Conspecific and Interspecific Interactions Between the FEM-2 and the FEM-3 Sex-Determining Proteins Despite Rapid Sequence Divergence

Abstract

Abstract. Using degenerate oligonucleotide primers, we isolated the Caenorhabditis remanei orthologue of the C. elegans sex-determining phosphatase gene fem-2 as well as two other protein phosphatase homologues. Despite the significant sequence divergence between C. elegans and C. remanei FEM-2, we used RNAi-mediated gene knockdown to demonstrate that at least some aspects of male development require FEM-2 function in C. remanei. Consistent with this functional conservation, the conspecific interaction between the FEM-2 and the FEM-3 proteins observed in C. elegans also occurs in C. remanei. To further explore whether the rapid evolution of FEM-2 and FEM-3 affects their molecular interactions, we tested for cross-species interactions between the proteins from C. elegans, C. briggsae, and C. remanei. Although all FEM-2/FEM-3 pairs from a single species interact, only two out of six interspecific pairs bind each other, showing that FEM-2 and FEM-3 are coevolving. Both interspecific interactions involved C. briggsae FEM-3. We constructed chimeric versions of FEM-2 consisting of various combinations of the C. elegans and C. remanei proteins. C. briggsae FEM-3 interacted with all the chimeras, even those that did not interact with either C. elegans or C. remanei FEM-3. We hypothesize that the promiscuity of C. briggsae FEM-3 reflects an increased reliance on evolutionarily constrained regions of FEM-2 for binding. If so, our data support the notion that the coevolution of two interacting proteins sometimes involves a shift in the domains that contribute to binding.

Patterns and Mechanisms of Evolutionary Transitions between Genetic Sex-Determining Systems

“…A thorough test of this hypothesis requires investigating how genes in the sex-determination pathway coevolve. There is growing evidence that such coevolution is occurring (Haag and Ackerman 2005;Stothard and Pilgrim 2006), and that it is associated with rapid evolution of sex-determining genes, often without sex-determination transitions or structural pathway rearrangements (Ferris et al 1997;O'Neill and O'Neill 1999;Chandler et al 2012). The evolutionary flexibility of sex determination may therefore be even higher than is currently appreciated.…”

Experimental Evolution of The caenorhabditis Elegans sex Determination Pathway

“…This prediction, too, enjoys empirical support. For instance, tra‐2 and fem‐3 in Caenorhabditis nematodes have coevolved in a species‐specific manner (Haag et al 2002), as have fem‐2 and fem‐3 (Stothard and Pilgrim 2006).…”

Mutations in Two Independent Pathways Are Sufficient to Create Hermaphroditic Nematodes

“…Orexin is a molecule that regulates wakefulness and other physiological functions, and is strongly implicated in narcolepsy and cataplexy, as well as disorders of sleep and arousal (6).…”