Post-transcriptional controls of mRNA activity are crucial for development of the nematode Caenorhabditis elegans. The onset of spermatogenesis in hermaphrodites is achieved by translational repression of the sex-determining gene
tra-2; this repression depends on a direct repeat element (DRE) located in the 3' untranslated region (3'UTR) of the
tra-2 mRNA. In addition, the switch from spermatogenesis to oogenesis in hermaphrodites depends on a negative regulatory element in the 3'UTR of the transcript of a second sex-determining gene,
fem-3. Thus, post-transcriptional controls of
tra-2 and
fem-3 are essential for development of an XX animal as a hermaphrodite instead of a female. Post-transcriptional regulation by regulatory elements localized in the 3'UTR also influences somatic development. Thus, the
tra-2 DRE also regulates
tra-2 somatic expression and the 3'UTR of
lin-14 is involved in the post-transcriptional regulation of larval-specific somatic cell lineages. The relevance of these controls to the regulation of maternal RNA is