Inhibition of mouse in vitro fertilization by an antibody against a unique 18-amino acid domain in the polysulfate-binding domain of proacrosin/acrosin

Abstract

Objective: To determine the contribution of the polysulfate-binding domain (PSBD) of acrosin during sperm penetration. Design: To inhibit the in vitro fertilization of mouse zona-intact oocytes by using a polyclonal antibody raised against an 18–amino acid peptide of proacrosin (anti-PSBD). Setting: Unit of Reproduction and Development, Faculty of Biological Sciences, Pontifical Catholic University of Chile. Patient(s): None. Intervention(s): A polyclonal antibody against the 43IFMYHNNRRYHTCGGILL 60 peptide was raised in New Zealand female rabbits. The specificity of the antibody was evaluated by an ELISA. Zona-intact mouse oocytes were coincubated with capacitated spermatozoa for 3 hours in the presence of 0.63 mg/mL of the antibody or preimmune serum. As a control, we used zona-free mouse oocytes under the same experimental conditions. Main Outcome Measure(s): We evaluated the fertilization rate of zona-intact and zona-free mouse oocytes by phase-contrast microscopy. An oocyte was considered fertilized when at least one decondensed sperm head was found within the egg cytoplasm. We evaluated 50–60 mouse oocytes in each group in three independent experiments. Result(s): The anti-PSBD antibody inhibited the fertilization of zona-intact, but not zona-free, mouse oocytes, by capacitated spermatozoa. In addition, the binding of the anti-PSBD to proacrosin/acrosin in a solid-phase assay was inhibited in the presence of polysulfates (fucoidan). Conclusion(s): The anti-PSBD directed against the PSBD of proacrosin/acrosin inhibited the penetration of capacitated mouse spermatozoa through the zona pellucida. This antibody may be a useful tool to define the roles of the different domains of proacrosin/acrosin during gamete interaction.