OOCYTE MATURATION AND FURROW FORMATION IN AN UNFERTILIZED EGG BY FUSION WITH A FERTILIZED EGG OR BLASTOMERES IN THE ASCIDIAN, ASCIDIA-SYDNEIENSIS-DIVISA

A technique for fusing an ascidian egg with blastomeres using a chemic al fusiogen was established and then used to identify cytoplasmic fact ors that regulate the process of oocyte maturation in ascidian eggs. U nfertilized eggs fused with fertilized eggs or blastomeres in hypotoni c artificial sea water containing 20% polyvinyl alcohol within 10 min. After fusion polar bodies were extruded from the unfertilized portion of the fused eggs. Furrows were formed not only in the fertilized por tion but also in the unfertilized portion in the fused eggs. No polar body extrusion and furrow formation occur in either portion of fused u nfertilized eggs. These results suggest that fertilized eggs and blast omeres contain a factor that induces oocyte maturation. Polar body ext rusion and furrow formation were not suppressed in the fertilized port ion of fused eggs, suggesting that unfertilized eggs do not contain a factor that inhibits oocyte maturation.