Summary
A bioRxiv preprint presents the first genome-wide maps of four major histone modifications in the reef-building coral Pocillopora damicornis. The maps associate distinct chromatin states with gene expression, receptor-related genes, developmental functions and transposable element-like regions.
A preprint reports the first genome-wide maps of four major histone modifications in the reef-building coral Pocillopora damicornis. The study combines these chromatin maps with RNA sequencing to show that different patterns of histone marks are associated with different levels and types of gene activity in adult coral maintained under ambient conditions.
The work, posted on bioRxiv on September 16, 2026, provides a baseline view of how DNA may be packaged and regulated in a reef-building coral. It is a preprint and has not been described in the supplied source as having undergone peer review.
How the coral genome was mapped
DNA in cells is wrapped around proteins called histones. Chemical modifications to those proteins can alter the local chromatin environment—the combination of DNA and associated proteins—and are used by cells as part of gene regulation. These modifications are often described as “marks” because they identify genomic regions with different regulatory states.
The researchers used chromatin immunoprecipitation sequencing, or ChIP-seq, to locate four marks across the coral genome. H3K4me3 and H3K27ac were treated as active marks, while H3K27me3 and H3K9me3 were treated as repressive marks. They then integrated the results with RNA-seq, which measures RNA produced from genes, to compare chromatin state with transcriptional output.
The two active marks were enriched near transcriptional start sites, the regions where transcription begins, and were positively associated with gene expression. The two repressive marks showed broader patterns and were negatively associated with transcription. These are genome-wide associations: the study maps how the marks and gene activity occur together rather than showing that changing a particular mark directly causes a specific gene to turn on or off.
Distinct regulatory states in highly expressed genes
The study found that genes with high expression could still have different promoter chromatin states. One group had strong H3K4me3 and H3K27ac signals at promoters and was enriched for YY1-family DNA-sequence motifs. These genes were associated with core cellular functions.
A second group had similar transcript abundance but lacked the same active promoter marks and motif pattern. This group was enriched for genes involving cell-surface receptors and proteolysis, the breakdown of proteins. The result indicates that comparable levels of gene transcription can occur through different regulatory configurations.
The repressive marks also separated functional genomic regions. H3K27me3 was enriched over lowly expressed receptor-like and developmental gene classes. H3K9me3 was prominent at transposable element-like loci and broad non-genic regions—parts of the genome outside annotated genes.
The researchers additionally identified candidate enhancer-like elements. These regions had high H3K27ac but relatively little H3K4me3 and were located near core promoters, the DNA regions controlling gene initiation. Many were close to genes with transcription-factor-related functions. Enhancers are regulatory DNA elements that can influence gene activity, although their specific roles require further testing.
Why the baseline matters
Corals can alter their physiology and patterns of gene expression in response to environmental and biological conditions. A genome-wide reference for chromatin states gives researchers a way to compare those responses at a regulatory level, rather than examining only the RNA produced by genes.
The maps may therefore support future studies of how coral gene regulation changes with environmental conditions, development or symbiosis. Their immediate contribution is a reference dataset for reef-building coral and a foundation for validating targeted chromatin assays.
The reported profile is limited to adult P. damicornis maintained under ambient conditions. It represents a baseline state, so comparisons across environmental challenges, developmental stages and symbiotic contexts remain future research directions. As a bioRxiv preprint, the findings should be read as preliminary research pending peer-reviewed evaluation.