Post-translational regulation of the sex determining protein TRA-1

Hermaphrodite development in the nematode Caenorhabditis elegans requires the activity of the terminal global sex-determining gene, tra-1. In XO animals tra-1 activity is repressed to allow male development. tra-1 activity is regulated by a number of genes that act in a well defined genetic pathway: however, the molecular mechanisms of TRA-1 regulation are not understood. I report a physical interaction between TRA-1 and the protein phosphatase, FEM-2. fem-2 is one of three fem genes that act upstream of tra-1 in XO animals to repress tra-1 activity. I propose that FEM-2 acts to promote male development by dephosphorylating and repressing TRA-1 activity. Consistent with this hypothesis I have demonstrated that TRA-1 is phosphorylated in vivo. These results represent the first indication of a biochemical mechanism of TRA-1 regulation.; During female somatic development the activities of three FEM proteins are inhibited by the activity of the membrane protein TRA-2 via a FEM-3/TRA-2 interaction. Thus, TRA-2 indirectly activates TRA-1. I report a direct interaction between the intracellular domain of TRA-2 and TRA-1. The TRA-1-binding domain within TRA-2 is distinct from the FEM-3-binding domain and is capable of partially feminizing XO males. Several unusual mutant alleles tra-2 specifically disrupt the TRA-2/TRA-1 interaction and eliminate the feminizing activity of the TRA-1-binding domain of TRA-2. My results suggest the TRA-2 intracellular domain can interact with TRA-1 in vivo and can increase TRA-1 feminizing activity. Consistent with a TRA-1/TRA-2 interaction in vivo, I demonstrate the ability of both TRA-1 and the TRA-2 intracellular domain to co-localize in the nucleus. My results suggest that TRA-2 plays a previously unsuspected role in sex determination by regulating TRA-1 through a physical interaction in the nucleus.