Holothurian Oocyte Maturation Induced by Radial Nerve

Endogeneous substances responsible for maturation of holothurian oocytes were examined. Water-extracts of radial nerves from five species of sea cucumbers induced oocyte maturation. Cross-experiments on the maturation-inducing activity of radial nerve extracts indicated that the radial nerve extracts cross-react effectively among the sea cucumbers examined. From its heat-stability, protease-sensitivity, dialyzability, and elution-patterns through `Sephadex' G-15 and G-50 columns, the active factor appears to be a heat-stable peptide of several thousands' daltons. The active factor, termed radial nerve factor, acted on oocytes in isolated ovaries or isolated oocytes having follicle cells to induce maturation. It was ineffective on oocytes deprived of follicle cells. Isolated ovaries or testes incubated with radial nerve factor produced a secondary factor which directly induces maturation of the follicle cell-free oocyte. Follicle cells isolated from follicle-oocyte complexes also produced the secondary factor in the presence of radial nerve factor. These results show that the radial nerve factor stimulates the follicle cells to produce a secondary factor, and the latter, in turn, directly induces oocyte maturation.