Diversity and evolution of chromatin regulatory states across eukaryotes

Histone post-translational modifications (hPTMs) are key regulators of chromatin states ^1,2 , influencing gene expression, epigenetic memory, and transposable element repression across eukaryotic genomes. While many hPTMs are evolutionarily conserved ³ , the extent to which the chromatin states they define are similarly preserved remains unclear. Here, we developed a combinatorial indexing ChIP-seq method to simultaneously profile specific hPTMs across diverse eukaryotic lineages ⁴ , including amoebozoans, rhizarians, discobans, and cryptomonads. Our analyses revealed highly conserved euchromatin states at active gene promoters and gene bodies. In contrast, we observed diverse configurations of repressive heterochromatin states associated with silenced genes and transposable elements, characterized by various combinations of hPTMs such as H3K9me3, H3K27me3 and/or different H3K79 methylations. These findings suggest that while core hPTMs are ancient and broadly conserved, their functional readout has diversified throughout eukaryotic evolution, shaping lineage-specific chromatin landscapes.