An acrosome reaction in sperm from the white sturgeon, Acipenser transmontanus

The A. transmontanus sperm possesses an elongate main body, a conspicuous acrosome, a midpiece, and a flagellum. Three membrane‐lined nuclear channels that are helically arranged extend from the acrosomal region to the midpiece. Sperm heads contain material that comigrates on sodium dodecyl sulfate (SDS)‐gels with actin. An acrosome reaction can be induced in freshwater with ionophore A23187, high pH, high Ca++, or egg water. This acrosomal reaction is a Ca+‐Mg+‐dependent event. The resulting acrosomal process (10 μm) originates from the subacrosome region and the nuclear channels. Non‐filamentous actin apparently polymerizes and forms the process.