Quantitative dual-color bioluminescence imaging in the mouse brain.

Bioluminescence imaging (BLI) is an optical imaging method that can be translated from the cell culture dish to cell tracking in small animal models . In contrast to the more widely used fluorescence imaging, which requires light excitation, in BLI the light is exclusively generated by the enzyme luciferase. The luciferase gene can be engineered to target and monitor almost every cell and biological process quantitatively and even from deep tissue . While initially used for tumor imaging, bioluminescence was recently optimized for mouse brain imaging of neural cells and monitoring of viability or differentiation of grafted stem cells. Here, we describe the use of bright color-shifted firefly luciferases (Flucs) based on the thermostable x5 Fluc that emit red and green for effective and quantitative unmixing of two human cell populations and after transplantation into the mouse brain . Spectral unmixing predicts the ratio of luciferases and a mixture of cells precisely for cortical grafts, however, with less accuracy for striatal grafts. This dual-color approach enables the simultaneous visualization and quantification of two cell populations on the whole brain scale, with particular relevance for translational studies of neurological disorders providing information on stem cell survival and differentiation in one imaging session .