Induction of yolk formation in hemipteran previtellogenic oocytes (Dysdercus intermedius)

Publisher Website
Google Scholar
Abstract
Yolk formation has been studied in previtellogenic oocytes of the telotrophic-meroistic ovariole of the red cotton bug Dysdercus intermedius (Heteroptera: Pyrrhocoridae) in the absence of the follicular epithelium (“skinned oocytes”). Early preparation for endocytosis was seen by urea gel electrophoresis and immunoblotting, which showed that cytosolic clathrin (light chain) is already present in the previtellogenic trophocyte-oocyte syncytium. The ability of these previtellogenic skinned oocytes to form yolk was studied by incubating them in physiological saline to which rhodarnine-labelled hemolymph proteins were added. These oocytes formed a peripheral band of fluorescent yolk spheres when incubated in vitellogenin-containing hemolymph proteins obtained from 6-day-old adult females but not when in hemolymph proteins from 3-day-old females, which lack vitellogenin. AVEC-DIC microscopy was used to record fluorescent protein uptake as it occurred in living, previtellogenic oocytes. Adsorption to the oolemma, endocytosis and deposition in larger vesicles in the oocyte cortex could be followed. The presence of coated pits and cortical yolk spheres in previtellogenic skinned oocytes was confirmed by electron microscopy. While juvenile hormone is known to be required for vitellogenin secretion by the fat body and for its penetration of the follicular epithelium, our results suggest that yolk formation by oocytes is more directly induced simply by exposure to vitellogenin.