Starting a new life: Sperm PLC‐zeta mobilizes the Ca 2+ signal that induces egg activation and embryo development

We have discovered that a single sperm protein, phospholipase C‐zeta (PLCζ), can stimulate intracellular Ca 2+ signalling in the unfertilized oocyte (‘egg’) culminating in the initiation of embryonic development. Upon fertilization by a spermatozoon, the earliest observed signalling event in the dormant egg is a large, transient increase in free Ca 2+ concentration. The fertilized egg responds to the intracellular Ca 2+ rise by completing meiosis. In mammalian eggs, the Ca 2+ signal is delivered as a train of long‐lasting cytoplasmic Ca 2+ oscillations that begin soon after gamete fusion and persist beyond the completion of meiosis. Sperm PLCζ effects Ca 2+ release from egg intracellular stores by hydrolyzing the membrane lipid PIP 2 and consequent stimulation of the inositol 1,4,5‐trisphosphate (InsP 3 ) receptor Ca 2+ ‐signalling pathway, leading to egg activation and early embryogenesis. Recent advances have refined our understanding of how PLCζ induces Ca 2+ oscillations in the egg and also suggest its potential dysfunction as a cause of male infertility.