Decondensation of human spermatozoal chromatin by nuclear actin polymerization

A critical relationship exists between nuclear actin polymerization and decondensation of sperm chromatin. Characteristic decondensation phenomena were brought about by the protein S-1 of heavy meromyosin of rabbit skeletal muscle in sperm that had undergone the acrosome reaction. Sperm treated with only calcium or only ionophore were not affected by the S-1 trigger, and the nucleus remained in the condensed state. Since S-1 specifically binds to actin, it was possible to demonstrate this phenomenon at the ultrastructural level. Maybe there are switches that operate at different steps for events leading to syngamy and fertilization. No switch can be operative until the preceding event has prepared the sperm for entering the next phase. The operations are performed in a perfect sequential order. This investigation leads to the conclusion that decondensation of sperm chromatin is brought about by nuclear actin polymerization.