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Mitochondrial transcription factor A regulates mtDNA copy number in mammals.

Journal article
Authors Mats I Ekstrand
Maria Falkenberg
Anja Rantanen
Chan Bae Park
Martina Gaspari
Kjell Hultenby
Pierre Rustin
Claes M Gustafsson
Nils-Göran Larsson
Published in Human molecular genetics
Volume 13
Issue 9
Pages 935-44
ISSN 0964-6906
Publication year 2004
Published at
Pages 935-44
Language en
Keywords Animals, Chromosomes, Artificial, P1 Bacteriophage, DNA, metabolism, DNA, Mitochondrial, genetics, Fetal Death, genetics, Gene Dosage, Gene Expression Regulation, Humans, Mammals, genetics, Mice, Mice, Knockout, Mice, Transgenic, Respiration, genetics, Transcription Factors, physiology, Transcription, Genetic, Up-Regulation, Xenopus Proteins, physiology
Subject categories Chemistry

Abstract

Mitochondrial DNA (mtDNA) copy number regulation is altered in several human mtDNA-mutation diseases and it is also important in a variety of normal physiological processes. Mitochondrial transcription factor A (TFAM) is essential for human mtDNA transcription and we demonstrate here that it is also a key regulator of mtDNA copy number. We initially performed in vitro transcription studies and determined that the human TFAM protein is a poor activator of mouse mtDNA transcription, despite its high capacity for unspecific DNA binding. Next, we generated P1 artificial chromosome (PAC) transgenic mice ubiquitously expressing human TFAM. The introduced human TFAM gene was regulated in a similar fashion as the endogenous mouse Tfam gene and expression of the human TFAM protein in the mouse did not result in down-regulation of the endogenous expression. The PAC-TFAM mice thus had a net overexpression of TFAM protein and this resulted in a general increase of mtDNA copy number. We used a combination of mice with TFAM overexpression and TFAM knockout and demonstrated that mtDNA copy number is directly proportional to the total TFAM protein levels also in mouse embryos. Interestingly, the expression of human TFAM in the mouse results in up-regulation of mtDNA copy number without increasing respiratory chain capacity or mitochondrial mass. It is thus possible to experimentally dissociate mtDNA copy number regulation from mtDNA expression and mitochondrial biogenesis in mammals in vivo. In conclusion, our results provide genetic evidence for a novel role for TFAM in direct regulation of mtDNA copy number in mammals.

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