Effect of Relaxin-Like Gonad-Stimulating Substance on Gamete Shedding and 1-Methyladenine Production in Starfish Ovaries

Abstract

As in lower vertebrates, starfish oocyte maturation and ovulation are induced by a hormonal substance. Gonad-stimulating substance (GSS) is the first mediator in inducing these maturation and ovulation. GSS secreted from the nervous system acts on the ovary to produce 1-methyladenine (1-MeAde) as a maturation-inducing hormone. 1-MeAde induces germinal vesicle breakdown (GVBD) and follicular envelope breakdown (FEBD), releasing the oocyte from the ovaries, that is, spawning. Recently, GSS was purified from the radial nerves of the starfish Asterina pectinifera and its chemical structure was determined to be a relaxin-like peptide. To further elucidate the physiological roles of GSS on oocyte maturation and ovulation, this study examined the effect of synthetic GSS on 1-MeAde production in intact ovaries, folliculated oocytes, isolated follicle cells, and spawned ovaries containing follicle cells of the starfish (sea star) A. pectinifera. Spawning was induced by synthetic GSS as a dose-dependent manner. However, a high concentration of GSS failed to induce spawning. 1-MeAde production in an ovarian fragment also declined at a high concentration of GSS. Similar dual effects of GSS were observed in folliculated oocytes. In contrast, 1-MeAde production in isolated follicle cells and spawned ovaries did not decrease at a high concentration of GSS. Interestingly, egg jelly inhibited GSS-induced 1-MeAde production in follicle cells. These results may suggest that egg jelly disturbs GSS action on 1-MeAde production and spawning in ovaries.Keywords1-MethyladenineEgg jellyGonad-stimulating substanceSpawningStarfish