ACTIVATION AT THE GERMINAL VESICLE STAGE OF STARFISH OOCYTES PRODUCESPARTHENOGENETIC DEVELOPMENT THROUGH THE FAILURE OF POLAR BODY EXTRUSION

Starfish oocytes can be fertilized after germinal vesicle breakdown (G VBD) and artificial parthenogenesis can be induced by activating the o ocytes after GVBD (post-GVBD activation). In the present study, parthe nogenotes were obtained by the activation of immature oocytes with caf feine before treatment with 1-methyladenine (1-MeAde) to induce oocyte maturation. Most of the caffeine-treated eggs developed as tetraploid s, as parthenogenotes produced by the post-GVBD activation. The parthe nogenotes were derived only from eggs that failed to extrude polar bod ies, mostly from eggs failing to extrude a second polar body. Eggs der ived from immature oocytes activated by A23187, treated with 1-MeAde a nd post-treated with cytochalasin B failed to extrude polar bodies, an d eventually developed into parthenogenetic embryos. These results ind icate that the present parthenogenesis mechanism shares the same chara cteristics as that achieved by post-GVBD activation in the suppression of polar body formation as a key means for successful starfish parthe nogenesis.