Long term expression of bicistronic vector driven by the FGF-1 IRES in mouse muscle

Our data demonstrate that the efficiency of the FGF-1 IRES is comparable to that of the EMCV IRES for long term expression of bicistronic transgenes in mouse muscle, whereas the FGF-2 IRES has a very poor activity. Interestingly, we show that despite the global decrease of vector expression over time, the ratio of firefly to renilla luciferase remains stable with bicistronic vectors containing the FGF-1 or FGF-2 IRES and is slightly affected with the EMCV IRES, whereas it is clearly unstable for mixed monocistronic vectors. In addition, long term expression more drastically decreases with monocistronic vectors, and is different for single or mixed vector injection.These data validate the use of bicistronic vectors rather than mixed monocistronic vectors for long term expression, and support the use of the FGF-1 IRES. The use of a cellular IRES over one of viral origin is of particular interest in the goal of eliminating viral sequences from transgenic vectors. In addition, the FGF-1 IRES, compared to the EMCV IRES, has a more stable activity, is shorter in length and more flexible in terms of downstream cloning of second cistrons. Finally, the FGF-1 IRES is very attractive to develop multicistronic expression cassettes for gene transfer in mouse muscle.Gene delivery to skeletal muscle is a promising strategy for the treatment of muscle disorders such as myopathies [1,2]. Furthermore, molecules containing secretion sequences can be expressed in muscle tissue and targeted to pathologies residing in other organs. Muscle is a highly vascularized tissue, often regarded as serving endocrine functions. By expressing therapeutic concentrations of secreted proteins, such as angiogenic and neurotrophic factors, in the muscle, a number of therapeutic applications can be envisioned. Skeletal muscle has been used for the production of IL-10 in gene therapy against atherosclerosis, coagulation factors against haemophilia, erythropoietin against anaemia and influenza protein for v