Epigenetic specification of centromeres by CENP-A

Centromeres are the chromosomal loci that direct the formation of the kinetochores. These macromolecular assemblies mediate the interaction between chromosomes and spindle microtubules and thereby power chromosome movement during cell division. They are also the sites of extensive regulation of the chromosome segregation process. Except in the case of budding yeast, centromere identity does not rely on DNA sequence but on the presence of a special nucleosome that contains a histone H3 variant known as CenH3 or CENP-A (Centromere Protein A). It has been therefore proposed that CENP-A is the epigenetic mark of the centromere. Upon DNA replication the mark is diluted two-fold and must be replenished to maintain centromere identity. What distinguishes CENP-A nucleosomes from those containing histone H3, how CENP-A nucleosomes are incorporated specifically into centromeric chromatin, and how this incorporation is coordinated with other cell cycle events are key issues that have been the focus of intensive research over the last decade. Here we review some of the highlights of this research.