Lionnet, T. et al. Nat. Methods 8, 165–170 (2011).

Park, H.Y. et al. Science 343, 422–424 (2014).

Rather than rely on exogenous reporters to monitor gene expression, a team of researchers has generated a transgenic mouse with fluorescently labeled endogenous mRNA. In 2011, Lionnet et al. published a report in Nature Methods describing a transgenic mouse that expresses an array of binding sites for the MS2 bacteriophage capsid protein (MCP) in the 3′ untranslated region of the β-actin gene. Park et al. have now crossed this mouse with a strain expressing an MCP-GFP fusion, which allowed them to follow MCP-GFP–labeled endogenous β-actin in all mouse tissues. They looked at expression patterns and localization dynamics of β-actin in primary fibroblasts and cultured neurons as well as acute brain slices and saw different modes of localization in the different cell types.