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Local chromatin context dictates the genetic determinants of the heterochromatin spreading reaction.

ABSTRACT: Heterochromatin spreading, the expansion of gene-silencing structures from DNA-encoded nucleation sites, occurs in distinct settings. Spreading re-establishes gene-poor constitutive heterochromatin every cell cycle, but also invades gene-rich euchromatin de novo to steer cell fate decisions. How chromatin context, i.e. euchromatic, heterochromatic, or different nucleator types, influences the determinants of this process remains poorly understood. Previously, we documented distinct behaviors of heterochromatin spreading in different contexts using a single-cell heterochromatin spreading sensor (Greenstein et al. 2018). In this work, building on this sensor system, we now genetically identify the factors that positively or negatively alter the propensity of a nucleation site to spread heterochromatin. We find that different chromatin contexts are dependent on unique sets of genes for the regulation of heterochromatin spreading. Further, we find that spreading in constitutive heterochromatin requires Clr6 histone deacetylase complexes containing the Fkh2 transcription factor, while the Clr3 deacetylase is globally required for silencing. Fkh2 acts by recruiting Clr6 to nucleation-distal chromatin sites. Our results segregate the pathways that control lateral heterochromatin spreading from those that instruct DNA-directed assembly in nucleation.

ORGANISM(S): Schizosaccharomyces pombe

PROVIDER: GSE184379 | GEO | 2021/09/24

REPOSITORIES: GEO

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The histone chaperone FACT facilitates heterochromatin spreading through regulation of histone turnover and H3K9 methylation states

Project description:Heterochromatin formation requires several steps involving: nucleation followed by spreading of large, silent domains and its faithful re-establishment and maintenance after each replication cycle. The essential histone chaperone FACT has been implicated in heterochromatin silencing, however, little is known about the specificity of FACT in this process. Here, by applying single cell assays, ChIP and genetics, we show that FACT mutants have defects in the spreading of heterochromatin at subtelomeres and mating type locus in fission yeast. Further, we demonstrate that the transition of H3K9me2 to me3 is impaired in the FACT mutant and we link the spreading function of FACT to its role in histone turnover suppression. We also identify Epe1 as a specific factor that counteracts heterochromatin spreading defects in the FACT mutants. Together, our studies identify FACT as a first histone chaperone that promotes heterochromatin spreading and add to the current models on histone turnover in propagation of epigenetic marks.

2021-10-12 | GSE174641 | GEO

Mediator directs co-transcriptional heterochromatin assembly by RNAi-dependent and -independent pathways.

Project description:Background: Heterochromatin at the pericentromeric repeats in fission yeast is assembled and spread by an RNAi-dependent mechanism, which is coupled to the transcription of non-coding RNA from the repeats by RNA polymerase II. In addition, Rrp6, a component of the nuclear exosome, also contributes to heterochromatin assembly and is coupled to non-coding RNA transcription. The multi-subunit complex Mediator, which directs initiation of RNA polymerase II-dependent transcription, has recently been suggested to function after initiation in processes such as elongation of transcription and splicing. However, the role of Mediator in the regulation of chromatin structure is not well understood. Results: We investigated the role of Mediator in pericentromeric heterochromatin formation and found that deletion of specific subunits of the head domain of Mediator compromised heterochromatin structure. The Mediator head domain was required for Rrp6-dependent heterochromatin nucleation at the pericentromere and for RNAi-dependent spreading of heterochromatin into the neighboring region. In the latter process, Mediator appeared to contribute to efficient processing of siRNA from transcribed non-coding RNA, which was required for efficient spreading of heterochromatin. Furthermore, the head domain directed efficient transcription in heterochromatin. Conclusions: These results reveal a pivotal role for Mediator in multiple steps of transcription-coupled formation of pericentromeric heterochromatin. This observation further extends the role of Mediator to co-transcriptional chromatin regulation. Gene expression profile at exponentially-growing phase.in the fission yeast deletion mutants of pmc6, med20 and dcr1.

2013-08-31 | E-GEOD-43543 | biostudies-arrayexpress

Rbm10 promotes heterochromatin assembly by interacting with Clr6 and chromatin remodeling complexes

Project description:Splicing factors have recently been shown to be involved in heterochromatin formation, but their role in controlling heterochromatin structure and function remains poorly understood. In this study, we identified a fission yeast homologue of human splicing factor RBM10, which has been linked to TARP syndrome. Overexpression of Rbm10 in fission yeast leads to strong global intron retention. Rbm10 also interacts with splicing factors in a pattern resembling that of human RBM10, suggesting that the function of Rbm10 as a splicing regulator is conserved. Surprisingly, our deep-sequencing data showed that deletion of Rbm10 caused only minor effect on genome-wide gene expression and splicing. However, the mutant displays severe heterochromatin defects. Further analyses confirmed that the heterochromatin defects in the mutant did not result from mis-splicing of heterochromatin factors. Our proteomic data revealed that Rbm10 associates with the histone deacetylase Clr6 complex and chromatin remodeling complexes known to be essential for heterochromatin silencing. We propose that Rbm10 serves as a platform to recruit Clr6 and chromatin remodelers to mediate heterochromatin formation. Our work together with previous findings further suggests that different splicing subunits may play distinct roles in heterochromatin regulation.

2017-01-23 | GSE93906 | GEO

LSD1 Prevents Aberrant Heterochromatin Formation in Neurospora crassa

Project description:Heterochromatin is a specialized form of chromatin that restricts access to DNA and inhibits genetic processes, including transcription and recombination. In Neurospora crassa, constitutive heterochromatin is characterized by trimethylation of lysine 9 on histone H3, hypoacetylation of histones, and DNA methylation. Here we explore whether the conserved histone demethylase, lysine-specific demethylase 1 (LSD1), regulates heterochromatin in Neurospora, and if so, how. Though LSD1 is implicated in heterochromatin regulation, its function is inconsistent across different systems; orthologs of LSD1 have been shown to either promote or antagonize heterochromatin expansion by removing H3K4me or H3K9me respectively. We identify three members of the Neurospora LSD complex (LSDC): LSD1, PHF1, and BDP-1, and strains deficient for any exhibit variable spreading of heterochromatin and establishment of new heterochromatin domains dispersed across the genome. Heterochromatin establishment outside of canonical domains in Neurospora share the unusual characteristic of DNA methylation-dependent H3K9me3; typically, H3K9me3 establishment is independent of DNA methylation. Consistent with this, the hyper-H3K9me3 phenotype of LSD1 knock-out strains is dependent on the presence of DNA methylation, as well as HCHC-mediated histone deacetylation, suggesting spreading is dependent on some feedback mechanism. Altogether, our results suggest LSD1 works in opposition to HCHC to maintain proper heterochromatin boundaries.

2021-07-21 | PXD017300 | Pride

Schizosaccharomyces pombe

Project description:Roles of the Clr4 methyltransferase complex in nucleation, spreading and maintenance of heterochromatin

| PRJNA107815 | ENA

Nucleation and spreading rejuvenate polycomb domains every cell cycle

Project description:Nucleation and spreading rejuvenate polycomb domains every cell cycle

2023-12-01 | GSE209818 | GEO

Leo1 is a Global Regulator of Heterochromatin Cis-spreading

Project description:Domains of heterochromatin play important roles in the maintenance and regulation of eukaryotic genomes. However, the repressive nature of heterochromatin combined with its propensity to self-propagate necessitates the existence of robust mechanisms that limit heterochromatin spreading and thereby avoid silencing of expressed genes. A number of specific sequence elements have been found to serve as barriers to heterochromatin spreading; however, the mechanisms by which spreading is curtailed are generally not well understood. Here we uncover a role for PAF complex component Leo1 in regulating heterochromatin cis-spreading. A genetic screen revealed that loss of Leo1 results in spreading of heterochromatin across a centromeric (IRC) boundary element in fission yeast. Similar heterochromatin spreading was seen upon deletion of other components of the PAF complex, but not other factors involved in transcription-coupled chromatin modification, indicating a specific role for the PAF complex in heterochromatin regulation. Loss of Leo1 is associated with reduced levels of H4K16 acetylation at the boundary, while tethering of the H4K16 acetyltransferase Mst1 to boundary chromatin suppresses heterochromatin spreading in leo1? cells, suggesting that Leo1 antagonises heterochromatin spreading by facilitating H4K16 acetylation. Interestingly, Leo1 also regulates heterochromatin spreading independently of boundaries, and loss of Leo1 causes redistribution of heterochromatin, in particular resulting in substantial expansion of telomeric heterochromatin domains. The PAF complex is known to be an important regulator of transcription-related chromatin modifications; our findings reveal a previously undescribed role for this complex in global regulation of heterochromatin spreading in cis. 8 samples: input (whole cell extract) and IP from H3K9me2 ChIP in wild-type and leo1? cells, in duplicate

2015-05-22 | E-GEOD-61688 | biostudies-arrayexpress

Proteasome-dependent truncation of the negative heterochromatin regulator Epe1 mediates antifungal resistance.

Project description:Epe1 histone demethylase restricts H3K9-methylation-dependent heterochromatin, preventing it from spreading over, and silencing, gene-containing regions in fission yeast. External stress induces an adaptive response allowing heterochromatin island formation that confers resistance on surviving wild-type lineages. Here we investigate the mechanism by which Epe1 is regulated in response to stress. Exposure to caffeine or antifungals results in Epe1 ubiquitylation and proteasome-dependent removal of the N-terminal 150 residues from Epe1, generating truncated tEpe1 which accumulates in the cytoplasm. Constitutive tEpe1 expression increases H3K9 methylation over several chromosomal regions, reducing expression of underlying genes and enhancing resistance. Reciprocally, constitutive non-cleavable Epe1 expression decreases resistance. tEpe1-mediated resistance requires a functional JmjC demethylase domain. Moreover, caffeine-induced Epe1-to-tEpe1 cleavage is dependent on an intact cell-integrity MAP kinase stress signalling pathway, mutations in which alter resistance. Thus, environmental changes provoke a mechanism that curtails the function of this key epigenetic modifier, allowing heterochromatin to reprogram gene expression, thereby bestowing resistance to some cells within a population. H3K9me-heterochromatin components are conserved in human and crop plant fungal pathogens for which a limited number of antifungals exist. Our findings reveal how transient heterochromatin-dependent antifungal resistant epimutations develop and thus inform on how they might be countered.

2022-10-13 | PXD030205 | Pride

Mediator directs co-transcriptional heterochromatin assembly by RNAi-dependent and -independent pathways.

2013-08-31 | GSE43543 | GEO

Proteomics of centromere repeat in distinct chromatin states reveals pathways to heterochromatin nucleation and transmission

Project description:Heritable heterochromatin domain formation is initiated by dynamic changes in the proteome on specialized loci, leading to chromatin modifier recruitment, heterochromatin assembly and propagation. Here we characterize the proteomes associated with a defined heterochromatin nucleation region in three distinct chromatin states: before de novo H3K9 methylation nucleation, following heterochromatin assembly and upon heterochromatin disassembly. Our analyses separate sequence-dependent from sequence-independent processes, providing a systematic examination of the template-driven nucleation and epigenetic wiring underlying heterochromatin transmission. We identify functional interactions that reveal an integral role for the conserved nucleolytic Grc3 complex, and its associated network, as pioneer factors in heterochromatin assembly. More broadly, we demonstrate the power of quantitative proteomics-based strategies for the unbiased scrutiny of the single regions assembled in distinct chromatin states.

2023-12-31 | GSE145076 | GEO

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