YOLK SPHERE FORMATION IS INITIATED IN OOCYTES BEFORE DEVELOPMENT OF PATENCY IN FOLLICLES OF THE MOTH, PLODIA-INTERPUNCTELLA

We describe a provitellogenic stage, a previously unrecognized stage o f follicle development in moths, and show that oocytes begin yolk sphe re formation prior to the development of patency by the follicular epi thelium. The vitellogenic activities of follicles from pharate adult f emale Plodia interpunctella (Hubner) were determined by visualizing th e subunits of vitellin (YP1 and YP3) and the follicular epithelium yol k protein (YP2 and YP4) using monospecific antisera to each subunit to immunolabel whole-mounted ovaries or ultrathin sections. At 92 h afte r pupation, yolk spheres that contained only YP2 began to proliferate in the oocytes. The inter-follicular epithelial cell spaces were close d at 92 h making vitellogenin inaccessible to the oocyte, and conseque ntly, the vitellin subunits were not observed in the yolk spheres. YP2 uptake most likely occurred across the brush border from the follicul ar epithelial cells to the oocyte at this time. At 105 h, the inter-fo llicular epithelial cell spaces appeared closed yet trace amounts of l abeling for vitellin were observed in the spaces and also in the yolk spheres along with YP2. Equivalent labeling for all four YPs in yolk s pheres was finally observed at 112 h after pupation when the follicula r epithelium had become patent. These data indicate that the provitell ogenic stage is an extended transition period between the previtelloge nic and vitellogenic stages that lasts for approximately 13 h, and it is marked at the beginning by YP2 yolk sphere formation in the oocyte and at the end by patency in the follicular epithelium.