The transmission process of Sex Ratio Organisms (SROs) into oocyte during oogenesis in Drosophila melanogaster was studied by electron microscopy. SROs break through a tunica propria, a non-cellular membrane surrounding the egg chamber, and move toward oocytes passing through the intercellular space of the follicle cell layer at previtellogenic stages. After reaching at the surface of an oocyte, they are incorporated into the ooplasm by pinocytosis with progress of vitellogenesis. By the final stages of oogenesis, most SROs become infolded in intracellular vesicles and yolk granules followed by transfer to the interior of the oocyte.
The Genetics Society of Japan