Abstract
BackgroundDisruption of mitochondrial genes may become a powerful tool for elucidating precisely the functions of individual mitochondrial genes. However, it is generally difficult to manipulate genetically mitochondrial genes, because 1) a mitochondrion is surrounded by inner and outer membranes, and 2) there are a large number of mtDNA copies in a single cell. This is the reason why we tried to establish a novel method for disrupting a certain mitochondrial gene (rps4), using Dictyostelium cells.ResultsHere, we have developed a new method for specifically disrupting a mitochondrial gene (rps4 ; ribosomal protein subunit S4), by a combination of homologous recombination and delivery of an appropriate restriction endonuclease (SfoI) into mitochondria. First, mitochondrially targeted SfoI whose expression is under control of the tetracycline (Tet)-regulated gene expression system was introduced into cells heteroplasmic with respect to the rps4 gene. Then, the heteroplasmic cells were produced by homologous recombination by use of the construct in which the unique SfoI site and the 5'-half of the rps4 coding region were deleted not to be digested by SfoI, and therefore their mitochondria have both the wild-type mtDNA and the mutant mtDNA with the disrupted rps4 gene. In response to removal of Tet from growth medium, SfoI was selectively delivered into mitochondria and digested only the wild-type mtDNA but not the mutated rps4. Thus one can gain rps4-null cells with only the mutated mtDNA, under the Tet-minus condition.ConclusionThe mitochondrial gene-disruption method presented here must be widely useful for precisely determining the functions of individual mitochondrial genes. This is the first report to demonstrate complete and specific mitochondrial gene disruption.
Highlights
Disruption of mitochondrial genes may become a powerful tool for elucidating precisely the functions of individual mitochondrial genes
As the first step to be tested, we needed to know if conditional targeting of restriction endonucleases such as EcoRI into Dictyostelium mitochondria can eliminate Mitochondrial DNA (mtDNA) completely to give mtDNA-null cells (ρ0-cells)
To deliver EcoRI into mitochondria, the EcoRI gene was fused with the presequence that encodes the signal peptide (MTS) of cytochrome c oxidase subunit IV, and the fusion gene was inserted into a Dictyostelium TRE-Pmin (Tet-mediated promoter)-plasmid shown in Additional data file 1b
Summary
Disruption of mitochondrial genes may become a powerful tool for elucidating precisely the functions of individual mitochondrial genes. It is generally difficult to manipulate genetically mitochondrial genes, because 1) a mitochondrion is surrounded by inner and outer membranes, and 2) there are a large number of mtDNA copies in a single cell. This is the reason why we tried to establish a novel method for disrupting a certain mitochondrial gene (rps4), using Dictyostelium cells. A single mitochondrion contains hundreds of proteins that together are responsible for the various biological functions of the organelle. The expression of the mitochondrial ribosomal protein (rps4) that is encoded by mtDNA is required for differentiation from the GDT point in the cell cycle [2]
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