Starting a new life: Sperm PLC-zeta mobilizes the Ca2+signal that induces egg activation and embryo development

We have discovered that a single sperm protein, phospholipase C-zeta (PLC?), can stimulate intracellular Ca2+ 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 Ca2+ concentration. The fertilized egg responds to the intracellular Ca2+ rise by completing meiosis. In mammalian eggs, the Ca2+ signal is delivered as a train of long-lasting cytoplasmic Ca2+ oscillations that begin soon after gamete fusion and persist beyond the completion of meiosis. Sperm PLC? effects Ca2+ release from egg intracellular stores by hydrolyzing the membrane lipid PIP2 and consequent stimulation of the inositol 1,4,5-trisphosphate (InsP3) receptor Ca2+-signalling pathway, leading to egg activation and early embryogenesis. Recent advances have refined our understanding of how PLC? induces Ca2+ oscillations in the egg and also suggest its potential dysfunction as a cause of male infertility.