Quantitative Bioluminescent Imaging of AHR Activity Using a Thermostable Variant of the Fungal Luciferase nnLuz

Bioluminescent reporters are important tools in biomedical research. Luciferase enzymes, expressed as part of transgenes or inserted into endogenous genomes, can be used to visualise molecular events with minimally invasive experiments. However, the reaction requires addition of the substrate, luciferin. Organisms with self-sustained luminescence that both express the luciferase and produce the luciferin would allow continuous, convenient and affordable acquisition of physiological information. The Neonothopanus nambi fungal bioluminescence pathway has been harnessed in this way to produce autoluminescent plants. However, progress into mammalian models has been hindered by temperature sensitivity of the wild-type fungal luciferase (nnLuz). We tested the efficacy of a thermostable variant of nnLuz (nnLuz_v3) in vivo at physiologically relevant levels, by generating a reporter of endogenous Cyp1a1 expression as a measure of aryl hydrocarbon receptor (AHR) activation. Previously published Cyp1a1-Fluc mice allowed a comparison between the novel luciferase nnLuz_v3 and the established firefly luciferase (Fluc). In Cyp1a1-nnLuz_v3 mice, the bioluminescence signal was sufficiently stable to enable well-resolved luminescence images to be captured on standard in vivo imaging equipment and consumer-grade cameras. These results derisk the use of nnLuz_v3 as an in vivo molecular reporter whilst providing a novel tool for AHR drug discovery and research.