Vitellogenin is glycosylated in the fat body of the stick insect Carausiusmorosus and not further modified upon transfer to the ovarian follicle

Synthesis and secretion of vitellogenin (Vg) polypeptides were studied in e gg-laying females of the stick insect Carausius morosus following in vivo e xposure to [S-35]-methionine and acetyl-N-[H-3] glucosamine. The specificit y of radioisotope incorporation was assessed by in vitro inhibition with tu nicamycin and carbohydrate extraction with endo-glycosidase H. Vg polypepti des change in molecular weight during synthesis in the fat body and are not further modified upon transfer to the haemolymph or to the oocyte, suggest ing that they are already fully glycosylated prior to secretion. Radioactivity in the fat body was initially distributed over cisternae of t he rough endoplasmic reticulum and gradually transferred to the Golgi appar atus. Within an hour of exposure, electron-dense granules budding from the trans-Golgi network became preferentially labeled. Radioactivity in the ova rian follicle was restricted to the yolk granules of the cortical ooplasm a nd to the amorphous material lying within the intercellular channels of the follicular epithelium, This amorphous material was also shown to react pos itively when tested with a monoclonal antibody raised specifically against a Vg polypeptide. (C) 1999 Elsevier Science Ltd.