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Histone deacetylation and cytosine methylation are required for the normal compartmentalization of heterochromatin in the genome organization of Neurospora crassa [Hi-C]

ABSTRACT: Chromosomes must correctly fold in eukaryotic nuclei for proper genome function. Eukaryotic organisms hierarchically organize their genomes: in the fungus Neurospora crassa, chromatin fiber loops compact into Topologically Associated Domain (TAD)-like structures that are anchored by heterochromatic region aggregates. However, insufficient information exists on how histone post-translational modifications, including acetylation, impact genome organization. In Neurospora, the HCHC (HDA-1, CDP-2, HP1, CHAP) complex deacetylates heterochromatic regions including centromeres: loss of individual HCHC members increases centromeric acetylation and cytosine methylation. Here, we evaluate the role of the HCHC complex on genome organization using chromosome conformation capture with high-throughput sequencing (Hi-C) in Δcdp-2 or Δchap deletion strains. CDP-2 loss increases interactions between intra- and inter-chromosomal heterochromatic regions, while removal of CHAP decreases heterochromatic region compaction. Individual HCHC mutants exhibit different histone PTM patterns genome-wide: in Dcdp-2, heterochromatic H4K16 acetylation is increased, yet some heterochromatic regions lose H3K9 trimethylation, which locally increases inter-heterochromatin contacts; CHAP loss produces minimal acetylation changes but increases H3K9me3 enrichment in heterochromatin. Furthermore, deletion of the DIM-2 DNA methyltransferase in a Δcdp-2 background causes extensive genome disorder, as heterochromatic-euchromatic contacts increase despite additional H3K9me3 enrichment. Our results highlight how enhanced cytosine methylation ensures heterochromatic compartmentalization when silenced regions are acetylated.

ORGANISM(S): Neurospora crassa

PROVIDER: GSE232934 | GEO | 2023/07/03

REPOSITORIES: GEO

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Project description:Cytosine methylation, a fundamental form of epigenetic regulation, is found in many eukaryotes and plays a significant role in cancer and other diseases. Using the genetically tractable model organism Neurospora crassa, we have identified genes that when mutated, cause the strains to be defective in methylation (dim). The process of DNA methylation in Neurospora has been shown to be dependent on DCDC, a five-member complex that directs the histone methyltransferase DIM-5 to tri-methylate Lysine 9 on histone H3 (H3K9me3). This mark is recognized by HP1, which directs DIM-2 to methylate DNA. In contrast, the HCHC complex employs HDA-1, CDP-2, HP1, and CHAP to deacetylate that same residue on H3. While we know a good deal about DNA methylation, it is still unclear whether we have identified all the genes involved in the process. Thus, we continued our search for dim mutants, using a selection for reactivation of silenced drug resistance genes. Interestingly, we predominantly identified known dim genes, including dim-5, dim-7, dim-8, dim-9, hpo, chap, cdp-2, and hda-1. Using a Sanger sequencing-based approach, we identified mutations in these known dim genes, presumably responsible for the Dim- phenotype; many mutations were unique point mutants that could compromise protein activity or structure, or impact protein-protein interactions. For mutants in which the gene was not placed into a complementation group, we employed a bulk segregant analysis and whole genome sequencing approach to identify additional mutations in known DNA methylation genes, including hH3 and dim-1, as well as a novel dim mutant: dim-10, a fungal-specific protein that may work with DCDC for H3K9me3 catalysis. Not only will this dim mutant collection be a useful resource to investigate the roles of these dim genes and their protein products in DNA methylation, but the isolation of a novel dim gene by a forward genetics approach provides an exciting avenue of research into how incipient heterochromatin formation is achieved.

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Histone deacetylation and cytosine methylation are required for the normal compartmentalization of heterochromatin in the genome organization of Neurospora crassa [Hi-C]

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