Dynamic regulation of astral microtubule growth in the meiotic spindle of mouse oocyte

The spindle apparatus is essential for both mitotic and meiotic cell division. In contrast to its mitotic counterpart, the meiotic spindle of mammalian oocytes lacks centrosomes and thus relies on acentrosomal microtubule organizing centers to assemble the spindle. In addition, the positioning of spindle in oocytes is mediated by the F-actin network, not the astral microtubules (MTs). Overall, the role of astral MTs in meiotic spindle positioning has been overlooked due to the lack of centrosomes. In this study, we present an optimized method for staining and super-resolution imaging of astral MTs during meiosis. Though lacking centrosomes, both interpolar and astral MTs were present in the spindle through meiosis. The growth of astral MTs was inhibited by CDK1 and actin-related protein 2/3. Premature extension of astral MTs at metaphase I impaired the positioning of meiotic spindle, resulting in symmetric division of oocytes after meiosis I. Collectively, these results provide novel insights into the regulation of astral MT growth to facilitate the positioning of meiotic spindle in oocytes.