Actin filaments, localized to the region of the developing acrosome during early stages, are lost during later stages of guinea pig spermiogenesis.

The presence and localization of actin was investigated in guinea pig spermatogenic cells and cauda epididymal sperm (CauE). Staining with rhodamine-phalloidin demonstrated the presence of actin filaments in the region of the developing acrosome in guinea pig spermatids. The actin filaments were visualized predominantly in the region of the inner acrosomal membrane in both round and elongating spermatids. As development progressed, the intensity of the staining diminished. No rhodamine-phalloidin staining was found in testicular sperm lacking a residual body or in CauE sperm. Analysis of actin levels by immunoblotting with an anti-actin monoclonal antibody showed that the disappearance of actin filaments is accompanied by a decrease in the level of actin per cell. By using immunoblotting techniques, actin was readily detected in preparations of purified spermatogenic cells, but not in preparations of purified CauE sperm. Actin was also not detected in cauda sperm by indirect immunofluorescence (IIF) with anti-actin antibodies or examination of whole cell extracts by two-dimensional gel electrophoresis.