Fate of amplified nucleoli in Xenopus laevis embryos☆
[摘要] Wehavefollowedthefateoftwocomponentsofextrachromosomalnucleoli,amplifiedribosomalDNA(rDNA)and7.5kbprecursorrRNA,duringearlyembryogenesisofXenopuslaevis.OtherworkershaveshownthattheamountofamplifiedrDNAaccumulatedduringoogenesisremainsunchangedthroughthe16-cellstageofembryogenesis.Hereweshowthatasembryoniccleavagecontinues,theamountofamplifiedrDNAdecreasesuntilitisnolongerdetectableintheearlygastrulaembryo.Incontrast,theamountof7.5kbprecursorrRNAineggs,earlycleavagestageembryos,orblastulastageembryosisthesameasinoocytenuclei.SincenorRNAsynthesisoccursduringtheseearlystages,weconcludethattheprecursorrRNAsequencessynthesizedintheoocyteareneitherprocessednordegradedduringearlydevelopment.TheamplifiedrDNAisnotreplicatedintheearlyembryoeventhoughthechromosomalDNAoftheembryoreplicatesevery30minduringthefirst7.5hrofembryogenesis.WhenamplifiedrDNAispurifiedandtheninjectedintocleavingembryos,however,wefindthatitisreplicated.Thisfindingsuggeststhatsomefactor(s)preventstheendogenousamplifiedrDNAfromrespondingtothecellularreplicationsignals.WeshowthatmethylationofcytosineintherDNAisnotrelatedtotheDNA'scapacityforreplicationinthissystemsinceamplified(unmethylated)andchromosomal(methylated)rDNAarebothreplicatedwheninjectedintoembryos.ThemethylationpatternoftheserDNAsappearstobemaintainedafterreplicationintheembryo.
[发布日期] [发布机构]
[效力级别] [学科分类] 生物科学（综合）
[关键词] [时效性]
