Sperm Surface Fibronectin Expression Following Capacitation

ABSTRACT: The Arg‐Gly‐Asp (RGD) amino acid sequence plays a role in many cell‐to‐cell and cell‐to‐matrix adhesion systems, as a recognition sequence for cell membrane receptors termed integrins. Receptors of the VLA subfamily of integrins recognize fibronectin, laminin, and collagen. Given the authors' findings that fibronectin‐derived, RGD‐containing peptides competitively inhibit sperm‐oolemmal adhesion and penetration in both heterologous (human‐hamster) and homologous (hamster‐hamster) gamete interactions, the expression of fibronectin on the surface of fresh, capacitated, and acrosome‐reacted human spermatozoa was studied. The majority of fresh spermatozoa did not display fibronectin on their plasma membrane (0 to 16% positive), as demonstrated by the lack of binding of both monoclonal and polyclonal anti‐fibronectin antibodies. In contrast, a significantly greater proportion of spermatozoa (varying between 18% to 100% for different donors) incubated overnight under capacitating conditions reacted with anti‐fibronectin antibodies. The induction of an acrosome reaction with progesterone did not alter the proportion of sperm displaying fibronectin or its distribution on the sperm surface. A physiologic role of fibronectin in sperm‐oolemmal interaction was suggested by the effects of anti‐fibronectin antibodies on sperm oolemmal adhesion and penetration of hamster eggs by human spermatozoa, which were both significantly reduced (P < 0.001). 1992 American Society of Andrology