Quantification of LucR and LucF activities in tibialis anterior muscle from C57BL/6J mice after bicistronic vector electrotransfer. Comparison between IRESs from EMCV, FGF-1A and FGF-2. A. Schematics of bicistronic expression vectors used to produce LucR and LucF/F+. The bicistronic cassette, transcriptionally regulated by the cytomegalovirus (CMV) promoter, encodes LucR in the first cistron (cap-dependent translation) and LucF (Fig. 1, 2) or LucF+ (Fig. 3, 4, 5) in the second cistron (IRES-dependent translation) [28, 36]. B. Bioluminescent signal quantification. Tibialis anterior muscle was taken from mice 5, 15 or 30 days after electrotransfer. LucR and LucF activities were measured from muscle extracts using a luminometer. LucR and LucF activities were expressed in Relative Luminescent Units per milligram of grinded muscle (RLU/mg) (see Mat. & Meth). Each value corresponds to an individual mouse from an experimental group (n = 5). C. Mean of bioluminescent signal quantification. Mean values of the LucR (top) and LucF (bottom) activities have been represented for each experimental group presented in Fig. 1B (RLU per mg of muscle ± sem, n = 6). D. IRES activity. It was obtained from the values shown in fig. 1B, using the following formula: LucF × 1000/LucR. For each time point, the median value was noted with a "-". No IRES activity could be calculated in the absence of detectable LucR activity.