Caspase 9 is constitutively activated in mouse oocytes and plays a key role in oocyte elimination during meiotic prophase progression

摘要

Inmanymammalianspecies,morethanhalfoftheinitialoocytepopulationiseliminatedbyneonatallife,thuslimitingtheoocytereserveforreproduction.Thecauseormechanismofthismajoroocytelossremainspoorlyunderstood.Weexaminedtheapoptoticpathwayinvolvedinoocyteeliminationinwild-typemouseovariesaswellasinemMsh5/emminus;/minus;ovaries,inwhichalloocyteswereeliminatedduetoalackofdoublestrandbreakrepair.Immunoblotandimmunofluorescencestainingshowedthataninitiatorcaspase9andaneffectorcaspase7wereconstitutivelyactivatedinalmostalloocytesinfetalovariesregardlessoftheirgenotypes.Incaspase9minus;/minus;ovaries,thetotalnumberofoocytesremainedhighwhilethatinwild-typeovariessteadilydeclinedduringovariandevelopment.Therefore,theactivationofcaspase9wasrequiredforbutdidnotimmediatelyleadtooocytedemise.WefoundthatXIAP,anendogenousinhibitorofapoptosis,wasalsoabundantinoocytesduringmeioticprophaseprogression.Ontheotherhand,acleavedformofPARP1,atargetofeffectorcaspases,waslocalizedtothenucleiofalimitednumberofoocytes,andthefrequencyofcleavedPARP1-positiveoocytenucleiincreasedsignificantlyhigherbeforealloocytesdisappearedinemMsh5/emminus;/minus;ovaries.Weconcludethatthemitochondrialapoptoticpathwaymediatedbycaspase9isconstitutivelyactivatedinoocytesandrenderstheeliminationofoocyteswithmeioticerrors,whichcanbecapturedbythecleavageofPARP1./p/div