SPE-51, a sperm-secreted protein with an immunoglobulin-like domain, is required for fertilization in C. elegans.

Fertilization is a fundamental process in sexual reproduction during which gametes fuse to combine their genetic material and start the next generation in their life cycle. Fertilization involves species-specific recognition, adhesion, and fusion between the gametes. In mammals and other model species, some proteins are known to be required for gamete interactions and have been validated with loss-of-function fertility phenotypes.

The EGF-motif-containing protein SPE-36 is a secreted sperm protein required for fertilization in C. elegans.

Identified through forward genetics, spe-9 was the first gene to be identified in C. elegans as necessary for fertilization. Since then, genetic screens in C.