Abstract
ABSTRACTOocyte 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 that is dependent on the microtubule-stabilising protein CLS-2, the orthologue of the mammalian CLASP proteins. The checkpoint kinase BUB-1 and CLS-2 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 previously that SUMO regulates BUB-1 localisation during metaphase I. Here, we found that SUMO modification of BUB-1 is regulated by the SUMO E3 ligase GEI-17 and the SUMO protease ULP-1. SUMO and GEI-17 are required for BUB-1 localisation between segregating chromosomes during early anaphase I. We also show that CLS-2 is subject to SUMO-mediated regulation; CLS-2 precociously localises in the midbivalent when either SUMO or GEI-17 are depleted. Overall, we provide evidence for a novel, SUMO-mediated control of protein dynamics during early anaphase I in oocytes.
Highlights
Faithful chromosome partitioning is essential for accurate cell division and is achieved by physically separating chromatids, or paired homologous chromosomes, in a process referred to as chromosome segregation
We addressed the role of the SUMO conjugation pathway during meiotic chromosome segregation in C. elegans oocytes
SUMO and BUB-1 localise within the segregating chromosomes with their levels peaking at early anaphase, and both proteins leave the spindle during late anaphase
Summary
Faithful chromosome partitioning is essential for accurate cell division and is achieved by physically separating chromatids, or paired homologous chromosomes, in a process referred to as chromosome segregation. This is achieved by a complex and dynamic structure known as the spindle (Wittmann et al, 2001; Gadde and Heald, 2004; Dumont and Desai, 2012). Some MTs contact chromosomes through the kinetochore, a multi-protein complex that assembles on specific regions on chromosomes called centromeres (Tanaka and Desai, 2008; Verdaasdonk and Bloom, 2011; Godek et al, 2015; Musacchio and Desai, 2017; Prosser and Pelletier, 2017).
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