Aurora B/C-dependent phosphorylation promotes Rec8 cleavage in mammalian oocytes

Abstract

To generate haploid gametes, cohesin is removed in a stepwise manner from chromosome arms in meiosis I and the centromere region in meiosis II, to segregate chromosomes and sister chromatids, respectively. Meiotic cohesin removal requires cleavage of the meiosis-specific kleisin subunit Rec8 by the protease Separase[1, 2]. In yeast, Rec8 is kept in a non-phosphorylated state by the action of PP2A-B56, which is localised to the centromere region, thereby preventing cohesin removal from this region in meiosis I[3-5]. However, it is unknown whether Rec8 has to be equally phosphorylated for cleavage, and whether centromeric cohesin protection is indeed brought about by dephosphorylation of Rec8 preventing cleavage, in mammalian meiosis. The identity of one or several potential Rec8-specific kinase(s) is also unknown. This is due to technical challenges, as Rec8 is poorly conserved preventing a direct translation of the knowledge gained from model systems such as yeast and C. elegans to mammals, and additionally, there is no turn-over of Rec8 after cohesion establishment, preventing phospho mutant analysis of functional Rec8. To address how Rec8 cleavage is brought about in mammals, we adapted a biosensor for Separase to study Rec8 cleavage in single mouse oocytes by live imaging, and identified phosphorylation sites promoting cleavage. We found that Rec8 cleavage by Separase depends on Aurora B/C kinase activity, and identified a residue promoting cleavage and being phosphorylated in an Aurora B/C kinase-dependent manner. Accordingly, inhibition of Aurora B/C kinase during meiotic maturation impairs endogenous Rec8 phosphorylation and chromosome segregation.

Meiotic defects in human oocytes: Potential causes and clinical implications

“…A recent study showed that phosphorylation of the cohesin protein REC8 by AURKB/C kinases is required for chromosome segregation in mouse oocytes, suggesting that deregulation of REC8 phosphorylation contributes to meiotic chromosome segregation errors. [ 25 ] Meanwhile, TEX19.1 (Testis expressed 19.1) was discovered as a previously unknown regulator of the cohesin complex by regulating UBR (ubiquitin‐protein ligase E3 component N‐recognin 2) protein activity to maintain the acetylation of the cohesin protein SMC3 in mouse oocytes. The acetylation of SMC3 is essential for establishment and maintain of sister chromatid cohesion.…”