Control of meiosis reinitiation in starfish : calcium ion as the primary effective trigger

In vitro experiments demonstrate that the spontaneous maturation of Mar- thasterias glacialis oocytes results from the release of preformed 1-MeAde from the follicles. Follicle-free prepared oocytes, taken early in the season, can however reinitiate meiosis under the influence of an increased level of extracellular Ca 2+ ions. This triggers a transient change in intracellular free Ca 2+ which can be monitored in aequorin-injected oocytes and appears to be similar to that resulting from 1-MeAde application. This hormone proved to be efficient in the complete absence of external Ca 2+ ions. Nuclear maturation and cortical reaction (either by sperm or ionophore A 23187) can be triggered independently. The matu- ration-free Ca 2+ peak appears less than 1 sec after the application of the efficients stimuli (Ca 2+ or 1-MeAde). It is about 20 times lower than the ionophore-induced peak and cor- responds to the release of 0.5 to 1.5 [L M Ca 2+ . Inhibition of both the Ca 2+ and the meiosis responses by D600 or EGTA supports the view that intracellular Ca 2+ release may be the primary trigger for meiosis reinitiation.