title: Human heart mitochondrial DNA is organized in complex catenated networks containing abundant four-way junctions and replication forks.
abstract: Analysis of human heart mitochondrial DNA (mtDNA) by electron microscopy and agarose gel electrophoresis revealed a complete absence of the -type replication intermediates seen abundantly in mtDNA from all other tissues. Instead only Y- and X-junctional forms were detected after restriction digestion. Uncut heart mtDNA was organized in tangled complexes of up to 20 or more genome equivalents, which could be resolved to genomic monomers, dimers, and linear fragments by treatment with the decatenating enzyme topoisomerase IV plus the cruciform-cutting T7 endonuclease I. Human and mouse brain also contained a population of such mtDNA forms, which were absent, however, from mouse, rabbit, or pig heart. Overexpression in transgenic mice of two proteins involved in mtDNA replication, namely human mitochondrial transcription factor A or the mouse Twinkle DNA helicase, generated abundant four-way junctions in mtDNA of heart, brain, and skeletal muscle. The organization of mtDNA of human heart as well as of mouse and human brain in complex junctional networks replicating via a presumed non- mechanism is unprecedented in mammals.
authors.affiliation: Institute of Medical Technology.
authors.forename: Jaakko L O
authors.initials: JL
authors.lastname: Pohjoismäki
authors.forename: Steffi
authors.initials: S
authors.lastname: Goffart
authors.forename: Henna
authors.initials: H
authors.lastname: Tyynismaa
authors.forename: Smaranda
authors.initials: S
authors.lastname: Willcox
authors.forename: Tomomi
authors.initials: T
authors.lastname: Ide
authors.forename: Dongchon
authors.initials: D
authors.lastname: Kang
authors.forename: Anu
authors.initials: A
authors.lastname: Suomalainen
authors.forename: Pekka J
authors.initials: PJ
authors.lastname: Karhunen
authors.forename: Jack D
authors.initials: JD
authors.lastname: Griffith
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Holt
authors.forename: Howard T
authors.initials: HT
authors.lastname: Jacobs
mesh_terms: D000328:Adult; D000368:Aged; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002675:Child, Preschool; D004272:DNA, Mitochondrial / Q000378:metabolism*; D005260:Female; D006321:Heart / Q000502:physiology*; D006801:Humans; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008875:Middle Aged; D009690:Nucleic Acid Conformation; D011817:Rabbits; D013045:Species Specificity; D013552:Swine; D014018:Tissue Distribution
chemical_list: D004272:DNA, Mitochondrial