Orateur
Description
Centromeric regions of eukaryotic chromosomes contain large arrays of tandemly repeated DNA sequences, known as satellite DNA. In mouse NIH3T3 cells, pericentromeric satellite sequences from distinct chromosomes cluster into chromocenters. These structures consist of constitutive heterochromatin enriched in specific epigenetic modifications, including H3K9me3, and they recruit HP1 proteins—both of which are known to be required for chromocenter formation. However, their precise roles and their interplay with other heterochromatin domains remain unclear. To dissect their roles, we engineered a TALE-KDM4D tool that specifically demethylates H3K9me3 at major pericentromeric satellites. Using 3D imaging, we found that local loss of H3K9me3 reduces HP1 recruitment at chromocenters but leaves their overall 3D architecture largely intact, indicating that additional factors contribute to chromocenter formation. Moreover, by combining 3D microscopy with ChIP-seq, we show that removing H3K9me3 from pericentromeres triggers a redistribution of the mark: methyltransferases are redirected to other genomic regions, leading to increased H3K9me3 at sites already enriched, coinciding with the emergence of compact, heterochromatin-rich domains outside chromocenters. Hi-C analysis further reveals that this redistribution is accompanied by a reorganization of interactions between heterochromatin domains. Together, these results reveal a novel crosstalk between distinct heterochromatin regions and challenge the notion that H3K9me3/HP1 alone is sufficient to drive chromocenter formation.