Adhesion proteins expressed on human gamete surfaces and egg activation

The initiation and propagation of a Ca2+ signal through the egg seems to be the pivotal event in triggering of meiosis resumption. Over the past decade evidence has accumulated suggesting that sperm contact is essential for this phenomenon to occur in most physiological groups. Given their ability to transduce signals, adhesive proteins which are involved in various binding mechanisms such as cell migration, lymphocyte activation, phagocytosis and virus fusion may play a similar role in fertilization. They have been the subject of serious investigation in non-human mammals and some emerging data indicate that they are active in humans as well. Our goal is to review the presence of such molecules on human gametes and their relevant physiological role, i.e., integrins and their ligands, selectins, IgG Fc receptors and leucocyte differentiation markers. We will discuss how they might trigger egg activation through signaling pathways in light of their identified functions in other adhesion systems. The putative participation of specific human sperm proteins will also be evaluated.