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A giant virus genome is densely packaged by stable nucleosomes

ABSTRACT: The doublet histones of Marseillevirus are distantly related to the four eukaryotic core histones and wrap DNA to form remarkably similar nucleosomes. By releasing Marseillevirus chromatin from virions into solution and performing genome-wide nuclease digestion and chemical cleavage assays, we find that the higher-order organization of Marseillevirus chromatin differs greatly from that of eukaryotes. Marseillevirus nucleosomes fully protect DNA within virions, without linker DNA or phasing along genes. Likewise, we observe that most nucleosomes reconstituted onto 3-copy tandem repeats of a nucleosome positioning sequence are tightly packed and fully wrapped. We also document repeat generation and instability during viral passage in amoeboid culture. Dense promiscuous packing of fully wrapped nucleosomes rather than “beads-on-a-string” with genic punctuation suggests a viral genome protection function for doublet histones.

ORGANISM(S): synthetic construct Marseillevirus marseillevirus Drosophila melanogaster

PROVIDER: GSE193224 | GEO | 2022/09/27

REPOSITORIES: GEO

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Project description:In mature human sperm, genes of importance for embryo development (i.e. transcription factors) lack DNA methylation and bear nucleosomes with distinctive histone modifications, suggesting the specialized packaging of these developmental genes in the germline. Here, we explored the tractable zebrafish model and found conceptual conservation as well as several new features. Biochemical and mass spectrometric approaches reveal the zebrafish sperm genome packaged in nucleosomes and histone variants (and not protamine), and we find linker histones high and H4K16ac absent - key factors which may contribute to genome condensation. We examined several activating (H3K4me2/3, H3K14ac, H2AFV) and repressing (H3K27me3, H3K36me3, H3K9me3, hypoacetylation) modifications/compositions genome-wide, and find developmental genes packaged in large blocks of chromatin with coincident activating and repressing marks and DNA hypomethylation, revealing complex ‘multivalent’ chromatin. Notably, genes that acquire DNA methylation in the soma (muscle) are enriched in transcription factors for alternative cell fates. Remarkably, we find H3K36me3 located in ‘silent’ developmental gene promoters, and not present at the 3’ ends of coding regions of genes heavily transcribed during sperm maturation, suggesting different rules for H3K36me3 in the germline and soma. We also reveal the chromatin patterns of transposons, rDNA, and tRNAs. Finally, high levels of H3K4me3 and H3K14ac in sperm are correlated with genes activated in embryos prior to the mid-blastula transition (MBT), whereas multivalent genes are correlated with activation at or after MBT. Taken together, gene sets with particular functions in the embryo are packaged by distinctive types of complex and often atypical chromatin in sperm. [DNA profiling]: H3K4me3, H3K4me2, H3K14ac, H3K36me3, H3K27me3, H3K9me3, and H2AFV ChIP-chip in zebrafish sperm; DNA methylation in zebrafish sperm and muscle by MeDIP-chip. (two replicates and dye-swaps for all experiments). Antibodies: H3K4me3 (Abcam ab8580 and Active Motif 39159), H3K4me2 (Abcam ab7766), H3K14Ac (Upstate 07-353), H2AZ (Abcam ab4174), H3K27me3 (Upstate 07-449), H3K9me3 (Active Motif 39161), H3K36me3 (Abcam ab9050), 5-methylcytidine (Eurogentec BI-MECY-1000). Supplementary files: Processed data files reporting calculated enrichment log2 ratio (mean ChIP/mean Input in the log2 ratio). Note: For analysis, "mean Input" from H3K4me3-rep1 ch1, H3K4me2-rep1 ch2, and H3K36me3-rep2 ch1 for all ChIP eluates. [mRNA profiling]: Transcripts in zebrafish mature sperm using zebrafish expression microarray from Agilent. (two replicates)

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A giant virus genome is densely packaged by stable nucleosomes

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