Unknown,Transcriptomics,Genomics,Proteomics

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H3K79 methylation - cell cycle

ABSTRACT: Mammalian DNA replication starts at distinct chromosomal sites in a tissue-specific pattern coordinated with transcription, but previous studies have not yet identified a chromatin modification that correlates with the initiation of DNA replication. This submission is associated with a paper in which we report that replication initiation events are associated with a high frequency of methylation of histone H3 on lysine K79 (H3K79Me2 and H3K79Me3). H3K79Me2-containing chromatin exhibited the highest enrichment of replication initiation events observed in a single chromatin modification. Importantly, H3K79 methylation was enriched in chromatin containing a replicator (a DNA sequence capable of initiating DNA replication), but not in chromatin containing a mutant replicator that could not initiate replication. The association of H3K79Me2 with replication initiation sites was independent and not synergistic with other chromatin modifications. H3K79 methylation exhibited a wider distribution and greater abundance during S-phase, but regions of chromatin that were only modified during S-phase were not enriched in replication initiation events. In addition, the paper shows that depletion of DOT1L, the sole enzyme responsible for H3K79 methylation, triggered limited genomic over-replication. These data are consistent with the hypothesis that methylation of H3K79 associates with replication origins and marks replicated chromatin during S-phase to prevent re-replication and preserve genomic stability. Evaluation of HeK79 methylation in chromatin samples from cell cycle fractionated K562 leukemia cells. Unsyncrhonized untreated cultures of K562 cells were fractionated by size using centrifugal elutriation. Chromatin was isolated and subject to ChIP-Seq with antibodies directed against dimethylated and trimethylated lysine on histone H3.

ORGANISM(S): Homo sapiens

SUBMITTER: Mirit Aladjem

PROVIDER: E-GEOD-35294 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:We report the genome-wide mapping of time-series ChIP-seq data sets of human ERα cell lines (MCF-7). The 4 time points cover 0, 1, 4 and 24 hours, respectively. MCF7 cells were maintained in a hormone-free medium (phenol red–free MEM with 2 mmol/L L-glutamine, 0.1 mmol/L nonessential amino acids, 50 units/mL penicillin, 50 Ag/mL streptomycin, 6 ng/mL insulin, and 10% charcoal-stripped FBS) for three days. MCF7 cells were treated with DMSO (as 0 hour time point) or E2 (108 mol/L) for 1, 4 and 24 hours. 5 x 107 cells were cross-linked with 1% formaldehyde for 10 min, at which point 0.125 M glycine was used to stop the crosslinking. In brief, after crosslinking, cells were treated by lysis buffers and sonicated to fragment the chromatin to a size range of 500bp-1kb. Chromatin fragments were then immunoprecipitated with 10ug of antibody/magnetic beads. The antibodies against ERα were purchased from Santa Cruz Biotechnology (Santa Cruz, sc-8005 X). After immunoprecipitation, washing, and elution, ChIP DNA was purified by phenol:chloroform:isoamyl alcohol and solubilized in 70 μl of water. The ChIP DNA sample was run in 12% PAGE and the 100-300bp DNA fraction was excised and eluted from the gel slice overnight at 4 °C in 300 μl of elution buffer (5:1, LoTE buffer (3 mM Tris-HCl, pH 7.5, 0.2 mM EDTA)-7.5 M ammonium acetate) and was purified using a QIAquick purification kit (Qiagen, Cat#28104). The library was constructed using Illumina genomic DNA prep kit by following its protocol (Illumina, cat# FC-102-1002), clusters were generated on the Illumina cluster station (Illumina, cat# FC-103-1002), DNA samples (20 nM per sample) quantified by an Agilent Bioanalyzer, were loaded onto Illumina Genome Analyzer IIx (GAIIx) for sequencing according to the manufacturer’s protocol. Reads generated from the Illumina GAIIx pipeline were aligned to the Human Genome Assembly (NCBI build 36.1/hg18) using ELAND algorithm. Experiments on human ERα breat cancer cell lines (MCF-7) in 4 time points.

Project description:A cardinal property of neural stem cells (NSCs) is their ability to adopt multiple fates upon differentiation. The epigenome is widely seen as a read-out of cellular potential and a manifestation of this can be seen in embryonic stem cells (ESCs), where promoters of many lineage-specific regulators are marked by a bivalent epigenetic signature comprising trimethylation of both lysine 4 and lysine 27 of histone H3 (H3K4me3 and H3K27me3, respectively). Bivalency has subsequently emerged as a powerful epigenetic indicator of stem cell potential. Here, we have interrogated the epigenome during differentiation of ESC-derived NSCs to immature GABAergic interneurons. We show that developmental transitions are accompanied by loss of bivalency at many promoters in line with their increasing developmental restriction from pluripotent ESC through multipotent NSC to committed GABAergic interneuron. At the NSC stage, the promoters of genes encoding many transcriptional regulators required for differentiation of multiple neuronal subtypes and neural crest appear to be bivalent, consistent with the broad developmental potential of NSCs. Upon differentiation to GABAergic neurons, all non-GABAergic promoters resolve to H3K27me3 monovalency, whereas GABAergic promoters resolve to H3K4me3 monovalency or retain bivalency. Importantly, many of these epigenetic changes occur prior to any corresponding changes in gene expression. Intriguingly, another group of gene promoters gain bivalency as NSCs differentiate toward neurons, the majority of which are associated with functions connected with maturation and establishment and maintenance of connectivity. These data show that bivalency provides a dynamic epigenetic signature of developmental potential in both NSCs and in early neurons. Neural stem cells derived from mouse embryonic stem cells were differentiated into neurons and FACS purified based on RedStar fluorescence driven by the Tau promoter. Chromatin was prepared from NSCs and neurons (n=1), sonicated to roughly 300bp and immunoprecipitated with antibodies against H3K4me3, H3K27me3, total Histone H3 and total IgG, alongside a 5% input sample. K4/K27 and corresponding input samples were analysed by ChIPSeq

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H3K79 methylation - cell cycle

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