An adapted MS2-MCP system to visualize endogenous cytoplasmic mRNA with live imaging in Caenorhabditis elegans

Live imaging of RNA molecules constitutes an invaluable means to track the dynamics of mRNAs, but live imaging in Caenorhabditis elegans has been difficult to achieve. Endogenous transcripts have been observed in nuclei, but endogenous mRNAs have not been detected in the cytoplasm, and functional mRNAs have not been generated. Here, we have adapted live imaging methods to visualize mRNA in embryonic epithelial cells. We have tagged endogenous transcripts with MS2 hairpins in the 3’ Untranslated Region (UTR) and visualized them after adjusting MS2 Coat Protein (MCP) expression. A reduced number of these transcripts accumulate in the cytoplasm, leading to loss-of-function phenotypes. In addition, mRNAs for dlg-1 fail to associate with the adherens junction, as observed for the endogenous mRNA. These defects are reversed by inactivating the nonsense-mediated decay pathway. RNA accumulates in the cytoplasm, dlg-1 associates with the adherens junction, and mutant phenotypes are rescued. These data suggest that MS2 repeats can induce the degradation of endogenous targets and alter the cytoplasmic distribution. Although our focus is RNAs expressed in epithelial cells during morphogenesis, this method can likely be applied to other cell types and stages. Summary statement An adapted MS2-MCP method to tag endogenous transcripts in C. elegans embryos for live imaging without affecting mRNA stability.