The earliest detected signalling event during mammalian oocyte activation by spermatozoa is the release of Ca2+ from intracellular stores (Stricker, 1999; Runft et al., 2002). In fertilized mammalian oocytes, this Ca2+ release occurs shortly after sperm–oocyte membrane fusion and is manifested as a striking series of cytosolic Ca2+ oscillations (Miyazaki et al., 1993; Swann, 1996; Stricker, 1999). The oscillations in cytosolic free Ca2+ are regular, continue for several hours, and cease around the time of formation of the pronuclei (Carroll, 2001). Ca2+ oscillations are essential for stimulating embryo development, as their inhibition with N, N’-(1, 2-ethanediylbis (oxy-2, 1-phenylene)) bis (N-(carboxymethyl))-glycine (BAPTA) blocks oocyte activation (Kline and Kline, 1992) and the premature termination of Ca2+ oscillations prevents the formation of pronuclei (Lawrence et al., 1998).