Genetics of the mammalian oxidative phosphorylation system: characterization of a new oligomycin-resistant Chinese hamster ovary cell line

The thankless task of playing genetics with mammalian mitochondrial DNA: a 30-year review

The advances obtained through the genetic tools available in yeast for studying the oxidative phosphorylation (OXPHOS) biogenesis and in particular the role of the mtDNA encoded genes, strongly contrast with the very limited benefits that similar approaches have generated for the study of mammalian mtDNA. Here we review the use of the genetic manipulation in mammalian mtDNA, its difficulty and the main types of mutants accumulated in the past 30 years and the information derived from them. We also point out the need for a substantial improvement in this field in order to obtain new tools for functional genetic studies and for the generation of animal models of mtDNA-linked diseases.

Oligomycin induces a decrease in the cellular content of a pathogenic mutation in the human mitochondrial ATPase 6 gene

A T --> G mutation at position 8993 in human mitochondrial DNA is associated with the syndrome neuropathy, ataxia, and retinitis pigmentosa and with a maternally inherited form of Leigh's syndrome. The mutation substitutes an arginine for a leucine at amino acid position 156 in ATPase 6, a component of the F0 portion of the mitochondrial ATP synthase complex. Fibroblasts harboring high levels of the T8993G mutation have decreased ATP synthesis activity, but do not display any growth defect under standard culture conditions. Combining the notions that cells with respiratory chain defects grow poorly in medium containing galactose as the major carbon source, and that resistance to oligomycin, a mitochondrial inhibitor, is associated with mutations in the ATPase 6 gene in the same transmembrane domain where the T8993G amino acid substitution is located, we created selective culture conditions using galactose and oligomycin that elicited a pathological phenotype in T8993G cells and that allowed for the rapid selection of wild-type over T8993G mutant cells. We then generated cytoplasmic hybrid clones containing heteroplasmic levels of the T8993G mutation, and showed that selection in galactose-oligomycin caused a significant increase in the fraction of wild-type molecules (from 16 to 28%) in these cells.

Altered form of subunit 6 of mitochondrial ATP synthase complex in oligomycin-resistant mutants of Chinese hamster ovary cells

Using an antiserum generated against a synthetic peptide predicted from the DNA sequence of the ATPase 6 gene of the mitochondrial DNA, we demonstrate that mitochondria from two oligomycin-resistant Chinese hamster ovary cell lines with a defined mutation in the ATPase 6 gene synthesize an altered ATPase 6 gene product. This altered gene product migrates in sodium dodecyl sulfate-polyacrylamide gels as if it has a molecular mass that is larger by 1000 daltons than the wild-type ATPase 6 gene product. We also demonstrate that mitochondria from four other independently isolated oligomycin-resistant Chinese hamster ovary mutant cell lines contain a similar altered ATPase 6 gene product. These results suggest that all six oligomycin-resistant cell lines have a similar mutation in the ATPase 6 gene of the mitochondrial DNA that encodes subunit 6 of the ATP synthase complex.

Two cytoplasmically inherited oligomycin-resistant Chinese hamster cell lines exhibit an altered mitochondrial translation product

Mitochondria from two different cytoplasmically inherited oligomycin-resistant Chinese hamster ovary cell lines synthesize an altered polypeptide compared to mitochondria from wild-type cells. For example, mitochondria from both oligomycin-resistant cell lines synthesize a polypeptide with a molecular weight of approximately 20,500, which is present in very low amounts in wild-type cells. In contrast, mitochondria from wild-type cells synthesize a polypeptide with a molecular weight of approximately 19,500, which is present in very low amounts in one of the oligomycin-resistant mutants and in reduced amounts in the other mutant. The gene which encodes this altered polypeptide is cytoplasmically transferred together with the oligomycin-resistant phenotype. This is the first example in mammalian cells where an altered mitochondrial gene product is shown to be associated with the cytoplasmic transfer of oligomycin resistance.

Biochemical genetics of the mammalian oxidative phosphorylation system: analysis of the difference in the sensitivity of various Chinese hamster cell lines to inhibitors of the mitochondrial ATP synthase complex

Seven different Chinese hamster cell lines were found to vary greatly in their sensitivity to inhibitors of the mitochondrial ATPase. In plating-efficiency experiments, Chinese hamster lung V79 and bone marrow M3-1 cells were approximately 10,000-fold more resistant to oligomycin, 100-fold more resistant to efrapeptin, and 10-fold more resistant to ossamycin and leucinostatin than were ovary CHO or peritoneal B14 cells. In vitro experiments indicated that the increased resistance of V79 versus CHO cells to these inhibitors was due to an increased resistance of the mitochondrial ATPase. Heat-inactivation experiments indicated that there was a difference in the structure of the mitochondrial ATPase of V79 and CHO cells. Genetic experiments indicated that the difference in the sensitivity of V79 and CHO cells to inhibitors of the ATPase and the difference in the structure of the mitochondrial ATPase of V79 and CHO cells was due to a difference in both a nuclear and a cytoplasmic gene.