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

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.