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Full activation of the rat oocyte by protein synthesis inhibition requires protein phosphatase activity
M Zernicka-Goetz1, M Weber, B Maro
1Département de Biologie du Développement, Institut Jacques Monod, C.N.R.S., Université Paris VII, France.
Abstract:
The rat oocyte provides an interesting system in which to dissect the control mechanisms involved in the transition between a meiotic M phase and a mitotic interphase. In this study, we show that in rat oocytes activated parthenogenetically by puromycin, okadaic acid (a potent inhibitor of protein phosphatases 1 and 2A) induced an increase in histone H1 kinase activity suggesting that MPF was reactivated. However, the inhibition of phosphatases 1 and 2A shortly after second polar body extrusion did not allow the formation of a metaphase-like spindle, although microtubule polymerization was not inhibited. Instead, the chromatin remained condensed as a single mass and a large aster formed around it.
Insights
In rat oocytes, inhibiting protein phosphatases 1 and 2A reactivated maturation-promoting factor (MPF) but prevented spindle formation. This suggests phosphatases are crucial for transitioning from meiosis to mitosis.
Area of Science:
- Cell Biology
- Developmental Biology
- Molecular Biology
Background:
- The transition between meiotic M phase and mitotic interphase is a critical regulatory process.
- Oocytes are valuable models for studying cell cycle control.
Purpose of the Study:
- To investigate the role of protein phosphatases 1 and 2A in regulating the meiotic to mitotic transition in rat oocytes.
- To understand the mechanisms controlling MPF activity and spindle formation post-meiosis.
Main Methods:
- Parthenogenetic activation of rat oocytes using puromycin.
- Treatment with okadaic acid, a specific inhibitor of protein phosphatases 1 and 2A.
- Assessment of histone H1 kinase activity to measure MPF activity.
- Microscopic observation of spindle formation and chromatin condensation.
Main Results:
- Okadaic acid treatment increased histone H1 kinase activity, indicating MPF reactivation.
- Inhibition of phosphatases 1 and 2A after second polar body extrusion prevented metaphase-like spindle formation.
- Microtubule polymerization remained unaffected, but chromatin stayed condensed.
- A large aster formed around the condensed chromatin.
Conclusions:
- Protein phosphatases 1 and 2A are essential for the formation of a functional spindle during the meiotic to mitotic transition in rat oocytes.
- MPF reactivation alone is insufficient for initiating mitotic interphase; phosphatase activity is also required.
- These findings highlight the complex regulatory network governing oocyte cell cycle progression.