The Cyclin B2/CDK1 Complex Conservatively Inhibits Separase Activity in Oocyte Meiosis II

Qing-Yuan Sun,Feng Wang,Wei-Ping Qian,Hong-Yong Zhang,Jian Li

doi:10.3389/fcell.2021.648053

Abstract

Recently, we have reported that the cyclin B2/CDK1 complex regulates homologous chromosome segregation through inhibiting separase activity in oocyte meiosis I, which further elucidates the compensation of cyclin B2 on cyclin B1’s function in meiosis I. However, whether cyclin B2/CDK1 complex also negatively regulates separase activity during oocyte meiosis II remains unknown. In the present study, we investigated the function of cyclin B2 in meiosis II of oocyte. We found that stable cyclin B2 expression impeded segregation of sister chromatids after oocyte parthenogenetic activation. Consistently, stable cyclin B2 inhibited separase activation, while introduction of non-phosphorylatable separase mutant rescued chromatid separation in the stable cyclin B2-expressed oocytes. Therefore, the cyclin B2/CDK1 complex conservatively regulates separase activity via inhibitory phosphorylation of separase in both meiosis I and meiosis II of mouse oocyte.

Highlights

Mammalian oocyte meiosis consists two continuous cell divisions, concomitantly, the chromosomes undergo two rounds of consecutive segregations, with segregation of homologous chromosomes in the first meiotic division and segregation of sister chromatids in the second meiotic division (Petronczki et al, 2003)
We recently described that the cyclin B2/CDK1 complex was involved in the regulation of homologous chromosome separation by inhibiting separase activity during mouse oocyte meiosis I, and that expression of non-degradable cyclin B2 arrested the oocytes at metaphase I (Li et al, 2019)
The 50cyclin B2-Venus mRNA was introduced into the metaphase II (MII) oocytes collected from the oviducts 14 h after human chorionic gonadotropin (HCG) injection, the oocytes were transferred into Ca2+-free SrCl2-CZB medium for parthenogenetic activation (PA) after 2 h incubation in KSOM medium to examine whether the oocytes could be activated as the control oocytes

Summary

Introduction

Mammalian oocyte meiosis consists two continuous cell divisions, concomitantly, the chromosomes undergo two rounds of consecutive segregations, with segregation of homologous chromosomes in the first meiotic division and segregation of sister chromatids in the second meiotic division (Petronczki et al, 2003). To accomplish this orderly and accurate transmission of the duplicated genome into haploid gametes, the homologous chromosomes synapsed and paired during prophase stage to facilitate subsequent chiasmata formation by the action of cohesin, a ringlike four-subunit complex (Gruber et al, 2003; Nasmyth and Haering, 2005). To achieve the segregation of homologs only in meiosis I, the centromeric cohesin is under protection in meiosis I by Shougoshin2-associated PP2A recruitment mechanism (Kitajima et al, 2006; Riedel et al, 2006).

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Conclusion