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Mitochondrial mutational spectra in human cells and tissues
K Khrapko1, H A Coller, P C André
1Division of Toxicology, Center for Environmental Health Sciences, E18-666, 400 Main Street, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Summary
Human organs and tumors share common mitochondrial hotspot mutations. These spontaneous mutations, primarily G to A transitions, occur at a much higher rate than nuclear mutations.
Area of Science:
- Genetics
- Molecular Biology
- Biochemistry
Background:
- Mitochondrial DNA (mtDNA) mutations are implicated in aging and disease.
- Understanding the origin and rate of mtDNA mutations is crucial for human health research.
Purpose of the Study:
- To identify and characterize hotspot point mutations in human mitochondrial DNA.
- To determine the mutation rate and heritability of mitochondrial DNA point mutations.
- To investigate the origin of mitochondrial DNA point mutations in human tissues and cell lines.
Main Methods:
- Sequencing of mitochondrial DNA hotspots in human organs (colon, lung, muscle) and their derived tumors.
- Analysis of mutant fractions across cell generations in a human B cell line (TK6).
- Comparison of in vivo and in vitro mutation spectra.
Main Results:
- Seventeen hotspot point mutations, predominantly G --> A and A --> G transitions, were identified in the mitochondrial sequence (10,030-10,130 bp).
- Mutant fractions increased with cell generations in TK6 cells, confirming heritable changes.
- The mitochondrial point mutation rate is over 100 times higher than the nuclear point mutation rate in TK6 cells and human tissues.
Conclusions:
- Human organs and their tumors share common mitochondrial hotspot point mutations, suggesting a common origin.
- Mitochondrial DNA point mutations are primarily spontaneous, likely arising from replication errors or endogenous metabolites.
- The high mutation rate and specific mutation spectrum indicate a significant role for spontaneous events in mitochondrial genome instability.