Accumulation of point mutations in mitochondrial DNA of aging mice.
Mitochondrial DNA (mtDNA) exists in a highly genotoxic environment created by exposure to reactive oxygen species, somewhat deficient DNA repair, and the relatively low fidelity of polymerase gamma. Given the severity of the environment, it was anticipated that mutation accumulation in the mtDNA of aging animals should exceed that of nuclear genes by several orders of magnitude. We have analyzed fragments amplified from the D-loop region of mtDNA from 2 to 22-month-old mice. The amplified 432 bp fragments were cloned into plasmid vectors, and plasmid DNAs from individual clones were purified and sequenced. None of 110 fragments from young mice contained a mutation, while 9 of 87 clones originating from old animals contained base substitutions (chi square = 11.9, P<0.001). The estimated mutation frequency in mtDNA from old mice was 11.6+/-2.7 or 25.4+/-7.8 per 10(5) nucleotides (depending on assumptions of clonality), which exceeds existing estimates for mutation frequencies for nuclear genes by approximately 1000-fold. Our data suggest that at 22 months of age, which roughly corresponds to 3/4 of the mouse natural life span, most mtDNA molecules carry multiple point mutations.
Khaidakov
Magomed
M
Division of Genetic and Reproductive Toxicology, US FDA National Center for Toxicological Research, 3900 NCTR Road, Jefferson, AR 72079, USA.
Heflich
Robert H
RH
Manjanatha
Mugimane G
MG
Myers
Meagan B
MB
Aidoo
Anane
A
D000375:Aging / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D004252:DNA Mutational Analysis; D017931:DNA Primers / Q000737:chemistry; D004272:DNA, Mitochondrial / Q000235:genetics*; D005787:Gene Frequency; D014644:Genetic Variation; D008099:Liver / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D010957:Plasmids; D017354:Point Mutation; D016133:Polymerase Chain Reaction
D017931:DNA Primers; D004272:DNA, Mitochondrial