MARKED DECREASE IN THE RIGIDITY OF STARFISH OOCYTES INDUCED BY 1-METHYLADENINE1

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Abstract
Extreme rigidity of immature starfish [Asterina pectinifera, Astropecten scoparius and Asterias amurensis] oocytes as measured by compression declined during the early phase of their maturation when induced by 1-methyladenine (1-MeAde). The onset of this decrease in stiffness occurred within 5-9 min of 1-MeAde treatment, well before the breakdown of the germinal vesicle, progressively declining to reach a minimum stiffness after 20 min. Dithiothreitol, an artificial maturation-inducing agent, caused a similar change. The stiffness is expected to serve as a quantitative indicator of the early process of cytoplasmic events, which would induce the breakdown of the germinal vesicle. Cytochalasin B (3 .mu.g/ml) also reduced the stiffness, but unlike the former 2 agents, the effect was reversible and did not interfere with the maturation proces. Due to the effect of cytochalasin B, it became possible to enucleate immature oocytes by centrifugal force. Non-nucleate fragments thus obtained still maintained their marked stiffness, which was decreased by the action of 1-MeAde, with a time-course similar to that of intact oocytes.