Studies on the Juvenile Hormone-controlled Synthesis of Vitellogenin in the African Migratory Locust, Locusta migratoria migratorioides R. & F.

Abstract

<p>The biosynthesis of the yolk-precursor protein, vitellogenin (VG), induced by juvenile hormone (JH) in the fat body of African migratory locusts, has been studied as a system for analyzing the mechanism of JH-controlled specific gene activation in insects. In order to isolate VG mRNA for further characterization, conditions for the isolation of undergrad VG mRNA-containing polysomes from the fat body of reproductively active females have been defined. The identity of these female-specific heavy polysomes as VG polysomes was confirmed by precipitation of the associated nascent polypeptides with antivitellin serum and by translation of the polysomal RNA in Xenopus oocytes. By EM observation these polysomes were found to contain 40-50 ribosomal monomers. In normal development, accumulation of ribosome monomers in the fat body of female locusts began at about day 4 after emergence (terminal oocyte length = 2 mm), then was followed by the appearance of VG polysomes beginning at about day 8 (terminal oocyte length = 3 mm). Vitellogenin polysomal content reached a maximum at about day 14 (terminal oocyte length = 5-6 mm), and then fell to an undetectable level as the terminal oocytes reached their maximal size (7 mm). In allatectomized (removal of the source of JH) females VG polysomes can be induced by ZR-515 (300 µg/animal) treatment. A single treatment with ZR-515 induced a rapid increase in ribosome monomers and light polysomes in the first 48 hr, but the maximal production of vitellogenin polysomes was observed at 72 hr. After the decay of this effect (12 days after hormone treatment) a second application of ZR-515 resulted in the rapid formation of vitellogenin polysomes without an initial accumulation of ribosome monomers. These and previous results are consistent with the action of juvenile hormone at the gene level.</p>