Nuclear envelope breakdown may deliver an inhibitor of protein phosphatase 1 which triggers cyclin B translation in starfish oocytes.
In vertebrates, enhanced translation of mRNAs in oocytes and early embryos entering M-phase is thought to occur through polyadenylation, involving binding, hyperphosphorylation and proteolytic degradation of Aurora-activated CPEB. In starfish, an unknown component of the oocyte nucleus is required for cyclin B synthesis following the release of G2/prophase block by hormonal stimulation. We have found that CPEB cannot be hyperphosphorylated following hormonal stimulation in starfish oocytes from which the nucleus has been removed. Activation of Aurora kinase, known to interact with protein phosphatase 1 and its specific inhibitor Inh-2, is also prevented. The microinjection of Inh-2 restores Aurora activation, CPEB hyperphosphorylation and cyclin B translation in enucleated oocytes. Nevertheless, we provide evidence that CPEB is in fact hyperphosphorylated by cdc2, without apparent involvement of Aurora or MAP kinase, and that cyclin B synthesis can be stimulated without previous degradation of phosphorylated CPEB. Thus, the regulation of cyclin B synthesis necessary for progression through meiosis can be explained by an equilibrium between CPEB phosphorylation and dephosphorylation, and both aspects of this control may rely on the sole activation of Cdc2 and subsequent nuclear breakdown.
Lapasset
Laure
L
Laboratoire Arago, UMR 7628, CNRS and Université Pierre et Marie Curie, BP 44, F 66651 Banyuls-sur-mer, France.
Pradet-Balade
Bérengère
B
Lozano
Jean-Claude
JC
Peaucellier
Gérard
G
Picard
André
A
D000818:Animals; D019926:Cyclin B / Q000235:genetics*; D004791:Enzyme Inhibitors / Q000378:metabolism; D005260:Female; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D009865:Oocytes / Q000166:cytology / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D014176:Protein Biosynthesis; D054645:Protein Phosphatase 1; D013215:Starfish / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D039221:mRNA Cleavage and Polyadenylation Factors / Q000235:genetics / Q000378:metabolism
D019926:Cyclin B; D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D014157:Transcription Factors; D039221:mRNA Cleavage and Polyadenylation Factors; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1