CPEB Degradation during Xenopus Oocyte Maturation Requires a PEST Domain and the 26S Proteasome

摘要

Cytoplasmicpoly(A)elongationiswidelyutilizedduringtheearlydevelopmentofmanyorganismsasamechanismfortranslationalactivation.TargetingofmRNAsforthismechanismrequiresthepresenceofaU-richelement,thecytoplasmicpolyadenylationelement(CPE),anditsbindingprotein,CPEB.BlockingcytoplasmicpolyadenylationbyinterferingwiththeCPEorCPEBpreventsthetranslationalactivationofmRNAsthatarecrucialforoocytematuration.TheCPEsequenceandCPEBarealsoimportantfortranslationalrepressionofmRNAsstoredintheemXenopus/emoocyteduringoogenesis.TounderstandthecontributionofproteinmetabolismtothesetworolesforCPEB,wehaveexaminedthemechanismsinfluencingtheexpressionofCPEBduringoogenesisandoocytematuration.ThroughacomparisonofCPEBmRNAlevels,proteinsynthesis,andaccumulation,wefindthatCPEBissynthesizedduringoogenesisandstockpiledintheoocyte.MinimalsynthesisofCPEB,3.6%,occursduringoocytematuration.Inlateoocytematuration,75%ofCPEBisdegradedcoincidentwithgerminalvesiclebreakdown.Usingproteasomeandubiquitinationinhibitors,wedemonstratethatCPEBdegradationoccursviatheproteasomepathway,mostlikelythroughubiquitin-conjugatedintermediates.Inaddition,wedemonstratethatdegradationrequiresa14aminoacidPESTdomain./p/div