The apparent requirement of two hormones, α- and β-ecdysone, for molting induction in insects

Abstract

Puff formations at loci I-18-C and IV-2-B of the salivary gland chromosomes are early indications of a beginning molting process in Chironomus tentans larvae. The effectiveness of the two ecdysone analogs, α- and β-ecdysone, in inducing these puffs was compared. Incubation of salivary glands in vitro with β-ecdysone causes only puff IV-2-B to appear; incubation with α-ecdysone stimulates initially puffing at only I-18-C. After an injection of α-ecdysone, puffing at I-18-C begins within less than 15 min, whereas puffing at IV-2-B is delayed for more than 30 min. Following an injection of β-ecdysone, puffing at IV-2-B begins within less than 15 min, whereas puffing at I-18-C is delayed. Injected 3H-α-ecdysone is converted to β-ecdysone and a polar compound. Injected 3H-β-ecdysone is converted to a compound less polar than α-ecdysone and a polar metabolite which stimulates puffing at I-18-C, like α-ecdysone. It is suggested that the two ecdysones have different targets in the cell, that they can be rapidly converted to compounds with the activity of the other analog, and that the induction of a complete molt requires the action of both hormones.