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FUCOSYLATED GLYCOPROTEINS FROM OVIDUCTAL EPITHELIUM BIND PDC-109 AND MAY BE INVOLVED IN CREATING THE RESERVOIR OF SPERM IN THE BOVINE OVIDUCT.
Suarez, Susan1, Ignotz, George1, 1
ABSTRACT- As mammalian sperm enter the oviduct, they become trapped by binding to the mucosal surface. Their numbers build up to form a reservoir of a few thousand. Shortly before ovulation, release of sperm is initiated, such that a few reach the oocyte just after it enters the oviduct. In cattle, binding of sperm to oviductal epithelium is specifically blocked by fucose, particularly in the linkage found in the trisaccharide called Lea. Using affinity chromatography with Lea as the ligand, a protein was isolated from sperm and identified as PDC-109, a secretion of the seminal vesicles that associates with the surface of sperm. PDC-109 was found to block binding of sperm to explants of epithelium. The objective of this study was to identify oviductal ligands for sperm, using a lectin specific for fucose and also PDC-109 to probe blots of electrophoretically separated proteins extracted from membranes of bovine oviductal epithelium. Epithelium was obtained by gently squeezing it out of the isthmuses of oviducts. Membranes were obtained by homogenizing epithelium in buffer containing 2% Tween-20, then membrane proteins were solubilized in SDS sample buffer. Blots of 1D and 2D SDS-PAGE gels were probed with biotinylated lectin from Lotus tetragonolobus(LTL), which binds fucose. Approximately 20 glycoproteins of various masses in a pI range of 4-7 were labeled. Labeling by 2 
g/ml LTL was blocked by fucoidan at 200 g/ml, but not by up to 3 mg/ml fetuin. Purified PDC-109 was biotinylated and used at 0.5-10 g/ml. Approximately 15 proteins were labeled with biotinylated PDC-109 and labeling was reduced by fucoidan but not fetuin. Most of these proteins appeared to be identical to those labeled by LTL. These results indicate that bull sperm may be trapped in the reservoir by binding to several fucosylated glycoproteins. Supported by USDA grant 97-35203-4734 and NIH grant F06 TW02351.
KEY WORDS: sperm, oviduct, sperm-reservoir, bovine