Nonrandom Mitochondrial DNA Segregation in Human Cell Hybrids and Clinical Application

Shougo Ishii, Jerry W. Shay* and Armand F. Miranda†

Division of Child Neurology, Institute of Neurological Sciences, Faculty of Medicine, Tottori University, Yonago 683, Japan, *Department of Cell Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX and †Department of Pathology, College of Physicians and Surgeons, Columbia University, New York, NY, United States

Several instances of mitochondrial DNA (mtDNA) heteroplasmy in mitochondrial cytopathies have been reported, and the degree of heteroplasmy may be important in the clinical manifestations of these diseases. But, Iittle is known about the mechanism of organellar heteroplasmy in mammalian cells. In order to understand the mechanism of mtDNA heteroplasmy, we have made somatic cell hybrids by fusion of cells containing mtDNA with differences in their restriction endonuclease patterns. This permits the artificial mixing of mitochondria and the study of mtDNA segregation patterns. In this study, we observed nonrandom mtDNA segregations. In HeLa × nontumorigenic cen hybrids, mtDNA from HeLa cells is usually lost several weeks of continuous cell culture, and in HeLa × tumorigenic cell hybrids, both type of mtDNA coexists. However, this correlation has exceptions occasionally. Also, we have used this nonrandom segregation for judging the mode of inheritance in one case of cytochrome c oxidase deficiency. The results demonstrate that the enzyme deficiency in used cell strain was derived from nuclear DNA-encoded factor. The mechanisms of this nonrandom mtDNA segregation is still unknown. But, this system can be used to determine whether different generalized mitochondrial disorders are due to mutations of nuclear or mtDNA.

Key words: clinical application; mtDNA; nonrandom segregation; tumorigenicity

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