Different cellular backgrounds confer a marked advantage to either mutant or wild-type mitochondrial genomes.

Abstract

After the introduction of mitochondria with a mixture of mutant and wild-type mitochondrial DNA (mtDNA) into a human p0 cell line (143B.206), Yoneda et al. [Yoneda, M., Chomyn, A., Martinuzzi, A., Hurko, 0. & Attardi, G. (1992) Proc. Natl. Acad. Sci. USA 89, [11164][11165][11166][11167][11168] observed a shift in the proportion of the two mitochondrial genotypes in a number of cybrid clones. In every case where a shift was observed, there was an increase in the proportion of mutant mtDNA. By using the same cell line (143B.206 p°), we also generated cybrids that were either stable in their mitochondrial genotype or showed an increase in the proportion of mutant mtDNA. However, temporal analysis of the same mutant mtDNA type in another p0 cell line revealed a quite distinct outcome. Those clones that showed a change shifted toward higher levels of wild-type rather than mutant mtDNA. These results indicate that the nuclear genetic background of the recipient (p0) cell can influence the segregation of mutant and wild-type mitochondrial genomes in cell cybrids.Disease-associated mitochondrial DNA (mtDNA) mutations were first recognized in 1988 (1). These mutations were large deletions, accounting for 15-50% of the 16.6-kb genome. All the patients showed the proliferation of skeletal muscle mitochondria characteristic of mitochondrial myopathy (2), and in each case, the partially deleted genomes were found to coexist with apparently wild-type genomes. Subsequently, a number of disease-associated mtDNA point mutations were identified (3-6). One of these, an A -> G point mutation in the mitochondrial tRNALeU(UUR) gene at bp 3243, accounts for the majority of cases of MELAS syndrome (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) (6). As with partial deletions of mtDNA, wild-type mtDNA molecules coexisted with the mutant molecules.A human cell line devoid of endogenous mtDNA (p°) was generated in 1989 (7) and was used to provide evidence that mitochondrial genomes with the bp-3243 mutation caused respiratory deficiency (8, 9). Mitochondria from patients with MELAS were introduced into p0 cells and cybrid cell lines were established. Clonal cell lines with high levels of mutant mtDNA showed decreased in vitro mitochondrial translation products and whole-cell oxygen consumption.Yoneda et al. (10) have described clonal cybrid lines that were derived from the fusion of cytoplasts containing MELAS patient mitochondria with a recipient p0 cell line. Some of the resulting cybrids contained a mixture of mutant and wild-type mitochondrial genomes. Temporal analysis revealed that in 5 of 13 clones investigated, the proportion of mutant mtDNA increased with time. In no case was a shift toward wild-type mtDNA observed. In addition, the level of mutant mtDNA reached 95% in only one cybrid line, and in this case, respi-The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734...

Preferential amplification and phenotypic selection in a population of deleted and wild-type mitochondrial DNA in cultured cells

“…Thus, in hybrids and cybrids preferential accumulation might be a property not only of del-mtDNA. A cybrid's nuclear genome may be involved in mtDNA segregation as well, as was clearly demonstrated in relation to the ME-LAS 3243 point mutation (Dunbar et al 1995). Although it is impossible from the present study to determine to what extent the accumulation of del-mtDNA was influenced by its original parental nucleus, the ease with which delmtDNA was selected against suggests a passive role of the nuclear genome.…”

“…It has been suggested that not only del-mtDNA but also mtDNA containing a point mutation may accumulate with time, in patients as well as in cell-culture (Yoneda et al 1992;Attardi et al 1995). Nuclear background was shown to influence this behaviour (Dunbar et al 1995), which raises questions regarding the mechanism(s) of the replicative advantage of any mutant mtDNA, including mtDNA molecules of smaller than wild-type size, and its relationship with the phenotypic effects of the mutation.…”

Characterization of a novel mitochondrial DNA deletion in a patient with a variant of the Pearson marrow–pancreas syndrome

“…11 Altogether, these mtDNA deletion in Pearson syndrome JMW van den Ouweland et al y data indicate that segregation of deleted mtDNA may, or may not occur depending on the nuclear background of the cell containing deleted mtDNA. Also, in cybrid cells containing partially duplicated mtDNA 25 or a specific point mutation in the mtDNA at np 3243, 26 uridine and the nuclear background were found as factors influencing the segregation of the mitochondrial phenotype.…”

The Potential Application of Mitochondrial Medicine in Toxicologic Poisoning

“…In an A549 lung carcinoma MELAS cybrid model, a 50 % mutational load results in a 50 % reduction in cytochrome oxidase activity [21]. This illustrates the important role the nuclear genome plays in the mitochondrial genotype-phenotype relationships [22].…”