Molecular analysis of the role of the FEM proteins in Caenorhabditis elegans sex determination

grantor: University of TorontoMale development in the nematode 'Caenorhabditis elegans' requires the activity of the three 'fem' genes, 'fem-1, fem-2,' and 'fem-3.' The products of these genes form part of a novel signal transduction pathway that controls 'C. elegans ' sex determination, but the mechanism by which the FEMs act remains unclear. I report the use of a 'fem-1' reporter construct to show that 'fem-1' is widely expressed throughout development in both sexes, indicating that 'fem-1' is regulated post-transcriptionally. I further characterize the sequences required for 'fem-1' expression, and characterize a dominant feminization of the germline caused by ' fem-1' transgenes. To identify regions of FEM-1 that are important for its activity, I cloned and characterized 'fem-1' homologues from two related nematode species. Overall, FEM-1 is more conserved than the other 'Caenorhabditis ' sex determining genes. Within FEM-1, the ANK repeats and a kinesin light chain-like repeat are the most conserved regions. Despite the sequence conservation, 'C. briggsae fem-1' is unable to functionally replace 'C. elegans fem-1.' A small region of ' fem-1' coding sequence, between the ANK and TPR encoding regions, appears to be responsible for the functional divergence. I also present data that suggests that in 'C. briggsae, fem-1' may not be required for germline sex determination, possibly revealing the rapid evolution of germline sex determination mechanisms. To elucidate how the FEMs function in the transduction of the sex determination signal, I examined the subcellular localization of each of the FEM proteins. I show that FEM-2 is cytosolic in both sexes, and can interact 'in vivo' with FEM-3, which also appears to function in the cytoplasm. In contrast, FEM-1 appears to localize to discrete compartments within the cell. This localization is at least partially dependent on the kinesin light chain-like repeat of FEM-1. I discuss the implications of the localization data and consider possible models for the mechanism of FEM activity.Ph.D