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In vivo regulation of MPF in Xenopus oocytes
1Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907.
Abstract:
Entry into M phase in the eukaryotic cell cycle is controlled by the oscillating activity of MPF. The active component of MPF is now known to be the p34cdc2 protein kinase originally found in yeast. The p34cdc2 protein kinase displays a characteristic M-phase-specific histone H1 kinase activity when it interacts with cyclins, which are proteins that oscillate through the cell cycle and are thought to regulate p34cdc2 activity. Cyclins can induce M phase when introduced into fully grown Xenopus oocytes and cyclin may play a role in normal oocyte maturation. Small Xenopus oocytes do not mature in response to the hormonal triggers which act on stage 6 oocytes. We introduced cyclin into stage 4 (small) Xenopus oocytes and showed that it activates MPF in these cells, probably by interacting with endogenous p34cdc2 kinase. We made labelled extracts from cyclin-mRNA-injected stage 4 oocytes and used them to show differential stability of clam cyclins A and B at oocyte maturation. The relative stability of the two forms of cyclin related directly to their ability to stabilize crude MPF preparations from injected stage 6 oocytes.
Insights
Cyclins activate maturation-promoting factor (MPF) in small Xenopus oocytes, demonstrating their role in cell cycle regulation. Differential cyclin stability influences MPF activity during oocyte maturation.
Area of Science:
- Cell Biology
- Molecular Biology
- Developmental Biology
Background:
- Entry into M phase of the eukaryotic cell cycle is regulated by the oscillating activity of maturation-promoting factor (MPF).
- MPF's active component is the p34cdc2 protein kinase, whose activity is modulated by cyclins.
- Cyclins are cell cycle-regulated proteins thought to control p34cdc2 kinase activity.
Purpose of the Study:
- To investigate the role of cyclins in regulating MPF activity and oocyte maturation.
- To determine if cyclin can induce M phase in immature Xenopus oocytes.
- To examine the differential stability of clam cyclins A and B during Xenopus oocyte maturation.
Main Methods:
- Introduction of cyclin into stage 4 Xenopus oocytes.
- Preparation of labeled extracts from cyclin-mRNA-injected oocytes.
- Assessment of MPF activation and stabilization in oocyte extracts.
Main Results:
- Cyclin introduction activated MPF in stage 4 Xenopus oocytes, suggesting interaction with endogenous p34cdc2 kinase.
- Differential stability of clam cyclins A and B was observed during oocyte maturation.
- The stability of cyclins correlated directly with their ability to stabilize MPF preparations.
Conclusions:
- Cyclins play a crucial role in activating MPF and inducing M phase entry in immature oocytes.
- Cyclin stability is a key factor in regulating MPF activity during oocyte maturation.
- These findings contribute to understanding cell cycle control mechanisms in eukaryotes.