Related Experiment Videos
The exit of mouse oocytes from meiotic M-phase requires an intact spindle during intracellular calcium release
N J Winston1, O McGuinness, M H Johnson
1Departement de Biologie du Développement, Institut Jacques Monod, CNRS-Université Paris VII, France.
Abstract:
To study the role of the metaphase spindle during the period of oocyte activation, mouse oocytes were fertilised or activated parthenogenetically in the presence or absence of the microtubule inhibitor nocodazole. In both cases, nocodazole caused the disappearance of the spindle and prevented the passage of the oocytes into interphase. However, the calcium spiking responses of the oocytes were not affected by nocodazole, being repetitive after fertilisation and a single spike after activation. If, after their activation or fertilisation in nocodazole, oocytes were later removed from the drug, only those that had been fertilised progressed into interphase. This progress was associated with continuing calcium spiking. Moreover, both the spiking and the progress to interphase could be blocked or reduced in incidence by removal of external calcium or addition of 5,5'-dimethyl BAPTA-AM. Oocytes that had been activated by ethanol in the presence of nocodazole and then removed from it, to allow re-formation of the spindle, only progressed into interphase if given a second exposure to ethanol, thereby eliciting a second calcium transient. These results show that exit from meiotic M-phase requires the simultaneous presence of a fully intact spindle during the release of calcium and that those factors leading to the degradation of cyclin B are only activated transiently. Since cyclin is being degraded continuously in the metaphase-II-arrested mouse oocyte and since this degradation is microtubule-dependent, these data suggest that the superimposition of a high concentration of intracellular calcium is required to tilt the equilibrium further in favour of cyclin degradation if exit from M-phase is to occur.
Insights
Oocyte activation requires both a stable spindle and calcium release. Mouse oocytes need an intact spindle during calcium release to exit M-phase, indicating transient activation of cyclin degradation factors.
Area of Science:
- Cell Biology
- Developmental Biology
- Reproductive Biology
Background:
- Oocyte activation is a critical process for fertilization and development.
- The role of the metaphase spindle in oocyte activation is not fully understood.
- Calcium signaling plays a key role in initiating oocyte activation.
Purpose of the Study:
- To investigate the role of the metaphase spindle in mouse oocyte activation.
- To determine the interplay between spindle integrity, calcium signaling, and cell cycle progression.
Main Methods:
- Mouse oocytes were fertilized or parthenogenetically activated.
- Microtubule inhibitor nocodazole was used to disrupt spindle formation.
- Calcium spiking patterns were monitored, and oocytes were observed after drug removal.
Main Results:
- Nocodazole disrupted the spindle and prevented entry into interphase, but did not affect calcium spiking.
- Oocytes fertilized in nocodazole progressed to interphase upon drug removal, associated with calcium spiking.
- Exit from M-phase required an intact spindle during calcium release, and cyclin B degradation factors are transiently activated.
Conclusions:
- Simultaneous presence of an intact spindle and calcium release is necessary for oocyte M-phase exit.
- Microtubule-dependent cyclin B degradation in metaphase-II arrested oocytes requires superimposed calcium signaling to promote M-phase exit.