Essential role of the inositol 1,4,5-trisphosphate receptor/Ca2+ release channel in Ca2+ waves and Ca2+ oscillations at fertilization of mammalian eggs.
At fertilization mammalian eggs exhibit repetitive rises in the cytoplasmic Ca2+ concentration (Ca2+ oscillations), associated with propagating Ca2+ waves in the initial responses. The Ca2+ oscillation causes cortical granule exocytosis and resumption of second meiosis and affects later embryonic development. Recent studies using a function-blocking monoclonal antibody to the inositol 1,4,5-trisphosphate (InsP3) receptor/Ca2+ release channel demonstrated direct evidence that InsP3-induced Ca2+ release (IICR) from intracellular stores operates at fertilization of the hamster egg and that IICR is essential in the initiation, propagation, and oscillation of the sperm-induced Ca2+ rises. Ca(2+)-induced Ca2+ release (CICR) has also been suggested, but a sensitizing action of Ca2+ on the InsP3 receptor, i.e., Ca(2+)-sensitized IICR, can serve as a regenerative process of Ca2+ release and could be the basis for Ca2+ waves and Ca2+ oscillations. It is now apparent that signal transduction at fertilization is dependent on sperm-stimulated activation of phospholipase C which causes hydrolysis of phosphatidylinositol bisphosphate and production of InsP3, leading to IICR. On the other hand, Ca2+ signaling at fertilization of the sea urchin egg may also involve ryanodine receptor-mediated CICR.
Department of Physiology, Tokyo Women's Medical College, Japan.
S
S
Miyazaki
H
H
Shirakawa
K
K
Nakada
Y
Y
Honda
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D005246:Feedback; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008322:Mammals; D008954:Models, Biological; D010063:Ovum / Q000378:metabolism*; D010507:Periodicity; D011956:Receptors, Cell Surface / Q000502:physiology*; D018160:Receptors, Cytoplasmic and Nuclear
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D002118:Calcium