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Inhibition of MEK or cdc2 kinase parthenogenetically activates mouse eggs and yields the same phenotypes as Mos(-/-)
Karen P Phillips1, Mary Ann F Petrunewich, Jennifer L Collins
1Ottawa Health Research Institute, Department of Cellular and Molecular Medicine, University of Ottawa, Ontario, Canada.
Abstract:
Mammalian eggs are arrested in metaphase II of meiosis until fertilization. Arrest is maintained by cytostatic factor (CSF) activity, which is dependent on the MOS-MEK-MAPK pathway. Inhibition of MEK1/2 with a specific inhibitor, U0126, parthenogenetically activated mouse eggs, producing phenotypes similar to Mos(-/-) parthenogenotes (premature, unequal cleavages and large polar bodies). U0126 inactivated MAPK in eggs within 1 h, in contrast to the 5 h required after fertilization, while the time course of MPF inactivation was similar in U0126-activated and fertilized eggs. We also found that inactivation of MPF by the cdc2 kinase inhibitor roscovitine induced parthenogenetic activation. Inactivation of MPF by roscovitine resulted in the subsequent inactivation of MAPK with a time course similar to that following fertilization. Notably, roscovitine also produced some Mos(-/-)-like phenotypes, indistinguishable from U0126 parthenogenotes. Simultaneous inhibition of both MPF and MAPK in eggs treated with roscovitine and U0126 produced a very high proportion of eggs with the more severe phenotype. These findings confirm that MEK is a required component of CSF in mammalian eggs and imply that the sequential inactivation of MPF followed by MAPK inactivation is required for normal spindle function and polar body emission.
Insights
Cytostatic factor (CSF) maintains meiotic arrest in mammalian eggs via the MOS-MEK-MAPK pathway. Inhibiting MEK or MPF triggers parthenogenetic activation, revealing sequential MPF and MAPK inactivation is crucial for egg development.
Area of Science:
- Cell Biology
- Developmental Biology
- Reproductive Biology
Background:
- Mammalian eggs arrest in metaphase II of meiosis, a state maintained by cytostatic factor (CSF) activity.
- The MOS-MEK-MAPK signaling pathway is essential for maintaining this meiotic arrest.
Purpose of the Study:
- To investigate the role of the MOS-MEK-MAPK pathway in maintaining meiotic arrest in mammalian eggs.
- To determine the specific contributions of MEK and MPF inactivation to parthenogenetic activation and normal egg development.
Main Methods:
- Utilized MEK inhibitor U0126 and cdc2 kinase inhibitor roscovitine to study parthenogenetic activation in mouse eggs.
- Monitored the inactivation kinetics of MAPK and MPF following inhibitor treatment and fertilization.
- Observed and compared phenotypes of parthenogenetically activated eggs with those of Mos(-/-) parthenogenotes.
Main Results:
- Inhibition of MEK1/2 with U0126 induced parthenogenetic activation, mimicking Mos(-/-) phenotypes by rapidly inactivating MAPK.
- MPF inactivation by roscovitine also induced parthenogenetic activation and subsequent MAPK inactivation.
- Simultaneous inhibition of MPF and MAPK resulted in a high proportion of severe developmental defects.
Conclusions:
- MEK is a necessary component of cytostatic factor (CSF) activity in mammalian eggs.
- Sequential inactivation of MPF followed by MAPK is essential for normal spindle function and polar body emission during egg development.