Malformation of immature starfish oocytes by theonellapeptolide Ie, a Tridecapeptide lactone from a marine sponge Petrosia species, through disturbance of cortical F-actin distribution.

Theonellapeptolide Ie (Tp), an oligopeptide lactone isolated from a marine sponge, Petrosia sp., was shown to induce an unprecedented morphological change in the immature oocytes of the starfish Asterina pectinifera. The cortical F-actin was disturbed and assembled to form dots and rings, as evidenced by staining with rhodamine-conjugated phalloidin. The oocyte eventually became malformed. When Tp was added to an immature oocyte which had been pretreated with cytochalasin B or D, inhibitors of actin polymerization, no malformation was observed. When Tp was added to an oocyte which had been induced to mature by 1-methyladenine (1-MeAde), a maturation-inducing substance in starfishes, no morphological changes were observed in the maturing oocytes which reached the first meiotic prometaphase 40 min after the start of 1-MeAde treatment. This is the first description of a chemical that induces aberrant redistribution of F-actin-based cytoskeleton in an animal oocyte which is arrested at the first meiotic prophase.