Castelletto, Michelle et al. (2013) International Worm Meeting "Host-finding strategies of mammalian-parasitic nematodes."

Castelletto, Michelle, Hallem, Elissa, Okubo, Ryo, Tselikova, Anastassia

[International Worm Meeting, 2013]

Soil-dwelling nematodes use environmental sensory cues to locate resources and potential mates. Many parasitic nematodes also use these cues to locate appropriate hosts. The human parasite Strongyloides stercoralis and the rat parasites Strongyloides ratti and Nippostrongylus brasiliensis are skin-penetrating nematodes that spend a portion of their life cycle in the soil. We are interested in how these worms use host-derived odorants to search for hosts. We examined the responses of S. stercoralis, S. ratti, and N. brasiliensis infective juveniles (IJs) to carbon dioxide (CO2), an important host cue for entomopathogenic nematodes (EPNs) as well as many hematophagous insects. We found that mammalian-parasitic IJs are not attracted to CO2, suggesting they rely instead on host-specific cues. We then examined the responses of these IJs to a large panel of human odorants, and found that many of these odorants attract parasitic IJs. Moreover, many of the odorants that elicited the strongest responses from S. stercoralis have also been shown to attract mosquitoes, suggesting that human-parasitic nematodes and mosquitoes use similar olfactory cues. These results raised the possibility that insect repellents might be effective against parasitic nematodes. However, we found that some insect repellents do not repel mammalian-parasitic nematodes, and in fact S. stercoralis and S. ratti are attracted to the insect repellent DEET. A comparison of the odor response profiles of the mammalian-parasitic IJs to those of EPN IJs and C. elegans dauers revealed that olfactory preferences reflect host range rather than phylogeny, suggesting an important role for olfaction in the evolution of host specificity among parasitic nematodes. Finally, we found that S. ratti IJs respond differently to odorants than S. ratti non-infective larvae and adults, indicating that the olfactory preferences of at least some parasitic nematodes are stage-specific. We are now expanding these studies to additional species of parasitic nematodes, including some that are passively ingested and some that have more diverse host ranges. We are also investigating the neural basis of odor-driven host-seeking behaviors in mammalian-parasitic nematodes.

Gang, Spencer et al. (2015) International Worm Meeting "Host-seeking strategies of skin-penetrating parasitic nematodes."

Tselikova, Anastassia, Okubo, Ryo, Hallem, Elissa, Castelletto, Michelle, Gang, Spencer, Barnia, Arezoo

[International Worm Meeting, 2015]

Skin-penetrating nematodes such as the threadworm Strongyloides stercoralis and the hookworms Ancylostoma duodenale and Necator Americanus infect approximately 1 billion people worldwide and pose dangerous health risks, including severe intestinal distress, stunted growth and cognitive impairment in children, and heightened susceptibility to other infectious diseases. The infective juveniles (IJs) of skin-penetrating nematodes are thought to search for hosts using sensory cues, but their host-seeking behavior is poorly understood. To understand host-seeking behavior in more detail, we asked how S. stercoralis moves in the absence of chemosensory stimuli. We found that S. stercoralis is highly motile and uses a cruising strategy to search for potential hosts. We next asked how increased temperature might alter host-seeking behavior. We found that at 37degC S. stercoralis shows increased speed and engages in local search behavior. S. stercoralis is also attracted to human skin and sweat odorants, many of which are known mosquito attractants. We tested olfactory preferences at different life stages and found that the free-living stages are highly attracted to host feces while IJs are not, suggesting a mechanism by which host seeking is restricted to IJs. We compared host odorant responses of S. stercoralis to six other nematode species and found that parasite olfactory preferences reflect host specificity rather than phylogeny, suggesting an important role for olfaction in host selection. We are now examining the neural basis of host-seeking behavior. We focused initially on the neural basis of CO2 response. In C. elegans, the receptor guanylate cyclase GCY-9 is required for CO2 detection by BAG neurons. We identified a gcy-9 homolog in S. stercoralis and generated a gcy9::GFP construct, which specifically labeled putative BAG neurons based on anatomical position. We then generated a gcy9::GCaMP3 construct and imaged CO2-evoked neural activity in BAG neurons of S. stercoralis infective juveniles. We found that S. stercoralis and C. elegans BAG neurons respond similarly to CO2, suggesting the neural basis of CO2 detection is conserved across species. We are now employing a similar reporter-based strategy to identify and image from S. stercoralis olfactory neurons in response to host-emitted odorants. To identify molecular components required for host seeking behavior, we are developing CRISPR-Cas9 mediated mutagenesis in S. stercoralis. Understanding how skin-penetrating nematodes target human hosts could lead to new strategies for preventing infections. .

Michelle S. Teng et al. (2006) European Worm Meeting "Expression of Mammalian GPCRs in C. elegans Generates Novel Behavioural Responses to Human Ligands"

John McCafferty, Martijn P.J. Dekkers, Andrew G. Fraser, Michelle S. Teng, Bee Ling Ng, Gert Jansen, Suzanne Rademakers

[European Worm Meeting, 2006]

Michelle S. Teng1, Martijn P.J. Dekkers2, Bee Ling Ng1, Suzanne Rademakers2, Gert Jansen2, Andrew G. Fraser1 & John McCafferty1. G protein coupled receptors (GPCRs) play a crucial role in many biological processes and represent a major class of drug targets. However purification of GPCRs for biochemical study is difficult and most methods of screening receptor-ligand interactions require cultured cells and endotoxin free compounds. In contrast, Caenorhabditis elegans is a soil dwelling nematode that feeds on bacteria and uses GPCRs expressed in chemosensory neurons to detect bacteria and environmental compounds. Here we report that expression of the mammalian somatostatin receptor (Sstr2) and chemokine receptor 5 (CCR5) in gustatory neurons allow C. elegans to specifically detect and respond to human somatostatin and MIP-1? respectively in a simple avoidance assay. The endogenous signalling components involved in this remarkable promiscuity of interaction, spanning 800 million years of evolution, are investigated. This system has practical utility in ligand screening. Using structure:function studies, we identified key amino acid residues involved in the interaction of somatostatin with its receptor. This in vivo system, which imparts novel avoidance behaviour on C. elegans, can therefore be used in screening impure GPCR ligands, including the identification of bacterial clones expressing agonists within recombinant libraries.

Woldemariam, Sarah et al. (2015) International Worm Meeting "Elucidating the role of cGMP dynamics in behavioral plasticity."

Schneider, Martin, Krzyzanowski, Michelle, Bethke, Mary, Nagpal, Jatin, Gottschalk, Alexander, Woldemariam, Sarah, Ferkey, Denise, L'Etoile, Noelle

[International Worm Meeting, 2015]

cGMP is a ubiquitous second messenger implicated in many important biological processes. In neurons, cGMP dynamics can regulate the function of ion channels and kinases, resulting in physiological changes. In the context of learning and memory, these changes result in short-term and long-term behavioral changes based on the organism's experience. We attempt to understand the molecular basis for long-term plasticity by studying the behavioral responses of the nematode C. elegans. Along with our collaborator Michelle Krzyzanowski from the Denise Ferkey lab in SUNY Buffalo, we are interested in how food might modulate behaviors. One food-modulated behavior is repulsion from quinine. This repulsion is mediated by the ASH neuron and it is down regulated by food withdrawal and the cGMP-dependent protein kinase EGL-4. This poses a conundrum since no guanylyl cyclases, which produce cGMP, are expressed in ASH. Genetic evidence suggests that guanylyl cyclases in other neurons are required for the food-modulated repulsion from quinine in ASH and that gap junctions are required for the transmission of cGMP from these neurons to ASH. In order to understand how cGMP dynamics in these neurons are modulated, we need a tool to visualize cGMP. To this end, we are using a cGMP sensor that will allow us to image cGMP dynamics in ASH and other neurons in the living behaving animal in the presence and absence of food.

Martijn Dekkers et al. (2006) European Worm Meeting "Dissecting Gustatory Plasticity in C. elegans Using Mammalian Receptors"

Martijn Dekkers, Gert Jansen, John McCafferty, Michelle Teng

[European Worm Meeting, 2006]

Martijn Dekkers1, Michelle Teng2, John McCafferty, Gert Jansen1. We use C. elegans to study the molecular and cellular mechanisms of salt perception, using behavioural assays and calcium imaging. We discriminate three distinct responses to NaCl: First, attraction to NaCl concentrations ranging from 0.1 to 200 mM. Second, avoidance of higher concentrations. Third, avoidance of an otherwise attractive NaCl concentration after prolonged exposure. We call this latter behaviour gustatory plasticity. Previous studies have shown that chemo attraction to NaCl is mediated primarily by ASE, and to a lesser extent by ASI, ADF and ASG, and avoidance of high concentrations of NaCl is mediated by ASH (Bargmann & Horvitz, 1991). In our lab we have identified 85 proteins and five pairs of gustatory neurons that mediate gustatory plasticity. Based on our results we propose a model in which prolonged exposure to 100 mM of NaCl, elicits a signal from the ASE neurons, leading to sensitisation of the avoidance signalling ASI, ADF, ADL and ASH neurons. This results in avoidance of low concentrations of NaCl.. In an effort to identify the roles of the individual cells in gustatory plasticity we expressed either a TRP channel or a G-Protein Coupled Receptor (GPCR) in the neurons that have been implicated in gustatory plasticity. This allows us to specifically activate those cells. The TRP channel that we use is the mammalian capsaicin receptor VR-1. Normally C. elegans does not respond to capsaicin. Previously it has been shown that expression of VR-1 in the ASH neurons results in avoidance of capsaicin (Tobin et al 2002). We have generated animals that express the VR-1 receptor in the ASE, ASI, ADL and ADF neurons. We are currently testing their responses to capsaicin and the effects of preexposure to NaCl on this response, using behavioural assays.. The GPCRs that we have chosen are the mouse SSTR-2 somatostatin receptor and the human CCR-5 chemokine receptor. We have expressed these receptors in the ASH cells, and tested the responses in a novel avoidance assay. We found that the transgenic animals display specific avoidance behaviour to the ligands of the receptors, indicating that these GPCRs are integrated into the endogenous C. elegans signalling machinery, which is remarkable, given the evolutionary distance between the species. We are now making constructs to express these GPCRs in the other cells to assess their role in gustatory plasticity.