Inhibiting actin polymerization does not prevent the fast block to polyspermy in the African clawed frog,Xenopus laevis

Fertilization of an egg by more than one sperm presents one of the earliest and most prevalent obstacles to successful reproduction. As such, eggs employ multiple mechanisms to prevent sperm entry into the nascent zygote. The fast block to polyspermy is a depolarization of the egg membrane initiated by sperm entry and is employed by diverse external fertilizers including frogs and sea urchins. For some external fertilizers, sperm entry is associated with actin polymerization during the initiation of the fast block. We therefore sought to determine whether the fast block to polyspermy in the African clawed frog, Xenopus laevis , requires actin polymerization. Although actin polymerization is required for sperm entry into eggs from diverse external fertilizers, including sea urchins and zebrafish, here we demonstrate that actin polymerization is not required for the fast block to polyspermy in X. laevis .