Unique mutations in mitochondrial DNA of senescence-accelerated mouse (SAM) strains

Mitochondrial DNA (mtDNA) is exclusively inherited maternally and hence cou ld offer a good method for tracing the lineage of mouse strains. We examine d the mtDNA sequence of senescence-accelerated mouse (SAM) strains as well as other laboratory strains of inbred mice to deduce the ancestral strain o f SAM. Four unique mutations were identified at bases 2256, 10,847, 11,181, and 13,053 in SAM strains. The mutations were not found in other mouse str ains including AKR/J, one of the parental strains of SAM. Comparison of the mtDNA sequences also led to the consensus mtDNA sequence of laboratory str ains of inbred mice. The seven laboratory strains of common inbred mice sho wed polymorphisms at base 9348, thymine repeat from base 9818, and adenine repeat from base 9821, and could be classified into five types by combinati on of the differences. Although we could not identify mouse strains with th e same type of mtDNA as SAM in this study, the polymorphisms would provide a promising clue to ascertain the ancestral strain(s) of SAM. The polymorph ism in mtDNA could be used to ascertain the genealogy of other mouse strain s as well.