Fertilization in amphibians: The cellular and molecular events from sperm approach to egg activation

Abstract

The mechanism of fertilization is important for understanding the role of sexual reproduction in animals. Amphibians are one of the most suitable systems to investigate the cellular and molecular mechanisms of fertilization. Inseminated sperm approach the egg by initiation of motility and chemotactic guidance in response to substances secreted from oviducts on the egg surface. Sperm undergoing the acrosome reaction penetrate the vitelline envelope, and then fuse with the egg plasma membrane. The fertilizing sperm induces an increase in the intracellular Ca2+ concentration, causing egg activation, and initiation of embryonic development. The activated egg elicits several blocks to polyspermy, ensuring development from only one sperm. Recent advances in cellular and molecular mechanisms in amphibian fertilization are summarized and their important roles for establishment of amphibian fertilization are discussed.