Juvenile hormone-controlled vitellogenin synthesis in the fat body of the locust ( Locusta migratoria): Isolation and characterization of vitellogenin polysomes and their induction in vivo

Abstract

With the aid of EGTA to control the endogenous RNase activity, a predominant population of heavy polysomes was isolated from the fat body of reproductively active female locusts. The identity of these as vitellogenin (Vg)-synthesizing polysomes was established by precipitation of the associated nascent polypeptides with anti-vitellin serum and by translation of the polysomal RNA in Xenopus laevis oöcytes. By EM observation these polysomes were found to contain 40–50 ribosome monomers. In normal development, accumulation of ribosomes in the fat body of female locusts began at about day 6 after adult ecdysis (terminal oöcyte = 2 mm or smaller), and was followed by the appearance of Vg-polysomes beginning at 3 mm terminal oöcyte length (about day 8–10 after adult ecdysis). The content of Vg-polysomes reached a maximum at 5–6 mm oöcyte length (about day 14), and then fell to an undetectable level as the oöcytes reached their maximum size (7 mm). In allatectomized females, Vg-polysomes were induced by treatment with an active juvenile hormone analogue, ZR-515. A single application with ZR-515 produced a massive accumulation of ribosomes and light polysomes in the first 48 hr which was followed by the rapid formation of Vg-polysomes to give a maximum at 72 hr. After the decay of this effect a second dose of ZR-515 resulted in the rapid appearance of Vg-polysomes without the initial generation of ribosomes.