Immunoelectronmicroscopic imaging of spermadhesin AWN epitopes on boar spermatozoa bound in vivo to the zona pellucida.

Spermadhesin AWN is a major protein of boar seminal plasma and a sperm surface-associated lectin. AWN binds to beta-galactosides and to porcine zona pellucida glycoproteins, suggesting a role for this protein in primary gamete interaction. However, because capacitation induces remodelling of the sperm surface and AWN is peripherally bound to the plasma membrane, the present study sought to investigate whether AWN is present or absent in the subpopulation of spermatozoa that reaches the ovulated oocyte at the period of fertilization in vivo. Therefore, tubal tissues and oocytes from sows mated with a fertile boar were collected 6-8 h after ovulation. Tissues and oocyte sperm complexes were fixed, immunolabelled with anti-AWN monoclonal antibodies, and examined by means of light and scanning electron microscopy. The results show that spermadhesin AWN is present in spermatozoa seen along the genital tract of the natural mated sow as well as on plasmalemmal remnants of spermatozoa bound to the zona pellucida in vivo.