Using mitochondrial DNA as a biosensor of early cancer development

Mitochondria can perform multiple cellular functions including energy production, cell proliferation and apoptosis. Each human cell contains hundreds to several thousand copies of the 16.5 kb human mitochondrial genome, which incidentally exhibits a maternal pattern of inheritance. This closed circular genome encodes 13 polypeptides of the respiratory chain complexes, as well as 22 transfer RNAs and two ribosomal RNAs used in mitochondrial protein synthesis. Compared to nuclear DNA, mitochondrial DNA (mtDNA) is highly susceptible to damage because it is not associated with protective histones, it is continually exposed to high levels of reactive oxygen species (ROS) generated by oxidative phosphorylation, and there is a limited capacity for mtDNA repair. The complete mtDNA sequence was determined in 1981 and resequenced in 1999. A growing collection of reported mtDNA mutations and rearrangements has been associated with muscle and neurodegenerative diseases ( Birch-Machin, 2000 ).