Somatic sex determination in Caenorhabditis elegans is modulated by SUP-26 repression of tra-2 translation

Translational repression mediated by RNA-binding proteins or micro RNAs has emerged as a major regulatory mechanism for fine-tuning important biological processes. In Caenorhabditis elegans, translational repression of the key sex-determination gene tra-2 (tra, transformer) is controlled by a 28-nucleotide repeat element, the TRA-2/GLI element (TGE), located in its 3′ untranslated region (UTR). Mutations that disrupt TGE or the germline-specific TGE-binding factor GLD-1 increase TRA-2 protein expression and inhibit sperm production in hermaphrodites. Here we report the characterization of the sup-26 gene, which regulates sex determination in the soma and encodes an RNA recognition motif (RRM)-containing protein. We show that SUP-26 regulates the level of the TRA-2 protein through TGE in vivo and binds directly to TGE in vitro through its RRM domain. Interestingly, SUP-26 associates with poly(A)-binding protein 1 (PAB-1) in vivo and may repress tra-2 expression by inhibiting the translation-stimulating activity of PAB-1. Taken together, our results provide further insight into how mRNA-binding factors repress translation and modulate sexual development in different tissues of C. elegans.