Ultrastructural Localization of M1 Fusion Protein on Equatorial Segment of Acrosome Intact and Free/Reacted Hamster Spermatozoa

This study was designed to investigate the precise localization of M1 antigen and its expression factor(s) on hamster sperm which subjected to physiological and non- physiological conditions for acrosome reaction by correlating light and electron microscope observation. Acrosome-intact and acrosome-free or reacted hamster sperm were prepared. In sperm preparation, the same samples of each preparation were subjected in parallel to indirect immunofluorescent staining (IIF) and indirect immunogold labeling (IIG). Acrosome-free or reacted sperm were prepared by mechanical (sonication), physiological (incubation in medium which can induced spontaneous acrosome reaction) and chemical (incubation in calcium ionophore) procedure, respectively. Acrosome-intact sperm remained untreated. Results showed the M1 antigen that involved in sperm-oocyte fusion is localized in the equatorial segment region of hamster sperm, and the expression is Ca2+ and acrosome reaction dependent.