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Genome-wide maps of HPSH-CTCF binding in prim-5 stage zebrafish embryos

ABSTRACT: CCCTC-binding factor (CTCF) is an architectural protein with context dependent functional outcomes. Although CTCF is conserved throughout Metazoan evolution, its functions have been only evaluated in a limited number of species. Here, we present the first analysis of CTCF binding in the zebrafish genome via chromatin immunoprecipitation followed by sequencing (ChIP-seq). To avoid the need of custom antibodies, we generated a transgenic line with an HA-tagged version of CTCF that enabled the identification of 37,625 CTCF peaks in 24 hours post-fertilization (hpf) embryos. We determined that CTCF peaks generally overlap with histone marks associated to enhancers and active promoters, and identified repeats that are enriched on CTCF binding sites. In addition, we show extended sites of CTCF binding as previously shown in mammals and lamprey, supporting the hypothesis of a CTCF “code” in vertebrates. Our results indicate a positive association between the abundance of CTCF at promoters and gene expression that could be explained by high DNA accessibility. Finally, analysis of chromosome conformation capture data confirms that histone marks associated with active chromatin are enriched at boundaries of topologically associating domains (TADs), but no general enrichment of CTCF peaks nor motifs is observed at these regions. Our zebrafish line and data generated will be important for future studies of genome organization aiming to characterize the roles of CTCF in non-mammalian vertebrates.

ORGANISM(S): Danio rerio

PROVIDER: GSE133437 | GEO | 2020/03/30

REPOSITORIES: GEO

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Project description:Histone modifications associated with gene silencing typically mark large contiguous regions of the genome forming repressive chromatin domain structures. Since the repressive domains exist in close proximity to active regions, maintenance of domain structure is critically important. This study shows that nickel, a nonmutagenic carcinogen, can disrupt histone H3 lysine 9 dimethylation (H3K9me2) domain structures genome-wide, resulting in spreading of H3K9me2 marks into the active regions, which is associated with gene silencing. Our results suggest inhibition of DNA binding of the insulator protein CCCTC-binding factor (CTCF) at the H3K9me2 domain boundaries as a potential reason for H3K9me2 domain disruption. These findings have major implications in understanding chromatin dynamics and the consequences of chromatin domain disruption during pathogenesis. Investigations into the genomic landscape of histone modifications in heterochromatic regions have revealed histone H3 lysine 9 dimethylation (H3K9me2) to be important for differentiation and maintaining cell identity. H3K9me2 is associated with gene silencing and is organized into large repressive domains that exist in close proximity to active genes, indicating the importance of maintenance of proper domain structure. Here we show that nickel, a nonmutagenic environmental carcinogen, disrupted H3K9me2 domains, resulting in the spreading of H3K9me2 into active regions, which was associated with gene silencing. We found weak CCCTC-binding factor (CTCF)-binding sites and reduced CTCF binding at the Ni-disrupted H3K9me2 domain boundaries, suggesting a loss of CTCF-mediated insulation function as a potential reason for domain disruption and spreading. We furthermore show that euchromatin islands, local regions of active chromatin within large H3K9me2 domains, can protect genes from H3K9me2-spreadingM-bM-^@M-^Sassociated gene silencing. These results have major implications in understanding H3K9me2 dynamics and the consequences of chromatin domain disruption during pathogenesis.

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Genome-wide maps of HPSH-CTCF binding in prim-5 stage zebrafish embryos

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