F-box proteins play critical roles promoting hermaphrodite development in two different species of Caenorhabditis. In C. elegans, the F-box protein FOG-2 interacts with GLD-1 to repress the translation of
tra-2 mRNAs. Low TRA-2 activity allows the XX hermaphrodites to make sperm. By contrast, C. briggsae lacks an ortholog of FOG-2, but the F-box protein SHE-1 down-regulates TRA-2; and does so without help from GLD-1. We want to learn how SHE-1 alters the sex-determination process.
Because a missense mutation in the F-box inactivates SHE-1, it might act as a classical F-box protein, bringing a target to the E3 ubiquitin ligase complex to be marked for degradation. To identify potential SHE-1 targets, we used the yeast two-hybrid system. From a screen of about 340,000 cDNAs, we identified three genes that that were represented by multiple, independent clones. The
pqn-94 gene passed two further tests. First, PQN-94 also interacts with SHE-1 when used as bait. Second,
pqn-94(RNAi) partially suppresses
she-1. At 25 deg C,
she-1(
v49); control(RNAi) mothers did not produce hermaphrodites, but
she-1(
v49);
pqn-94(RNAi) mothers produced 7% hermaphrodites. Tests with
she-1(
v35) showed the same pattern of suppression, whereas knocking down
pqn-94 on its own had no phenotype.
To confirm that SHE-1 controls germ cell fates by interacting with PQN-94, we used TALEN technology to generate a
pqn-94 null mutant with a frame-shifting deletion. These
pqn-94(
v203) animals are healthy, but
she-1(
v35);
pqn-94(
v203) mothers produced 12% hermaphrodites at 25 deg C, whereas
she-1(
v35) controls were all female. Since experiments with the null allele resembled those done with RNAi, we conclude that the absence of PQN-94 partially compensates for a loss of SHE-1. This result supports models in which SHE-1 targets PQN-94 for degradation. However, PQN-94 cannot be the sole target of SHE-1, since
pqn-94(
v203) is not completely epistatic to
she-1.