Global analysis of dauer gene expression in Caenorhabditis elegans

Evidence for Bxy-npr-21 on controlling juveniles' growth and modulating male sexual arousal: from molecules to behaviors

BACKGROUND

Bursaphelenchus xylophilus is considered a quarantine plant nematode species, that causes major damage to pine ecosystems globally. However, there are few reports on the identification and function of the sex pheromone receptors involved in mating. The function of Bxy-npr-21 as a potential sex pheromone receptor gene was verified from molecules to behaviors in this study.

RESULTS

Here, we firstly report that Bxy-npr-21 is a receptor gene involved in sexual attraction. The bioinformatic analysis indicated that the Bxy-npr-21 gene in B. xylophilus encodes a GPCR. The expression characterization for Bxy-npr-21 showed that it is widely expressed in whole body of larvae and sex organs of adults. The RNAi results suggested that the Bxy-npr-21 gene was involved mainly in movement, feeding, and mating. Sexual arousal experiments further validated that the Bxy-npr-21 gene was involved in the activation of males by female chemical signaling.

CONCLUSIONS

Our results strongly suggest that the Bxy-npr-21 gene is a key gene that regulates nematode growth, development and reproduction. The results of this study lay the foundation for revealing the molecular mechanisms of growth and reproduction of B. xylophilus. It can also provide an important basis for further control of B. xylophilus. © 2025 Society of Chemical Industry.

Nutrient control of growth and metabolism through mTORC1 regulation of mRNA splicing

Cellular growth and organismal development are remarkably complex processes that require the nutrient-responsive kinase mechanistic target of rapamycin complex 1 (mTORC1). Anticipating that important mTORC1 functions remained to be identified, we employed genetic and bioinformatic screening in C. elegans to uncover mechanisms of mTORC1 action. Here, we show that during larval growth, nutrients induce an extensive reprogramming of gene expression and alternative mRNA splicing by acting through mTORC1. mTORC1 regulates mRNA splicing and the production of protein-coding mRNA isoforms largely independently of its target p70 S6 kinase (S6K) by increasing the activity of the serine/arginine-rich (SR) protein RSP-6 (SRSF3/7) and other splicing factors. mTORC1-mediated mRNA splicing regulation is critical for growth; mediates nutrient control of mechanisms that include energy, nucleotide, amino acid, and other metabolic pathways; and may be conserved in humans. Although mTORC1 inhibition delays aging, mTORC1-induced mRNA splicing promotes longevity, suggesting that when mTORC1 is inhibited, enhancement of this splicing might provide additional anti-aging benefits.

Robustness and variability in Caenorhabditis elegans dauer gene expression

Both plasticity and robustness are pervasive features of developmental programs. The dauer in Caenorhabditis elegans is an arrested, hypometabolic alternative to the third larval stage of the nematode. Dauers undergo dramatic tissue remodeling and extensive physiological, metabolic, behavioral, and gene expression changes compared to conspecifics that continue development and can be induced by several adverse environments or genetic mutations that act as independent and parallel inputs into the larval developmental program. Therefore, dauer induction is an example of phenotypic plasticity. However, whether gene expression in dauer larvae induced to arrest development by different genetic or environmental triggers is invariant or varies depending on their route into dauer has not been examined. By using RNA-sequencing to characterize gene expression in different types of dauer larvae and computing the variance and concordance within Gene Ontologies (GO) and gene expression networks, we find that the expression patterns within most pathways are strongly correlated between dauer larvae, suggestive of transcriptional robustness. However, gene expression within specific defense pathways, pathways regulating some morphological traits, and several metabolic pathways differ between the dauer larvae. We speculate that the transcriptional robustness of core dauer pathways allows for the buffering of variation in the expression of genes involved in adaptation, allowing the dauers induced by different stimuli to survive in and exploit different niches.

Neuronal IL-17 controls Caenorhabditis elegans developmental diapause through CEP-1/p53

During metazoan development, how cell division and metabolic programs are coordinated with nutrient availability remains unclear. Here, we show that nutrient availability signaled by the neuronal cytokine, ILC-17.1, switches Caenorhabditis elegans development between reproductive growth and dormancy by controlling the activity of the tumor suppressor p53 ortholog, CEP-1. Specifically, upon food availability, ILC-17.1 signaling by amphid neurons promotes glucose utilization and suppresses CEP-1/p53 to allow growth. In the absence of ILC-17.1, CEP-1/p53 is activated, up-regulates cell-cycle inhibitors, decreases phosphofructokinase and cytochrome C expression, and causes larvae to arrest as stress-resistant, quiescent dauers. We propose a model whereby ILC-17.1 signaling links nutrient availability and energy metabolism to cell cycle progression through CEP-1/p53. These studies describe ancestral functions of IL-17 s and the p53 family of proteins and are relevant to our understanding of neuroimmune mechanisms in cancer. They also reveal a DNA damage-independent function of CEP-1/p53 in invertebrate development and support the existence of a previously undescribed C. elegans dauer pathway.

Filarial DAF-12 sense the host serum to resume iL3 development during infection

Nematode parasites enter their definitive host at the developmentally arrested infectious larval stage (iL3), and the ligand-dependent nuclear receptor DAF-12 contributes to trigger their development to adulthood. Here, we characterized DAF-12 from the filarial nematodes Brugia malayi and Dirofilaria immitis and compared them with DAF-12 from the non-filarial nematodes Haemonchus contortus and Caenorhabditis elegans. Interestingly, Dim and BmaDAF-12 exhibit high sequence identity and share a striking higher sensitivity than Hco and CelDAF-12 to the natural ligands Δ4- and Δ7-dafachronic acids (DA). Moreover, sera from different mammalian species activated specifically Dim and BmaDAF-12 while the hormone-depleted sera failed to activate the filarial DAF-12. Accordingly, hormone-depleted serum delayed the commencement of development of D. immitis iL3 in vitro. Consistent with these observations, we show that spiking mouse charcoal stripped-serum with Δ4-DA at the concentration measured in normal mouse serum restores its capacity to activate DimDAF-12. This indicates that DA present in mammalian serum participate in filarial DAF-12 activation. Finally, analysis of publicly available RNA sequencing data from B. malayi showed that, at the time of infection, putative gene homologs of the DA synthesis pathways are coincidently downregulated. Altogether, our data suggest that filarial DAF-12 have evolved to specifically sense and survive in a host environment, which provides favorable conditions to quickly resume larval development. This work sheds new light on the regulation of filarial nematodes development while entering their definitive mammalian host and may open the route to novel therapies to treat filarial infections.

Nematode Pheromones: Structures and Functions

Pheromones are chemical signals secreted by one individual that can affect the behaviors of other individuals within the same species. Ascaroside is an evolutionarily conserved family of nematode pheromones that play an integral role in the development, lifespan, propagation, and stress response of nematodes. Their general structure comprises the dideoxysugar ascarylose and fatty-acid-like side chains. Ascarosides can vary structurally and functionally according to the lengths of their side chains and how they are derivatized with different moieties. In this review, we mainly describe the chemical structures of ascarosides and their different effects on the development, mating, and aggregation of nematodes, as well as how they are synthesized and regulated. In addition, we discuss their influences on other species in various aspects. This review provides a reference for the functions and structures of ascarosides and enables their better application.

Regulation of dormancy during tumor dissemination: the role of the ECM

The study of the metastatic cascade has revealed the complexity of the process and the multiple cellular states that disseminated cancer cells must go through. The tumor microenvironment and in particular the extracellular matrix (ECM) plays an important role in regulating the transition from invasion, dormancy to ultimately proliferation during the metastatic cascade. The time delay from primary tumor detection to metastatic growth is regulated by a molecular program that maintains disseminated tumor cells in a non-proliferative, quiescence state known as tumor cell dormancy. Identifying dormant cells and their niches in vivo and how they transition to the proliferative state is an active area of investigation, and novel approaches have been developed to track dormant cells during dissemination. In this review, we highlight the latest research on the invasive nature of disseminated tumor cells and their link to dormancy programs. We also discuss the role of the ECM in sustaining dormant niches at distant sites.

Insect diapause: from a rich history to an exciting future

Diapause, a stage-specific developmental arrest, is widely exploited by insects to bridge unfavorable seasons. Considerable progress has been made in understanding the ecology, physiology and evolutionary implications of insect diapause, yet intriguing questions remain. A more complete understanding of diapause processes on Earth requires a better geographic spread of investigations, including more work in the tropics and at high latitudes. Questions surrounding energy management and trade-offs between diapause and non-diapause remain understudied. We know little about how maternal effects direct the diapause response, and regulators of prolonged diapause are also poorly understood. Numerous factors that were recently linked to diapause are still waiting to be placed in the regulatory network leading from photoreception to engagement of the diapause program. These factors include epigenetic processes and small noncoding RNAs, and emerging data also suggest a role for the microbiome in diapause regulation. Another intriguing feature of diapause is the complexity of the response, resulting in a diverse suite of responses that comprise the diapause syndrome. Select transcription factors likely serve as master switches turning on these diverse responses, but we are far from understanding the full complexity. The richness of species displaying diapause offers a platform for seeking common components of a 'diapause toolbox'. Across latitudes, during invasion events and in a changing climate, diapause offers grand opportunities to probe evolutionary change and speciation. At a practical level, diapause responses can be manipulated for insect control and long-term storage. Diapausing insects also contain a treasure trove of pharmacological compounds and offer promising models for human health.

Mitochondrial genome recovery by ATFS-1 is essential for development after starvation

Nutrient availability regulates the C. elegans life cycle as well as mitochondrial physiology. Food deprivation significantly reduces mitochondrial genome (mtDNA) numbers and leads to aging-related phenotypes. Here we show that the bZIP (basic leucine zipper) protein ATFS-1, a mediator of the mitochondrial unfolded protein response (UPRmt), is required to promote growth and establish a functional germline after prolonged starvation. We find that recovery of mtDNA copy numbers and development after starvation requires mitochondrion-localized ATFS-1 but not its nuclear transcription activity. We also find that the insulin-like receptor DAF-2 functions upstream of ATFS-1 to modulate mtDNA content. We show that reducing DAF-2 activity represses ATFS-1 nuclear function while causing an increase in mtDNA content, partly mediated by mitochondrion-localized ATFS-1. Our data indicate the importance of the UPRmt in recovering mitochondrial mass and suggest that atfs-1-dependent mtDNA replication precedes mitochondrial network expansion after starvation.

De Novo Transcriptome Assembly and Analysis of Longevity Genes Using Subterranean Termite (Reticulitermes chinensis) Castes

The longevity phenomenon is entirely controlled by the insulin signaling pathway (IIS-pathway). Both vertebrates and invertebrates have IIS-pathways that are comparable to one another, though no one has previously described de novo transcriptome assembly of IIS-pathway-associated genes in termites. In this research, we analyzed the transcriptomes of both reproductive (primary kings “PK” and queens “PQ”, secondary worker reproductive kings “SWRK” and queens “SWRQ”) and non-reproductive (male “WM” and female “WF” workers) castes of the subterranean termite Reticulitermes chinensis. The goal was to identify the genes responsible for longevity in the reproductive and non-reproductive castes. Through transcriptome analysis, we annotated 103,589,264 sequence reads and 184,436 (7G) unigenes were assembled, GC performance was measured at 43.02%, and 64,046 sequences were reported as CDs sequences. Of which 35 IIS-pathway-associated genes were identified, among 35 genes, we focused on the phosphoinositide-dependent kinase-1 (Pdk1), protein kinase B2 (akt2-a), tuberous sclerosis-2 (Tsc2), mammalian target of rapamycin (mTOR), eukaryotic translation initiation factor 4E (EIF4E) and ribosomal protein S6 (RPS6) genes. Previously these genes (Pdk1, akt2-a, mTOR, EIF4E, and RPS6) were investigated in various organisms, that regulate physiological effects, growth factors, protein translation, cell survival, proliferation, protein synthesis, cell metabolism and survival, autophagy, fecundity rate, egg size, and follicle number, although the critical reason for longevity is still unclear in the termite castes. However, based on transcriptome profiling, the IIS-pathway-associated genes could prolong the reproductive caste lifespan and health span. Therefore, the transcriptomic shreds of evidence related to IIS-pathway genes provide new insights into the maintenance and relationships between biomolecular homeostasis and remarkable longevity. Finally, we propose a strategy for future research to decrypt the hidden costs associated with termite aging in reproductive and non-reproductive castes.

Alternative somatic and germline gene-regulatory strategies during starvation-induced developmental arrest

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.

Webster et al. show that the transcriptional response to starvation is mounted early in larval somatic cells supporting survival but that it wanes over time. In contrast, they show that the germline remains transcriptionally quiescent deep into starvation, supporting reproductive potential, while maintaining its transcriptome via transcript stability.

The CHARGE syndrome ortholog CHD-7 regulates TGF-β pathways in Caenorhabditis elegans

CHARGE syndrome is a complex developmental disorder caused by mutations in the chromodomain helicase DNA-binding protein-7 (CHD7) and characterized by retarded growth and malformations in the heart and nervous system. Despite the public health relevance of this disorder, relevant cellular pathways and targets of CHD7 that relate to disease pathology are still poorly understood. Here we report that chd-7, the nematode ortholog of Chd7, is required for dauer morphogenesis, lifespan determination, stress response, and body size determination. Consistent with our discoveries, we found chd-7 to be allelic to scd-3, a previously identified dauer suppressor from the DAF-7/ tumor growth factor-β (TGF-β) pathway. Epistatic analysis places CHD-7 at the level of the DAF-3/DAF-5 complex, but we found that CHD-7 also directly impacts the expression of multiple components of this pathway. Transcriptomic analysis revealed that chd-7 mutants fail to repress daf-9 for execution of the dauer program. In addition, CHD-7 regulates the DBL-1/BMP pathway components and shares roles in male tail development and cuticle synthesis. To explore a potential conserved function for chd-7 in vertebrates, we used Xenopus laevis embryos, an established model to study craniofacial development. Morpholino-mediated knockdown of Chd7 led to a reduction in col2a1 messenger RNA (mRNA) levels, a collagen whose expression depends on TGF-β signaling. Both embryonic lethality and craniofacial defects in Chd7-depleted tadpoles were partially rescued by overexpression of col2a1 mRNA. We suggest that Chd7 has conserved roles in regulation of the TGF-β signaling pathway and pathogenic Chd7 could lead to a defective extracellular matrix deposition.

Microenvironment-mediated cancer dormancy: Insights from metastability theory

Dormancy is an evolutionarily conserved protective mechanism widely observed in nature. A pathological example is found during cancer metastasis, where cancer cells disseminate from the primary tumor, home to secondary organs, and enter a growth-arrested state, which could last for decades. Recent studies have pointed toward the microenvironment being heavily involved in inducing, preserving, or ceasing this dormant state, with a strong focus on identifying specific molecular mechanisms and signaling pathways. Increasing evidence now suggests the existence of an interplay between intracellular as well as extracellular biochemical and mechanical cues in guiding such processes. Despite the inherent complexities associated with dormancy, proliferation, and growth of cancer cells and tumor tissues, viewing these phenomena from a physical perspective allows for a more global description, independent from many details of the systems. Building on the analogies between tissues and fluids and thermodynamic phase separation concepts, we classify a number of proposed mechanisms in terms of a thermodynamic metastability of the tumor with respect to growth. This can be governed by interaction with the microenvironment in the form of adherence (wetting) to a substrate or by mechanical confinement of the surrounding extracellular matrix. By drawing parallels with clinical and experimental data, we advance the notion that the local energy minima, or metastable states, emerging in the tissue droplet growth kinetics can be associated with a dormant state. Despite its simplicity, the provided framework captures several aspects associated with cancer dormancy and tumor growth.

Endocrine pheromones couple fat rationing to dauer diapause through HNF4α nuclear receptors

Developmental diapause is a widespread strategy for animals to survive seasonal starvation and environmental harshness. Diapaused animals often ration body fat to generate a basal level of energy for enduring survival. How diapause and fat rationing are coupled, however, is poorly understood. The nematode Caenorhabditis elegans excretes pheromones to the environment to induce a diapause form called dauer larva. Through saturated forward genetic screens and CRISPR knockout, we found that dauer pheromones feed back to repress the transcription of ACOX-3, MAOC-1, DHS-28, DAF-22 (peroxisomal β-oxidation enzymes dually involved in pheromone synthesis and fat burning), ALH-4 (aldehyde dehydrogenase for pheromone synthesis), PRX-10 and PRX-11 (peroxisome assembly and proliferation factors). Dysfunction of these pheromone enzymes and factors relieves the repression. Surprisingly, transcription is repressed not by pheromones excreted but by pheromones endogenous to each animal. The endogenous pheromones regulate the nuclear translocation of HNF4α family nuclear receptor NHR-79 and its co-receptor NHR-49, and, repress transcription through the two receptors. The feedback repression maintains pheromone homeostasis, increases fat storage, decreases fat burning, and prolongs dauer lifespan. Thus, the exocrine dauer pheromones possess an unexpected endocrine function to mediate a peroxisome-nucleus crosstalk, coupling dauer diapause to fat rationing.

Kinetic characterization and thermostability of C. elegans cytoplasmic and mitochondrial malate dehydrogenases

Malate dehydrogenase (MDH) catalyzes the conversion of NAD⁺ and malate to NADH and oxaloacetate in the citric acid cycle. Eukaryotes have one MDH isozyme that is imported into the mitochondria and one in the cytoplasm. We overexpressed and purified Caenorhabditis elegans cytoplasmic MDH-1 and mitochondrial MDH-2 in E. coli. Our goal was to compare the kinetic and structural properties of these enzymes because C. elegans can survive adverse environmental conditions, such as lack of food and elevated temperatures. In steady-state enzyme kinetics assays, we measured K_M values for oxaloacetate of 54 and 52 μM and K_M values for NADH of 61 and 107 μM for MDH-1 and MDH-2, respectively. We partially purified endogenous MDH-1 and MDH-2 from a mixed population of worms and separated them using anion exchange chromatography. Both endogenous enzymes had a K_M for oxaloacetate similar to that of the corresponding recombinant enzyme. Recombinant MDH-1 and MDH-2 had maximum activity at 40 °C and 35 °C, respectively. In a thermotolerance assay, MDH-1 was much more thermostable than MDH-2. Protein homology modeling predicted that MDH-1 had more intersubunit salt-bridges than mammalian MDH1 enzymes, and these ionic interactions may contribute to its thermostability. In contrast, the MDH-2 homology model predicted fewer intersubunit ionic interactions compared to mammalian MDH2 enzymes. These results suggest that the increased stability of MDH-1 may facilitate its ability to remain active in adverse environmental conditions. In contrast, MDH-2 may use other strategies, such as protein binding partners, to function under similar conditions.

Bone morphogenetic proteins (BMPs) in the central regulation of energy balance and adult neural plasticity

The current worldwide obesity pandemic highlights a need to better understand the regulation of energy balance and metabolism, including the role of the nervous system in controlling energy intake and energy expenditure. Neural plasticity in the hypothalamus of the adult brain has been implicated in full-body metabolic health, however, the mechanisms surrounding hypothalamic plasticity are incompletely understood. Bone morphogenetic proteins (BMPs) control metabolic health through actions in the brain as well as in peripheral tissues such as adipose, together regulating both energy intake and energy expenditure. BMP ligands, receptors, and inhibitors are found throughout plastic adult brain regions and have been demonstrated to modulate neurogenesis and gliogenesis, as well as synaptic and dendritic plasticity. This role for BMPs in adult neural plasticity is distinct from their roles in brain development. Existing evidence suggests that BMPs induce weight loss through hypothalamic pathways, and part of the mechanism of action may be through inducing neural plasticity. In this review, we summarize the data regarding how BMPs affect neural plasticity in the adult mammalian brain, as well as the relationship between central BMP signaling and metabolic health.

The Caenorhabditis elegans 12-kDa small heat shock proteins with little in vitro chaperone activity play crucial roles for its dauer formation, longevity, and reproduction

Small heat shock proteins (sHSPs) are known to exhibit in vitro chaperone activity by suppressing the aggregation of misfolded proteins. The 12-kDa sHSPs (Hsp12s) subfamily members from Caenorhabditis elegans, including Hsp12.2, Hsp12.3, and Hsp12.6, however, are devoid of such chaperone activity, and their in vivo functions are poorly understood. Here we verified that Hsp12.1, similar to its homologs Hsp12.2, Hsp12.3, and Hsp12.6, hardly exhibited any chaperone activity. Strikingly, we demonstrated that these Hsp12s seem to play crucial physiological roles in C. elegans, for suppressing dauer formation and promoting both longevity and reproduction. A unique sHSP gene from Filarial nematode worm Brugia malayi was identified such that it encodes two products, one as a full-length Hsp12.6 protein and the other one having an N-terminal arm of normal length but lacks the C-terminal extension. This gene may represent an intermediate form in evolution from a common sHSP to a Hsp12. Together, our study offers insights on what biological functions the chaperone-defective sHSPs may exhibit and also implicates an evolutionary scenario for the unique Hsp12s subfamily.

CREB mediates the C. elegans dauer polyphenism through direct and cell-autonomous regulation of TGF-β expression

Animals can adapt to dynamic environmental conditions by modulating their developmental programs. Understanding the genetic architecture and molecular mechanisms underlying developmental plasticity in response to changing environments is an important and emerging area of research. Here, we show a novel role of cAMP response element binding protein (CREB)-encoding crh-1 gene in developmental polyphenism of C. elegans. Under conditions that promote normal development in wild-type animals, crh-1 mutants inappropriately form transient pre-dauer (L2d) larvae and express the L2d marker gene. L2d formation in crh-1 mutants is specifically induced by the ascaroside pheromone ascr#5 (asc-ωC3; C3), and crh-1 functions autonomously in the ascr#5-sensing ASI neurons to inhibit L2d formation. Moreover, we find that CRH-1 directly binds upstream of the daf-7 TGF-β locus and promotes its expression in the ASI neurons. Taken together, these results provide new insight into how animals alter their developmental programs in response to environmental changes.

Superoxide dismutase 1 (SOD1) and cadmium: A three models approach to the comprehension of its neurotoxic effects

Cadmium (Cd) is a widespread toxic environmental contaminant, released by anthropogenic activities. It interferes with essential metal ions homeostasis and affects protein structures and functions by substituting zinc, copper and iron. In this study, the effect of cadmium on SOD1, a CuZn metalloenzyme catalyzing superoxide conversion into hydrogen peroxide, has been investigated in three different biological models. We first evaluated the effects of cadmium combined with copper and/or zinc on the recombinant GST-SOD1, expressed in E. coli BL21. The enzyme activity and expression were investigated in the presence of fixed copper and/or zinc doses with different cadmium concentrations, in the cellular medium. Cadmium caused a dose-dependent reduction in SOD1 activity, while the expression remains constant. Similar results were obtained in the cellular model represented by the human SH-SY5Y neuronal cell line. After cadmium treatment for 24 and 48 h, SOD1 enzymatic activity decreased in a dose- and time-dependent way, while the protein expression remained constant. Finally, a 16 h cadmium treatment caused a 25 % reduction of CuZn-SOD activity without affecting the protein expression in the Caenorhabditis elegans model. Taken together our results show an inhibitory effect of cadmium on SOD1 enzymatic activity, without affecting the protein expression, in all the biological models used, suggesting that cadmium can displace zinc from the enzyme catalytic site.

Neuronal SKN-1B modulates nutritional signalling pathways and mitochondrial networks to control satiety

The feeling of hunger or satiety results from integration of the sensory nervous system with other physiological and metabolic cues. This regulates food intake, maintains homeostasis and prevents disease. In C. elegans, chemosensory neurons sense food and relay information to the rest of the animal via hormones to control food-related behaviour and physiology. Here we identify a new component of this system, SKN-1B which acts as a central food-responsive node, ultimately controlling satiety and metabolic homeostasis. SKN-1B, an ortholog of mammalian NF-E2 related transcription factors (Nrfs), has previously been implicated with metabolism, respiration and the increased lifespan incurred by dietary restriction. Here we show that SKN-1B acts in two hypothalamus-like ASI neurons to sense food, communicate nutritional status to the organism, and control satiety and exploratory behaviours. This is achieved by SKN-1B modulating endocrine signalling pathways (IIS and TGF-β), and by promoting a robust mitochondrial network. Our data suggest a food-sensing and satiety role for mammalian Nrf proteins.

Deciding when and how much to eat is important for maintaining health and preventing disease. It requires an intricate molecular level of communication between our nervous, physiological, and metabolic systems. These signals stimulate food intake, and afterwards the feeling of satiety which makes us stop eating. We have studied these phenomena using the simple nematode worm C. elegans which has a fully mapped nervous system and quantifiable food-related behaviours. In C. elegans, chemosensory neurons sense food and communicate this to the rest of the animal via hormones to control food-related behaviour and associated physiological changes. Here we identify a new central node of this system, the C. elegans gene SKN-1B, which acts in two sensory neurons to sense food, communicate food-status to the rest of the worm, and control satiety and exploratory behaviours. It does this by altering hormonal signalling (Insulin and Transforming Growth Factor-β), and by promoting a strong mitochondrial network. The mammalian equivalents of SKN-1B are the NF-E2 related transcription factors (Nrfs), which have previously been implicated with metabolism and respiration. Our data suggest a new food-sensing and satiety role for mammalian Nrf proteins.

Developmental plasticity and the response to nutrient stress in Caenorhabditis elegans

Developmental plasticity refers the ability of an organism to adapt to various environmental stressors, one of which is nutritional stress. Caenorhabditis elegans require various nutrients to successfully progress through all the larval stages to become a reproductive adult. If nutritional criteria are not satisfied, development can slow or completely arrest. In poor growth conditions, the animal can enter various diapause stages, depending on its developmental progress. In C. elegans, there are three well-characterized diapauses: the L1 arrest, the dauer diapause, and adult reproductive diapause, each associated with drastic changes in metabolism and germline development. At the centre of these changes is AMP-activated protein kinase (AMPK). AMPK is a metabolic regulator that maintains energy homeostasis, particularly during times of nutrient stress. Without AMPK, metabolism is disrupted during dauer, leading to the rapid consumption of lipid stores as well as misregulation of metabolic enzymes, leading to reduced survival. During the L1 arrest and dauer diapause, AMPK is responsible for ensuring germline quiescence by modifying the germline chromatin landscape to maintain germ cell integrity until conditions improve. Similar to classic hormonal signalling, small RNAs also play a critical role in regulating development and behaviour in a cell non-autonomous fashion. Thus, during the challenges associated with developmental plasticity, AMPK summons an army of signalling pathways to work collectively to preserve reproductive fitness during these periods of unprecedented uncertainty.

Starvation Responses Throughout the Caenorhabditiselegans Life Cycle

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.

PROTEIN l-ISOASPARTYL METHYLTRANSFERASE (PIMT) in plants: regulations and functions

Proteins are essential molecules that carry out key functions in a cell. However, as a result of aging or stressful environments, the protein undergoes a range of spontaneous covalent modifications, including the formation of abnormal l-isoaspartyl residues from aspartyl or asparaginyl residues, which can disrupt the protein's inherent structure and function. PROTEIN l-ISOASPARTYL METHYLTRANSFERASE (PIMT: EC 2.1.1.77), an evolutionarily conserved ancient protein repairing enzyme (PRE), converts such abnormal l-isoaspartyl residues to normal l-aspartyl residues and re-establishes the protein's native structure and function. Although originally discovered in animals as a PRE, PIMT emerged as a key PRE in plants, particularly in seeds, in which PIMT plays a predominant role in preserving seed vigor and viability for prolonged periods of time. Interestingly, higher plants encode a second PIMT (PIMT2) protein which possesses a unique N-terminal extension, and exhibits several distinct features and far more complexity than non-plant PIMTs. Recent studies indicate that the role of PIMT is not restricted to preserving seed vigor and longevity but is also implicated in enhancing the growth and survivability of plants under stressful environments. Furthermore, expression studies indicate the tantalizing possibility that PIMT is involved in various physiological processes apart from its role in seed vigor, longevity and plant's survivability under abiotic stress. This review article particularly describes new insights and emerging interest in all facets of this enzyme in plants along with a concise comparative overview on isoAsp formation, and the role and regulation of PIMTs across evolutionary diverse species. Additionally, recent methods and their challenges in identifying isoaspartyl containing proteins (PIMT substrates) are highlighted.

HLH-11 modulates lipid metabolism in response to nutrient availability

The ability of organisms to sense nutrient availability and tailor their metabolic states to withstand nutrient deficiency is critical for survival. To identify previously unknown regulators that couple nutrient deficiency to body fat utilization, we performed a cherry-picked RNAi screen in C. elegans and found that the transcription factor HLH-11 regulates lipid metabolism in response to food availability. In well-fed worms, HLH-11 suppresses transcription of lipid catabolism genes. Upon fasting, the HLH-11 protein level is reduced through lysosome- and proteasome-mediated degradation, thus alleviating the inhibitory effect of HLH-11, activating the transcription of lipid catabolism genes, and utilizing fat. Additionally, lipid profiling revealed that reduction in the HLH-11 protein level remodels the lipid landscape in C. elegans. Moreover, TFAP4, the mammalian homolog of HLH-11, plays an evolutionarily conserved role in regulating lipid metabolism in response to starvation. Thus, TFAP4 may represent a potential therapeutic target for lipid storage disorders.

Organismal metabolism fluctuates depending on nutritional conditions. Here, the authors show that, in C. elegans, HLH-11 negatively regulates lipid metabolism genes in the presence of nutrients and that its abundance decreased in response to starvation, thereby promoting fat utilization.

Caenorhabditis elegans dauers vary recovery in response to bacteria from natural habitat

Many species use dormant stages for habitat selection by tying recovery to informative external cues. Other species have an undiscerning strategy in which they recover randomly despite having advanced sensory systems. We investigated whether elements of a species' habitat structure and life history can bar it from developing a discerning recovery strategy. The nematode Caenorhabditis elegans has a dormant stage called the dauer larva that disperses between habitat patches. On one hand, C. elegans colonization success is profoundly influenced by the bacteria found in its habitat patches, so we might expect this to select for a discerning strategy. On the other hand, C. elegans' habitat structure and life history suggest that there is no fitness benefit to varying recovery, which might select for an undiscerning strategy. We exposed dauers of three genotypes to a range of bacteria acquired from the worms' natural habitat. We found that C. elegans dauers recover in all conditions but increase recovery on certain bacteria depending on the worm's genotype, suggesting a combination of undiscerning and discerning strategies. Additionally, the worms' responses did not match the bacteria's objective quality, suggesting that their decision is based on other characteristics.

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.

It is known that high levels of dietary sugar can negatively impact human health, but the mechanisms underlying this remain unclear. Here we use the facile Caenorhabditis elegans genetic model to extend understanding of the impact of glucose and glucose metabolism on health and aging. We show that the two opposing glucose metabolism pathways–glycolysis and gluconeogenesis–have dramatically opposite effects on health: glycolytic activity responsible for sugar catabolism is detrimental, but driving gluconeogenesis promotes healthy aging. The powerful longevity regulator DAF-16 is required for the healthspan effects of gluconeogenesis. Our data highlight the intriguing possibility that driving the biosynthetic gluconeogenesis pathway could be a novel strategy for healthspan promotion. Indeed, we find that increasing levels of the core gluconeogenic enzyme PEPCK (PCK-2) in just a few intestinal cells can increase overall health in a DAF-16-dependent manner. Dietary restriction, which can promote health and longevity across species, increases PCK-2 levels in the intestine via DAF-16, and PCK-2 is required for the health benefits seen when calories are limited. Our results define gluconeogenic metabolism as a key component of healthy aging, and suggest that interventions that promote gluconeogenesis may help combat the onset of age-related diseases, including diabetes.

The development of the dog heartworm is highly sensitive to sterols which activate the orthologue of the nuclear receptor DAF-12

Prevention therapy against Dirofilaria immitis in companion animals is currently threatened by the emergence of isolates resistant to macrocyclic lactone anthelmintics. Understanding the control over developmental processes in D. immitis is important for elucidating new approaches to heartworm control. The nuclear receptor DAF-12 plays a role in the entry and exit of dauer stage in Caenorhabditis elegans and in the development of free-living infective third-stage larvae (iL3) of some Clade IV and V parasitic nematodes. We identified a DAF-12 ortholog in the clade III nematode D. immitis and found that it exhibited a much higher affinity for dafachronic acids than described with other nematode DAF-12 investigated so far. We also modelled the DimDAF-12 structure and characterized the residues involved with DA binding. Moreover, we showed that cholesterol derivatives impacted the molting process from the iL3 to the fourth-stage larvae. Since D. immitis is unable to synthesize cholesterol and only completes its development upon host infection, we hypothesize that host environment contributes to its further molting inside the host vertebrate. Our discovery contributes to a better understanding of the developmental checkpoints of D. immitis and offers new perspectives for the development of novel therapies against filarial infections.

Cytochrome P450 metabolism mediates low-temperature resistance in pinewood nematode

Pinewood nematode (PWN; Bursaphelenchus xylophilus) is a devastating invasive species that is expanding into colder regions. Here, we investigated the molecular mechanisms underlying low-temperature resistance of PWN. We identified differentially expressed genes enriched under low temperature in previously published transcriptome data using the Kyoto Encyclopedia of Genes and Genomes. Quantitative real-time PCR was used to further validate the transcript level changes of three known cytochrome P450 genes under low temperature. RNA interference was used to validate the low-temperature resistance function of three cytochrome P450 genes from PWN. We report that differentially expressed genes were significantly enriched in two cytochrome P450-related pathways under low-temperature treatment. Heatmap visualization of transcript levels of cytochrome P450-related genes revealed widely different transcript patterns between PWNs treated under low and regular temperatures. Transcript levels of three cytochrome P450 genes from PWNs were elevated at low temperature, and knockdown of these genes decreased the survival rates of PWNs under low temperature. In summary, these findings suggest that cytochrome P450 metabolism plays a critical role in the low-temperature resistance mechanism of PWN.

Dafachronic acid and temperature regulate canonical dauer pathways during Nippostrongylus brasiliensis infectious larvae activation

BACKGROUND

While immune responses to the murine hookworm Nippostrongylus brasiliensis have been investigated, signaling pathways regulating development of infectious larvae (iL3) are not well understood. We hypothesized that N. brasiliensis would use pathways similar to those controlling dauer development in the free-living nematode Caenorhabditis elegans, which is formally known as the "dauer hypothesis."

METHODS

To investigate whether dafachronic acid activates the N. brasiliensis DAF-12 homolog, we utilized an in vitro reporter assay. We then utilized RNA-Seq and subsequent bioinformatic analyses to identify N. brasiliensis dauer pathway homologs and examine regulation of these genes during iL3 activation.

RESULTS

In this study, we demonstrated that dafachronic acid activates the N. brasiliensis DAF-12 homolog. We then identified N. brasiliensis homologs for members in each of the four canonical dauer pathways and examined their regulation during iL3 activation by either temperature or dafachronic acid. Similar to C. elegans, we found that transcripts encoding antagonistic insulin-like peptides were significantly downregulated during iL3 activation, and that a transcript encoding a phylogenetic homolog of DAF-9 increased during iL3 activation, suggesting that both increased insulin-like and DAF-12 nuclear hormone receptor signaling accompanies iL3 activation. In contrast to C. elegans, we observed a significant decrease in transcripts encoding the dauer transforming growth factor beta ligand DAF-7 during iL3 activation, suggesting a different role for this pathway in parasitic nematode development.

CONCLUSIONS

Our data suggest that canonical dauer pathways indeed regulate iL3 activation in the hookworm N. brasiliensis and that DAF-12 may be a therapeutic target in hookworm infections.

A metabolic switch regulates the transition between growth and diapause in C. elegans

BACKGROUND

Metabolic activity alternates between high and low states during different stages of an organism's life cycle. During the transition from growth to quiescence, a major metabolic shift often occurs from oxidative phosphorylation to glycolysis and gluconeogenesis. We use the entry of Caenorhabditis elegans into the dauer larval stage, a developmentally arrested stage formed in response to harsh environmental conditions, as a model to study the global metabolic changes and underlying molecular mechanisms associated with growth to quiescence transition.

RESULTS

Here, we show that the metabolic switch involves the concerted activity of several regulatory pathways. Whereas the steroid hormone receptor DAF-12 controls dauer morphogenesis, the insulin pathway maintains low energy expenditure through DAF-16/FoxO, which also requires AAK-2/AMPKα. DAF-12 and AAK-2 separately promote a shift in the molar ratios between competing enzymes at two key branch points within the central carbon metabolic pathway diverting carbon atoms from the TCA cycle and directing them to gluconeogenesis. When both AAK-2 and DAF-12 are suppressed, the TCA cycle is active and the developmental arrest is bypassed.

CONCLUSIONS

The metabolic status of each developmental stage is defined by stoichiometric ratios within the constellation of metabolic enzymes driving metabolic flux and controls the transition between growth and quiescence.

smFISH in chips: a microfluidic-based pipeline to quantify in situ gene expression in whole organisms

Gene expression and genetic regulatory networks in multi-cellular organisms control complex physiological processes ranging from cellular differentiation to development to aging. Traditional methods to investigate gene expression relationships rely on using bulk, pooled-population assays (e.g. RNA-sequencing and RT-PCR) to compare gene expression levels in hypo- or hyper-morphic mutant animals (e.g. gain-of-function or knockout). This approach is limited, especially in complex gene networks, as these genetic mutations may affect the expressions of related genes in unforseen ways. In contrast, we developed a microfluidic-based pipeline to discover gene relationships in a single genetic background. The microfluidic device provides efficient reagent exchange and the ability to track individual animals. By automating a robust microfluidic reagent exchange strategy, we adapted and validated single molecule fluorescent in situ hybridization (smFISH) on-chip and combined this technology with live-imaging of fluorescent transcriptional reporters. Together, this multi-level information enabled us to quantify a gene expression relationship with single-animal resolution. While this microfluidic-based pipeline is optimized for live-imaging and smFISH C. elegans studies, the strategy is highly-adaptable to other biological models as well as combining other live and end-point biological assays, such as behavior-based toxicology screening and immunohistochemistry.

DAF-16/FoxO in Caenorhabditis elegans and Its Role in Metabolic Remodeling

DAF-16, the only forkhead box transcription factors class O (FoxO) homolog in Caenorhabditis elegans, integrates signals from upstream pathways to elicit transcriptional changes in many genes involved in aging, development, stress, metabolism, and immunity. The major regulator of DAF-16 activity is the insulin/insulin-like growth factor 1 (IGF-1) signaling (IIS) pathway, reduction of which leads to lifespan extension in worms, flies, mice, and humans. In C. elegans daf-2 mutants, reduced IIS leads to a heterochronic activation of a dauer survival program during adulthood. This program includes elevated antioxidant defense and a metabolic shift toward accumulation of carbohydrates (i.e., trehalose and glycogen) and triglycerides, and activation of the glyoxylate shunt, which could allow fat-to-carbohydrate conversion. The longevity of daf-2 mutants seems to be partially supported by endogenous trehalose, a nonreducing disaccharide that mammals cannot synthesize, which points toward considerable differences in downstream mechanisms by which IIS regulates aging in distinct groups.

Ascaroside Pheromones: Chemical Biology and Pleiotropic Neuronal Functions

Pheromones are neuronal signals that stimulate conspecific individuals to react to environmental stressors or stimuli. Research on the ascaroside (ascr) pheromones in Caenorhabditis elegans and other nematodes has made great progress since ascr#1 was first isolated and biochemically defined in 2005. In this review, we highlight the current research on the structural diversity, biosynthesis, and pleiotropic neuronal functions of ascr pheromones and their implications in animal physiology. Experimental evidence suggests that ascr biosynthesis starts with conjugation of ascarylose to very long-chain fatty acids that are then processed via peroxisomal β-oxidation to yield diverse ascr pheromones. We also discuss the concentration and stage-dependent pleiotropic neuronal functions of ascr pheromones. These functions include dauer induction, lifespan extension, repulsion, aggregation, mating, foraging and detoxification, among others. These roles are carried out in coordination with three G protein-coupled receptors that function as putative pheromone receptors: SRBC-64/66, SRG-36/37, and DAF-37/38. Pheromone sensing is transmitted in sensory neurons via DAF-16-regulated glutamatergic neurotransmitters. Neuronal peroxisomal fatty acid β-oxidation has important cell-autonomous functions in the regulation of neuroendocrine signaling, including neuroprotection. In the future, translation of our knowledge of nematode ascr pheromones to higher animals might be beneficial, as ascr#1 has some anti-inflammatory effects in mice. To this end, we propose the establishment of pheromics (pheromone omics) as a new subset of integrated disciplinary research area within chemical ecology for system-wide investigation of animal pheromones.

A universal transcriptomic signature of age reveals the temporal scaling of Caenorhabditis elegans aging trajectories

We collected 60 age-dependent transcriptomes for C. elegans strains including four exceptionally long-lived mutants (mean adult lifespan extended 2.2- to 9.4-fold) and three examples of lifespan-increasing RNAi treatments. Principal Component Analysis (PCA) reveals aging as a transcriptomic drift along a single direction, consistent across the vastly diverse biological conditions and coinciding with the first principal component, a hallmark of the criticality of the underlying gene regulatory network. We therefore expected that the organism's aging state could be characterized by a single number closely related to vitality deficit or biological age. The "aging trajectory", i.e. the dependence of the biological age on chronological age, is then a universal stochastic function modulated by the network stiffness; a macroscopic parameter reflecting the network topology and associated with the rate of aging. To corroborate this view, we used publicly available datasets to define a transcriptomic biomarker of age and observed that the rescaling of age by lifespan simultaneously brings together aging trajectories of transcription and survival curves. In accordance with the theoretical prediction, the limiting mortality value at the plateau agrees closely with the mortality rate doubling exponent estimated at the cross-over age near the average lifespan. Finally, we used the transcriptomic signature of age to identify possible life-extending drug compounds and successfully tested a handful of the top-ranking molecules in C. elegans survival assays and achieved up to a +30% extension of mean lifespan.

Diapause induces functional axonal regeneration after necrotic insult in C. elegans

Many neurons are unable to regenerate after damage. The ability to regenerate after an insult depends on life stage, neuronal subtype, intrinsic and extrinsic factors. C. elegans is a powerful model to test the genetic and environmental factors that affect axonal regeneration after damage, since its axons can regenerate after neuronal insult. Here we demonstrate that diapause promotes the complete morphological regeneration of truncated touch receptor neuron (TRN) axons expressing a neurotoxic MEC-4(d) DEG/ENaC channel. Truncated axons of different lengths were repaired during diapause and we observed potent axonal regrowth from somas alone. Complete morphological regeneration depends on DLK-1 but neuronal sprouting and outgrowth is DLK-1 independent. We show that TRN regeneration is fully functional since animals regain their ability to respond to mechanical stimulation. Thus, diapause induced regeneration provides a simple model of complete axonal regeneration which will greatly facilitate the study of environmental and genetic factors affecting the rate at which neurons die.

Transgenerational Effects of Extended Dauer Diapause on Starvation Survival and Gene Expression Plasticity in Caenorhabditis elegans

Phenotypic plasticity is facilitated by epigenetic regulation, and remnants of such regulation may persist after plasticity-inducing cues are gone. However, the relationship between plasticity and transgenerational epigenetic memory is not understood. Dauer diapause in Caenorhabditis elegans provides an opportunity to determine how a plastic response to the early-life environment affects traits later in life and in subsequent generations. We report that, after extended diapause, postdauer worms initially exhibit reduced reproductive success and greater interindividual variation. In contrast, F3 progeny of postdauers display increased starvation resistance and lifespan, revealing potentially adaptive transgenerational effects. Transgenerational effects are dependent on the duration of diapause, indicating an effect of extended starvation. In agreement, RNA-seq demonstrates a transgenerational effect on nutrient-responsive genes. Further, postdauer F3 progeny exhibit reduced gene expression plasticity, suggesting a trade-off between plasticity and epigenetic memory. This work reveals complex effects of nutrient stress over different time scales in an animal that evolved to thrive in feast and famine.

Working with dauer larvae

Dauer diapause is a stress-resistant, developmentally quiescent, and long-lived larval stage adopted by Caenorhabditis elegans when conditions are unfavorable for growth and reproduction. This chapter contains methods to induce dauer larva formation, to isolate dauer larvae, and to study pre- and post-dauer stages.

Optical imaging of metabolic dynamics in animals

Direct visualization of metabolic dynamics in living animals with high spatial and temporal resolution is essential to understanding many biological processes. Here we introduce a platform that combines deuterium oxide (D2O) probing with stimulated Raman scattering (DO-SRS) microscopy to image in situ metabolic activities. Enzymatic incorporation of D2O-derived deuterium into macromolecules generates carbon-deuterium (C-D) bonds, which track biosynthesis in tissues and can be imaged by SRS in situ. Within the broad vibrational spectra of C-D bonds, we discover lipid-, protein-, and DNA-specific Raman shifts and develop spectral unmixing methods to obtain C-D signals with macromolecular selectivity. DO-SRS microscopy enables us to probe de novo lipogenesis in animals, image protein biosynthesis without tissue bias, and simultaneously visualize lipid and protein metabolism and reveal their different dynamics. DO-SRS microscopy, being noninvasive, universally applicable, and cost-effective, can be adapted to a broad range of biological systems to study development, tissue homeostasis, aging, and tumor heterogeneity.

Proteomic identification of galectin-11 and 14 ligands from Haemonchus contortus

Haemonchus contortus is the most pathogenic nematode of small ruminants. Infection in sheep and goats results in anaemia that decreases animal productivity and can ultimately cause death. The involvement of ruminant-specific galectin-11 (LGALS-11) and galectin-14 (LGALS-14) has been postulated to play important roles in protective immune responses against parasitic infection; however, their ligands are unknown. In the current study, LGALS-11 and LGALS-14 ligands in H. contortus were identified from larval (L4) and adult parasitic stages extracts using immobilised LGALS-11 and LGALS-14 affinity column chromatography and mass spectrometry. Both LGALS-11 and LGALS-14 bound more putative protein targets in the adult stage of H. contortus (43 proteins) when compared to the larval stage (two proteins). Of the 43 proteins identified in the adult stage, 34 and 35 proteins were bound by LGALS-11 and LGALS-14, respectively, with 26 proteins binding to both galectins. Interestingly, hematophagous stage-specific sperm-coating protein and zinc metalloprotease (M13), which are known vaccine candidates, were identified as putative ligands of both LGALS-11 and LGALS-14. The identification of glycoproteins of H. contortus by LGALS-11 and LGALS-14 provide new insights into host-parasite interactions and the potential for developing new interventions.

Regulation of reproduction and longevity by nutrient-sensing pathways

Nutrients are necessary for life, as they are a crucial requirement for biological processes including reproduction, somatic growth, and tissue maintenance. Therefore, signaling systems involved in detecting and interpreting nutrient or energy levels-most notably, the insulin/insulin-like growth factor 1 (IGF-1) signaling pathway, mechanistic target of rapamycin (mTOR), and adenosine monophosphate-activated protein kinase (AMPK)-play important roles in regulating physiological decisions to reproduce, grow, and age. In this review, we discuss the connections between reproductive senescence and somatic aging and give an overview of the involvement of nutrient-sensing pathways in controlling both reproductive function and lifespan. Although the molecular mechanisms that affect these processes can be influenced by distinct tissue-, temporal-, and pathway-specific signaling events, the progression of reproductive aging and somatic aging is systemically coordinated by integrated nutrient-sensing signaling pathways regulating somatic tissue maintenance in conjunction with reproductive capacity.

Studying the Symbiotic Bacterium Xenorhabdus nematophila in Individual, Living Steinernema carpocapsae Nematodes Using Microfluidic Systems

Animal-microbe symbioses are ubiquitous in nature and scientifically important in diverse areas, including ecology, medicine, and agriculture. Steinernema nematodes and Xenorhabdus bacteria compose an established, successful model system for investigating microbial pathogenesis and mutualism. The bacterium Xenorhabdus nematophila is a species-specific mutualist of insect-infecting Steinernema carpocapsae nematodes. The bacterium colonizes a specialized intestinal pocket within the infective stage of the nematode, which transports the bacteria between insects that are killed and consumed by the pair for reproduction. Current understanding of the interaction between the infective-stage nematode and its bacterial colonizers is based largely on population-level, snapshot time point studies on these organisms. This limitation arises because investigating temporal dynamics of the bacterium within the nematode is impeded by the difficulty of isolating and maintaining individual living nematodes and tracking colonizing bacterial cells over time. To overcome this challenge, we developed a microfluidic system that enables us to spatially isolate and microscopically observe individual, living Steinernema nematodes and monitor the growth and development of the associated X. nematophila bacterial communities-starting from a single cell or a few cells-over weeks. Our data demonstrate, to our knowledge, the first direct, temporal, in vivo visual analysis of a symbiosis system and the application of this system to reveal continuous dynamics of the symbiont population in the living host animal. IMPORTANCE This paper describes an experimental system for directly investigating population dynamics of a symbiotic bacterium, Xenorhabdus nematophila, in its host-the infective stage of the entomopathogenic nematode Steinernema carpocapsae. Tracking individual and groups of bacteria in individual host nematodes over days and weeks yielded insight into dynamic growth and topology changes of symbiotic bacterial populations within infective juvenile nematodes. Our approach for studying symbioses between bacteria and nematodes provides a system to investigate long-term host-microbe interactions in individual nematodes and extrapolate the lessons learned to other bacterium-animal interactions.

FMRFamide-like peptides expand the behavioral repertoire of a densely connected nervous system

Animals, including humans, can adapt to environmental stress through phenotypic plasticity. The free-living nematode Caenorhabditis elegans can adapt to harsh environments by undergoing a whole-animal change, involving exiting reproductive development and entering the stress-resistant dauer larval stage. The dauer is a dispersal stage with dauer-specific behaviors for finding and stowing onto carrier animals, but how dauers acquire these behaviors, despite having a physically limited nervous system of 302 neurons, is poorly understood. We compared dauer and reproductive development using whole-animal RNA sequencing at fine time points and at sufficient depth to measure transcriptional changes within single cells. We detected 8,042 genes differentially expressed during dauer and reproductive development and observed striking up-regulation of neuropeptide genes during dauer entry. We knocked down neuropeptide processing using sbt-1 mutants and demonstrate that neuropeptide signaling promotes the decision to enter dauer rather than reproductive development. We also demonstrate that during dauer neuropeptides modulate the dauer-specific nictation behavior (carrier animal-hitchhiking) and are necessary for switching from repulsion to CO₂ (a carrier animal cue) in nondauers to CO₂ attraction in dauers. We tested individual neuropeptides using CRISPR knockouts and existing strains and demonstrate that the combined effects of flp-10 and flp-17 mimic the effects of sbt-1 on nictation and CO₂ attraction. Through meta-analysis, we discovered similar up-regulation of neuropeptides in the dauer-like infective juveniles of diverse parasitic nematodes, suggesting the antiparasitic target potential of SBT-1. Our findings reveal that, under stress, increased neuropeptide signaling in C. elegans enhances their decision-making accuracy and expands their behavioral repertoire.

daf-16/FoxO promotes gluconeogenesis and trehalose synthesis during starvation to support survival

daf-16/FoxO is required to survive starvation in Caenorhabditis elegans, but how daf-16IFoxO promotes starvation resistance is unclear. We show that daf-16/FoxO restructures carbohydrate metabolism by driving carbon flux through the glyoxylate shunt and gluconeogenesis and into synthesis of trehalose, a disaccharide of glucose. Trehalose is a well-known stress protectant, capable of preserving membrane organization and protein structure during abiotic stress. Metabolomic, genetic, and pharmacological analyses confirm increased trehalose synthesis and further show that trehalose not only supports survival as a stress protectant but also serves as a glycolytic input. Furthermore, we provide evidence that metabolic cycling between trehalose and glucose is necessary for this dual function of trehalose. This work demonstrates that daf-16/FoxO promotes starvation resistance by shifting carbon metabolism to drive trehalose synthesis, which in turn supports survival by providing an energy source and acting as a stress protectant.

Most animals rarely have access to a constant supply of food, and so have evolved ways to cope with times of plenty and times of shortage. Insulin is a hormone that travels throughout the body to signal when an animal is well fed. Insulin signaling inhibits the activity of a protein called FoxO, which otherwise switches on and off hundreds of genes to control the starvation response.

The roundworm, Caenorhabditis elegans, has been well studied in the laboratory, and often has to cope with starvation in the wild. These worms can pause their development if no food is available, or divert to a different developmental path if they anticipate that food will be short in future. As with more complex animals, the worm responds to starvation by reducing insulin-like signaling, which in turn activates a FoxO protein called daf-16. When the worms stop feeding, daf-16 is switched on, which is crucial for survival.

It was known how daf-16 stops the roundworm’s development, but it was not known how it helps the worms to survive starvation. Now, Hibshman et al. have compared normal roundworm larvae to larvae that are missing the gene for daf-16 to determine how this protein influences the roundworm’s ability to survive starvation.

The worms were examined with and without food, to look for which genes were switched on and off by daf-16 during starvation. This revealed that daf-16 controls metabolism, activating a metabolic shortcut that makes the worms produce glucose and begin turning it into another type of sugar, called trehalose. This sugar usually promotes survival in conditions where water is limiting, like dehydration and high salt, but it can also be broken down to release energy. The levels of trehalose in the worms rose within hours of the onset of starvation.

To confirm the importance of trehalose in surviving starvation, roundworms with mutations in genes involved in glucose or trehalose production were examined, as was the effect of giving starving worms glucose or trehalose. Disrupting the production of sugars caused the worms to die sooner of starvation, while supplementing with sugar had the opposite effect meaning the worms survived for longer.

Taken together, these findings reveal that daf-16 protects against starvation by shifting metabolism towards the production of trehalose. This helps worms to survive by both protecting them from stress and providing them with a source of energy. These findings not only extend the current understanding of how animals respond to starvation, but could also lead to improved understanding of diseases where this response goes wrong, including diabetes and obesity.

Absence of juvenile hormone signalling regulates the dynamic expression profiles of nutritional metabolism genes during diapause preparation in the cabbage beetle Colaphellus bowringi

Temperate insects have evolved diapause, a period of programmed developmental arrest during specific life stages, to survive unfavourable conditions. During the diapause preparation phase (DPP), diapause-destined individuals generally store large amounts of fat by regulating nutrition distribution for the energy requirement during diapause maintenance and postdiapause development. Although nutritional patterns during the DPP have been investigated at physiological and biochemical levels in many insects, it remains largely unknown how nutritional metabolism is regulated during the DPP at molecular levels. We used RNA sequencing to compare gene expression profiles of adult female cabbage beetles Colaphellus bowringi during the preoviposition phase (POP) and the DPP. Most differentially expressed genes were involved in specific metabolic pathways during the DPP. Genes related to lipid and carbohydrate metabolic pathways were clearly highly expressed during the DPP, whereas genes related to protein metabolic pathways were highly expressed during the POP. Hormone challenge and RNA interference experiments revealed that juvenile hormone via its nuclear receptor methoprene-tolerant mediated the expression of genes associated with nutritional metabolism during the DPP. This work not only sheds light on the mechanisms of diapause preparation, but also provides new insights into the molecular basis of environmental plasticity in insects.

Forward and reverse genetics approaches to uncover metabolic aging pathways in Caenorhabditis elegans

The biological mechanisms of aging have been studied in depth and prominent findings in this field promote the development of new therapies for age-associated disorders. Various model organisms are used for research on aging; among these, the nematode Caenorhabditis elegans has been widely used and has provided valuable knowledge in determining the regulatory mechanisms driving the aging process. Many genes involved in lifespan regulation are associated with metabolic pathways and are influenced by genetic and environmental factors. In line with this, C. elegans provides a promising platform to study such gene by environment interactions, in either a reverse or forward genetics approach. In this review, we discuss longevity mechanisms related to metabolic networks that have been discovered in C. elegans. We also highlight the use of wild populations to study the complex genetic basis of natural variation for quantitative traits that mediate longevity.

Phenotypic plasticity and remodeling in the stress-induced Caenorhabditis elegans dauer

Organisms are often capable of modifying their development to better suit their environment. Under adverse conditions, the nematode Caenorhabditis elegans develops into a stress-resistant alternative larval stage called dauer. The dauer stage is the primary survival stage for C. elegans in nature. Large-scale tissue remodeling during dauer conveys resistance to harsh environments. The environmental and genetic regulation of the decision to enter dauer has been extensively studied. However, less is known about the mechanisms regulating tissue remodeling. Changes to the cuticle and suppression of feeding in dauers lead to an increased resistance to external stressors. Meanwhile reproductive development arrests during dauer while preserving the ability to reproduce once favorable environmental conditions return. Dramatic remodeling of neurons, glia, and muscles during dauer likely facilitate dauer-specific behaviors. Dauer-specific pulsation of the excretory duct likely mediates a response to osmotic stress. The power of C. elegans genetics has uncovered some of the molecular pathways regulating dauer tissue remodeling. In addition to genes that regulate single remodeling events, several mutants result in pleiotropic defects in dauer remodeling. This review details the individual aspects of morphological changes that occur during dauer formation and discusses molecular mechanisms regulating these processes. The dauer stage provides us with an excellent model for understanding phenotypic plasticity and remodeling from the individual cell to an entire animal. WIREs Dev Biol 2017, 6:e278. doi: 10.1002/wdev.278 For further resources related to this article, please visit the WIREs website.

Niche-specific gene expression in a parasitic nematode; increased expression of immunomodulators in Teladorsagia circumcincta larvae derived from host mucosa

Metazoan parasites have to survive in many different niches in order to complete their life-cycles. In the absence of reliable methods to manipulate parasite genomes and/or proteomes, identification of the molecules critical for parasite survival within these niches has largely depended on comparative transcriptomic and proteomic analyses of different developmental stages of the parasite; however, changes may reflect differences associated with transition between developmental stages rather than specific adaptations to a particular niche. In this study, we compared the transcriptome of two fourth-stage larval populations of the nematode parasite, Teladorsagia circumcincta, which were of the same developmental stage but differed in their location within the abomasum, being either mucosal-dwelling (MD) or lumen-dwelling (LD). Using RNAseq, we identified 57 transcripts which were significantly differentially expressed between MD and LD larvae. Of these transcripts, the majority (54/57) were up-regulated in MD larvae, one of which encoded for an ShKT-domain containing protein, Tck6, capable of modulating ovine T cell cytokine responses. Other differentially expressed transcripts included homologues of ASP-like proteins, proteases, or excretory-secretory proteins of unknown function. Our study demonstrates the utility of niche- rather than stage-specific analysis of parasite transcriptomes to identify parasite molecules of potential importance for survival within the host.

Pheromone-sensing neurons regulate peripheral lipid metabolism in Caenorhabditis elegans

It is now established that the central nervous system plays an important role in regulating whole body metabolism and energy balance. However, the extent to which sensory systems relay environmental information to modulate metabolic events in peripheral tissues has remained poorly understood. In addition, it has been challenging to map the molecular mechanisms underlying discrete sensory modalities with respect to their role in lipid metabolism. In previous work our lab has identified instructive roles for serotonin signaling as a surrogate for food availability, as well as oxygen sensing, in the control of whole body metabolism. In this study, we now identify a role for a pair of pheromone-sensing neurons in regulating fat metabolism in C. elegans, which has emerged as a tractable and highly informative model to study the neurobiology of metabolism. A genetic screen revealed that GPA-3, a member of the Gα family of G proteins, regulates body fat content in the intestine, the major metabolic organ for C. elegans. Genetic and reconstitution studies revealed that the potent body fat phenotype of gpa-3 null mutants is controlled from a pair of neurons called ADL(L/R). We show that cAMP functions as the second messenger in the ADL neurons, and regulates body fat stores via the neurotransmitter acetylcholine, from downstream neurons. We find that the pheromone ascr#3, which is detected by the ADL neurons, regulates body fat stores in a GPA-3-dependent manner. We define here a third sensory modality, pheromone sensing, as a major regulator of body fat metabolism. The pheromone ascr#3 is an indicator of population density, thus we hypothesize that pheromone sensing provides a salient 'denominator' to evaluate the amount of food available within a population and to accordingly adjust metabolic rate and body fat levels.

The central nervous system plays a vital role in regulating whole body metabolism and energy balance. However, the precise cellular, genetic and molecular mechanisms underlying these effects remain a major unsolved mystery. C. elegans has emerged as a tractable and highly informative model to study the neurobiology of metabolism. Previously, we have identified instructive roles for serotonin signaling as a surrogate for food availability, as well as oxygen sensing, in the control of whole body metabolism. In our current study we have identified a role for a pair of pheromone-sensing neurons in regulating fat metabolism in C. elegans. cAMP acts as a second messenger in these neurons, and regulates body fat stores via acetylcholine signaling in the nervous system. We find that the population-density-sensing pheromone detected by these neurons regulates body fat stores. Together, we define a third sensory modality, population density sensing, as a major regulator of body fat metabolism.

Sequestration of polyunsaturated fatty acids in membrane phospholipids of Caenorhabditis elegans dauer larva attenuates eicosanoid biosynthesis for prolonged survival

Mechanistic basis governing the extreme longevity and developmental quiescence of dauer juvenile, a "non-ageing" developmental variant of Caenorhabditis elegans, has remained largely obscure. Using a lipidomic approach comprising multiple reaction monitoring transitions specific to distinct fatty acyl moieties, we demonstrated that in comparison to other developmental stages, the membrane phospholipids of dauer larva contain a unique enrichment of polyunsaturated fatty acids (PUFAs). Esterified PUFAs in phospholipids exhibited temporal accumulation throughout the course of dauer endurance, followed by sharp reductions prior to termination of diapause. Reductions in esterified PUFAs were accompanied by concomitant increases in unbound PUFAs, as well as their corresponding downstream oxidized derivatives (i.e. eicosanoids). Global phospholipidomics has unveiled that PUFA sequestration in membrane phospholipids denotes an essential aspect of dauer dormancy, principally via suppression of eicosanoid production; and a failure to upkeep membrane lipid homeostasis is associated with termination of dauer endurance.