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

Abstract

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, Xenopus laevis, 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 X. laevis.

Figure 1

Representative whole-cell recordings made during fertilization in control conditions (A) or 10 µg/ml cytochalasin B (B). Grey dashed lines denote 0 mV. Tukey box plot distributions of the resting (n = 10) and fertilization (n = 4) potentials (C). (D) Average percentage (± s.e.m.) of embryos inseminated under control conditions (red) or with 10 µg/ml cytochalasin B (blue), that developed normally to the 4-cell (NF 3) stage, with incomplete cytokinesis, or with abnormal cleavage furrows (n = 14), colors correspond to images shown in E. (E) Representative images of a NF 3 embryo, two cytochalasin B treated embryos with incomplete cytokinesis and a polyspermic embryo with abnormal cleavage furrows. *** denotes P < 0.001 and n.s denotes a P > 0.05 as determined by Student’s t-tests with the Bonferroni correction.