Seshadri, A. | Search bioRxiv

bioRxiv2024

Exonuclease action of replicative polymerase gamma drives damage-induced mitochondrial DNA clearance

Mitochondrial DNA (mtDNA) replication is essential for mitochondrial function. This is carried out by a dedicated DNA polymerase gamma, with 5-3 polymerase and 3-5 proofreading/ exonuclease activity. Perturbations to either properties can have pathological consequences. Predominant sources for replication stress are DNA lesions, such as those induced by oxidative damage. How mtDNA lesions affect the polymerase activity and mtDNA stability in vivo is not fully understood. To address this, we induce mtDNA-specific damage in S. cerevisiae. We observe that mtDNA damage results in significant mtDNA loss. This loss occurs independent of cell cycle progression or cell division, suggesting an active mechanism for damaged mtDNA clearance. We implicate the 3-5 exonuclease activity of the mtDNA polymerase in this clearance, with rates of loss being affected by cellular dNTP levels. Overall, our findings reveal context-dependent, selective regulation of two critical but opposing functions of polymerase gamma to ensure mitochondrial genome integrity.

microbiology↗

bioRxiv2022

Dynamic reorganization and selective segregation of mitochondria under DarT-mediated mtDNA damage

Mitochondria are dynamic organelles that play essential roles in cell growth and survival. Processes of fission and fusion are critical for distribution, segregation and maintenance of mitochondria and their genomes (mtDNA). While recent work has revealed the significance of mitochondrial organization for mtDNA maintenance, impact of mtDNA perturbations on mitochondrial dynamics remains less understood. Here we develop a tool to induce mitochondria-specific DNA damage, using a mitochondrial-targeted base modifying bacterial toxin, DarT. Following damage, we observe dynamic reorganization of mitochondrial networks, likely driven by mitochondrial dysfunction. Changes in organization are associated with loss of mtDNA, independent of mitophagy. Unexpectedly, perturbation to exonuclease function of mtDNA replicative polymerase, Mip1, results in rapid loss of mtDNA. Our data suggest that, under damage, partitioning of defective mtDNA and organelle are de-coupled, with emphasis on mitochondrial segregation independent of its DNA. Together, our works underscores the importance of genome maintenance on mitochondrial function, that can act as a modulator of organelle organization and segregation.

cell biology↗