Prolonged metaphase II arrest weakens Aurora B/C- dependent error correction in mouse oocytes

Abstract

ABSTRACTChromosome segregation during oocyte meiosis is highly error prone in mammals. Whereas control mechanisms at work during meiosis I have been studied quite extensively, our knowledge of these mechanisms in meiosis II is rather limited. The spindle assembly checkpoint (SAC) and error correction (EC) have to be adapted to the specificities of meiosis II, where attachments to the spindle are bipolar, and not monopolar. Additionally, errors occurring during meiosis I, are carried over into meiosis II. In this study we asked whether oocytes in meiosis II have the capacity to respond to attachments that are under less tension. We found that this was indeed the case, and Aurora B/C-dependent EC through SAC activation can mediate a metaphase delay. We also found that during the extended metaphase II arrest, necessary to await fertilization, spindle tension naturally decreases. However, this occurs concomitantly with a decrease in the sensitivity of EC due to an increase in PP2A at centromeres, with the result that only oocytes in early but not late metaphase II can respond to missing spindle tension.