In Vivo Optical Imaging

Optical imaging was performed using an IVIS Spectrum scanner (Caliper Life Sciences, Hopkinton, MA). EGFP was detected using an excitation light of 500 nm and an emission filter set at 540 nm. tdTomato was detected using an excitation light of 570 nm and an emission filter set at 620 nm as described earlier [25]. To detect the expression of luc in vivo with bioluminescent imaging (BLI), 100 μl of a 30 mg/ml solution of D-luciferin (Promega, P1042, VivoGlo Luciferin, In Vivo Grade, potassium salt) dissolved in PBS was injected intraperitoneally (~3 mg/mouse) 15 minutes prior to imaging. We used an exposure time of 1 second for GFP and tdTomato and 1 minute for BLI, with a 6.4×6.4-cm field of view.