Porcine oviduct sperm binding glycoprotein and its deleterious effect on sperm: a mechanism for negative selection of sperm?

In their journey through the oviduct some subpopulations of sperm are preserved in a reservoir, while others are negatively selected. Sperm binding glycoprotein (SBG) is a pig oviductal epithelial cell glycoprotein that produces, under capacitating conditions, acrosome alteration, p97 tyrosine-phosphorylation and reduction of the motility of sperm. In this paper, we show that SBG is accessible at the extracellular surface of the oviductal epithelial cells, supporting a sperm interaction biological role in situ. We analyze the possible dependence of the tyrosine-phosphorylation of p97 on the PKA mechanism, finding that apparently it is not PKA dependent. Also, after SBG treatment the phosphorylated proteins locate mainly at the detached periacrosomal region and at the tail of sperm; the latter may be related to SBG's motility reduction effect. The study of the time course effect of SBG on sperm as detected by chlortetracycline (CTC) staining and of its binding to sperm by immunodetection in conjunction with CTC, shows results in agreement with the hypothesis that this glycoprotein is involved in the alteration of acrosomes in a specific sperm subpopulation. The results suggest that SBG may be part of a mechanism for negative selection of sperm.

Effect of heparin on in vitro capacitation of boar sperm

Chlortetracycline (CTC) fluorescent pattern, the ability to undergo acrosome reaction (AR) upon exposure to 10 µM calcium ionophore A23187 and vitality estimation were used to investigate the effect of the sulfated glycosaminoglycan heparin on the in vitro capacitation of porcine spermatozoa. Sperm incubation in capacitating medium (CM) supplemented with 10 mM heparin for up to 120 min, showed an increase in the number of capacitated sperm (B pattern) and acrosome reacted sperm (AR pattern), without affecting their viability. In this condition, spermatozoa were incubated in CM depleted of albumin, calcium, bicarbonate or combinations, in the presence of heparin. In either calcium or bicarbonate-free media, capacitation was only basal and did not show variations in the presence of heparin. In absence of albumin the presence of calcium and bicarbonate stimulated capacitation, which was further increased by the addition of heparin. These results suggest that heparin enhances in vitro capacitation of porcine sperm only under capacitating conditions. Additionally, when sperm were incubated with 100 µg/ml biotinylated heparin in the presence or absence of unlabeled heparin, we observed that heparin binding sites were located mostly on the acrosomal region of boar sperm in an specific and saturable manner. The in vitro effect of heparin described in this work indicates that sulfated glycosaminoglycans, which are normally present in the female reproductive tract, might play an important role in the fertilization process in porcines.