Reprogramming of Human Cells to Pluripotency Induces CENP-A Chromatin Depletion

Abstract

Pluripotent stem cells (PSCs) are central to development as they are the precursors of all cell types in the embryo. Therefore, maintaining a stable karyotype is essential, both for their physiological role as well as for use in regenerative medicine. In culture, an estimated 10-30% of PSC lines present karyotypic abnormalities, but the underlying causes remain unknown. To gain insight into the mitotic capacity of human embryonic stem cells and induced pluripotent stem cells, we explore the structure of the centromere and kinetochore. Centromere function depends on CENP-A nucleosome-defined chromatin. We show that while PSCs maintain abundant pools of CENP-A, CENP-C and CENP-T, these essential centromere components are strongly reduced at stem cell centromeres. Outer kinetochore recruitment is also impaired to a lesser extent, indicating an overall weaker kinetochore. This impairment is specific for the kinetochore forming centromere complex while the inner centromere protein Aurora B remains unaffected. We further show that, similar to differentiated human cells, CENP-A chromatin assembly in PSCs requires transition into G1 phase. Finally, reprogramming experiments indicate that reduction of centromeric CENP-A levels is an early event during dedifferentiation, coinciding with global chromatin remodelling. Our characterisation of centromeres in human stem cells drives new hypotheses including a possible link between impaired centromere function and stem cell aneuploidies.