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Origin of a sperm motility inhibitor from boar seminal plasma
1Department of Urology, St. Marianna University School of Medicine, Montreal, Canada.
Abstract:
We have investigated the origin of the sperm motility inhibitor (SPMI) from boar seminal plasma. SPMI was measured by its capacity to inhibit the motility of demembranated spermatozoa and by an enzyme-linked immunosorbent assay (ELISA). Among the various reproductive and now reproductive tissues and fluids tested, only the seminal vesicle fluid and seminal plasma contained significant amounts of SPMI biological activity and SPMI antigen. Like other seminal vesicle fluid proteins, SPMI is diluted 6- to 8-fold upon ejaculation. By immunohistochemical detection at the light microscope with antibodies obtained from rabbits immunized with SPMI purified from boar seminal plasma, SPMI was found in the cytosol and/or on the plasma membrane bordering the lumen of the seminal vesicles. At the electron microscope level, SPMI appeared to be present only on the surface of the secretory cells. The data indicate that SPMI originates from a single tissue, the seminal vesicle, and suggest that only the mature form present on the luminal surface of the gland can react with the antibody generated from rabbits immunized with the secreted form of SPMI.
Insights
The sperm motility inhibitor (SPMI) originates from boar seminal vesicles. This protein is diluted during ejaculation and found on the surface of seminal vesicle secretory cells.
Area of Science:
- Reproductive biology
- Biochemistry
Background:
- Sperm motility is crucial for fertilization.
- The seminal plasma contains factors that can inhibit sperm motility.
- The origin of the sperm motility inhibitor (SPMI) was previously unknown.
Purpose of the Study:
- To determine the tissue of origin for SPMI in boars.
- To investigate the localization of SPMI within the reproductive tract.
Main Methods:
- Measurement of SPMI biological activity via inhibition of demembranated sperm motility.
- Quantification of SPMI antigen using enzyme-linked immunosorbent assay (ELISA).
- Immunohistochemical detection using antibodies against purified SPMI at light and electron microscopy levels.
Main Results:
- SPMI biological activity and antigen were predominantly found in seminal vesicle fluid and seminal plasma.
- SPMI is diluted 6- to 8-fold upon ejaculation.
- Immunohistochemistry localized SPMI to the cytosol and/or plasma membrane of seminal vesicle secretory cells, specifically on the luminal surface.
Conclusions:
- The seminal vesicle is the sole origin of SPMI.
- The mature form of SPMI on the luminal surface of seminal vesicles is likely responsible for the antibody response generated from secreted SPMI.