Figure 3.

CRISP proteins in spermatozoa during their transit along the male and female reproductive tracts. Spermatozoa leaving the testis carry CRISP2 inside the head and tail. During epididymal transit, CRISP1, CRISP3, and CRISP4, soluble or associated with epididymosomes, bind loosely or strongly to the sperm surface. CRISP3 can also bind to the cells during ejaculation. In the female tract, the loosely associated proteins are partially released from sperm cells during capacitation whereas the intracellular or tightly-bound population remain in the cells and relocalize to the equatorial segment of acrosome-reacted spermatozoa. Each sperm CRISP protein participates in more than one step of fertilization and cooperates with other CRISP homologs in each fertilization step.