WIDE ANGLE

Mitochondria or the powerhouse of the cell carry out many important functions in the cell like maintaining energy homeostasis, regulating ROS levels, etc. Evolutionarily 2 billion years ago, endosymbiosis of an alpha proteobacteria gave rise to the first early eukaryotes. This bacterium underwent many transformations to form the present-day mitochondria. Mitochondrial genome, a circular DNA codes for just 13 proteins that form the complexes of ETC cycle, other proteins are nuclear encoded and translocated to mitochondria by TOM-TIM complex. Mutations in the mtDNA can cause a range of incurable life-limiting metabolic diseases in humans1. Mitochondrial disease can be sub-divided into two groups- childhood onset and adult-onset. Diagnosis of mitochondrial disease and prediction of disease progression is not easy as it can involve any organ or tissue and can have a wide variety of clinical symptoms, either neurological or non-neurological. Some mitochondrial diseases can be very common like LHON disease or very rare like MELAS. Current therapies to treat mitochondrial diseases are small molecule therapies which increase OXPHOS levels, pronuclear transfer to exchange disease mitochondria with healthy ones, or to induce mitophagy. But all these techniques fail to reverse the mutation in the mtDNA. Therefore, developing tools that can precisely edit mtDNA has been of utmost importance. A recent advance in this field developed a new tool that can precisely edit mtDNA. Mok et al., discovered a bacterial toxin DddA, a cytidine deaminase enzyme that can act on ddDNA2. This enzyme can carry out CG to TA conversions with less off-target effects. Since it can act on ddDNA, it can be used to edit the mitochondrial genome, but it’s a toxin. To overcome this, they engineered the enzyme such that the toxin is split into two halves, and targeted to the mtDNA such that the two halves become functional when bound to the target. Since this tool is RNA-free, it becomes easier to target this to mitochondria3. They further carried out CG to TA transitions in 5 mitochondrial genes to validate their finding. This molecular tool is the first agent that is capable of performing precise genome editing in mtDNA4. Using this tool, we can model different mitochondrial diseases and gain a better understanding of disease progression. This tool can be further developed to gain more insights in various diseases that are caused by genetic mutations like cancer.  

 

References

1. Mitochondrial Diseases: Hope for the Future
2. A bacterial cytidine deaminase toxin enables CRISPR-free mitochondrial base editing
3. Mitochondrial Genome Engineering: The Revolution May Not Be CRISPR-Ized
4. Mitochondrial genome editing gets precise

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Kinjal Sanghrajka