Ecdysone-regulated chromosome puffing in the salivary glands of the Mediterranean fruit fly, Ceratitis capitata

The effect of ecdysone on the puffing activity of the polytene chromosomes of Ceratitis capitata has been studied in organ cultures of late-larval sal ivary glands. Culture of glands from 120-h-old larvae (puff stage 1) in the presence of ecdysone resulted in the initiation of the late-larval puffing cycle that is normally observed in 145-h-old larvae (puff stage 4). During a 7-h period in the presence of ecdysone, the puffing patterns of most loc i resembled the in vivo patterns observed in the period between puff stages 4 and 10, indicating that the first puffing cycle can be initiated by the hormone and proceed almost to completion, in vitro. Culture of salivary gla nds in the presence of ecdysone and a protein-synthesis inhibitor, as well as ecdysone withdrawal and readdition experiments, indicated that most of t he ecdysone-regulated puffs could be categorized into three classes: (i) th e puffs that were suppressed immediately by ecdysone, even in the absence o f protein synthesis; (ii) the puffs that were induced directly by ecdysone; and (iii) the puffs that were induced indirectly by ecdysone, that is, the y were induced after a lag period of a few hours and required protein synth esis for their induction.