LOCALIZATION OF FIBRONECTIN ON THE SURFACE OF HUMAN SPERMATOZOA AND RELATION TO THE SPERM-EGG INTERACTION

Objectives: The mechanism of human sperm-oolemma adhesion and penetrat ion as well as localization of fibronectin on the sperm head and its r elation to fertilization were investigated. Design: Sperm-oolemma inte raction was examined with an in vitro assay of the human sperm-zona-fr ee hamster egg interaction. Localization of fibronectin on the surface of human spermatozoa was observed by the back scattered electron imag ing mode of the scanning electron microscopy (SEM). Results: It was co nfirmed by observations under SEM that the anterior tip of the sperm h ead is the first to come into contact with the egg plasma membrane but that the equatorial segment of the sperm head is the first to be trap ped by microvilli of the plasma membrane and that the postacrosomal re gion is first incorporated into ooplasm. Localization of fibronectin o n the equatorial segment of the human sperm head was detected by SEM. Antifibronectin antibodies inhibited human sperm-oolemma adhesion sign ificantly. Conclusions: Important involvement of fibronectin in the ga mete interaction was made clear by the fact that fibronectin is locali zed in the region where a spermatozoon is fused first with the egg pla sma membrane during fertilization and that the sperm adhering to the e gg is inhibited by antifibronectin antibodies.