For the determination of the enzymatic activity of luciferase, cells were lysed in Reporter Lysis Buffer (Promega). For luciferase activity assays from tissue, weight of tissue fragments was determined and fragments were homogenized in proportional volumes of Reporter Lysis Buffer using Lysing Matrix A on a FastPrep-24 (MP Biomedicals). Lysates were mixed with LARII (Promega) and measured in a luminometer (Berthold). For in vivo imaging, mice were injected i.v. with 150 mg/kg of D-luciferin (Synchem) in PBS, anesthetized using Isofluran (Baxter) and monitored using an IVIS 200 imaging system (CaliperLS). Photon flux was quantified using the Living Image 3.2 software (CaliperLS).