Cellular differentiation and pattern formation during metamorphosis of the milkweed bug Oncopeltus

[摘要] TheintegumentofOncopeltusisverydifferentinlarvaeandadults,andthetransformationissensitivetojuvenilehormone.Theeffectsofasyntheticjuvenilehormoneanalogoncellularmetamorphosis(hereregardedasanexampleofcellulardifferentiation)wereanalyzedattwolevels:1.A.Effectsoncuticlesecretedbyindividualcells1.1.1.Potentdoses(1.25μgofthecrudeextract)wheninjectedearlyinthelastmoltofOncopeltuscausedcompleteinhibitionofmetamorphosisandcurtailedthemoltcycle.1.2.2.Afterinjectionofthesamedoseat27and49hoursafterecdysis,larvalcuticlewasformed;butinjectionat64and74hoursproducedaseriesofadult/larvalintermediateinsectswhoseabdominalintegumentconsistedofintermediatecells.Thewholeinsectwasaffectedandtheepidermalcellsrespondeduniformly.Acontinuousseriesofintegumentsshowingincreasingcellularmetamorphosiswasobtained.1.3.3.Whenthresholddoses(0.06μg)ofthehormonewereinjectedearlyinthemolt,onlytheepidermiswasaffectedandtheresponseoftheepidermalcellswasheterogeneous,resultinginmosaicinsects.2.B.EffectsonthehairpatternDuringmetamorphosisinOncopeltusevenlyspacedhairsdevelop.Thesestructuresaredistinctfrom,andmuchdenserthan,thelarvalbristles.Theirdevelopmentissensitivetothejuvenilehormone.2.1.1.Injectionofpotentdosesofjuvenilehormonewithinafewhoursofthepreviousecdysiscompletelysuppressedhairdevelopment.Afterthistimeandupuntil64hoursafterecdysishairdevelopmentwasonlypartiallyreduced,eventhoughthecuticlesecretedwascompletelylarvalbyothercriteria.Therewasnoeffectonhairdensityafter64hours,eventhoughthevisiblecytologicaleventsassociatedwithhairdifferentiationdonotbeginuntil70hours.2.2.2.Theintermediatescouldbearrangedinacontinuousseriesofincreasinghairdensity.Theuniformityofdistributionwasmeasuredquantitativelyandfoundtoimprovewithdensity.2.3.3.MitomycinCwasinjectedandfoundtodisrupthairdevelopmentindependentlyfromjuvenilehormone,probablybydirectinterferencewithhairdevelopment.2.4.4.ThehairandbristlepatternwasanalyzedquantitativelyaccordingtothemethodofClaxton(1964):theresultssupportedtheadoptionoftheWigglesworthmodelforbristledevelopmentasaworkinghypothesis.Withinthetermsofthismodel,thejuvenilehormonewasshowntomaintainthethresholdofepidermalcellstothebristle-formingsubstance,athresholdwhichfallsduringnormalcellularmetamorphosis.2.5.5.Theprocessofcellularmetamorphosisanddifferentiationinthissystemisconsideredtobeagradualone,whichcanbehaltedbyjuvenilehormone.Thedevelopmentofsmallnumbersofevenlyspacedhairsinintermediatesisregardedasanexpressionofpartialmetamorphosisordifferentiation.

[学科分类] 生物科学（综合）