Role of the oocyte nucleus in physiological maturation in Rana pipiens☆

[摘要] Theeventsofmaturation(germinalvesicledissolutionandmeiosistothesecondmetaphase)havebeeninducedwithprogesteroneinvitroinfull-grownoocytesdissectedfromtheirovarianfollicles.Oocytesfromwhichgerminalvesicles(GV)wereremovedpriortoprogesteroneexposureweresubsequentlytestedforthecapacitytobeartificiallyactivated,cleave,andsynthesizecontrollevelsofprotein.Theenucleatedeggsrespondedtoanactivationstimuluswhentestedabout48hoursaftera1-hourexposuretoprogesterone.Thispositiveresponseincludedbreakdownofthecorticalgranules,elevationofthevitellinemembrane,rotationwithintheperivitellinespace,increaseineggturgidity,andchangesintheappearanceoftheeggsurface.Removaloftheeggvitellinemembraneandanyadherentfolliclecellswithpronase,priortoprogesteroneexposure,didnotpreventenucleatedeggsfromundergoingactivation;thesolecriterioninthiscasewasbreakdownofthecorticalgranules.Manyoftheenucleated,activatedeggsdisplayedabortivecleavages.EnucleatedeggslackingGVmaterialintheircytoplasmwereincapableofgenuinecleavagewhentestedbynucleartransplantation.ThisrestrictionwaspartiallyremovedbyinjectingGVmaterialbackintotheenucleatedprogesterone-stimulatedeggs.DonorGVmaterialfromnon-hormone-treatedeggswasessentiallyaseffectiveinthisrespectasGVmaterialfromprogesterone-stimulatedeggs.IncubationofoocyteswithactinomycinDatconcentrationsashighas50μg/mlhadnoeffectinprogesterone-inducedmaturation.Likewise,injectionofactinomycinDdirectlyintooocytesdidnotpreventprogesterone-inducedmaturation.Puromycin,ontheotherhand,suppressedallstagesofmaturation.TheseresultssuggestthatmaturationdoesnotrequireconcomitantDNA-dependentRNAsynthesis,butthatproteinsynthesisisobligatoryforallstagesofmaturation.Proteinsynthesiswasmeasuredineggsenucleatedpriortoprogesteroneexposureandatseveraltimesafterthehormonestimulation.Therateofproteinsynthesisduringtheentireperiodofmaturationwasessentiallyidenticalinenucleatedeggsandtheirnucleatedcontrols.Theratewasinitiallylow,increasedonlyafterprogesteroneexposure,reachedamaximumlevelaboutwhennucleatedcontrolsgaveofftheirfirstpolarbodies,andtheelevatedratewasmaintainedforatleastadayafternucleatedcontrolswerefirstcapableofbeingfertilized.Basedontheseexperiments,weconcludethatthemixingofGVmaterialwiththeeggcytoplasmisnotaprerequisitetoattainingthecapacitytoundergoartificialactivationortosynthesizeprotein,butisrequiredfortheenucleatedeggstocleave.Wefurthersuggestthatthesiteofactionofprogesteroneininducingmaturationisextranuclear,possiblyattheeggsurface.

[学科分类] 生物科学（综合）