Figure 1

Two routes to the nucleus in the germline cell-fate pathway in C. elegans. HER-1 is a secreted protein that specifies male cell fates in C. elegans, including spermatogenesis. It binds the transmembrane receptor TRA-2 and inhibits its activity in XO animals, causing male development. The inactivation of TRA-2 permits three interacting cytoplasmic proteins - FEM-1, FEM-2 and FEM-3 - to direct male fates by inhibiting the transcription factor TRA-1. When TRA-1 is inactive, genes like fog-3 are free to specify spermatogenesis. (Although XX hermaphrodites do not produce HER-1, the FOG-2 and GLD-1 proteins prevent the production of TRA-2 during larval development, allowing the FEM proteins to direct spermatogenesis for a brief time in a female gonad.) Surprisingly, a fragment cleaved from TRA-2 (TRA-2ic, for intracellular) can also interact directly with TRA-1. Mutations that block this interaction cause oogenesis. In the figure, male-promoting factors are shown in blue, female ones in pink, and all proteins that touch are known to interact.