Role of PLC-zeta in generating Ca2+ oscillations and triggering egg activation at fertilization. (360G-Wellcome-080701_Z_06_Z)

At fertilization, a sperm activates the egg by causing a large transient increase in intracellular Ca2+ concentration. Mammalian eggs characteristically exhibit a series of cytosolic Ca2+ oscillations lasting several hours, mediated by elevations in inositol 1,4,5-trisphosphate (InsP3) concentration. However, the molecular mechanism explaining how a sperm induces increased InsP3 in the egg remains unclear. The sperm factor theory proposes that the sperm releases a specific factor into the egg cytoplasm at fertilization, which triggers Ca2+ release and egg activation. We have discovered a novel, sperm-specific phospholipase C isoform, PLC-zeta, (PLCz), and demonstrated that PLCz causes Ca2+ oscillations and activation of mouse eggs indistinguishable from fertilization. These observations are consistent with PLCz as the sperm factor. We aim to establish whether PLCz constitutes the exclusive physiological signal for development at fertilization by studying the phenotype of a PLCz knockout mouse. We also wish to define the subcellular targetting of PLCz within sperm and zygotes, and elucidate how PLCz causes repetitive Ca2+ changes in eggs and other cells. To understand how PLCz enzyme activity is regulated, we will examine the structural and functional contribution of distinct domains to the structure and interactions of this novel signalling protein.