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Cyclin D2 arrests Xenopus early embryonic cell cycles
F Taieb1, I Chartrain, S Chevalier
1Laboratoire de Physiologie de la Reproduction, INRA/URA-CNRS 1449, Université Pierre et Marie Curie, Paris, France.
Abstract:
Xenopus cyclin D2 mRNA is a member of the class of maternal RNAs. It is rare and stable during early embryonic development. To investigate the potential role of cyclin D2 during early embryonic cell cycles, cyclin D2 was injected into one blastomere of a two-cell embryo. This injection induced a cell cycle arrest in the injected blastomere. To analyze more precisely the mechanism of this arrest, we took advantage of cycling egg extracts that recapitulate major events of the cell cycle when supplemented with demembranated sperm heads. When Xenopus cyclin D2 is added to egg extracts, the first round of DNA replication occurs as in control extracts. However, Xenopus cyclin D2 blocks subsequent rounds of DNA replication and the oscillations of histone H1 kinase activity associated with cdc2 kinase, indicating that the cell cycle is arrested after the first S-phase. The block induced by Xenopus cyclin D2 is not due to a lack of the mitotic cyclin B2 that accumulates normally. Radiolabeled Xenopus cyclin D2 enters nuclei after completion of the first S-phase and remains stable over the entire period of the arrest. These features suggest that Xenopus cyclin D2 could play an original role during early development, controlling the G2-phase and/or the G2/M transition.
Insights
Xenopus cyclin D2, a maternal RNA, halts early embryonic cell cycles after the first DNA replication. This suggests cyclin D2 controls the G2 phase or G2/M transition in early development.
Area of Science:
- Developmental Biology
- Cell Cycle Regulation
Background:
- Maternal RNAs are crucial for early embryonic development.
- Xenopus cyclin D2 is a rare, stable maternal RNA during early development.
Purpose of the Study:
- To investigate the role of Xenopus cyclin D2 in early embryonic cell cycle progression.
- To elucidate the mechanism by which cyclin D2 influences cell division.
Main Methods:
- Injection of Xenopus cyclin D2 into a blastomere of a two-cell Xenopus embryo.
- Utilizing cycling Xenopus egg extracts supplemented with sperm heads to mimic cell cycle events.
- Monitoring DNA replication and histone H1 kinase activity in response to cyclin D2 addition.
Main Results:
- Cyclin D2 injection caused cell cycle arrest in the injected blastomere.
- In egg extracts, cyclin D2 allowed the first DNA replication but blocked subsequent rounds.
- Cell cycle arrest occurred after the first S-phase, not due to lack of cyclin B2.
- Radiolabeled cyclin D2 localized to nuclei and remained stable during arrest.
Conclusions:
- Xenopus cyclin D2 plays a role in controlling early embryonic cell cycles.
- Cyclin D2 appears to arrest the cell cycle at the G2 phase or the G2/M transition.
- This suggests an original regulatory function for cyclin D2 in Xenopus development.