Project description:Bivalency, the paradoxical juxtaposition of transcriptionally activating trimethylation of histone H3 lysine 4 (H3K4me3) and the repressive trimethylation of histone H3 lysine 27 (H3K27me3), has been proposed to decorate developmental genes poised for gene expression regulation. Here, we report development of sequential internally calibrated chromatin immunoprecipitation (Re-ICeChIP-seq), capable of measuring absolute quantities of nucleosomal patterns of histone marks in a genome-wide fashion, combined with in situ control of antibody specificity. Re-ICeChIP-seq of H3K4me3/H3K27me3 in mESC reveals that bivalent genes can be delineated into two classes, distinguished by the nucleosomal ratio of H3K4me3 to H3K27me3. Consistent with the canonical role of bivalency, H3K27me3-rich bivalent nucleosomes demarcate promoters of poorly expressed developmental genes that may be poised for activation or repression. Yet our measurements reveal surprisingly widespread presence of bivalency at promoters of highly-expressed housekeeping genes, characterized by H3K4me3-rich bivalent nucleosomes. Moreover, the ratio of H3K4me3 to H3K27me3 at transcription start sites better correlates with gene expression than H3K4me3 or H3K27me3 alone, suggesting cooperation between opposing marks to fine-tune gene expression. Finally, we report that major H3K4 methyltransferases exhibit wide acceptance of various H3K27me3 substrates.
Project description:Coordinated regulation of stemness gene activity by transcriptional and translational controls poise stem cells for a timely cell-state transition during differentiation. Although important for all stemness-to-differentiation transitions, mechanistic understanding of the fine-tuning of stemness gene transcription is lacking due to the compensatory effect of translational control. We used intermediate neural progenitor (INP) identity commitment to define the mechanisms that fine-tune stemness gene transcription in fly neural stem cells (neuroblasts). We demonstrate that the transcription factor FruitlessC (FruC) binds cis-regulatory elements of most genes uniquely transcribed in neuroblasts. Loss of fruC function alone has no effect on INP commitment but drives INP dedifferentiation when translational control is reduced. FruC negatively regulates gene expression by promoting low-level enrichment of the repressive histone mark H3K27me3 in gene cis-regulatory regions. Identical to fruC loss-of-function, reducing Polycomb Repressive Complex 2 activity increases stemness gene activity. We propose low-level H3K27me3 enrichment fine-tunes stemness gene transcription in stem cells, a mechanism likely conserved from flies to humans.
Project description:Coordinated regulation of stemness gene activity by transcriptional and translational controls poise stem cells for a timely cell-state transition during differentiation. Although important for all stemness-to-differentiation transitions, mechanistic understanding of the fine-tuning of stemness gene transcription is lacking due to the compensatory effect of translational control. We used intermediate neural progenitor (INP) identity commitment to define the mechanisms that fine-tune stemness gene transcription in fly neural stem cells (neuroblasts). We demonstrate that the transcription factor FruitlessC (FruC) binds cis-regulatory elements of most genes uniquely transcribed in neuroblasts. Loss of fruC function alone has no effect on INP commitment but drives INP dedifferentiation when translational control is reduced. FruC negatively regulates gene expression by promoting low-level enrichment of the repressive histone mark H3K27me3 in gene cis-regulatory regions. Identical to fruC loss-of-function, reducing Polycomb Repressive Complex 2 activity increases stemness gene activity. We propose low-level H3K27me3 enrichment fine-tunes stemness gene transcription in stem cells, a mechanism likely conserved from flies to humans.
Project description:We performed ChIP-Seq against histones H3K4me3, H3K27me3, and H3K79me2 in MCF10A cells to identify transcription factors with bivalent and pseudo-bivalent epigenetic modifications.
Project description:The ability of cells to perceive and translate versatile cues into differential chromatin and transcriptional states is critical for many biological processes1-4. In plants, timely transition to a flowering state is crucial for successful reproduction5-7. EARLY BOLTING IN SHORT DAY (EBS) is a negative transcriptional regulator that prevents premature flowering in Arabidopsis8,9. Here, we revealed that bivalent bromo-adjacent homology (BAH)-plant homeodomain (PHD) reader modules of EBS bind H3K27me3 and H3K4me3, respectively. A subset of EBS-associated genes was co-enriched with H3K4me3, H3K27me3, and the Polycomb repressor complex 2 (PRC2). Interestingly, EBS adopts an auto-inhibition mode to mediate its binding preference switch between H3K27me3 and H3K4me3. This binding balance is critical because disruption of either EBS-H3K27me3 or EBS-H3K4me3 interaction induces EBS-mediated early floral transition. This study identifies a single bivalent chromatin reader capable of recognizing two antagonistic histone marks and reveals a distinct mechanism of interplay between active and repressive chromatin states.The ability of cells to perceive and translate versatile cues into differential chromatin and transcriptional states is critical for many biological processes1-4. In plants, timely transition to a flowering state is crucial for successful reproduction5-7. EARLY BOLTING IN SHORT DAY (EBS) is a negative transcriptional regulator that prevents premature flowering in Arabidopsis8,9. Here, we revealed that bivalent bromo-adjacent homology (BAH)-plant homeodomain (PHD) reader modules of EBS bind H3K27me3 and H3K4me3, respectively. A subset of EBS-associated genes was co-enriched with H3K4me3, H3K27me3, and the Polycomb repressor complex 2 (PRC2). Interestingly, EBS adopts an auto-inhibition mode to mediate its binding preference switch between H3K27me3 and H3K4me3. This binding balance is critical because disruption of either EBS-H3K27me3 or EBS-H3K4me3 interaction induces EBS-mediated early floral transition. This study identifies a single bivalent chromatin reader capable of recognizing two antagonistic histone marks and reveals a distinct mechanism of interplay between active and repressive chromatin states.v
Project description:Bivalent chromatin modification containing opposing H3K4me3 and H3K27me3 marks controls various biological processes by fine-tuning gene expression in animals and plants, however how this bivalent modification regulates pathogenicity of fungal pathogen remains exclusive. Here, we provided a genome-wide landscape of H3K4me3 and H3K27me3 of wheat head blight fungus Fusarium graminearum (Fg), leading to the identification of infection-induced bivalent chromatin-marked genes (BCGs). Among those, BCG1, which encodes a novel xylanase with a G/Q rich motif, is required for the full virulence of Fg pathogenicity through degradation of host cell wall. However, the G/Q rich motif is recognized by pattern-recognition receptors and triggers plant innate immunity. Further data illustrates that Fg employs H3K4me3 modification to induce BCG1 expression rapidly during the early infection, and then switches to bivalent H3K4me3-H3K27me3 chromatin state that renders rapid epigenetic silencing of BCG1 for escaping from host immune monitor, therefore leading to the successful invasion. Collectively, our study highlights the molecular mechanism of how fungal pathogen employs bivalent epigenetic modification to facilitate the successful infection by escaping of host immunity, which provides conceptual insights into plant-microbe interaction.
Project description:Bivalent chromatin modification containing opposing H3K4me3 and H3K27me3 marks controls various biological processes by fine-tuning gene expression in animals and plants, however how this bivalent modification regulates pathogenicity of fungal pathogen remains exclusive. Here, we provided a genome-wide landscape of H3K4me3 and H3K27me3 of wheat head blight fungus Fusarium graminearum (Fg), leading to the identification of infection-induced bivalent chromatin-marked genes (BCGs). Among those, BCG1, which encodes a novel xylanase with a G/Q rich motif, is required for the full virulence of Fg pathogenicity through degradation of host cell wall. However, the G/Q rich motif is recognized by pattern-recognition receptors and triggers plant innate immunity. Further data illustrates that Fg employs H3K4me3 modification to induce BCG1 expression rapidly during the early infection, and then switches to bivalent H3K4me3-H3K27me3 chromatin state that renders rapid epigenetic silencing of BCG1 for escaping from host immune monitor, therefore leading to the successful invasion. Collectively, our study highlights the molecular mechanism of how fungal pathogen employs bivalent epigenetic modification to facilitate the successful infection by escaping of host immunity, which provides conceptual insights into plant-microbe interaction.
Project description:Background Thousands of mammalian promoters are defined by co-enrichment of the histone tail modifications H3K27me3 (repressive) and H3K4me3 (activating) and are thus termed bivalent. It was previously observed that bivalent genes in human ES cells (hESC) are frequent targets for hypermethylation in human cancers, and depletion of DNA methylation in mouse embryonic stem cells has a marked impact on H3K27me3 distribution at bivalent promoters. However, only a fraction of bivalent genes in stem cells are targets of hypermethylation in cancer, and it is currently unclear whether all bivalent promoters are equally sensitive to DNA hypomethylation and whether H3K4me3 levels play a role in the interplay between DNA methylation and H3K27me3. Results We report the sub-classification of bivalent promoters into two groups—promoters with a high H3K27me3:H3K4me3 (hiBiv) ratio or promoters with a low H3K27me3:H3K4me3 ratio (loBiv). HiBiv are enriched in canonical Polycomb components, show a higher degree of local intrachromosomal contacts and are highly sensitive to DNA hypomethylation in terms of H3K27me3 depletion from broad Polycomb domains. In contrast, loBiv promoters are enriched in non-canonical Polycomb components, show lower intrachromosomal contacts and are less sensitive to DNA hypomethylation at the same genomic resolution. Multiple systems reveal that hiBiv promoters are more depleted of Polycomb complexes than loBiv promoters following a reduction in DNA methylation, and we demonstrate that H3K27me3 re-accumulates at promoters when DNA methylation is restored. In human cancer, we show that hiBiv promoters lose H3K27me3 and are more susceptible to DNA hypermethylation than loBiv promoters. Conclusion We conclude that bivalency as a general term to describe mammalian promoters is an over-simplification and our sub-classification has revealed novel insights into the interplay between the largely antagonistic presence of DNA methylation and Polycomb systems at bivalent promoters. This approach redefines molecular pathologies underlying disease in which global DNA methylation is aberrant or where Polycomb mutations are present.
Project description:Cotton is an excellent model for studying heterosis, crop domestication and bioengineering improvement. Chromatin profiling helps to reveal how histone modifications are involved in controlling differential gene expression between A and D subgenome in allotetraploid cotton. However, the detailed profiling and functional characterization of H3K27me3 and H3K4me3/H3K27me3 bivalent mark are still understudied in cotton. In this study, we conducted H3K4me3 and H3K27me3-related ChIP-seq followed by comprehensively characterizing their roles in regulating gene transcription in cotton. We found that H3K4me3 and H3K27me3 exhibited active and repressive roles in regulating expression of genes between A and D subgenome, respectively. Expression of H3K4me3-H3K27me3 bivalent genes was regulated by combinatorial actions of both marks and may be dominantly controlled by H3K4me3. More importantly, H3K4me3 exhibited enrichment levels, positioning and distance-related effects on expression levels of related genes. In addition, H3K4me3, H3K27me3 and bivalent mark can indirectly influence gene expression through TF-mediated regulatory networks. Thus, our study provides insights in functions of H3K4me3 and H3K27me3 in regulating differential gene expression between A and D subgenome in cotton.