Human heart mitochondrial DNA is organized in complex catenated networks containing abundant four-way junctions and replication forks.
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.
Pohjoismäki
Jaakko L O
JL
Institute of Medical Technology.
Goffart
Steffi
S
Tyynismaa
Henna
H
Willcox
Smaranda
S
Ide
Tomomi
T
Kang
Dongchon
D
Suomalainen
Anu
A
Karhunen
Pekka J
PJ
Griffith
Jack D
JD
Holt
Ian J
IJ
Jacobs
Howard T
HT
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
D004272:DNA, Mitochondrial