PINK1/parkin are key mediators of stress-induced mitophagy in vitro, but their impact on basal mitophagy in vivo is unclear. Novel Drosophila reporter lines reveal abundant mitophagy in many tissues, including dopaminergic neurons, that is unaffected by loss of PINK1/parkin.

Summary Mitochondrial Ca 2+ uptake is an important mediator of metabolism and cell death. Identification of components of the highly conserved mitochondrial Ca 2+ uniporter has opened it up to genetic analysis in model organisms. Here, we report a comprehensive genetic characterization of all known uniporter components conserved in Drosophila . While loss of pore-forming MCU or EMRE abolishes fast mitochondrial Ca 2+ uptake, this results in only mild phenotypes when young, despite shortened lifespans. In contrast, loss of the MICU1 gatekeeper is developmentally lethal, consistent with unregulated Ca 2+ uptake. Mutants for the neuronally restricted regulator MICU3 are viable with mild neurological impairment. Genetic interaction analyses reveal that MICU1 and MICU3 are not functionally interchangeable. More surprisingly, loss of MCU or EMRE does not suppress MICU1 mutant lethality, suggesting that this results from uniporter-independent functions. Our data reveal the interplay among components of the mitochondrial Ca 2+ uniporter and shed light on their physiological requirements in vivo .

Somatic mutations in the mitochondrial genome (mtDNA) have been linked to multiple disease conditions and to ageing itself. In Drosophila , knock-in of a proofreading deficient mtDNA polymerase ( POLG ) generates high levels of somatic point mutations and also small indels, but surprisingly limited impact on organismal longevity or fitness. Here we describe a new mtDNA mutator model based on a mitochondrially-targeted cytidine deaminase, APOBEC1. mito-APOBEC1 acts as a potent mutagen which exclusively induces C:G>T:A transitions with no indels or mtDNA depletion. In these flies, the presence of multiple non-synonymous substitutions, even at modest heteroplasmy, disrupts mitochondrial function and dramatically impacts organismal fitness. A detailed analysis of the mutation profile in the POLG and mito-APOBEC1 models reveals that mutation type (quality) rather than quantity is a critical factor in impacting organismal fitness. The specificity for transition mutations and the severe phenotypes make mito-APOBEC1 an excellent mtDNA mutator model for ageing research.

Mutations in PINK1 and Parkin/PRKN cause the degeneration of dopaminergic neurons in familial forms of Parkinson’s disease but the precise pathogenic mechanisms are unknown. The PINK1/Parkin pathway has been described to play a central role in mitochondrial homeostasis by signalling the targeted destruction of damaged mitochondria, however, how disrupting this process leads to neuronal death was unclear until recently. An elegant study in mice revealed that the loss of Pink1 or Prkn coupled with an additional mitochondrial stress resulted in the aberrant activation of the innate immune signalling, mediated via the cGAS/STING pathway, causing degeneration of dopaminergic neurons and motor impairment. Genetic knockout of Sting was sufficient to completely prevent neurodegeneration and accompanying motor deficits. To determine whether Sting plays a conserved role in Pink1/parkin related pathology, we tested for genetic interactions between Sting and Pink1/parkin in Drosophila. Surprisingly, we found that loss of Sting, or its downstream effector Relish, was insufficient to suppress the behavioural deficits or mitochondria disruption in the Pink1/parkin mutants. Thus, we conclude that phenotypes associated with loss of Pink1/parkin are not universally due to aberrant activation of the STING pathway.

SummaryPINK1/parkin are key mediators of stress-induced mitophagy in vitro but their impact on basal mitophagy in vivo is unclear. Novel Drosophila reporters lines reveal abundant mitophagy in many tissues including dopaminergic neurons but is unaffected by loss of PINK1/parkin. . CC-BY 4.0 International license It is made available under a (which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/235077 doi: bioRxiv preprint first posted online Jan. 12, 2018; 2 Abstract Parkinson's disease factors, PINK1 and parkin, are strongly implicated in stress-induced mitophagy in vitro, but little is known about their impact on basal mitophagy in vivo. We generated transgenic Drosophila expressing fluorescent mitophagy reporters to evaluate the impact of Pink1/parkin mutations on basal mitophagy under physiological conditions. We find that mitophagy is readily detectable and abundant in many tissues including Parkinson's disease relevant dopaminergic neurons. However, we did not detect mitolysosomes in flight muscle. Surprisingly, in Pink1 or parkin null flies we did not observe any substantial impact on basal mitophagy. As these flies exhibit locomotor defects and dopaminergic neuron loss, our findings raise questions about current assumptions of the pathogenic mechanism associated with the PINK1/Parkin pathway. Our findings provide evidence that Pink1 and parkin are not essential for bulk basal mitophagy in Drosophila. They also emphasize that mechanisms underpinning basal mitophagy remain largely obscure.

Most eukaryotic proteins are N-terminally acetylated, but the functional impact on a global scale has remained obscure. Using genome-wide CRISPR knockout screens in human cells, we reveal a strong genetic dependency between a major N-terminal acetyltransferase and specific ubiquitin ligases. Biochemical analyses uncover that both the ubiquitin ligase complex UBR4-KCMF1 and the acetyltransferase NatC recognize proteins bearing an unacetylated N-terminal methionine followed by a hydrophobic residue. NatC KO-induced protein degradation and phenotypes are reversed by UBR knockdown, demonstrating the central cellular role of this interplay. We reveal that loss of Drosophila NatC is associated with male sterility, reduced longevity, and age-dependent loss of motility due to developmental muscle defects. Remarkably, muscle-specific overexpression of UbcE2M, one of the proteins targeted for NatC KO-mediated degradation, suppresses defects of NatC deletion. In conclusion, NatC-mediated N-terminal acetylation acts as a protective mechanism against protein degradation, which is relevant for increased longevity and motility.

Parkinson's disease-related proteins, PINK1 and Parkin, act in a common pathway to maintain mitochondrial quality control. While the PINK1-Parkin pathway can promote autophagic mitochondrial turnover (mitophagy) following mitochondrial toxification in cell culture, alternative quality control pathways are suggested. To analyse the mechanisms by which the PINK1-Parkin pathway operates in vivo, we developed methods to detect Ser65phosphorylated ubiquitin (pS65-Ub) in Drosophila. Exposure to the oxidant paraquat led to robust, Pink1-dependent pS65-Ub production, while pS65-Ub accumulates in unstimulated parkin-null flies, consistent with blocked degradation. Additionally, we show that pS65-Ub specifically accumulates on disrupted mitochondria in vivo. Depletion of the core autophagy proteins Atg1, Atg5 and Atg8a did not cause pS65-Ub accumulation to the same extent as loss of parkin, and overexpression of parkin promoted turnover of both basal and paraquat-induced pS65-Ub in an Atg5-null background. Thus, we have established that pS65-Ub immunodetection can be used to analyse Pink1-Parkin function in vivo as an alternative to reporter constructs. Moreover, our findings suggest that the Pink1-Parkin pathway can promote mitochondrial turnover independently of canonical autophagy in vivo.

Mitochondrial Ca 2+ uptake is an important mediator of metabolism and cell death. Identification of components of the highly conserved mitochondrial Ca 2+ uniporter has opened it up to genetic analysis in model organisms. Here we report a comprehensive genetic characterisation of the known uniporter components conserved in Drosophila. While loss of MCU or EMRE abolishes fast mitochondrial Ca 2+ uptake, this results in surprisingly mild phenotypes. In contrast, loss of the regulatory gatekeeper component MICU1 has a much more severe phenotype, being developmental lethal, consistent with unregulated Ca 2+ uptake. Mutants for MICU3 are viable with mild neurological phenotypes. Genetic interaction studies reveal that MICU1 and MICU3 are not functionally interchangeable. More surprisingly, loss of MCU or EMRE does not suppress MICU1 mutant lethality, suggesting that the lethality results from MCU-independent functions. This study helps shed light on the physiological requirements of the mitochondrial Ca 2+ uniporter, and provides a suite of tools to interrogate their interplay in homeostasis and disease conditions. B. DNA analysis of MCU 1 . Primer sequences are detailed in the 'Materials and Methods' section.The control genotype yielded a ~2.5 kb band, compared to ~900 bp for MCU 1 homozygotes. C. Western blot analysis of MCU 1 . Immunoblots were probed with the indicated antibodies. Asterisk denotes a non-specific band. Mitochondrial ATP5A is used as a loading control. D.Representative traces of Ca 2+ uptake in mitochondria isolated from adult flies of the indicated genotypes after addition of 45 μM CaCl2. Extramitochondrial Ca 2+ was measured by Calcium Green-5N fluorescence. Ca 2+ was released from mitochondria by addition of 1 μM FCCP. a.u.: arbitrary units. The control genotype is w 1118 . Addition of the MCU inhibitor Ruthenium Red (RuR; 2 μM) blocks mitochondrial Ca 2+ uptake, which is mirrored by MCU 1 . Mitochondrial Ca 2+ uptake is restored by transgenic re-expression of MCU. E. Relative uptake kinetics were determined through linear fits of the initial phase of Ca 2+ uptake and normalized to the wild type control (mean ± SEM, n = 3). Figure 2. MCU 1 shortens lifespan without impacting organismal phenotypes despite respiratory defects. A. The percentage of adult flies eclosing as homozygous MCU 1 mutants versus balanced heterozygotes, together with the expected Mendelian ratio in the offspring (n > 700). B. Lifespan curves of MCU 1 male flies compared with control (w 1118 ) and transgenic rescue (MCU 1 + MCU). Statistical analysis: Mantel-Cox log-rank test (n ≧ 74). C. Climbing assay of control (da/+) and MCU 1 flies, 2 and 20 days post-eclosion. Significance measured by Kruskal-Wallis test with Dunn's post-hoc correction for multiple comparisons (mean ± 95% confidence interval; n > 50; ns, non-significant). D. Relative ATP levels from control and MCU 1 flies. Statistical analysis: unpaired t-test (mean ± SD; n 2-3; **** P < 0.0001, ns, non-significant). E, F. Oxygen consumption rate (OCR) of control and MC...