Translation-dependent mRNA localization to Caenorhabditis elegans adherens junctions.

mRNA localization is an evolutionarily widespread phenomenon that can facilitate subcellular protein targeting. Extensive work has focused on mRNA targeting through "zip-codes" within untranslated regions (UTRs), while much less is known about translation-dependent cues. Here, we examine mRNA localization in Caenorhabditis elegans embryonic epithelia. From an smFISH-based survey, we identified mRNAs associated with the cell membrane or cortex, and with apical junctions in a stage- and cell type-specific manner. Mutational analyses for one of these transcripts, dlg-1/discs large, revealed that it relied on a translation-dependent process and did not require its 5' or 3'UTRs. We suggest a model in which dlg-1 transcripts are co-translationally localized with the nascent protein: first the translating complex goes to the cell membrane using sequences located at the carboxy-terminus/3' end, and then apically using amino-terminal/5' sequences. These studies identify a translation-based process for mRNA localization within developing epithelia and determine the necessary cis-acting sequences for dlg-1 mRNA targeting.