New Tool Facilitates Study of Mitochondrial DNA Variation

It is a factor for the severity of mitochondrial diseases. Since most eukaryotic cells contain many hundreds of mitochondria with hundreds of copies of mtDNA, it is possible and indeed very frequent for mutations to affect only some mitochondria while others are unaffected. Heteroplasmy can be beneficial rather than detrimental insofar as centenarians show a higher than average degree of heteroplasmy.

Study of mitochondrial heteroplasmy has been complicated by the relatively small amount of mtDNA in each cell (less than 1% of the total DNA) and the intercellular variability of mtDNA content. To counter these problems, the Mt. Sinai investigators developed Mseek, which combines an enzymatic technique that purifies mitochondrial DNA by deleting the nuclear DNA and an advanced deep DNA sequencing procedure for analysis of the pure mitochondrial DNA.

The investigators reported that Mseek yielded high purity (greater than 90%) mtDNA, and that its ability to detect rare variants was limited only by sequencing depth, providing unprecedented sensitivity and specificity. Using Mseek, they confirmed the ubiquity of heteroplasmy by analyzing mtDNA from a diverse set of cell lines and human samples. Applying Mseek to colonies derived from single cells, they found that heteroplasmy was stably maintained in individual daughter cells over multiple cell divisions.

“Researchers have struggled to sequence mtDNA accurately and in a cost effective manner,” said senior author Dr. Ravi Sachidanandam, assistant professor of oncological sciences at the Icahn School of Medicine at Mount Sinai. “The technique we have developed will allow us to identify dysfunction within mitochondria and makes mtDNA a useful biomarker as well as a potential therapeutic target in cancer and many inherited diseases. We hypothesized that heteroplasmy could be stabilized by intercellular exchange of mtDNA. Our results demonstrated the exchange of mtDNA is possible and heteroplasmy can be maintained stably through this mechanism. This technique could provide a novel platform to investigate features of heteroplasmy in normal and diseased state and in the future, the exchange mechanism could be used as a treatment that targets bad mtDNA and exchanges it with good mtDNA.”

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Icahn School of Medicine at Mount Sinai