The wild type
tra-2 gene promotes female development in XX hermaphrodites. In the hermaphrodite germline,
tra-2 is repressed at the translational level to achieve spermatogenesis. Two 28nt direct repeat elements (DREs), located in the
tra-2 3' untranslated region (3'UTR), are necessary for translational control. XX gain-of-function
tra-2 mutants have disrupted DREs and develop as females; they make no sperm. In an attempt to identify translational regulators of
tra-2, we have focused on the
laf-1 gene. Five
laf-1 mutations have been independently isolated. All five cause semi-dominant feminization of the XX germline, recessive lethality, and appear to reduce
laf-1 gene function. Three lines of evidence suggest that
laf-1 may control
tra-2 translation. First,
laf-1 mutations disrupt the regulation of a transgene by the DREs. Second, double mutant analysis indicates
laf-1 acts upstream of
tra-2 in a genetic hierarchy, a predicted position for a repressor of
tra-2. Third, the germline feminization caused by
laf-1 mutations is a predicted phenotype for a loss-of-function mutation in a translational repressor of
tra-2. Since,
laf-1 acts upstream of
tra-2 in a genetic hierarchy, we next asked where
laf-1 acts with respect to two other sex determination genes,
tra-3 and
tra-1.
tra-3 and
tra-1, like
tra-2, promote female development; loss of activity of either gene leads to male development. In previous studies,
tra-2 and
tra-3 have been inseparable in the genetic hierarchy. However, the
laf-1/+;
tra-3(lf) double mutant is feminized both in the germline and soma. The simplest interpretation is that
tra-3 acts upstream of
laf-1, and may promote female fate by inactivating the translational repression on
tra-2.
tra-1 is thought to be the terminal regulator in the sex determination pathway, and therefore, necessary for female development. Surprisingly, the
laf-1tra-1(lf)/+
tra-1(lf) double mutant is feminized both in the germline and soma, suggesting that
tra-1 activity is not essential for female development The implications of these results will be discussed with respect to the sex determination pathway.