Effect of actinomycin D on the development of the early imaginal eye disks of Drosophila melanogaster☆

[摘要] Astudywasmadeoftheeffectof10μg/mlofactinomycinD(placedinthefoodofD.melanogasterduringthefirstandsecondinstar)onthedevelopmentoftheimaginaleyedisks.Histologicalstudiesindicatedthatalthoughtheheadanlagenoftreatedlarvae(whichweighone-thirdasmuchasthecontrollarvae)aresomewhatsmallerattheendofthefirstinstar,theycontainthesamenumberofcells.Celldivisionduringthefirstinstarisnotaffectedbyactinomycin.Duringthesecondinstar,allcelldivisionceasesinthetreatedanlagen,whilethesecellsincontrollarvaeundergothreedivisions.Thisisanabruptchangeinsensitivitytothedrugsinceanlagenoflarvaeonnormalfoodduringthefirstinstarcompletelystopcelldivisionwhenplacedonactinomycinfoodattheendofthisinstar.ThefateofthepresumptiveeyecellswithintheheadanlagewasdeterminedbymeasuringthefrequencyandsizeoftwinspotsproducedintheadulteyeresultingfromX-rayinducedsomaticcrossingover.Actinomycin-treatedandcontrollarvaewereirradiatedattheendofthefirstorattheendofthesecondinstar.Thecontrolresultswerethoseexpectedfromthetotalcellcountsoftheanlage;however,norelevantdifferencewasobservedbetweenthecontrolandactinomycinseriesinthefrequencyoftwinspotsorintheirsizewhenthesomaticcrossingoverwasinducedattheendofthesecondinstar.Thecountsofcellnumberduringthesecondinstarindicatenocelldivisionintheactinomycin-treatedanlagen,butthreecelldivisionsinthecontrolanlagen.Thelatterfactisinterpretedtomeanthefollowing.Actinomycinblockedcelldivisionduringthesecondinstarbutallowedthechromosomestoreplicate.Thechromosomesweresubsequentlydistributednormallytothecellsformedwhencelldivisionresumeduponremovalofthelarvaefromtheactinomycinfood.Ifthisinterpretationiscorrect,itfollowsthatthedeterminativeeventwhichlaysdownthepatternofvariegationattheendofthefirstinstarincasesofpositioneffect,andwhichisunaffectedbyactinomycin(Baker,1967),isonethatactsonthechromosomesthemselves,andnotthroughcytoplasmiccomponents.

[学科分类] 生物科学（综合）