Introduction of Heteroplasmic Mitochondrial DNA (MtDNA) from a Patient with NARP Into Two Human    cell Lines Is Associated Either With Selection and Maintenance of NARP Mutant MtDNA or Failure to Maintain MtDNA

Abstract

Mitochondria from a patient heteroplasmic at nucleo-tide position 8993 of mitochondrial DNA (mtDNA) were introduced into two human tumour cell lines lacking mtDNA. The donor mitochondria contained between 85 and 95% 8993G:C mtDNA. All detectable mtDNA in the mitochondrially transformed cells contained the pathological 8993G:C mutation 3 months after transformation. These results suggest that 8993G:C mtDNA had a selective advantage over 8993T:A mtDNA in both lung carcinoma and osteo-sarcoma cell backgrounds. In contrast, two other presumed pathological mtDNA variants were lost in favour of 'wild-type' mtDNA molecules in the same lung carcinoma cell background. Taken together, these findings suggest that the transmission bias of mtDNA variants is dependent upon a combination of nuclear background and mtDNA genotype. A second phenomenon observed was a marked decrease in the growth rate of many putative transformed cell lines after 6 weeks of culturing in selective medium, and in these cell lines mtDNA was not readily detectable by Southern blotting. Restriction endonuclease analysis and sequencing of amplified mtDNA demonstrated that the slow growing cells contained little or no mtDNA. It is concluded that these cells represented transient mitochondrial transformants.

Mitochondrial Encephalomyopathy inDrosophila

“…This could result from any of the following conditions: (1) the ATP6 mutation improved the overall fitness of the animal (which appears unlikely given our lifespan, locomotor impairment, and histological data), (2) continued selection in the laboratory for the most affected animals in the strain, or (3) selective inheritance such as a meiotic drive system operating in the female germ line of the animals. The latter is supported by experimental data demonstrating selective maintenance of the variant ATP6 (T8993G) mtDNA (Vergani et al, 1999) and selective inheritance during oogenesis (Blok et al, 1997). Interestingly, in MILS disease, a more severe variant of NARP manifests when the mutant heteroplasmy is above ϳ90%.…”

Segregation pattern and biochemical effect of the G3460A mtDNA mutation in 27 members of LHON family

“…Recent and prevailing opinion is that changes in mutation load from one generation to the next could be explained by random drift model of segregation [24,25,30]. Experimental data obtained from studies on mtDNA mutation models other than LHON cells show, however, that the nuclear environment may play a role [31]. In our study, increasing mutation load in all investigated tissues in two branches of pedigree differed from trend to maintain the low level of heteroplasmy in the third branch of the family, suggesting a contribution of specific paternal genes that remains preserved in subsequent generations.…”

Detection of mitochondrial DNA depletion in living human cells using PicoGreen staining

“…Equally, the method could also be applied to isolate U + cells from a population of U 0 cells without the need to select for respiratory competence. In addition, it will be useful for quantitative analysis of cybrid cell lines undergoing depletion, such as transient cybrids containing the 8993 G:C pathological mutations, which have been shown to undergo progressive depletion of mtDNA during culture [47].…”