Abstract
The appearance of giant Hn[heteronuclear]RNA in Calliphora epidermal cells in the transition period from larva to pupa is ecdysone-dependent. In this specific developmental stage, the initial increase of this RNA species occurs shortly after the appearance of a small peak of ecdysone. Another main peak of the hormone is a prerequisite for pupation. The removal of the ring gland, the source of ecdysone, prior to the appearance of the 2nd hormone peak had no pronounced effect on HnRNA synthesis for at least 48 h after the operation. The larval pupal differentiation is a 2-step process. Initially, a gene activation occurs dependent on a low ecdysone titer. This is followed by a 2nd final step of pupal cuticle synthesis and pupation, dependent on the presence of a high concentration of the hormone.