Browsing by Author "Aballay, Alejandro"
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Item Open Access C. elegans germline-deficient mutants respond to pathogen infection using shared and distinct mechanisms.(PLoS One, 2010-07-26) TeKippe, Michael; Aballay, AlejandroReproduction extracts a cost in resources that organisms are then unable to utilize to deal with a multitude of environmental stressors. In the nematode C. elegans, development of the germline shortens the lifespan of the animal and increases its susceptibility to microbial pathogens. Prior studies have demonstrated germline-deficient nematodes to have increased resistance to gram negative bacteria. We show that germline-deficient strains display increased resistance across a broad range of pathogens including gram positive and gram negative bacteria, and the fungal pathogen Cryptococcus neoformans. Furthermore, we show that the FOXO transcription factor DAF-16, which regulates longevity and immunity in C. elegans, appears to be crucial for maintaining longevity in both wild-type and germline-deficient backgrounds. Our studies indicate that germline-deficient mutants glp-1 and glp-4 respond to pathogen infection using common and different mechanisms that involve the activation of DAF-16.Item Open Access Immunity in Caenorhabditis Elegans: a Tale of Two Transcription Factors(2009) TeKippe, Michael JonRecently, the study of invertebrate innate immunity has garnered considerable attention after the discovery that mammalian homologues of the Drosophila melanogaster
Toll pathway play a role in mammalian innate immunity. One invertebrate model system that has begun to be intensely studied is the nematode Caenorhabditis elegans. Immunity in C. elegans has been shown to be inducible in that it responds uniquely to different pathogens. These changes in gene expression require transcription factors in order for certain genes to be transcribed. We utilized an RNA interference screen of potential transcription factors to identify the GATA transcription factor ELT-2 as a possible transcription factor involved in immunity. We then demonstrated that ELT-2 was required for resistance to a wide range of pathogens and was responsible for regulating expression of the C-type lectin clec-67, a marker of immunity.
We also studied another transcription factor known to play a role in C. elegans immune function, the FOXO transcription factor DAF-16. We specifically focused in on the role of DAF-16 in germline-deficient mutants, and we demonstrated that such mutants are resistant to many different pathogens. This led to further investigation of the germline-deficient mutant glp-4, which should also show broad range resistance to pathogens but fails to do so. Through whole genome sequencing, we identified mutations that may be responsible for the glp-4 phenotype. We also demonstrated that DAF-16 was active in glp-4 mutants, leading to us proposing a model where glp-4 plays a role in influencing C. elegans immunity besides its involvement in germline development.
Item Open Access Inhibition of Nucleolar Proteins in Caenorhabditis Elegans Confers Enhanced Resistance to Salmonella Enterica through a P53/cep-1-Dependent Mechanism(2009) Fuhrman, Laura ElizabethThe relatively simple innate immune system of Caenorhabditis elegans and the number of traits that facilitate genetic and genomic analysis using this organism have nurtured rapid advances into the understanding of C. elegans innate immunity during the last few years. However, traditional methods of isolating and mapping C. elegans mutants exhibiting aberrant immune responses to pathogen infection are often labor intensive and time consuming. Therefore, a simple and rapid means of isolating and mapping C. elegans immune mutants will increase the number of mutants that can be studied. Salmonella enterica, as well as other bacterial pathogens, has been described to cause a significant distension of the C. elegans intestinal lumen, which correlates with death of the nematode. C. elegans mutants which exhibit a weakened immune response would therefore be expected to develop intestinal distension at an earlier time point than wild type. Likewise, mutants which exhibit an enhanced immune response would be expected to develop intestinal distension at a later time point than wild type. Taking advantage of this correlation, we designed a novel approach to isolating C. elegans mutants which exhibit aberrant immune responses to the bacterial pathogen, S. enterica. Furthermore, we validated and optimized the use of Amplifluor®, a high-throughput genotyping system, for use in C. elegans single nucleotide polymorphism (SNP) mapping.
To date, the only known negative regulators of innate immunity in C. elegans are dependent on the FOXO transcription factor, DAF-16 and regulate lifespan in addition to immunity. Therefore, we focused our efforts on identifying additional negative regulators of innate immunity by screening for mutants which display a reduced accumulation of S. enterica at a time point when wild-type nematodes are packed with bacteria. In a genetic screen for C. elegans mutants which display reduced accumulation of S. enterica/GFP, we identified a mutation in nol-6, a nucleolar protein containing a nucleolar RNA-associated protein (Nrap) domain which is conserved across eukaryotic organisms. nol-6 is implicated in ribosomal RNA (rRNA) processing during the early stages of ribosome biogenesis. We show that knockdown of nol-6 as well as other nucleolar genes leads to a reduction of pathogen accumulation and enhanced resistance to killing by pathogen. In addition, we demonstrate that enhanced resistance is dependent on p53/cep-1. Furthermore, microarray analysis shows a significant enrichment of upregulated genes that have previously been shown to be dependent on p53/cep-1 for induction following ultraviolet radiation. These results represent the first evidence that C. elegans innate immunity is regulated by the nucleolus through a p53/cep-1-dependent mechanism.
Item Open Access Neuronal Regulation of the Innate Immune Response in Caenorhabditis elegans(2017) Cao, XiouThe innate immune system is the front line of host defense against microbial infections, but its rapid and uncontrolled activation elicits microbicidal mechanisms that have deleterious effects. Increasing evidence indicates that the metazoan nervous system, which responds to stimuli originating from both the internal and the external environment, functions as a modulatory apparatus that controls not only microbial killing pathways but also cellular homeostatic mechanisms. Exploiting simple organism Caenorhabditis elegans, we performed whole-animal screen and identified antibiotic colistin and dopamine antagonists as immune activators that target conserved immune pathways. The goal of this work is to investigate the role of dopamine signaling and underlying neuronal circuits in regulating the C. elegans innate immune response.
Through genetic and pharmacological studies, we identified a D1-like dopamine receptor, DOP-4, which suppresses the conserved PMK-1/p38 immune pathway in C. elegans. We also demonstrated that the manipulation of a dopaminergic neural circuit can alter the immune response upon pathogen infection. Previous studies showed that an octopamine receptor, OCTR-1, functions in chemosensory neurons to inhibit innate immunity. We found that OCTR-1-expressing neurons, ASH, and interneurons, AIA, are involved in controlling the resistance to pathogen infection. This work provides direct evidence that a neuronal network exists in C. elegans to orchestrate defenses against pathogen invasion.
Item Open Access Particulate allergens potentiate allergic asthma in mice through sustained IgE-mediated mast cell activation.(2010) Jin, CongIn recent years, the incidence of allergic asthma as well as the severity of disease has rapidly increased worldwide. Numerous epidemiological studies have related the exacerbation of allergic asthma with exposure to increased ambient particles from air pollutants. However, the mechanism by which particulate allergens (pAg) exacerbate allergic asthma remains undefined. To evaluate this, we modeled environmental pAg induced allergic asthma by exposing mice to polystyrene beads coated with natural allergen extracts. Compared to equal amounts of soluble allergen extracts (sAg), pAg triggered markedly enhanced airway hyper-responsiveness and pulmonary eosinophilia in allergen sensitized mice. The cellular basis for this effect was determined to be mast cells (MCs), as both airway allergic responses were attenuated in MC deficient KitWsh/KitW-sh mice compared to MC reconstituted KitW-sh/KitW-sh mice. The divergent responses of MCs to pAg versus sAg were due to differences in the termination rate of IgE/FcεRI initiated signaling. Following ligation of sAg, IgE/FcεRI rapidly shuttled into a degradative endosome/lysosome pathway. However, following ligation by pAg, IgE/FcεRI migrated into lipid raft enriched compartments and subsequently failed to follow a degradative pathway, which resulted in a prolonged signaling and heightened synthesis of proinflammatory mediators. These observations highlight the overlooked contributions of the particulate nature of allergens and mast cell endocytic circuitry to the aggravation of allergic asthma.Item Open Access Recovery from an acute infection in C. elegans requires the GATA transcription factor ELT-2.(PLoS Genet, 2014-10) Head, Brian; Aballay, AlejandroThe 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.Item Open Access Unfolded protein response genes regulated by CED-1 are required for Caenorhabditis elegans innate immunity.(2008) Haskins, Kylie AnneThe first line of defense against pathogens is the phylogenetically ancient innate immune system. This system consists of physical barriers and conserved signaling pathways are activated upon infection to produce effector molecules that mount a microbicidal response. Recently, C. elegans has been established as a model organism for the study of innate immunity due to C. elegans genetic tractability and origins predating the evolution of adaptive immunity. Conserved defense pathways essential for mammalian innate immunity have been identified in C. elegans. However, most receptors critical for the activation of the defense signaling pathways in C. elegans remain unknown. The goal of this work was to study CED-1 and its potential role as a cell-surface signaling receptor essential for C. elegans immune response. In this study, we performed a full-genome microarray analysis and discovered that CED-1 functions to activate the expression of pqn/abu unfolded protein response (UPR) genes. The unfolded protein response has been implicated in the normal physiology of immune defense and in several disorders including diabetes, cancer, and neurodegenerative disease. Here we show that ced-1 and pqn/abu genes are required for the survival of C. elegans exposed to live S. enterica. We also show that the overexpression of pqn/abu genes confers protection to pathogen-mediated killing. Taken together, these results indicate that the apoptotic receptor CED-1 and a network of PQN/ABU proteins involved in a non-canonical UPR response are required for proper defense to pathogen infection in Caenorhabditis elegans.Item Open Access Using Genetic Analysis and the Model Organism Caenorhabditis Elegans to Identify Bacterial Virulence Factors and Innate Immune Defenses against Pathogens(2008-04-25) Styer, Katie LetitiaAn estimated twenty-five percent of the fifty-seven million annual deaths worldwide can be directly attributed to infectious disease. Mammals contain both adaptive and innate immune systems to deal with invading pathogens. The genetic model organism Caenorhabditis elegans lacks an adaptive immune system, which makes it a powerful model organism to study the innate immune system without the added complexity of an adaptive immune system. Multiple human pathogens can cause lethal infections in C. elegans and several C. elegans innate immune pathways have been identified that are conserved with mammals and protect the nematode from infection. The goal of this work was to identify novel bacterial virulence factors and innate immune defenses against pathogens by using the genetic model organism C. elegans. We established C. elegans as a model for Yersinia pestis infection and used this model to identify novel bacterial virulence factors that were also important for virulence in a mammalian model of infection. Previous studies demonstrated that C. elegans can identify bacterial pathogens using sensory neurons and activate an avoidance response that requires components of G-protein signaling pathways. We screened forty C. elegans strains containing mutations in chemosensory G-protein coupled receptors for altered survival on pathogen and identified npr-1 to be required for full C. elegans defense against pathogens. We found that activation of the NPR-1 nervous circuit enhances host susceptibility to microbial infection while inhibition of the circuit boosts innate immunity. This data provides the first evidence that innate immunity in C. elegans is directly linked to the nervous system and establishes the nematode as a novel system to study neuroimmunology. From this work, we have identified Y. pestis virulence-related genes and C. elegans innate immune effector genes required for innate immunity to human bacterial pathogens.