Genes expressed during the differentiation of the pupal wings are also transiently expressed during the larval moult in Bombyx mori.

By a differential screening of cDNA libraries made with RNAs present in differentiating imaginal wing discs of Bombyx mori, we have isolated clones whose expression is dramatically modified during the formation of the pupal wings. The RNAs corresponding to all but one of these clones are also transiently accumulated in the wing primordia during the last larvo-larval moult and in response to 20-hydroxyecdysone injections. If the injections are made to juvenilized larvae the expression of the same genes is stimulated but the range of the stimulation is reduced. It is suggested that in Bombyx, cells of the wings reach the pupal stage of differentiation by steps corresponding to the phases during which high levels of ecdysteroids are present.