A dual role of the Wnt signaling pathway during aging in Caenorhabditis elegans

Wnt signaling is a major and highly conserved developmental pathway that guides many important events during embryonic and larval development. In adulthood, misregulation of Wnt signaling has been implicated in tumorigenesis and various age‐related diseases. These effects occur through highly complicated cell‐to‐cell interactions mediated by multiple Wnt‐secreted proteins. While they share a high degree of sequence similarity, their function is highly diversified. Although the role of Wnt ligands during development is well studied, very little is known about the possible actions of Wnt signaling in natural aging. In this study, Caenorhabditis elegans serves, for the first time, as a model system to determine the role of Wnt ligands in aging. Caenorhabditis elegans has five Wnt proteins, mom‐2, egl‐20, lin‐44, cwn‐1, and cwn‐2. We show that all five Wnt ligands are expressed and active past the development stages. The ligand mom‐2/Wnt plays a major detrimental role in longevity, whereas the function of lin‐44/Wnt is beneficial for long life. Interestingly, no evidence was found for Wnt signaling being involved in cellular or oxidative stress responses during aging. Our results suggest that Wnt signaling regulates aging‐intrinsic genetic pathways, opening a new research direction on the role of Wnt signaling in aging and age‐related diseases.     

A neuromedin-pyrokinin-like neuropeptide signaling system in Caenorhabditis elegans

Neuromedin U (NMU) in vertebrates is a structurally highly conserved neuropeptide of which highest levels are found in the pituitary and gastrointestinal tract. In Drosophila, two neuropeptide genes encoding pyrokinins (PKs), capability (capa) and hugin, are possible insect homologs of vertebrate NMU. Here, the ligand for an orphan G protein-coupled receptor in the nematode Caenorhabditis elegans (Ce-PK-R) was found using a bioinformatics approach. After cloning and expressing Ce-PK-R in HEK293T cells, we found that it was activated by a neuropeptide from the C. elegans NLP-44 precursor (EC₅₀ = 18 nM). This neuropeptide precursor is reminiscent of insect CAPA precursors since it encodes a PK-like peptide and two periviscerokinin-like peptides (PVKs). Analogous to CAPA peptides in insects and NMUs in vertebrates, whole mount immunostaining in C. elegans revealed that the CAPA precursor is expressed in the nervous system. The present data also suggest that the ancestral CAPA precursor was already present in the common ancestor of Protostomians and Deuterostomians and that it might have been duplicated into CAPA and HUGIN in insects. In vertebrates, NMU is the putative homolog of a protostomian CAPA-PK.     

Dopamine signaling architecture in Caenorhabditis elegans

1. AIMS: In this review, we highlight the identification and analysis of molecules orchestrating dopamine (DA) signaling in the nematode Caenorhabditis elegans, focusing on recent characterizations of DA transporters and receptors. 2. METHODS: We illustrate the isolation and characterization of molecules important for C. elegans DA synthesis, packaging, reuptake and signaling and examine how mutations in these proteins are being exploited through in vitro and in vivo paradigms to yield novel insights of protein structure, DA signaling pathways and DA-supported behaviors. 3. RESULTS: DA signaling in the worm, as in man, arises by synaptic and nonsynaptic release from a small number of cells that exert modulatory control over a larger network underlying C. elegans behavior. 4. CONCLUSIONS: The C. elegans model system offers unique opportunities to elucidate ill-defined pathways that support DA release, inactivation, and signaling in addition to clarifying mechanisms of DA-mediated behavioral plasticity. Further use of the model offers prospects for the identification of novel genes and proteins whose study may yield benefits for DA-supported neural disorders in man.     

Role of the Caenorhabditis elegans Shc adaptor protein in the c-Jun N-terminal kinase signaling pathway

Mitogen-activated protein kinases (MAPKs) are integral to the mechanisms by which cells respond to physiological stimuli and a wide variety of environmental stresses. In Caenorhabditis elegans, the stress response is controlled by a c-Jun N-terminal kinase (JNK)-like mitogen-activated protein kinase (MAPK) signaling pathway, which is regulated by MLK-1 MAPK kinase kinase (MAPKKK), MEK-1 MAPK kinase (MAPKK), and KGB-1 JNK-like MAPK. In this study, we identify the shc-1 gene, which encodes a C. elegans homolog of Shc, as a factor that specifically interacts with MEK-1. The shc-1 loss-of-function mutation is defective in activation of KGB-1, resulting in hypersensitivity to heavy metals. A specific tyrosine residue in the NPXY motif of MLK-1 creates a docking site for SHC-1 with the phosphotyrosine binding (PTB) domain. Introduction of a mutation that perturbs binding to the PTB domain or the NPXY motif abolishes the function of SHC-1 or MLK-1, respectively, thereby abolishing the resistance to heavy metal stress. These results suggest that SHC-1 acts as a scaffold to link MAPKKK to MAPKK activation in the KGB-1 MAPK signal transduction pathway.     

An insulin-like signaling pathway affects both longevity and reproduction in Caenorhabditis elegans.

Mutations in daf-2 and age-1 cause a dramatic increase in longevity as well as developmental arrest at the dauer diapause stage in Caenorhabditis elegans. daf-2 and age-1 encode components of an insulin-like signaling pathway. Both daf-2 and age-1 act at a similar point in the genetic epistasis pathway for dauer arrest and longevity and regulate the activity of the daf-16 gene. Mutations in daf-16 cause a dauer-defective phenotype and are epistatic to the diapause arrest and life span extension phenotypes of daf-2 and age-1 mutants. Here we show that mutations in this pathway also affect fertility and embryonic development. Weak daf-2 alleles, and maternally rescued age-1 alleles that cause life span extension but do not arrest at the dauer stage, also reduce fertility and viability. We find that age-1(hx546) has reduced both maternal and zygotic age-1 activity. daf-16 mutations suppress all of the daf-2 and age-1 phenotypes, including dauer arrest, life span extension, reduced fertility, and viability defects. These data show that insulin signaling, mediated by DAF-2 through the AGE-1 phosphatidylinositol-3-OH kinase, regulates reproduction and embryonic development, as well as dauer diapause and life span, and that DAF-16 transduces these signals. The regulation of fertility, life span, and metabolism by an insulin-like signaling pathway is similar to the endocrine regulation of metabolism and fertility by mammalian insulin signaling.     

The Drosophila Toll signaling pathway

The identification of the Drosophila melanogaster Toll pathway cascade and the subsequent characterization of TLRs have reshaped our understanding of the immune system. Ever since, Drosophila NF-κB signaling has been actively studied. In flies, the Toll receptors are essential for embryonic development and immunity. In total, nine Toll receptors are encoded in the Drosophila genome, including the Toll pathway receptor Toll. The induction of the Toll pathway by gram-positive bacteria or fungi leads to the activation of cellular immunity as well as the systemic production of certain antimicrobial peptides. The Toll receptor is activated when the proteolytically cleaved ligand Spatzle binds to the receptor, eventually leading to the activation of the NF-κB factors Dorsal-related immunity factor or Dorsal. In this study, we review the current literature on the Toll pathway and compare the Drosophila and mammalian NF-κB pathways.     

Generation of an external guide sequence library for a reverse genetic screen in Caenorhabditis elegans

Background  

A method for inhibiting the expression of particular genes using external guide sequences (EGSs) has been developed in bacteria, mammalian cells and maize cells.     

A uniform genetic nomenclature for the nematode Caenorhabditis elegans.

Summary A uniform system of genetic nomenclature for the nematode Caenorhabditis elegans is described. Convenient ways are specified to designate genes, mutations and strains, and to attempt to avoid name duplications.     

A mutational analysis of Caenorhabditis elegans in space

The International Caenorhabditis elegans Experiment First Flight (ICE-First) was a project using C. elegans as a model organism to study the biological effects of short duration spaceflight (11 days in the International Space Station). As a member of the ICE-First research team, our group focused on the mutational effects of spaceflight. Several approaches were taken to measure mutational changes that occurred during the spaceflight including measurement of the integrity of poly-G/poly-C tracts, determination of the mutation frequency in the unc-22 gene, analysis of lethal mutations captured by the genetic balancer eT1(III;V), and identification of alterations in telomere length. By comparing the efficiency, sensitivity, and convenience of these methods, we deduced that the eT1 balancer system is well-suited for capturing, maintaining and recovering mutational events that occur over several generations during spaceflight. In the course of this experiment, we have extended the usefulness of the eT1 balancer system by identifying the physical breakpoints of the eT1 translocation and have developed a PCR assay to follow the eT1 chromosomes. C. elegans animals were grown in a defined liquid media during the spaceflight. This is the first analysis of genetic changes in C. elegans grown in the defined media. Although no significant difference in mutation rate was detected between spaceflight and control samples, which is not surprising given the short duration of the spaceflight, we demonstrate here the utility of worms as an integrating biological dosimeter for spaceflight.     

Quantitative genetic analysis of life-history traits of Caenorhabditis elegans in stressful environments

In Figure 1 of [Harvey et al (Evolutionary Biology 2008, 8:15)] the plotted data were inverted. The correct Figure is shown below. The text and statistical analyses in [Harvey et al (Evolutionary Biology 2008, 8:15)] are correct.     

Fibroblast growth factor signaling in Caenorhabditis elegans.

Growth factor receptor tyrosine kinases (RTKs), such as the fibroblast growth factor receptor (FGFR), play a major role in how cells communicate with their environment. FGFR signaling is crucial for normal development, and its misregulation in humans has been linked to developmental abnormalities and cancer. The precise molecular mechanisms by which FGFRs transduce extracellular signals to effect specific biologic responses is an area of intense research. Genetic analyses in model organisms have played a central role in our evolving understanding of these signal transduction cascades. Genetic studies in the nematode C. elegans have contributed to our knowledge of FGFR signaling by identifying genes involved in FGFR signal transduction and linking their gene products together into signaling modules. This review will describe FGFR-mediated signal transduction in C. elegans and focus on how these studies have contributed to our understanding of how FGFRs orchestrate the assembly of intracellular signaling pathways.     

PKC-1 acts with the ERK MAPK signaling pathway to regulate Caenorhabditis elegans mechanosensory response

In most animals, multiple genes encode protein kinase C (PKC) proteins. Pharmacological studies have revealed numerous roles for this protein family, yet the in vivo roles of specific PKC proteins and the functional targets of PKC activation are poorly understood. We find that in Caenorhabditis elegans, two PKC genes, pkc-1 and tpa-1, are required for mechanosensory response; the role of the nPKCε/η ortholog, pkc-1, was examined in detail. pkc-1 function is required for response to nose touch in adult C. elegans and pkc-1 likely acts in the interneurons that regulate locomotion which are direct synaptic targets of mechanosensory neurons. Previous studies have suggested numerous possible targets of pkc-1; our analysis indicates that pkc-1 may act via the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathway. We find that ERK/MAPK pathway function is required for mechanosensory response in C. elegans and that at least one component of this pathway, lin-45 Raf, acts in interneurons of the mechanosensory circuit. Genetic analysis indicates that lin-45 and pkc-1 act together to regulate nose touch response. Thus, these results functionally link two conserved signaling pathways in adult C. elegans neurons and define distinct roles for PKC genes in vivo.     

High-throughput reverse genetics: RNAi screens in Caenorhabditis elegans

Two recent chromosome-wide screens for phenotypes caused by RNA-mediated interference (RNAi) in Caenorhabditis elegans have increased our understanding of essential genes in nematodes. These papers represent a major advance in functional genomics.     

5'-AMP-activated protein kinase signaling in Caenorhabditis elegans

5'-AMP-activated protein kinase (AMPK) has been called "the metabolic master switch" because of its central role in regulating fuel homeostasis. AMPK, a heterotrimeric serine/threonine protein kinase composed of alpha, beta, and gamma subunits, is activated by upstream kinases and by 5'-AMP in response to various nutritional and stress signals. Downstream effects include regulation of metabolism, protein synthesis, cell growth, and mediation of the actions of a number of hormones, including leptin. However, AMPK research represents a young and growing field; hence, there are many unanswered questions regarding the control and action of AMPK. This review presents evidence for the existence of AMPK signaling pathways in Caenorhabditis elegans, a genetically tractable model organism that has yet to be fully exploited to elucidate AMPK signaling mechanisms.