Role of integrins and polyphosphoinositide metabolism during fertilization in sea urchin egg and hamster oocyte

In almost all species studied to date, a transient increase in the intracellular free calcium concentration (Ca-i) occurs after fertilization and is essential for egg activation. How the sperm triggers this calcium signal remains, however, to be determined. In this brief review, we compare the mechanisms that are common to mammalian and invertebrate systems. In the light of our own data, we discuss how integrins that have recently been proposed to mediate sperm-egg binding and fusion in mammals might trigger egg activation through cytoskeletal structures. We suggest a model, leading to the calcium signal and common to all species, where phosphorylation on tyrosine and phospholipase C gamma (PLC gamma) are interconnected pathways stimulated by a multimolecular complex involving integrins.