Mitochondrial DNA deletions in mice in men: substantia nigra is much less affected in the mouse.

Mitochondrial DNA (mtDNA) deletions have been reported to accumulate to high levels in substantia nigra of older humans, and these mutations are suspected of causing age-related degeneration in this area. We have compared levels of mtDNA deletions in humans and mice and report here that levels of deletions in the mouse are very significantly lower than in humans. While human mtDNA from substantia nigra contained more than 5% of deleted molecules, mouse substantia nigra contained less than 0.5%. These results imply that mtDNA deletions are unlikely to play any significant role in of murine substantia nigra aging and further call for caution in using mouse models in studies of the role of mtDNA deletions in aging and neurodegeneration. On a more general note, these results support the view that critical targets of the various aging processes may differ significantly between distant species.

Quantitation of Mitochondrial DNA Deletions Via Restriction Digestion/Long-Range Single-Molecule PCR.

Quantification of deletions in mtDNA is a long-standing problem in mutational analysis. We describe here an approach that combines the power of single-molecule PCR of the entire mitochondrial genome with the enrichment of the deletions by restriction digestion. This approach is indispensable if information about wide range of deletion types in a sample is critical, such as in studies concerning distribution of deletion breakpoints (as opposed to approaches where fraction of a single deletion or a limited set of deletions is used as a proxy for total deletion load). Because deletions in a sample are quantified almost exhaustively, the other important application of this approach involves studies where only small amounts of tissue, such as biopsies, are available.