Binding patterns of bovine seminal plasma proteins A1/A2, 30 kDa and osteopontin on ejaculated sperm before and after incubation with isthmic and ampullary oviductal fluid.

Previous studies from our laboratory have reported empirical associations between bovine seminal plasma protein(s) (BSP) A1/A2 and 30 kDa and osteopontin (OPN) in accessory sex gland fluid and bull fertility. These BSP and OPN are believed to bind to sperm at ejaculation and to remain bound until sperm reach the oviduct. The objective of the present study was to evaluate the topographical distribution of BSP A1/A2, 30 kDa and OPN binding on: (1) bovine ejaculated sperm; (2) ejaculated sperm incubated with isthmic oviductal fluid (ODF); (3) ejaculated sperm+isthmic ODF incubated in ampullary ODF. From each of these media, aliquots of sperm for BSP and OPN were processed for immunocytochemistry and analysis by laser scanning confocal microscopy. Isthmic and ampullary ODF was collected from indwelling catheters and used as pools from three cows in the non-luteal phase of the estrous cycle. Anti-BSP A1/A2 was detected bound to the midpiece, post-equatorial and equatorial segments and acrosome of sperm after ejaculation and after incubation with isthmic and ampullary ODF. The BSP A1/A2 fluorescence was more concentrated on the midpiece and increased as acrosome-intact sperm came in contact with ODF. As compared with acrosome-intact sperm, non-intact acrosome intact sperm had 39 and 68% reductions of acrosome fluorescence and 36% and 90% increases of post-equatorial fluorescence after contact with isthmic and ampullary ODF (P<0.05). Anti-BSP 30 kDa was more intense on the midpiece than on post-equatorial, equatorial and acrosome regions of sperm after ejaculation and contact with ODF. However, equatorial fluorescence was 141% and 89% more intense and acrosome stainning was 80% and 76% less (P<0.05) in non-intact acrosome sperm than in acrosome intact cells, during all ODF incubations. Anti-OPN was identified on the acrosome of ejaculated sperm, but with less fluorescence (P<0.05) on the post-equatorial segment and midpiece. Incubation of sperm with isthmic ODF increased fluorescence on post-equatorial segment (P<0.05). There were 72% and 78% reductions (P<0.05) of acrosome fluorescence and intensification (P<0.05) in equatorial fluorescence in non-intact acrosome sperm as compared with acrosome intact cells incubated with isthmic and ampullary ODF. In summary, interactions of BSP A1/A2 and 30 kDa and osteopontin with the sperm membrane undergo modifications dictated by the oviductal fluid. The BSP are thought to modulate cholesterol and phospholipid movement from the sperm membrane and help sperm binding to the oviductal epithelium. Furthermore, our model suggests that OPN participates in sperm-oocyte interaction, affecting fertilization and early embryonic development.