Abstract
ABSTRACTSeveral focal adhesion proteins are known to cooperate with integrins to link the extracellular matrix to the actin cytoskeleton; as a result, many intracellular signaling pathways are activated and several focal adhesion complexes are formed. However, how these proteins function in mammalian spermatozoa remains unknown. We confirm the presence of focal adhesion proteins in guinea pig spermatozoa, and we explore their role during capacitation and the acrosome reaction, and their relationship with the actin cytoskeleton. Our results suggest the presence of a focal adhesion complex formed by β1-integrin, focal adhesion kinase (FAK), paxillin, vinculin, talin, and α-actinin in the acrosomal region. Inhibition of FAK during capacitation affected the protein tyrosine phosphorylation associated with capacitation that occurs within the first few minutes of capacitation, which caused the acrosome reaction to become increasingly Ca2+ dependent and inhibited the polymerization of actin. The integration of vinculin and talin into the complex, and the activation of FAK and paxillin during capacitation, suggests that the complex assembles at this time. We identify that vinculin and α-actinin increase their interaction with F-actin while it remodels during capacitation, and that during capacitation focal adhesion complexes are structured. FAK contributes to acrosome integrity, likely by regulating the polymerization and the remodeling of the actin cytoskeleton.
Highlights
Specific bands corresponding with relative molecular weight (Mr) of ∼130, 70, 125, 120, 100, and 230 kDa were detected for β1-integrin, paxillin, focal adhesion kinase (FAK), vinculin, α-actinin, and talin, respectively (Fig. 1A)
These results confirm that the proteins we found in guinea pig spermatozoa are the focal adhesion proteins β1-integrin, paxillin, FAK, vinculin, α-actinin, and talin, and that they are expressed in the spermatozoa of other species
We provide evidence (1) for the formation of focal adhesion complexes during capacitation in guinea pig spermatozoa, (2) that FAK could be related with the normal course of Tyr phosphorylation associated to capacitation, (3) for a relationship between FAK and the polymerization and remodeling of the actin cytoskeleton during capacitation, and (4) that maintaining acrosome integrity during capacitation requires active FAK and the association of focal adhesion complexes with the actin cytoskeleton
Summary
Successful fertilization of the oocyte requires that spermatozoa undergo physiological and biochemical changes that are known as capacitation: increased metabolism, membrane fluidity, intracellular Ca2+ concentration, membrane hyperpolarization, intracellular. Inhibition of actin polymerization is known to diminish the ability of spermatozoa to fertilize the oocyte (Brener et al, 2003; Rogers et al, 1989; Sanchez-Gutierrez et al, 2002), a detailed understanding of how actin polymerization is regulated during capacitation remains unknown
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