Caenorhabditis sex determination is an appealing area for exploring the evolution of development. It is well understood in C. elegans, the genes are among the most rapidly evolving in its genome, and there is variation in reproductive strategies within the genus. Further, recent phylogenetic studies suggest C. elegans and C. briggsae may have evolved hermaphroditism independently (1,2). Comparative studies using RNA interference (RNAi) have revealed many similarities in sex determination across the genus, but also some intriguing differences (3-7). It is unclear if these results are a biological reality or a limitation of RNAi; true mutations are needed to clarify the results. With this in mind our lab used reverse genetics to generate mutants in C. briggsae sex determination genes, focusing on the fem class. The fem genes promote development of all male cell types in C. elegans. In addition, they are also required for hermaphrodite spermatogenesis, and
fem-3 must be negatively regulated to allow the switch to oogenesis (8). A PCR-based deletion mutation screen of over 900,000 haploid genomes produced a deletion in
Cb-fem-2, removing its entire PP2C protein phosphatase domain. Interestingly, the characteristic self-sterile phenotype of XX C. elegans
fem-2 mutants is not seen. In addition, three independent lines of genetic evidence show that XO
Cb-fem-2 are transformed into hermaphrodites, and not females as in C. elegans. Despite these differences, in situ mRNA localization shows expression of
Cb-fem-2 in the hermaphrodite germline is similar to that of C. elegans. Two more recent screens produced deletions in
Cb-fem-1 and
Cb-fem-3. We will report our characterization of these mutations as well. Our results to date strongly support the hypothesis of independent origns of self-fertility in C. elegans and C. briggsae. References; (1) Cho, S, et al. (2004). Genome Research,14: 1207-1220. (2) Kiontke, K, et al. (2004). Proc Natl Acad Sci USA,101(24):9003-8. (3) Streit,A, et al.(1999). Genetics,152: 1573-84. (4) Haag, ES and Kimble, J (2000). Genetics,155: 105116. (5) Chen, PJ, Cho, S, Jin, SW, and Ellis, RE (2001). Genetics,158: 15131525. (6) Haag,ES, Wang, S, and Kimble, J (2002). Current Biol, 12: 2035-41. (7) Stothard, P, Hansen, D, and Pilgrim, D (2002). J Mol Evol,. 54:267282. (8) Kuwabara, PE and Perry, MD (2001). BioEssays, 23:596-604.