A common hot spot for somatic and germline mutations in rat mitochondrial DNA: analysis by fluorescence-based SSCP

To estimate the degree of sequence heterogeneity of mtDNA, we have developed an efficient system for mutant detection using fluorescence-based single strand conformational polymorphism (F-SSCP). The F-SSCP analysis 200 clones from Wistar rat and sequencing of 2 clones from each 40 inbred Wistar rats at the age of 7 weeks detected no sequence differences, suggesting that the mtDNA sequence heterogeneity is low in young rat hearts. One of the 387 clones isolated from a Donryu rat showed a different mobility in the F-SSCP from other clones. Sequencing of the mutant clone revealed double contiguous TT-->CC transitions at nucleotide positions 15443 and 15444, compared with the normal Donryu clone. The nucleotide at 15444 was different between the Wistar and Donryu rats, indicating that this is the site of germline mutation. These results suggest that the somatic and germline mutations can occur at a common hot spot.