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Chromatin landscape of budding yeast acquiring H3K9 methylation and its reader molecule HP1 [ChIP-Seq]

ABSTRACT: Histone H3 lysine 9 (H3K9) methylation and heterochromatin protein 1 (HP1) are well conserved epigenetic silencing mark and its reader molecule, and crucial for heterochromatin formation. However, the details of the importance of H3K9 methylation and HP1 in heterochromatin formation still remain unclear. One of the reason is the redundancy problem, as there are multiple reader molecules for H3K9 methylation, including HP1, and HP1 itself functions as a hub that recruits various effector molecules. To overcome the redundancy issue, we took synthetic biology approach and introduced H3K9 methylation and HP1 into budding yeast Saccharomyces cerevisiae, which does not have this system, and examined its impact on transcription and chromatin compaction. We observed that mammalian H3K9 methyltransferase can induce genome wide H3K9 di- and tri-methylation (H3K9me2,3) in budding yeast, and that HP1 accumulates over the H3K9 methylated regions. However, H3K9 methylation occurred mainly in the gene body region of the genes and excluded around TSS where H3K9ac pre-exists. Correspondingly, expression of H3K9 methyltransferase and HP1 did not affect transcription in budding yeast, including repression. ATAC-seq analysis also showed no impact on chromatin accessibility, and Hi-C-seq analysis of chromatin 3D structure revealed no significant differences. These results suggest that even though H3K9 methylation and recruitment of HP1 play essential roles in epigenetic regulation of heterochromatin, they are not sufficient to build up heterochromatin, at least at gene body regions, and further participation of effector molecules, including downstream factors of HP1, is required.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE224639 | GEO | 2024/02/03

REPOSITORIES: GEO

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Project description:Methylation of histone H3 at lysine 9 (H3K9) is a hallmark of heterochromatin that plays crucial roles in chromatin-dependent gene silencing and maintenance of genome stability by repressing repetitive DNA elements and recruiting downstream factors essential for faithful chromosome segregation. Fundamental principles of these processes have been elucidated in the fission yeast Schizosaccharomyces pombe (S. pombe), in which Clr4, the homologue of mammalian SUV39H, is the sole H3K9 methyltransferase. Although H3K9 methylation has been intensely studied in mitotic cells, occurrence and regulation during sexual differentiation remain largely unknown. Whether distinct H3 methylation states are relevant for gametogenesis is also not known. Here, using diploid S. pombe cells, we map H3K9 methylation genome-wide during the meiotic program and show that constitutive heterochromatin temporarily loses H3K9me2 and becomes H3K9me3 when cells exit mitosis and commit to the meiotic life cycle. Cells lacking the ability to tri-methylate H3K9 exhibit severe meiotic chromosome segregation defects, which does not occur in mitotic cells. Artificially increasing the affinity of the fission yeast heterochromatin protein 1 (HP1) homologue Swi6 towards H3K9me2 rescues chromosome segregation in the absence of H3K9me3. Thus, the H3K9me2 to H3K9me3 switch during early meiosis serves to retain Swi6 at centromeres, which is necessary for cohesin recruitment and kinetochore assembly. Finally, we show that the H3K9 methylation switch is regulated by differential phosphorylation of Clr4 by the cyclin-dependent kinase (CDK) Cdk1. Our results reveal how a highly conserved master regulator of the cell cycle regulates the specificity of the H3K9 methyltransferase and thereby controls the ratio of H3K9me2 to H3K9me3 to prevent unwanted gene silencing and to ensure faithful meiotic chromosome segregation. High degree of conservation of the proteins involved in our study and CDK-dependent phosphorylation of the mammalian SUV39H1 homologue suggest broad conservation of the mechanisms described here.

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Chromatin landscape of budding yeast acquiring H3K9 methylation and its reader molecule HP1 [ChIP-Seq]

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