Histone deacetylase-1 is required for epigenomic stability in Neurospora crassa [HiC]
Polycomb group 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 and the H3K9me3-binding protein HETEROCHROMATIN PROTEIN 1 (HP1). How constitutive heterochromatin impacts PRC2 activity is unclear. HP1 forms multiple protein complexes including the HCHC complex, which removes acetyl groups from histones in constitutive heterochromatin, and contains the proteins Histone Deacetylase 1(HDA-1) and Chromodomain Protein-2 (CDP-2). To identify genes required for Polycomb repression in N. crassa, we performed a genetic screen and identified HDA-1 as necessary for PRC2-targeted gene silencing. In the absence of HDA-1, H3K27me2/3 is lost from the subtelomeres and aberrantly accumulates at constitutive heterochromatin domains normally enriched for H3K9me3; CDP-2 is also important for wildtype H3K27me3 localization. The H3K27me2/3 redistribution in ?hda-1 or ?cdp-2 strains is variable and incomplete, and mutant progeny obtained following a sexual cross displayed wild-type H3K27me3 patterns, consistent with HCHC loss leading to progressive changes in H3K27me3 enrichment. Indeed, a newly constructed ?hda-1 deletion strain displays a wild-type H3K27me3 pattern that relocalizes to constitutive heterochromatic regions after sequential passages. Thus, HCHC-specific deacetylation prevents aberrant recruitment of PRC2 to constitutive heterochromatin. Overall design: Chromosome conformation capture coupled with high-throughput sequencing of two independent strains of the filamentous fungus Neurospora crassa deleted of the gene hda-1 (histone deacetylase-1), which is the catalytic subunit of the HCHC histone deacetylase complex