Events and seminars

During cell division, spindle microtubules guarantee the equal partitioning of genetic material into daughter cells. Meiotic spindles in most species lack centrosomes and the mechanisms that warrant faithful chromosome segregation are not well understood. In C. elegans oocytes, spindle microtubules exert a poleward force on chromosomes, effectively pushing them apart, dependent on the microtubule-stabilising protein CLS-2^CLASP. In addition, other proteins like AIR-2^{Aurora B} and BUB-1^Bub1 localise in the central-spindle and display a highly dynamic localisation pattern throughout meiotic anaphase. However, the relevance and regulation of their dynamic behaviour has remained elusive.

We have shown previously that the Small Ubiquitin-related Modifier, SUMO, is important for chromosome congression during meiosis I. In the present work, we found that SUMO is crucial for BUB-1 to localise to discrete regions within the central-spindle during early anaphase I and to avoid premature CLS-2 targeting to the central-spindle. Furthermore, BUB-1 is a SUMO substrate and its sumoylation is regulated by the SUMO E3 ligase GEI-17 and the SUMO protease ULP-1. Importantly, ULP-1 depletion leads to high levels of BUB-1 and to a partial impairment in BUB-1 release from the central spindle. Overall, we provide evidence for a tight, SUMO-mediated control of central-spindle protein dynamics during chromosome segregation in female meiosis.