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Heterochromatic 3D genome organization is directed by HP1a and H3K9-dependent and independent mechanisms[FAIRE-seq]

ABSTRACT: Histone post-translational modifications and the proteins that bind them are proposed to be drivers of 3D genome organization, but whether and how they do so remain unanswered. Here, we evaluate the contribution of H3K9-methylated constitutive heterochromatin to 3D genome organization in Drosophila tissues. We find that the predominant organizational feature of wildtype tissues is segregation of euchromatic chromosome arms from heterochromatic pericentromeres. Reciprocal perturbation of HP1a•H3K9 binding, using a point mutation in the HP1a chromodomain or replacement of the replication-dependent H3 with H3K9R mutant histones, revealed that HP1a binding to methylated H3K9 in constitutive heterochromatin is required to restrict long-range interactions between pericentromeres and chromosome arms. Surprisingly, self-association of pericentromeric heterochromatin is largely preserved upon disruption of HP1a•H3K9 binding despite loss of pericentromeric H3K9 methylation and HP1a occupancy. Thus, the HP1a•H3K9 interaction contributes to, but does not solely drive, segregation of euchromatin and heterochromatin inside the nucleus.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE236965 | GEO | 2024/05/24

REPOSITORIES: GEO

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Heterochromatic 3D genome organization is directed by HP1a and H3K9-dependent and independent mechanisms [RNA-seq]

Project description:Histone post-translational modifications and the proteins that bind them are proposed to be drivers of 3D genome organization, but whether and how they do so remain unanswered. Here, we evaluate the contribution of H3K9-methylated constitutive heterochromatin to 3D genome organization in Drosophila tissues. We find that the predominant organizational feature of wildtype tissues is segregation of euchromatic chromosome arms from heterochromatic pericentromeres. Reciprocal perturbation of HP1a•H3K9 binding, using a point mutation in the HP1a chromodomain or replacement of the replication-dependent H3 with H3K9R mutant histones, revealed that HP1a binding to methylated H3K9 in constitutive heterochromatin is required to restrict long-range interactions between pericentromeres and chromosome arms. Surprisingly, self-association of pericentromeric heterochromatin is largely preserved upon disruption of HP1a•H3K9 binding despite loss of pericentromeric H3K9 methylation and HP1a occupancy. Thus, the HP1a•H3K9 interaction contributes to, but does not solely drive, segregation of euchromatin and heterochromatin inside the nucleus.

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Heterochromatic 3D genome organization is directed by HP1a and H3K9-dependent and independent mechanisms [Hi-C]

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Heterochromatic 3D genome organization is directed by HP1a and H3K9-dependent and independent mechanisms[CUT&RUN]

Project description:Whether and how histone post-translational modifications and the proteins that bind them drive 3D genome organization remains unanswered. Here, we evaluate the contribution of H3K9-methylated constitutive heterochromatin to 3D genome organization in Drosophila tissues. We find that the predominant organizational feature of wildtype tissues is segregation of euchromatic chromosome arms from heterochromatic pericentromeres. Reciprocal perturbation of HP1a•H3K9me binding, using a point mutation in the HP1a chromodomain or replacement of the replication-dependent histone H3 with H3K9R mutant histones, revealed that HP1a binding to methylated H3K9 in constitutive heterochromatin is required to limit contact frequency between pericentromeres and chromosome arms and regulate the distance between arm and pericentromeric regions. Surprisingly, self-association of pericentromeric regions is largely preserved despite loss of H3K9 methylation and HP1a occupancy. Thus, the HP1a•H3K9 interaction contributes to, but does not solely drive, segregation of euchromatin and heterochromatin inside the nucleus.

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Project description:We replaced the endogenous histones of Drosophila melanogaster with histones containing an H3K9R mutation to interrogate the role of H3K9 in heterochromatin formation and function. We queried heterochromatin formation through Formaldhyde Assisted Isolation of Regulatory Elements coupled with sequencing to examine nucleosome occupancy and Heterochromatin Protein 1a ChIP sequencing to determine the localization of the major reader of H3K9me. We found that regions of pericentromeric heterochromatin exhibit decreased HP1a and nucleosome occupancy in H3K9R mutants. To examine potential consequences of these changes of chromatin architecture, we performed total RNA-seq. In H3K9R mutants we observed increased levels of transposon and pIRNA cluster transcripts; however, the protein-coding transcriptome was similar to controls.

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H3K9 promotes under-replication of pericentromeric heterochromatin in Drosophila salivary gland polytene chromosomes

Project description:We replaced the endogenous histones of Drosophila melanogaster with either histones containing an H3K9R mutation or histones containing an H4K16R mutation to interrogate direct functions for histone residues in salivary gland endoreplication. We performed genomic DNA sequencing in HWT (Histone Wild Type) control, H3K9R, and H4K16R females. We found that H3K9 promotes under-replication of pericentromeric heterochromatin but not along chromosome arms and H4K16 is dispensable for under-replication.

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HP1a recruitment to promoters is independent of H3K9 methylation in Drosophila melanogaster

Project description:Heterochromatin protein 1 (HP1) proteins are important regulators of heterochromatin mediated gene silencing and chromosome structure and it is well known as the reader of the heterochromatin mark methylation of histone H3 lysine 9 (H3K9me). In Drosophila three different histone lysine methyl transferases (HKMTs) are associated with the methylation of H3K9; Su(var)3-9, Setdb1 and G9a. To gain insights on the dependence of HP1a on the three different HKMTs, the division of labor between these methyl transferases and the dependence of HP1a on H3K9me we have studied HP1a binding in relation to H3K9me in mutants of these HKMTs. We show that Su(var)3-9 is responsible for the HP1a H3K9me-dependent binding in pericentromeric regions while Setdb1 controls the HP1a H3K9me-dependent binding to cytological region 2L:31 and together with POF chromosome 4. HP1a binds to the promoters and within gene bodies of active genes in these three regions. More importantly, HP1a bound at promoters of active genes are independent of H3K9me and POF and is associated to heterochromatin protein 2 (HP2) and open chromatin. Our results supports a model where HP1a nucleates with high affinity independent of H3K9me in promoters of active genes and then spreads via H3K9 methylation and transient looping contacts with those H3K9me target sites. In total 44 samples; 2 replicates for each genotype and for each ChIP (HP1a, H3K9me2 and H3K9me3)

2012-12-21 | E-GEOD-38366 | biostudies-arrayexpress

HP1a recruitment to promoters is independent of H3K9 methylation in Drosophila melanogaster

2012-12-21 | GSE38366 | GEO

Chromatin conformation and transcriptional activity are permissive regulators of DNA replication initiation in Drosophila

Project description:We replaced the endogenous histones of Drosophila melanogaster with either histones containing an H3K9R mutation or histones containing an H4K16R mutation to interrogate established genome-wide correlations between chromatin state, transcription, and DNA replication timing. We performed total RNA-seq in H4K16R males and females to investigate the role of H4K16 in dosage compensation of the male X chromosome. We found that H4K16 directly promotes hyper-expression of the male X chromosome in Drosophila. To generate replication timing profiles, we performed Repli-seq in HWT males and females, H4K16R males and females, and H3K9R females. We found that H3K9 promotes late replication of the pericentromeric heterochromatin and H4K16 promotes early replication of the male X chromosome.

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Various modes of HP1a interactions with the euchromatic chromosome arms in Drosophila ovarian somatic cells

Project description:Heterochromatin protein 1a (HP1a) is a well-known component of pericentromeric and telomeric heterochromatin in Drosophila. However, its role and the mechanisms of its binding in the chromosome arms (ChAs) remain largely unclear. Here, we identified HP1a-interacting domains in the somatic cells of Drosophila ovaries using a DamIDseq approach and compared them with insertion sites of transposable elements (TEs) revealed by genome sequencing. Although HP1a domains cover only 13% of ChAs, they non-randomly associate with 42% of TE insertions. Furthermore, HP1a propagates from TE insertions at distances up to 10-kb. These data confirm the role of TEs in formation of HP1a islands in ChAs. However, only 18% of HP1a domains have adjacent TEs, indicating the existence of other mechanisms of HP1a domain formation besides spreading from TEs. In particular, many TE-independent HP1a domains correspond to the regions attached to the nuclear pore complexes (NPCs), or contain active gene promoters. Surprisingly, HP1a occupancy on the promoters of these genes does not lead to their repression. However, the steady-state transcript level of many genes located outside of HP1a domains was altered upon HP1a knockdown in the somatic cells of ovaries, thus pointing to the strong indirect effect of HP1a depletion. Collectively, our results support an existence of at least three different mechanisms of HP1a domain emergence in ChAs: spreading from TE insertions, interaction with the chromatin located near NPCs and targeting to the promoters of moderately expressed genes.

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Project description:A large portion of the mammalian genome is assembled into constitutive heterochromatin which is highly compact and transcriptionally silent throughout the cell cycle. On the molecular level it is characterized by DNA methylation, “repressive” histone marks (hypoacethylation, H3K9 trimethylation, H4K20 trimethylation) and the presence of heterochromatin protein 1 (HP1). Regions of constitutive heterochromatin such as telomeres, pericentromeres and centromeres play a critical role in the maintenance of the genome integrity. Using a technique called Proteomics of Isolated Chromatin Segments (PICh) we have identified SMCHD1 as a novel component of telomeres and pericentomeres. SMCHD1 was previously shown to be involved in the inactivaction of the X chromosome and imprinting, but the its exact role in these processes is not understood. Our study aims to unravel the role of SMCHD1 in the formation and/or maintenance of constitutive chromatin. Using human cancer cells as research model we are trying to discover its mechanism of action by identifying its interacting partners, characterizing its genome wide binding sites and characterizing the effect of SMCHD1 knockout on the heterochromatin function. Characterization of SMCHD1 binding sites in HCT-116 cells.

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