Mammalian sperm-egg interaction: Fertilization of mouse eggs triggers modification of the major zona pellucida glycoprotein, ZP2☆

摘要

Sperm-egginteractioninmammalsisinitiatedbybindingofspermtothezonapellucida,anacellularcoatcompletelysurroundingtheplasmamembraneofunfertilizedeggsandpreimplantationembryos.Fertilizationresultsintransformationofthezonapellucida(a€?zonareactiona€?),suchthatadditionalspermareunabletobindtothezonapellucidaoffertilizedeggsandembryos,andspermthathadpartiallypenetratedthezonapellucidaofeggspriortofertilizationarepreventedfromfurtherpenetrationafterfertilization.Thefailureofspermtobindtofertilizedmouseeggsandembryosisattributabletomodificationofthespermreceptor,ZP3,an83,000-molecularweightglycoproteinpresentinzonaepellucidaeisolatedfrombotheggsandembryos[Bleil,J.D.,andWassarman,P.M.(1980).Cell,20,873a€“882].Inthisinvestigation,ZP2,themajorglycoproteinfoundinmousezonaepellucidae[Bleil,J.D.,andWassarman,P.M.(1980).Develop.Biol.,76,185a€“202]wasanalyzedbygelelectrophoresisunderavarietyofconditionsinordertodeterminewhetherornotitundergoesmodificationasaresultoffertilization.Undernonreducingconditions,ZP2presentinsolubilizedzonaepellucidaethatwereisolatedindividuallyfrommouseoocytes,eggs,andembryosmigratesonSDS-polyacrylamidegelswithanapparentmolecularweightof120,000.However,underreducingconditions,ZP2fromembryos,butnotfromoocytesorunfertilizedeggs,migrateswithanapparentmolecularweightof90,000andhasbeendesignatedZP2f.TheevidencepresentedsuggeststhatmodificationofZP2followingfertilizationinvolvesproteolysisoftheglycoprotein,butthatintramoleculardisulfidebondspreventthereleaseofpeptidefragments.ItisshownthatthesamechangeinZP2canbegeneratedinvitrobyartificialactivationofunfertilizedmouseeggswiththecalciumionophoreA23187,thuseliminatingthepossibilitythataspermcomponentisresponsibleforthemodificationofZP2followingfertilization.Theseresultssuggestthatsomeofthechangesinthebiochemicalandbiologicalpropertiesofzonaepellucidae,observedfollowingfertilizationoractivationofmouseeggs,resultfrommodificationofthemajorzonapellucidaglycoprotein,ZP2.