title: Ribonucleotide reductase is not limiting for mitochondrial DNA copy number in mice.
abstract: Ribonucleotide reductase (RNR) is the rate-limiting enzyme in deoxyribonucleoside triphosphate (dNTP) biosynthesis, with important roles in nuclear genome maintenance. RNR is also essential for maintenance of mitochondrial DNA (mtDNA) in mammals. The mechanisms regulating mtDNA copy number in mammals are only being discovered. In budding yeast, RNR overexpression resulted in increased mtDNA levels, and rescued the disease phenotypes caused by a mutant mtDNA polymerase. This raised the question of whether mtDNA copy number increase by RNR induction could be a strategy for treating diseases with mtDNA mutations. We show here that high-level overexpression of RNR subunits (Rrm1, Rrm2 and p53R2; separately or in different combinations) in mice does not result in mtDNA copy number elevation. Instead, simultaneous expression of two RNR subunits leads to imbalanced dNTP pools and progressive mtDNA depletion in the skeletal muscle, without mtDNA mutagenesis. We also show that endogenous RNR transcripts are downregulated in response to large increases of mtDNA in mice, which is indicative of nuclear-mitochondrial crosstalk with regard to mtDNA copy number. Our results establish that RNR is not limiting for mtDNA copy number in mice, and provide new evidence for the importance of balanced dNTP pools in mtDNA maintenance in postmitotic tissues.
authors: Biomedicum Helsinki, Research Programme of Molecular Neurology, University of Helsinki, Haartmaninkatu 8, PO Box 63, 00290 Helsinki, Finland.
authors: Emil
authors: E
authors: Ylikallio
authors: Jennifer L
authors: JL
authors: Page
authors: Xia
authors: X
authors: Xu
authors: Milla
authors: M
authors: Lampinen
authors: Gerold
authors: G
authors: Bepler
authors: Tomomi
authors: T
authors: Ide
authors: Henna
authors: H
authors: Tyynismaa
authors: Robert S
authors: RS
authors: Weiss
authors: Anu
authors: A
authors: Suomalainen
mesh_terms: D000818:Animals; D056915:DNA Copy Number Variations; D004272:DNA, Mitochondrial / Q000737:chemistry / Q000378:metabolism*; D003854:Deoxyribonucleotides / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D018482:Muscle, Skeletal / Q000378:metabolism; D016296:Mutagenesis; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D012264:Ribonucleotide Reductases / Q000235:genetics / Q000378:metabolism*
chemical_list: D004272:DNA, Mitochondrial; D003854:Deoxyribonucleotides; D021122:Protein Subunits; D012264:Ribonucleotide Reductases