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Dynamic association of H3K36me3 with pericentromeric heterochromatin regulates its replication time.

The flexibility of the spatio-temporal genome replication program during development and disease highlights the regulatory role of plastic epigenetic mechanisms over genetic determinants. Histone post-translational modifications are broadly implicated in replication timing control, yet the specific mechanisms through which individual histone marks influence replication dynamics, particularly in heterochromatin, remain unclear. Here, we demonstrate that H3K36me3 dynamically enriches at pericentromeric heterochromatin, composed of major satellite DNA repeats, prior to replication during mid S phase in mouse embryonic stem cells. By knocking down lysine 36-specific methyltransferases or by targeting the H3K36M oncohistone to pericentromeric heterochromatin, we reduce global or local H3K36me3 levels, respectively, revealing its essential role in preserving the replication timing of constitutive heterochromatin. Loss of H3K36me3 accompanies increased RNA polymerase II serine-5 phosphorylation and lowered major satellite RNA levels, indicating transcriptional dysregulation. Notably, we identify a strand-specific contribution of major satellite forward transcripts in regulating the replication timing of constitutive heterochromatin and maintaining chromatin stability, highlighting the importance of non-coding RNAs as critical regulators of replication timing.

Heterochromatin

Multiomics Reveal Associations Between CpG Methylation, Histone Modifications and Transcription in a Species That has Lost DNMT3, the Colorado Potato Beetle.

Insects display exceptional phenotypic plasticity, which can be mediated by epigenetic modifications, including CpG methylation and histone modifications. In vertebrates, both are interlinked and CpG methylation is associated with gene repression. However, little is known about these regulatory systems in invertebrates, where CpG methylation is mainly restricted to gene bodies of transcriptionally active genes. A widely conserved mechanism involves the co-transcriptional deposition of H3K36 trimethylation and the targeted methylation of unmethylated CpGs by the de novo DNA methyltransferase DNMT3. However, DNMT3 has been lost multiple times in invertebrate lineages raising the question of how the links between CpG methylation, histone modifications and gene expression are affected by its loss. Here, we report the epigenetic landscape of Leptinotarsa decemlineata, a beetle species that has lost DNMT3 but retained CpG methylation. We combine RNA-seq, enzymatic methyl-seq and CUT&Tag to study gene expression, CpG methylation and patterns of H3K36me3 and H3K27ac histone modifications on a genome-wide scale. Despite the loss of DNMT3, H3K36me3 mirrors CpG methylation patterns. Together, they give rise to signature profiles for expressed and not expressed genes. H3K27ac patterns show a prominent peak at the transcription start site that is predictive of expressed genes irrespective of their methylation status. Our study provides new insights into the evolutionary flexibility of epigenetic modification systems that urge caution when generalizing across species.

Animals

Epigenetic maps of pearl millet reveal a prominent role for CHH methylation in regulating tissue-specific gene expression.

UNLABELLED: Pearl millet (Pennisetum glaucum) is a major staple food in arid and semi-arid regions of sub-Saharan Africa, India, and South Asia. However, how epigenetic mechanisms regulate tissue-specific gene expression in this crop remains poorly understood. In this study, we profiled multiple epigenetic features in the young panicles and roots of pearl millet using RNA-seq, ATAC-seq, whole-genome bisulfite sequencing, and ChIP-seq (H3K4me3 and H3K36me3). We identified thousands of genes that were differentially expressed between these two tissues. Root-specific genes were enriched for plant hormone signaling, oxidative phosphorylation, and stress responses. Analysis of chromatin accessibility revealed that root-specific accessible chromatin regions (ACRs) were enriched in binding motifs for stress-responsive transcription factors (e.g., NAC, WRKY), whereas ACRs in young panicles were enriched in motifs for developmental regulators (e.g., AP2/ERF). DNA methylation profiling revealed 25,141 tissue-specific differentially methylated regions, with CHH methylation-rather than CG or CHG methylation-showing the strongest tissue specificity. Promoters of root-specific genes had higher levels of CHH methylation compared to those of young panicle-specific genes, suggesting that the roles of CHH methylation in regulating transcription might be tissue dependent. Notably, promoter-associated H3K4me3 marked panicle-specific genes, whereas root-specific expression was primarily linked to chromatin accessibility, suggesting a transcription factor-mediated regulatory mechanism. Together, our findings highlight the distinct epigenetic frameworks governing tissue-specific gene expression in pearl millet and provide valuable insights for advancing the genetic improvement of this crop. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s42994-025-00243-2.

CHH methylation

Using the DNA language model, GROVER, to parse effects of sequence, chromatin and regulatory features on genome stability.

MOTIVATION: Genome stability is shaped by DNA sequence and chromatin context, but their relative contributions to double-strand break (DSB) sensitivity remain unclear. RESULTS: We show that the DNA language model, GROVER, can infer DSB location based on sequence. DSB hotspots tend to contain GC-rich sequences that belong to promoters, genes and short interspersed nuclear elements (SINEs). Additionally, we identified several specific short sequences (tokens) that are associated with modulating DSB sensitivity. Another model using chromatin and genome regulatory features outperforms the sequence-only model, highlighting complementary and cell-type specific information. Integrating sequence and genome biological features yields the best performance, demonstrating their synergy. Analyzing this model revealed that, dependent on the sample, genome stability information encoded in H3K36me3 and DNase-seq can be learned from the sequence, but not H3K27ac or H3K9me3. Embedding chromatin data directly into the GROVER architecture enabled cell-type specific modeling with performance matching the full chromatin feature model. Our results suggest that while chromatin and regulatory context provides important information, such as cell-type specificity, much of the information shaping DSB patterns is already encoded in the DNA sequence itself. Our integrative modeling approach not only reveals DSB patterns but also provides a generalizable strategy for tracing predictions in genomic data. AVAILABILITY: Data, models, and a tutorial are available on Zenodo.

Chromatin

Chromatin Landscape Is Associated With Sex-Biased Expression and Drosophila-Like Dosage Compensation of the Z Chromosome in Artemia franciscana.

The males and females of the brine shrimp Artemia franciscana are highly dimorphic, and this dimorphism is associated with substantial sex-biased gene expression in heads and gonads. How these sex-specific patterns of expression are regulated at the molecular level is unknown. A. franciscana also has differentiated ZW sex chromosomes, with complete dosage compensation, but the molecular mechanism through which compensation is achieved is unknown. Here, we conducted CUT&TAG assays targeting 7 post-translational histone modifications (H3K27me3, H3K9me2, H3K9me3, H3K36me3, H3K27ac, H3K4me3, and H4K16ac) in heads and gonads of A. franciscana, allowing us to divide the genome into 12 chromatin states. We further defined functional chromatin signatures for all genes, which were correlated with transcript level abundances. Differences in the occupancy of the profiled epigenetic marks between sexes were associated with differential gene expression between males and females. Finally, we found a significant enrichment of the permissive H4K16ac histone mark in the Z-specific region in both tissues of females but not males, supporting the role of this histone mark in mediating dosage compensation of the Z chromosome.

Animals

Deficiency of Setd2 in mesenchymal stem cells facilitates the progression of myelodysplastic syndrome to leukemia.

While previous studies have indicated that H3K36me3, which is mediated by Setd2, may regulate the cell fate of mesenchymal stem cells (MSCs) both in vitro and in vivo, the specific role of MSCs in the onset and progression of MDS remains unclear. Thus, the histone methyltransferase Setd2 is implicated in MDS-associated leukemia. This study utilized NUP98-HOXD13 (NHD13) mice with targeted deletion of Setd2 in MSCs. Here, we found that Setd2-deficient mice undergo faster leukemia transformation than control mice do, as evidenced by the abnormal differentiation of hematopoietic stem progenitor cells in the bone marrow, abnormal hematopoiesis, and increased number of blast cells. Compared with that of control mice, the morphology of NHD13 mouse MSCs with Setd2 deficiency was irregular, and the support function of hematopoietic cells was compromised. This study demonstrated that targeted deletion of Setd2 in MSCs facilitates the advancement of MDS. Furthermore, we identified increased expression of coagulation factor XII as a key leukemic transformation mediator in Setd2-deficient MSCs. Moreover, we found that SETD2 expression is significantly lower in high-risk MDS patients than in low-risk MDS patients, further suggesting that the targeted deletion of Setd2 in MSCs is associated with MDS progression. Collectively, our results suggest that Setd2 in MSCs suppresses MDS progression to leukemia through coagulation factor XII-mediated suppression of the stem cell support capacity of MSCs. Overall, this study sheds light on the pathogenesis of MDS and provides a therapeutic strategy for regulating the microenvironment in patients with MDS who cannot be cured by haematopoietic stem cell transplantation.

Animals