Moss Chloe F, Dalla Rosa Ilaria, Hunt Lilian E, Yasukawa Takehiro, Young Robert, Jones Aleck W E, Reddy Kaalak, Desai Radha, Virtue Sam, Elgar Greg, Voshol Peter, Taylor Martin S, Holt Ian J, Reijns Martin A M, Spinazzola Antonella
MRC Laboratory, Mill Hill, London NW7 1AA, UK.
Department of Clinical Neurosciences, Institute of Neurology, Royal Free Campus, University College London NW3 2PF, UK.
Nucleic Acids Res. 2017 Dec 15;45(22):12808-12815. doi: 10.1093/nar/gkx1009.
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 misincorporation occurs in tissues, or whether this plays a role in human disease. Here, we show that mtDNA of solid tissues contains many more embedded ribonucleotides than that of cultured cells, consistent with the high ratio of ribonucleotide to deoxynucleotide triphosphates in tissues, and that riboadenosines account for three-quarters of them. The pattern of embedded ribonucleotides changes in a mouse model of Mpv17 deficiency, which displays a marked increase in rGMPs in mtDNA. However, while the mitochondrial dGTP is low in the Mpv17-/- liver, the brain shows no change in the overall dGTP pool, leading us to suggest that Mpv17 determines the local concentration or quality of dGTP. Embedded rGMPs are expected to distort the mtDNA and impede its replication, and elevated rGMP incorporation is associated with early-onset mtDNA depletion in liver and late-onset multiple deletions in brain of Mpv17-/- mice. These findings suggest aberrant ribonucleotide incorporation is a primary mtDNA abnormality that can result in pathology.
尽管所有DNA聚合酶都更倾向于脱氧核糖核苷酸，但仍会错误掺入核糖核苷酸。对培养细胞的分析表明，哺乳动物线粒体DNA（mtDNA）能够容忍这种复制错误。然而，目前尚不清楚在组织中错误掺入的程度如何，也不清楚这是否在人类疾病中起作用。在这里，我们表明，实体组织的mtDNA比培养细胞的mtDNA含有更多嵌入的核糖核苷酸，这与组织中核糖核苷酸与三磷酸脱氧核苷酸的高比例一致，并且核糖腺苷占其中的四分之三。在Mpv17缺陷小鼠模型中，嵌入核糖核苷酸的模式发生了变化，该模型显示mtDNA中的rGMP显著增加。然而，虽然Mpv17基因敲除小鼠肝脏中的线粒体dGTP含量较低，但大脑中的总体dGTP池没有变化，这使我们认为Mpv17决定了dGTP的局部浓度或质量。嵌入的rGMP预计会扭曲mtDNA并阻碍其复制，而rGMP掺入增加与Mpv17基因敲除小鼠肝脏中早发性mtDNA耗竭和大脑中迟发性多处缺失有关。这些发现表明，异常的核糖核苷酸掺入是一种原发性mtDNA异常，可导致病理变化。
