Calcium Signaling in Mammalian Eggs at Fertilization

2016 
The innovation and development of live-cell fluorescence imaging methods have revealed the dynamic aspects of intracellular Ca 2+ in a wide variety of cells. The fertilized egg, the very first cell to be a new individual, has long been under extensive investigations utilizing Ca 2+ imaging since its early days, and spatiotemporal Ca 2+ dynamics and underlying mechanisms of Ca 2+ mobilization, as well as physiological roles of Ca 2+ at fertilization, have become more or less evident in various animal species. In this article, we illustrate characteristic patterns of Ca 2+ dynamics in mammalian gametes and molecular basis for Ca 2+ release from intracellular stores leading to the elevation in cytoplasmic Ca 2+ concentration, and describe the identity and properties of sperm-borne egg-activating factor in relation to the induction of Ca 2+ waves and Ca 2+ oscillations, referring to its potential use in artificial egg activation as infertility treatment. In addition, a possible Ca 2+ influx-driven mechanism for slow and long-lasting Ca 2+ oscillations characteristic of mammalian eggs is proposed, based on the recent experimental findings and mathematical modeling. Cumulative knowledge about the roles of Ca 2+ in the egg activation leading to early embryogenesis is summarized, to emphasize the diversity of functions that Ca 2+ can perform in a single type of cell.
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