Rise of intracellular Ca2+ level causes the decrease of cyclin B1 and Mos in the newt eggs at fertilization

Abstract

Unfertilized eggs of the newt, Cynops pyrrhogaster, are arrested at the second meiotic metaphase, with activity of the M‐phase promoting factor (MPF) maintained at a high level. After fertilization, the eggs resume the cell cycle, and emit the second polar body. When the change in [Ca2+]i in the fertilized eggs was monitored by aequorin, an early increase in [Ca2+]i was observed 5–10 min after insemination and continued for about 30 sec. A late increase in [Ca2+]i then occurred 10–15 min after fertilization and continued for 30–40 min. The injection of 1,2‐Bis (2 aminophenoxy) ethane‐N,N,N′,N′,‐tetraacetic acid (BAPTA) into unfertilized eggs inhibited reinitiation of the cell cycle after fertilization. Western blot analysis with antibodies against cyclin B1 or Mos indicated that both cyclin B1 and Mos were present in unfertilized eggs, but both disappeared within 30 min after fertilization. Treatment with Ca2+‐ionophore decreased both cyclin B1 and Mos. Chymotryptic activity in Cynops egg extracts was not significantly increased after fertilization or activation by treatment with the Ca2+‐ionophore. No change in [Ca2+]i was observed following treatment with cycloheximide, but the amount of both cyclin B1 and Mos rapidly decreased. These results indicate that resumption of meiosis in Cynops eggs is induced by an increase in [Ca2+]i at fertilization, which causes degradation of both cyclin B1 and Mos by inhibition of de novo synthesis of those proteins. Mol. Reprod. Dev. 53:341–349, 1999. © 1999 Wiley‐Liss, Inc.

Extra-mitochondrial citrate synthase initiates calcium oscillation and suppresses age-dependent sperm dysfunction

“…The newt Cynops pyrrhogaster exhibits physiological polyspermic fertilization, during which multiple sperm enter a single egg [14]. Harada et al [15] discovered that microinjection of a mitochondrial citrate synthase (CS) into unfertilized eggs induces a transient intracellular calcium ion concentration ([Ca 2+ ] i ) rise.…”

Comparative biology of sperm factors and fertilization‐induced calcium signals across the animal kingdom

“…Exactly how such citrate‐derived breakdown products might facilitate Ca 2+ ‐wave production during egg activation has yet to be determined, although acetyl‐CoA has been shown to sensitize IP 3 receptors in the endoplasmic reticulum of other cell types, and the Ca 2+ wave observed following injection of oxaloacetate into unfertilized Cynops oocytes could arise from an oxaloacetate‐induced release of Ca 2+ from mitochondria, as noted for hepatocytes (Harada et al, ). In any case, regardless of the precise signaling pathways triggered by citrate synthase, the fertilization‐induced Ca 2+ response of Cynops and related amphibians is capable of driving MPF/MAPK inactivation and cell‐cycle progression (Sakamoto et al, ; Yamamoto et al, ; Pelczar et al, ; Iwao, ).…”

Egg Activation at Fertilization: Where It All Begins

“…The Ca 2ϩ increase at fertilization is necessary and sufficient for restarting cell cycle events in eggs of ascidians (Sensui and Morisawa, 1996;Russo et al, 1996), vertebrates Kline, 1988;Kline and Kline, 1992;Yamamoto et al, 1999), and echinoderms Nomura and Nemoto, 1998;Carroll et al, 1999Carroll et al, , 2000. The Ca 2ϩ increase causes ascidian and vertebrate eggs to enter anaphase and complete meiosis, and causes sea urchin eggs, which have already completed meiosis, to undergo DNA synthesis (see Jaffe et al, 2001, for a discussion of the more complex case of starfish).…”