Evolution and instability of human centromeres are accelerated by heterochromatin boundary loss and CENP-A overexpression

Abstract

Centromere location is specified by CENP-A, a centromere-specific histone that epigenetically defines centromere identity. How CENP-A is maintained at one location in rapidly evolving centromeric DNA is unknown. Using single-cell-derived clones of human cell lines, we demonstrate single-cell heterogeneity in CENP-A position within cell populations at neocentromeres and a native centromere. CENP-A heterogeneity is accompanied by unique DNA methylation and H3K9me3 patterns, with DNA methylation shifting according to CENP-A position. We further demonstrate centromere epigenetic evolution over prolonged proliferation, with native centromeres maintaining stable heterochromatin boundaries, but neocentromeres exhibiting DNA methylation instability, H3K9me3 gain, boundary loss and fragility. Lastly, prolonged CENP-A and HJURP overexpression leads to centromere and neocentromere expansion, gradual CENP-A depletion, neocentromere destabilization and CENP-A re-localization that is accompanied by local heterochromatin remodeling. This study reveals the naturally evolving epigenetic plasticity of human centromeres and neocentromeres and highlights the importance of repressive chromatin boundaries in maintaining centromere stability.