactome and epigenetic marks and report that the heterochromatic knob on the short arm of chromosome 4 (hk4s) maintained a pericentromere-like interaction profile and interactome despite its euchromatic surrounding. Conclusion: Despite the extreme condensation that is necessary to pack the chromosomes into the nucleus, the Arabidopsis genome appears to be packed in a predictive manner, according to the following criteria: (i) heterochromatin and euchromatin represent two distinct interactomes, (ii) interactions between chromosomes correlates with the linear position on the chromosome arm, and (iii) distal chromosome regions have a higher potential to interact with other chromosomes. This study includes circular chromosome conformation capture (4C) sequencing information of 13 samples, present in two batches, each present in duplicates (A and B). The individual 4C sequencing information can be retrieved by the 4C primer sequence, given in the 4C primer information file.
Project description:Whole genome doubling (WGD) is a recurrent event in human cancers and it promotes chromosomal instability and acquisition of aneuploidies. However, the 3D organization of the chromatin in WGD cells and its contribution to oncogenic phenotypes are currently unknown. Here, we show that in p53 deficient cells WGD induces loss of chromatin segregation (LCS), characterized by reduced segregation between short and long chromosomes, A and B sub-compartments, and adjacent chromatin domains. LCS is driven by downregulation of CTCF and H3K9me3 in cells that bypassed activation of the tetraploid checkpoint. Longitudinal analyses revealed that LCS primed genomic regions for sub-compartment repositioning in WGD cells, which resulted in chromatin and epigenetic changes associated with oncogene activation in tumours ensuing from WGD cells. Importantly, sub-compartment repositioning events were largely independent of chromosomal alterations, indicating that these were complementary mechanisms contributing to tumour development and progression. Overall, LCS initiates chromatin conformation changes that ultimately result in oncogenic epigenetic and transcriptional modifications, suggesting that chromatin evolution is a hallmark of WGD-driven cancer.
Project description:Whole genome doubling (WGD) is a recurrent event in human cancers and it promotes chromosomal instability and acquisition of aneuploidies. However, the 3D organization of the chromatin in WGD cells and its contribution to oncogenic phenotypes are currently unknown. Here, we show that in p53 deficient cells WGD induces loss of chromatin segregation (LCS), characterized by reduced segregation between short and long chromosomes, A and B sub-compartments, and adjacent chromatin domains. LCS is driven by downregulation of CTCF and H3K9me3 in cells that bypassed activation of the tetraploid checkpoint. Longitudinal analyses revealed that LCS primed genomic regions for sub-compartment repositioning in WGD cells, which resulted in chromatin and epigenetic changes associated with oncogene activation in tumours ensuing from WGD cells. Importantly, sub-compartment repositioning events were largely independent of chromosomal alterations, indicating that these were complementary mechanisms contributing to tumour development and progression. Overall, LCS initiates chromatin conformation changes that ultimately result in oncogenic epigenetic and transcriptional modifications, suggesting that chromatin evolution is a hallmark of WGD-driven cancer.