[Is it possible to generate artificial mitochondrial genome?]

The mitochondrial genome (mtDNA) is a circular DNA of approximately 16.5 kbp, present at several thousand copies per cell. Although mtDNA is extremely small compared with the nuclear genome, it is quite important for life system because it encodes components essential for ATP production through oxidative phosphorylation. Since mtDNA mutations are thought to be implicated in a wide range of diseases, gene therapies targeting mtDNA are expected to provide promising treatment options for such disorders; however, current methods allow only limited manipulation of mtDNA. In this article, our recent efforts toward establishing mtDNA writing, a technology that would enable unrestricted and precise manipulation of mtDNA, are introduced. We hypothesized that creation of specialized host cells that preferentially accept exogenous mtDNA would be the key to achieving mtDNA writing. We named such host cells "e-mt cells" and assumed that cells maintaining a deviated type of mtDNA in a homoplasmic state could function as e-mt cells. To create e-mt cells, we developed a novel mitochondrial transfer method using a microfluidic device. This microfluidic device allowed direct and non-invasive mitochondrial transfer between live single cells by fusing them through a micro aperture (microslit/microtunnel). Furthermore, we successfully demonstrated single-mitochondrion transfer as well as cybrid generation via mitochondrial transfer into ρ⁰ cells. These findings suggest that the microfluidic device has the potential to achieve homoplasmic mtDNA modification through mtDNA cloning and is therefore expected to contribute to the creation of e-mt cells.