INDUCTION OF YOLK FORMATION IN HEMIPTERAN PREVITELLOGENIC OOCYTES (DYSDERCUS-INTERMEDIUS)

Yolk formation has been studied in previtellogenic oocytes of the telo trophic-meroistic ovariole of the red cotton bug Dysdercus intermedius (Heteroptera: Pyrrhocoridae) in the absence of the follicular epithel ium (''skinned oocytes''). Early preparation for endocytosis was seen by urea gel electrophoresis and immunoblotting, which showed that cyto solic clathrin (light chain) is already present in the previtellogenic trophocyte-oocyte syncytium. The ability of these previtellogenic ski nned oocytes to form yolk was studied by incubating them in physiologi cal saline to which rhodamine-labelled hemolymph proteins were added. These oocytes formed a peripheral. band of fluorescent yolk spheres wh en incubated in vitellogenin-containing hemolymph proteins obtained fr om B-day-old adult females but not when in hemolymph proteins from 3-d ay-old females, which lack vitellogenin. AVEC-DIC microscopy was used to record fluorescent protein uptake as it occurred in living, previte llogenic oocytes. Adsorption to the oolemma, endocytosis acid depositi on in larger vesicles in the oocyte cortex could be followed. The pres ence of coated pits and cortical yolk spheres in previtellogenic skinn ed oocytes was confirmed by electron microscopy. While juvenile hormon e is known to be required for vitellogenin secretion by the fat body a nd for its penetration of the follicular epithelium, our results sugge st that yolk formation by oocytes is more directly induced simply by e xposure to vitellogenin.