Giant RNA in insects. I. Differential changes during Calliphora development and the role of ecdysone.

The pattern of newly synthesized RNA in the epidermis cells of Calliphora during the larval life to the early pupal stage was analysed by electrophoretic separation of RNA extracts on polyacrylamide gels. During larval life, mainly rRNA was synthesized. The elevation of ecdysone concentration during the synthesis of the new larval cuticle resulted primarily in the stimulation of rRNA synthesis. In the transition period from larva to pupa, the principal RNA synthesized was rapidly labelled giant DNA-like RNA, with an average life span of 30 min. Prior to the change in RNA metabolism at this development stage, the synthesis of all classes of RNA was depressed. The initial increase in hnRNA synthesis occurs at the onset of the wandering stage, shortly after the appearance of a small peak of ecdysone and about two days prior to the main peak of hormone secretion and pupariation. During induced pupariation by ecdysterone, 1 h after hormone treatment, more label was observed in giant hnRNA followed by elevation of rRNA synthesis. Processing and maturation of rRNA also seemed to be stimulated.