Three Phases of Cortical Maturation during Meiosis Reinitiation in Starfish Oocytes

Abstract

Oocytes of the starfish, Asterina pectinifera, respond differently to calcium ionophore A23187 depending upon their stage of maturation. Oocytes not-treated with 1-methyladenine (1-MA) formed only a partial fertilization envelope (FE) in response to A23187. Those treated with 1-MA formed no FE if the ionophore was introduced to them before germinal vesicle breakdown (GVBD), in contrast with which they did fully elevate the FE if it was introduced after GVBD. Similar stage-dependent results were obtained if the intracellular concentration of calcium was increased by microinjection of calcium-EGTA buffers. In good accordance with the FE formation, a stage-dependent protease release from oocytes by the ionophore was observed. It is concluded from these results that, in starfish oocytes, their ability to undergo the exocytosis of cortical granules in response to an increase in intracellular calcium greatly changes along the way of maturation.