The histone variant H2A.Z is required to establish normal patterns of H3K27 methylation in Neurospora crassa

Neurospora crassa contains a minimal Polycomb repression system, which provides rich opportunities to explorePolycomb-mediated repression across eukaryotes and enables genetic studies that can be difficult in plant and animal systems.& Polycomb Repressive Complex 2 (PRC2) is a multi-subunit complex that deposits mono-, di-, and tri-methyl groups on lysine 27 of histone H3, and tri-methyl H3K27 is a molecular marker of transcriptionally repressed facultative heterochromatin. In mouse embryonic stem cells and multiple plant species, H2A.Z has been found to be co-localized with H3K27 methylation. H2A.Z is required for normal H3K27 methylation in these experimental systems, though the regulatory mechanisms are not well understood. We report here that Neurospora crassa mutants lacking H2A.Z or SWR-1, the ATP-dependent histone variant exchanger, exhibit a striking reduction in levels of H3K27 methylation. RNA-sequencing revealed downregulation of eed in an hH2Az mutant compared to wild type, encoding a subunit of PRC2, and overexpression of EED in a ? hH2Az ;? eed background restored most H3K27 methylation. Reduced eed expression leads to region-specific losses of H3K27 methylation suggesting that EED-dependent mechanisms are critical for normal H3K27 methylation at certain regions in the genome.