Actin polymerization is not required for the fast block to polyspermy in the African clawed frog, Xenopus laevis .

Fertilization of an egg by multiple sperm presents one of the earliest and most prevalent obstacles to successful reproduction. Eggs employ multiple mechanisms to prevent sperm entry into the nascent zygote. The fast block to polyspermy uses a depolarization to inhibit sperm entry. For some external fertilizers, fertilization and the fast block require actin polymerization. Here we explored whether the fast block to polyspermy in the external fertilizer, , requires actin polymerization. Inseminating in the presence of inhibitor cytochalasin B, here we demonstrate that actin polymerization is not required for the fast block to polyspermy in .