Changes in translatable mRNAs during the larval-pupal transformation of the epidermis of the tobacco hornworm☆☆☆

[摘要] Attheinitiationofmetamorphosiswhenexposedtoecdysteroidintheabsenceofjuvenilehormone(JH),thelepidopteranepidermischangesitscommitmentfromoneforlarvaldifferentiationtooneforpupaldifferentiation.ChangesinmRNApopulationsduringthischangebothinvivoandinvitrowerefollowedbyaone-dimensionalSDS-gelelectrophoreticanalysisoftranslationproductsmadeinamRNA-dependentrabbitreticulocytelysatesystem.ThelarvalepidermalcellwasfoundtoloseitstranslatablemRNAsforlarvalcuticularproteinsandthelarval-specificpigmentinsecticyaninduringthechangeincommitment;theseneverreappeared.ForClassIcuticularproteinsandforinsecticyanin,thislossoccurredduringtheexposuretoecdysteroid,eachwithadifferingtimecourse.Bycontrast,ClassIIcuticularmRNAsfirstincreasedduringthistime,thenalsodisappearedbythetimethecellswerepupallycommitted.InvitrothesemRNAsappearedinonlytraceamountsinresponseto20-hydroxyecdysone(20-HE).Thepupallycommittedcell(lateinthewanderingstage)containedmRNAsforthreelow-molecular-weightproteinswhichwereprecipitablewiththepupalcuticularantiserum.TheremainderofthepupalcuticularmRNAswerenottranslatableuntilthethirddayafterwandering,atimewhenpupalcuticleisbeingdepositedinresponsetoamoltingsurgeofecdysteroid.ThepupallycommittedcellalsohadatleastonenewnoncuticularmRNAwhichcodedfora34Kproteinandwhichwasabsentfrombothlarvalandpupalepidermalcellsmakingcuticle.Sinceitsappearanceinresponseto20-HEinvitroisrepressedbyJH,itiscalledapupalcommitment-specificprotein.Thus,duringthechangeofcommitment20-HEinactivateslarval-specificgenesirreversiblyinasequentialcascadeofevents.Theactivationofmostpupal-specificgenesthenrequiresasubsequentexposuretomoreecdysteroid.

[学科分类] 生物科学（综合）