. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 9. Schematic diagram depicting the effects of SBTI in causing polyspermy and inhibiting the cortical reaction in sea urchin eggs. The transition from A to C is normally completed in control Arbacia punclulata eggs within 60 s after insemination. From Schuel (1978), reprinted with permission of Alan R. Liss. Inc. A: Surface of an unfertilized egg showing regions where cortical granules (CG) are tightly packed under the plasma membrane (PM) interspersed with randomly distributed areas devoid of subjacent cortical granul
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 9. Schematic diagram depicting the effects of SBTI in causing polyspermy and inhibiting the cortical reaction in sea urchin eggs. The transition from A to C is normally completed in control Arbacia punclulata eggs within 60 s after insemination. From Schuel (1978), reprinted with permission of Alan R. Liss. Inc. A: Surface of an unfertilized egg showing regions where cortical granules (CG) are tightly packed under the plasma membrane (PM) interspersed with randomly distributed areas devoid of subjacent cortical granules. The vitelline layer (VL) is attached to the outer surface of the egg's plasma membrane (PM). Transition from A to B is sensitive to inhibition of SBTI. B: Surface of SBTI-treated egg at 3 min after insemination. The fertilization envelope has elevated over regions previously occupied by the discharged cortical granules. The vitelline layer remains attached to the egg's plasma membrane at the apex of the cortical projections. These sites correspond to regions where the plasma membrane was devoid of subjacent cortical granules before fertilization. Sperm can continue to fuse with and penetrate the egg at these sites as long as they are available. Transition from B to C sensitive to inhibition by SBTI. C: Surface of SBTI- treated egg at 20 min after insemination. The fertilization envelope has elevated from the entire surface of the egg and prevents the entrance of additional sperm. of the vitelline layer from the cortical projections over the next 15-20 min (Fig. 9C). Sperm penetration can continue at these sites in SBTI-treated eggs as long as they are available (Fig. 10). Detachment of the vitelline layer from these potential penetration sites is required to complete the cortical block to polyspermy. Refertilization (poly- spermy) also is facilitated because SBTI-treated eggs can not produce H2O2 to inactivate sperm at their surfaces (Cobum et al, 1981). However, SBTI-treat
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