Gamete Interactions in Caenorhabditis elegans

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DESCRIPTION (provided by applicant): Fertilization is biological process with important medical, social and economic implications. From extensive study, the events of fertilization are known in some detail. However, the molecular underpinnings of these events generally remain elusive. Most previous work on fertilization has relied on biochemical and immunological approaches. Our work is groundbreaking in the application of classic genetic analysis to this vital area of research. My lab has been helping to pioneer the use of C. elegans for addressing the mechanisms of sperm-egg interactions. Many of the genetic and molecular tools developed for C. elegans are not available or are very difficult to utilize in other organisms traditionally used for studying fertilization. One of the most significant advantages of C. elegans is our ability to isolate and maintain mutants that affect sperm or eggs and no other cells. Previously, through the study of sterile mutants, we have identified some of the first sperm molecules required for productive gamete interactions in C. elegans. These sperm molecules include SPE-9 and SPE-38. SPE-9 is a sperm surface transmembrane molecule with an extracellular domain that contains ten epidermal growth factor (EGF)-like repeats. We hypothesize that SPE-9 functions as a ligand for an egg surface sperm receptor. The spe-38 gene encodes a novel four pass transmembrane molecule. Based on protein localization and genetic interaction studies, we hypothesize that SPE-38 regulates the localization and/or activity of a calcuim channel (SPE-41/TRP-3) and other sperm molecules. We recently identified the first egg molecules required for fertilization in C. elegans. The egg-1 and egg-2 genes encode egg surface Low Density Lipoprotein (LDL) receptor repeat-containing proteins. We hypothesize that EGG-1 and EGG-2 function semi-redundantly as egg surface receptors for sperm during fertilization. The goal of this proposal is to further our understanding of fertilization in C. elegans by conducting the following experimental aims: 1) to further characterize the roles of SPE-9 and EGG-1/EGG-2 in fertilization by developing reagents to test for potential ligand-receptor interactions between them and/or other molecules. 2) to gain a better understanding SPE-38 and SPE-41/TRP-3 function in fertilization by investigating the connection between them through protein interaction studies and mutagenesis. 3) to clone the sperm function gene spe-36 in order to determine its molecular nature and role in fertilization. The spe-36 gene is defined by a sterile mutant phenotype that is identical to spe-9, spe-38 and spe-41/trp-3 mutants. This work will complement fertility studies in other organisms as well as provide insights into the mechanisms of cell-cell interactions and the diversity of reproductive strategies. PUBLIC HEALTH RELEVANCE: Although the events of fertilization are fairly well described for a number of species, the molecular underpinnings of the process are not well understood. We are identifying the molecules and molecular mechanisms of fertilization in the model system Caenorhabditis elegans. This work will complement studies of fertilization in other species and could eventually lead to a better understanding of the causes of infertility, the diversity of reproductive strategies and the design of new contraceptives.