Hormonal regulation and developmental role of Krüppel homolog 1, a repressor of metamorphosis, in the silkworm Bombyx mori

摘要

Juvenilehormone(JH)hasanabilitytorepresstheprecociousmetamorphosisofinsectsduringtheirlarvaldevelopment.Kruuml;ppelhomolog1(emKr-h1/em)isanearlyJH-induciblegenethatmediatesthisactionofJH;however,thefinehormonalregulationofemKr-h1/emandthemolecularmechanismunderlyingitsantimetamorphiceffectarelittleunderstood.Inthisstudy,weattemptedtoelucidatethehormonalregulationanddevelopmentalroleofemKr-h1/em.WefoundthattheexpressionofemKr-h1/emintheepidermisofpenultimate-instarlarvaeofthesilkwormemBombyxmori/emwasinducedbyJHsecretedbythecorporaallata(CA),whereastheCAwerenotinvolvedinthetransientinductionofemKr-h1/emattheprepupalstage.TissuecultureexperimentssuggestedthatthetransientpeakofemKr-h1/emattheprepupalstageislikelytobeinducedcooperativelybyJHderivedfromgland(s)otherthantheCAandtheprepupalsurgeofecdysteroid,althoughinvolvementofunknownfactor(s)couldnotberuledout.ToelucidatethedevelopmentalroleofemKr-h1/em,wegeneratedtransgenicsilkwormsoverexpressingemKr-h1/em.Thetransgenicsilkwormsgrewnormallyuntilthespinningstage,buttheirdevelopmentwasarrestedattheprepupalstage.ThetransgenicsilkwormsfromwhichtheCAwereremovedinthepenultimateinstardidnotundergoprecociouspupationorlarvalndash;larvalmoltbutfellintoprepupalarrest.ThisresultdemonstratedthatemKr-h1/emisindeedinvolvedintherepressionofmetamorphosisbutthatemKr-h1/emaloneisincapableofimplementingnormallarvalmolt.Moreover,theexpressionprofilesandhormonalresponsesofearlyecdysone-induciblegenes(emE74/em,emE75/em,andemBroad/em)intransgenicsilkwormssuggestedthatemKr-h1/emisnotinvolvedintheJH-dependentmodulationofthesegenes,whichisassociatedwiththecontrolofmetamorphosis./p/div