FORMATION OF THE FERTILIZATION MEMBRANE BY INSEMINATION OF IMMATURE STARFISH OOCYTES PRETREATED WITH CALCIUM-FREE SEAWATER

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Abstract
When immature oocytes of the starfish, Asterina pectinifera, were treated with calcium-free seawater for 1 hr and then inseminated in normal seawater, they formed several blisters, indicative of polyspermy, and raised fertilization membranes. These oocytes continued to have intact germinal vesicles. Electron microscopic study revealed that the egg surface remained virtually unchanged after the treatment with calcium-free seawater. Upon insemination, however, the cortical granules broke down and the fertilization membrane was formed. These immature oocytes with ferilization membranes underwent maturation (germinal vesicle breakdown) after treatment with 1-methyladenine. The treatment with calcium-free seawater seems to bring about some physiological change on the surface of immature oocyte, which bestows some attributes of maturation but is insufficient to mature the oocytes completely.