The innovation and development of live-cell fluorescence imaging methods have revealed the dynamic aspects
of intracellular Ca2+ 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 Ca2+ imaging since its early days, and spatiotemporal Ca2+ dynamics and underlying
mechanisms of Ca2+ mobilization, as well as physiological roles of Ca2+ at fertilization, have become more or less evident
in various animal species. In this article, we illustrate characteristic patterns of Ca2+ dynamics in mammalian gametes
and molecular basis for Ca2+ release from intracellular stores leading to the elevation in cytoplasmic Ca2+ concentration,
and describe the identity and properties of sperm-borne egg-activating factor in relation to the induction of Ca2+ waves
and Ca2+ oscillations, referring to its potential use in artificial egg activation as infertility treatment. In addition, a possible
Ca2+ influx-driven mechanism for slow and long-lasting Ca2+ oscillations characteristic of mammalian eggs is proposed,
based on the recent experimental findings and mathematical modeling. Cumulative knowledge about the roles of Ca2+ in
the egg activation leading to early embryogenesis is summarized, to emphasize the diversity of functions that Ca2+ can
perform in a single type of cell.
Keywords: Calcium influx, Calcium oscillations, Calcium release, Calcium wave, Egg activation, Fertilization, Fluorescence
imaging, Infertility, Inositol 1, 4, 5-trisphosphate, Phospholipase Cζ.
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