A Role for Cyclin A1 in the Activation of MPF and G2–M Transition during Meiosis of Male Germ Cells in Mice

[摘要] Cell-cycletransitionatG2ndash;MiscontrolledbyMPF(M-phase-promotingfactor),acomplexconsistingoftheCdc2kinaseandaB-typecyclin.Wehaveshownthatinmice,targeteddisruptionofanA-typecyclingene,cyclinA1,resultsinablockofspermatogenesispriortotheentryintometaphaseI.ThemeioticarrestisaccompaniedbyadefectinCdc2kinaseactivationattheG2ndash;-Mtransition,raisingthepossibilitythatacyclinA1-dependentprocessdictatestheactivationofMPF.HereweshowthatlikeCdc2,theexpressionofB-typecyclinsisretainedincyclinA1-deficientspermatocytes,whiletheirassociatedkinasesarekeptatinactivestates.Treatmentofarrestedgermcellswiththeproteinphosphatasetype-1and-2AinhibitorokadaicacidrestorestheMPFactivityandinducesentryintoMphaseandtheformationofnormallycondensedchromosomebivalents,concomitantwithhyperphosphorylationofCdc25proteins.Conversely,inhibitionoftyrosinephosphatases,includingCdc25s,byvanadatesuppressestheokadaicacid-inducedmetaphaseinduction.ThehighestlevelsofCdc25AandCdc25CexpressionandtheirsubcellularlocalizationduringmeioticprophasecoincidewiththatofcyclinA1,andwhenoverexpressedinHeLacells,cyclinA1coimmunoprecipitateswithCdc25A.Furthermore,theproteinkinasecomplexesconsistingofcyclinA1andeitherCdc2orCdk2phosphorylatebothCdc25AandCdc25Cinvitro.Theseresultssuggestthatinnormalmeioticmalegermcells,cyclinA1participatesintheregulationofotherproteinkinasesorphosphatasescriticalfortheG2ndash;Mtransition.Inparticular,itmaybedirectlyinvolvedintheinitialamplificationofMPFthroughtheactivatingphosphorylationonCdc25phosphatases.