ROLE OF THE FOLLICLE CELLS FOR YOLK UPTAKE IN OVARIAN FOLLICLES OF THE HONEY-BEE APIS-MELLIFERA L (HYMENOPTERA, APIDAE)

In previtellogenic and early vitellogenic follicles of the honey bee Apis mellifera (Hymenoptera: Apidae), the follicle cells form a tight epithelium without intercellular spaces. During vitellogenesis, electron-dense granules of 2 distinct sizes are present in the cells; the smaller ones are mostly located in the apical region of the cells. Immunogold labelling reveals that they contain vitellogenin. Their contents are exocytosed into the narrow perivitelline space between the follicular epithelium and the oocyte, from where the oocyte takes up vitellogenin by endocytosis. In vitellogenic follicles, tiny pore-like canals appear where 3 follicle cells contact one another. The broad intercellular spaces present at this stage between the basal parts of the follicle cells are connected by these canals with the perivitelline space between the follicular epithelium and the oocyte. Accumulation of vitellogenin is found only in the perivitelline space, i.e. between oocyte and the canals of the follicular epithelium, but not in the intercellular spaces between these canals and the basal lamina of the follicular epithelium.