Chromosomal and embryological analyses of nuclear changes occurring in embryos derived from transfers of nuclei between Rana pipiens and Rana sylvatica☆☆☆

[摘要] DiploidnucleifromnormalblastulaeofRanapipiensweretransplantedintoenucleatedeggsofRanasylvatica.Following10–12divisionsintheforeigncytoplasm,theirnucleardescendantsweretransferredbackintoenucleatedpipienseggs.Allbutoneoftheembryosderivedfromtheseeggsdevelopedabnormallyandwerearrestedatvariousstagesrangingfromlateblastulaetoyoungtadpoles.Theseresults,likethoseobtainedbyMoore(1958a,b,1960),demonstratethatpipiensnucleiarechangedasaconsequenceofreplicatinginsylvaticacytoplasmandarenolongercapableofpromotingnormaldevelopmentwhenreturnedtotheirowntypeofcytoplasm.Themainobjectiveofthisinvestigationwastodeterminewhethertherestrictionsinthedevelopmentalcapacityofthesenucleiinvolvecytologicallydetectablealterationsinthechromosomecomplement.Analysisofmetaphaseplatesfromtheabnormallydevelopingback-transferembryosshowedthatalloftheseembryosdidinfactpossessabnormalnumbersandtypesofchromosomesasfollows:1.1.Thechromosomalabnormalitiesweremostpronouncedinback-transferembryosarrestinginearlystagesofdevelopment(gastrulae,neurulae,andearlytailbudembryos).Whencomparedwiththenormalpipienskaryotype,thechromosomecomplementsoftheseembryoswerefoundtopossessthefollowingabnormalities:(a)gainsandlossesoffromonetofourchromosomes,(b)ringchromosomes,minutechromosomes,andinonecase,acentricfragments,and(c)adecreaseinthenumberoflargechromosomescoupledwithanincreaseinthenumberofsmallones.Thekaryotypesweresoabnormalthatitwasnotpossibletospecifywhichchromosomeswereinvolvedintherearrangements.2.2.Thechromosomalalterationsinback-transferembryosarrestinginlaterstagesofdevelopment(latetailbudembryosandabnormaltadpoles)werelessextensiveandconsequentlycouldbeanalyzedingreaterdetail.Theseembryoswereaneuploidbyoneortwochromosomesand,unlikethemoredeficientembryosdescribedabove,didnotpossessringsorminutes.Adetailedkaryotypeanalysisofoneclonerevealedthatthechromosomecomplementsoftheseembryoslackedoneormorespecificchromosomesknowntobepresentinthenormaldiploidsetand,atthesametime,possessednewstructuraltypesnormallynotfoundinRanapipiens.Someofthesenewtypesofchromosomesappearedtobetheresultofatranslocationinvolvingadistinctivechromosome(no.10)ofthenormalpipienscomplement.KaryotypicabnormalitiesofthetypesjustdescribedcanaccountforthechangesinthedevelopmentalcapacityofpipiensnucleiasaconsequenceofreplicatinginsylvaticacytoplasmandfortheresultsobtainedbyMoore(1960),whichshowthatthesechangesareirreversible.Accordingtotheevidencepresentedinthisreport,alterationsinthechromosomecomplementsariseduringthetimethatpipiensnucleiaredividinginsylvaticacytoplasmbutexactlywhenandhowtheyareproducedremainstobeworkedout.

[学科分类] 生物科学（综合）