The sodium dependence of embryonic induction☆

[摘要] Inductionofnerveandpigmentcellsinpresumptiveepidermisofthefroggastrulahasbeenfoundtobedependentupontheconcentrationofthesodiumion.Thissodiumdependenceisshownbysmallaggregatesofpresumptiveepidermiscellsinducedbysucroseorbyions(Li+,Ca2+,Mg2+,Mn2+)todifferentiateintonerveorpigmentcells.Followingthesetreatments,inductiontakesplacewhentheexternalNaClconcentrationis0.088M,butdoesnotoccurat0.044M.Thisrangeofconcentrationsiswithinthephysiologicalrangeforcontinuouscultureofcellaggregatesandexplantsofamphibianembryoscommonlyusedforstudiesofinduction.Similarly,normalinductionofnerveandpigmentcellsbymesoderminsmallexplants,preparedfromthedorsallipandlateralmarginalzonesoftheearlygastrula,isdependentupontheexternalconcentrationofsodium.Nerveandpigmentcellsareinducedbythemesodermwhentheculturemediumcontains0.088MNaCl.At0.044MNaCl,however,themesodermdifferentiatesintomuscleandmesenchyme,butinductionofnerveandpigmentcellsdoesnotoccur.Thesodiumdependencyofaggregatespreparedfromearlygastrulaisrestrictedtotheperiodofinduction.Theendofthisperiodcorrespondsindurationtotheendofgastrulation.Cellaggregatesprepareddirectlyfrompresumptiveneuralplateattheendofgastrulationsimilarlyhavebecomeindependentofsodium.Thesodiumdependencyofinductioninpresumptiveepidermiscellaggregatesbyionsiscomparedtosodiumdependencyofinductionofectodermbymesodermincellaggregatesfromearlygastrula.Theworkinghypothesispresentedisthatnormalembryonicinductiondependsuponanendogenoussourceofions,andthatthereisanintracellularreleaseofionswithintheembryoduringlategastrulation.PreliminaryexperimentshaverevealedathreefoldincreaseinexchangeableCa2+withinthecellsandaforty-foldincreaseinintracellularNa+duringgastrulation.Thesodiumdependencedemonstratedinthepresentexperimentalsystemandpostulatedfornormalembryonicinductioniscomparedtoothersodium-dependentsystemsintransportattissue,cellular,nuclear,andorganellelevels.

[学科分类] 生物科学（综合）