Potential role of the acrosome of sturgeon spermatozoa in the fertilization process

Sturgeon gametes are unique in that their spermatozoa possess acrosome containing acrosomal enzymes whereas their eggs are perforated by numerous micropyles. Thus the function of acrosome, which undergoes acrosomal reaction and filament formation, is unclear. The acrosomal reaction of sterlet Acipenser ruthenus spermatozoa was induced by sperm exposure to the solution containing Ca2+ and high pH. The rate of affected spermatozoa was evaluated using Soybean Trypsin Inhibitor-Alexa conjugate fluorescent staining. Fertilization and hatching test using sperm of this way disrupted acrosome and non-treated sperm as a control proofed necessity of acrosome integrity for fertilization. Increasing percentage of spermatozoa with disrupted acrosome highly decreased percentage of hatching, in spite of electron microscopy verification that the spermatozoa bearing such disrupted acrosomes were able to reach the micropyle. In addition the significant positive correlation between the ability of spermatozoa to induce acrosomal reaction by activation solution and sperm fertilizing ability suggested that spermatozoa, which are able to activate the acrosomal reaction, are more successful in fertilization.