ATFS-1 counteracts mitochondrial DNA damage by promoting repair over transcription.

The ability to balance conflicting functional demands is critical for ensuring organismal survival. The transcription and repair of the mitochondrial genome (mtDNA) requires separate enzymatic activities that can sterically compete1, suggesting a life-long trade-off between these two processes. Here in Caenorhabditis elegans, we find that the bZIP transcription factor ATFS-1/Atf5 (refs. 2,3) regulates this balance in favour of mtDNA repair by localizing to mitochondria and interfering with the assembly of the mitochondrial pre-initiation transcription complex between HMG-5/TFAM and RPOM-1/mtRNAP. ATFS-1-mediated transcriptional inhibition decreases age-dependent mtDNA molecular damage through the DNA glycosylase NTH-1/NTH1, as well as the helicase TWNK-1/TWNK, resulting in an enhancement in the functional longevity of cells and protection against decline in animal behaviour caused by targeted and severe mtDNA damage. Together, our findings reveal that ATFS-1 acts as a molecular focal point for the control of balance between genome expression and maintenance in the mitochondria.

PINK1 and parkin shape the organism-wide distribution of a deleterious mitochondrial genome.

In multiple species, certain tissue types are prone to acquiring greater loads of mitochondrial genome (mtDNA) mutations relative to others, but the mechanisms that drive these heteroplasmy differences are unknown. We find that the conserved PTEN-induced putative kinase (PINK1/PINK-1) and the E3 ubiquitin-protein ligase parkin (PDR-1), which are required for mitochondrial autophagy (mitophagy), underlie stereotyped differences in heteroplasmy of a deleterious mitochondrial genome mutation (ΔmtDNA) between major somatic tissues types in Caenorhabditis elegans. We demonstrate that tissues prone to accumulating ΔmtDNA have lower mitophagy responses than those with low mutation levels. Moreover, we show that ΔmtDNA heteroplasmy increases when proteotoxic species that are associated with neurodegenerative disease and mitophagy inhibition are overexpressed in the nervous system. These results suggest that PINK1 and parkin drive organism-wide patterns of heteroplasmy and provide evidence of a causal link between proteotoxicity, mitophagy, and mtDNA mutation levels in neurons.

Publisher Correction: Affinity purification of cell-specific mitochondria from whole animals resolves patterns of genetic mosaicism.

In the version of this Technical Report originally published, chromosome representations (indicated by black lines) were missing from Fig. 2a due to a technical error. The corrected version of Fig. 2a is shown below. This has now been amended in all online versions of the Technical Report.

Affinity purification of cell-specific mitochondria from whole animals resolves patterns of genetic mosaicism.

Although mitochondria are ubiquitous organelles, they exhibit tissue-specific morphology, dynamics and function. Here, we describe a robust approach to isolate mitochondria from specific cells of diverse tissue systems in Caenorhabditis elegans. Cell-specific mitochondrial affinity purification (CS-MAP) yields intact and functional mitochondria with exceptional purity and sensitivity (>96% enrichment, >96% purity, and single-cell and single-animal resolution), enabling comparative analyses of protein and nucleic acid composition between organelles isolated from distinct cellular lineages. In animals harbouring a mixture of mutant and wild-type mitochondrial genomes, we use CS-MAP to reveal subtle mosaic patterns of cell-type-specific heteroplasmy across large populations of animals (>10,000 individuals). We demonstrate that the germline is more prone to propagating deleterious mitochondrial genomes than somatic lineages, which we propose is caused by enhanced mtDNA replication in this tissue.