CGC Bibliography Paper 5602

Rapid coevolution of the nematode sex-determining genes fem-3 and tra-2.

Haag ES, Wang S, Kimble J

Medline:

12477393

Citation:

Current Biology 12: 2035-2041 2002

Type:

ARTICLE

Genes:

fem-1 fem-2 fem-3 tra-2 twk-19

Abstract:

Unlike many features of metazoan development, sex determination is not widely conserved among phyla [1-3]. However, the recent demonstration [4] that one gene family controls sexual development in Drosophila, C. elegans, and vertebrates suggests that sex determination mechanisms may have evolved from a common pathway that has diverged radically since the Cambrian. Sex determination gene sequences often evolve quickly (e.g., [5, 69 7]), but it is not known how this relates to higher-order pathways or what selective or neutral forces are driving it. In such a rapidly evolving developmental pathway, the fate of functionally linked genes is of particular interest. To investigate a pair of such genes, we cloned orthologs of the key C. elegans male-promoting gene fem-3 from two sister species, C. briggsae and C. remanei. We employed RNA interference to show that in all three species, the male-promoting function of fem-3 and its epistatic relationship with its female-promoting upstream repressor, tra-2, are conserved. Consistent with this, the FEM-3 protein interacts with TRA-2 in each species, but in a strictly species-specific manner. Because FEM-3 is the most divergent protein yet described in Caenorhabditis and the FEM-3 binding domain of TRA-2 is itself hypervariable [8, 9], a key protein-protein interaction is rapidly evolving in concert. Extrapolation of this result to larger phylogenetic scales helps explain the dissimilarity of the sex determination systems across phyla.