Effects of Okadaic Acid on Embryonic Development of the Starfish Asterina pectinifera

The effects of okadaic acid, an inhibitor of protein phosphatases types 1 and 2A, from the sponge Halichondria okadai Kadota, on the embryonic development of the starfish Asterina pectinifera, were investigated. When cultured in okadaic acid from fertilization, the embryo divided synchronously without any abnormalities such as lysis, swelling or morphological changes different from control embryos up to the 32-cell stage. However, okadaic acid prevented development before the onset of blastulation. Cytological examination showed that chromosomes condensed but did not align in a plane in the mitotic apparatus in each of the blastomeres of the treated embryo at the sixth cleavage, suggesting that this was the root cause of the arrest of further development.