Remodeling of the Actin Cytoskeleton During Mammalian Sperm Capacitation and Acrosome Reaction1

Abstract

The sperm acrosome reaction and penetration of the egg follow zona pellucida binding only if the sperm has previously undergone the poorly understood maturation process known as capacitation. We demonstrate here that in vitro capacitation of bull, ram, mouse, and human sperm was accompanied by a time-dependent increase in actin polymerization. Induction of the acrosome reaction in capacitated cells initiated fast F-actin breakdown. Incubation of sperm in media lacking BSA or methyl-beta-cyclodextrin, Ca(2+), or NaHCO(3), components that are all required for capacitation, prevented actin polymerization as well as capacitation, as assessed by the ability of the cells to undergo the acrosome reaction. Inhibition of F-actin formation by cytochalasin D blocked sperm capacitation and reduced the in vitro fertilization rate of metaphase II-arrested mouse eggs. It has been suggested that protein tyrosine phosphorylation may represent an important regulatory pathway that is associated with sperm capacitation. We show here that factors known to stimulate sperm protein tyrosine phosphorylation (i.e., NaHCO(3), cAMP, epidermal growth factor, H(2)O(2), and sodium vanadate) were able to enhance actin polymerization, whereas inhibition of tyrosine kinases prevented F-actin formation. These data suggest that actin polymerization may represent an important regulatory pathway in with sperm capacitation, whereas F-actin breakdown occurs before the acrosome reaction.

Role and Regulation of Sperm Gelsolin Prior to Fertilization

“…We have previously shown that actin polymerization occurs during sperm capacitation and that F-actin breakdown must take place to achieve the AR (3). In this study, we describe the role of the actin-severing protein, gelsolin, its regulation both during capacitation and during the AR, and how this regulation affects F-actin formation and breakdown.…”

“…Capacitation-In our previous studies, we showed that actin polymerization occurs during sperm capacitation (3,28). Gelsolin, an actin-severing protein, is expected to be localized with the F-actin fraction in the cell when activated.…”

“…1,2). Another important process that occurs during sperm capacitation is actin polymerization; however, at the end of the capacitation, the polymers must disperse to achieve the AR (3). It has been suggested that an increase in F-actin creates a network between the plasma and the outer acrosomal membranes, and the dispersion of F-actin between the two membranes is needed to enable the AR (3)(4)(5)(6).…”

Decavanadate interactions with actin: Inhibition of G-actin polymerization and stabilization of decameric vanadate

“…It has been described that vanadate stabilizes F-actin filaments through the formation of F-actin-ADP.Vi complexes [24] and it induces actin polymerization by inhibiting specific tyrosine phosphatases [25]. It was recently reported some vanadate effects on actin polymerization including sperm capacitation, detachment of pathogenic microorganisms and chemotherapy of solid tumors [25][26][27].…”

“…It was recently reported some vanadate effects on actin polymerization including sperm capacitation, detachment of pathogenic microorganisms and chemotherapy of solid tumors [25][26][27]. In plant cells it has been described that vanadate (up to 4 mM) inhibits cell elongation due to the disruption of actin microfilaments [28].…”