Cell and animal imaging of electrically mediated gene transfer.

Electropermeabilization is a nonviral method successfully used to transfer genes into cells in vitro as in vivo. Although it shows promise in field of gene therapy, very little is known on the basic processes supporting the DNA transfer. The aim of the present investigation is to visualize gene electrotransfer and expression both in vitro and in vivo. In vitro studies have been performed by using digitized fluorescence microscopy. Membrane permeabilization occurs at the sides of the cell membrane facing the two electrodes. A free diffusion of propidium iodide across the membrane to the cytoplasm is observed in the seconds following electric pulses. Fluorescently labeled plasmids only interact with the electropermeabilized side of the cell facing the cathode. The plasmid interaction with the electropermeabilized cell surface is stable over a few minutes. Changing the polarity and the orientation of the pulses lead to an increase in gene expression. In vivo experiments have been performed in Tibialis Cranialis mice muscle. Electric field application lead to the in vivo expression of plasmid DNA. We directly visualize gene expression of the Green Fluorescent Protein (GFP) on live animals. GFP expression is shown to be increased by applying electric field pulses with different polarities and orientations.