The INO80 complex regulates epigenetic inheritance of heterochromatin (ChIP-seq, Mnase-seq)

One key aspect of epigenetic inheritance is that chromatin structure can be stably inherited through generations even after removal of the signal that establishes such structure. In fission yeast, the RNA interference (RNAi) machinery is critical for initial targeting of histone methyltransferase Clr4 to pericentric repeats to establish heterochromatin. However, pericentric heterochromatin cannot be properly inherited in the absence of RNAi, suggesting the existence of mechanisms that counteract chromatin structure inheritance. Here we show that in the absence of certain components of the INO80 chromatin-remodeling complex, pericentric heterochromatin can be properly inherited in RNAi mutants. The ability of INO80 to counter heterochromatin inheritance is attributed to one accessory subunit Iec5, which promotes histone turnover at heterochromatin regions, but has little effects on nucleosome positioning at heterochromatin, gene expression, or the DNA damage response. Slow histone turnover preserves parental histones at repeat regions to enhance epigenetic inheritance of heterochromatin not only in RNAi mutants but also in wild type cells. Our analyses demonstrate the importance of INO80 in controlling heterochromatin inheritance and maintaining the proper heterochromatin landscape of the genome. ChIP-seq of H3K9me2 of iec5Δ. MNase-seq of three Ino80 mutants and dcr1Δ. MNase-seq for wild-type and iec5Δ in strains with tetO-ura4-GFP reporter