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A Hierarchy of H3K4me3 and H3K27me3 Acquisition in Spatial Gene Regulation in Xenopus Embryos

ABSTRACT: Epigenetic mechanisms set apart the active and inactive regions in the genome of multicellular organisms to produce distinct cell fates during embryogenesis. Here, we report on the epigenetic and transcriptome genome-wide maps of gastrula-stage Xenopus tropicalis embryos using massive parallel sequencing of cDNA (RNA-seq) and DNA obtained by chromatin immunoprecipitation (ChIP-seq) of histone H3 K4 and K27 trimethylation and RNA Polymerase II (RNAPII). These maps identify promoters and transcribed regions. Strikingly, genomic regions featuring opposing histone modifications are mostly transcribed, reflecting spatially regulated expression rather than bivalency as determined by expression profile analyses, sequential ChIP, and ChIP-seq on dissected embryos. Spatial differences in H3K27me3 deposition are predictive of localized gene expression. Moreover, the appearance of H3K4me3 coincides with zygotic gene activation, whereas H3K27me3 is predominantly deposited upon subsequent spatial restriction or repression of transcriptional regulators. These results reveal a hierarchy in the spatial control of zygotic gene activation.

ORGANISM(S): Xenopus tropicalis

PROVIDER: GSE14025 | GEO | 2009/09/15

SECONDARY ACCESSION(S): PRJNA112449

REPOSITORIES: GEO

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Project description:During development histone modifying enzymes are required for cell identity and lineage commitment, however little is known about the regulatory origins of the epigenome during embryonic development. Here we generate a comprehensive set of embryonic epigenome reference maps, which we use to determine the extent to which maternal factors shape chromatin state in Xenopus embryos. Using Î±-amanitin to inhibit zygotic transcription, we find that the majority of H3K4me3 and H3K27me3-enriched regions form a maternally defined epigenetic regulatory space with an underlying logic of hypomethylated islands. This maternal regulatory space extends to a substantial proportion of neurula stage-activated promoters. In contrast, p300-recruitment to distal regulatory regions requires embryonic transcription at most loci. The results show that H3K4me3 and H3K27me3 are part of a regulatory space that exerts an extended maternal control well into post-gastrulation development, and highlight the combinatorial action of maternal and zygotic factors through proximal and distal regulatory sequences. We have performed ChIP-sequencing of eight histone modifications, RNA polymerase II (RNAPII) and the enhancer protein p300 at five stages of development: blastula (st. 9), gastrula (st. 10.5, 12.5), neurula (st. 16) and tailbud (st. 30). These experiments allow identification of enhancers (H3K4me1, p300), promoters (H3K4me3, H3K9ac), transcribed regions (H3K36me3, RNAPII) and repressed and heterochromatic domains (H3K27me3, H3K9me2, H3K9me3, H4K20me3). In addition we generated pre-MBT (st. 8) maps for three histone modifications (H3K4me3, H3K9ac, H3K27me3) and single-base resolution DNA methylome maps using whole genome bisulfite sequencing of blastula and gastrula (st. 9 and 10.5) embryos. To determine the maternal and zygotic contributions to chromatin state, we used alpha-amanitin to block embryonic transcription. Fertilised eggs were injected with 2.3 nl of 2.67 ng/ul alpha-amanitin and developed until the control embryos reached mid-gastrulation. Alpha-amanitin and control embryos were used for RNA-seq and ChIP-seq of RNAPII, H3K4me3, H3K27me3 and p300. For all ChIP-seq samples of the epigenome reference maps and RNAPII ChIP-seq samples of the Î±-amanitin experiments three biological replicates of different chromatin isolations of 45 embryos were pooled. Two biological replicates for H3K4me3 (Î±-amanitin injected: resp. 90 and 56 embryo equivalents (eeq); control: resp. 45 and 67 eeq), H3K27me3 (Î±-amanitin injected: resp. 90 and 180 eeq; control: resp. 45 and 202 eeq) and p300 (Î±-amanitin injected: resp. 112 and 56 eeq; control: resp. 112 and 67 eeq) ChIP-seq samples of the Î±-amanitin experiments were generated. For RNA-seq samples of the Î±-amanitin experiments RNA from 5 embryos from one biological replicate was isolated and depleted of ribosomal RNA

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A Hierarchy of H3K4me3 and H3K27me3 Acquisition in Spatial Gene Regulation in Xenopus Embryos

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