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Inhibitory phosphorylation of Cdk1 mediates prolonged prophase I arrest in female germ cells and is essential for female reproductive lifespan
Introduction
In mammals, female germ cells enter meiosis in the embryonic gonad, but they are subsequently arrested at the dictyate stage of prophase I in the form of dormant oocytes that are enclosed within primordial follicles1. Such meiosis arrest can last for a very long time, which can be, for example, up to 50 years in humans and more than 1 year in mice. In addition, before the oocytes can resume meiotic maturation, they must undergo a prolonged growth period from small primary oocytes to fully grown oocytes. During such growth, which usually takes weeks to months or even longer, the oocytes remain arrested at prophase I2,3,4. In other words, throughout the lengthy dormancy and growth of oocytes, the oocytes are incompetent for meiosis resumption5.
The pool of primordial follicles with dormant oocytes provides the ovarian re
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The role of the Cdk regulatory protein cyclin A2 and its dynamics in female meiosis are unclear. Zhang et al. show that, unlike in mitosis, cyclin A2 persists during metaphase of meiosis II (MII). Cyclin A2 regulates microtubule stability, allows normal MII spindle formation, and prevents merotelic attachments and lagging chromosomes at MII exit.
Abstract
Cyclin A2 is a crucial mitotic Cdk regulatory partner that coordinates entry into mitosis and is then destroyed in prometaphase within minutes of nuclear envelope breakdown. The role of cyclin A2 in female meiosis and its dynamics during the transition from meiosis I (MI) to meiosis II (MII) remain unclear. We found that cyclin A2 decreases in prometaphase I but recovers after the first meiotic division and persists, uniquely for metaphase, in MII-arrested oocytes. Conditional deletion of cyclin A2 from mouse oocytes has no discernible effect on MI but leads to disrupted MII spindles and increased merotelic attachments. On stimu