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

Abstract

In the genus <em>Caenorhabditis<em>, self-fertile hermaphrodites in <em>C.elegans<em> and <em>C.briggsae<em> 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 <em>C.elegans<em> hermaphrodites. RNAi results of the fem genes in <em>C.briggsae<em> hermaphrodites differed from results in <em>C.elegans<em>, 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 <em>fem<em> genes in the sex determination pathway of <em>C.briggsae<em>, deletion mutants of <em>Cbr-fem-2<em> and <em>Cbr-fem-3<em> were generated and characterized. Double <em>Cbr-tra-1;Cbr-fem-2<em> and <em>Cbr-tra-1;Cbr-fem-3<em> were also generated to further characterize the role of the <em>fem<em> genes and their relationship to <em>tra-1<em>.

Our results show that while the somatic role of the <em>fem<em> genes have been conserved in both species, their germline role differs. Males of both species require the <em>fem genes for somatic development and to suppress oocyte production. However, <em>C.briggsae<em> hermaphrodites do not require the <em>fem<em> genes for spermatogenesis or the sperm-to-ooycte switch. The double mutant analysis results suggest that, unlike <em>C.elegans<em>, <em>Cbr-tra-1<em> remains epistatic to the <em>Cbr-fem<em> genes in the germline sex determination system in <em>C.briggsae<em>. While there is overall similarity in phenotypic categories between the double mutants, the percentages within each category differs. The double <em>tra-1;fem3<em> mutant phenotype differs significantly from the single <em>tra-1<em> mutant, suggesting a role for <em>Cbr-fem-3<em> in regulating <em>Cbr-tra-1<em> activity. A previously undescribed Emo phenotype was also discovered in both single and double mutants in <em>C.briggsae<em> and in <em>C.elegans tra-1<em> mutant alleles <em>e1099<em> and <em>e1781<em>.

The overall results of this study are consistent with the convergent evolution of hermaphroditism within the genus <em>Caenorhabditis<em> and suggest considerable genetic flexibility in this developmental pathway.<p/>