The many faces of egg activation at fertilization

The signaling networks controlling calcium release and cortical granule exocytosis at fertilization are complex and multilayered, providing various points for regulatory input and quality control. Though it is clear that many of the mechanisms leading to both calcium release and cortical granule exocytosis are conserved, a great deal of variability exists between homologous signaling pathways in different species. The signaling pathways responsible for the release of calcium seen at fertilization vary from species to species, yet they center around the importance of IP3-mediated signaling. Similarly, while there are differences in the mechanisms of regulated secretion between species and between intracellular membrane trafficking events, particularly with respect to time and space, all seem to be dependent on the SNARE proteins and their regulator and effector proteins. What has been most helpful in these studies is the convergence of studies from many different species of eggs. With the amazing divergence of reproductive processes and mechanisms that exists throughout phylogeny, it is comforting to see such strong overlapping roles of key players in widely disparate eggs.