**3. Constructing bioluminescent mammalian cells and animal models**

In the following sections the application of biological models expressing luciferase are described in detail. Mammalian systems do not naturally express luciferase and therefore these systems must be engineered to expresse the enzyme. A vector capable of constitutive expression of luciferase or vectors designed to achieve controlled expression of the enzyme can be used Fusion genes can be used as reporter constructs to track gene delivery and integration. Expression of fusion proteins can be used to follow protein localization and protein-protein interactions. Cells with stable expression of luciferase can be used for in vitro assays or be injected into animals to examine metabolism, immunity, angiogenesis, or to establish disease that can be monitored using BLI. Additionally, transgenic animals may also be developed where reporter gene expression is introduced through the germline.
