Myosin-X is dispensable for spindle morphogenesis and positioning in the mouse oocyte

Abstract

Off-center spindle positioning in mammalian oocytes enables asymmetric divisions in size, important for subsequent embryogenesis. The migration of the meiosis I spindle from the oocyte center to its cortex is mediated by F-actin. Specifically, an F-actin-cage surrounds the microtubule spindle and applies forces to it. To better understand how F-actin transmits forces to the spindle, we studied a potential direct link between F-actin and microtubules. For this, we tested the implication of Myosin-X, a known F-actin and microtubule binder involved in spindle morphogenesis and/or positioning in somatic cells, amphibian oocytes and embryos. Using a mouse strain conditionally invalidated for Myosin-X in oocytes and by live cell imaging, we show that Myosin-X is not localized on the spindle and dispensable for spindle and F-actin assembly. It is not required for force transmission since spindle migration and chromosome alignment occur normally. More broadly, Myosin-X is dispensable for oocyte developmental potential and female fertility. We therefore exclude a role for Myosin-X in transmitting F-actin-mediated forces to the spindle, opening new perspectives regarding this mechanism in mouse oocytes, which differs from most mitotic cells.

Antioxidant procyanidin B2 protects oocytes against cryoinjuries via mitochondria regulated cortical tension

“…PCB2 not only played a positive role in spindle formation, but also significantly reduced the aneuploidy rate of vitrified oocytes. The functional integrity of the spindle is also demonstrated by the migration from the oocyte center to the cortex during the MI phase, which is mediated by F-actin [65]. Disruption of F-actin also contributes to the generation of aneuploid oocytes [66].…”

The filipodia-like protrusions of adjacent somatic cells shape the developmental potential of mouse oocytes

“…In control follicles, MYO10 is found diffuse in the cytoplasm of the oocyte and of follicular cells 17 (Fig. 1 A, S1 D) and accumulates into foci within the zona pellucida where TZPs are located 12,16 (Fig.…”

“…S1 B). In addition to this strain, we used our previously generated mouse strain conditionally deleted for Myo10 in oocytes from early growth on (named Myo10 -/oo thereafter) as a control to potentially distinguish oocyte phenotypes related to germline loss of MYO10 versus those of somatic loss of MYO10 17 (Fig. S1 A, D).…”

“…We previously showed that MYO10 expressed in oocytes is dispensable for meiotic divisions and female fertility 17 , suggesting that the meiotic arrest observed in a subset of Myo10 -/full oocytes may be a consequence of decreased follicular cell contacts prior to meiosis resumption. We also observed that the subpopulation of Myo10 -/full oocytes that extruded a polar body did so with a timing similar to controls (Movie.S3; Fig.…”

“…We generated a full knockout mouse of Myo10 in all cell types to completely deplete it from the ovarian follicle ( Myo10 -/- full). Furthermore, we took advantage of our previously generated mouse strain conditionally deleted for Myo10 specifically in oocytes from early growth on ( Myo10 -/- oo) 17 to help distinguishing phenotypes caused by loss of somatic MYO10 or loss of oocyte MYO10. We show that the loss of somatic but not oocyte MYO10 greatly decreases the density of TZPs.…”