Immunocytochemical analysis of the association of bovine oviduct‐specific glycoproteins with early embryos

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Abstract
The bovine oviductal epithelium synthesizes and secretes a class of oviduct‐specific glycoproteins that is present in the luminal fluid when fertilization and early embryonic development occur. The objective of this study was to determine if these characterized glycoproteins become associated with oviductal embryos. Ovarian ova and oviductal embryos were recovered from super‐ovulated cows at 72 h after onset of estrus. Eggs were fixed in 3% paraformaldehyde‐1% gluteraldehyde and subsequently embedded in Lowicryl K4M. Sections (1 μm) were processed for peroxidase‐antiperoxidase immunocytochemistry. Immunolabeling was not detected in any region of ovarian ova. Oviductal embryos, regardless of cleavage stage, exhibited immunoperoxidase staining localized within their zona pellucidae. Sections (100 nm) obtained from a 4‐ and an 8‐cell embryo were also subjected to colloidal gold immunoelectron microscopy to determine conclusively the subcellular distribution of the oviduct‐specific glycoproteins. Gold particles were distributed uniformly throughout the width of the zona pellucida. Also, immunoreactivity was observed associated with flocculent material in the perivitelline space and with the vitelline membrane. These results indicate that the bovine oviduct‐specific secretory glycoproteins become associated with oviductal embryos. This association may be biologically important to the developing embryo.