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Protein phosphorylation during meiotic maturation of Xenopus oocytes: cdc2 protein kinase targets
1Laboratoire de Physiologie de la Reproduction, Université Pierre et Marie Curie, Paris, France.
Abstract:
M-Phase specific protein kinase or cdc2 protein kinase is a component of MPF (M-Phase promoting factor). During meiotic maturation of Xenopus oocytes, cdc2 protein kinase is activated in correlation with MPF activity. A protein phosphorylation cascade takes place involving several protein kinases, among which casein kinase II, and different changes associated with meiosis occur such as germinal vesicle breakdown, chromosome condensation, cytoskeletal reorganization and increase in protein synthesis. Our results provide a biochemical link between cdc2 protein kinase and protein synthesis since they show that the kinase phosphorylates in vitro a p47 protein identified as elongation factor EF1 (gamma subunit) and that the in vitro site of p47 corresponds to the site phosphorylated in vivo. Immunofluorescence showed that the elongation factor (EF1-beta gamma) is localized in the oocyte cortex. Furthermore, they show that cdc2 kinase phosphorylates and activates casein kinase II in vitro, strongly supporting the view that casein kinase II is involved in the phosphorylation cascade originated by cdc2 kinase.
Insights
cdc2 protein kinase, a key M-Phase factor, phosphorylates elongation factor EF1 and activates casein kinase II during Xenopus oocyte maturation, linking cell cycle control to protein synthesis.
Area of Science:
- Cell Biology
- Molecular Biology
- Developmental Biology
Background:
- M-Phase promoting factor (MPF) regulates meiotic maturation.
- cdc2 protein kinase activity correlates with MPF activity during Xenopus oocyte maturation.
- Meiosis involves germinal vesicle breakdown, chromosome condensation, and increased protein synthesis.
Purpose of the Study:
- To establish a biochemical link between cdc2 protein kinase and protein synthesis.
- To investigate the role of cdc2 protein kinase in the meiotic phosphorylation cascade.
- To identify substrates and regulators of cdc2 protein kinase during oocyte maturation.
Main Methods:
- In vitro kinase assays using cdc2 protein kinase.
- Identification of phosphorylated proteins (p47) and their corresponding sites.
- Immunofluorescence to determine the localization of elongation factor EF1.
- In vitro phosphorylation and activation assays for casein kinase II.
Main Results:
- cdc2 protein kinase phosphorylates p47 protein (elongation factor EF1 gamma subunit) in vitro at a site corresponding to in vivo phosphorylation.
- Elongation factor EF1 (EF1-beta gamma) is localized to the oocyte cortex.
- cdc2 protein kinase phosphorylates and activates casein kinase II in vitro.
Conclusions:
- cdc2 protein kinase directly links cell cycle control to protein synthesis via phosphorylation of elongation factor EF1.
- Casein kinase II is likely involved in the cdc2 kinase-initiated phosphorylation cascade during meiosis.
- These findings elucidate key molecular mechanisms governing meiotic maturation in Xenopus oocytes.