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Updated: Aug 21, 2026
Meiotic Spindle Assessment in Mouse Oocytes by siRNA-mediated Silencing
Published on: October 11, 2015
Functional interaction between p90Rsk2 and Emi1 contributes to the metaphase arrest of mouse oocytes
Maria Paola Paronetto1, Ezio Giorda, Rita Carsetti
1Department of Public Health and Cell Biology, Section of Anatomy, University of Rome Tor Vergata, Rome, Italy.
Abstract:
Vertebrate eggs arrest at metaphase of the second meiotic division before fertilization under the effect of a cytostatic factor (CSF). This arrest is established during oocyte maturation by the MAPK kinase module, comprised of Mos, MEK, MAPKs and p90Rsk. Maintenance of CSF arrest at metaphase requires inhibitors of the anaphase-promoting complex (APC) like Emi1, which sequesters the APC activator Cdc20. Although it was proposed that the Mos pathway and Emi1 act independently, neither one alone is sufficient to entirely reproduce CSF arrest. Herein we demonstrate that p90Rsk2 associates with and phosphorylates Emi1 upstream of the binding region for Cdc20, thus stabilizing their interaction. Experiments in transfected cells and two-cell embryos indicate that Emi1 and p90Rsk2 cooperate to induce the metaphase arrest. Moreover, oocyte maturation was impaired by interfering with the interaction between p90Rsk2 and Emi1 or by RNA interference of Emi1. Our results indicate that p90Rsk2 and Emi1 functionally interact during oocyte maturation and that the Mos pathway establishes CSF activity through stabilization of an APC-inhibitory complex composed by Emi1 and Cdc20 before fertilization.
Insights
Vertebrate eggs arrest at metaphase due to cytostatic factor (CSF). The p90Rsk2 protein and Emi1 cooperate to stabilize an inhibitory complex, ensuring metaphase arrest during oocyte maturation before fertilization.
Area of Science:
- Cell Biology
- Developmental Biology
- Molecular Biology
Background:
- Vertebrate eggs arrest at metaphase of meiosis II before fertilization, mediated by cytostatic factor (CSF).
- CSF activity is established by the MAPK kinase pathway (Mos, MEK, MAPKs, p90Rsk) during oocyte maturation.
- Maintenance of metaphase arrest requires anaphase-promoting complex (APC) inhibitors, such as Emi1, which binds to the APC activator Cdc20.
Purpose of the Study:
- To investigate the functional interaction between the Mos pathway and Emi1 in establishing CSF arrest.
- To elucidate the mechanism by which p90Rsk2 and Emi1 cooperate to maintain metaphase arrest.
Main Methods:
- Transfected cell experiments
- Two-cell embryo studies
- RNA interference (RNAi) of Emi1
- Analysis of protein-protein interactions and phosphorylation
Main Results:
- p90Rsk2 directly associates with and phosphorylates Emi1, stabilizing its interaction with Cdc20.
- Co-expression of Emi1 and p90Rsk2 is sufficient to induce metaphase arrest in transfected cells and embryos.
- Interference with p90Rsk2-Emi1 interaction or Emi1 RNAi impairs oocyte maturation and metaphase arrest.
Conclusions:
- p90Rsk2 and Emi1 functionally cooperate to establish and maintain CSF-mediated metaphase arrest during oocyte maturation.
- The Mos pathway stabilizes CSF activity by promoting the formation of an Emi1-Cdc20 inhibitory complex prior to fertilization.
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