Inducible antibacterial defense system in C. elegans

Recovery from an acute infection in C. elegans requires the GATA transcription factor ELT-2

The mechanisms involved in the recognition of microbial pathogens and activation of the immune system have been extensively studied. However, the mechanisms involved in the recovery phase of an infection are incompletely characterized at both the cellular and physiological levels. Here, we establish a Caenorhabditis elegans-Salmonella enterica model of acute infection and antibiotic treatment for studying biological changes during the resolution phase of an infection. Using whole genome expression profiles of acutely infected animals, we found that genes that are markers of innate immunity are down-regulated upon recovery, while genes involved in xenobiotic detoxification, redox regulation, and cellular homeostasis are up-regulated. In silico analyses demonstrated that genes altered during recovery from infection were transcriptionally regulated by conserved transcription factors, including GATA/ELT-2, FOXO/DAF-16, and Nrf/SKN-1. Finally, we found that recovery from an acute bacterial infection is dependent on ELT-2 activity.

Antinematode activity of Violacein and the role of the insulin/IGF-1 pathway in controlling violacein sensitivity in Caenorhabditis elegans

The purple pigment violacein is well known for its numerous biological activities including antibacterial, antiviral, antiprotozoan, and antitumor effects. In the current study we identify violacein as the antinematode agent produced by the marine bacterium Microbulbifer sp. D250, thereby extending the target range of this small molecule. Heterologous expression of the violacein biosynthetic pathway in E. coli and experiments using pure violacein demonstrated that this secondary metabolite facilitates bacterial accumulation in the nematode intestine, which is accompanied by tissue damage and apoptosis. Nematodes such as Caenorhabditis elegans utilise a well-defined innate immune system to defend against pathogens. Using C. elegans as a model we demonstrate the DAF-2/DAF-16 insulin/IGF-1 signalling (IIS) component of the innate immune pathway modulates sensitivity to violacein-mediated killing. Further analysis shows that resistance to violacein can occur due to a loss of DAF-2 function and/or an increased function of DAF-16 controlled genes involved in antimicrobial production (spp-1) and detoxification (sod-3). These data suggest that violacein is a novel candidate antinematode agent and that the IIS pathway is also involved in the defence against metabolites from non-pathogenic bacteria.

Caenorhabditis elegans: a simple nematode infection model for Penicillium marneffei

Penicillium marneffei, one of the most important thermal dimorphic fungi, is a severe threat to the life of immunocompromised patients. However, the pathogenic mechanisms of P. marneffei remain largely unknown. In this work, we developed a model host by using nematode Caenorhabditis elegans to investigate the virulence of P. marneffei. Using two P. marneffei clinical isolate strains 570 and 486, we revealed that in both liquid and solid media, the ingestion of live P. marneffei was lethal to C. elegans (P<0.001). Meanwhile, our results showed that the strain 570, which can produce red pigment, had stronger pathogenicity in C. elegans than the strain 486, which can’t produce red pigment (P<0.001). Microscopy showed the formation of red pigment and hyphae within C. elegans after incubation with P. marneffei for 4 h, which are supposed to be two contributors in nematodes killing. In addition, we used C. elegans as an in vivo model to evaluate different antifungal agents against P. marneffei, and found that antifungal agents including amphotericin B, terbinafine, fluconazole, itraconazole and voriconazole successfully prolonged the survival of nematodesinfected by P. marneffei. Overall, this alternative model host can provide us an easy tool to study the virulence of P. marneffei and screen antifungal agents.

Activation of a G protein-coupled receptor by its endogenous ligand triggers the innate immune response of Caenorhabditis elegans

Immune defenses are triggered by microbe-associated molecular patterns or as a result of damage to host cells. The elicitors of immune responses in the nematode Caenorhabditis elegans are unclear. Using a genome-wide RNA-mediated interference (RNAi) screen, we identified the G protein-coupled receptor (GPCR) DCAR-1 as being required for the response to fungal infection and wounding. DCAR-1 acted in the epidermis to regulate the expression of antimicrobial peptides via a conserved p38 mitogen-activated protein kinase pathway. Through targeted metabolomics analysis we identified the tyrosine derivative 4-hydroxyphenyllactic acid (HPLA) as an endogenous ligand. Our findings reveal DCAR-1 and its cognate ligand HPLA to be triggers of the epidermal innate immune response in C. elegans and highlight the ancient role of GPCRs in host defense.

Selenite enhances immune response against Pseudomonas aeruginosa PA14 via SKN-1 in Caenorhabditis elegans

Background

Selenium (Se) is an important nutrient that carries out many biological processes including maintaining optimal immune function. Here, inorganic selenite (Se(IV)) was evaluated for its pathogen resistance and potential-associated factors in Caenorhabditis elegans. The immune effects of Se(IV) were investigated by examining the responses of C. elegans to Pseudomonas aerugonisa PA14 strain.

Principal Findings

Se(IV)-treated C. elegans showed increased survival under PA14 infection compared with untreated controls. The significant pathogen resistance of Se(IV) on C. elegans might not be attributed to the effects of Se(IV) on PA14 as Se(IV) showed no effect on bacterial quorum-sensing and virulence factors of PA14. This study showed that Se(IV) enhanced the expression of a gene pivotal for the innate immunity in C. elegans. The study found that the pathogen-resistant phenotypes contributed by Se(IV) was absent from the skn-1 mutant worms. Moreover, Se(IV) influenced the subcellular distribution of SKN-1/Nrf in C. elegans upon PA14 infection. Furthermore, Se(IV) increased mRNA levels of SKN-1 target genes (gst-4 and gcs-1).

Conclusions

This study found evidence of Se(IV) protecting C. elegans against P. aeruginosa PA14 infection by exerting effects on the innate immunity of C. elegans that is likely mediated via regulation of a SKN-1-dependent signaling pathway.

A functional genomic screen for evolutionarily conserved genes required for lifespan and immunity in germline-deficient C. elegans

The reproductive system regulates lifespan in insects, nematodes and vertebrates. In Caenorhabditis elegans removal of germline increases lifespan by 60% which is dependent upon insulin signaling, nuclear hormone signaling, autophagy and fat metabolism and their microRNA-regulators. Germline-deficient C. elegans are also more resistant to various bacterial pathogens but the underlying molecular mechanisms are largely unknown. Firstly, we demonstrate that previously identified genes that regulate the extended lifespan of germline-deficient C. elegans (daf-2, daf-16, daf-12, tcer-1, mir-7.1 and nhr-80) are also essential for resistance to the pathogenic bacterium Xenorhabdus nematophila. We then use a novel unbiased approach combining laser cell ablation, whole genome microarrays, RNAi screening and exposure to X. nematophila to generate a comprehensive genome-wide catalog of genes potentially required for increased lifespan and innate immunity in germline-deficient C. elegans. We find 3,440 genes to be upregulated in C. elegans germline-deficient animals in a gonad dependent manner, which are significantly enriched for genes involved in insulin signaling, fatty acid desaturation, translation elongation and proteasome complex function. Using RNAi against a subset of 150 candidate genes selected from the microarray results, we show that the upregulated genes such as transcription factor DAF-16/FOXO, the PTEN homolog lipid phosphatase DAF-18 and several components of the proteasome complex (rpn-6.1, rpn-7, rpn-9, rpn-10, rpt-6, pbs-3 and pbs-6) are essential for both lifespan and immunity of germline deficient animals. We also identify a novel role for genes including par-5 and T12G3.6 in both lifespan-extension and increased survival on X. nematophila. From an evolutionary perspective, most of the genes differentially expressed in germline deficient C. elegans also show a conserved expression pattern in germline deficient Pristionchus pacificus, a nematode species that diverged from C. elegans 250-400 MYA.

Regulation of extracellular matrix organization by BMP signaling in Caenorhabditis elegans

In mammals, Bone Morphogenetic Protein (BMP) pathway signaling is important for the growth and homeostasis of extracellular matrix, including basement membrane remodeling, scarring, and bone growth. A conserved BMP member in Caenorhabditis elegans, DBL-1, regulates body length in a dose-sensitive manner. Loss of DBL-1 pathway signaling also results in increased anesthetic sensitivity. However, the physiological basis of these pleiotropic phenotypes is largely unknown. We created a DBL-1 over-expressing strain and show that sensitivity to anesthetics is inversely related to the dose of DBL-1. Using pharmacological, genetic analyses, and a novel dye permeability assay for live, microwave-treated animals, we confirm that DBL-1 is required for the barrier function of the cuticle, a specialized extracellular matrix. We show that DBL-1 signaling is required to prevent animals from forming tail-entangled aggregates in liquid. Stripping lipids off the surface of wild-type animals recapitulates this phenotype. Finally, we find that DBL-1 signaling affects ultrastructure of the nematode cuticle in a dose-dependent manner, as surface lipid content and cuticular organization are disrupted in animals with genetically altered DBL-1 levels. We propose that the lipid layer coating the nematode cuticle normally prevents tail entanglement, and that reduction of this layer by loss of DBL-1 signaling promotes aggregation. This work provides a physiological mechanism that unites the DBL-1 signaling pathway roles of not only body size regulation and drug responsiveness, but also the novel Hoechst 33342 staining and aggregation phenotypes, through barrier function, content, and organization of the cuticle.

The C-type lectin-like domain containing proteins Clec-39 and Clec-49 are crucial for Caenorhabditis elegans immunity against Serratia marcescens infection

Caenorhabditis elegans exhibits protective immunity against a variety of fungal and bacterial pathogens. Since C. elegans lacks an adaptive immune system, pathogen recognition is mediated entirely by innate immunity. To date, little is known about the involvement of pattern recognition receptors (PRRs) in pathogen sensing as part of the C. elegans immunity. C-type lectin-like domain (CTLD) containing proteins represent a superfamily of PRRs. A large number of genes encoding for CTLD proteins are present in the C. elegans genome, however the role of CTLD proteins in bacterial recognition and antibacterial immunity has not yet been determined. In this study, we investigated the function of selected C. elegans CTLD proteins during infection with the Gram-negative bacterium Serratia marcescens. Wild-type and CTLD gene-deficient C. elegans strains were compared in their susceptibility to S. marcescens infection. Interestingly, survival and egg laying were significantly reduced in strains deficient for clec-39 and clec-49 indicating a role for both CTLD proteins in C. elegans immune defense against bacteria as evidenced by using S. marcescens infection. Binding studies with recombinantly expressed Clec-39-Fc and Clec-49-Fc fusion proteins revealed that both CTLD proteins recognized live bacteria in a Ca(2+)-independent manner. This study provides insight into the role of CTLD proteins in C. elegans immunity and demonstrates their function during bacterial infection.

Orthosiphon stamineus protects Caenorhabditis elegans against Staphylococcus aureus infection through immunomodulation

Amidst growing concerns over the spread of antibiotic-resistant Staphylococcus aureus strains, the identification of alternative therapeutic molecules has become paramount. Previously, we utilized a Caenorhabditis elegans–S. aureus screening platform to identify potential anti-infective agents from a collection of natural extracts and synthetic compounds. One of the hits obtained from the screen was the aqueous extract of Orthosiphon stamineus leaves (UE-12) that enhanced the survival of infected nematodes without interfering with bacterial growth. In this study, we used a fluorescent transgenic reporter strain and observed that the repressed expression of the lys-7 defense gene in infected nematodes was restored in the presence of UE-12. Analysis of a selected panel of PMK-1 and DAF-16-regulated transcripts and loss-of-function mutants in these pathways indicates that the protective role of UE-12 is mediated via the p38 MAP kinase and insulin-like signaling pathways. Further analysis of a panel of known bioactive compounds of UE-12 proposed eupatorin (C₁₈H₁₆O₇) as the possible candidate active molecule contributing to the anti-infective property of UE-12. Taken together, these findings strongly suggest that the O. stamineus leaf extract is a promising anti-infective agent that confers an advantage in survival against S. aureus infection by modulating the immune response of the infected host.

Comparative genomics RNAi screen identifies Eftud2 as a novel regulator of innate immunity

The extent of the innate immune response is regulated by many positively and negatively acting signaling proteins. This allows for proper activation of innate immunity to fight infection while ensuring that the response is limited to prevent unwanted complications. Thus mutations in innate immune regulators can lead to immune dysfunction or to inflammatory diseases such as arthritis or atherosclerosis. To identify novel innate immune regulators that could affect infectious or inflammatory disease, we have taken a comparative genomics RNAi screening approach in which we inhibit orthologous genes in the nematode Caenorhabditis elegans and murine macrophages, expecting that genes with evolutionarily conserved function also will regulate innate immunity in humans. Here we report the results of an RNAi screen of approximately half of the C. elegans genome, which led to the identification of many candidate genes that regulate innate immunity in C. elegans and mouse macrophages. One of these novel conserved regulators of innate immunity is the mRNA splicing regulator Eftud2, which we show controls the alternate splicing of the MyD88 innate immunity signaling adaptor to modulate the extent of the innate immune response.

Insights from the worm: the C. elegans model for innate immunity

The nematode worm Caenorhabditis elegans comprises an ancestral immune system. C. elegans recognizes and responds to viral, bacterial, and fungal infections. Components of the RNA interference machinery respond to viral infection, while highly conserved MAPK signaling pathways activate the innate immune response to bacterial infection. C. elegans has been particularly important for exploring the role of innate immunity in organismal stress resistance and the regulation of longevity. Also functions of neuronal sensing of infectious bacteria have recently been uncovered. Studies on nematode immunity can be instructive in exploring innate immune signaling in the absence of specialized immune cells and adaptive immunity.

Analysis of the transcriptome of Hirschmanniella oryzae to explore potential survival strategies and host-nematode interactions

The rice root nematode Hirschmanniella oryzae is the most abundant plant-parasitic nematode in flooded rice fields and is distributed world-wide. Although it is economically less important than sedentary nematodes, it can cause severe yield reductions and economic losses in specific environmental conditions. No transcriptome data for this genus were available until now. We have performed 454 sequencing on a mixed life stages population to gain an insight into nematode-plant interactions and nematode survival strategies. The results of two assembly strategies were combined to reduce the redundancy of the data, generating a final dataset of 21 360 contigs. The data were screened for putative plant cell wall-modifying proteins, which facilitate nematode migration through host roots. A β-mannanase, previously not reported in nematodes, was detected in the dataset. The data were screened for putative effector proteins that may alter the host defence mechanism. Two enzymes, chorismate mutase and isochorismatase, thought to be involved in the salicyclic acid pathway, were identified. Experimental treatments of H. oryzae with artificial seawater showed that late embryogenesis abundant (LEA) proteins and SXP/RAL-2 are induced, suggesting that these proteins are involved in the process of anhydrobiosis. The newly generated data can highlight potential differences between sedentary and migratory nematodes, and will be useful in the further study of host-nematode interactions and the developmental biology of this nematode.

High-throughput screening for novel anti-infectives using a C. elegans pathogenesis model

In recent history, the nematode Caenorhabditis elegans has provided a compelling platform for the discovery of novel antimicrobial drugs. In this protocol, we present an automated, high-throughput C. elegans pathogenesis assay, which can be used to screen for anti-infective compounds that prevent nematodes from dying due to Pseudomonas aeruginosa. New antibiotics identified from such screens would be promising candidates for treatment of human infections, and also can be used as probe compounds to identify novel targets in microbial pathogenesis or host immunity.

Functional characterization of thioredoxin 3 (TRX-3), a Caenorhabditis elegans intestine-specific thioredoxin

Thioredoxins are a class of evolutionarily conserved proteins that have been demonstrated to play a key role in many cellular processes involving redox reactions. We report here the genetic and biochemical characterization of Caenorhabditis elegans TRX-3, the first metazoan thioredoxin with an intestine-specific expression pattern. By using green fluorescent protein reporters we have found that TRX-3 is expressed in both the cytoplasm and the nucleus of intestinal cells, with a prominent localization at the apical membrane. Although intestinal function, reproductive capacity, longevity, and resistance of trx-3 loss-of-function mutants to many stresses are indistinguishable from those of wild-type animals, we have observed a slight reduction in size and a minor reduction in the defecation cycle timing of trx-3 mutants. Interestingly, trx-3 is induced upon infection by Photorhabdus luminescens and Candida albicans, and TRX-3 overexpression provides a modest protection against these pathogens. Together, our data indicate that TRX-3 function in the intestine is dispensable for C. elegans development but may be important to fight specific bacterial and fungal infections.

Multigenic natural variation underlies Caenorhabditis elegans olfactory preference for the bacterial pathogen Serratia marcescens

The nematode Caenorhabditis elegans can use olfaction to discriminate among different kinds of bacteria, its major food source. We asked how natural genetic variation contributes to choice behavior, focusing on differences in olfactory preference behavior between two wild-type C. elegans strains. The laboratory strain N2 strongly prefers the odor of Serratia marcescens, a soil bacterium that is pathogenic to C. elegans, to the odor of Escherichia coli, a commonly used laboratory food source. The divergent Hawaiian strain CB4856 has a weaker attraction to Serratia than the N2 strain, and this behavioral difference has a complex genetic basis. At least three quantitative trait loci (QTLs) from the CB4856 Hawaii strain (HW) with large effect sizes lead to reduced Serratia preference when introgressed into an N2 genetic background. These loci interact and have epistatic interactions with at least two antagonistic QTLs from HW that increase Serratia preference. The complex genetic architecture of this C. elegans trait is reminiscent of the architecture of mammalian metabolic and behavioral traits.

Lactobacillus zeae protects Caenorhabditis elegans from enterotoxigenic Escherichia coli-caused death by inhibiting enterotoxin gene expression of the pathogen

BACKGROUND

The nematode Caenorhabditis elegans has become increasingly used for screening antimicrobials and probiotics for pathogen control. It also provides a useful tool for studying microbe-host interactions. This study has established a C. elegans life-span assay to preselect probiotic bacteria for controlling K88(+) enterotoxigenic Escherichia coli (ETEC), a pathogen causing pig diarrhea, and has determined a potential mechanism underlying the protection provided by Lactobacillus.

METHODOLOGY/PRINCIPAL FINDINGS

Life-span of C. elegans was used to measure the response of worms to ETEC infection and protection provided by lactic acid-producing bacteria (LAB). Among 13 LAB isolates that varied in their ability to protect C. elegans from death induced by ETEC strain JG280, Lactobacillus zeae LB1 offered the highest level of protection (86%). The treatment with Lactobacillus did not reduce ETEC JG280 colonization in the nematode intestine. Feeding E. coli strain JFF4 (K88(+) but lacking enterotoxin genes of estA, estB, and elt) did not cause death of worms. There was a significant increase in gene expression of estA, estB, and elt during ETEC JG280 infection, which was remarkably inhibited by isolate LB1. The clone with either estA or estB expressed in E. coli DH5α was as effective as ETEC JG280 in killing the nematode. However, the elt clone killed only approximately 40% of worms. The killing by the clones could also be prevented by isolate LB1. The same isolate only partially inhibited the gene expression of enterotoxins in both ETEC JG280 and E. coli DH5α in-vitro.

CONCLUSIONS/SIGNIFICANCE

The established life-span assay can be used for studies of probiotics to control ETEC (for effective selection and mechanistic studies). Heat-stable enterotoxins appeared to be the main factors responsible for the death of C. elegans. Inhibition of ETEC enterotoxin production, rather than interference of its intestinal colonization, appears to be the mechanism of protection offered by Lactobacillus.

f57f4.4p::gfp as a fluorescent reporter for analysis of the C. elegans response to bacterial infection

Host defense mechanisms are multi-layered and involve constitutive as well as inducible components. The dissection of these complex processes can be greatly facilitated using a reporter gene strategy with a transparent animal. In this study, we use Caenorhabditis elegans as a model host and introduce a new pathogen-inducible fluorescent reporter involving the promoter of f57f4.4, a gene encoding a putative component of the glycocalyx. We show that this reporter construct does not respond to heavy metal or hypertonic environments, but is specifically and locally induced in the intestine upon Photorhabus luminescens and Pseudomonas aeruginosa infections. We further demonstrate that its upregulation requires live pathogens as well as elements of the nematode p38 MAP kinase and TGF-beta pathways. In addition to introducing a new tool for the study of the interactions between C. elegans and a pathogen, our results suggest a role for the glycocalyx in gut immunity.

A bifunctional invertebrate-type lysozyme from the disk abalone, Haliotis discus discus: genome organization, transcriptional profiling and biological activities of recombinant protein

Lysozyme is an important enzyme in the innate immune system that plays a vital role in fighting microbial infections. In the current study, we identified, cloned, and characterized a gene that encodes an invertebrate-type lysozyme from the disk abalone, Haliotis discus discus (abLysI). The full-length cDNA of abLysI consisted of 545 bp with an open reading frame of 393 bp that encodes 131 amino acids. The theoretical molecular mass of mature abLysI was 12.3 kDa with an isoelectric point of 8.03. Conserved features in other homologs, such as catalytic sites for lytic activity (Glu(30) and Asp(41)), isopeptidase activity (His(107)), and ten cysteine residues were identified in abLysI. Genomic sequence analysis with respect to its cDNA showed that abLysI was organized into four exons interrupted by three introns. Several immune-related transcription factor binding sites were discovered in the putative promoter region. Homology and phylogeny analysis of abLysI depicted high identity and closer proximity, respectively, with an annelid i-type lysozyme from Hirudo medicinalis, and indicated that abLysI is a novel molluscan i-type lysozyme. Tissue-specific expressional studies revealed that abLysI is mainly transcribed in hepatopancreas followed by mantle. In addition, abLysI mRNA expression was induced following bacterial (Vibrio parahaemolyticus and Listeria monocytogenes) and viral (viral hemorrhagic septicemia virus) challenges. Recombinantly expressed abLysI [(r)abLysI] demonstrated strong lytic activity against Micrococcus lysodeikticus, isopeptidase activity, and antibacterial activity against several Gram-positive and Gram-negative bacteria. Moreover, (r)abLysI showed optimum lytic activity at pH 4.0 and 60 °C, while exhibiting optimum isopeptidase activity at pH 7.0. Taken together, these results indicate that abLysI is potentially involved in immune responses of the disk abalone to protect it from invaders.

Components of the cultivated red seaweed Chondrus crispus enhance the immune response of Caenorhabditis elegans to Pseudomonas aeruginosa through the pmk-1, daf-2/daf-16, and skn-1 pathways

Marine macroalgae are rich in bioactive compounds that can, when consumed, impart beneficial effects on animal and human health. The red seaweed Chondrus crispus has been reported to have a wide range of health-promoting activities, such as antitumor and antiviral activities. Using a Caenorhabditis elegans infection model, we show that C. crispus water extract (CCWE) enhances host immunity and suppresses the expression of quorum sensing (QS) and the virulence factors of Pseudomonas aeruginosa (strain PA14). Supplementation of nematode growth medium with CCWE induced the expression of C. elegans innate immune genes, such as irg-1, irg-2, F49F1.6, hsf-1, K05D8.5, F56D6.2, C29F3.7, F28D1.3, F38A1.5 ZK6.7, lys-1, spp-1, and abf-1, by more than 2-fold, while T20G5.7 was not affected. Additionally, CCWE suppressed the expression of PA14 QS genes and virulence factors, although it did not affect the growth of the bacteria. These effects correlated with a 28% reduction in the PA14-inflicted killing of C. elegans. Kappa-carrageenan (K-CGN), a major component of CCWE, was shown to play an important role in the enhancement of host immunity. Using C. elegans mutants, we identified that pmk-1, daf-2/daf-16, and skn-1 are essential in the K-CGN-induced host immune response. In view of the conservation of innate immune pathways between C. elegans and humans, the results of this study suggest that water-soluble components of C. crispus may also play a health-promoting role in higher animals and humans.

Burkholderia pseudomallei suppresses Caenorhabditis elegans immunity by specific degradation of a GATA transcription factor

Burkholderia pseudomallei is a Gram-negative soil bacterium that infects both humans and animals. Although cell culture studies have revealed significant insights into factors contributing to virulence and host defense, the interactions between this pathogen and its intact host remain to be elucidated. To gain insights into the host defense responses to B. pseudomallei infection within an intact host, we analyzed the genome-wide transcriptome of infected Caenorhabditis elegans and identified ∼6% of the nematode genes that were significantly altered over a 12-h course of infection. An unexpected feature of the transcriptional response to B. pseudomallei was a progressive increase in the proportion of down-regulated genes, of which ELT-2 transcriptional targets were significantly enriched. ELT-2 is an intestinal GATA transcription factor with a conserved role in immune responses. We demonstrate that B. pseudomallei down-regulation of ELT-2 targets is associated with degradation of ELT-2 protein by the host ubiquitin-proteasome system. Degradation of ELT-2 requires the B. pseudomallei type III secretion system. Together, our studies using an intact host provide evidence for pathogen-mediated host immune suppression through the destruction of a host transcription factor.

Physiological and Immunological Regulations in Caenorhabditis elegans Infected with Salmonella enterica serovar Typhi

Studies pertaining to Salmonella enterica serovar Typhimurium infection by utilizing model systems failed to mimic the essential aspects of immunity induced by Salmonella enterica serovar Typhi, as the determinants of innate immunity are distinct. The present study investigated the physiological and innate immune responses of S. Typhi infected Caenorhabditis elegans and also explored the Ty21a mediated immune enhancement in C. elegans. Ty21a is a known live vaccine for typhoidal infection in human beings. Physiological responses of C. elegans infected with S. Typhi assessed by survival and behavioral assays revealed that S. Typhi caused host mortality by persistent infection. However, Ty21a exposure to C. elegans was not harmful. Ty21a pre-exposed C. elegans, exhibited significant resistance against S. Typhi infection. Elevated accumulation of S. Typhi inside the infected host was observed when compared to Ty21a exposures. Transcript analysis of candidate innate immune gene (clec-60, clec-87, lys-7, ilys-3, scl-2, cpr-2, F08G5.6, atf-7, age-1, bec-1 and daf-16) regulations in the host during S. Typhi infection have been assessed through qPCR analysis to understand the activation of immune signaling pathways during S. Typhi infections. Gene silencing approaches confirmed that clec-60 and clec-87 has a major role in the defense system of C. elegans during S. Typhi infection. In conclusion, the study revealed that preconditioning of host with Ty21a protects against subsequent S. Typhi infection.

A lover and a fighter: the genome sequence of an entomopathogenic nematode Heterorhabditis bacteriophora

Heterorhabditis bacteriophora are entomopathogenic nematodes that have evolved a mutualism with Photorhabdus luminescens bacteria to function as highly virulent insect pathogens. The nematode provides a safe harbor for intestinal symbionts in soil and delivers the symbiotic bacteria into the insect blood. The symbiont provides virulence and toxins, metabolites essential for nematode reproduction, and antibiotic preservation of the insect cadaver. Approximately half of the 21,250 putative protein coding genes identified in the 77 Mbp high quality draft H. bacteriophora genome sequence were novel proteins of unknown function lacking homologs in Caenorhabditis elegans or any other sequenced organisms. Similarly, 317 of the 603 predicted secreted proteins are novel with unknown function in addition to 19 putative peptidases, 9 peptidase inhibitors and 7 C-type lectins that may function in interactions with insect hosts or bacterial symbionts. The 134 proteins contained mariner transposase domains, of which there are none in C. elegans, suggesting an invasion and expansion of mariner transposons in H. bacteriophora. Fewer Kyoto Encyclopedia of Genes and Genomes Orthologies in almost all metabolic categories were detected in the genome compared with 9 other sequenced nematode genomes, which may reflect dependence on the symbiont or insect host for these functions. The H. bacteriophora genome sequence will greatly facilitate genetics, genomics and evolutionary studies to gain fundamental knowledge of nematode parasitism and mutualism. It also elevates the utility of H. bacteriophora as a bridge species between vertebrate parasitic nematodes and the C. elegans model.

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.

Mucosal immunity in the gut: the non-vertebrate perspective

Much is now known about the vertebrate mechanisms involved in mucosal immunity, and the requirement of commensal microbiota at mucosal surfaces for the proper functioning of the immune system. In comparison, very little is known about the mechanisms of immunity at the barrier epithelia of non-vertebrate organisms. The purpose of this review is to summarize key experimental evidence illustrating how non-vertebrate immune mechanisms at barrier epithelia compare to those of higher vertebrates, using the gut as a model organ. Not only effector mechanisms of gut immunity are similar between vertebrates and non-vertebrates, but it also seems that the proper functioning of non-vertebrate gut defense mechanisms requires the presence of a resident microbiota. As more information becomes available, it will be possible to obtain a more accurate picture of how mucosal immunity has evolved, and how it adapts to the organisms' life styles.

Live and dead GFP-tagged bacteria showed indistinguishable fluorescence in Caenorhabditis elegans gut

Caenorhabditis elegans has been used for studying host-pathogen interactions since long, and many virulence genes of pathogens have been successfully identified. In several studies, fluorescent pathogens were fed to C. elegans and fluorescence observed in the gut was considered an indicator for bacterial colonization. However, the grinder in the pharynx of these nematodes supposedly crushes the bacterial cells, and the ground material is delivered to the intestine for nutrient absorption. Therefore, it remains unclear whether intact bacteria pass through the grinder and colonize in the intestine. Here we investigated whether the appearance of fluorescence is indicative of intact bacteria in the gut using both fluorescence microscopy and transmission electron microscopy. In wild-type N2 C. elegans, Escherichia coli DH5α, and Vibrio vulnificus 93U204, both of which express the green fluorescence protein, were found intact only proximal to the grinder, while crushed bacterial debris was found in the post-pharyngeal lumen. Nevertheless, the fluorescence was evident throughout the lumen of worm intestines irrespective of whether the bacteria were intact or not. We further investigated the interaction of the bacteria with C. elegans phm-2 mutant, which has a dysfunctional grinder. Both strains of bacteria were found to be intact and accumulated in the pharynx and intestine owing to the defective grinder. The fluorescence intensity of intact bacteria in phm-2 worms was indistinguishable from that of crushed bacterial debris in N2 worms. Therefore, appearance of fluorescence in the C. elegans intestine should not be directly interpreted as successful bacterial colonization in the intestine.

The role of Candida albicans AP-1 protein against host derived ROS in in vivo models of infection

Candida albicans is a major fungal pathogen of humans, causing mucosal infections that are difficult to eliminate and systemic infections that are often lethal primarily due to defects in the host's innate status. Here we demonstrate the utility of Caenorhabditis elegans, a model host to study innate immunity, by exploring the role of reactive oxygen species (ROS) as a critical innate response against C. albicans infections. Much like a human host, the nematode's innate immune response is activated to produce ROS in response to fungal infection. We use the C. albicans cap1 mutant, which is susceptible to ROS, as a tool to dissect this physiological innate immune response and show that cap1 mutants fail to cause disease and death, except in bli-3 mutant worms that are unable to produce ROS because of a defective NADPH oxidase. We further validate the ROS-mediated host defense mechanism in mammalian phagocytes by demonstrating that chemical inhibition of the NADPH oxidase in cultured macrophages enables the otherwise susceptible cap1 mutant to resists ROS-mediated phagolysis. Loss of CAP1 confers minimal attenuation of virulence in a disseminated mouse model, suggesting that CAP1-independent mechanisms contribute to pathogen survival in vivo. Our findings underscore a central theme in the process of infection-the intricate balance between the virulence strategies employed by C. albicans and the host's innate immune system and validates C. elegans as a simple model host to dissect this balance at the molecular level.

A cytoprotective perspective on longevity regulation

There are many mechanisms of lifespan extension, including the disruption of insulin/insulin-like growth factor 1 (IGF-1) signaling, metabolism, translation, and feeding. Despite the disparate functions of these pathways, inhibition of each induces responses that buffer stress and damage. Here, emphasizing data from genetic analyses in Caenorhabditis elegans, we explore the effectors and upstream regulatory components of numerous cytoprotective mechanisms activated as major elements of longevity programs, including detoxification, innate immunity, proteostasis, and oxidative stress response. We show that their induction underpins longevity extension across functionally diverse triggers and across species. Intertwined with the evolution of longevity, cytoprotective pathways are coupled to the surveillance of core cellular components, with important implications in normal and aberrant responses to drugs, chemicals, and pathogens.

Effects of sequential infections of Caenorhabditis elegans with Staphylococcus aureus and Proteus mirabilis

Caenorhabditis elegans can be used to study the dynamics of polymicrobial infections, specifically those between Gram-positive and Gram-negative bacteria. With C. elegans, Proteus mirabilis acts as an opportunistic pathogen and does not kill this host. Hence, in the present study, C. elegans was immunochallenged by pre-infecting it with the pathogen Staphylococcus aureus in order to study the subsequent effect of P. mirabilis on the host. It was found that 12 hrs of S. aureus and 80 hrs of subsequent P. mirabilis infection significantly reduced the life span of exposed C. elegans by 80%. However, preinfection with S. aureus for 8 and 4 hrs reduced the life span of C. elegans by only 60 and 30%, respectively. Further, there was greater production of reactive oxygen species in the sequentially infected samples than in the S. aureus and P. mirabilis controls. Real time PCR analysis indicated regulation of candidate immune regulatory genes, lysozyme (lys-7), CUB-like proteins (F08G5.6), neuropeptide-like factors (nlp-29), transcription factors of mitogen-activated protein kinase (ATF-7) and daf-2-daf-16 (daf-16), insulin-like signaling pathways and C-type lectin (clec-60 and clec-87) family members during S. aureus and subsequent P. mirabilis-mediated infections, indicating possible roles of, and contributions by, the above factors during host immune responses against these sequential infections. The present findings demonstrate that S. aureus infections increase the vulnerability of the C. elegans host by subverting its immune system, which then permits the opportunistic pathogen P. mirabilis to be pathogenic to this host.

MXL-3 and HLH-30 transcriptionally link lipolysis and autophagy to nutrient availability

Fat is stored or mobilized according to food availability. Malfunction of the mechanisms that ensure this coordination underlie metabolic diseases in humans. In mammals, lysosomal and autophagic function is required for normal fat storage and mobilization in the presence or absence of food. Autophagy is tightly linked to nutrients. However, if and how lysosomal lipolysis is coupled to nutritional status remains to be determined. Here we identify MXL-3 and HLH-30 (TFEB orthologue) [corrected] as transcriptional switches coupling lysosomal lipolysis and autophagy to nutrient availability and controlling fat storage and ageing in Caenorhabditis elegans. Transcriptional coupling of lysosomal lipolysis and autophagy to nutrients is also observed in mammals. Thus, MXL-3 and HLH-30 orchestrate an adaptive and conserved cellular response to nutritional status and regulate lifespan.

RFX transcription factor DAF-19 regulates 5-HT and innate immune responses to pathogenic bacteria in Caenorhabditis elegans

In Caenorhabditis elegans the Toll-interleukin receptor domain adaptor protein TIR-1 via a conserved mitogen-activated protein kinase (MAPK) signaling cascade induces innate immunity and upregulates serotonin (5-HT) biosynthesis gene tph-1 in a pair of ADF chemosensory neurons in response to infection. Here, we identify transcription factors downstream of the TIR-1 signaling pathway. We show that common transcription factors control the innate immunity and 5-HT biosynthesis. We demonstrate that a cysteine to tyrosine substitution in an ARM motif of the HEAT/Arm repeat region of the TIR-1 protein confers TIR-1 hyperactivation, leading to constitutive tph-1 upregulation in the ADF neurons, increased expression of intestinal antimicrobial genes, and enhanced resistance to killing by the human opportunistic pathogen Pseudomonas aeruginosa PA14. A forward genetic screen for suppressors of the hyperactive TIR-1 led to the identification of DAF-19, an ortholog of regulatory factor X (RFX) transcription factors that are required for human adaptive immunity. We show that DAF-19 concerts with ATF-7, a member of the activating transcription factor (ATF)/cAMP response element-binding B (CREB) family of transcription factors, to regulate tph-1 and antimicrobial genes, reminiscent of RFX-CREB interaction in human immune cells. daf-19 mutants display heightened susceptibility to killing by PA14. Remarkably, whereas the TIR-1-MAPK-DAF-19/ATF-7 pathway in the intestinal immunity is regulated by DKF-2/protein kinase D, we found that the regulation of tph-1 expression is independent of DKF-2 but requires UNC-43/Ca²⁺/calmodulin-dependent protein kinase (CaMK) II. Our results suggest that pathogenic cues trigger a common core-signaling pathway via tissue-specific mechanisms and demonstrate a novel role for RFX factors in neuronal and innate immune responses to infection.

Toll-interleukin receptor (TIR)–domain adaptor proteins are keys to activate signaling cascades inducing transcriptional responses to internal and external pathogenic signals in evolutionary disparate organisms. Despite lacking a homolog of the mammalian innate immunity transcriptional regulator nuclear factor-kappaB (NF-κB), the nematode Caenorhabditis elegans responds to infections by activating TIR-1 signaling targets in the innate immune system and in neurons. Through a genetic screen for factors required for TIR-1 signaling to upregulate the serotonin biosynthesis gene tph-1, we identified DAF-19, an ortholog of regulatory factor X (RFX) transcription factors that were initially discovered in human immune cells. We show that DAF-19 concerts with ATF-7, a member of the activating transcription factor (ATF)/cAMP response element-binding B (CREB) family of transcription factors, to upregulate tph-1 in the ADF chemosensory neurons and antimicrobial genes in the intestine in response to bacterial infection, reminiscent of RFX-CREB interaction in human immune cells. daf-19 mutants display heightened susceptibility to killing by the human pathogen Pseudomonas aeruginosa PA14. Our studies suggest that RFX transcriptional regulation, which is essential for human adaptive immunity, has an ancient role in controlling serotonin biosynthesis and innate immunity.

The Caenorhabditis elegans JNK signaling pathway activates expression of stress response genes by derepressing the Fos/HDAC repressor complex

MAP kinases are integral to the mechanisms by which cells respond to a wide variety of environmental stresses. In Caenorhabditis elegans, the KGB-1 JNK signaling pathway regulates the response to heavy metal stress. In this study, we identified FOS-1, a bZIP transcription factor, as a target of KGB-1-mediated phosphorylation. We further identified two transcriptional targets of the KGB-1 pathway, kreg-1 and kreg-2/lys-3, which are required for the defense against heavy metal stress. FOS-1 plays a critical role in the transcriptional repression of the kreg-1 gene by recruiting histone deacetylase (HDAC) to its promoter. KGB-1 phosphorylation prevents FOS-1 dimerization and promoter binding, resulting in promoter derepression. Thus, HDAC behaves as a co-repressor modulating FOS-1-mediated transcriptional regulation. This study describes the direct link from JNK signaling, Fos phosphorylation, and regulation of kreg gene transcription, which modulates the stress response in C. elegans.

Effect of the bacterium Serratia marcescens SCBI on the longevity and reproduction of the nematode Caenorhabditis briggsae KT0001

Background

Extensive research effort has advanced our understanding of Caenorhabditis as a model system, but its natural association with bacteria remains to be explored in an ecological context. Explored associations vary vastly from mutualistic to parasitic. Serratia marcescens has been shown to be pathogenic to Caenorhabditis with a fitness cost. The recent isolation of an entomopathogenic Caenorhabditis briggsae KT0001/S. marcescens SCBI association from the wild has allowed us to examine under laboratory conditions whether such an association poses a serious cost to Caenorhabditis as previously surmised for other Serratia.

Results

A fecundity table of Caenorhabditis briggsae KT0001 fed on S. marcescens SCBI and the control fed on E. coli OP50 is presented. We found no significant difference in survivorship or total fecundity between the S. marcescens SCBI fed and E. coli OP50 fed Caenorhabditis briggsae KT0001. Only the mean onset of reproduction was significantly different between the two groups with E. coli fed C. briggsae maturing earlier (2.12 days) than those fed on Serratia (2.42 days).

Conclusion

S. marcescens SCBI is not highly pathogenic to C. briggsae KT0001 indicating that the entomopathogenicity reported for this association may be beneficial for both the nematode and bacteria. In light of the fact that hitherto conducted experimental tests conform to widely held view that Serratia are highly pathogenic to Caenorhabditis, the absence of a high fitness cost for C. briggsae we report here may indicate that this entomopathogenic association is non-transient suggesting nematode/bacterial associations in the wild may vary greatly. Consequently, broad generalizations about nematode/bacterial associations should be interpreted with care.

An evolutionarily conserved innate immunity protein interaction network

The innate immune response plays a critical role in fighting infection; however, innate immunity also can affect the pathogenesis of a variety of diseases, including sepsis, asthma, cancer, and atherosclerosis. To identify novel regulators of innate immunity, we performed comparative genomics RNA interference screens in the nematode Caenorhabditis elegans and mouse macrophages. These screens have uncovered many candidate regulators of the response to lipopolysaccharide (LPS), several of which interact physically in multiple species to form an innate immunity protein interaction network. This protein interaction network contains several proteins in the canonical LPS-responsive TLR4 pathway as well as many novel interacting proteins. Using RNAi and overexpression studies, we show that almost every gene in this network can modulate the innate immune response in mouse cell lines. We validate the importance of this network in innate immunity regulation in vivo using available mutants in C. elegans and mice.

Effect of Caenorhabditis elegans age and genotype on horizontal gene transfer in intestinal bacteria

Horizontal gene transfer (HGT) between bacteria occurs in the intestinal tract of their animal hosts and facilitates both virulence and antibiotic resistance. A model in which both the pathogen and the host are genetically tractable facilitates developing insight into mechanistic processes enabling or restricting the transfer of antibiotic resistance genes. Here we develop an in vivo experimental system to study HGT in bacteria using Caenorhabditis elegans as a model host. Using a thermosensitive conjugative system, we provide evidence that conjugation between two Escherichia coli strains can take place in the intestinal lumen of N2 wild-type worms at a rate of 10(-3) and 10(-2) per donor. We also show that C. elegans age and genotype are important determinants of the frequency of conjugation. Whereas ∼1 transconjugant for every 100 donor cells could be recovered from the intestine of N2 C. elegans, for the age-1 and tol-1 mutants, the detected rate of transconjugation (10(-3) and 10(-4) per donor cell, respectively) was significantly lower. This work demonstrates that increased recombination among lumenal microbial populations is a phenotype associated with host aging, and the model provides a framework to study the dynamics of bacterial horizontal gene transfer within the intestinal environment.

Strength in numbers: "Omics" studies of C. elegans innate immunity

For more than ten years the nematode Caenorhabditis elegans has proven to be a valuable model for studies of the host response to various bacterial and fungal pathogens. When exposed to a pathogenic organism, a clear response is elicited in the nematode, which is characterized by specific alterations on the transcriptional and translational levels. Early on, researchers took advantage of the possibility to conduct large-scale investigations of the C. elegans immune response. Multiple studies demonstrated that C. elegans does indeed mount a protective response against invading pathogens, thus rendering this small nematode a very useful and simple host model for the study of innate immunity and host-pathogen interactions. Here, we provide an overview of key aspects of innate immunity in C. elegans revealed by recent whole-genome transcriptomics and proteomics studies of the global response of C. elegans to various bacterial and fungal pathogens.

System wide analysis of the evolution of innate immunity in the nematode model species Caenorhabditis elegans and Pristionchus pacificus

The evolution of genetic mechanisms used to combat bacterial infections is critical for the survival of animals and plants, yet how these genes evolved to produce a robust defense system is poorly understood. Studies of the nematode Caenorhabditis elegans have uncovered a plethora of genetic regulators and effectors responsible for surviving pathogens. However, comparative studies utilizing other free-living nematodes and therefore providing an insight into the evolution of innate immunity have been lacking. Here, we take a systems biology approach and use whole genome microarrays to profile the transcriptional response of C. elegans and the necromenic nematode Pristionchus pacificus after exposure to the four different pathogens Serratia marcescens, Xenorhabdus nematophila, Staphylococcus aureus and Bacillus thuringiensis DB27. C. elegans is susceptible to all four pathogens whilst P. pacificus is only susceptible to S. marcescens and X. nematophila. We show an unexpected level of specificity in host responses to distinct pathogens within and across species, revealing an enormous complexity of effectors of innate immunity. Functional domains enriched in the transcriptomes on different pathogens are similar within a nematode species but different across them, suggesting differences in pathogen sensing and response networks. We find translation inhibition to be a potentially conserved response to gram-negative pathogens in both the nematodes. Further computational analysis indicates that both nematodes when fed on pathogens up-regulate genes known to be involved in other stress responses like heat shock, oxidative and osmotic stress, and genes regulated by DAF-16/FOXO and TGF-beta pathways. This study presents a platform for comparative systems analysis of two nematode model species, and a catalog of genes involved in the evolution of nematode immunity and identifies both pathogen specific and pan-pathogen responses. We discuss the potential effects of ecology on evolution of downstream effectors and upstream regulators on evolution of nematode innate immunity.

DBL-1, a TGF-β, is essential for Caenorhabditis elegans aversive olfactory learning

The TGF-β superfamily is conserved throughout metazoan, and its members play essential roles in development and disease. TGF-β has also been implicated in adult neural plasticity. However, the underlying mechanisms are not well understood. Here we report that DBL-1, a Caenorhabditis elegans TGF-β homolog known to control body morphology and immunity, is essential for aversive olfactory learning of potentially harmful bacteria food. We show that DBL-1 generated by the AVA command interneurons, which are critical for sensorimotor responses, regulates aversive olfactory learning, and that the activity of the type I TGF-β receptor SMA-6 in the hypodermis is needed during adulthood to generate olfactory plasticity. These spatial and temporal mechanisms are critical for the DBL-1 signaling to achieve its diverse functions in development and adult neural plasticity. Interestingly, aversive training decreases AVA calcium response, leading to an increase in the DBL-1 signal secreted from AVA, revealing an experience-dependent change that can underlie the role of TGF-β signaling in mediating plasticity.

The saposin-like protein SPP-12 is an antimicrobial polypeptide in the pharyngeal neurons of Caenorhabditis elegans and participates in defence against a natural bacterial pathogen

Caenopores are antimicrobial and pore-forming polypeptides in Caenorhabditis elegans belonging to the saposin-like protein superfamily and are considered important elements of the nematode's intestinal immune system. In the present study, we demonstrate that, unlike the other members of the multifarious gene family (spps) coding for caenopores, spp-12 is expressed exclusively in two pharyngeal neurons. Recombinantly expressed SPP-12 binds to phospholipid membranes and forms pores in a pH-dependent manner characteristic of caenopores. Moreover, SPP-12 kills viable Gram-positive bacteria, yeast cells and amoebae by permeabilizing their membranes, suggesting a wide-target cell spectrum. A spp-12 knockout mutant is more susceptible to pathogenic Bacillus thuringiensis than wild-type worms and is tolerant to non-pathogenic bacteria. By contrast, SPP-1, a caenopore, whose gene is expressed only in the intestine and reported to be regulated by the same pathway as spp-12, is apparently non-protective against pathogenic B. thuringiensis, although it also does display antimicrobial activity. The transcription of spp-1 is down-regulated in wild-type worms in the presence of pathogenic B. thuringiensis and a spp-1 knockout mutant is hyposusceptible to this bacterium. This implies that SPP-12, but not SPP-1, contributes to resistance against B. thuringiensis, a natural pathogen of the nematode.

SPP-3, a saposin-like protein of Caenorhabditis elegans, displays antimicrobial and pore-forming activity and is located in the intestine and in one head neuron

Caenopores belong to the saposin-like protein superfamily in Caenorhabditis elegans with 33 putative antimicrobial and pore-forming proteins. In this study, we analysed one selected member of this multifarious protein family, namely SPP-3, in detail, as its coding gene has been described to be inducible after bacterial challenge. The recombinant protein was antimicrobially active against a wide range of gram-negative and gram-positive bacteria and displayed membrane-permeabilizing and pH-dependent pore-forming activity. Promoter activity of the respective gene, spp-3, was localized to the intestine and the head neuron SDQR. While gene silencing had no apparent effect on the number of surviving Escherichia coli bacteria in the intestine, it increased the egg laying significantly. Accordingly, SPP-3 is a protein with antimicrobial activity that is presumably part of the redundant armamentarium of effector proteins in the worm's intestine, may help to protect neurons, and appears to be involved in regulating reproduction.

Effects of Lactobacillus salivarius, Lactobacillus reuteri, and Pediococcus acidilactici on the nematode Caenorhabditis elegans include possible antitumor activity

This study examined the effects of three lactic acid bacteria (LAB) strains on the nematode Caenorhabditis elegans. Lactobacillus salivarius, Lactobacillus reuteri, and Pediococcus acidilactici were found to inhibit the development and growth of the worm. Compared to Escherichia coli used as the control, L. reuteri and P. acidilactici reduced the lifespan of wild-type and short-lived daf-16 worms. On the contrary, L. salivarius extended the lifespan of daf-16 worms when used live, but reduced it as UV-killed bacteria. The three LAB induced the expression of genes involved in pathogen response and inhibited the growth of tumor-like germ cells, without affecting DAF16 localization or increasing corpse cells. Our results suggest the possible use of C. elegans as a model for studying the antitumor attributes of LAB. The negative effects of these LAB strains on the nematode also indicate their potential use against parasitic nematodes.

Genome-wide analysis of germline signaling genes regulating longevity and innate immunity in the nematode Pristionchus pacificus

Removal of the reproductive system of many animals including fish, flies, nematodes, mice and humans can increase lifespan through mechanisms largely unknown. The abrogation of the germline in Caenorhabditis elegans increases longevity by 60% due to a signal emitted from the somatic gonad. Apart from increased longevity, germline-less C. elegans is also resistant to other environmental stressors such as feeding on bacterial pathogens. However, the evolutionary conservation of this pathogen resistance, its genetic basis and an understanding of genes involved in producing this extraordinary survival phenotype are currently unknown. To study these evolutionary aspects we used the necromenic nematode Pristionchus pacificus, which is a genetic model system used in comparison to C. elegans. By ablation of germline precursor cells and subsequent feeding on the pathogen Serratia marcescens we discovered that P. pacificus shows remarkable resistance to bacterial pathogens and that this response is evolutionarily conserved across the Genus Pristionchus. To gain a mechanistic understanding of the increased resistance to bacterial pathogens and longevity in germline-ablated P. pacificus we used whole genome microarrays to profile the transcriptional response comparing germline ablated versus un-ablated animals when fed S. marcescens. We show that lipid metabolism, maintenance of the proteasome, insulin signaling and nuclear pore complexes are essential for germline deficient phenotypes with more than 3,300 genes being differentially expressed. In contrast, gene expression of germline-less P. pacificus on E. coli (longevity) and S. marcescens (immunity) is very similar with only 244 genes differentially expressed indicating that longevity is due to abundant gene expression also involved in immunity. By testing existing mutants of Ppa-DAF-16/FOXO and the nuclear hormone receptor Ppa-DAF-12 we show a conserved function of both genes in resistance to bacterial pathogens and longevity. This is the first study to show that the influence of the reproductive system on extending lifespan and innate immunity is conserved in evolution.

Studies on Shigella boydii infection in Caenorhabditis elegans and bioinformatics analysis of immune regulatory protein interactions

Shigella boydii causes bacillary dysentery or shigellosis and generates a significant burden in the developing nations. S. boydii-mediated infection assays were performed at both physiological and molecular levels using Caenorhabditis elegans as a host. Continuous exposure of worms to S. boydii showed a reduced life span indicating the pathogenicity of Shigella. Quantitative Real-Time PCR analysis was performed to analyze the expression and regulation of host specific candidate-antimicrobial genes (clec-60, clec-87, lys-7), which were expressed significantly during early infection, but weakened during the latter hours. Increased mortality of mutant RB1285 by S. boydii and Shigella flexneri indicated the role of lys-7 during Shigella infection. Protein-protein interactions (PPIs) database was used to analyze the interaction of immune proteins in both C. elegans and humans. In addition, the expression and regulation were revealed about immune genes (clec-61, clec-62, clec-63, F54D5.3 and ZK1320.2), which encode several intermediate immune protein partners (CLEC-61, CLEC-62, CLEC-63, F54D5.3, ZK1320.2, W03D2.6 and THN-2) that interact with LYS-7 and CLEC-60 and were found to play a role in C. elegans immune defense against S. boydii infections. Similarly, the immune genes that are specific to the human defense system, which encode IGHV4-39, A2M, LTF, and CD79A, were predicted to be expressed with LYZ and MBL2, thus indicating their regulation during Shigella infections. Our results using the lowest eukaryotic model system and human database indicated that the major players involved in immunity-related processes appear to be common in cases of Shigella sp. mediated immune responses. This article is part of a Special Issue entitled: Computational Methods for Protein Interaction and Structural Prediction.

Modulation of Caenorhabditis elegans infection sensitivity by the LIN-7 cell junction protein

In Caenorhabditis elegans, the LIN-2/7/10 protein complex regulates the activity of signalling proteins. We found that inhibiting lin-7 function, and also lin-2 and lin-10, resulted in enhanced C. elegans survival after infection by Burkholderia spp., implicating a novel role for these genes in modulating infection outcomes. Genetic experiments suggested that this infection phenotype is likely caused by modulation of the DAF-2 insulin/IGF-1 signalling pathway. Supporting these observations, yeast two-hybrid assays confirmed that the LIN-2 PDZ domain can physically bind to the DAF-2 C-terminus. Loss of lin-7 activity also altered DAF-16 nuclear localization kinetics, indicating an additional contribution by hsf-1. Unexpectedly, silencing lin-7 in the hypodermis, but not the intestine, was protective against infection, implicating the hypodermis as a key tissue in this phenomenon. Finally, consistent with lin-7 acting as a general host infection factor, lin-7 mutants also exhibited enhanced survival upon infectionby two other Gram-negative pathogens, Pseudomonas and Salmonella spp.

An engineering approach to extending lifespan in C. elegans

We have taken an engineering approach to extending the lifespan of Caenorhabditis elegans. Aging stands out as a complex trait, because events that occur in old animals are not under strong natural selection. As a result, lifespan can be lengthened rationally using bioengineering to modulate gene expression or to add exogenous components. Here, we engineered longer lifespan by expressing genes from zebrafish encoding molecular functions not normally present in worms. Additionally, we extended lifespan by increasing the activity of four endogenous worm aging pathways. Next, we used a modular approach to extend lifespan by combining components. Finally, we used cell- and worm-based assays to analyze changes in cell physiology and as a rapid means to evaluate whether multi-component transgenic lines were likely to have extended longevity. Using engineering to add novel functions and to tune endogenous functions provides a new framework for lifespan extension that goes beyond the constraints of the worm genome.

Pre-feeding of a glycolipid binding protein LEC-8 from Caenorhabditis elegans revealed enhanced tolerance to Cry1Ac toxin in Helicoverpa armigera

Crystal toxins from Bacillus thuringiensis bind to glycolipids and glycoproteins using two different lectin domains in the toxin protein. Our previous observations suggested that the sequestration of crystal toxin depends on the functional interaction of a toxin lectin with glycolipids. Given the finding that competition of a galectin LEC-8 with Cry5B for binding to glycolipids resulting in reduced Bt toxicity in nematode, it is interesting to explore the role of LEC-8 in insects. Here, we reported that the LEC-8 can also be exploited by insect for their survival when they were fed with Bt toxin food. Bioassay with LEC-8 showed that pre-feeding of Helicoverpa armigera larvae reduced the Cry1Ac susceptibility. Both LEC-8 and Cry1Ac bind to the midgut glycolipid in a similar way. Further ELISA indicated that LEC-8 interacts with glycolipid from insect midgut, thus reduce Cry1Ac binding to glycolipid. This in turn enhances insect tolerance to Cry1Ac toxin. The sugar determinants of LEC-8 were studied by using haemagglutination (HA) and haemagglutination inhibition (HAI) assay. It was suggested that the terminal sugar of LEC-8 has multiple sugar binding property.

A UPR-independent infection-specific role for a BiP/GRP78 protein in the control of antimicrobial peptide expression in C. elegans epidermis

The nematode C. elegans responds to infection by the fungus Drechmeria coniospora with a rapid increase in the expression of antimicrobial peptide genes. To investigate further the molecular basis of this innate immune response, we took a two-dimensional difference in-gel electrophoresis (2D-DIGE) approach to characterize the changes in host protein that accompany infection. We identified a total of 68 proteins from differentially represented spots and their corresponding genes. Through class testing, we identified functional categories that were enriched in our proteomic data set. One of these was “protein processing in endoplasmic reticulum,” pointing to a potential link between innate immunity and endoplasmic reticulum function. This class included HSP-3, a chaperone of the BiP/GRP78 family known to act coordinately in the endoplasmic reticulum with its paralog HSP-4 to regulate the unfolded protein response (UPR). Other studies have shown that infection of C. elegans can provoke a UPR. We observed, however, that in adult C. elegans infection with D. coniospora did not induce a UPR, and conversely, triggering a UPR did not lead to an increase in expression of the well-characterized antimicrobial peptide gene nlp-29. On the other hand, we demonstrated a specific role for hsp-3 in the regulation of nlp-29 after infection that is not shared with hsp-4. Epistasis analysis allowed us to place hsp-3 genetically between the Tribbles-like kinase gene nipi-3 and the protein kinase C delta gene tpa-1. The precise function of hsp-3 has yet to be determined, but these results uncover a hitherto unsuspected link between a BiP/GRP78 family protein and innate immune signaling.