GAMETE INTERACTION AND ADHESION PROTEINS

Fertilization implicates the intervention of adhesion and activation m echanisms between male and female mammalian gametes comparable to thos e already described for metastasis, embryonal development, immune syst eme functionning and viral infection. Recognition proteins thus far di scovered in animals intervene at essentially two levels: (1) associati on of the spermatozoa with, and penetration of the acellular protectiv e envelope of the oocyte, the zona pellucida; (2) sperm attachment to the oocyte plasma membrane. The first step involves interactions with oligosaccharides associated with the proteins of the zona pellucida. I t is at this stage that species barriers take place to prevent cross f ertilization. This association activates the spermatozoa by triggerrin g the acrosomal reaction which allows release of the proteolytic enzym es necessary to dissociate the zona pellucida. The attachment to the o ocyte plasma membrane seems to depend on peptidic sequences. It culmin ates in the activation of the oocyte and continuation of meiosis; Reco gnition events between complementary molecules initiate, at each of th e two steps, the transduction pathways responsible for the activation of the respective gametes.