Sperm-associated seminal plasma proteins - A novel approach for the evaluation of sperm fertilizing ability of stallions?

Abstract

Mammalian cysteine-rich secretory proteins (CRISP) are characterized by 16 cysteine residues forming 8 disulfide bonds. In the horse male genital tract CRISP proteins have been identified in the testis (CRISP-2), in the epididymis (CRISP-1) and in the ampulla (CRISP-3). Using a monospecific avian antibody that recognizes all equine members of the equine CRISP family, CRISP proteins have been immunolocalized at the postacrosomal region of the sperm head and the tail midpiece being associated to the sperm surface during epididymal transit. CRISP's appear to be tightly bound to the sperm surface surviving the passage through the female genital tract, in vitro capacitation and acrosome reaction and extensive washing at high salt concentrations. The number of CRISP molecules tightly bound to the sperm surface could be determined by means of a competitive inhibition ELISA assay and have been shown to correlate (p ≤ 0.069, Pearson correlation)/ to correlate significantly (p < 0.01, Spearman rank correlation analysis) with the fertility of stallions. Protein concentration of more than 18000 molecules/ sperm cell correlates with good pregnancy and foaling rates. Together with conventional sperm parameters, e.g. progressive motility and sperm concentration, the biochemical marker (CRISP molecules/ sperm cell) allows a better prediction (R2 = 0.54, p< 0.02) of the stallion fertility rate in vivo and is alternative to other functional tests such as the expensive and time-consuming hemizona assay.