Nature of the 1-Methyladenine-Requiring Phase in Maturation of Starfish Oocytes. (1-methyladenine/oocyte maturation/oocyte stiffness/caffeine/starfish)

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Abstract
Reinitiation of meiosis in starfish oocytes requires the continuous presence of 1-methyladenine (1-MeAde) in the surrounding medium for a definite period. The length of the hormone-dependent phase (HDP) in A. pectinifera, which was defined as the time necessary for induction of 50% germinal vesicle breakdown (GVBD), was .apprx. 11 min at 17.degree. C, and 8 min at 20.degree. C. Repeated treatments for shorter periods with 1-MeAde revealed that the action of this agent was cumulative and that stable intermediate states between the unstimulated and fully stimulated levels existed during the HDP. Measurement of the stiffness of oocytes also demonstrated this stable intermediate state. Thus, there may be a factor(s) in the cytoplasm that accumulates continuously during the HDP and triggers GVBD when it reaches a critical level. When dithiothreitol (DTT) was used as an artificial maturation-inducing agent, the intermediate state was far less stable, suggesting a difference in the modes of action of 1-MeAde and DTT. Isotonic CaCl2, the Ca2+ ionophore (A 23187) [calcimycin] and methylxanthines, which are known to cause increase in intracellular Ca2+, had additive effects with 1-MeAde. Part of the action of 1-MeAde probably is to release Ca2+ in the oocyte cytoplasm.