POSTTRANSCRIPTIONAL REGULATION OF SEX DETERMINATION IN CAENORHABDITIS-ELEGANS - WIDESPREAD EXPRESSION OF THE SEX-DETERMINING GENE FEM-1 IN BOTH SEXES

The fem-1 gene of C. elegans is one of three genes required for all as pects of male development in the nematode. Cur rent models of sex dete rmination propose that the products of the fem genes act in a novel si gnal-transduction pathway and that their activity is regulated primari ly at the post-translational level in somatic tissues. We analyzed the expression of fem-1 to determine whether it revealed any additional l evels of regulation. Both XX hermaphrodites and XO males express fem-1 at approximately constant levels throughout development. Somatic tiss ues in hermaphrodites adopt female fates, but they nonetheless express fem-2 mRNA and FEM-1 protein, suggesting that the regulation of fem-1 activity is post-transcriptional and probably post-translational. A c ompact promoter directs functional expression of fem-1 transgenes, as assayed by their masculinizing activity in fem-1 mutants. Activity als o requires any two or more introns, suggesting that splicing may enhan ce fem-1 expression. The minimal noncoding sequences required for acti vity of fem-1 transgenes suffice to direct expression of a fem-1::lacZ reporter gene in all somatic tissues in both sexes. Many fem-1 transg enes, including those that rescue male somatic development in fem-1 mu tants, paradoxically feminize the germline. We suggest that they do so by interfering with the germline expression of the endogenous fem-1 g ene.