Fertilization and early embryology: The role of calcium in mammalian oocyte maturation and egg activation

The maturation of the immature oocyte and the fertilizationof a mature egg are two absolute prerequisites for mammalianembryo development. There is increasing evidence in mammalsthat both oocyte maturation and egg activation at fertilizationare controlled by changes in intracellular free Ca²⁺ levels.The role of Ca²⁺ changes at fertilization is clear in that theyare both required and sufficient for egg activation. However,it is not established how the sperm causes Ca²⁺ changes in eggsat fertilization, nor how different patterns of Ca²⁺ changeaffect embryo development. The role of Ca²⁺ in triggering oocytematuration is less clear, although preventing intracellularCa²⁺ changes can inhibit meiotic maturation at specific stages.Studies on how Ca²⁺ regulates meiosis and fertilization in mammalsmay provide new insights into the causes of failed fertilizationin human IVF procedures.