Isolation of mtDNA knock-out mice by introduction of disease-related mtDNA mutation

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For isolation of the mouse mtDNA-less (rho^0) cell lines, we searched for various anti-mitochondrial drugs which were expected to decrease the mtDNA content, and found that treatment with ditercalinium, an antitumor bis-intercalating agent, was extremely effective for completely excluding mtDNA in all the mouse cell lines we tested. The resulting rho^0 mouse cells were successfully used for trapping mtDNA of living nerve cells into dividing cultured cells by fusion of the rho^0 cells with mouse brain synaptosomes, which represent synaptic endings isolated from nerve cells. The cybrid clones with neuronal mtDNA obtained all restored mitochondrial translation activity similarly irrespective of whether the mtDNA was derived from young or aged mice, suggesting that at least defects in mitochondrial genomes are not involved in the age-associated mitochondrial dysfunction observed in the brain of aged mice. Furthermore, we could trap a very small amount of a common 5823 bp-deletion mutant mtDNA (DELTAmtDNA^<5823>) that was detectable by PCR in the cybrid clones. As the amount of mutant mtDNA with large-scale deletions was expected to increase during prolonged cultivation of the cybrids, these cells should be available for establishment of mice containing the deletion mutant mtDNA.