Pattern and activity of polyribosomes from the integument of blowfly larvae during development. Stimulation of polyribosome formation with -ecdysone

Synthesis of giant HnRNA in the epidermal cells of Calliphora and the role of the ring gland

The appearance of giant HnRNA in the epidermal cells of Calliphora in the transition period from larva to pupa is ecdysone-dependent. In this specific stage of development, 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 second peak of the hormone, was found to have no pronounced effect on HnRNA synthesis for at least 48 h after the operation. It is concluded that the larval pupal differentiation is a two-step process. Initially a gen activation occurs dependent on a low ecdysone titer. This is followed by a second final step of pupal cuticle synthesis and pupation, dependent on the presence of a high concentration of the hormone.

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.