RESUMO
Background: There are >14,500 structurally diverse per- and polyfluoroalkyl substances (PFAS). Despite knowledge that these "forever chemicals" are in 99% of humans, mechanisms of toxicity and adverse health effects are incompletely known. Furthermore, the contribution of genetic variation to PFAS susceptibility and health consequences is unknown. Objectives: We determined the toxicity of a structurally distinct set of PFAS in twelve genetically diverse strains of the genetic model system Caenorhabditis elegans. Methods: Dose-response curves for four perfluoroalkyl carboxylic acids (PFNA, PFOA, PFPeA, and PFBA), two perfluoroalkyl sulfonic acids (PFOS and PFBS), two perfluoroalkyl sulfonamides (PFOSA and PFBSA), two fluoroether carboxylic acids (GenX and PFMOAA), one fluoroether sulfonic acid (PFEESA), and two fluorotelomers (6:2 FCA and 6:2 FTS) were determined in the C. elegans laboratory reference strain, N2, and eleven genetically diverse wild strains. Body length was quantified by image analysis at each dose after 48 hr of developmental exposure of L1 arrest-synchronized larvae to estimate effective concentration values (EC50). Results: There was a significant range in toxicity among PFAS: PFOSA > PFBSA ≈ PFOS ≈ PFNA > PFOA > GenX ≈ PFEESA > PFBS ≈ PFPeA ≈ PFBA. Long-chain PFAS had greater toxicity than short-chain, and fluorosulfonamides were more toxic than carboxylic and sulfonic acids. Genetic variation explained variation in susceptibility to PFBSA, PFOS, PFBA, PFOA, GenX, PFEESA, PFPeA, and PFBA. There was significant variation in toxicity among C. elegans strains due to chain length, functional group, and between legacy and emerging PFAS. Conclusion: C. elegans respond to legacy and emerging PFAS of diverse structures, and this depends on specific structures and genetic variation. Harnessing the natural genetic diversity of C. elegans and the structural complexity of PFAS is a powerful New Approach Methodology (NAM) to investigate structure-activity relationships and mechanisms of toxicity which may inform regulation of other PFAS to improve human and environmental health.
RESUMO
Insulin/IGF signaling (IIS) regulates developmental and metabolic plasticity. Conditional regulation of insulin-like peptide expression and secretion promotes different phenotypes in different environments. However, IIS can also be regulated by other, less-understood mechanisms. For example, stability of the only known insulin/IGF receptor in C. elegans, DAF-2/INSR, is regulated by CHIP-dependent ubiquitination. Disruption of chn-1/CHIP reduces longevity in C. elegans by increasing DAF-2/INSR abundance and IIS activity in adults. Likewise, mutation of a ubiquitination site causes daf-2(gk390525) to display gain-of-function phenotypes in adults. However, we show that this allele displays loss-of-function phenotypes in larvae, and that its effect on IIS activity transitions from negative to positive during development. In contrast, the allele acts like a gain-of-function in larvae cultured at high temperature, inhibiting temperature-dependent dauer formation. Disruption of chn-1/CHIP causes an increase in IIS activity in starved L1 larvae, unlike daf-2(gk390525). CHN-1/CHIP ubiquitinates DAF-2/INSR at multiple sites. These results suggest that the sites that are functionally relevant to negative regulation of IIS vary in larvae and adults, at different temperatures, and in nutrient-dependent fashion, revealing additional layers of IIS regulation.
RESUMO
Nutrient availability governs growth and quiescence, and many animals arrest development when starved. Using C. elegans L1 arrest as a model, we show that gene expression changes deep into starvation. Surprisingly, relative expression of germline-enriched genes increases for days. We conditionally degrade the large subunit of RNA polymerase II using the auxin-inducible degron system and analyze absolute expression levels. We find that somatic transcription is required for survival, but the germline maintains transcriptional quiescence. Thousands of genes are continuously transcribed in the soma, though their absolute abundance declines, such that relative expression of germline transcripts increases given extreme transcript stability. Aberrantly activating transcription in starved germ cells compromises reproduction, demonstrating important physiological function of transcriptional quiescence. This work reveals alternative somatic and germline gene-regulatory strategies during starvation, with the soma maintaining a robust transcriptional response to support survival and the germline maintaining transcriptional quiescence to support future reproductive success.
Assuntos
Proteínas de Caenorhabditis elegans , Inanição , Animais , Caenorhabditis elegans/fisiologia , Proteínas de Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Células Germinativas/metabolismo , Ácidos Indolacéticos/metabolismo , RNA Polimerase II/genética , RNA Polimerase II/metabolismo , Inanição/metabolismoRESUMO
Starvation resistance is important to disease and fitness, but the genetic basis of its natural variation is unknown. Uncovering the genetic basis of complex, quantitative traits such as starvation resistance is technically challenging. We developed a synthetic-population (re)sequencing approach using molecular inversion probes (MIP-seq) to measure relative fitness during and after larval starvation in Caenorhabditis elegans. We applied this competitive assay to 100 genetically diverse, sequenced, wild strains, revealing natural variation in starvation resistance. We confirmed that the most starvation-resistant strains survive and recover from starvation better than the most starvation-sensitive strains using standard assays. We performed genome-wide association (GWA) with the MIP-seq trait data and identified three quantitative trait loci (QTL) for starvation resistance, and we created near isogenic lines (NILs) to validate the effect of these QTL on the trait. These QTL contain numerous candidate genes including several members of the Insulin/EGF Receptor-L Domain (irld) family. We used genome editing to show that four different irld genes have modest effects on starvation resistance. Natural variants of irld-39 and irld-52 affect starvation resistance, and increased resistance of the irld-39; irld-52 double mutant depends on daf-16/FoxO. DAF-16/FoxO is a widely conserved transcriptional effector of insulin/IGF signaling (IIS), and these results suggest that IRLD proteins modify IIS, although they may act through other mechanisms as well. This work demonstrates efficacy of using MIP-seq to dissect a complex trait and it suggests that irld genes are natural modifiers of starvation resistance in C. elegans.
Assuntos
Proteínas de Caenorhabditis elegans , Inanição , Animais , Caenorhabditis elegans/genética , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/metabolismo , Fatores de Transcrição Forkhead/metabolismo , Estudo de Associação Genômica Ampla , Insulina/metabolismo , Inanição/genéticaRESUMO
Mutations in the well-known tumor suppressor PTEN are observed in many cancers. PTEN is a dual-specificity phosphatase that harbors lipid and protein-phosphatase activities. The Caenorhabditis elegans PTEN ortholog is daf-18, which has pleiotropic effects on dauer formation, aging, starvation resistance, and development. Function of 3 daf-18 point-mutants, G174E, D137A, and C169S, had previously been investigated using high-copy transgenes in a daf-18 null background. These alleles were generated based on their mammalian counterparts and were treated as though they specifically disrupt lipid or protein-phosphatase activity, or both, respectively. Here, we investigated these alleles using genome editing of endogenous daf-18. We assayed 3 traits relevant to L1 starvation resistance, and we show that each point mutant is essentially as starvation-sensitive as a daf-18 null mutant. Furthermore, we show that G174E and D137A do not complement each other, suggesting overlapping effects on lipid and protein-phosphatase activity. We also show that each allele has strong effects on nucleocytoplasmic localization of DAF-16/FoxO and dauer formation, both of which are regulated by PI3K signaling, similar to a daf-18 null allele. In addition, each allele also disrupts M-cell quiescence during L1 starvation, though D137A has a weaker effect than the other alleles, including the null. Our results confirm that daf-18/PTEN is important for promoting starvation resistance and developmental arrest and that it is a potent regulator of PI3K signaling, and they highlight challenges of using genetic analysis to link specific DAF-18/PTEN enzymatic activities to particular phenotypes.
Assuntos
Proteínas de Caenorhabditis elegans , Caenorhabditis elegans , PTEN Fosfo-Hidrolase , Inanição , Animais , Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/genética , Larva/genética , Lipídeos , Mutação de Sentido Incorreto , PTEN Fosfo-Hidrolase/genética , Fosfatidilinositol 3-Quinases/genética , Inanição/genéticaRESUMO
The publication of the Caenorhabditis briggsae reference genome in 2003 enabled the first comparative genomics studies between C. elegans and C. briggsae, shedding light on the evolution of genome content and structure in the Caenorhabditis genus. However, despite being widely used, the currently available C. briggsae reference genome is substantially less complete and structurally accurate than the C. elegans reference genome. Here, we used high-coverage Oxford Nanopore long-read and chromosome-conformation capture data to generate chromosome-level reference genomes for two C. briggsae strains: QX1410, a new reference strain closely related to the laboratory AF16 strain, and VX34, a highly divergent strain isolated in China. We also sequenced 99 recombinant inbred lines generated from reciprocal crosses between QX1410 and VX34 to create a recombination map and identify chromosomal domains. Additionally, we used both short- and long-read RNA sequencing data to generate high-quality gene annotations. By comparing these new reference genomes to the current reference, we reveal that hyper-divergent haplotypes cover large portions of the C. briggsae genome, similar to recent reports in C. elegans and C. tropicalis. We also show that the genomes of selfing Caenorhabditis species have undergone more rearrangement than their outcrossing relatives, which has biased previous estimates of rearrangement rate in Caenorhabditis. These new genomes provide a substantially improved platform for comparative genomics in Caenorhabditis and narrow the gap between the quality of genomic resources available for C. elegans and C. briggsae.
Assuntos
Caenorhabditis , Animais , Caenorhabditis/genética , Caenorhabditis elegans/genética , Cromossomos , Genoma , GenômicaRESUMO
Despite reports of parental exposure to stress promoting physiological adaptations in progeny in diverse organisms, there remains considerable debate over the significance and evolutionary conservation of such multigenerational effects. Here, we investigate four independent models of intergenerational adaptations to stress in Caenorhabditis elegans - bacterial infection, eukaryotic infection, osmotic stress, and nutrient stress - across multiple species. We found that all four intergenerational physiological adaptations are conserved in at least one other species, that they are stress -specific, and that they have deleterious tradeoffs in mismatched environments. By profiling the effects of parental bacterial infection and osmotic stress exposure on progeny gene expression across species, we established a core set of 587 genes that exhibited a greater than twofold intergenerational change in expression in response to stress in C. elegans and at least one other species, as well as a set of 37 highly conserved genes that exhibited a greater than twofold intergenerational change in expression in all four species tested. Furthermore, we provide evidence suggesting that presumed adaptive and deleterious intergenerational effects are molecularly related at the gene expression level. Lastly, we found that none of the effects we detected of these stresses on C. elegans F1 progeny gene expression persisted transgenerationally three generations after stress exposure. We conclude that intergenerational responses to stress play a substantial and evolutionarily conserved role in regulating animal physiology and that the vast majority of the effects of parental stress on progeny gene expression are reversible and not maintained transgenerationally.
Assuntos
Adaptação Biológica , Caenorhabditis elegans , Evolução Molecular , Animais , Caenorhabditis elegans/genética , Caenorhabditis elegans/microbiologia , Caenorhabditis elegans/parasitologia , Caenorhabditis elegans/fisiologia , Estado Nutricional , Pressão OsmóticaRESUMO
Quiescence, an actively-maintained reversible state of cell cycle arrest, is not well understood. PTEN is one of the most frequently lost tumor suppressors in human cancers and regulates quiescence of stem cells and cancer cells. The sole PTEN ortholog in Caenorhabditis elegans is daf-18. In a C. elegans loss-of-function mutant for daf-18, primordial germ cells (PGCs) divide inappropriately in L1 larvae hatched into starvation conditions, in a TOR-dependent manner. Here, we further investigated the role of daf-18 in maintaining PGC quiescence in L1 starvation. We found that maternal or zygotic daf-18 is sufficient to maintain cell cycle quiescence, that daf-18 acts in the germ line and soma, and that daf-18 affects timing of PGC divisions in fed animals. Importantly, our results also implicate daf-18 in repression of germline zygotic gene activation, though not in germline fate specification. However, TOR is less important to germline zygotic gene expression, suggesting that in the absence of food, daf-18/PTEN prevents inappropriate germline zygotic gene activation and cell division by distinct mechanisms.
Assuntos
Proteínas de Caenorhabditis elegans/metabolismo , Pontos de Checagem do Ciclo Celular/fisiologia , Células Germinativas/metabolismo , Animais , Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/fisiologia , Divisão Celular/genética , Proliferação de Células/genética , Larva/genética , PTEN Fosfo-Hidrolase/genética , PTEN Fosfo-Hidrolase/metabolismo , Transdução de Sinais/genética , Ativação Transcricional/genética , Zigoto/metabolismoRESUMO
Across diverse taxa, selfing species have evolved independently from outcrossing species thousands of times. The transition from outcrossing to selfing decreases the effective population size, effective recombination rate and heterozygosity within a species. These changes lead to a reduction in genetic diversity, and therefore adaptive potential, by intensifying the effects of random genetic drift and linked selection. Within the nematode genus Caenorhabditis, selfing has evolved at least three times, and all three species, including the model organism Caenorhabditis elegans, show substantially reduced genetic diversity relative to outcrossing species. Selfing and outcrossing Caenorhabditis species are often found in the same niches, but we still do not know how selfing species with limited genetic diversity can adapt to these environments. Here, we examine the whole-genome sequences from 609 wild C. elegans strains isolated worldwide and show that genetic variation is concentrated in punctuated hyper-divergent regions that cover 20% of the C. elegans reference genome. These regions are enriched in environmental response genes that mediate sensory perception, pathogen response and xenobiotic stress response. Population genomic evidence suggests that genetic diversity in these regions has been maintained by long-term balancing selection. Using long-read genome assemblies for 15 wild strains, we show that hyper-divergent haplotypes contain unique sets of genes and show levels of divergence comparable to levels found between Caenorhabditis species that diverged millions of years ago. These results provide an example of how species can avoid the evolutionary dead end associated with selfing.
Assuntos
Caenorhabditis elegans , Variação Genética , Animais , Evolução Biológica , Caenorhabditis elegans/genética , Genoma , HaplótiposRESUMO
Standard laboratory culture of Caenorhabditis elegans utilizes solid growth media with a bacterial food source. However, this culture method limits control of food availability and worm population density, factors that impact many life-history traits. Here, we describe liquid-culture protocols for precisely modulating bacterial food availability and population density, facilitating reliable production of arrested L1 larvae, dauer larvae, dietarily restricted worms, or well-fed worms. Worms can be grown in small quantities for standard assays or in the millions for other applications. For complete details on the use and execution of these protocols, please refer to Hibshman et al. (2016), Webster et al. (2018), and Jordan et al. (2019).
Assuntos
Caenorhabditis elegans/crescimento & desenvolvimento , Inanição , AnimaisRESUMO
Mating systems have profound effects on genetic diversity and compatibility. The convergent evolution of self-fertilization in three Caenorhabditis species provides a powerful lens to examine causes and consequences of mating system transitions. Among the selfers, Caenorhabditis tropicalis is the least genetically diverse and most afflicted by outbreeding depression. We generated a chromosomal-scale genome for C. tropicalis and surveyed global diversity. Population structure is very strong, and islands of extreme divergence punctuate a genomic background that is highly homogeneous around the globe. Outbreeding depression in the laboratory is caused largely by multiple Medea-like elements, genetically consistent with maternal toxin/zygotic antidote systems. Loci with Medea activity harbor novel and duplicated genes, and their activity is modified by mito-nuclear background. Segregating Medea elements dramatically reduce fitness, and simulations show that selfing limits their spread. Frequent selfing in C. tropicalis may therefore be a strategy to avoid Medea-mediated outbreeding depression.
Assuntos
Evolução Biológica , Caenorhabditis/fisiologia , Autofertilização , AnimaisRESUMO
Caenorhabditis elegans survives on ephemeral food sources in the wild, and the species has a variety of adaptive responses to starvation. These features of its life history make the worm a powerful model for studying developmental, behavioral, and metabolic starvation responses. Starvation resistance is fundamental to life in the wild, and it is relevant to aging and common diseases such as cancer and diabetes. Worms respond to acute starvation at different times in the life cycle by arresting development and altering gene expression and metabolism. They also anticipate starvation during early larval development, engaging an alternative developmental program resulting in dauer diapause. By arresting development, these responses postpone growth and reproduction until feeding resumes. A common set of signaling pathways mediates systemic regulation of development in each context but with important distinctions. Several aspects of behavior, including feeding, foraging, taxis, egg laying, sleep, and associative learning, are also affected by starvation. A variety of conserved signaling, gene regulatory, and metabolic mechanisms support adaptation to starvation. Early life starvation can have persistent effects on adults and their descendants. With its short generation time, C. elegans is an ideal model for studying maternal provisioning, transgenerational epigenetic inheritance, and developmental origins of adult health and disease in humans. This review provides a comprehensive overview of starvation responses throughout the C. elegans life cycle.
Assuntos
Envelhecimento/genética , Caenorhabditis elegans/genética , Regulação da Expressão Gênica no Desenvolvimento , Estágios do Ciclo de Vida , Inanição/genética , Animais , Caenorhabditis elegans/crescimento & desenvolvimento , Caenorhabditis elegans/metabolismoRESUMO
A rapidly growing body of literature in several organisms suggests that environmentally-induced adaptive changes in phenotype can be transmitted across multiple generations. Although within-generation plasticity has been well documented, multigenerational plasticity represents a significant departure from conventional evolutionary thought. Studies of C. elegans have been particularly influential because this species exhibits extensive phenotypic plasticity, it is often essentially isogenic, and it has well-documented molecular and cellular mechanisms through which nongenetic inheritance occurs. However, while experimentalists are eager to claim that nongenetic modes of inheritance characterized in this and other model systems enhance fitness, many biologists remain skeptical given the extraordinary nature of this claim. We establish three criteria to evaluate how compelling the evidence for adaptive multigenerational plasticity is, and we use these criteria to critically examine putative cases of it in C. elegans. We conclude by suggesting potentially fruitful avenues for future research.
Assuntos
Adaptação Fisiológica/genética , Caenorhabditis elegans/fisiologia , Epigênese Genética/fisiologia , Animais , Caenorhabditis elegans/genéticaRESUMO
To understand the genetic basis of complex traits, it is important to be able to efficiently phenotype many genetically distinct individuals. In the nematode Caenorhabditis elegans, individuals have been isolated from diverse populations around the globe and whole-genome sequenced. As a result, hundreds of wild strains with known genome sequences can be used for genome-wide association studies (GWAS). However, phenotypic analysis of these strains can be laborious, particularly for quantitative traits requiring multiple measurements per strain. Starvation resistance is likely a fitness-proximal trait for nematodes, and it is related to metabolic disease risk in humans. However, natural variation in C. elegans starvation resistance has not been systematically characterized, and precise measurement of the trait is time-intensive. Here, we developed a population-selection-and-sequencing-based approach to phenotype starvation resistance in a pool of 96 wild strains. We used restriction site-associated DNA sequencing (RAD-seq) to infer the frequency of each strain among survivors in a mixed culture over time during starvation. We used manual starvation survival assays to validate the trait data, confirming that strains that increased in frequency over time are starvation-resistant relative to strains that decreased in frequency. Further, we found that variation in starvation resistance is significantly associated with variation at a region on chromosome III. Using a near-isogenic line (NIL), we showed the importance of this genomic interval for starvation resistance. This study demonstrates the feasibility of using population selection and sequencing in an animal model for phenotypic analysis of quantitative traits, documents natural variation of starvation resistance in C. elegans, and identifies a genomic region that contributes to such variation.
Assuntos
Adaptação Biológica/genética , Caenorhabditis elegans/genética , Caenorhabditis elegans/metabolismo , Mapeamento Cromossômico , Cromossomos , Seleção Genética , Inanição , Animais , Estudo de Associação Genômica Ampla , Fenótipo , Característica Quantitativa HerdávelRESUMO
The roundworm C. elegans reversibly arrests larval development during starvation [1], but extended early-life starvation reduces reproductive success [2, 3]. Maternal dietary restriction (DR) buffers progeny from starvation as young larvae, preserving reproductive success [4]. However, the developmental basis of reduced fertility following early-life starvation is unknown, and it is unclear how maternal diet modifies developmental physiology in progeny. We show here that extended starvation in first-stage (L1) larvae followed by unrestricted feeding results in a variety of developmental abnormalities in the reproductive system, including proliferative germ-cell tumors and uterine masses that express neuronal and epidermal cell fate markers. We found that maternal DR and reduced maternal insulin/insulin-like growth factor (IGF) signaling (IIS) increase oocyte provisioning of vitellogenin lipoprotein, reducing penetrance of starvation-induced abnormalities in progeny, including tumors. Furthermore, we show that maternal DR and reduced maternal IIS reduce IIS in progeny. daf-16/FoxO and skn-1/Nrf, transcriptional effectors of IIS, are required in progeny for maternal DR and increased vitellogenin provisioning to suppress starvation-induced abnormalities. daf-16/FoxO activity in somatic tissues is sufficient to suppress starvation-induced abnormalities, suggesting cell-nonautonomous regulation of reproductive system development. This work reveals that early-life starvation compromises reproductive development and that vitellogenin-mediated intergenerational insulin/IGF-to-insulin/IGF signaling mediates adaptation to nutrient availability.
Assuntos
Adaptação Fisiológica , Caenorhabditis elegans/fisiologia , Transdução de Sinais , Animais , Caenorhabditis elegans/genética , Caenorhabditis elegans/crescimento & desenvolvimento , Proteínas de Caenorhabditis elegans/metabolismo , Insulina/metabolismo , Larva/genética , Larva/crescimento & desenvolvimento , Larva/fisiologia , Nutrientes/fisiologia , Somatomedinas/metabolismo , Vitelogeninas/metabolismoRESUMO
The Caenorhabditis elegans insulin-like signaling network supports homeostasis and developmental plasticity. The genome encodes 40 insulin-like peptides and one known receptor. Feedback regulation has been reported, but the extent of feedback and its effect on signaling dynamics in response to changes in nutrient availability has not been determined. We measured messenger RNA expression for each insulin-like peptide, the receptor daf-2, components of the PI3K pathway, and its transcriptional effectors daf-16/FoxO and skn-1/Nrf at high temporal resolution during transition from a starved, quiescent state to a fed, growing state in wild type and mutants affecting daf-2/InsR and daf-16/FoxO. We also analyzed the effect of temperature on insulin-like gene expression. We found that most PI3K pathway components and insulin-like peptides are affected by signaling activity, revealing pervasive positive and negative feedback regulation at intra- and intercellular levels. Reporter gene analysis demonstrated that the daf-2/InsR agonist daf-28 positively regulates its own transcription and that the putative agonist ins-6 cross-regulates DAF-28 protein expression through feedback. Our results show that positive and negative feedback regulation of insulin-like signaling is widespread, giving rise to an organismal FoxO-to-FoxO signaling network that supports homeostasis during fluctuations in nutrient availability.
Assuntos
Proteínas de Caenorhabditis elegans/metabolismo , Retroalimentação Fisiológica , Receptor de Insulina/metabolismo , Transdução de Sinais , Somatomedinas/metabolismo , Animais , Caenorhabditis elegans , Proteínas de Caenorhabditis elegans/genética , Fatores de Transcrição Forkhead/genética , Fatores de Transcrição Forkhead/metabolismo , Fator 1 Relacionado a NF-E2/genética , Fator 1 Relacionado a NF-E2/metabolismo , Receptor de Insulina/genética , Somatomedinas/genéticaRESUMO
Insulin and insulin-like signaling regulates a broad spectrum of growth and metabolic responses to a variety of internal and environmental stimuli. For example, the inhibition of insulin-like signaling in C. elegans mediates its response to both osmotic stress and starvation. We report that in response to osmotic stress the cytosolic sulfotransferase SSU-1 antagonizes insulin-like signaling and promotes developmental arrest. Both SSU-1 and the DAF-16 FOXO transcription factor, which is activated when insulin signaling is low, are needed to drive specific responses to reduced insulin-like signaling. We demonstrate that SSU-1 functions in a single pair of sensory neurons to control intercellular signaling via the nuclear hormone receptor NHR-1 and promote both the specific transcriptional response to osmotic stress and altered lysophosphatidylcholine metabolism. Our results show the requirement of a sulfotransferase-nuclear hormone receptor neurohormonal signaling pathway for some but not all consequences of reduced insulin-like signaling.
Assuntos
Caenorhabditis elegans/metabolismo , Proteínas do Tecido Nervoso/efeitos dos fármacos , Neurotransmissores/metabolismo , Receptor de Insulina/efeitos dos fármacos , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/fisiologia , Sulfotransferases/antagonistas & inibidores , Animais , Proteínas de Caenorhabditis elegans/antagonistas & inibidores , Proteínas de Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/metabolismo , Clonagem Molecular , Embrião não Mamífero , Desenvolvimento Embrionário/genética , Fatores de Transcrição Forkhead/antagonistas & inibidores , Fatores de Transcrição Forkhead/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Insulina/metabolismo , Lisofosfatidilcolinas/metabolismo , Mutagênese , Pressão Osmótica , RNA Mensageiro/biossíntese , RNA Mensageiro/genética , Receptor de Insulina/metabolismo , Receptores Citoplasmáticos e Nucleares/metabolismo , Células Receptoras Sensoriais/efeitos dos fármacos , Inanição , Estresse Fisiológico , Sulfotransferases/genética , Sulfotransferases/metabolismoRESUMO
BACKGROUND: Developmental physiology is very sensitive to nutrient availability. For instance, in the nematode Caenorhabditis elegans, newly hatched L1-stage larvae require food to initiate postembryonic development. In addition, larvae arrested in the dauer diapause, a non-feeding state of developmental arrest that occurs during the L3 stage, initiate recovery when exposed to food. Despite the essential role of food in C. elegans development, the contribution of food perception versus ingestion on physiology has not been delineated. RESULTS: We used a pharmacological approach to uncouple the effects of food (bacteria) perception and ingestion in C. elegans. Perception was not sufficient to promote postembryonic development in L1-stage larvae. However, L1 larvae exposed to food without ingestion failed to develop upon return to normal culture conditions, instead displaying an irreversible arrest phenotype. Inhibition of gene expression during perception rescued subsequent development, demonstrating that the response to perception without feeding is deleterious. Perception altered DAF-16/FOXO subcellular localization, reflecting activation of insulin/IGF signaling (IIS). The insulin-like peptide daf-28 was specifically required, suggesting perception in chemosensory neurons, where it is expressed, regulates peptide synthesis and possibly secretion. However, genetic manipulation of IIS did not modify the irreversible arrest phenotype caused by food perception, revealing that wild-type function of the IIS pathway is not required to produce this phenotype and that other pathways affected by perception of food in the absence of its ingestion are likely to be involved. Gene expression and Nile red staining showed that food perception could alter lipid metabolism and storage. We found that starved larvae sense environmental polypeptides, with similar molecular and developmental effects as perception of bacteria. Environmental polypeptides also promoted recovery from dauer diapause, suggesting that perception of polypeptides plays an important role in the life history of free-living nematodes. CONCLUSIONS: We conclude that actual ingestion of food is required to initiate postembryonic development in C. elegans. We also conclude that polypeptides are perceived as a food-associated cue in this and likely other animals, initiating a signaling and gene regulatory cascade that alters metabolism in anticipation of feeding and development, but that this response is detrimental if feeding does not occur.
Assuntos
Caenorhabditis elegans/efeitos dos fármacos , Ingestão de Alimentos/efeitos dos fármacos , Expressão Gênica/efeitos dos fármacos , Ivermectina/administração & dosagem , Peptídeos/fisiologia , Animais , Caenorhabditis elegans/crescimento & desenvolvimento , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/metabolismo , Sinais (Psicologia) , Alimentos , Insulina/metabolismo , Larva/efeitos dos fármacos , Larva/crescimento & desenvolvimento , Larva/metabolismo , Transdução de Sinais/efeitos dos fármacos , Somatomedinas/metabolismoRESUMO
Starvation significantly alters cellular physiology, and signs of aging have been reported to occur during starvation. Mitochondria are essential to the regulation of cellular energetics and aging. We sought to determine whether mitochondria exhibit signs of aging during starvation and whether quality control mechanisms regulate mitochondrial physiology during starvation. We describe effects of starvation on mitochondria in the first and third larval stages of the nematode Caenorhabditis elegans. When starved, C. elegans larvae enter developmental arrest. We observed fragmentation of the mitochondrial network, a reduction in mitochondrial DNA (mtDNA) copy number, and accumulation of DNA damage during starvation-induced developmental arrest. Mitochondrial function was also compromised by starvation. Starved worms had lower basal, maximal, and ATP-linked respiration. These observations are consistent with reduced mitochondrial quality, similar to mitochondrial phenotypes during aging. Using pharmacological and genetic approaches, we found that worms deficient for autophagy were short-lived during starvation and recovered poorly from extended starvation, indicating sensitivity to nutrient stress. Autophagy mutants unc-51/Atg1 and atg-18/Atg18 maintained greater mtDNA content than wild-type worms during starvation, suggesting that autophagy promotes mitochondrial degradation during starvation. unc-51 mutants also had a proportionally smaller reduction in oxygen consumption rate during starvation, suggesting that autophagy also contributes to reduced mitochondrial function. Surprisingly, mutations in genes involved in mitochondrial fission and fusion as well as selective mitophagy of damaged mitochondria did not affect mitochondrial content during starvation. Our results demonstrate the profound influence of starvation on mitochondrial physiology with organismal consequences, and they show that these physiological effects are influenced by autophagy.
Assuntos
Proteína Homóloga à Proteína-1 Relacionada à Autofagia/genética , Autofagia/genética , Caenorhabditis elegans/fisiologia , Dinâmica Mitocondrial/genética , Inanição/genética , Animais , Proteínas Relacionadas à Autofagia/genética , Proteínas Relacionadas à Autofagia/metabolismo , Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/metabolismo , Dano ao DNA/genética , DNA Mitocondrial/genética , Larva/genética , Larva/metabolismo , Longevidade/genética , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Mitocôndrias/genética , Mitocôndrias/metabolismo , Dinâmica Mitocondrial/fisiologia , Mitofagia/genética , Inanição/metabolismoRESUMO
[This corrects the article DOI: 10.1371/journal.pgen.1006396.].