Nucleocytoplasmic hybrids between Rana pipiens and Rana palustris: I. Analysis of the developmental properties of the nuclei by means of nuclear transplantation☆

摘要

AlthoughdiploidhybridsbetweenRanapipiensandRanapalustrisarenormal,theandrogenetichaploidhybridsdevelopmuchmorepoorlythandoordinaryhaploidsofeitherspecies.Thissuggestedtheexistenceofanucleocytoplasmicincompatibilitywhichisexpressedwhenanucleuscontainingchromosomesfromonlyoneofthesespeciesispresentinthecytoplasmoftheother.Sincehaploids,inanycase,arenotviable,avalidtestrequiredthestudyofdiploids.Suchastudy,asreportedinthispaper,demonstratesthatthisnucleocytoplasmicincompatibilitydoesinfactexist.Whendiploidpipiensblastulanucleiweretransplantedintoenucleatedpalustriseggs,theresultingnucleocytoplasmichybridsdisplayedaspecificpatternofdeficienciesleadingtotheirdevelopmentalarrestinpostneurulastages.Whetherornotthisincompatibilitycausesstablechangesinthedevelopmentalpropertiesofthenucleiwasthentestedbytransferringpipiensnucleiafterdivisionforone,two,andthreeblastulagenerationsinpalustriscytoplasmbackintoenucleatedpipienseggs.Thelargemajority(84%)oftheback-transferembryosdevelopednormally,thusdemonstratingthatthenucleiremainedunchangedintheirabilitytofunctionnormallyintheirowncytoplasmfollowingasmanyas36divisionsintheforeigneggcytoplasm.Thepossibilitythatsuchchangesmighttakeplacelaterinthedevelopmentofthenucleocytoplasmichybridsremainstobeworkedout.Cytologicalanalysesofthenucleocytoplasmichybridsandtheback-transferembryosrevealedthatbothtypesofembryospossessednormalchromosomecomplements.Thisresultisparticularlysignificantwithregardtothenucleocytoplasmichybridssinceitshowsthattheirdeficientdevelopmentisnotcausedbygrosschromosomalabnormalities.Inaddition,workdescribedelsewhereshowsthattheabnormalbehavioroftheseembryoscanbecompletelycorrectedbytheadditionofahaploidsetofpalustrischromosomes.Thus,thishybridcombinationoffersauniqueopportunityforanalyzinggeneticandbiochemicaleventsinvolvedintheformationofapredictablesetofdevelopmentaldeficienciesinembryoswhosenucleihavenormalchromosomecomplementsandareknown,underdefinedconditions,tobegeneticallycompetent.