Molecular mechanisms involved in the fertilization process

Mammalian fertilization involves a series of sperm-egg interactions mediated by ligand-receptor mechanisms. One of the molecules proposed to participate in this process is epididymal protein CRISP1 (Cysteine Rich Secretory Protein 1) which associates with two different affinities with sperm during maturation. While the loosely bound population is released from the cell during capacitation, the strongly bound population behaves as an integral protein, remains on the sperm after capacitation, and participates in gamete interaction. Recent results revealed that although CRISP1 knockout mice are fertile, their sperm exhibit lower levels of protein tyrosine phosphorylation during capacitation as well as a significantly reduced ability to interact with both ZP and the oolema (fusion). Considering evidence showing that testicular CRISP2 also participates in gamete fusion, this protein is a likely candidate to compensate for the lack of CRISP1 in knockout mice. Together, these results support the idea of different roles for the same CRISP protein, and a functional cooperation between homologous CRISP proteins to ensure the success of fertilization.