Cid dynamics at the centromere

The maintenance of one – and only one – functional centromere per chromosome during cell proliferation is crucial for accurate chromosome segregation. Centromeres are specified epigenetically and contain marks such as the histone 3 variant Cenp-A. In mammalian cells, more than 20 proteins were found to associate with centromeres. In Drosophila, centromere complexity is reduced. Maintenance of the Drosophila Cenp-A ortholog, centromere-identifier (Cid), might depend on only two additional centromere proteins, Cenp-C and Cal1. Therefore, Drosophila is an ideal model system to investigate the molecular mechanisms that underly centromere maintenance and, on page 4782, Christian Lehner and co-workers set out to analyse the dynamics of Cid, Cenp-C and Cal1 in Drosophila S2R+ cells. By using quantitative in vivo imaging and fluorescence recovery after photobleaching (FRAP), they show that the behaviour of Cid throughout the cell cycle is more complex than anticipated. It had been proposed that Cid is loaded onto centrosomes during a defined window in the cell cycle and then remains stably associated. However, the authors now demonstrate that, in these cells, there are five different centromere states, some of which include turnover or reduction in centromeric Cid. Taken together, these results provide new insights into centromere dynamics that might help to further elucidate the mechanisms that underly genome stability.