The Caenorhabditis elegans hermaphrodite is essentially a female that produces sperm. In C. elegans,
tra-2 promotes female fates and must be repressed to achieve hermaphrodite spermatogenesis. In an effort to learn how mating systems evolve, we have cloned
tra-2 from C. remanei, the closest gonochoristic relative of C. elegans. We found its structure to be similar to that of
Ce-tra-2 but its sequence to be divergent. RNA interference demonstrates that
Cr-tra-2 promotes female fates. Two sites of
tra-2 regulation are required for the onset of hermaphrodite spermatogenesis in C. elegans. One, the MX region of TRA-2, is as well conserved in C. remanei as it is in C. briggsae (another male/hermaphrodite species), suggesting that this control is not unique to hermaphrodites. Another, the DRE/TGE element of the
tra-2 3'' UTR, was not detected by sequence analysis. However, gel-shift assays demonstrate that a factor in C. remanei can bind specifically to the
Cr-tra-2 3'' UTR, suggesting that this translational control is also conserved. We propose that both controls are general and do not constitute a novel "switch" that enables sexual mosaicism in hermaphrodites. However, subtle quantitative or qualitative differences in their employment may underlie differences in mating system seen in Caenorhabditis.