Departments of Anatomy3

The zona pellucida (ZP), a glycoprotein layer that encloses the mammalian oocyte, is formed during follicu-lar development in the ovary, persists at the time of fert#{220}ization within the oviduct, and then surrounds the embryo until implantation in the uterus. Although the structure and chemical properties of the ZP have been extensively studied, the precise site of origin of the ZP remains a matter of controversy. Moreover, the me-chanism of synthesis and secretion of the ZP constituents is not fully elucidated. We have recently developed monoclonal antibodies (MAt’s) against oviductal ZP of the golden hamster. We have used one of these MAbs (an immunoglobulin G) and the protein A-gold technique to study the localization of the corresponding antigenic sites, and we report here their distribution in the oviduct and within the cumulus oopborus complex of the superovulated banister. In the oviductal epithelium, immunolabeling was observed in non-ciliated secretory cells in structures involved in protein secretion. In the cumulus masses collected from the oviduct, the sites of im-munoreactivity were localized exclusively in the ZP encompassing the oocyte. Gold particles were evenly distributed throughout the entire thickness of the ZP. Treatment of the cumulus masses with hyaluronidase prior to preparation of isolated oocytes for immunocytochemistry did not affect this uniformity. The ZP of the preovulatory oocytes in ovarian follicles was not labeled. Our study provides immunocytochemical evidence for the secretion of an oviductal antigen that becomes intimately associated with the ZP of the oocytes during their passage through the oviduct