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Marked replicative advantage of human mtDNA carrying a point mutation that causes the MELAS encephalomyopathy
M Yoneda1, A Chomyn, A Martinuzzi
1Division of Biology, California Institute of Technology, Pasadena 91125.
Abstract:
The segregation of mutant and wild-type mtDNA was investigated in transformants constructed by transferring human mitochondria from individuals belonging to four pedigrees with the MELAS encephalomyopathy-associated mtDNA mutation (MELAS is mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes) into human mtDNA-less (rho 0) cells. Five of 13 clonal cell lines containing mixtures of wild-type and mutant mtDNAs were found to undergo a rapid shift of their genotype toward the pure mutant type. The other 8 cell lines, which included 6 exhibiting nearly homoplasmic mutant mtDNA, on the contrary, maintained a stable genotype. Subcloning experiments and growth rate measurements clearly indicated that an intracellular replicative advantage of mutant mtDNA was mainly responsible for the dramatic shift toward the mutant genotype observed in the unstable cell lines.
Insights
Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) mutant mtDNA showed a replicative advantage, causing a rapid shift toward pure mutant genotypes in unstable cell lines. Stable cell lines maintained their mixed or mutant mtDNA composition.
Area of Science:
- Genetics
- Cell Biology
- Mitochondrial Medicine
Background:
- Mitochondrial DNA (mtDNA) mutations are linked to various human diseases, including MELAS.
- Understanding mtDNA segregation dynamics is crucial for disease progression and therapeutic strategies.
Purpose of the Study:
- To investigate the segregation patterns of mutant and wild-type mtDNA in human cells.
- To identify factors influencing the shift towards mutant mtDNA genotypes in MELAS pedigrees.
Main Methods:
- Constructed transformants by transferring human mitochondria from MELAS patients into mtDNA-less (rho 0) cells.
- Analyzed genotype shifts in clonal cell lines using subcloning and growth rate measurements.
Main Results:
- Five of 13 clonal cell lines rapidly shifted towards a pure mutant mtDNA genotype.
- Eight cell lines, including 6 near homoplasmic for mutant mtDNA, maintained stable genotypes.
- Intracellular replicative advantage of mutant mtDNA was identified as the primary driver of genotype shifts in unstable lines.
Conclusions:
- Mutant mtDNA in MELAS can possess a replicative advantage, leading to rapid shifts in cellular genotype.
- mtDNA segregation stability is influenced by the replicative capacity of mutant mtDNA, impacting disease phenotype.