A degron-based strategy reveals new insights into Aurora B function in C. elegans

Abstract

The widely conserved kinase Aurora B regulates important events during cell division. Surprisingly, recent work has uncovered a few functions of Aurora-family kinases that do not require kinase activity. Thus, understanding this important class of cell cycle regulators will require strategies to distinguish kinase-dependent from independent functions. Here, we address this need in C. elegans by combining germline-specific, auxin-induced Aurora B (AIR-2) degradation with the transgenic expression of kinase-inactive AIR-2. Through this approach, we find that kinase activity is essential for AIR-2’s major meiotic functions and also for mitotic chromosome segregation. Moreover, our analysis revealed insight into the assembly of the ring complex (RC), a structure that is essential for chromosome congression in C. elegans oocytes. AIR-2 localizes to chromosomes and recruits other components to form the RC. However, we found that while kinase-dead AIR-2 could load onto chromosomes, other components were not recruited. This failure in RC assembly appeared to be due to a loss of RC SUMOylation, suggesting that there is crosstalk between SUMOylation and phosphorylation in building the RC and implicating AIR-2 in regulating the SUMO pathway in oocytes. Similar conditional depletion approaches may reveal new insights into other cell cycle regulators.

Multiple motors cooperate to establish and maintain acentrosomal spindle bipolarity in C. elegans oocyte meiosis

“…Aurora B kinase (AIR-2) has been shown to be required for BMK-1 spindle localization and AIR-2 can phosphorylate BMK-1 in vitro ( Bishop et al, 2005 ) implicating AIR-2 in BMK-1 regulation. Inhibition of AIR-2’s kinase activity also leads to collapsed oocyte spindles ( Divekar et al, 2021a ), consistent with a role for AIR-2 in regulating spindle force generation. However, it is likely that other factors also regulate BMK-1.…”

Cohesin is required for meiotic spindle assembly independent of its role in cohesion in C. elegans

“…6D) did not coalesce. This phenotype is consistent with that previously observed by fixed immunofluorescence of air-2(degron) embryos (Divekar et al, 2021). In addition, the mean fluorescence intensity of mNeonGreen::tubulin, indicative of microtubule density, was significantly reduced in apolar metaphase I spindles of bir-1(E69A, D70A) and spo- 11 rec-8 coh-4 coh-3 embryos relative to the bipolar spindles in control and spo-11 rec- 8 metaphase I spindles (Fig.…”

“…The survivin (BIR-1 in C. elegans ) subunit of the CPC binds to the phosphorylated histone thereby recruiting Aurora B to chromosomes (Kelly et al, 2010; Wang et al, 2010; Yamagishi, Honda, Tanno, & Watanabe, 2010). In C. elegans , haspin (HASP-1) is required to promote recruitment of Aurora B (AIR-2) to the midbivalent region in diakinesis oocytes (Ferrandiz et al, 2018) and AIR-2 is essential for bipolar meiotic spindle assembly in C. elegans (Divekar et al, 2021; Dumont et al, 2010), therefore we hypothesized that chromatids that lack cohesin-recruited AIR-2 would be unable to form bipolar meiotic spindles. Time-lapse imaging of control embryos with endogenously tagged AIR-2::GFP (Fig.…”

“…CC-BY 4.0 International license available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made midbivalent region in diakinesis oocytes (Ferrandiz et al, 2018) and AIR-2 is essential for bipolar meiotic spindle assembly in C. elegans (Divekar et al, 2021;Dumont et al, 2010), therefore we hypothesized that chromatids that lack cohesin-recruited AIR-2 would be unable to form bipolar meiotic spindles. Time-lapse imaging of control embryos with endogenously tagged AIR-2::GFP (Fig.…”

“…Depletion of CPC components resulted in a lack of spindle microtubules in Drosophila oocytes (Radford, Jang, & McKim, 2012) and in Xenopus egg extracts to which sperm nuclei or DNA-coated beads are added (Kelly et al, 2007; Maresca et al, 2009; Sampath et al, 2004). In C. elegans oocytes, the CPC subunits, BIR-1/survivin (Speliotes, Uren, Vaux, & Horvitz, 2000), INCENP (Wignall & Villeneuve, 2009), and the Aurora B-homolog AIR-2 (Divekar, Davis-Roca, Zhang, Dernburg, & Wignall, 2021; Dumont, Oegema, & Desai, 2010) contribute to meiotic spindle assembly.…”