mitoTALENs

mitoTALENs are engineered nucleases designed to modify mitochondrial DNA (mtDNA) by delivering catalytic domains specifically to mitochondria. They combine transcription activator-like effector (TALE) DNA-binding domains with a programmable FokI nuclease and mitochondrial targeting sequences to direct the complex into mitochondria where the mtDNA resides. By using two TALENs that bind on opposite sides of a target mutation, a double-strand break is generated in the mutant mtDNA, triggering degradation of the cleaved molecule and a shift in mtDNA heteroplasmy toward wild-type genomes.

The mechanism relies on the limited repair pathways available in mitochondria. Once the mtDNA copy containing the pathogenic mutation is cleaved, it is typically degraded, reducing the proportion of mutant genomes within a cell. Over time, cells may repopulate mtDNA with non-mutant copies, potentially restoring mitochondrial function in affected tissues. mitoTALENs have been designed to target a range of heteroplasmic mtDNA mutations and have been tested in cellular models and in vivo systems using tissue-specific delivery.

Applications include research into mitochondrial diseases caused by heteroplasmic mtDNA mutations and exploration of therapeutic strategies aimed at lowering mutant mtDNA load. In vivo studies have employed delivery methods such as adeno-associated viruses to target specific tissues, highlighting both potential applications and ongoing challenges in achieving uniform distribution and sustained efficacy across organs.

Limitations involve delivery efficiency across all affected tissues, the requirement for precise heteroplasmy shifts, potential off-target cleavage within mtDNA, and donor-vector immunogenicity. mitoTALENs remain one approach among mitochondrial genome editing tools, with continued development focused on improving specificity, safety, and delivery for therapeutic use.