Related Experiment Video
Updated: Aug 26, 2026
Xenopus laevis as a Model to Identify Translation Impairment
Published on: September 27, 2015
Polo-like kinase confers MPF autoamplification competence to growing Xenopus oocytes
Anthi Karaiskou1, Anne-Claire Leprêtre, Golbahar Pahlavan
1Laboratoire de Biologie du Développement, UMR-CNRS 7622, Equipe 'Biologie de l'ovocyte', Université Pierre et Marie Curie, boîte 24, 4 place Jussieu, 75252 Paris cedex 05, France.
Abstract:
During oogenesis, the Xenopus oocyte is blocked in prophase of meiosis I. It becomes competent to resume meiosis in response to progesterone at the end of its growing period (stage VI of oogenesis). Stage IV oocytes contain a store of inactive pre-MPF (Tyr15-phosphorylated Cdc2 bound to cyclin B2); the Cdc25 phosphatase that catalyzes Tyr15 dephosphorylation of Cdc2 is also present. However, the positive feedback loop that allows MPF autoamplification is not functional at this stage of oocyte growth. We report that when cyclin B is overexpressed in stage IV oocytes, MPF autoamplification does not occur and the newly formed cyclin B-Cdc2 complexes are inactivated by Tyr15 phosphorylation, indicating that Myt1 kinase remains active and that Cdc25 is prevented to be activated. Plx1 kinase (or polo-like kinase), which is required for Cdc25 activation and MPF autoamplification in full grown oocytes is not expressed at the protein level in small stage IV oocytes. In order to determine if Plx1 could be the missing regulator that prevents MPF autoamplification, polo kinase was overexpressed in stage IV oocytes. Under these conditions, the MPF-positive feedback loop was restored. Moreover, we show that acquisition of autoamplification competence does not require the Mos/MAPK pathway.
Insights
Plx1 kinase is crucial for initiating meiosis in Xenopus oocytes by enabling MPF autoamplification. Overexpressing Plx1 in stage IV oocytes restores this process, which is essential for meiotic resumption.
Area of Science:
- Cell biology
- Developmental biology
- Molecular biology
Background:
- Xenopus oocytes are arrested in meiosis I prophase.
- Meiotic resumption is triggered by progesterone, initiating maturation.
- Inactive pre-MPF (M-phase promoting factor) and Cdc25 phosphatase are present in stage IV oocytes, but MPF autoamplification is non-functional.
Purpose of the Study:
- To investigate the molecular mechanisms preventing MPF autoamplification in immature Xenopus oocytes.
- To determine the role of Plx1 kinase in regulating MPF autoamplification and meiotic resumption.
Main Methods:
- Overexpression of cyclin B and Plx1 kinase in stage IV Xenopus oocytes.
- Analysis of MPF activity, Tyr15 phosphorylation of Cdc2, and Cdc25 activation.
- Assessment of the requirement for the Mos/MAPK pathway in autoamplification competence.
Main Results:
- Cyclin B overexpression in stage IV oocytes did not restore MPF autoamplification; complexes remained inactive due to Tyr15 phosphorylation.
- Plx1 kinase is not expressed at the protein level in stage IV oocytes.
- Overexpression of Plx1 kinase in stage IV oocytes restored the MPF autoamplification feedback loop.
- Acquisition of MPF autoamplification competence is independent of the Mos/MAPK pathway.
Conclusions:
- Plx1 kinase is a key regulator required for MPF autoamplification and meiotic resumption in Xenopus oocytes.
- The absence of Plx1 protein prevents the functional activation of the MPF feedback loop in immature oocytes.
- Meiotic maturation competence is acquired independently of the Mos/MAPK pathway, highlighting a distinct regulatory mechanism.
