title: POLRMT regulates the switch between replication primer formation and gene expression of mammalian mtDNA.
abstract: Mitochondria are vital in providing cellular energy via their oxidative phosphorylation system, which requires the coordinated expression of genes encoded by both the nuclear and mitochondrial genomes (mtDNA). Transcription of the circular mammalian mtDNA depends on a single mitochondrial RNA polymerase (POLRMT). Although the transcription initiation process is well understood, it is debated whether POLRMT also serves as the primase for the initiation of mtDNA replication. In the nucleus, the RNA polymerases needed for gene expression have no such role. Conditional knockout of Polrmt in the heart results in severe mitochondrial dysfunction causing dilated cardiomyopathy in young mice. We further studied the molecular consequences of different expression levels of POLRMT and found that POLRMT is essential for primer synthesis to initiate mtDNA replication in vivo. Furthermore, transcription initiation for primer formation has priority over gene expression. Surprisingly, mitochondrial transcription factor A (TFAM) exists in an mtDNA-free pool in the Polrmt knockout mice. TFAM levels remain unchanged despite strong mtDNA depletion, and TFAM is thus protected from degradation of the AAA(+) Lon protease in the absence of POLRMT. Last, we report that mitochondrial transcription elongation factor may compensate for a partial depletion of POLRMT in heterozygous Polrmt knockout mice, indicating a direct regulatory role of this factor in transcription. In conclusion, we present in vivo evidence that POLRMT has a key regulatory role in the replication of mammalian mtDNA and is part of a transcriptional mechanism that provides a switch between primer formation for mtDNA replication and mitochondrial gene expression.
authors.affiliation: Department of Mitochondrial Biology, Max Planck Institute for Biology of Ageing, 50931 Cologne, Germany.
authors.forename: Inge
authors.initials: I
authors.lastname: Kühl
authors.affiliation: Department of Mitochondrial Biology, Max Planck Institute for Biology of Ageing, 50931 Cologne, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Miranda
authors.affiliation: Department of Medical Biochemistry and Cell Biology, Göteborgs Universitet, 40530 Göteborg, Sweden.
authors.forename: Viktor
authors.initials: V
authors.lastname: Posse
authors.affiliation: Department of Mitochondrial Biology, Max Planck Institute for Biology of Ageing, 50931 Cologne, Germany.
authors.forename: Dusanka
authors.initials: D
authors.lastname: Milenkovic
authors.affiliation: Department of Mitochondrial Biology, Max Planck Institute for Biology of Ageing, 50931 Cologne, Germany.; Université de Bordeaux and the Centre National de la Recherche Scientifique, Institut de Biochimie et Génétique Cellulaires UMR 5095, Saint-Saëns, F-33077 Bordeaux, France.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Mourier
authors.affiliation: Harry Perkins Institute of Medical Research, Centre for Medical Research and School of Chemistry and Biochemistry, The University of Western Australia, Perth 6009, Australia.
authors.forename: Stefan J
authors.identifier: 0000-0002-8391-0143
authors.initials: SJ
authors.lastname: Siira
authors.affiliation: Department of Mitochondrial Biology, Max Planck Institute for Biology of Ageing, 50931 Cologne, Germany.
authors.forename: Nina A
authors.initials: NA
authors.lastname: Bonekamp
authors.affiliation: Central Microscopy, Max Planck Institute for Plant Breeding Research, 50829 Cologne, Germany.
authors.forename: Ulla
authors.initials: U
authors.lastname: Neumann
authors.affiliation: Harry Perkins Institute of Medical Research, Centre for Medical Research and School of Chemistry and Biochemistry, The University of Western Australia, Perth 6009, Australia.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Filipovska
authors.affiliation: Department of Biosciences, Biotechnologies, and Biopharmaceutics, University of Bari Aldo Moro, 70125 Bari, Italy.
authors.forename: Paola Loguercio
authors.initials: PL
authors.lastname: Polosa
authors.affiliation: Department of Medical Biochemistry and Cell Biology, Göteborgs Universitet, 40530 Göteborg, Sweden.
authors.forename: Claes M
authors.initials: CM
authors.lastname: Gustafsson
authors.affiliation: Department of Mitochondrial Biology, Max Planck Institute for Biology of Ageing, 50931 Cologne, Germany.; Department of Medical Biochemistry and Biophysics, Karolinska Institutet, 17177 Stockholm, Sweden.
authors.forename: Nils-Göran
authors.initials: NG
authors.lastname: Larsson
mesh_terms: D000818:Animals; D004261:DNA Replication / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D012321:DNA-Directed RNA Polymerases / Q000235:genetics*; D005786:Gene Expression Regulation; D054629:Genome, Mitochondrial; D006609:High Mobility Group Proteins / Q000235:genetics*; D051379:Mice; D014158:Transcription, Genetic
chemical_list: D004272:DNA, Mitochondrial; D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; C081930:Tfam protein, mouse; D012321:DNA-Directed RNA Polymerases; C000588975:Polrmt protein, mouse
keywords: 7S RNA; Mitochondria; POLRMT knockout mouse; light strand promoter; mitochondrial RNA polymerase; mitochondrial gene expression; mtDNA; mtDNA replication; mtDNA-free TFAM pool; twinkle