Borealin regulates bipolar spindle formation but may not act as chromosomal passenger during mouse oocyte meiosis

Abstract

In mitosis, Borealin is a member of the chromosomal passenger complex (CPC), which plays interaction roles with INCENP and survivin in the complex. Its roles in mammalian meiosis are unknown. Here, we report the expression, localization, and function of Borealin and its relation with survivin in mouse oocyte meiosis. Borealin expression was gradually increased from GV stage to MII. Immunofluorescence results revealed that Borealin accumulated near chromosomes after GVBD, localized at the spindle poles in MI, AI and MII, and at the midbody in TI stage. Taxol and nocodazole treatment showed that the localization of Borealin was dependent on microtubule dynamics, whereas survivin was independent of this. Disruption of Borealin function by antibody injection resulted in severe spindle assembly defects, but did not affect PBE. We also found that depletion of survivin by MO injection had no effect on the localization of Borealin. In conclusion, our data suggest that Borealin is required for bipolar spindle formation, but may not regulate spindle checkpoint activity as a component of the CPC during mouse oocyte meiosis.

Echinoderm Microtubule Associated Protein Like 1 Is Indispensable for Oocyte Spindle Assembly and Meiotic Progression in Mice

“…Although the RanGTP pathway is initially found to be indispensable for only human oocyte spindle assembly (Holubcova et al, 2015), a recent study demonstrates that it is also crucial for mouse oocyte spindle formation (Drutovic et al, 2020). The CPC is composed of the Aurora B/C, INCENP (inner centromeric protein), Survin, and Borealin, which are localized at the kinetochore and are all crucial for the formation of normal bipolar spindles and meiotic progression in oocytes (Sharif et al, 2010;Sun et al, 2010;Jiang et al, 2014;Nguyen et al, 2018). Augmin is a hetero-octameric protein complex comprised of HAUS 1-8, which triggers new microtubule growth by recruiting γ-tubulin to pre-existing microtubules.…”