The maturation response of stage IV, V, and VI Xenopus oocytes to progesterone stimulation in vitro☆

摘要

Full-grownXenopusoocytes,StageVI(1200a€“1300??m),undergomeioticmaturationwhenexposedtoprogesterone.SmallerstageIV(800??m)andstageV(1000??m)oocytesremaininprophasearrestwhenexposedtothissteroid.ThelargerstageVIoocytesundergoanintracellularalkalizationfrom7.2to7.6,asix-toeightfoldincreaseinthephosphorylationofthe40SribosomalproteinS-6,andatwo-tothreefoldincreaseintotalproteinsynthesiswhenexposedtoprogesterone.Itwasfoundthat800-to1000-??moocytesdonotundergothesephysiologicalchangeswhenexposedtoprogesterone.Thislackofresponsecouldexplainthefailureofsmalloocytestoundergogerminalvesiclebreakdown(GVBD).However,whenstageIVandVoocyteswereartificiallyalkalizedtoapHiof7.6bytheweakbases,trimethylamine,procaine,ormethylamine,S-6phosphorylationwasstimulatedfour-tosixfoldandproteinsynthesiswasstimulatedtwo-tothreefold,buttheystilldidnotundergoGVBD.StageIVandVoocytesareabletoamplifyMPFinjectedintotheircytoplasmandundergoGVBD.Thus,800-to1000-??moocytesappeartocontainastoreofinactiveMPFintheircytoplasm.Itseemsthatanadditionalphysiologicalparameter(s),thatisuniquetosteroid-treatedstageVIoocytes,isresponsibleforactivatingthisMPFwhichinducesGVBD.