An acrosome reaction in natantian sperm

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Abstract
Sperm of the natantian Sicyonia ingentis are highly polarized with a conical cap and single spike extending from a spherical main body. Previous studies have shown the acrosome consists of two periodic acid‐Schiff‐positive cap components and the spike. During sperm‐egg interaction the spike is lost and the cell dehisces to expose the components of the acrosome, which lie directly apposed to the egg surface. Treatment of sperm with ionophore A23187 initiates this reaction and facilitates sequencing of the reaction. The ionophore‐induced reaction begins with retraction of the spike and concomitant swelling of the cap. These events result in the opening of the cap and exposure of the internal acrosomal components which become the new anterior surface of the sperm.