Thirty years of calcium signals at fertilization

It was discovered about 30 years ago that a dramatic increase in intracellular calcium ion concentration ([Ca2+]i) occurs at fertilization and that this increase acts as the pivotal signal for egg activation. Later, the Ca2+ signal at fertilization turned out to be ubiquitous among animal species. Extensive advance has been brought during these 30 years in research on spatiotemporal aspects and signaling mechanisms of the [Ca2+]i increase, sperm factors that induce the Ca2+ response, and cell cycle resumption caused by the [Ca2+]i rise. I provide a historical account of these advances in mammals, sea urchins, and a few other models.