Oviduct ampullary epithelium contributes a glycoprotein to the zona pellucida, perivitelline space and blastomeres membrane of sheep embryos

Previous studies have identified a glycoprotein (sOP 92) that is secreted by sheep oviductal epithelium and subsequently becomes associated with developing embryos. The objective of this study was to more definitively demonstrate the localization of this protein in the oviductal epithelium of cycling ewes and in the embryos (developmental stage ranging between 1 and 8 cells) by using the light and electron microscopic immuno-gold techniques. In the oviduct, sOP 92 was present only in nonciliated cells of the ampulla but not in the isthmus. No major differences in signal intensity, in its organ or intracellular distribution were observed between the postovulatory and the luteal phase of the cycle. At the embryonic level, sOP 92 uniformly covered the surface of the zona pellucida and permeated its width. Moreover, the protein was present in the perivitelline space and on the blastomeres membrane but not in the cytoplasm or in the nucleus. These observations suggest that a marked regional difference in sheep oviduct secretions exists and confirm that there is a close association of these secretions with the developing embryos.