Extracellular Ca2+ Is Required for Fertilization in the African Clawed Frog, Xenopus laevis.

Background: The necessity of extracellular Ca2+ for fertilization and early embryonic development in the African clawed frog, Xenopus laevis, is controversial. Ca2+ entry into X. laevis sperm is reportedly required for the acrosome reaction, yet fertilization and embryonic development have been documented to occur in high concentrations of the Ca2+ chelator BAPTA.