FOXO Transcription Factor DAF-16 Research Articles

Regulation of Caenorhabditis elegans HLH-30 subcellular localization dynamics: Evidence for a redox-dependent mechanism

Basic Helix-Loop-Helix (bHLH) transcription factors TFEB/TFE3 and HLH-30 are key regulators of autophagy induction and lysosomal biogenesis in mammals and C. elegans, respectively. While much is known about the regulation of TFEB/TFE3, how HLH-30 subcellular dynamics and transactivation are modulated are yet poorly understood. Thus, elucidating the regulation of C. elegans HLH-30 will provide evolutionary insight into the mechanisms governing the function of bHLH transcription factor family. We report here that HLH-30 is retained in the cytoplasm mainly through its conserved Ser201 residue and that HLH-30 physically interacts with the 14-3-3 protein FTT-2 in this location. The FoxO transcription factor DAF-16 is not required for HLH-30 nuclear translocation upon stress, despite that both proteins partner to form a complex that coordinately regulates several organismal responses. Similar as described for DAF-16, the importin IMB-2 assists HLH-30 nuclear translocation, but constitutive HLH-30 nuclear localization is not sufficient to trigger its distinctive transcriptional response. Furthermore, we identify FTT-2 as the target of diethyl maleate (DEM), a GSH depletor that causes a transient nuclear translocation of HLH-30. Together, our work demonstrates that the regulation of TFEB/TFE3 and HLH-30 family members is evolutionarily conserved and that, in addition to a direct redox regulation through its conserved single cysteine residue, HLH-30 can also be indirectly regulated by a redox-dependent mechanism, probably through FTT-2 oxidation.

Global histone H2B degradation regulates insulin/IGF signaling-mediated nutrient stress.

Eukaryotic organisms adapt to environmental fluctuations by altering their epigenomic landscapes and transcriptional programs. Nucleosomal histones carry vital epigenetic information and regulate gene expression, yet the mechanisms underlying chromatin-bound histone exchange remain elusive. Here, we found that histone H2Bs are globally degraded in Caenorhabditis elegans during starvation. Our genetic screens identified mutations in ubiquitin and ubiquitin-related enzymes that block H2B degradation in starved animals, identifying lysine 31 as the crucial residue for chromatin-bound H2B ubiquitination and elimination. Retention of aberrant nucleosomal H2B increased the association of the FOXO transcription factor DAF-16 with chromatin, generating an ectopic gene expression profile detrimental to animal viability when insulin/IGF signaling was reduced in well-fed animals. Furthermore, we show that the ubiquitin-proteasome system regulates chromosomal histone turnover in human cells. During larval development, C. elegans epidermal cells undergo H2B turnover after fusing with the epithelial syncytium. Thus, histone degradation may be a widespread mechanism governing dynamic changes of the epigenome.

AMPK–FOXO–IP3R signaling pathway mediates neurological and developmental defects caused by mitochondrial DNA mutations

Pathological mutations in human mitochondrial genomes (mtDNA) can cause a series of neurological, behavioral, and developmental defects, but the underlying molecular mechanisms are poorly understood. We show here that the energy-sensing adenosine monophosphate (AMP)-activated protein kinase (AMPK) signaling pathway plays a key role in mediating similar defects caused by different mtDNA mutations in Caenorhabditis elegans, including loss or reduction of osmotic, chemical and olfactory sensing, locomotion, and associative learning and memory, as well as increased embryonic lethality. mtDNA mutations cause reduced ATP (adenosine triphosphate) levels, activation of C. elegans AMPK AAK-2, and nuclear translocation of the FOXO transcription factor DAF-16. Activated DAF-16 up-regulates the expression of inositol triphosphate receptor ITR-1, an endoplasmic reticulum calcium channel, leading to increased basal cytosolic Ca2+ levels, decreased neuronal responsiveness, compromised synapses, and increased embryonic death. Treatment of mtDNA mutants with vitamin MK-4 restores cellular ATP and cytosolic Ca2+ levels, improves synaptic development, and suppresses sensory and behavioral defects and embryonic death. Our study provides crucial mechanistic insights into neuronal and developmental defects caused by mtDNA mutations and will improve understanding and treatment of related mitochondrial diseases.

Aminopeptidase MNP-1 triggers intestine protease production by activating daf-16 nuclear location to degrade pore-forming toxins in Caenorhabditis elegans.

Pore-forming toxins (PFTs) are effective tools for pathogens infection. By disrupting epithelial barriers and killing immune cells, PFTs promotes the colonization and reproduction of pathogenic microorganisms in their host. In turn, the host triggers defense responses, such as endocytosis, exocytosis, or autophagy. Bacillus thuringiensis (Bt) bacteria produce PFT, known as crystal proteins (Cry) which damage the intestinal cells of insects or nematodes, eventually killing them. In insects, aminopeptidase N (APN) has been shown to act as an important receptor for Cry toxins. Here, using the nematode Caenorhabditis elegans as model, an extensive screening of APN gene family was performed to analyze the potential role of these proteins in the mode of action of Cry5Ba against the nematode. We found that one APN, MNP-1, participate in the toxin defense response, since the mnp-1(ok2434) mutant showed a Cry5Ba hypersensitive phenotype. Gene expression analysis in mnp-1(ok2434) mutant revealed the involvement of two protease genes, F19C6.4 and R03G8.6, that participate in Cry5Ba degradation. Finally, analysis of the transduction pathway involved in F19C6.4 and R03G8.6 expression revealed that upon Cry5Ba exposure, the worms up regulated both protease genes through the activation of the FOXO transcription factor DAF-16, which was translocated into the nucleus. The nuclear location of DAF-16 was found to be dependent on mnp-1 under Cry5Ba treatment. Our work provides evidence of new host responses against PFTs produced by an enteric pathogenic bacterium, resulting in activation of host intestinal proteases that degrade the PFT in the intestine.

Glia of C. elegans coordinate a protective organismal heat shock response independent of the neuronal thermosensory circuit.

Aging organisms lose the ability to induce stress responses, becoming vulnerable to protein toxicity and tissue damage. Neurons can signal to peripheral tissues to induce protective organelle-specific stress responses. Recent work shows that glia can independently induce such responses. Here, we show that overexpression of heat shock factor 1 (hsf-1) in the four astrocyte-like cephalic sheath cells of Caenorhabditis elegans induces a non-cell-autonomous cytosolic unfolded protein response, also known as the heat shock response (HSR). These animals have increased lifespan and heat stress resistance and decreased protein aggregation. Glial HSR regulation is independent of canonical thermosensory circuitry and known neurotransmitters but requires the small clear vesicle release protein UNC-13. HSF-1 and the FOXO transcription factor DAF-16 are partially required in peripheral tissues for non-cell-autonomous HSR, longevity, and thermotolerance. Cephalic sheath glial hsf-1 overexpression also leads to pathogen resistance, suggesting a role for this signaling pathway in immune function.

Insulin/IGF signaling regulates presynaptic glutamate release in aversive olfactory learning.

Insulin/insulin-like growth factor (IGF) receptor signaling (IIS) supports context-dependent learning in vertebrates and invertebrates. Here, we identify cell-specific mechanisms of IIS that integrate sensory information with food context to drive synaptic plasticity and learning. In the nematode Caenorhabditis elegans, pairing food deprivation with an odor such as butanone suppresses attraction to that odor. We find that aversive olfactory learning requires the insulin receptor substrate (IRS) protein IST-1 and atypical signaling through the insulin/IGF-1 receptor DAF-2. Cell-specific knockout and rescue demonstrate that DAF-2 acts in the AWCON sensory neuron, which detects butanone, and that learning preferentially depends upon the axonally localized DAF-2c isoform. Acute food deprivation increases DAF-2 levels in AWCON post-transcriptionally through an insulin- and insulin receptor substrate-1 (ist-1)-dependent process. Aversive learning alters the synaptic output of AWCON by suppressing odor-regulated glutamate release in wild-type animals, but not in ist-1 mutants, suggesting that axonal insulin signaling regulates synaptic transmission to support aversive memory.

Mild mitochondrial impairment enhances innate immunity and longevity through ATFS-1 and p38 signaling.

While mitochondrial function is essential for life in all multicellular organisms, a mild impairment of mitochondrial function can extend longevity in model organisms. By understanding the molecular mechanisms involved, these pathways might be targeted to promote healthy aging. In studying two long‐lived mitochondrial mutants in C. elegans, we found that disrupting subunits of the mitochondrial electron transport chain results in upregulation of genes involved in innate immunity, which is driven by the mitochondrial unfolded protein response (mitoUPR) but also dependent on the canonical p38‐mediated innate immune signaling pathway. Both of these pathways are required for the increased resistance to bacterial pathogens and extended longevity of the long‐lived mitochondrial mutants, as is the FOXO transcription factor DAF‐16. This work demonstrates that both the p38‐mediated innate immune signaling pathway and the mitoUPR act in concert on the same innate immunity genes to promote pathogen resistance and longevity and that input from the mitochondria can extend longevity by signaling through these pathways. This indicates that multiple evolutionarily conserved genetic pathways controlling innate immunity also function to modulate lifespan.

Specific collagens maintain the cuticle permeability barrier in Caenorhabditis elegans.

Collagen-enriched cuticle forms the outermost layer of skin in nematode Caenorhabditis elegans. The nematode’s genome encodes 177 collagens, but little is known about their role in maintaining the structure or barrier function of the cuticle. In this study, we found six permeability determining (PD) collagens. Loss of any of these PD collagens—DPY-2, DPY-3, DPY-7, DPY-8, DPY-9, and DPY-10—led to enhanced susceptibility of nematodes to paraquat (PQ) and antihelminthic drugs- levamisole and ivermectin. Upon exposure to PQ, PD collagen mutants accumulated more PQ and incurred more damage and death despite the robust activation of antioxidant machinery. We find that BLMP-1, a zinc finger transcription factor, maintains the barrier function of the cuticle by regulating the expression of PD collagens. We show that the permeability barrier maintained by PD collagens acts in parallel to FOXO transcription factor DAF-16 to enhance survival of insulin-like receptor mutant, daf-2. In all, this study shows that PD collagens regulate cuticle permeability by maintaining the structure of C. elegans cuticle and thus provide protection against exogenous toxins.

OGT-1 Collaborates with Insulin Signaling Pathway to Regulate Synaptic Assembly

Synaptic formation and maintenance are precisely regulated, and their defects often lead to neurodevelopmental or neurodegenerative disorders. In addition to intrinsic molecular pathways, synaptic structure and function are also regulated by nutrient-related signals. O-GlcNAc transferase (OGT), a nutrient sensor that catalyzes O-GlcNAcylation, is highly abundant in the nervous system and required for synaptic plasticity, learning and memory. However, if and how OGT is involved in presynaptic assembly are largely unknown. In this study, we found that OGT-1 is required for presynaptic assembly specifically in a subset of neurons in the nematode C. elegans. Mechanistically, depending on its glycosyltransferase activity, OGT-1 acts downstream of the insulin receptor DAF-2 and upstream of the FOXO transcription factor DAF-16. Additionally, we also found that OGT-1 is required for associative learning. Our findings indicate that O-GlcNAc signaling collaborates with insulin signaling pathway to regulate presynaptic assembly, providing a potential molecular mechanism underlying the metabolic-related neurological disorders.

Gluconeogenesis and PEPCK are critical components of healthy aging and dietary restriction life extension

High glucose diets are unhealthy, although the mechanisms by which elevated glucose is harmful to whole animal physiology are not well understood. In Caenorhabditis elegans, high glucose shortens lifespan, while chemically inflicted glucose restriction promotes longevity. We investigated the impact of glucose metabolism on aging quality (maintained locomotory capacity and median lifespan) and found that, in addition to shortening lifespan, excess glucose negatively impacts locomotory healthspan. Conversely, disrupting glucose utilization by knockdown of glycolysis-specific genes results in large mid-age physical improvements via a mechanism that requires the FOXO transcription factor DAF-16. Adult locomotory capacity is extended by glycolysis disruption, but maximum lifespan is not, indicating that limiting glycolysis can increase the proportion of life spent in mobility health. We also considered the largely ignored role of glucose biosynthesis (gluconeogenesis) in adult health. Directed perturbations of gluconeogenic genes that specify single direction enzymatic reactions for glucose synthesis decrease locomotory healthspan, suggesting that gluconeogenesis is needed for healthy aging. Consistent with this idea, overexpression of the central gluconeogenic gene pck-2 (encoding PEPCK) increases health measures via a mechanism that requires DAF-16 to promote pck-2 expression in specific intestinal cells. Dietary restriction also features DAF-16-dependent pck-2 expression in the intestine, and the healthspan benefits conferred by dietary restriction require pck-2. Together, our results describe a new paradigm in which nutritional signals engage gluconeogenesis to influence aging quality via DAF-16. These data underscore the idea that promotion of gluconeogenesis might be an unappreciated goal for healthy aging and could constitute a novel target for pharmacological interventions that counter high glucose consequences, including diabetes.

Isoflurane Exposure in Juvenile Caenorhabditis elegans Causes Persistent Changes in Neuron Dynamics.

Animal studies demonstrate that anesthetic exposure during neurodevelopment can lead to persistent behavioral impairment. The changes in neuronal function underlying these effects are incompletely understood. Caenorhabditis elegans is well suited for functional imaging of postanesthetic effects on neuronal activity. This study aimed to examine such effects within the neurocircuitry underlying C. elegans locomotion. C. elegans were exposed to 8% isoflurane for 3 h during the neurodevelopmentally critical L1 larval stage. Locomotion was assessed during early and late adulthood. Spontaneous activity was measured within the locomotion command interneuron circuitry using confocal and light-sheet microscopy of the calcium-sensitive fluorophore GCaMP6s. C. elegans exposed to isoflurane demonstrated attenuation in spontaneous reversal behavior, persisting throughout the animal's lifespan (reversals/min: untreated early adulthood, 1.14 ± 0.42, vs. isoflurane-exposed early adulthood, 0.83 ± 0.55; untreated late adulthood, 1.75 ± 0.64, vs. isoflurane-exposed late adulthood, 1.14 ± 0.68; P = 0.001 and 0.006, respectively; n > 50 animal tracks/condition). Likewise, isoflurane exposure altered activity dynamics in the command interneuron AVA, which mediates crawling reversals. The rate at which AVA transitions between activity states was found to be increased. These anesthetic-induced effects were more pronounced with age (off-to-on activity state transition time (s): untreated early adulthood, 2.5 ± 1.2, vs. isoflurane-exposed early adulthood, 1.9 ± 1.3; untreated late adulthood, 4.6 ± 3.0, vs. isoflurane-exposed late adulthood, 3.0 ± 2.4; P = 0.028 and 0.008, respectively; n > 35 traces acquired from more than 15 animals/condition). Comparable effects were observed throughout the command interneuron circuitry, indicating that isoflurane exposure alters transition rates between behavioral crawling states of the system overall. These effects were modulated by loss-of-function mutations within the FoxO transcription factor daf-16 and by rapamycin-mediated mechanistic Target of Rapamycin (mTOR) inhibition. Altered locomotive behavior and activity dynamics indicate a persistent effect on interneuron dynamics and circuit function in C. elegansafter developmental exposure to isoflurane. These effects are modulated by a loss of daf-16 or mTOR activity, consistent with a pathologic activation of stress-response pathways.

Amyloid-beta (Aβ1–42)-induced paralysis in Caenorhabditis elegans is reduced through NHR-49/PPARalpha

Alzheimer´s disease is a neurodegenerative disorder characterized by the misfolding and aggregation of amyloid β (Aβ). Agonists of peroxisomal proliferator-activated receptors (PPARs) are discussed as anti-amyloidogenic compounds, e.g. due to their cholesterol-lowering activities. In a previous study we have shown in Caenorhabditis elegans expressing human Aβ in muscle cells, that inhibition of steroid-signaling, by RNAi of respective members of the signaling pathway or by reducing cellular cholesterol uptake, both increases the nuclear translocation of the foxo transcription factor DAF-16 and concomitantly reduces Aβ-induced paralysis. Using RNAi in the present study we show that NHR-49/PPARalpha inhibits steroidal-signaling upstream of DAF-9, a cytochrome P450-dependent enzyme which generates dafachronic acids as ligands for the nuclear hormone receptor DAF-12, and upstream of DAF-12 itself. The NHR-49/PPARalpha agonist fenofibrate reduces Aβ-induced paralysis in dependence on nhr-49 and nuclear translocation of DAF-16.In conclusion, activation of NHR-49/PPARalpha inhibits the steroidal-signaling pathway which increases the nuclear translocation of DAF-16 and inhibits the Aβ-induced phenotype in an Alzheimer model of C. elegans.

The FOXO's Advantages of Being a Family: Considerations on Function and Evolution.

The nematode Caenorhabditis elegans possesses a unique (with various isoforms) FOXO transcription factor DAF-16, which is notorious for its role in aging and its regulation by the insulin-PI3K-AKT pathway. In humans, five genes (including a protein-coding pseudogene) encode for FOXO transcription factors that are targeted by the PI3K-AKT axis, such as in C. elegans. This common regulation and highly conserved DNA-binding domain are the pillars of this family. In this review, I will discuss the possible meaning of possessing a group of very similar proteins and how it can generate additional functionality to more complex organisms. I frame this discussion in relation to the much larger super family of Forkhead proteins to which they belong. FOXO members are very often co-expressed in the same cell type. The overlap of function and expression creates a certain redundancy that might be a safeguard against the accidental loss of FOXO function, which could otherwise lead to disease, particularly, cancer. This is one of the points that will be examined in this “family affair” report.

Profiling microRNAs through development of the parasitic nematode Haemonchus identifies nematode-specific miRNAs that suppress larval development

Parasitic nematodes transition between dramatically different free-living and parasitic stages, with correctly timed development and migration crucial to successful completion of their lifecycle. However little is known of the mechanisms controlling these transitions. microRNAs (miRNAs) negatively regulate gene expression post-transcriptionally and regulate development of diverse organisms. Here we used microarrays to determine the expression profile of miRNAs through development and in gut tissue of the pathogenic nematode Haemonchus contortus. Two miRNAs, mir-228 and mir-235, were enriched in infective L3 larvae, an arrested stage analogous to Caenorhabditis elegans dauer larvae. We hypothesized that these miRNAs may suppress development and maintain arrest. Consistent with this, inhibitors of these miRNAs promoted H. contortus development from L3 to L4 stage, while genetic deletion of C. elegans homologous miRNAs reduced dauer arrest. Epistasis studies with C. elegans daf-2 mutants showed that mir-228 and mir-235 synergise with FOXO transcription factor DAF-16 in the insulin signaling pathway. Target prediction suggests that these miRNAs suppress metabolic and transcription factor activity required for development. Our results provide novel insight into the expression and functions of specific miRNAs in regulating nematode development and identify miRNAs and their target genes as potential therapeutic targets to limit parasite survival within the host.

Amyloid-beta induced paralysis is reduced by cholecalciferol through inhibition of the steroid-signaling pathway in an Alzheimer model of Caenorhabditis elegans

ABSTRACT Objectives: Alzheimer’s disease (AD) is a neurodegenerative disorder resulting from the accumulation of toxic β-amyloid (Aβ) aggregates in the human brain. Epidemiological studies have shown that elevated cholesterol plasma levels are associated with the development of AD and we have previously shown that cholesterol restriction reduces the Aβ-induced paralysis in an Alzheimer model of the nematode Caenorhabditis elegans. In the present study we investigated the effects of the cholesterol homolog cholecalciferol, i.e. vitamin D, on Aβ-induced paralysis in C. elegans and its interference with the steroid-signaling pathway. Methods: Aβ-induced paralysis was assessed in the C. elegans strain CL2006, expressing human Aβ1-42 under control of a muscle-specific promoter. Knockdown of members of the steroid-signaling pathway was achieved by RNA interference (RNAi). Nuclear translocation of foxo transcription factor DAF-16 was visualized using the strain TJ356, carrying a daf-16::gfp transgene. Results: Cholecalciferol at a concentration of 1 µM reduced the Aβ-induced paralysis in CL2006 significantly, which was reverted by increasing the cholesterol concentration in the medium. Knockdown of nhr-8, daf-36, daf-9 or daf-12, all reduced Aβ-induced paralysis to the same extent as cholecalciferol with no additional or synergistic effects under co-application. Functional DAF-16 proved to be crucial for the effects of cholecalciferol and DAF-16 nuclear translocation was increased by cholecalciferol and also RNAi versus nhr-8, daf-36, daf-9 or daf-12 with no additive or synergistic effects. Conclusions: Our results suggest, that cholecalciferol inhibits Aβ-induced paralysis in C. elegans through inhibition of steroid-signaling and the concomitant nuclear translocation of DAF-16.

Betaine-rich sugar beet molasses protects from homocysteine-induced reduction of survival in Caenorhabditis elegans.

Homocysteine (Hcy) in humans represents a blood-borne biomarker which predicts the risk of age-related diseases and mortality. Using the nematode Caenorhabditis elegans, we tested whether feeding betaine-rich sugar beet molasses affects the survival under heat stress in the presence of Hcy, in spite of a gene loss in betaine-homocysteine methyltransferase. Knockdown of the genes relevant for remethylation or transsulfuration of Hcy was achieved by RNA interference (RNAi). Survival assay was conducted under heat stress at 37°C and Hcy levels were determined by enzyme-linked immunosorbent assay. Addition of 500mg/l betaine-rich sugar beet molasses (SBM) prevented the survival reduction that was caused by exposure to Hcy at 37°C. Although SBM was no longer capable of reducing Hcy levels under RNAi versus homologues for 5, 10-methylenetetrahydrofolate reductase or cystathionine-β-synthase, it still enabled the survival extension by SBM under exposure to Hcy. In contrast, RNAi for the small heat shock protein hsp-16.2 or the foxo transcription factor daf-16 both prevented the extension of survival by betaine-rich molasses in the presence of Hcy. Our studies demonstrate that betaine-rich SBM is able to prevent survival reduction caused by Hcy in C. elegans in dependence on hsp-16.2 and daf-16 but independent of the remethylation pathway.

Glyphosate-based herbicides modulate oxidative stress response in the nematode Caenorhabditis elegans

Glyphosate-based formulation is used as non-selective and post-emergent herbicides in urban and rural activities. In view of its recurring applications in agricultural producing countries, the increase of glyphosate concentration in the environment stresses the need to test the adverse effects on non-target organisms and assess the risk of its use. This paper analyzes the toxicological and oxidative stress and modulatory effects of a glyphosate commercial formulation (glyphosate F) on the nematode Caenorhabditis elegans. We detected ROS production and enhancement of oxidative stress response in glyphosate F-treated nematodes. Particularly, we found an increased ctl-1 catalase gene expression of a catalase specific activity. In addition, we showed that glyphosate F treatment activated the FOXO transcription factor DAF-16, a critical target of the insulin/IGF-1 signaling pathway, which modulates the transcription of a broad range of genes involved in stress resistance, reproductive development, dauer formation, and longevity. In summary, the exposure of glyphosate F induces an oxidative imbalance in C. elegans that leads to the DAF-16 activation and consequently to the expression of genes that boost the antioxidant defense system. In this regard, clt-1 gene and catalase activity proved to be excellent biomarkers to develop more sensitive protocols to assess the environmental risk of glyphosate use.

O-GlcNAc Signaling Orchestrates the Regenerative Response to Neuronal Injury in Caenorhabditis elegans

Regrowth of an axon after injury is an inherently metabolic undertaking. Yet the mechanisms of metabolic regulation that influence repair following injury are not well understood. O-linked β-N-acetylglucosamine (O-GlcNAc) is a post-translational modification of serines and threonines that functions as a sensor of cellular nutrients. Performing invivo laser axotomies in Caenorhabditis elegans, we find that neuronal regeneration is substantially increased by disruptions of either the O-GlcNAc transferase or the O-GlcNAcase that decrease and increase O-GlcNAc levels, respectively. A lack of O-GlcNAc induces the AKT-1 branch in the insulin-signaling pathway to use glycolysis. In contrast, increased O-GlcNAc levels activate an opposing branch of the insulin-signaling pathway whereby SGK-1 modulates the FOXO transcription factor DAF-16 to influence mitochondrial function. The existence of this toggle-like mechanism between metabolic pathways suggests that O-GlcNAc signaling conveys cellular nutrient status to orchestrate metabolism in a damaged neuron and maximize the regenerative response.

MPK-1/ERK pathway regulates DNA damage response during development through DAF-16/FOXO.

Ultraviolet (UV) induces distorting lesions to the DNA that can lead to stalling of the RNA polymerase II (RNAP II) and that are removed by transcription-coupled nucleotide excision repair (TC-NER). In humans, mutations in the TC-NER genes CSA and CSB lead to severe postnatal developmental defects in Cockayne syndrome patients. In Caenorhabditis elegans, mutations in the TC-NER genes csa-1 and csb-1, lead to developmental growth arrest upon UV treatment. We conducted a genetic suppressor screen in the nematode to identify mutations that could suppress the developmental defects in csb-1 mutants. We found that mutations in the ERK1/2 MAP kinase mpk-1 alleviate the developmental retardation in TC-NER mutants, while constitutive activation of the RAS-MAPK pathway exacerbates the DNA damage-induced growth arrest. We show that MPK-1 act via insulin/insulin-like signaling pathway and regulates the FOXO transcription factor DAF-16 to mediate the developmental DNA damage response.

Activation of DAF-16/FOXO by reactive oxygen species contributes to longevity in long-lived mitochondrial mutants in Caenorhabditis elegans.

Mild deficits in mitochondrial function have been shown to increase lifespan in multiple species including worms, flies and mice. Here, we study three C. elegans mitochondrial mutants (clk-1, isp-1 and nuo-6) to identify overlapping genetic pathways that contribute to their longevity. We find that genes regulated by the FOXO transcription factor DAF-16 are upregulated in all three strains, and that the transcriptional changes present in these worms overlap significantly with the long-lived insulin-IGF1 signaling pathway mutant daf-2. We show that DAF-16 and multiple DAF-16 interacting proteins (MATH-33, IMB-2, CST-1/2, BAR-1) are required for the full longevity of all three mitochondrial mutants. Our results suggest that the activation of DAF-16 in these mutants results from elevated levels of reactive oxygen species. Overall, this work reveals an overlapping genetic pathway required for longevity in three mitochondrial mutants, and, combined with previous work, demonstrates that DAF-16 is a downstream mediator of lifespan extension in multiple pathways of longevity.