Epigenetic rewriting at centromeric DNA repeats leads to increased chromatin accessibility and chromosomal instability

Centromeric regions of human chromosomes contain large numbers of tandemly repeated -satellite sequences. These sequences are covered with constitutive heterochromatin which is enriched in trimethylation of histone H3 on lysine 9 (H3K9me3). Although well studied using artificial chromosomes and global perturbations, the contribution of this epigenetic mark to chromatin structure and genome stability remains poorly known in a more natural context. Using transcriptional activator-like effectors (TALEs) fused to a histone lysine demethylase (JMJD2B), we were able to reduce the level of H3K9me3 on the -satellites repeats of human chromosome 7. We show that the removal of H3K9me3 affects chromatin structure by increasing the accessibility of DNA repeats to the TALE protein. Tethering TALE-demethylase to centromeric repeats impairs the recruitment of HP1 and proteins of Chromosomal Passenger Complex (CPC) on this specific centromere. Finally, the epigenetic re-writing by the TALE-JMJD2B affects specifically the stability of chromosome 7 upon mitosis, highlighting the importance of H3K9me3 in centromere integrity and chromosome stability, mediated by the recruitment of HP1 and the CPC.