Centromeres consist of specialised centrochromatin containing CENP-A nucleosomes intermingled with H3 nucleosomes carrying transcription-associated modifications. We have designed a novel synthetic biology “in situ epistasis” analysis in which H3K4me2 demethylase LSD2 plus synthetic modules with competing activities are simultaneously targeted to a synthetic alphoidtetO HAC centromere. This allows us to uncouple transcription from histone modifications at the centromere. Here we report that H3K4me2 loss decreases centromeric transcription, CENP-A assembly and stability and causes spreading of H3K9me3 across the HAC, ultimately inactivating the centromere. Surprisingly, CENP-28/Eaf6-induced transcription of the alphoidtetO array associated with H4K12 acetylation does not rescue the phenotype, whereas p65-induced transcription associated with H3K9 acetylation does rescue. Thus mitotic transcription plus histone modifications including H3K9ac constitute the “epigenetic landscape” allowing CENP-A assembly and centrochromatin maintenance. H3K4me2 is required for the transcription and H3K9ac may form a barrier to prevent heterochromatin spreading and kinetochore inactivation at human centromeres.
- Chromosome Segregation
- Human artificial chromosome