Crosslinking mass spectrometry of DDM1 complexed with the nucleosome
Ontology highlight
ABSTRACT: DECREASE IN DNA METHYLATION 1 (DDM1) is the chromatin remodeling factor that has been genetically identified in Arabidopsis thaliana as a factor involved in the maintenance of repressive epigenomic modifications over transposons. In this study, we performed crosslinking mass spectrometry and biochemical analysis using reconstituted nucleosome to understand the chromatin remodeling activity of DDM1. We found that the unique C-terminal tail of heterochromain-specific H2A.W variant binds to DDM1. This result suggest that DDM1 functions with specific histone variants for the maintenance of repressive modifications and epigenetic regulation of transposon activity.
Project description:Nucleation and spreading of H3K27me3 are critical steps for the initiation and maintenance, respectively, of mitotically inheritable Polycomb-mediated repressive chromatin states in cell identity memory, in both animals and plants. Although a semiconservative read-and-write mechanism is proposed to play a key role in H3K27me3 propagation, the specific determinant and underlying mechanism by which the Polycomb Repressive Complex 2 (PRC2) accesses unmodified nucleosomes for propagating H3K27me3 remain enigmatic. Using Arabidopsis thaliana as a model, we show that the chromatin remodeling activity of PICKLE (PKL) has a specialized role in H3K27me3 spreading to safeguard cell identity during differentiation. PKL specifically binds to H3K27me3 spreading regions but not nucleation sites of Polycomb target genes and physically interacts with the MSI1 subunit of PRC2. Loss of PKL abolishes the occupancy of the PRC2 catalytic subunit CLF in spreading regions and leads to aberrant differentiation. Nucleosome condensing endowed by the ATPase function of PKL ensures that unmodified nucleosomes are accessible to PRC2 catalytic activity. Our findings highlight that PKL-dependent nucleosome compaction is critical for PRC2-mediated H3K27me3 read-and-write functions in H3K27me3 spreading, thus revealing a mechanism by which repressive chromatin domains are established and propagated.
Project description:Nucleation and spreading of H3K27me3 are critical steps for the initiation and maintenance, respectively, of mitotically inheritable Polycomb-mediated repressive chromatin states in cell identity memory, in both animals and plants. Although a semiconservative read-and-write mechanism is proposed to play a key role in H3K27me3 propagation, the specific determinant and underlying mechanism by which the Polycomb Repressive Complex 2 (PRC2) accesses unmodified nucleosomes for propagating H3K27me3 remain enigmatic. Using Arabidopsis thaliana as a model, we show that the chromatin remodeling activity of PICKLE (PKL) has a specialized role in H3K27me3 spreading to safeguard cell identity during differentiation. PKL specifically binds to H3K27me3 spreading regions but not nucleation sites of Polycomb target genes and physically interacts with the MSI1 subunit of PRC2. Loss of PKL abolishes the occupancy of the PRC2 catalytic subunit CLF in spreading regions and leads to aberrant differentiation. Nucleosome condensing endowed by the ATPase function of PKL ensures that unmodified nucleosomes are accessible to PRC2 catalytic activity. Our findings highlight that PKL-dependent nucleosome compaction is critical for PRC2-mediated H3K27me3 read-and-write functions in H3K27me3 spreading, thus revealing a mechanism by which repressive chromatin domains are established and propagated.
Project description:Histone post-translational modifications play pivotal roles in eukaryotic gene expression. To date, most studies have focused on modifications in unstructured histone N-terminal tail domains and their binding proteins. However, transcriptional regulation by chromatin-effector proteins that directly recognize modifications in histone globular domains has yet to be clearly demonstrated, despite the richness of their multiple modifications. Here, we show that the ATP-dependent chromatin-remodeling BAF complex stimulates p53-dependent transcription through direct interaction with H3K56ac located on the lateral surface of the histone globular domain. Mechanistically, the BAF complex recognizes nucleosomal H3K56ac via the DPF domain in the DPF2 subunit and exhibits enhanced nucleosome-remodeling activity in the presence of H3K56ac. We further demonstrate that a defect in H3K56ac–BAF complex interaction leads to impaired p53-dependent gene expression and DNA damage responses. Our study provides direct evidence that histone globular domain modifications participate in the regulation of gene expression.
Project description:Precise nucleosome positioning is an increasingly recognized feature of promoters and enhancers, reflecting complex contributions of DNA sequence, nucleosome positioning, histone modification and transcription factor binding to enhancer activity and regulation of gene expression. Changes in nucleosome position and occupancy, histone variants and modifications, and chromatin remodeling are also critical elements of dynamic transcriptional regulation, but poorly understood at enhancers. We investigated glucocorticoid receptor-associated (GR) nucleosome dynamics at enhancers in acute lymphoblastic leukemia. For the first time, we demonstrate functionally distinct modes of nucleosome remodeling upon chromatin binding by GR, which we term central, non-central, phased, and minimal. Central and non-central remodeling reflect nucleosome eviction by GR and cofactors, respectively. Phased remodeling involves nucleosome repositioning and is associated with rapidly activated enhancers and induction of gene expression. Minimal remodeling sites initially have low levels of enhancerassociated histone modification, but the majority of these regions gain H3K4me2 or H3K27Ac to become de novo enhancers. Minimal remodeling regions are associated with gene ontologies specific to decreased B cell number and mTOR inhibition and may make unique contributions to glucocorticoid-induced leukemia cell death. Our findings form a novel framework for understanding the dynamic interplay between transcription factor binding, nucleosome remodeling, enhancer function, and gene expression in the leukemia response to glucocorticoids.
Project description:During transcription, nucleosomes are evicted from regulatory and coding regions yet chromatin structure is stable. Restoration of chromatin structure involves concerted action of chromatin modifying activities. Our analysis demonstrates a genome wide function of the INO80 remodeling complex for stable repositioning of the nucleosome immediately proximal to the transcription initiation site. INO80 dependent remodeling of the promoter proximal nucleosomes has a global repressive role. Recruitment of INO80 to proximal nucleosomes overlaps with the elongating Polymerase II complex assembly. The amount of associated Polymerase II at start sites correlates with INO80 recruitment for inducible and constantly transcribed genes. Furthermore, at highly inducible promoters INO80 is required for repression of bidirectional transcription. Therefore, we suggest a function for INO80 after transcription initiation to achieve Polymerase II dependent reassembly of promoter proximal nucleosomes.
Project description:Histone modifying enzymes play a central role in maintaining cell identity by establishing a conducive chromatin environment for lineage specific transcription factor activity. Pluripotent embryonic stem cells (ESCs) identity is characterized by lower abundance of gene repression associated histone modifications that enables rapid response to differentiation cues. The KDM3 histone demethylase family removes the repressive histone H3 lysine 9 dimethylation (H3K9me2). Here we uncover a surprising role for the KDM3 proteins in the maintenance of the pluripotent state through post-transcriptional regulation. We find through immunoaffinity purification of the KDM3A or KDM3B interactome and proximity ligation assays that KDM3A and KDM3B interact with RNA processing factors such as EFTUD2 and PRMT5. By generating double “degron” ESCs to degrade KDM3A and KDM3B in the rapid timescale of splicing, we find altered splicing, independent of H3K9me2 status. These splicing changes partially resemble the splicing pattern of the more blastocyst-like ground state of pluripotency and occurred in important chromatin and transcription factors such as Dnmt3b, Tbx3 and Tcf12. Our findings reveal non-canonical roles of histone modifying enzymes in splicing to regulate cell identity.
Project description:Heterochromatin-specific histone modifications frequently coexist with mammalian DNA methylation to orchestrate a repressive chromatin state. However, it remains elusive how these epigenetic modifications crosstalk. Here, we report that the first bromoadjacent homology (BAH1) domain and the replication foci targeting sequence (RFTS) of maintenance DNA methyltransferase DNMT1 function as readers for H4K20me3 and H3K9me3, respectively. Engagements of H4K20me3 by BAH1 and H3K9me3 by RFTS ensure localization of DNMT1 to heterochromatin in cells, and cooperate with the RFTS-ubiquitination readout to allosterically stimulate DNMT1 s methylation activity at both global and focal levels. Strikingly, there is intramolecular crosstalk between the RFTS and BAH1 domains, which profoundly impacts the maintenance of DNA methylation and genomic resistance to radiation damage. Together, our study reveals an all-in-one model for DNMT1 in which repressive histone modifications directly influence the cellular landscape of DNA methylation and genomic stability, a process implicative of the DNMT1-related pathogenesis.
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.
Project description:Histone post-translational modifications play pivotal roles in eukaryotic gene expression. To date, most studies have focused on modifications in unstructured histone N-terminal tail domains and their binding proteins. However, transcriptional regulation by chromatin-effector proteins that directly recognize modifications in histone globular domains has yet to be clearly demonstrated, despite the richness of their multiple modifications. Here, we show that the ATP-dependent chromatin-remodeling BAF complex stimulates p53-dependent transcription through direct interaction with H3K56ac located on the lateral surface of the histone globular domain. Mechanistically, the BAF complex recognizes nucleosomal H3K56ac via the DPF domain in the DPF2 subunit and exhibits enhanced nucleosome-remodeling activity in the presence of H3K56ac. We further demonstrate that a defect in H3K56ac–BAF complex interaction leads to impaired p53-dependent gene expression and DNA damage responses. Our study provides direct evidence that histone globular domain modifications participate in the regulation of gene expression.
Project description:Polycomb repressive complex 2 (PRC2) interacts with RNAs in cells, but there is no consensus on how RNA regulates its canonical functions, including chromatin modification and the maintenance of transcription programs in lineage-committed cells. We assayed two separation-of-function mutants of the catalytic subunit EZH2, defective in RNA binding but active in methyltransferase. We find that part of the RNA-binding surface of EZH2 is required for chromatin modification, yet this activity is independent of RNA. Mechanistically, the RNA-binding surface within EZH2 is required for chromatin modification in vitro and in cells, through interactions with nucleosomal DNA. Contrarily, an RNA-binding defective mutant exhibited normal chromatin modification activity in vitro and in lineage-committed cells, accompanied by normal gene repression activity. Collectively, we show that part of the RNA-binding surface of PRC2, rather than the RNA-binding activity per se, is required for the histone methylation of chromatin in vitro and in cells.