Oviductal protein produces fluorescence staining of the perivitelline space in mouse oocytes

Mouse oocytes were previously observed to undergo structural changes involving the perivitelline space (PVS) within the oviduct following ovulation, as visualized by staining with fluorochrome-protein conjugates. In the present study, this phenomenon was investigated in detail to determine the role of the oviduct and oocyte. Mouse ovarian oocytes matured in vitro were further incubated in medium or within explanted oviducts in vitro for varying periods of time and then stained with fluorescein isothiocyanate (FITC)-casein. Twenty percent of oocytes incubated within explanted oviducts for 3 hr showed distinct fluorescence staining of the PVS, whereas after 20 hr incubation, most (89%) oocytes were similarly stained. In contrast, no ovarian oocytes was stained when incubated in medium alone. Puromycin treatment during incubation of oocytes within explanted oviducts produced a dose-dependent decrease in the percentage of oocyte exhibiting PVS staining after FITC-casein exposure. FITC-casein staining of the PVS also occurred in all oocytes following incubation of in vitro-matured oocytes with oviductal tissue extract. In contrast, no oocytes incubated with serum exhibited fluorescence staining. Additionally, the PVS of oocytes failed to stain after incubation with either 0.001% of trypsin- or heat-treated oviductal homogenate. When zona pellucida (ZP) ghosts, devoid of ooplasm, were incubated within explanted oviducts, their PVS was stained brightly following FITC-casein treatment. From these results, it is concluded that proteinaceous material(s) secreted by the mouse oviduct is responsible for the fluorescence staining of the PVS of mouse oocytes and of ghost ZP. The ooplasm does not appear to play any role in altering the properties of the PVS staining.