Split Luciferase-Fragment Reconstitution for Unveiling RNA Localization and Dynamics in Live Cells

The intracellular distribution and dynamics of RNAs play pivotal roles in various physiological phenomena. The ability to monitor the amount and localization of endogenous RNAs in living cells allows for elucidating the mechanisms of various intracellular events. Protein-based fluorescent RNA probes are now widely used to visualize and analyze RNAs in living cells. However, continuously monitoring the temporal changes in RNA localization and dynamics in living cells is challenging. In this study, we developed a bioluminescent probe for spatiotemporal monitoring of RNAs in living cells by using a split-luciferase reconstitution technique. The probe consists of split fragments of a bioluminescent protein, NanoLuc, connected with RNA-binding protein domains generated from a custom-made mutation of a PUM-HD. The probe showed rapid luminescence intensity changes in response to an increase or decrease in the amount of a target RNA in vitro. In live-cell imaging, temporal alteration of the intracellular distribution of endogenous β-actin mRNA was visualized in response to extracellular stimulation. Furthermore, the application of the probe to the visualization of the specific localization of β-actin mRNA in primary hippocampal neurons was conducted. These results demonstrate the capability of the bioluminescent RNA probe to monitor the changes in localization, dynamics, and the amount of target RNA in living cells.