Characterization of the Role of the fem genes in the Sex Determination Pathway of Caenorhabditis briggsae

In the genus Caenorhabditis, self-fertile hermaphrodites in C.elegans and C.briggsae evolved from females by developing the ability to generate a limited number of self sperm. The fem genes are crucial for spermatogenesis and the sperm-to-oocyte switch in C.elegans hermaphrodites. RNAi results of the fem genes in C.briggsae hermaphrodites differed from results in C.elegans, suggesting regulation of germ line sex determination pathway differs between the two species. To more definitively address this possibility, and to further investigate the role of the fem genes in the sex determination pathway of C.briggsae, deletion mutants of Cbr-fem-2 and Cbr-fem-3 were generated and characterized. Double Cbr-tra-1;Cbr-fem-2 and Cbr-tra-1;Cbr-fem-3 were also generated to further characterize the role of the fem genes and their relationship to tra-1. Our results show that while the somatic role of the fem genes have been conserved in both species, their germline role differs. Males of both species require the fem genes for somatic development and to suppress oocyte production. However, C.briggsae hermaphrodites do not require the fem genes for spermatogenesis or the sperm-to-ooycte switch. The double mutant analysis results suggest that, unlike C.elegans, Cbr-tra-1 remains epistatic to the Cbr-fem genes in the germline sex determination system in C.briggsae. While there is overall similarity in phenotypic categories between the double mutants, the percentages within each category differs. The double tra-1;fem3 mutant phenotype differs significantly from the single tra-1 mutant, suggesting a role for Cbr-fem-3 in regulating Cbr-tra-1 activity. A previously undescribed Emo phenotype was also discovered in both single and double mutants in C.briggsae and in C.elegans tra-1 mutant alleles e1099 and e1781. The overall results of this study are consistent with the convergent evolution of hermaphroditism within the genus Caenorhabditis and suggest considerable genetic flexibility in this developmental pathway.