Molecular mechanisms involved in gamete interaction
Anim Reprod, vol.3, n2, p.127-129, 2006
Epididymal protein DE and testicular protein Tpx-1 are two cysteine-rich secretory proteins also known as CRISP1 and CRISP2, respectively. DE/CRISP1 is localized on the equatorial segment of acrosome-reacted sperm and participates in rat gamete fusion through its binding to egg-complementary sites. Recent results using bacterially-expressed recombinant fragments of DE as well as synthetic peptides revealed that the ability of DE to bind to the egg surface and inhibit gamete fusion resides in a region of 12 amino acids corresponding to an evolutionary conserved motif of the CRISP family named Signature 2. Interestingly, protein Tpx-1 exhibits only two substitutions in Signature 2 when compared to DE, and was also capable of binding to the rat egg, opening the possibility for a role of Tpx-1 in gamete fusion. Results showed the ability of recombinant Tpx-1 to significantly inhibit zona-free egg penetration, supporting the participation of this protein in gamete fusion through its interaction with egg-binding sites. Subsequent in vitro competition studies showed that incubation of zona-free eggs with a fixed concentration of recombinant Tpx-1 and increasing amounts of DE, gradually reduced the binding of recTpx-1 to the egg, indicating that both CRISPs would be sharing the egg complementary sites. The possible participation of both epididymal DE/CRISP1 and testicular Tpx-1/CRISP2 in gamete fusion provides important information on the molecular mechanisms involved in this process and supports the idea of a functional cooperation between homologue molecules as a mechanism to ensure the success of fertilization.
sperm, egg, gamete fusion, fertilization, CRISP