ROLE OF CALCIUM INFLUX DURING THE LATENT PERIOD IN SEA-URCHIN FERTILIZATION

After similar to 7-40 s following gamete fusion, a steadily increasing fraction of a sea urchin's zygotes initiate an activating calcium wav e. The fertilization membrane then rises, the cell cycle resumes and d evelopment begins. This study focuses on the so-called latent period t hat occurs between the time that gamete fusion occurs and the initiati on of the activating calcium wave. We inhibited calcium influx during this period by adding lanthanum or by reducing external calcium with a buffer at various time points after insemination. Both of these treat ments blocked the activation of eggs that had not yet started a wave a t the time of treatment. This indicates that an influx of calcium is n eeded during the latent period to induce egg activation. These results support the sperm conduit model of egg activation in the sea urchin, where calcium flows from the sea through the fused sperms' acrosomal p rocess into a cortical region of the eggs' endoplasmic reticulum.