Replication of mitochondrial DNA occurs throughout the mitochondria of cultured human cells.
Replication of mitochondrial DNA (mtDNA) is dependent on nuclear-encoded factors. It has been proposed that this reliance may exert spatial restrictions on the sites of mtDNA replication within the cytoplasm, as a previous study only detected mtDNA synthesis in perinuclear mitochondria. We have studied mtDNA replication in situ in a variety of human cell cultures labeled with 5-bromo-2'-deoxyuridine. In contrast to what has been reported, mtDNA synthesis was detected at multiple sites throughout the mitochondrial network following short pulses with bromodeoxyuridine. Although no bromodeoxyuridine incorporation was observed in anuclear platelets, incorporation into mtDNA of fibroblasts that had been enucleated 2 h prior to labeling was readily detectable. Blotting experiments indicated that the bromodeoxyuridine incorporation into mtDNA observed in situ represents replication of the entire mtDNA molecule. The studies also showed that replication of mtDNA occurred at any stage of the cell cycle in proliferating cells and continued in postmitotic cells, although at a lower level. These results demonstrate that mtDNA replication is not restricted to mitochondria in the proximity of the nucleus and imply that all components of the replication machinery are available at sufficient levels throughout the mitochondrial network to permit mtDNA replication throughout the cytoplasm.
Magnusson
Jessica
J
University Department of Clinical Neurosciences, Royal Free and University College Medical School, University College London, London NW3 2PF, UK.
Orth
Michael
M
Lestienne
Patrick
P
Taanman
Jan-Willem
JW
D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism; D001973:Bromodeoxyuridine; D002451:Cell Compartmentation / Q000235:genetics*; D002453:Cell Cycle / Q000235:genetics; D002478:Cells, Cultured; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism*; D000074002:DNA Polymerase gamma; D004261:DNA Replication / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000096:biosynthesis / Q000235:genetics*; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007223:Infant; D007231:Infant, Newborn; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D004272:DNA, Mitochondrial; D014157:Transcription Factors; D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase; D001973:Bromodeoxyuridine