Human mitochondria and mitochondrial genome function as a single dynamic cellular unit.
rho 0 HeLa cells entirely lacking mitochondrial DNA (mtDNA) and mitochondrial transfection techniques were used to examine intermitochondrial interactions between mitochondria with and without mtDNA, and also between those with wild-type (wt) and mutant-type mtDNA in living human cells. First, unambiguous evidence was obtained that the DNA-binding dyes ethidium bromide (EtBr) and 4',6-diamidino-2-phenylindole (DAPI) exclusively stained mitochondria containing mtDNA in living human cells. Then, using EtBr or DAPI fluorescence as a probe, mtDNA was shown to spread rapidly to all rho 0 HeLa mitochondria when EtBr- or DAPI-stained HeLa mitochondria were introduced into rho 0 HeLa cells. Moreover, coexisting wt-mtDNA and mutant mtDNA with a large deletion (delta-mtDNA) were shown to mix homogeneously throughout mitochondria, not to remain segregated by use of electron microscopic analysis of cytochrome c oxidase activities of individual mitochondria as a probe to identify mitochondria with predominantly wt- or delta-mtDNA in single cells. This rapid diffusion of mtDNA and the resultant homogeneous distribution of the heteroplasmic wt- and delta-mtDNA molecules throughout mitochondria in a cell suggest that the mitochondria in living human cells have lost their individuality. Thus, the actual number of mitochondria per cell is not of crucial importance, and mitochondria in a cell should be considered as a virtually single dynamic unit.
Hayashi
J
J
Institute of Biological Sciences, University of Tsukuba, Ibaraki, Japan.
Takemitsu
M
M
Goto
Y
Y
Nonaka
I
I
D004272:DNA, Mitochondrial / Q000235:genetics* / Q000378:metabolism; D004058:Diffusion; D003576:Electron Transport Complex IV / Q000378:metabolism; D005796:Genes; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000502:physiology*; D008933:Mitochondrial Swelling; D012333:RNA, Messenger / Q000378:metabolism; D017384:Sequence Deletion
D004272:DNA, Mitochondrial; D012333:RNA, Messenger; D003576:Electron Transport Complex IV