Histone deacetylase-1 is required for epigenomic stability in Neurospora crassa [ChIP-seq]
Polycomb group (PcG) proteins assemble into chromatin modifying complexes that regulate stem cell identity and multicellular development. The trimethylation of lysine 27 on histone H3 (H3K27me3) is catalyzed by the conserved Polycomb Repressive Complex 2 (PRC2). In Neurospora crassa, the typically-subtelomeric pattern of H3K27me3 depends on other chromatin regulators including the H3K36 methyltransferase ASH1, the chromatin remodeling enzyme IMITATION SWITCH, and components of constitutive heterochromatin including the H3K9 methyltransferase DEFECTIVE IN METHYLATION-5 (DIM-5) and the H3K9me3-binding protein HETEROCHROMATIN PROTEIN 1 (HP1). How constitutive heterochromatin impacts PRC2 activity is unclear. We performed a genetic screen to identify histone deacetylase genes required to repress PRC2-methylated genes in N. crassa. We found that HISTONE DEACETYLASE-1 (HDA-1) is required for transcriptional repression in PcG-repressed domains and for normal patterns of H3K27me3. In the absence of HDA-1, H3K27me3 is lost from typical PRC2-methylated domains and instead is enriched at a subset of constitutive heterochromatin domains normally marked for H3K9me3. In addition to altered H3K27me3 patterns, HDA-1-deficient mutants displayed aberrant patterns of H3K9me3, H3K36me3, and lysine acetylation (Kac). Mutants lacking the HP1/HDA-1-interacting protein CHROMO DOMAIN PROTEIN-2 (CDP-2) displayed a similar but non-identical phenotype, and we observed variable patterns of aberrant H3K7me3 enrichment in genetically identical ?hda-1 strains, raising the possibility that loss of HDA-1 activity leads to progressive changes in H3K27me3 enrichment. Indeed, a newly constructed ?hda-1 deletion strain displayed a near-wild type H3K27me3 chromatin modification profile that decayed over multiple strain passages corresponding to hundreds of nuclear divisions. Together, our data indicate that HDA-1 is a critical regulator of epigenome stability in N. crassa. Overall design: Zachary Lewis