Induction of the Acrosomal Reaction in Sperm from the White Sturgeon, Acipenser Transmontanus

Summary

Sperm from the white sturgeon, Acipenser transmontanus possess an acrosome while the eggs possess numerous micropyles. The sperm undergo an acrosome reaction that includes exocytosis and process formation. This acrosomal reaction can be induced in freshwater with ionophore A23187, high pH, high Ca⁺⁺, or egg water. In addition, this event is dependent on extracellular Ca⁺⁺ and Mg⁺⁺. Upon immersion of eggs in freshwater, a water-soluble jelly layer hydrates and forms a highly adhesive coating surrounding the eggs. Jelly release and hydration appears dependent on both a trypsin-like protease and Ca⁺⁺ and Mg⁺⁺ ions. Isolated egg jelly (110,000 dalton glycoprotein) does not possess acrosome reaction inducing activity. The acrosome reaction inducing activity in egg water resides in a water-soluble 66,000 dalton glycoprotein. Egg water appears species specific in its ability to elicit a response. Prior to freshwater exposure, the egg envelope possesses a water-insoluble glycoprotein with a molecular weight of 70,000 daltons. When isolated from polyacrylamide gels, the 70,000 dalton component induces acrosome reactions in a species specific manner. Following freshwater exposure, the egg envelope possesses the water-soluble 66,000 dalton glycoprotein in addition to the 70,000 dalton component. The 70,000–66,000 dalton conversion can be blocked by incubating eggs in freshwater containing inhibitors of trypsin-like proteases. Both the 66,000 dalton and 70,000 dalton glycoproteins originate and reside in layer three of the egg envelope.