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Monday, 2 August 2010

Mitochondria DNA in Different Parts of Our Body Vary


Mitochondria are tiny capsule-shaped structures that produce energy for the cell. Each cell has dozens to hundreds of mitochondria, and each mitochondrion contains several copies of circular strands of DNA. This DNA is distinct from the main genome in the cell's nucleus, which is inherited from both the mother and father. Mitochondria, in contrast, are passed directly from a mother's egg cell to her offspring. Until recently, most scientists believed that nearly all of a person's cells contain identical copies of mtDNA inherited from the mother. A new approach for analyzing DNA shows that each person's mitochondrial DNA (mtDNA) is surprisingly variable in different body tissues. The finding may eventually prove useful for spotting and monitoring cancer, as it leads to telltale mtDNA variations that can be detected in the bloodstream. A research team led by Drs. Nickolas Papadopoulos and Bert Vogelstein of Johns Hopkins University used new, highly sensitive DNA sequencing technologies to take a closer look at mtDNA variability in different tissues within several individuals. The research was supported by NIH's National Cancer Institute (NCI) and the Howard Hughes Medical Institute. The researchers described a series of mtDNA analyses, including a detailed evaluation of 10 different tissues taken from a single person. Although most analyzed mtDNA was identical, the researchers detected at least 1 variant form of mtDNA in each tissue, and 4 tissues harbored at least 4 variants. The proportion of variant mtDNA in tissues differed widely. In some cases, certain tissues - like kidney and liver - shared a variant that wasn't found in other tissues.The technique can detect relatively rare single-letter variants in stretches of DNA - even those found in as few as 1 in 10,000 mitochondrial genomes.

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