Sumoylation regulates central spindle protein dynamics during chromosome segregation in oocytes

Abstract

Meiotic spindles in most species lack centrosomes and the mechanisms that underlie faithful chromosome segregation in acentrosomal meiotic spindles are not well understood. In C. elegans oocytes, spindle microtubules exert a poleward force on chromosomes dependent on the microtubule-stabilising protein CLS-2^CLASP. The kinase BUB-1^Bub1 and CLS-2^CLASP localise in the central-spindle and display a dynamic localisation pattern throughout anaphase but the signals regulating their anaphase-specific localisation remains unknown. We have shown that SUMO regulates BUB-1 localisation during metaphase I. Here, we found that SUMO modification of BUB-1^Bub1 is regulated by the SUMO E3 ligase GEI-17 and the SUMO protease ULP-1. SUMO is required for BUB-1 localisation in between segregating chromosomes during early anaphase I, and SUMO depletion partially phenocopies BUB-1^Bub1 depletion. We also show that CLS-2^CLASP is subject to SUMO-mediated regulation. Over-all, we provide evidence for a novel, SUMO-mediated control of protein dynamics during early anaphase I in oocytes.