Inhibition of bovine sperm-oocyte fusion by the carbohydrate GalNAc

dThe TEC-2 epitope is a carbohydrate located on the plasma membrane (oolemm a) of the oocyte and appears to be involved in bovine sperm-oolemma fusion. The carbohydrates N-acetyl-galactosamine (GalNAc) and galactose are part o f the TEC-2 epitope and this study investigated the involvement of these ca rbohydrates during bovine fertilization. Gametes were exposed to the carboh ydrates GalNAc, galactose, and fructose, and the lectins DBA and Con A to d etermine whether there was an effect on fertilization. The DBA lectin recog nizes the carbohydrate GalNAc, whereas Con A recognizes the carbohydrates g lucose and mannose. Oocytes pretreated with the DBA lectin prior to fertili zation showed a reduction in cleavage corresponding to an increase in lecti n concentrations. There was a significant increase in sperm-oolemma binding although fusion was inhibited. Oocytes exposed to GalNAc prior to sperm in semination had no effect on fertilization, however, sperm pretreatment with the carbohydrate caused inhibition of fertilization, with a reduction in c leavage rates as the GalNAc concentration increased. There was also a signi ficant decrease in sperm-oolemma fusion and a significant increase in sperm -oolemma binding. When gametes were exposed to GalNAc at the time of fertil ization a similar response to that seen with sperm pretreatment was observe d. The carbohydrates galactose and fructose and the lectin Con A did not af fect fertilization. In conclusion, the carbohydrate GalNAc, which is associ ated with the TEC-2 epitope, has a specific role during bovine sperm-oolemm a fusion. This study also suggests that there is a carbohydrate-binding mol ecule on the sperm that binds GalNAc. (C) 1999 Wiley-Liss, Inc.