The luciferase gene is fused behind a promoter of interest in a genetically engineered mouse. Luciferase is synthesized, which upon exposure to administered luciferin causes a chemiluminescent reaction to occur with a wavelength of 560 nm. Hence this effectively provides an internal indicator light, which turns on when the gene of interest is upregulated and turns off when it is no longer synthesized. Using highly sensitive optical detection systems capable of counting single photons, this light signal can be measured through several centimeters of biologically soft tissue, due to the fact that although tissue is highly light scattering at 560 nm wavelength, absorption is modest. An added advantage of this method is that serial measurements can be made in the same animals over time thus minimizing both the number of animals needed as well as decreasing the variance of the data collected.
This technology can examine both stably integrated and transiently transfected bioluminescent reporter gene fusions in both cell culture and living mice. For the in vivo study of mice luciferin (126 mg/kg), the substrate for luciferase, will be administered intravenously (if they already have catheters implanted) or intraperitoneally 20 min before measurements are made. The mice will be anesthetized and placed in a light tight chamber. The image will be collected over 5 to 30 minutes.