PLCζ:: a sperm-specific trigger of Ca2+ oscillations in eggs and embryo development

Upon fertilisation by sperm, mammalian eggs are activated by a series of intracellular Ca(2+) oscillations that are essential for embryo development. The mechanism by which sperm induces this complex signalling phenomenon is unknown. One proposal is that the sperm introduces an exclusive cytosolic factor into the egg that elicits serial Ca(2+) release. The 'sperm factor' hypothesis has not been ratified because a sperm-specific protein that generates repetitive Ca(2+) transients and egg activation has not been found. We identify a novel, sperm-specific phospholipase C, PLCzeta, that triggers Ca(2+) oscillations in mouse eggs indistinguishable from those at fertilisation. PLCzeta removal from sperm extracts abolishes Ca(2+) release in eggs. Moreover, the PLCzeta content of a single sperm was sufficient to produce Ca(2+) oscillations as well as normal embryo development to blastocyst. Our results are consistent with sperm PLCzeta as the molecular trigger for development of a fertilised egg into an embryo.