The influence of folic acid analogs on development and nucleic acid metabolism in Rana pipiens embryos☆

[摘要] 1.1.TheinfluenceofthefolicacidanalogsAmethopterinandAmino-AnfolonRanapipiensdevelopmentwasdeterminedafterinjectionofsolutionsoftheanalogsintofertilizedeggs.TheeffectoftheseanalogsonthesynthesisofDNAandRNAandtheireffectontheincorporationofglycine-2-C14intonucleicacidshavebeenstudied.Finally,analysesoffolicacidcompoundsduringdevelopment,usingthreemicrobiologicalassays(Lactobacilluscasei,Leuconostoccitrovorum,andStreptococcusfaecalis),havebeencompleted.2.2.Atdosesrangingfrom0.008×10−5μmolepereggto3.2×10−5μmoleperegg,cleavagewascompletelyunaffected.Atthelowestdoses(0.008to0.016×10−5μmolperegg),abnormalitiesofthesenseorgans,brain,andneuraltubeweremostevident.Atstillhigherdoses(0.032to0.08×10−5μmoleperegg),severeretardationsduringneurulationwereobserved.Atconcentrationsof0.32to0.64×10−5μmoleperegg,gastrulationwasretardedandabnormal.Finally,atdosesrangingfrom0.8to3.2×10−5μmoleperegg,mostembryosdidnotdevelopbeyondthelateblastulastage.3.3.Mitoticindexdataindicatedthat:(a)theanaloginterferedwithcelldivision;(b)theretardationofcelldivisionoccurredpriortotheappearanceofanymorphogeneticeffect;(c)regionsexhibitinghighmitoticactivity(neuralfolds,somites)weremostsensitivetotheanalogs,andnotochordandendodermexhibitedleastsensitivity.4.4.Theeffectoftheanalogcouldbepartiallyorcompletelypreventedbyasimultaneousinjectionofcitrovorum(folinicacid).AratioofcitrovorumtoAmethopterinof4:1resultedincompleteprotectionin28%oftheembryos.Thereversalbycitrovorumbehavesinanoncompetitivemanner.5.5.Thymidine,ataratioof99to210:1(thymidinetoAmethopterin),gavepartialreversalwheninjectedintotheblastocoelofamid-blastulastage.Itgavelittleprotection,however,wheninjectedsimultaneouslywiththeanalogintofertilizedeggs.Deoxyuridinegaveslightreversal.6.6.Thesensitiveperiodsofdevelopmentinorderofdecreasingsensitivityareasfollows:neurulation,gastrulation,blastulation.Cleavageisleastsensitiveandthereisevidenceofadecreaseinsensitivityattheendofneurulation.7.7.Amethopterin,ataconcentrationof1.6×10−5μmoleperegg(whichpreventsgastrulation),resultsinacompleteinhibitionofDNAsynthesisafter20hoursofdevelopmentat18°C,amid-blastulastage.NoeffectontheamountofRNAperembryowasobserved.8.8.Amino-Anfol,atadoseof3.2×10−5μmoleperegg(whichpreventsgastrulation),inhibitstheincorporationofglycine-2-C14intoDNAafter16hoursofdevelopmentat20°C,amid-blastulastage.NoeffectontheincorporationintoRNAorotherfractionswasobserved.9.9.Analysesoffolicacidactivityperembryorevealthatthefertilizedeggcontains8.9×10−3μgofL.caseiactivity,1.8×10−3μgofL.citrovorumactivity,and0.58×10−3μgofS.faecalisactivity.Duringcleavage,thereisadecreaseof20–25%intheL.citrovorumandL.caseiactivity,respectively,untilthemid-blastulastage.Fromthisstagethroughgastrulationandneurulation,thislowlevelofactivityremainsconstant.Attheendofneurulation(Shumwaystage15),thereisanincreaseinactivityuntiltheoriginallevelsatfertilizationarerestored.10.10.Theseobservationsarediscussedinrelationtoaproposedhypothesisforthesynthesisofnucleicacidsduringamphibiandevelopment.

[学科分类] 生物科学（综合）