Multiple deletions in mitochondrial DNA are present in senescent mouse brain

We report for the first time that multiple deletions occur during ageing of mice brain mitochondrial DNA (mtDNA). Deletions were detected by electrophoresis after amplification using the nested Polymerase Chain Reaction (N-PCR) method. Three mutant mtDNAs with 3726-, 3867- and 4236-bp deletions were directly detected by N-PCR which were undetectable in young brain mice. Each deletion was sequenced: in the region containing the junction fragment three different repeats of 13, 14 and 15 bp were observed. These results support the hypothesis that direct repeats are an initiating factor involved in ageing-associated accumulation of deletion.