Sperm-egg Interactions in Caenorhabditis Elegans

Singson

0000182

The reproductive biology of the nematode worm Caenorhabditis elegans facilitates the identification of mutations that affect sperm and no other cells. This provides a unique opportunity to define sperm components required for sperm-egg interactions. Worms with mutations in the spe-9 gene produce spermatozoa with wild type morphology and motility that cannot fertilize oocytes even after contact between gametes. Therefore, disruption of spe-9 function affects either gamete recognition, adhesion, signaling and/or fusion. The spe-9 gene encodes a sperm transmembrane protein with an extracellular domain that contains ten epidermal growth factor (EGF)-like repeats. A common feature of proteins that include EGF-like motifs is their involvement in extracellular functions such as adhesive and ligand-receptor interactions. Additionally, the overall structure of the predicted SPE-9 protein is similar to that of ligands for the Notch/LIN-12/GLP-1 family of transmembrane receptors. These results suggest that SPE-9 functions in the specialized cell-cell interactions required for fertilization. In order to gain a better understanding of the role of SPE-9 during fertilization we will follow several lines of investigation. Immunofluorescence will be used to localize the SPE-9 protein in sperm and reveal the cellular region important for gamete interactions. Mutation analysis experiments will be conducted in order to determine important functional domains of the SPE-9 protein. Finally, extragenic suppressors of spe-9 will be isolated in order to identify additional genes involved in worm sperm-egg interactions. This work will provide new insights into conception and complement studies of fertilization in other organisms.