In many organisms, mRNAs are localised to specific subcellular loci. One of the functions of mRNA localisation is to enrich proteins at their subcellular location through localised transcription. A variety of mechanisms direct mRNA localisation, such as trafficking via the 3′ untranslated region (UTR); however, not all mRNAs require the 3′UTR for their localisation. Now, Cristina Tocchini, Susan Mango and colleagues investigate the localisation of mRNAs in epithelia during formation of Caenorhabditis elegans apical junctions (CeAJs). Using single molecule fluorescence in situ hybridisation (smFISH), the authors characterise the localisation of mRNA transcripts that encode components of the CeAJ and identify dlg-1, which is enriched at the CeAJ in a stage- and cell type-specific manner. dlg-1 constructs without a 5′UTR or 3′UTR remain enriched at CeAJs, indicating that the UTRs are not required for localisation. Using a non-translatable dlg-1 construct and heat-induced inhibition of translation, the researchers show a loss of mRNA localisation at the CeAJ. Finally, structure-function analyses of the DLG-1 protein show that the carboxy-terminal and amino-terminal regions of the protein are required for initial dlg-1 mRNA membrane localisation and subsequent subcellular enrichment, respectively. Together, these data reveal a translation-based mechanism of mRNA localisation.
