A PAX6-regulated receptor tyrosine kinase pairs with a pseudokinase to activate immune defense upon oomycete recognition in Caenorhabditis elegans.

Oomycetes were recently discovered as natural pathogens of Caenorhabditis elegans, and pathogen recognition alone was shown to be sufficient to activate a protective transcriptional program characterized by the expression of multiple chitinase-like (chil) genes. However, the molecular mechanisms underlying oomycete recognition in animals remain fully unknown. We performed here a forward genetic screen to uncover regulators of chil gene induction and found several independent loss-of-function alleles of old-1 and flor-1, which encode receptor tyrosine kinases belonging to the C. elegans-specific KIN-16 family. We report that OLD-1 and FLOR-1 are both necessary for mounting the immune response and act in the epidermis. FLOR-1 is a pseudokinase that acts downstream of the active kinase OLD-1 and regulates OLD-1 levels at the plasma membrane. Interestingly, the old-1 locus is adjacent to the chil genes in the C. elegans genome, thereby revealing a genetic cluster important for oomycete resistance. Furthermore, we demonstrate that old-1 expression at the anterior side of the epidermis is regulated by the VAB-3/PAX6 transcription factor, well known for its role in visual system development in other animals. Taken together, our study reveals both conserved and species-specific factors shaping the activation and spatial characteristics of the immune response to oomycete recognition.

Infection of C. elegans by Haptoglossa Species Reveals Shared Features in the Host Response to Oomycete Detection.

Oomycetes are a group of eukaryotic organisms that includes many important pathogens of animals and plants. Within this group, the Haptoglossa genus is characterised by the presence of specialised gun cells carrying a harpoon-like infection apparatus. While several Haptoglossa pathogens have been morphologically described, there are currently no host systems developed to study the infection process or host responses in the lab. In this study, we report that Haptoglossa species are potent natural pathogens of Caenorhabditis nematodes. Using electron microscopy, we characterise the infection process in C. elegans and demonstrate that the oomycete causes excessive tissue degradation upon entry in the body cavity, whilst leaving the host cuticle intact. We also report that the host transcriptional response to Haptoglossa infection shares similarities with the response against the oomycete Myzocytiopsis humicola, a key example of which is the induction of chitinase-like (chil) genes in the hypodermis. We demonstrate that this shared feature of the host response can be mounted by pathogen detection without any infection, as previously shown for M. humicola. These results highlight similarities in the nematode immune response to natural infection by phylogenetically distinct oomycetes.

Chemosensory Neurons Modulate the Response to Oomycete Recognition in Caenorhabditis elegans.

Understanding how animals detect and respond to pathogen threats is central to dissecting mechanisms of host immunity. The oomycetes represent a diverse eukaryotic group infecting various hosts from nematodes to humans. We have previously shown that Caenorhabditis elegans mounts a defense response consisting of the induction of chitinase-like (chil) genes in the epidermis to combat infection by its natural oomycete pathogen Myzocytiopsis humicola. We provide here evidence that C. elegans can sense the oomycete by detecting an innocuous extract derived from animals infected with M. humicola. The oomycete recognition response (ORR) leads to changes in the cuticle and reduction in pathogen attachment, thereby increasing animal survival. We also show that TAX-2/TAX-4 function in chemosensory neurons is required for the induction of chil-27 in the epidermis in response to extract exposure. Our findings highlight that neuron-to-epidermis communication may shape responses to oomycete recognition in animal hosts.

Natural Infection of C. elegans by an Oomycete Reveals a New Pathogen-Specific Immune Response.

In its natural habitat, the nematode Caenorhabditis elegans encounters a plethora of other organisms, including many that are pathogenic [1, 2]. The study of interactions between C. elegans and various pathogens has contributed to characterizing key mechanisms of innate immunity [2-4]. However, how C. elegans recognizes different pathogens to mount pathogen-specific immune responses remains still largely unknown [3, 5-8]. Expanding the range of known C. elegans-infecting pathogens and characterizing novel pathogen-specific immune responses are key steps toward answering this question. We report here that the oomycete Myzocytiopsis humicola is a natural pathogen of C. elegans, and we describe its infection strategy. We identify a new host immune response to pathogen exposure that involves induction of members of a previously uncharacterized gene family encoding chitinase-like (CHIL) proteins. We demonstrate that this response is highly specific against M. humicola and antagonizes the infection. We propose that CHIL proteins may diminish the ability of the oomycete to infect by hindering pathogen attachment to the host cuticle. This work expands our knowledge of natural eukaryotic pathogens of C. elegans and introduces a new pathosystem to address how animal hosts recognize and respond to oomycete infections.

Response of Caenorhabditis elegans to wireless devices radiation exposure.

PURPOSE: To examine the impact of electromagnetic radiation, produced by GSM (Global System for Mobile communications) mobile phones, Wi-Fi (Wireless-Fidelity) routers and wireless DECT (Digital Enhanced Cordless Telecommunications) phones, on the nematode Caenorhabditis elegans. MATERIALS AND METHODS: We exposed synchronized populations, of different developmental stages, to these wireless devices at E-field levels below ICNIRP's (International Commission on Non-Ionizing Radiation Protection) guidelines for various lengths of time. WT (wild-type) and aging- or stress-sensitive mutant worms were examined for changes in growth, fertility, lifespan, chemotaxis, short-term memory, increased ROS (Reactive Oxygen Species) production and apoptosis by using fluorescent marker genes or qRT-PCR (quantitative Reverse Transcription-Polymerase Chain Reaction). RESULTS: No statistically significant differences were found between the exposed and the sham/control animals in any of the experiments concerning lifespan, fertility, growth, memory, ROS, apoptosis or gene expression. CONCLUSIONS: The worm appears to be robust to this form of (pulsed) radiation, at least under the exposure conditions used.

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.

The Caenorhabditis elegans parvulin gene subfamily and their expression under cold or heat stress along with the fkb subfamily.

Parvulins and FKBPs are members of the peptidyl-prolyl cis/trans isomerases (PPIase) enzyme family whose role is to catalyze the interconversion between the cis trans forms of a peptide bond preceding internal proline residues in a polypeptide substrate. Members of the parvulin subfamily have been found to be involved in a variety of diseases, including Alzheimer's disease and cancer and are also considered possible antiparasitic targets. Genes Y110A2AL.13 (pin-1) and Y48C3A.16 (pin-4) were found in the worm's genome, possibly encoding parvulins. One is homologous to human and fly PIN1 whereas the other is homologous to human and fly PIN4. Both were expressed in Escherichia coli, purified and found to have in vitro PPIase activity. Expression levels of both genes, as well as the fkb genes (that encode FK506-binding proteins) were measured during development and under cold or heat stress conditions. The results revealed a potential role for these genes under temperature-related stress. RNAi silencing was performed for wild type and mutant strain worms under normal and cold or heat stress conditions. A reduced lifespan was observed when pin-4 dsRNA was fed to the fkb-5 deficient worms. Our work presents a first attempt to characterize the Caenorhabditis elegans parvulins and may present an interesting starting point for further experimentation concerning their role, along with the FKBP subfamily, in nematode physiology and their possible use as antiparasitic targets.

Molecular and biochemical analysis of the α class carbonic anhydrases in Caenorhabditis elegans.

In this study, in silico analysis of the Caenorhabditis elegans genome revealed six genes (cah-1, cah-2, cah-3, cah-4, cah-5, and cah-6) possibly encoding α class CAs (carbonic anhydrase). Real-time RT-PCR analysis revealed the temporal expression pattern of each gene, as well as changes in expression levels under different atmospheric conditions (stress). Cah-3 and cah-4 showed the highest levels of transcript accumulation, while most genes responded to the stress conditions. Yeast complementation showed that cah-3 was able to complement the function of Saccharomyces cerevisiae CA (NCE103) in vivo. Recombinant CAH-3, CAH-4a and CAH-5 enzymes, expressed in Escherichia coli were used for in vitro measurement of CA activity. However, in vitro activity was only detectable for CAH-4a. RNAi by feeding was performed on wild-type C. elegans for all genes. The worms were examined for a visible phenotype under normal and stress conditions (pH, CO(2)/O(2)). Silencing cah-3 and cah-4 may reduce the life-span of the worms (at 22 °C).

Molecular and biochemical analysis of the beta class carbonic anhydrases in Caenorhabditis elegans.

The beta class of the carbonic anhydrase (CA) enzyme family has been found in plants, yeast, bacteria and algae, but not in animals. Also, little is known concerning the CAs of C. elegans. Genes possibly encoding beta-CAs were revealed by in silico analysis of the C. elegans genome. Amino acid sequence and 3D structure analysis revealed a resemblance to both plant and cab-type beta-CAs. Temporal expression patterns of the two genes, as well as changes in expression levels under different atmospheric conditions (stress) were analyzed by real-time RT-PCR. Recombinant enzymes, expressed in E. coli were used for in vitro measurement of CA activity, while a yeast complementation experiment was performed in order to assess their ability to complement the function of S. crevisieae beta-CA (NCE103) in vivo. RNAi by feeding was performed on wild-type populations that were then examined for a visible phenotype under normal or various stress conditions (pH, CO(2)/O(2)). Two genes possibly encoding beta-CAs were revealed (bca-1 and y116a8c.28). Their products contain elements of both plant and cab-type CAs. Both assays showed that Y116a8c.28 is an active CA. Both genes showed significant levels of transcript accumulation during development, while they also responded to the stress conditions. No visible phenotype was scored under normal or stress conditions.