The cytosolic sperm factor that triggers Ca2+ oscillations and egg activation in mammals is a novel phospholipase C: PLCζ

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Abstract
When sperm activate eggs at fertilization the signal for activation involves increases in the intracellular free Ca2+concentration. In mammals the Ca2+changes at fertilization consist of intracellular Ca2+oscillations that are driven by the generation of inositol 1,4,5-trisphosphate (InsP3). It is not established how sperm trigger the increases in InsP3and Ca2+at fertilization. One theory suggests that sperm initiate signals to activate the egg by introducing a specific factor into the egg cytoplasm after membrane fusion. This theory has been mainly based upon the observation that injecting a cytosolic sperm protein factor into eggs can trigger the same pattern of Ca2+oscillations induced by the sperm. We have recently shown that this soluble sperm factor protein is a novel form of phospholipase C (PLC), and it is referred to as PLCζ(zeta). We describe the evidence that led to the identification of PLCζ and discuss the issues relating to its potential role in fertilization.