Fertilization is a biological process that has important social, economic and medical implications. Our primary research interest is the mechanisms of sperm-egg interactions. The long-term goal of research in the lab is to understand the molecular events that mediate gamete recognition, adhesion, signaling and fusion. The genetic and molecular dissection of these events will also provide insights relevant to other important cell-cell interactions during the development of multicellular organisms.
We are helping to pioneer the use of the nematode worm Caenorhabditis elegans for addressing the mechanisms of sperm-egg interactions. The powerful tools of classical and molecular genetics developed for the worm are not available or are very difficult to utilize in the other organisms traditionally used for studying fertilization. The ameboid sperm of C. elegans, despite lacking an acrosome and flagellum, carry out the same basic functions common to all spermatozoa. The reproductive biology of C. elegans facilitates the identification of mutations that affect sperm and no other cells. The worm exists as a hermaphrodite that makes both sperm and oocytes or as a male that makes only sperm. Mutant hermaphrodites that are spermatogenesis-defective (spe) are self-sterile and lay unfertilized oocytes. However, when these otherwise healthy worms are crossed to wild type males (a source of sperm) they can produce outcrossed progeny. We have focused on a set of spe genes that produce sperm with normal morphology and motility that cannot fertilize eggs even after contact. From this phenotype we infer that these mutants disrupt either sperm-egg recognition, adhesion, signaling or fusion. The characterization of these genes is a critical step in formulating a model concerning their role in wild-type fertilization.
Since we expect that not every gene required for fertilization will be sperm specific, we are employing both forward and reverse genetic approaches to identify additional genes required for fertility in C. elegans. Our work on C. elegans reproductive biology complements studies of fertilization in other organisms and provides insights relevant to the understanding of cell-cell interactions.