Observations on the cortical reaction in eggs of <i>Brachydanio rerio</i> as seen with the scanning electron microscope

Abstract

Abstract Ripe eggs of Brachydanio rerio were fixed at selected intervals of time after activation, dechorionated, and prepared by standard techniques for viewing under the scanning electron microscope (SEM). The surfaces of eggs fixed two to four minutes after activation show all stages in the activation and extrusion of the cortical granules. At least four morphologically distinct and temporally sequential stages for the cortical granule reaction are observed with the SEM. These include the elevation of the cortical granule above the egg surface, the extrusion of the contents of the cortical granule, the transient participation of the limiting membrane of the cortical granule in egg surface membrane formation, and replacement of the granule limiting membrane by the egg plasma membrane. We propose that a consequence of egg activation is the retrieval of the cortical granule membrane.