Sequential gene activation by ecdysone in polytene chromosomes of Drosophila melanogaster,: III. Consequences of ecdysone withdrawal☆

摘要

EcdysoneinducesasequenceofchangesinpuffingactivityofthepolytenesalivaryglandchromosomesofDrosophilamelanogaster.Inthecontinuouspresenceofecdysonethissequencetakesabout12hrtocomplete.Salivaryglandswereincubatedinthepresenceofecdysoneforvarioustimesandthentransferredtohormone-freemediumtostudytheeffectsofthehormone'sremovalonthesequenceofpuffingactivities.Theearlyecdysone-inducedpuffsimmediatelyregressonremovalofhormone.Theycanbefullyreinducedifexposedtohormoneagain,butonlyiftheinitialperiodofexposuretothehormonewas2hrorless;withlongerperiodsofinitialexposuretheearlypuffsbecomeprogressivelyrefractorytoreinduction.Thisprocessisinhibitedbycycloheximide.Agroupofthelatepuffsmaybeinducedprematurelybyremovalofthehormonea€”theextentoftheirprematureinductioniscorrelatedwiththesizeoftheearlypuffsduringtheperiodofecdysoneexposure.Ecdysoneinhibitstheprematureinductionoftheselatepuffs.