Inheritance of each chromosome depends upon its centromere. A histone H3 variant, CENP-A, is essential for epigenetically marking centromere location. We find that CENP-A is quantitatively retained at the centromere upon which it is initially assembled. CENP-C binds to CENP-A nucleosomes and is a prime candidate to stabilize centromeric chromatin. Using purified components, we find that CENP-C reshapes the octameric histone core of CENP-A nucleosomes, rigidifies both surface and internal nucleosome structure, and modulates terminal DNA to match the loose wrap that is found on native CENP-A nucleosomes at functional human centromeres. Thus, CENP-C affects nucleosome shape and dynamics in a manner analogous to allosteric regulation of enzymes. CENP-C depletion leads to rapid removal of CENP-A from centromeres, indicating their collaboration in maintaining centromere identity.

Maintenance of genome stability during cell division depends on establishing correct attachments between chromosomes and spindle microtubules. Correct, bi-oriented attachments are stabilized, while incorrect attachments are selectively destabilized. This process relies largely on increased phosphorylation of kinetochore substrates of Aurora B kinase at misaligned versus aligned kinetochores. Current models explain this differential phosphorylation by spatial changes in the position of substrates relative to a constant pool of kinase at the inner centromere. However, these models are based on studies in aneuploid cells. We show that normal diploid cells have a more robust error correction machinery. Aurora B is enriched at misaligned centromeres in these cells, and the dynamic range of Aurora B substrate phosphorylation at misaligned versus aligned kinetochores is increased. These findings indicate that in addition to Aurora B regulating kinetochore-microtubule binding, the kinetochore also controls Aurora B recruitment to the inner centromere. We show that this recruitment depends on both activity of Plk1, a kinetochore-localized kinase, and activity of Aurora B itself. Our results suggest a feedback mechanism in which Aurora B both regulates and is regulated by chromosome attachment to the spindle, which amplifies the differential phosphorylation of kinetochore substrates and increases the efficiency of error correction.

Summary Centromeres control genetic inheritance by directing chromosome segregation but are not genetically encoded themselves. Rather, centromeres are defined by nucleosomes containing CENP-A, a histone H3 variant [1]. In cycling somatic cells, centromere identity is maintained by an established cell cycle-coupled CENP-A chromatin assembly pathway, but how centromeres are inherited through the mammalian female germline is unclear because of the long (months to decades) prophase I arrest. We show that mouse oocytes retain the pool of CENP-A nucleosomes assembled before birth, and this pool is sufficient for centromere function, fertility, and genome transmission to embryos. Indeed, oocytes lack any measurable CENP-A nucleosome assembly through the entire fertile lifespan of the female (>1 year). Thus, the remarkable stability of CENP-A nucleosomes confers transgenerational centromere identity in mammals.

The centromere directs chromosome segregation and genetic inheritance but is not itself heritable in a canonical, DNA-based manner. In most species, centromeres are epigenetically defined by the presence of a histone H3 variant CENP-A (Centromere Protein A), independent of underlying DNA sequence. Therefore, centromere inheritance depends on maintaining the CENP-A nucleosome mark across generations. Experiments in cycling somatic cells have led to a model in which centromere identity is maintained by a cell cycle-coupled CENP-A chromatin assembly pathway. However, the processes of animal gametogenesis pose unique challenges to centromere inheritance because of the extended cell cycle arrest and the massive genome reorganization in the female and male germline respectively. Here, we review our current understanding of germline centromere inheritance and highlight outstanding questions.

This work was supported by a Research Grant from the American Society of Reproductive Medicine and support from the Charles and Johanna Busch Memorial Fund at Rutgers, the State University of NJ to K.S. and the Foundation for Embryonic Competence, Inc to N.T. The authors declare no conflicts of interest.