ena-STUDY-The Francis Crick Institute-18-10-2017-14:32:04:730-14
Aberrant ribonucleotide incorporation and multiple deletions in mitochondrial DNA of the murine MPV17 disease model
All DNA polymerases misincorporate ribonucleotides despite their preference for deoxyribonucleotides, and analysis of cultured cells indicates that mammalian mitochondrial DNA (mtDNA) tolerates such replication errors. However, it is not clear to what extent ribonucleotides are incorporated into the mtDNA of solid tissues, or whether they might play a role in human pathologies. Here, we show that the DNA in mitochondria of solid tissues contains many more embedded ribonucleotides than that of cultured cells, consistent with the former's high ratio of ribonucleotide to deoxynucleotide triphosphates, and that rAMPs are the predominant ribosubstitution events. This pattern changes in a mouse model of Mpv17 deficiency, as rGMPs are the major embedded ribonucleotides of mtDNA. However, while mitochondrial dGTP is reduced in the liver of the KO mice, the brain shows no change in the overall dGTP pool, leading us to infer that Mpv17 determines the local concentration or quality of dGTP. Embedded rGMPs are expected to impede DNA replication more than other rNMPs, and elevated rGMP incorporation is associated with early-onset mtDNA depletion in liver and late-onset multiple deletions in brain of the Mpv17 ablated mice. These findings suggest that aberrant ribonucleotide incorporation is a primary mtDNA abnormality that can result in pathology.
All DNA polymerases misincorporate ribonucleotides despite their preference for deoxyribonucleotides, and analysis of cultured cells indicates that mammalian mitochondrial DNA (mtDNA) tolerates such replication errors. However, it is not clear to what extent ribonucleotides are incorporated into the mtDNA of solid tissues, or whether they might play a role in human pathologies. Here, we show that the DNA in mitochondria of solid tissues contains many more embedded ribonucleotides than that of cultured cells, consistent with the former's high ratio of ribonucleotide to deoxynucleotide triphosphates, and that rAMPs are the predominant ribosubstitution events. This pattern changes in a mouse model of Mpv17 deficiency, as rGMPs are the major embedded ribonucleotides of mtDNA. However, while mitochondrial dGTP is reduced in the liver of the KO mice, the brain shows no change in the overall dGTP pool, leading us to infer that Mpv17 determines the local concentration or quality of dGTP. Embedded rGMPs are expected to impede DNA replication more than other rNMPs, and elevated rGMP incorporation is associated with early-onset mtDNA depletion in liver and late-onset multiple deletions in brain of the Mpv17 ablated mice. These findings suggest that aberrant ribonucleotide incorporation is a primary mtDNA abnormality that can result in pathology.