The Ability to Develop an Activity That Transfers Histones onto Sperm Chromatin Is Acquired with Meiotic Competence during Oocyte Growth

[摘要] Followingfertilization,theoocyteremodelsthespermchromatinintothemalepronucleus.Asacomponentofthisprocess,duringmeioticmaturation,oocytesdevelopanactivitythattransfershistonesontospermDNA.Tofurthercharacterizethisactivity,wetestedwhetheroocytesatdifferentstagesofgrowthcould,uponentryintometaphaseofmaturation,transferhistonesontospermDNA,asjudgedbychromatinmorphologyandimmunocytochemistry.Meioticallycompetentgrowingoocytes,whichspontaneouslyentermetaphaseuponculture,tranferredhistonesontospermchromatin,whereasincompetentoocytesdidnot,evenwhentreatedwithokadaicacidtoinducegerminalvesiclebreakdown(GVBD)andchromosomecondensation.WhenincompetentoocyteswerecultureduntiltheyacquiredtheabilitytoundergoGVBD,onlyasmallproportionalsodevelopedhistone-transferactivityduringmaturation.However,thisproportionsignificantlyincreasedwhentheoocyteswereculturedasgranulosa–oocytecomplexes.Thefailureofhistone-transferactivitytodevelopinincompetentoocytestreatedwithokadaicacidwasnotlinkedtolowH1kinaseactivitynorrescuedbyinjectedhistones.Becausecompetent,butnotincompetent,oocytesproducenaturalcalciumoscillations,incompetentoocyteswereexposedtoSrCl2.One-thirdoftreatedoocytesproducedatleastoneCa2+oscillationand,followinginsemination,thesameproportiontransferredhistonesontospermDNA.HistonetransferdidnotoccurinoocytespretreatedwiththeCa2+chelator,BAPTA-AM.Theseresultsindicatethattheabilitytodevelophistone-transferactivityisacquiredbygrowingoocytesnearthetimeofmeioticcompetence,thatitisseparablefromthisevent,andthatitmayberegulatedthroughaCa2+-dependentprocess.

[学科分类] 生物科学（综合）

[关键词] sperm;chromatin;histones;oocyte growth;meiotic competence;calcium