Epigenetic resetting in the human germline entails histone modification remodelling [ChIP-Seq]
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ABSTRACT: Epigenetic resetting in the mammalian germ line entailsacute DNA demethylation, which lays the foundation for gametogenesis, totipotency,and embryonic development. We characterize the epigenome of hypomethylated human primordial germ cells (hPGCs) to reveal mechanisms preventing the widespread derepression of genesand transposable elements (TEs). Along with the loss of DNA methylation, we show that hPGCsexhibit a profound reduction of repressive histone modifications resulting in diminished heterochromatic signaturesat most genesand TEsand the acquisition of a neutral or paused epigenetic state without transcriptional activation.Efficient maintenance of a heterochromatic state is limited to a subset of genomic loci, such asevolutionarily young TEsand some developmental genes, which require H3K9me3 and H3K27me3, respectively, forefficient transcriptional repression. Accordingly, transcriptional repression in hPGCs presentsan exemplary balanced system relying on local maintenance of heterochromatic featuresand a lack of inductive cues.
Project description:Epigenetic resetting in the mammalian germ line entailsacute DNA demethylation, which lays the foundation for gametogenesis, totipotency,and embryonic development. We characterize the epigenome of hypomethylated human primordial germ cells (hPGCs) to reveal mechanisms preventing the widespread derepression of genesand transposable elements (TEs). Along with the loss of DNA methylation, we show that hPGCsexhibit a profound reduction of repressive histone modifications resulting in diminished heterochromatic signaturesat most genesand TEsand the acquisition of a neutral or paused epigenetic state without transcriptional activation.Efficient maintenance of a heterochromatic state is limited to a subset of genomic loci, such asevolutionarily young TEsand some developmental genes, which require H3K9me3 and H3K27me3, respectively, forefficient transcriptional repression. Accordingly, transcriptional repression in hPGCs presentsan exemplary balanced system relying on local maintenance of heterochromatic featuresand a lack of inductive cues.
Project description:Epigenetic resetting in the mammalian germ line entailsacute DNA demethylation, which lays the foundation for gametogenesis, totipotency,and embryonic development. We characterize the epigenome of hypomethylated human primordial germ cells (hPGCs) to reveal mechanisms preventing the widespread derepression of genesand transposable elements (TEs). Along with the loss of DNA methylation, we show that hPGCsexhibit a profound reduction of repressive histone modifications resulting in diminished heterochromatic signaturesat most genesand TEsand the acquisition of a neutral or paused epigenetic state without transcriptional activation.Efficient maintenance of a heterochromatic state is limited to a subset of genomic loci, such asevolutionarily young TEsand some developmental genes, which require H3K9me3 and H3K27me3, respectively, forefficient transcriptional repression. Accordingly, transcriptional repression in hPGCs presentsan exemplary balanced system relying on local maintenance of heterochromatic featuresand a lack of inductive cues.
Project description:Epigenetic resetting in the mammalian germ line entailsacute DNA demethylation, which lays the foundation for gametogenesis, totipotency,and embryonic development. We characterize the epigenome of hypomethylated human primordial germ cells (hPGCs) to reveal mechanisms preventing the widespread derepression of genesand transposable elements (TEs). Along with the loss of DNA methylation, we show that hPGCsexhibit a profound reduction of repressive histone modifications resulting in diminished heterochromatic signaturesat most genesand TEsand the acquisition of a neutral or paused epigenetic state without transcriptional activation.Efficient maintenance of a heterochromatic state is limited to a subset of genomic loci, such asevolutionarily young TEsand some developmental genes, which require H3K9me3 and H3K27me3, respectively, forefficient transcriptional repression. Accordingly, transcriptional repression in hPGCs presentsan exemplary balanced system relying on local maintenance of heterochromatic featuresand a lack of inductive cues.
Project description:Specification of primordial germ cells (PGCs) marks the beginning of the totipotent state. However, without a tractable experimental model, the mechanism of human PGC (hPGC) specification remains unclear. Here, we demonstrate specification of hPGC-like cells (hPGCLCs) from germline competent pluripotent stem cells. The characteristics of hPGCLCs are consistent with the embryonic hPGCs and a germline seminoma that share a CD38 cell-surface marker, which collectively defines likely progression of the early human germline. Remarkably, SOX17 is the key regulator of hPGC-like fate, whereas BLIMP1 represses endodermal and other somatic genes during specification of hPGCLCs. Notable mechanistic differences between mouse and human PGC specification could be attributed to their divergent embryonic development and pluripotent states, which might affect other early cell-fate decisions. We have established a foundation for future studies on resetting of the epigenome in hPGCLCs and hPGCs for totipotency and the transmission of genetic and epigenetic information. RNA-Seq analysis to investigate transcriptomes of hPGC-like cells (hPGCLCs), fetal hPGCs, TCam-2 and hESCs
Project description:Replication disrupts chromatin organization. Thus, rapid resetting of nucleosome positioning is essential to maintain faithful gene expression. The initial step of this reconfiguration occurs at Nucleosome-Depleted Regions (NDRs). While studies have elucidated the role of Transcription Factors (TFs) and Chromatin Remodelers (CRs) in vitro or in maintaining NDRs in vivo, none has addressed their in vivo function shortly after replication. Through purification of nascent chromatin coupled with yeast genetics, we dissected the choreography of events governing the proper positioning of the -1/+1 nucleosomes flanking promoter NDRs. Our findings reveal that CRs are the primary contributors of -1/+1 repositioning post-replication, with RSC acting upstream of INO80. Surprisingly, while Reb1 and Abf1 TFs are not essential for NDR resetting, they are required for NDR maintenance via the promotion of H3 acetylations. Taken together, we propose a two-step model for NDR resetting in S. cerevisiae: first, CRs alone reset promoter NDRs after replication, while a combination of TFs and CRs is required for subsequent maintenance.