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Residual Cdc2 activity remaining at meiosis I exit is essential for meiotic M-M transition in Xenopus oocyte extracts
M Iwabuchi1, K Ohsumi, T M Yamamoto
1CREST Research Project and Laboratory of Cell and Developmental Biology, Graduate School of Bioscience and Biotechnology, Tokyo, Japan.
Abstract:
To investigate the regulatory mechanisms of the cell cycle transition from M phase to M phase in meiotic cycles, a Xenopus oocyte extract that performs the M-M transition has been developed. Using the meiotic extract, we found that a low level of Cdc2 activity remained at the exit of meiosis I (MI), due to incomplete degradation of cyclin B. The inactivation of the residual Cdc2 activity induced both entry into S phase and tyrosine phosphorylation on Cdc2 after MI. Quantitative analysis demonstrated that a considerable amount of Wee1 was present at the MI exit and Cdc2 inhibitory phosphorylation during this period was suppressed by the dominance of Cdc2 over Wee1. Consistently, the addition of more than a critical amount of Wee1 to the extract induced Cdc2 inhibitory phosphorylation, changing the M-M transition into an M-S-M transition. Thus, the Cdc2 activity remaining at MI exit is required for suppressing entry into S phase during the meiotic M-M transition period.
Insights
Residual Cdc2 activity after meiosis I (MI) prevents S phase entry in Xenopus oocytes. Maintaining this activity is crucial for the meiotic M-M transition, ensuring proper cell cycle progression.
Area of Science:
- Cell Biology
- Developmental Biology
- Molecular Biology
Background:
- Understanding cell cycle regulation is fundamental to cell biology.
- Meiotic cell divisions involve unique regulatory mechanisms distinct from mitotic cycles.
- The transition between meiotic M phases (M-M) requires precise control of key cell cycle regulators.
Purpose of the Study:
- To elucidate the regulatory mechanisms governing the M-M transition in meiotic cycles.
- To investigate the role of Cdc2 activity and its regulation at the exit of meiosis I (MI).
- To determine the factors influencing the switch between meiotic M-M and M-S-M transitions.
Main Methods:
- Development of a Xenopus oocyte extract system capable of performing the M-M transition.
- Analysis of Cdc2 activity, cyclin B degradation, and Wee1 presence during meiotic progression.
- Quantitative assessment of Wee1's role in Cdc2 inhibitory phosphorylation and its impact on cell cycle transitions.
Main Results:
- A low level of Cdc2 activity persists at MI exit due to incomplete cyclin B degradation.
- Inactivation of residual Cdc2 activity triggers S phase entry and Cdc2 tyrosine phosphorylation.
- Wee1 is present at MI exit, but Cdc2 activity is dominant; adding excess Wee1 induces inhibitory phosphorylation and an M-S-M transition.
Conclusions:
- Residual Cdc2 activity at MI exit is essential for suppressing S phase entry during the meiotic M-M transition.
- The balance between Cdc2 and Wee1 activity dictates the progression through meiotic M-M or M-S-M phases.
- This study reveals a critical regulatory checkpoint ensuring proper meiotic cell cycle progression in Xenopus oocytes.