In vivo imaging of MLC2v-luciferase, a cardiac-specific reporter gene expression in mice

A reporter or marker gene that is detectable by in vivo imaging permits longitudinal monitoring of certain fundamental biological processes (eg, differentiation) within the context of physiologically authentic environments. Tissue-specific expression of a reporter gene can be achieved when it is under the transcriptional control of a tissue-specific promoter. The objective of this study was to construct a plasmid vector containing firefly luciferase (Fluc) marker gene downstream of the promoter sequence of rat ventricular myosin light chain 2 (MLC2v); to detect the in vivo expression of this cardiac-specific reporter (MLC2v-Fluc) in the mouse heart by bioluminescent imaging; and to correlate the bioluminescent signal with postmortem luminometer assay. MLC2v-Fluc plasmid was generated by molecular cloning of 3 kb promoter sequence into a pGL3-Basic vector containing the Fluc reporter. Twenty microg of MLC2v-Fluc plasmid DNA in phosphate-buffered saline was directly injected into mouse myocardium through a midline sternotomy. At 1 week after injection, MLC2v-Fluc expression was detected by in vivo bioluminescent imaging in 60% of injected animals; the average in vivo signal intensity was (1.5 +/- 0.6) x 10(4) radiance (p/sec/cm2/sr); in vivo signal was well above the detection threshold over 3 weeks after injection. In vivo bioluminescent signal is correlated (r2 = 0.8) with the luminometer assay results from homogenized heart samples. The capability of noninvasive imaging of the MLC2v-Fluc in the heart will encourage applications that aim at monitoring and tracking the marker gene expression over time in cells undergoing cardiac differentiation.