Osteopontin localization in the Holstein bull reproductive tract

Previously we reported that the 55-kDa fertility-associated protein in Holstein bull seminal plasma (SP) is osteopontin (OPN). The objective of the present study was to localize OPN in tissues and fluids in the Holstein bull reproductive tract to determine its origin. Antisera generated against human recombinant OPN, as well as antiserum prepared against purified bovine seminal plasma OPN, reacted with protein in SP, accessory sex gland fluid, seminal vesicle fluid, ampullary fluid, and urine using one- and two-dimensional SDS-PAGE Western blot analysis. However, these antisera failed to detect OPN in cauda epididymal fluid or solubilized sperm membranes. Immunofluorescence histochemistry localized OPN in the lumen and epithelial cells of the seminal vesicle and ampulla, but not in tissues of testis, epididymis, prostate, and bulbourethral gland. OPN was not detected immunohistochemically in epididymal, ampullary, or ejaculated sperm treated with or without Triton X-100. We concluded that the primary sources of OPN in bull SP are the seminal vesicles and ampulla.