Regulation of Intracellular Calcium in the Mouse Egg: Evidence for Inositol Trisphosphate-Induced Calcium Release, but not Calcium-Induced Calcium Release1

Abstract

Fertilization of the mammalian egg initiates transient and repetitive release of Ca2+ from intracellular stores. The mechanism by which these Ca2+ transients are produced is not completely known. We examined the role of two principal Ca2+ release mechanisms, inositol trisphosphate-induced Ca2+ release and Ca(2+)-induced Ca2+ release, in altering intracellular Ca2+ in the mouse egg. Microinjection of inositol 1,4,5-trisphosphate (IP3) transiently elevated intracellular Ca2+ and, at higher concentrations, produced repetitive Ca2+ transients. Addition of 100 microM thimerosal, a sulfhydryl reagent, caused repetitive Ca2+ transients. IP3 and thimerosal responses were inhibited by prior injection of heparin, a competitive antagonist of IP3-induced Ca2+ release. Addition of caffeine or injection of caffeine, ryanodine, or cyclic ADP-ribose, which are known to initiate or modulate Ca(2+)-induced Ca2+ release in sea urchin eggs and other cells, produced no change in intracellular Ca2+. The response to injection of Ca2+ was not altered by prior injection of ryanodine. The magnitude of the Ca2+ transients produced by injection of IP3 was not changed by prior injection of cyclic ADP-ribose or external caffeine. We found no evidence of Ca(2+)-induced Ca2+ release from ryanodine- or caffeine-sensitive stores. It is most likely that release of Ca2+ from intracellular stores in the mouse egg is dependent on IP3-induced Ca2+ release.

Ca2+ signaling differentiation during oocyte maturation

“…It is clear that Ca 2þ release through the IP 3 R is essential for egg activation at fertilization (Miyazaki et al, 1992;Kline and Kline, 1994). In contrast, the role of the RyR is contentious and seems to be more subtle in terms of regulating Ca 2þ -induced Ca 2þ release during the Ca 2þ oscillations that follow the initial Ca 2þ spike (Miyazaki et al, 1992Swann, 1992;Jones et al, 1994;Kline and Kline, 1994). In Xenopus, the situation is less complicated with only a single Ca 2þ release pathway detected functionally and biochemically, the type 1 IP 3 R (Parys et al, 1992;Parys and Bezprozvanny, 1995).…”

Effect of Oocyte Aging on Parthenogenetic Activation with Cycloheximide and A Iteration of the Activity of Maturation Promoting Factor during Aging of Bovine Oocytes.

“…Taken together, these results suggest that the agedoocytes are more sensitive to various activation stimuli than newly matured oocytes in all mammalian species. It is well known that when matured oocytes are treated with activation stimuli such as ethanol [21][22][23], Ca 2+ ionophore A23187 [24,25], IP 3 [26,27], thimerosal [26,28], strontium [24,29], and electric pulses [30,31], transient intracellular calcium [Ca 2+ ] i increases are triggered. Additionally, it is postulated that the sensitivity of the oocyte's activation mechanism to calcium increases with culture time following maturation.…”

Calcium signalling in early embryos

“…These commonly studied species are all deuterostomes. Stricker's excellent survey of calcium signalling across the animal kingdom (Stricker 1999) demonstrates that all eggs from protostomes tested so far (cnidarians, nemerteans, molluscs and echiurans) respond to InsP 3 , as do algal gametes (Roberts & Brownlee 1995 (Nuccitelli et al 1993), sea urchins (Crossley et al 1991;Galione et al 1993;Lee et al 1993;Lee & Shen 1998;Mohri et al 1995), starfish (Stricker 1995;Santella et al 1999a), ascidians (McDougall & Sardet 1995 and mice (Kline & Kline 1994). Only in frog (Stith et al 1993(Stith et al , 1994 and sea urchin (Ciapa & Whitaker 1986;Kuroda et al 2001) eggs has InsP 3 been shown to increase at fertilization; measurements have not been reported in other species.…”

“…Eggs of species lacking functional RyR responses at fertilization nonetheless possess RyRs (Swann 1992;Ayabe et al 1995). In these mammalian eggs, calcium release from RyR at the egg periphery may nonetheless contribute to cortical granule exocytosis (Kline & Kline 1994) and to sustaining the multiple calcium oscillations that follow fertilization (Swann 1992).…”

“…In eggs with RyR receptors but lacking a functional RyR response, cADPr does not cause global calcium release when microinjected (Kline & Kline 1994;Ayabe et al 1995). The receptor for cADPr has not yet been identified but its action requires calmodulin, which appears to increase affinity for cADPr and to increase the sensitivity of the RyR to CICR by several orders of magnitude (Lee et al 1994Thomas et al 2001).…”