Intracellular targets for DNA delivery: nuclei and mitochondria

All discussions on the intracellular delivery of DNA are based on a seemingly evident assumption that the key task is to bring the intact DNA into the cell cytoplasmic compartment, and then the DNA will find its way to a right place. The nuclear genome is usually considered to be this "right place." However, until recently, in numerous experiments on the intracellular DNA delivery, it has been almost completely neglected that cells contain another genome, the mitochondrial one. And, in many cases, this genome should become a therapeutic target. Being delivered inside the cell, DNA actually has two ways to go--to nuclei and to mitchondria, and the proper choice between these two ways may be decisive for the success of gene therapy. Certainly, nuclear DNA delivery is far more advanced than mitochondrial delivery one. In addition, free DNA from the cytoplasm has a strong tendency to spontaneously associate with the nuclear genome. Mitochondria as a target for DNA have much less accessibility, still remaining an important site to reach. Whereas the nuclear delivery of DNA is under active investigation and just awaits better protocols to be elaborated, practically applicable mitochondrial DNA delivery is at its early stage and must be developed almost from scratch. In our studies on intracellular DNA delivery, we have attempted to develop new protocols for targeting DNA to nuclei and to mitochondria. In this chapter we provide a brief description of our recent experiments in both of these important areas.