11 Furthermore, the luciferase gene was engineered to monitor the stem cell fate, for example, the differentiation of stem cells into early neurons in vivo.
9, 10 The survival rate of the transplanted cells, which is an important factor to determine the outcome of translational stem cell studies, can be derived from the quantitative BLI signal, which requires adenosine triphosphate for the luciferase enzyme reaction. The efficiency of in vivo light production enables the detection of a minimal number of 1500 to 3000 neural stem cells (NSCs) engrafted to the mouse brain, through the intact skull, connecting tissue, and skin.
3 – 8 BLI has some unique advantages such as the light is produced directly in the Fluc-expressing cells without the need of an excitation source, promoting a very low background and high signal-to-noise ratios. 1 While the first bioluminescence imaging (BLI) was limited to tumor applications, 2 the firefly gene and the detection hardware were continuously optimized to monitor other cell types, such as stem cells and neurons, in deep tissue with higher or equal sensitivity and specificity compared to, for example, fluorescence imaging. 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 in vivo.įirefly luciferases (Flucs) are very efficient molecular and biochemical tools to track cells and proteins and to monitor gene expression in living organisms. Spectral unmixing predicts the ratio of luciferases in vitro and a mixture of cells precisely for cortical grafts, however, with less accuracy for striatal grafts. 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 in vitro and after transplantation into the mouse brain in vivo. 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. The luciferase gene can be engineered to target and monitor almost every cell and biological process quantitatively in vitro and even from deep tissue in vivo. In contrast to the more widely used fluorescence imaging, which requires light excitation, in BLI the light is exclusively generated by the enzyme luciferase. Bioluminescence imaging (BLI) is an optical imaging method that can be translated from the cell culture dish in vitro to cell tracking in small animal models in vivo.
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