A high-sensitivity bi-directional reporter to monitor NF-κB activity in cell culture and zebrafish in real time

Nuclear factor (NF)-kappa B transcription factors play major roles in numerous biological processes including development and immunity. Here, we engineered a novel bi-directional NF-kappa B-responsive reporter, pSGNluc, in which a high-affinity NF-kappa B promoter fragment simultaneously drives expression of luciferase and GFP. Treatment with TNF alpha (also known as TNF) induced a strong, dosedependent luciferase signal in cell culture. The degree of induction over background was comparable to that of other NF-kappa B-driven luciferase reporters, but the absolute level of expression was at least 20-fold higher. This extends the sensitivity range of otherwise difficult assays mediated exclusively by endogenously expressed receptors, as we show for Nod1 signaling in HEK293 cells. To measure NF-kappa B activity in the living organism, we established a transgenic zebrafish line carrying the pSGNluc construct. Live in toto imaging of transgenic embryos revealed the activation patterns of NF-kappa B signaling during embryonic development and as responses to inflammatory stimuli. Taken together, by integrating qualitative and quantitative NF-kappa B reporter activity, pSGNluc is a valuable tool for studying NF-kappa B signaling at high spatiotemporal resolution in cultured cells and living animals that goes beyond the possibilities provided by currently available reporters.