Inhibition of bovine sperm-oocyte fusion by the carbohydrate GalNAc.
The TEC-2 epitope is a carbohydrate located on the plasma membrane (oolemma) of the oocyte and appears to be involved in bovine sperm-oolemma fusion. The carbohydrates N-acetylgalactosamine (GalNAc) and galactose are part of the TEC-2 epitope and this study investigated the involvement of these carbohydrates during bovine fertilization. Gametes were exposed to the carbohydrates GalNAc, galactose, and fructose, and the lectins DBA and Con A to determine whether there was an effect on fertilization. The DBA lectin recognizes the carbohydrate GalNAc, whereas Con A recognizes the carbohydrates glucose and mannose. Oocytes pretreated with the DBA lectin prior to fertilization showed a reduction in cleavage corresponding to an increase in lectin concentrations. There was a significant increase in sperm-oolemma binding although fusion was inhibited. Oocytes exposed to GalNAc prior to sperm insemination had no effect on fertilization, however, sperm pretreatment with the carbohydrate caused inhibition of fertilization, with a reduction in cleavage rates as the GalNAc concentration increased. There was also a significant decrease in sperm-oolemma fusion and a significant increase in sperm-oolemma binding. When gametes were exposed to GalNAc at the time of fertilization a similar response to that seen with sperm pretreatment was observed. The carbohydrates galactose and fructose and the lectin Con A did not affect fertilization. In conclusion, the carbohydrate GalNAc, which is associated with the TEC-2 epitope, has a specific role during bovine sperm-oolemma fusion. This study also suggests that there is a carbohydrate-binding molecule on the sperm that binds GalNAc.
Gougoulidis
T
T
Centre for Early Human Development, Institute of Reproduction and Development, Monash University, Clayton, Victoria, Australia.
Trounson
A
A
Dowsing
A
A
D000116:Acetylgalactosamine / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D002417:Cattle; D002843:Chromatin / Q000378:metabolism; D003208:Concanavalin A / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D000939:Epitopes / Q000494:pharmacology / Q000502:physiology*; D005260:Female; D005306:Fertilization / Q000187:drug effects / Q000502:physiology*; D005690:Galactose / Q000378:metabolism / Q000494:pharmacology; D037102:Lectins / Q000378:metabolism / Q000494:pharmacology; D008297:Male; D008562:Membrane Glycoproteins / Q000494:pharmacology / Q000502:physiology*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D013084:Sperm-Ovum Interactions / Q000187:drug effects / Q000502:physiology; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism
D002843:Chromatin; D000939:Epitopes; D037102:Lectins; D008562:Membrane Glycoproteins; D003208:Concanavalin A; D000116:Acetylgalactosamine; D005690:Galactose