Like most nematodes, Caenorhabditis remanei has two sexes: XO animals become males and XX animals become females. However, Caenorhabditis elegans is hermaphroditic: XO animals are male and XX animals develop as self-fertile hermaphrodites. These hermaphrodites appear female in most respects, but produce sperm during larval development which can be used for self-fertilization. Thus these species provide a system to study how well defined differences in sex-determination arose. In C. elegans, two genes appear to directly control the decision to make sperm: fog-1 and fog-3. Mutations in either gene cause all germ cells to differentiate as oocytes, even in males. Thus, one simple model is that these genes would be active only in male C. remanei and that a crucial step in the evolution of hermaphroditism involved their expression and function in XX individuals of C. elegans. Four approaches will be used to test this model. 1) The C. remanei homologs of fog-1 and fog-3 will be isolated and sequenced. In addition, RNA-mediated interference will be used to determine the function of each gene in C. remanei. 2) Comparison of the promoters for these C. elegans and C. remanei genes should aid in identifying regulatory elements that control transcription. Any identified elements will be tested in transgenic animals. 3) Comparison of the protein products of these genes will help to identify crucial domains and potential regulatory sites. These products will also be tested in transgenic animals. 4) C. elegans will be genetically analyzed to find and characterize new genes that regulate fog-1 or fog-3 which will be subjects for future study in C. remanei. The introductory Genetics course will be amplified to include new material from human genome studies, as it becomes available. Discussion of ethical issues raised by human genomic studies will also be added to the course and new computer technology will be utilized in order to teach students about the power and limitations of the genetic databases available on the Internet.
Insight into the evolution of sexual differences in animals will be enhanced by the results of this investigation of two nematodes with different modes of reproduction. The use of information from the extensive database for C. elegans will be used to introduce undergraduate students to the technology necessary to effectively use available databases. The Introductory Genetics course will be expanded to encompass new information from the Human Genome Project and to discuss ethical issues arising from that project.
