The Distribution and Exocytosis of Cortical Granules in the Mammal

Abstract

As long as 35 years ago the observation was made that as a result of fertilization the zona pellucida was altered such that it became refractory to the ingress of supernumerary spermatozoa (Braden, Austin and David, 1954) and cortical granules were reported to disappear from the surface of the oocyte. It was a short step to suggest that substances liberated from these exocytosed organelles acted on the zona pellucida in some unknown manner to prevent the passage of sperm (Austin and Braden, 1956). Since this time it has become clear that a trypsin-like protease is involved (Gwatkin et al. 1973; Wolf and Hamada, 1977) although, while considerable progress has been made towards a full analysis of the contents of cortical granules from invertebrates such as the sea urchin, we are still far from an understanding in regard of the mammal. Further, it is clear that the granules must have a precise relationship with the oocyte plasma membrane in order that they may fuse with it, and, in addition, they must and also be capable of responding to signals resulting from sperm/oocyte fusion. It is with the distribution of the granules within the oocyte and the possible nature of intracellular signals involved in the exocytotic process that this communication will be concerned.