Absence of extensive recombination between inter- and intraspecies mitochondrial DNA in mammalian cells

Recombination of mammalian mitochondrial DNA (mtDNA) was examined using mouse X rat somatic cell hybrid clones and rat cybrid clones. The mouse X rat hybrids were isolated by fusion of chloramphenicol-sensitive (CAPs) mouse and CAP-resistant (CAPr) rat cells. The rat cybrids were isolated by fusion of rat cells with type B mtDNA and enucleated cells with type A mtDNA. Genetic and physical analyses showed that the mtDNAs of the hybrids and cybrids were simple mixtures of the two parental mtDNAs except in the following two cases: One was subclone H2-9 of mouse X rat hybrids, which was CAPr even though mtDNA from the CAPs mouse parent was predominantly retained. The other was rat cybrid subclones, Y12-24 and -61, which showed specific loss of one Hinf I fragment of type B mtDNA, B10. These observations suggest that, in contrast to the case with plant mtDNA, recombination of mammalian mtDNA occurs rarely, if at all.