Suppressors of transforming growth factor-beta pathway mutants in the Caenorhabditis elegans dauer formation pathway

ALK in cancer: from function to therapeutic targeting

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase (RTK) that acts as an oncogenic driver in solid and haematological malignancies in both children and adults. Although ALK-expressing (ALK+) tumours show strong initial responses to the series of ALK inhibitors currently available, many patients will develop resistance. In this Review, we discuss recent advances in ALK oncogenic signalling, together with existing and promising new modalities to treat ALK-driven tumours, including currently approved ALK-directed therapies, namely tyrosine kinase inhibitors, and novel approaches such as ALK-specific immune therapies. Although ALK inhibitors have changed the management and clinical history of ALK+ tumours, they are still insufficient to cure most of the patients. Therefore, more effort is needed to further improve outcomes and prevent the tumour resistance, recurrence and metastatic spread that many patients with ALK+ tumours experience. Here, we outline how a multipronged approach directed against ALK and other essential pathways that sustain the persistence of ALK+ tumours, together with potent or specific immunotherapies, could achieve this goal. We envision that the lessons learned from treating ALK+ tumours in the clinic could ultimately accelerate the implementation of innovative combination therapies to treat tumours driven by other tyrosine kinases or oncogenes with similar properties.

Neuroendocrine gene expression coupling of interoceptive bacterial food cues to foraging behavior of C. elegans

Animal internal state is modulated by nutrient intake, resulting in behavioral responses to changing food conditions. The neural mechanisms by which internal states are generated and maintained are not well understood. Here, we show that in the nematode Caenorhabditis elegans, distinct cues from bacterial food - interoceptive signals from the ingestion of bacteria and gustatory molecules sensed from nearby bacteria - act antagonistically on the expression of the neuroendocrine TGF-beta ligand DAF-7 from the ASJ pair of sensory neurons to modulate foraging behavior. A positive-feedback loop dependent on the expression of daf-7 from the ASJ neurons acts to promote transitions between roaming and dwelling foraging states and influence the persistence of roaming states. SCD-2, the C. elegans ortholog of mammalian anaplastic lymphoma kinase (ALK), which has been implicated in the central control of metabolism of mammals, functions in the AIA interneurons to regulate foraging behavior and cell-non-autonomously control the expression of DAF-7 from the ASJ neurons. Our data establish how a dynamic neuroendocrine daf-7 expression feedback loop regulated by SCD-2 functions to couple sensing and ingestion of bacterial food to foraging behavior. We further suggest that this neuroendocrine feedback loop underlies previously characterized exploratory behaviors in C. elegans. Our data suggest that the expression of daf-7 from the ASJ neurons contributes to and is correlated with an internal state of 'unmet need' that regulates exploratory foraging behavior in response to bacterial cues in diverse physiological contexts.

Neuroendocrine Gene Expression Coupling of Interoceptive Bacterial Food Cues to Foraging Behavior of C. elegans

Animal internal state is modulated by nutrient intake, resulting in behavioral responses to changing food conditions. The neural mechanisms by which internal states are generated and maintained are not well understood. Here, we show that in the nematode Caenorhabditis elegans, distinct cues from bacterial food - interoceptive signals from the ingestion of bacteria and gustatory molecules sensed from nearby bacteria - act antagonistically on the expression of the neuroendocrine TGF-beta ligand DAF-7 from the ASJ pair of sensory neurons to modulate foraging behavior. A positive-feedback loop dependent on the expression of daf-7 from the ASJ neurons acts to promote transitions between roaming and dwelling foraging states and influence the persistence of roaming states. SCD-2, the C. elegans ortholog of mammalian Anaplastic Lymphoma Kinase (ALK), which has been implicated in the central control of metabolism of mammals, functions in the AIA interneurons to regulate foraging behavior and cell-non-autonomously control the expression of DAF-7 from the ASJ neurons. Our data establish how a dynamic neuroendocrine daf-7 expression feedback loop regulated by SCD-2 functions to couple sensing and ingestion of bacterial food to foraging behavior. We further suggest that this neuroendocrine feedback loop underlies previously characterized exploratory behaviors in C. elegans. Our data suggest that the expression of daf-7 from the ASJ neurons contributes to and is correlated with an internal state of "unmet need" that regulates exploratory foraging behavior in response to bacterial cues in diverse physiological contexts.

Transcriptional and spatiotemporal regulation of the dauer program

Caenorhabditis elegans can enter a diapause stage called "dauer" when it senses that the environment is not suitable for development. This implies a detour from the typical developmental trajectory and requires a tight control of the developmental clock and a massive tissue remodeling. In the last decades, core components of the signaling pathways that govern the dauer development decision have been identified, but the tissues where they function for the acquisition of dauer-specific traits are still under intense study. Growing evidence demonstrates that these pathways engage in complex cross-talk and feedback loops. In this review, we summarize the current knowledge regarding the transcriptional regulation of the dauer program and the relevant tissues for its achievement. A better understanding of this process will provide insight on how developmental plasticity is achieved and how development decisions are under a robust regulation to ensure an all-or-nothing response. Furthermore, this developmental decision can also serve as a simplified model for relevant developmental disorders.Abbreviations: AID Auxin Induced Degron DA dafachronic acid Daf-c dauer formation constitutive Daf-d dauer formation defective DTC Distal Tip Cells ECM modified extracellular matrix GPCRs G protein-coupled receptors IIS insulin/IGF-1 signaling ILPs insulin-like peptides LBD Ligand Binding Domain PDL4 Post Dauer L4 TGF-β transforming growth factor beta WT wild-type.

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.

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.

Gene structure and expression patterns of Acdaf-1, a TGF-β type I receptor in Ancylostoma caninum

The components of the transforming growth factor β (TGF-β) signaling pathway in parasitic nematodes remain unknown. In this research, a type I receptor for TGF-β was isolated from the hookworm Ancylostoma caninum. The new gene was designated as Acdaf-1, a Caenorhabditis elegans daf-1 homolog. The full-length cDNA of Acdaf-1 encodes a 595-amino-acid protein with an NH₂-terminal signal peptide. This protein has a cytoplasm tail (209-595aa region) which corresponds to the type 1a membrane topology. Between amino acid position 295-500, the protein contains the ATP binding site, substrate binding sites, and PKC-kinase-like domain. Real-time RT-PCR showed that the transcript was expressed in three main stages of A. caninum. It reached the maximal level in the female adult worm stage with lower transcript level in the first and second larvae (L1/L2) and intermediate level in L3 stages as well as in the male worms. After serum activation, the activity of Acdaf-1 was decreased in L3 larvae. These data implied that Acdaf-1 might relate to the infection ability of the larvae. Immunolocalization revealed that AcDAF-1 was present in eggs, intestine, and epidermis cells of larvae (L1, L2, and L3 stages) with strong signal in primordium of the gonads in L3 and was abundant in epidermis, intestine, and ovary of adult worm. These results suggested that Acdaf-1 might be involved in the interaction of the parasite and host relationship and provide a potential target for parasite control.

The role of the ALK receptor in cancer biology

A vast array of oncogenic variants has been identified for anaplastic lymphoma kinase (ALK). Therefore, there is a need to better understand the role of ALK in cancer biology in order to optimise treatment strategies. This review summarises the latest research on the receptor tyrosine kinase ALK, and how this information can guide the management of patients with cancer that is ALK-positive. A variety of ALK gene alterations have been described across a range of tumour types, including point mutations, deletions and rearrangements. A wide variety of ALK fusions, in which the kinase domain of ALK and the amino-terminal portion of various protein partners are fused, occur in cancer, with echinoderm microtubule-associated protein-like 4 (EML4)-ALK being the most prevalent in non-small-cell lung cancer (NSCLC). Different ALK fusion proteins can mediate different signalling outputs, depending on properties such as subcellular localisation and protein stability. The ALK fusions found in tumours lack spatial and temporal regulation, which can also affect dimerisation and substrate specificity. Two ALK tyrosine kinase inhibitors (TKIs), crizotinib and ceritinib, are currently approved in Europe for use in ALK-positive NSCLC and several others are in development. These ALK TKIs bind slightly differently within the ATP-binding pocket of the ALK kinase domain and are associated with the emergence of different resistance mutation patterns during therapy. This emphasises the need to tailor the sequence of ALK TKIs according to the ALK signature of each patient. Research into the oncogenic functions of ALK, and fast paced development of ALK inhibitors, has substantially improved outcomes for patients with ALK-positive NSCLC. Limited data are available surrounding the physiological ligand-stimulated activation of ALK signalling and further research is needed. Understanding the role of ALK in tumour biology is key to further optimising therapeutic strategies for ALK-positive disease.

The TGF-β Family in Caenorhabditis elegans

Transforming growth factor β (TGF-β) and related ligands have potent effects on an enormous diversity of biological functions in all animals examined. Because of the strong conservation of TGF-β family ligand functions and signaling mechanisms, studies from multiple animal systems have yielded complementary and synergistic insights. In the nematode Caenorhabditis elegans, early studies were instrumental in the elucidation of TGF-β family signaling mechanisms. Current studies in C. elegans continue to identify new functions for the TGF-β family in this organism as well as new conserved mechanisms of regulation.

Expanding the view on the evolution of the nematode dauer signalling pathways: refinement through gene gain and pathway co-option

BACKGROUND

Signalling pathways underlie development, behaviour and pathology. To understand patterns in the evolution of signalling pathways, we undertook a comprehensive investigation of the pathways that control the switch between growth and developmentally quiescent dauer in 24 species of nematodes spanning the phylum.

RESULTS

Our analysis of 47 genes across these species indicates that the pathways and their interactions are not conserved throughout the Nematoda. For example, the TGF-β pathway was co-opted into dauer control relatively late in a lineage that led to the model species Caenorhabditis elegans. We show molecular adaptations described in C. elegans that are restricted to its genus or even just to the species. Similarly, our analyses both identify species where particular genes have been lost and situations where apparently incorrect orthologues have been identified.

CONCLUSIONS

Our analysis also highlights the difficulties of working with genome sequences from non-model species as reliance on the published gene models would have significantly restricted our understanding of how signalling pathways evolve. Our approach therefore offers a robust standard operating procedure for genomic comparisons.

Detection of Autophagy in Caenorhabditis elegans

Autophagy is a dynamic and catabolic process that results in the breakdown and recycling of cellular components through the autophagosomal-lysosomal pathway. Many autophagy genes identified in yeasts and mammals have orthologs in the nematode Caenorhabditis elegans. In recent years, gene inactivation by RNA interference (RNAi) and chromosomal mutations has been useful to probe the functions of autophagy in C. elegans, and a role for autophagy has been shown to contribute to multiple processes, such as the adaptation to stress, longevity, cell death, cell growth control, clearance of aggregation-prone proteins, degradation of P granules during embryogenesis, and apoptotic cell clearance. Here, we discuss some of these roles and describe methods that can be used to study autophagy in C. elegans. Specifically, we summarize how to visualize autophagy in embryos, larva, or adults, how to detect the lipidation of the ubiquitin-like modifier LGG-1 by western blot, and how to inactivate autophagy genes by RNAi.

Detection of Autophagy in Caenorhabditis elegans Using GFP::LGG-1 as an Autophagy Marker

In yeast and mammalian cells, the autophagy protein Atg8/LC3 (microtubule-associated proteins 1A/1B light chain 3B encoded by MAP1LC3B) has been the marker of choice to detect double-membraned autophagosomes that are produced during the process of autophagy. A lipid-conjugated form of Atg8/LC3B is localized to the inner and outer membrane of the early-forming structure known as the phagophore. During maturation of autophagosomes, Atg8/LC3 bound to the inner autophagosome membrane remains in situ as the autophagosomes fuse with lysosomes. The nematode Caenorhabditis elegans is thought to conduct a similar process, meaning that tagging the nematode ortholog of Atg8/LC3-known as LGG-1-with a fluorophore has become a widely accepted method to visualize autophagosomes. Under normal growth conditions, GFP-modified LGG-1 displays a diffuse expression pattern throughout a variety of tissues, whereas, when under conditions that induce autophagy, the GFP::LGG-1 tag labels positive punctate structures, and its overall level of expression increases. Here, we present a protocol for using fluorescent reporters of LGG-1 coupled to GFP to monitor autophagosomes in vivo. We also discuss the use of alternative fluorescent markers and the possible utility of the LGG-1 paralog LGG-2.

Loss of C. elegans GON-1, an ADAMTS9 Homolog, Decreases Secretion Resulting in Altered Lifespan and Dauer Formation

ADAMTS9 is a metalloprotease that cleaves components of the extracellular matrix and is also implicated in transport from the endoplasmic reticulum (ER) to the Golgi. It has been reported that an ADAMTS9 gene variant is associated with type 2 diabetes. The underlying pathology of type 2 diabetes is insulin resistance and beta-cell dysfunction. However, the molecular mechanisms underlying ADAMTS9 function in beta cells and peripheral tissues are unknown. We show that loss of C. elegans GON-1, an ADAMTS9 homolog, alters lifespan and dauer formation. GON-1 loss impairs secretion of proteins such as insulin orthologs and TGF-beta, and additionally impacts insulin/IGF-1 signaling in peripheral tissues. The function of the GON domain, but not the protease domain, is essential for normal lifespan and dauer formation in these scenarios. We conclude that the GON domain is critical for ADAMTS9/GON-1 function across species, which should help the understanding of type 2 diabetes in humans.

The Drosophila midkine/pleiotrophin homologues Miple1 and Miple2 affect adult lifespan but are dispensable for alk signaling during embryonic gut formation

Midkine (MDK) and Pleiotrophin (PTN) are small heparin-binding cytokines with closely related structures. The Drosophila genome harbours two genes encoding members of the MDK/PTN family of proteins, known as miple1 and miple2. We have investigated the role of Miple proteins in vivo, in particular with regard to their proposed role as ligands for the Alk receptor tyrosine kinase (RTK). Here we show that Miple proteins are neither required to drive Alk signaling during Drosophila embryogenesis, nor are they essential for development in the fruit fly. Additionally we show that neither MDK nor PTN can activate hALK in vivo when ectopically co-expressed in the fly. In conclusion, our data suggest that Alk is not activated by MDK/PTN related growth factors Miple1 and Miple 2 in vivo.

The dauer hypothesis and the evolution of parasitism: 20 years on and still going strong

How any complex trait has evolved is a fascinating question, yet the evolution of parasitism among the nematodes is arguably one of the most arresting. How did free-living nematodes cross that seemingly insurmountable evolutionary chasm between soil dwelling and survival inside another organism? Which of the many finely honed responses to the varied and harsh environments of free-living nematodes provided the material upon which natural selection could act? Although several complementary theories explain this phenomenon, I will focus on the dauer hypothesis. The dauer hypothesis posits that the arrested third-stage dauer larvae of free-living nematodes such as Caenorhabditis elegans are, due to their many physiological similarities with infective third-stage larvae of parasitic nematodes, a pre-adaptation to parasitism. If so, then a logical extension of this hypothesis is that the molecular pathways which control entry into and recovery from dauer formation by free-living nematodes in response to environmental cues have been co-opted to control the processes of infective larval arrest and activation in parasitic nematodes. The molecular machinery that controls dauer entry and exit is present in a wide range of parasitic nematodes. However, the developmental outputs of the different pathways are both conserved and divergent, not only between populations of C. elegans or between C. elegans and parasitic nematodes but also between different species of parasitic nematodes. Thus the picture that emerges is more nuanced than originally predicted and may provide insights into the evolution of such an interesting and complex trait.

Mechanistic insight into ALK receptor tyrosine kinase in human cancer biology

The burgeoning field of anaplastic lymphoma kinase (ALK) in cancer encompasses many cancer types, from very rare cancers to the more prevalent non-small-cell lung cancer (NSCLC). The common activation of ALK has led to the use of the ALK tyrosine kinase inhibitor (TKI) crizotinib in a range of patient populations and to the rapid development of second-generation drugs targeting ALK. In this Review, we discuss our current understanding of ALK function in human cancer and the implications for tumour treatment.

TGF-β signaling in C. elegans

Transforming Growth Factor-β (TGF-β) superfamily ligands regulate many aspects of cell identity, function, and survival in multicellular animals. Genes encoding five TGF-β family members are present in the genome of C. elegans. Two of the ligands, DBL-1 and DAF-7, signal through a canonical receptor-Smad signaling pathway; while a third ligand, UNC-129, interacts with a noncanonical signaling pathway. No function has yet been associated with the remaining two ligands. Here we summarize these signaling pathways and their biological functions.

HID-1 is a novel player in the regulation of neuropeptide sorting

Peptide hormones and neuropeptides are packaged and stored in a specialized intracellular organelle called the dense core vesicle. It remains elusive how peptide cargoes are correctly sorted. In the present study, we show that a highly conserved Golgi-localized protein named HID-1 acts to prevent mis-sorting of peptide cargoes to lysosomes for degradation via a PtdIns3P-dependent trafficking pathway. Epistasis analysis suggests that rab-2 is epistatic to hid-1.

HID-1 is a peripheral membrane protein primarily associated with the medial- and trans- Golgi apparatus

Caenorhabditis elegans hid-1 gene was first identified in a screen for mutants with a high-temperature-induced dauer formation (Hid) phenotype. Despite the fact that the hid-1 gene encodes a novel protein (HID-1) which is highly conserved from Caenorhabditis elegans to mammals, the domain structure, subcellular localization, and exact function of HID-1 remain unknown. Previous studies and various bioinformatic softwares predicted that HID-1 contained many transmembrane domains but no known functional domain. In this study, we revealed that mammalian HID-1 localized to the medial- and trans- Golgi apparatus as well as the cytosol, and the localization was sensitive to brefeldin A treatment. Next, we demonstrated that HID-1 was a peripheral membrane protein and dynamically shuttled between the Golgi apparatus and the cytosol. Finally, we verified that a conserved N-terminal myristoylation site was required for HID-1 binding to the Golgi apparatus. We propose that HID-1 is probably involved in the intracellular trafficking within the Golgi region.

Regulation of longevity by genes required for the functions of AIY interneuron in nematode Caenorhabditis elegans

In Caenorhabditis elegans, functional ttx-3, sra-11, ceh-10, and ceh-23 genes are required for the functions of AIY interneuron. Compared to wild-type N2, mutations in ttx-3 and ceh-10 significantly decreased lifespan, whereas mutations in sra-11 and ceh-23 did not obviously influence nematode lifespan. Mutations in ttx-3 and ceh-10 were associated closely with lower pumping rates at adult day 8 and caused a more rapid accumulated intestinal autofluorescence than wild-type N2. Mutations in ceh-10 remarkably affected fertility and egg number in the uterus. The regulation of ttx-3 and ceh-10 on longevity was not temperature-dependent, and ttx-3, and ceh-10 mutants all formed very few dauers at 27°C. The shortened lifespan of the ttx-3 or ceh-10 mutants was completely or largely rescued by expression of TTX-3 or CEH-10 in AIY interneurons. Moreover, the long-lived phenotype of the daf-2 mutant could be suppressed by both the ttx-3 and the ceh-10 mutations. Furthermore, ablation of AIY interneurons shortened the longevity of wild-type and the daf-2 mutant. Therefore, ttx-3 and ceh-10 regulate the longevity through influencing the insulin/IGF signaling pathway in C. elegans.

Genes required for the functions of olfactory AWA neuron regulate the longevity of Caenorhabditis elegans in an insulin/IGF signaling-dependent fashion

OBJECTIVE

To investigate the interaction between the genes required for the functions of AWA olfactory neuron and insulin/IGF signaling in regulating the longevity of nematode Caenorhabditis elegans (C. elegans).

METHODS

The mutants that had loss-of-function mutation of the genes required for AWA, AWC, ASE, and AFD sensory neurons were employed. Lifespan, the speed of pharynx pumping, the intestinal autofluorescence, the dauer formation, and the brood size were examined. Rescue experiments were performed to confirm the role of the genes required for the functions of AWA neuron in regulating lifespan. Moreover, genetic interactions between genes required for the functions of AWA neuron and insulin/IGF signaling were investigated.

RESULTS

Mutations of odr-7, odr-2, and odr-3 genes required for the functions of AWA neuron significantly increased the mean lifespan of nematodes and slowed the accumulation of intestinal autofluorescence. Besides, these mutations were closely associated with higher pumping rates during aging. However, mutation of odr-7, odr-2, or odr-3 did not obviously affect the brood size or the dauer formation, and the regulation of longevity by odr-7, odr-2, and odr-3 was temperature-independent. In contrast, mutations of genes required for the functions of ASE, AWC, and AFD sensory neurons did not influence the nematode lifespan. Moreover, expression of odr-7, odr-2 and odr-3 in AWA neuron could completely or largely restore the altered lifespan in odr-7, odr-2 and odr-3 mutants. Furthermore, genetic interaction assay demonstrated that the extended lifespan in odr-7 mutant could be suppressed by daf-16 mutation and enhanced by daf-2 or age-1 mutation, whereas mev-1 and pha-4 were not required for the long lifespan of odr-7 mutant.

CONCLUSION

The genes required for the function of AWA sensory neuron could regulate the nematode longevity in an insulin/IGF signaling-dependent fashion in C. elegans.

Confirmation of combinational effects of calcium with other metals in a paper recycling mill effluent on nematode lifespan with toxicity identification evaluation method

We used toxicity identification evaluation (TIE) method to confirm the combinational effects of identified toxic metals in a paper recycling mill effluent in inducing the decreased lifespan in nematode Caenorhabditis elegans. Exposure to Ca + Al caused more severely decreased lifespan than that exposed to Ca, or Al; and exposure to Ca + Fe induced more severely decreased lifespan than that exposed to Ca, or Fe. Exposure to Ca+Al+Fe caused more severely decreased lifespan than that exposed to Ca, or Ca+Fe. Moreover, the baseline toxicity on lifespan was doubled by doubling the concentration of combined metals (Ca+Al+Fe) in spiking test in original effluent (oe), and lifespan defects in oe+Ca+Al+Fe exposed nematodes were more severe than that in Ca+Al+Fe exposed nematode. Therefore, Ca+Al+Fe exposure may largely explain the formation of decreased lifespan induced by the examined industrial effluent. Furthermore, the observed reduction of lifespan induced by the combination of high level of Ca with other metals may be at least partially independent of the insulin-like pathway.

C. elegans longevity pathways converge to decrease mitochondrial membrane potential

Energy production via oxidative phosphorylation generates a mitochondrial membrane potential (DeltaPsi(m)) across the inner membrane. In this work, we show that a lower DeltaPsi(m) is associated with increased lifespan in Caenorhabditis elegans. The long-lived mutants daf-2(e1370), age-1(hx546), clk-1(qm30), isp-1(qm150) and eat-2(ad465) all have a lower DeltaPsi(m) than wild type animals. The lower DeltaPsi(m) of daf-2(e1370) is daf-16 dependent, indicating that the insulin-like signaling pathway not only regulates lifespan but also mitochondrial energetics. RNA interference (RNAi) against 17 genes shown to extend lifespan also decrease DeltaPsi(m). Furthermore, lifespan can be significantly extended with the uncoupler carbonylcyanide-3-chlorophenylhydrazone (CCCP), which dissipates DeltaPsi(m). We conclude that longevity pathways converge on the mitochondria and lead to a decreased DeltaPsi(m). Our results are consistent with the 'uncoupling to survive' hypothesis, which states that dissipation of the DeltaPsi(m) will extend lifespan.

Caenorhabditis elegans: an emerging model in biomedical and environmental toxicology

The nematode Caenorhabditis elegans has emerged as an important animal model in various fields including neurobiology, developmental biology, and genetics. Characteristics of this animal model that have contributed to its success include its genetic manipulability, invariant and fully described developmental program, well-characterized genome, ease of maintenance, short and prolific life cycle, and small body size. These same features have led to an increasing use of C. elegans in toxicology, both for mechanistic studies and high-throughput screening approaches. We describe some of the research that has been carried out in the areas of neurotoxicology, genetic toxicology, and environmental toxicology, as well as high-throughput experiments with C. elegans including genome-wide screening for molecular targets of toxicity and rapid toxicity assessment for new chemicals. We argue for an increased role for C. elegans in complementing other model systems in toxicological research.

The anticonvulsant ethosuximide disrupts sensory function to extend C. elegans lifespan

Ethosuximide is a medication used to treat seizure disorders in humans, and we previously demonstrated that ethosuximide can delay age-related changes and extend the lifespan of the nematode Caenorhabditis elegans. The mechanism of action of ethosuximide in lifespan extension is unknown, and elucidating how ethosuximide functions is important for defining endogenous processes that influence lifespan and for exploring the potential of ethosuximide as a therapeutic for age-related diseases. To identify genes that mediate the activity of ethosuximide, we conducted a genetic screen and identified mutations in two genes, che-3 and osm-3, that cause resistance to ethosuximide-mediated toxicity. Mutations in che-3 and osm-3 cause defects in overlapping sets of chemosensory neurons, resulting in defective chemosensation and an extended lifespan. These findings suggest that ethosuximide extends lifespan by inhibiting the function of specific chemosensory neurons. This model is supported by the observation that ethosuximide-treated animals displayed numerous phenotypic similarities with mutants that have chemosensory defects, indicating that ethosuximide inhibits chemosensory function. Furthermore, ethosuximide extends lifespan by inhibiting chemosensation, since the long-lived osm-3 mutants were resistant to the lifespan extension caused by ethosuximide. These studies demonstrate a novel mechanism of action for a lifespan-extending drug and indicate that sensory perception has a critical role in controlling lifespan. Sensory perception also influences the lifespan of Drosophila, suggesting that sensory perception has an evolutionarily conserved role in lifespan control. These studies highlight the potential of ethosuximide and related drugs that modulate sensory perception to extend lifespan in diverse animals.

Aging is a major factor that contributes to disease and disability in humans, but no medicines have been demonstrated to delay human aging. We previously conducted a screen for FDA-approved drugs that can extend the lifespan of the nematode worm C. elegans, resulting in the identification of ethosuximide, a medicine used to treat epilepsy. To elucidate the mechanism of action of ethosuximide in lifespan extension, we conducted a genetic screen for C. elegans mutations that cause resistance to ethosuximide. Here, we describe the identification of genes that are critical for ethosuximide sensitivity. These genes are necessary for the function of neurons that mediate sensory perception. Furthermore, ethosuximide treatment caused defects in sensory perception. These results indicate that ethosuximide affects lifespan by inhibiting neurons that function in the perception of sensory cues. These studies highlight the importance of sensory neurons in lifespan determination and demonstrate that a drug can act on specific cells within the nervous system to extend lifespan. Sensory perception also modulates Drosophila lifespan, suggesting this is an evolutionarily conserved relationship. Our results indicate that sensory perception may be a promising target for pharmacological extension of lifespan in a variety of animals.

TGF-beta as a candidate bone marrow niche signal to induce hematopoietic stem cell hibernation

Hematopoietic stem cells (HSCs) reside in a bone marrow niche in a nondividing state from which they occasionally are aroused to undergo cell division. Yet, the mechanism underlying this unique feature remains largely unknown. We have recently shown that freshly isolated CD34-KSL hematopoietic stem cells (HSCs) in a hibernation state exhibit inhibited lipid raft clustering. Lipid raft clustering induced by cytokines is essential for HSCs to augment cytokine signals to the level enough to re-enter the cell cycle. Here we screened candidate niche signals that inhibit lipid raft clustering, and identified that transforming growth factor-beta (TGF-beta) efficiently inhibits cytokine-mediated lipid raft clustering and induces HSC hibernation ex vivo. Smad2 and Smad3, the signaling molecules directly downstream from and activated by TGF-beta receptors were specifically activated in CD34-KSL HSCs in a hibernation state, but not in cycling CD34+KSL progenitors. These data uncover a critical role for TGF-beta as a candidate niche signal in the control of HSC hibernation and provide TGF-beta as a novel tool for ex vivo modeling of the HSC niche.

A potent dauer pheromone component in Caenorhabditis elegans that acts synergistically with other components

In the model organism Caenorhabditis elegans, the dauer pheromone is the primary cue for entry into the developmentally arrested, dauer larval stage. The dauer is specialized for survival under harsh environmental conditions and is considered "nonaging" because larvae that exit dauer have a normal life span. C. elegans constitutively secretes the dauer pheromone into its environment, enabling it to sense its population density. Several components of the dauer pheromone have been identified as derivatives of the dideoxy sugar ascarylose, but additional unidentified components of the dauer pheromone contribute to its activity. Here, we show that an ascaroside with a 3-hydroxypropionate side chain is a highly potent component of the dauer pheromone that acts synergistically with previously identified components. Furthermore, we show that the active dauer pheromone components that are produced by C. elegans vary depending on cultivation conditions. Identifying the active components of the dauer pheromone, the conditions under which they are produced, and their mechanisms of action will greatly extend our understanding of how chemosensory cues from the environment can influence such fundamental processes as development, metabolism, and aging in nematodes and in higher organisms.

C. elegans anaplastic lymphoma kinase ortholog SCD-2 controls dauer formation by modulating TGF-beta signaling

BACKGROUND

Different environmental stimuli, including exposure to dauer pheromone, food deprivation, and high temperature, can induce C. elegans larvae to enter the dauer stage, a developmentally arrested diapause state. Although molecular and cellular pathways responsible for detecting dauer pheromone and temperature have been defined in part, other sensory inputs are poorly understood, as are the mechanisms by which these diverse sensory inputs are integrated to achieve a consistent developmental outcome.

RESULTS

In this paper, we analyze a wild C. elegans strain isolated from a desert oasis. Unlike wild-type laboratory strains, the desert strain fails to respond to dauer pheromone at 25 degrees C, but it does respond at higher temperatures, suggesting a unique adaptation to the hot desert environment. We map this defect in dauer response to a mutation in the scd-2 gene, which, we show, encodes the nematode anaplastic lymphoma kinase (ALK) homolog, a proto-oncogene receptor tyrosine kinase. scd-2 acts in a genetic pathway shown here to include the HEN-1 ligand, the RTK adaptor SOC-1, and the MAP kinase SMA-5. The SCD-2 pathway modulates TGF-beta signaling, which mediates the response to dauer pheromone, but SCD-2 might mediate a nonpheromone sensory input, such as food.

CONCLUSIONS

Our studies identify a new sensory pathway controlling dauer formation and shed light on ALK signaling, integration of signaling pathways, and adaptation to extreme environmental conditions.

Caenorhabditis elegans EAK-3 inhibits dauer arrest via nonautonomous regulation of nuclear DAF-16/FoxO activity

Insulin regulates development, metabolism, and lifespan via a conserved PI3K/Akt pathway that promotes cytoplasmic sequestration of FoxO transcription factors. The regulation of nuclear FoxO is poorly understood. In the nematode Caenorhabditis elegans, insulin-like signaling functions in larvae to inhibit dauer arrest and acts during adulthood to regulate lifespan. In a screen for genes that modulate C. elegans insulin-like signaling, we identified eak-3, which encodes a novel protein that is specifically expressed in the two endocrine XXX cells. The dauer arrest phenotype of eak-3 mutants is fully suppressed by mutations in daf-16/FoxO, which encodes the major target of C. elegans insulin-like signaling, and daf-12, which encodes a nuclear receptor regulated by steroid hormones known as dafachronic acids. eak-3 mutation does not affect DAF-16/FoxO subcellular localization but enhances expression of the direct DAF-16/FoxO target sod-3 in a daf-16/FoxO- and daf-12-dependent manner. eak-3 mutants have normal lifespans, suggesting that EAK-3 decouples insulin-like regulation of development and longevity. We propose that EAK-3 activity in the XXX cells promotes the synthesis and/or secretion of a hormone that acts in parallel to AKT-1 to inhibit the expression of DAF-16/FoxO target genes. Similar hormonal pathways may regulate FoxO target gene expression in mammals.

Involvement of genes required for synaptic function in aging control in C. elegans

OBJECTIVE

To identify new genes required for neurosecretory control of aging in C. elegans.

METHODS

In view of the importance of nervous system in aging regulation, we performed the screen for genes involved in the aging regulation from genetic loci encoding synaptic proteins by lifespan assay and accumulation of lipofuscin autofluorescence. We further investigated the dauer formation phenotypes of their corresponding mutants and whether they were possibly up-regulated by the insulin-like signaling pathway.

RESULTS

The genetic loci of unc-10, syd-2, hlb-1, dlk-1, mkk-4, scd-2, snb-1, ric-4, nrx-1, unc-13, sbt-1 and unc-64 might be involved in the aging control. In addition, functions of unc-10, syd-2, hlb-1, dlk-1, mkk-4, scd-2, snb-1, ric-4 and nrx-1 in regulating aging may be opposite to those of unc-13, sbt-1 and unc-64. The intestinal autofluorescence assay further indicated that the identified long-lived and short-lived mutants were actually due to the suppressed or accelerated aging. Among the identified genes, syd-2, hlb-1, mkk-4, scd-2, snb-1, ric-4 and unc-64 were also involved in the control of dauer formation. Moreover, daf-2 mutation positively regulated the expression of syd-2 and hlb-1, and negatively regulated the expression of mkk-4, nrx-1, ric-4, sbt-1, rpm-1, unc-10, dlk-1 and unc-13. The daf-16 mutation positively regulated the expression of syd-2 and hlb-1, and negatively regulated the expression of mkk-4, nrx-1, sbt-1, rpm-1, unc-10, dlk-1 and unc-13.

CONCLUSION

These data suggest the possibly important status of the synaptic transmission to the animal's life-span control machinery, as well as the dauer formation control.

Public and private mechanisms of life extension in Caenorhabditis elegans

Model organisms have been widely used to study the ageing phenomenon in order to learn about human ageing. Although the phylogenetic diversity between vertebrates and some of the most commonly used model systems could hardly be greater, several mechanisms of life extension are public (common characteristic in divergent species) and likely share a common ancestry. Dietary restriction, reduced IGF-signaling and, seemingly, reduced ROS-induced damage are the best known mechanisms for extending longevity in a variety of organisms. In this review, we summarize the knowledge of ageing in the nematode Caenorhabditis elegans and compare the mechanisms of life extension with knowledge from other model organisms.

Isolation and Characterization of High-Temperature-Induced Dauer Formation Mutants in Caenorhabditis elegans

Dauer formation in Caenorhabditis elegans is regulated by at least three signaling pathways, including an insulin receptor-signaling pathway. These pathways were defined by mutants that form dauers constitutively (Daf-c) at 25°. Screens for Daf-c mutants at 25° have probably been saturated, but failed to identify all the components involved in regulating dauer formation. Here we screen for Daf-c mutants at 27°, a more strongly dauer-inducing condition. Mutations identified include novel classes of alleles for three known genes and alleles defining at least seven new genes, hid-1–hid-7. Many of the genes appear to act in the insulin branch of the dauer pathway, including pdk-1, akt-1, aex-6, and hid-1. We also molecularly identify hid-1 and show that it encodes a novel highly conserved putative transmembrane protein expressed in neurons.

Targets of TGF beta-related signaling in Caenorhabditis elegans

With the characterization of the Smads 5 years ago, it became possible to trace the TGFbeta signal transduction pathway from the plasma membrane to the nucleus. Since that time, many Smad interaction partners, cofactors and target genes have been identified using a variety of experimental approaches and model systems. Understanding how these partners generate tissue specificity and crosstalk between pathways is an ongoing pursuit for the field of TGFbeta signal transduction. The nematode Caenorhabditis elegans provides a simple, genetically tractable model organism in which to address this goal. This review will examine progress towards the identification of cellular and molecular targets of TGFbeta-related signaling in C. elegans.