Chemosensory signal transduction in Caenorhabditis elegans

GPCR Sense Communication Among Interaction Nematodes with Other Organisms

Interactions between species give rise to chemical pathways of communication that regulate the interactions of transboundary species. The communication between nematodes and other species primarily occurs through the regulation of chemicals, with key species including plants, insects, bacteria, and nematode-trapping fungi that are closely associated with nematodes. G protein-coupled receptors (GPCRs) play a crucial role in interspecies communication. Certain flp genes, which function as GPCRs, exert varying degrees of influence on how nematodes interact with other species. These receptors facilitate the transmission of corresponding signals, thereby completing the interactions between species. This paper introduces the interactions between nematodes and other species and discusses the role of GPCRs in these organisms, contributing to a deeper understanding of the impact and significance of GPCRs in cross-border regulation between nematodes and other species. Furthermore, it is essential to leverage GPCRs in efforts to control pests.

Lineage-Specific Class-A GPCR Dynamics Reflect Diverse Chemosensory Adaptations in Lophotrochozoa

Sensing external chemosensory cues via Class-A G protein-coupled receptors (GPCRs) is crucial for a multitude of behavioral and biological functions, influencing animal evolution and ecological adaptations. While extensively studied in vertebrates and echinoderms, the role of GPCR-mediated chemoreception in major protostome clades like Lophotrochozoa remains obscure despite their remarkable ecological adaptations across diverse aquatic and terrestrial environments. Utilizing 238 lophotrochozoan genomes across eight phyla, we conducted a large-scale comparative genomics analysis to identify lineage-specific expansions of Class-A GPCR subsets that are likely adapted for chemoreception. Using phylogeny and orthology-inference-based clustering, we distinguished these expansions from conserved orthogroups of prospective endogenous ligand-binding Class-A GPCR subsets. Across phyla, lineage-specific expansions correlated with adaptations to various habitats, ecological niches, and lifestyles, while the influence of whole-genome duplications in driving these lineage-specific expansions appeared to be less significant. Species adapted to various coastal, freshwater, and terrestrial habitats across several classes of Mollusca, Annelida, and other analyzed phyla exhibit large and diverse lineage-specific expansions, while adaptations to extreme deep-sea environments, parasitic lifestyles, sessile behaviors, or alternative chemosensory mechanisms consistently exhibit reductions. Sequence heterogeneity, signatures of positive selection, and conformational flexibility in ligand-binding pockets further highlighted adaptations to environmental signals. In summary, the evolutionary dynamics of Class-A GPCRs in lophotrochozoans reveal a widespread pattern of lineage-specific expansions driven by adaptations for chemoreception across diverse environmental niches, mirroring the trends and prominent roles seen in deuterostome lineages. The comprehensive datasets spanning numerous genomes offer a valuable foundation for advancing GPCR-mediated chemoreception studies in Lophotrochozoa.

Satiety, TAX-4, and OSM-9 Tune the Attraction of C. elegans Nematodes to Microbial Fermentation Products

Animals are sensitive to selective pressures associated with nutrient acquisition, underscoring the evolutionary significance of chemosensation in foraging and its intersection with satiety. For the model nematode Caenorhabditis elegans, isoamyl alcohol (3-methyl-1-butanol) and 2-methyl-1-butanol are produced by microbial fermentation and present in bacterial food sources collected from the natural environments. Both compounds, which are structural isomers of one another, elicit strong attraction in laboratory settings. Using laboratory chemotaxis assays, we show that starvation attenuates attraction to both compounds. Well-fed C. elegans is largely insensitive to the biosynthetic precursors of both alcohols, with the exception of 4-methyl-2-oxovaleric acid, which is a mild repellent. C. elegans chemosensation relies on expression of tax-4 cyclic nucleotide-gated (CNG) and osm-9 transient receptor potential, vanilloid (TRPV) ion channels and animals lacking both genes are taste- and smell-blind. Animals lacking tax-4 fail to attract isoamyl alcohol and 2-methyl-1-butanol and those lacking osm-9 exhibit stronger attraction than the wild-type. Starvation not only attenuates attraction, but also enhances repulsion to 4-methyl-2-oxovaleric acid and uncovers repulsion in tax-4 mutants absent in their well-fed counterparts. Collectively, these findings implicate satiety in regulating response strength, tax-4-dependent chemotaxis in attraction to isoamyl alcohol and 2-methyl-1-butanol, and osm-9-dependent chemotaxis in suppressing responses to biosynthetic precursors.

An Extensive Gap Junction Neural Network Modulates Caenorhabditis elegans Aversive Behavior

BACKGROUND/OBJECTIVES

Caenorhabditis elegans rely on sensory perception of environmental cues for survival in their native soil and compost habitats. These cues provide information about nutrient availability, mating partners, or predatory and hazardous beacons. In C. elegans, the two bilaterally-symmetric head sensory neurons termed ASH are the main detectors of aversive nociceptive signals. Through their downstream connections in the nervous system, ASH activation causes the animal to initiate backward locomotion to escape and avoid the harmful stimulus. Modulation of avoidance behavior allows for situation-appropriate sensitivity and response to stimuli. We previously reported a role for gap junctions in the transport of regulatory cGMP to the ASHs where it functions to dampen avoidance responses.

METHODS

Here, we used genetic mutants and a combination of cell-selective rescue and knockdown experiments to identify gap junction proteins (innexins) involved in modulating ASH-mediated nociceptive behavioral responses.

RESULTS

We have characterized six additional C. elegans innexins that have overlapping and distinct roles within this regulatory network: INX-7, INX-15, INX-16, INX-17, UNC-7, and UNC-9.

CONCLUSIONS

This work expands our understanding of the extent to which ASH sensitivity can be tuned in a non-cell-autonomous manner.

ARL13B regulates juxtaposed cilia-cilia elongation in BBSome dependent manner in Caenorhabditis elegans

The interaction of cilia with various cellular compartments, such as axons, has emerged as a new form of cellular communication. Cilia often extend in proximity to cilia from neighboring cells. However, the mechanisms driving this process termed juxtaposed cilia-cilia elongation (JCE) remain unclear. We use fluorescence-based visualization to study the mechanisms of coordinated cilia elongation in sensory neurons of Caenorhabditis elegans. Conducting a selective gene-based screening strategy reveals that ARL-13/ARL13B and MKS-5/RPGRIP1L are essential for JCE. We demonstrate that ARL-13 modulates JCE independently of cilia length. Loss of NPHP-2/inversin along with HDAC-6 enhances the cilia misdirection phenotype of arl-13 mutants, while disruption of the BBSome complex, but not microtubule components, partially suppresses the JCE defects in arl-13 mutants. We further show changes in the phospholipid compositions in arl-13 mutants. We suggest that ARL-13 contributes to JCE, in part, through the modulation of the ciliary membrane.

Calcium levels in ASER neurons determine behavioral valence by engaging distinct neuronal circuits in C. elegans

The valence of stimuli is shaped by various factors, including environmental cues, internal states, genetic variability, and past experience. However, the mechanisms behind this flexibility remain elusive. In the nematode C. elegans, we found that ethanol, an olfactory stimulus, can elicit opposite chemotaxis responses - attraction vs. aversion - depending on NaCl concentration, demonstrating the role of environmental factors in altering valence. Remarkably, a single chemosensory neuron, ASER, orchestrate this bidirectional ethanol chemotaxis by integrating information from both stimuli - ethanol and NaCl - into its neuronal activity dynamics. Specifically, different calcium dynamics in the ASER neuron differentially activate the signaling molecule CMK-1, thereby engaging different downstream interneurons and leading to opposite chemotaxis directions. Consistently, optogenetic manipulations of the ASER neuron reverse the chemotaxis directions, by altering its calcium dynamics. Our findings reveal a mechanism by which a single neuron integrates multisensory inputs to determine context-dependent behavioral valence, contributing to our current understanding of valence encoding.

Balancing selfing and outcrossing: the genetics and cell biology of nematodes with three sexual morphs

Trioecy, a rare reproductive system where hermaphrodites, females, and males coexist, is found in certain algae, plants, and animals. Though it has evolved independently multiple times, its rarity suggests it may be an unstable or transitory evolutionary strategy. In the well-studied Caenorhabditis elegans, attempts to engineer a trioecious strain have reverted to the hermaphrodite/male system, reinforcing this view. However, these studies did not consider the sex-determination systems of naturally stable trioecious species. The discovery of free-living nematodes of the Auanema genus, which have naturally stable trioecy, provides an opportunity to study these systems. In Auanema, females produce only oocytes, while hermaphrodites produce both oocytes and sperm for self-fertilization. Crosses between males and females primarily produce daughters (XX hermaphrodites and females), while male-hermaphrodite crosses result in sons only. These skewed sex ratios are due to X-chromosome drive during spermatogenesis, where males produce only X-bearing sperm through asymmetric cell division. The stability of trioecy in Auanema is influenced by maternal control over sex determination and environmental cues. These factors offer insights into the genetic and environmental dynamics that maintain trioecy, potentially explaining its evolutionary stability in certain species.

Prospects on non-canonical olfaction in the mosquito and other organisms: why co-express?

The Aedes aegypti mosquito utilizes olfaction during the search for humans to bite. The attraction to human body odor is an innate behavior for this disease-vector mosquito. Many well-studied model species have olfactory systems that conform to a particular organization that is sometimes referred to as the 'one-receptor-to-one-neuron' organization because each sensory neuron expresses only a single type of olfactory receptor that imparts the neuron's chemical selectivity. This sensory architecture has become the canon in the field. This review will focus on the recent finding that the olfactory system of Ae. aegypti has a different organization, with multiple olfactory receptors co-expressed in many of its olfactory sensory neurons. We will discuss the canonical organization and how this differs from the non-canonical organization, examine examples of non-canonical olfactory systems in other species, and discuss the possible roles of receptor co-expression in odor coding in the mosquito and other organisms.

The AWC OFF neuron is important for attraction to 1-butanol in Caenorhabditis elegans

C. elegans uses chemosensation to recognize a variety of odors, many of which are released by bacteria, the major food source of C. elegans . Specific amphid sensory neurons are known to detect different odorants. Here we show that the AWC OFF neuron detects the attractive odorant 1-butanol. Because few odorants that are specifically recognized by the AWC OFF neuron have been identified, we hope that the identification of this additional odorant will facilitate studies of the role of the AWC OFF neuron in odor detection and discrimination.

Involvement of G-protein alpha subunit in soybean cyst nematode chemotaxis

The soybean cyst nematode (SCN; Heterodera glycines Ichinohe) is a significant agricultural pest that causes extensive damage to soybean production worldwide. Second-stage juveniles (J2s) of the SCN migrate through the soil and infest the roots of host plants in response to certain chemical substances secreted from the host roots. Therefore, controlling SCN chemotaxis could be an effective strategy for its management. In the present study, we identified the Hg-gpa-3d gene, which encodes the G protein alpha subunit, as a key regulator of SCN chemotaxis. Gene silencing of Hg-gpa-3d reduced the attraction of SCN J2s to host roots, as well as to nitrate ions, a chemoattractant recognized through a mechanism different from that of host recognition. However, silencing of Hg-gpa-3d did not affect avoidance behavior towards unpleasant temperatures or stylet protrusion. These results suggest that Hg-gpa-3d is a crucial gene in the regulation of SCN chemotaxis and provide new insights into the chemotactic mechanisms of the SCN.

C. elegans PPEF-type phosphatase (Retinal degeneration C ortholog) functions in diverse classes of cilia to regulate nematode behaviors

Primary (non-motile) cilia represent structurally and functionally diverse organelles whose roles as specialized cellular antenna are central to animal cell signaling pathways, sensory physiology and development. An ever-growing number of ciliary proteins, including those found in vertebrate photoreceptors, have been uncovered and linked to human disorders termed ciliopathies. Here, we demonstrate that an evolutionarily-conserved PPEF-family serine-threonine phosphatase, not functionally linked to cilia in any organism but associated with rhabdomeric (non-ciliary) photoreceptor degeneration in the Drosophila rdgC (retinal degeneration C) mutant, is a bona fide ciliary protein in C. elegans. The nematode protein, PEF-1, depends on transition zone proteins, which make up a 'ciliary gate' in the proximal-most region of the cilium, for its compartmentalization within cilia. Animals lacking PEF-1 protein function display structural defects to several types of cilia, including potential degeneration of microtubules. They also exhibit anomalies to cilium-dependent behaviors, including impaired responses to chemical, temperature, light, and noxious CO2 stimuli. Lastly, we demonstrate that PEF-1 function depends on conserved myristoylation and palmitoylation signals. Collectively, our findings broaden the role of PPEF proteins to include cilia, and suggest that the poorly-characterized mammalian PPEF1 and PPEF2 orthologs may also have ciliary functions and thus represent ciliopathy candidates.

Cilia structure and intraflagellar transport differentially regulate sensory response dynamics within and between C. elegans chemosensory neurons

Sensory neurons contain morphologically diverse primary cilia that are built by intraflagellar transport (IFT) and house sensory signaling molecules. Since both ciliary structural and signaling proteins are trafficked via IFT, it has been challenging to decouple the contributions of IFT and cilia structure to neuronal responses. By acutely inhibiting IFT without altering cilia structure and vice versa, here we describe the differential roles of ciliary trafficking and sensory ending morphology in shaping chemosensory responses in Caenorhabditis elegans. We show that a minimum cilium length but not continuous IFT is necessary for a subset of responses in the ASH nociceptive neurons. In contrast, neither cilia nor continuous IFT are necessary for odorant responses in the AWA olfactory neurons. Instead, continuous IFT differentially modulates response dynamics in AWA. Upon acute inhibition of IFT, cilia-destined odorant receptors are shunted to ectopic branches emanating from the AWA cilia base. Spatial segregation of receptors in these branches from a cilia-restricted regulatory kinase results in odorant desensitization defects, highlighting the importance of precise organization of signaling molecules at sensory endings in regulating response dynamics. We also find that adaptation of AWA responses upon repeated exposure to an odorant is mediated by IFT-driven removal of its cognate receptor, whereas adaptation to a second odorant is regulated via IFT-independent mechanisms. Our results reveal unexpected complexity in the contribution of IFT and cilia organization to the regulation of responses even within a single chemosensory neuron type and establish a critical role for these processes in the precise modulation of olfactory behaviors.

Meloidogyne incognita genes involved in the repellent behavior in response to ascr#9

Meloidogyne incognita is one of the globally serious plant parasitic nematodes. New control measure is urgently needed to replace the common chemical control method. Ascarosides are pheromones regulating the nematodes' aggregation, avoidance, mating, dispersal and dauer recovery and formation. Ascr#9, one of the ascarosides, exhibits the potential to repel M. incognita. However, the nematode genes involved in the perception of ascr# 9 signal are totally unknown. In this study, the transcriptome of ascr#9-treated second stage M. incognita juveniles (J2s) was analyzed, 44 pathways were significantly affected, multiple ligand-receptor and mucin type O-glycan were induced, and olfactory transduction was disturbed. A total of 11 highly differentially expressed genes involved in neuroactive ligand-receptor interaction and FMRFamide-like peptide related process were identified and knocked down by RNAi. The dispersal rates of M. incognita with three knocked-down genes (flp-14, mgl-1 and ADOR-1) significantly decreased, respectively, when ascr#9 was present. The results demonstrate that flp-14, mgl-1, and ADOR-1 are involved in the dispersal behavior of M. incognita nematodes responding to ascr#9, which promotes the interaction study between ascarosides and M. incognita, and provides new ideas for the prevention and control of M. incognita by using pheromone ascarosides.

Olfactory combinatorial coding supports risk-reward decision making in C. elegans

Olfactory-driven behaviors are essential for animal survival, but mechanisms for decoding olfactory inputs remain poorly understood. We have used whole-network Ca ++ imaging to study olfactory coding in Caenorhabditis elegans. We show that the odorant 1-octanol is encoded combinatorially in the periphery as both an attractant and a repellant. These inputs are integrated centrally, and their relative strengths determine the sensitivity and valence of the behavioral response through modulation of locomotory reversals and speed. The balance of these pathways also dictates the activity of the locomotory command interneurons, which control locomotory reversals. This balance serves as a regulatory node for response modulation, allowing C. elegans to weigh opportunities and hazards in its environment when formulating behavioral responses. Thus, an odorant can be encoded simultaneously as inputs of opposite valence, focusing attention on the integration of these inputs in determining perception, response, and plasticity.

Sensory integration of food and population density during the diapause exit decision involves insulin-like signaling in Caenorhabditis elegans

Decisions made over long time scales, such as life cycle decisions, require coordinated interplay between sensory perception and sustained gene expression. The Caenorhabditis elegans dauer (or diapause) exit developmental decision requires sensory integration of population density and food availability to induce an all-or-nothing organismal-wide response, but the mechanism by which this occurs remains unknown. Here, we demonstrate how the Amphid Single Cilium J (ASJ) chemosensory neurons, known to be critical for dauer exit, perform sensory integration at both the levels of gene expression and calcium activity. In response to favorable conditions, dauers rapidly produce and secrete the dauer exit-promoting insulin-like peptide INS-6. Expression of ins-6 in the ASJ neurons integrates population density and food level and can reflect decision commitment since dauers committed to exiting have higher ins-6 expression levels than those of noncommitted dauers. Calcium imaging in dauers reveals that the ASJ neurons are activated by food, and this activity is suppressed by pheromone, indicating that sensory integration also occurs at the level of calcium transients. We find that ins-6 expression in the ASJ neurons depends on neuronal activity in the ASJs, cGMP signaling, and the pheromone components ascr#8 and ascr#2. We propose a model in which decision commitment to exit the dauer state involves an autoregulatory feedback loop in the ASJ neurons that promotes high INS-6 production and secretion. These results collectively demonstrate how insulin-like peptide signaling helps animals compute long-term decisions by bridging sensory perception to decision execution.

Olfactory dysfunction as an early pathogenic indicator in C. elegans models of Alzheimer's and polyglutamine diseases

Neurodegenerative diseases such as Alzheimer's disease and polyglutamine diseases are characterized by abnormal accumulation of misfolded proteins, leading to neuronal dysfunction and subsequent neuron death. However, there is a lack of studies that integrate molecular, morphological, and functional analyses in neurodegenerative models to fully characterize these time-dependent processes. In this study, we used C. elegans models expressing Aβ1-42 and polyglutamine to investigate early neuronal pathogenic features in olfactory neurons. Both models demonstrated significant reductions in odor sensitivity in AWB and AWC chemosensory neurons as early as day 1 of adulthood, while AWA chemosensory neurons showed no such decline, suggesting cell-type-specific early neuronal dysfunction. At the molecular level, Aβ1-42 or Q40 expression caused age-dependent protein aggregation and morphological changes in neurons. By day 6, both models displayed prominent protein aggregates in neuronal cell bodies and neurites. Notably, AWB neurons in both models showed significantly shortened cilia and increased instances of enlarged cilia as early as day 1 of adulthood. Furthermore, AWC neurons expressing Aβ1-42 displayed calcium signaling defects, with significantly reduced responses to odor stimuli on day 1, further supporting early behavioral dysfunction. In contrast, AWA neuron did not exhibit reduced calcium responses, consistent with the absence of detectable decreases in olfactory sensitivity in these neurons. These findings suggest that decreased calcium signaling and dysfunction in specific sensory neuron subtypes are early indicators of neurodegeneration in C. elegans, occurring prior to the formation of visible protein aggregates. We found that the ER unfolded protein response (UPR) is significantly activated in worms expressing Aβ1-42. Activation of the AMPK pathway alleviates olfactory defects and reduces fibrillar Aβ in these worms. This study underscores the use of C. elegans olfactory neurons as a model to elucidate mechanisms of proteostasis in neurodegenerative diseases and highlights the importance of integrated approaches.

Mechanism of sensory perception unveiled by simultaneous measurement of membrane voltage and intracellular calcium

Measuring neuronal activity is important for understanding neuronal function. Ca2+ imaging by genetically encoded calcium indicators (GECIs) is a powerful way to measure neuronal activity. Although it revealed important aspects of neuronal function, measuring the neuronal membrane voltage is important to understand neuronal function as it triggers neuronal activation. Recent progress of genetically encoded voltage indicators (GEVIs) enabled us fast and precise measurements of neuronal membrane voltage. To clarify the relation of the membrane voltage and intracellular Ca2+, we analyzed neuronal activities of olfactory neuron AWA in Caenorhabditis elegans by GCaMP6f (GECI) and paQuasAr3 (GEVI) responding to odorants. We found that the membrane voltage encodes the stimuli change by the timing and the duration by the weak semi-stable depolarization. However, the change of the intracellular Ca2+ encodes the strength of the stimuli. Furthermore, ODR-3, a G-protein alpha subunit, was shown to be important for stabilizing the membrane voltage. These results suggest that the combination of calcium and voltage imaging provides a deeper understanding of the information in neural circuits.

Behavioral plasticity

Behavioral plasticity allows animals to modulate their behavior based on experience and environmental conditions. Caenorhabditis elegans exhibits experience-dependent changes in its behavioral responses to various modalities of sensory cues, including odorants, salts, temperature, and mechanical stimulations. Most of these forms of behavioral plasticity, such as adaptation, habituation, associative learning, and imprinting, are shared with other animals. The C. elegans nervous system is considerably tractable for experimental studies-its function can be characterized and manipulated with molecular genetic methods, its activity can be visualized and analyzed with imaging approaches, and the connectivity of its relatively small number of neurons are well described. Therefore, C. elegans provides an opportunity to study molecular, neuronal, and circuit mechanisms underlying behavioral plasticity that are either conserved in other animals or unique to this species. These findings reveal insights into how the nervous system interacts with the environmental cues to generate behavioral changes with adaptive values.

oxi-1 is required for chemotaxis to odorants sensed by AWA but not AWC neurons

This study examines the role of the oxi-1 UBE3B gene in chemotaxis of C. elegans to volatile odorants. Compared to wild type worms, oxi-1 mutants showed no difference in chemotaxis to the AWC-specific odorant, isoamyl alcohol but a significant decrease in chemotaxis compared to odr-7 mutants. Both oxi-1 and odr-7 mutants exhibited significant decreases in chemotaxis to AWA-specific odorants, pyrazine and diacetyl. For thiazole, which is sensed by both AWA and AWC neurons, only odr-7 mutants showed significantly decreased chemotaxis. These data demonstrate oxi-1 is required for chemotaxis to AWA- but not AWC-specific odorants, the mechanisms of which should be investigated.

Intricate response dynamics enhances stimulus discrimination in the resource-limited C. elegans chemosensory system

BACKGROUND

Sensory systems evolved intricate designs to accurately encode perplexing environments. However, this encoding task may become particularly challenging for animals harboring a small number of sensory neurons. Here, we studied how the compact resource-limited chemosensory system of Caenorhabditis elegans uniquely encodes a range of chemical stimuli.

RESULTS

We find that each stimulus is encoded using a small and unique subset of neurons, where only a portion of the encoding neurons sense the stimulus directly, and the rest are recruited via inter-neuronal communication. Furthermore, while most neurons show stereotypical response dynamics, some neurons exhibit versatile dynamics that are either stimulus specific or network-activity dependent. Notably, it is the collective dynamics of all responding neurons which provides valuable information that ultimately enhances stimulus identification, particularly when required to discriminate between closely related stimuli.

CONCLUSIONS

Together, these findings demonstrate how a compact and resource-limited chemosensory system can efficiently encode and discriminate a diverse range of chemical stimuli.

Neural Sequences Underlying Directed Turning in C. elegans

Complex behaviors like navigation rely on sequenced motor outputs that combine to generate effective movement. The brain-wide organization of the circuits that integrate sensory signals to select and execute appropriate motor sequences is not well understood. Here, we characterize the architecture of neural circuits that control C. elegans olfactory navigation. We identify error-correcting turns during navigation and use whole-brain calcium imaging and cell-specific perturbations to determine their neural underpinnings. These turns occur as motor sequences accompanied by neural sequences, in which defined neurons activate in a stereotyped order during each turn. Distinct neurons in this sequence respond to sensory cues, anticipate upcoming turn directions, and drive movement, linking key features of this sensorimotor behavior across time. The neuromodulator tyramine coordinates these sequential brain dynamics. Our results illustrate how neuromodulation can act on a defined neural architecture to generate sequential patterns of activity that link sensory cues to motor actions.

A multiscale sensorimotor model of experience-dependent behavior in a minimal organism

To survive in ever-changing environments, living organisms need to continuously combine the ongoing external inputs they receive, representing present conditions, with their dynamical internal state, which includes influences of past experiences. It is still unclear in general, however 1) how this happens at the molecular and cellular levels and 2) how the corresponding molecular and cellular processes are integrated with the behavioral responses of the organism. Here, we address these issues by modeling mathematically a particular behavioral paradigm in a minimal model organism, namely chemotaxis in the nematode C. elegans. Specifically, we use a long-standing collection of elegant experiments on salt chemotaxis in this animal, in which the migration direction varies depending on its previous experience. Our model integrates the molecular, cellular, and organismal levels to reproduce the experimentally observed experience-dependent behavior. The model proposes specific molecular mechanisms for the encoding of current conditions and past experiences in key neurons associated with this response, predicting the behavior of various mutants associated with those molecular circuits.

Unraveling the Roles of Neuropeptides in the Chemosensation of the Root-Knot Nematode Meloidogyne javanica

The identification of novel drug targets in plant-parasitic nematodes (PPNs) is imperative due to the loss of traditional nematicides and a lack of replacements. Chemosensation, which is pivotal for PPNs in locating host roots, has become a focus in nematode behavioral research. However, its underlying molecular basis is still indistinct in such a diverse group of PPNs. To characterize genes participating in chemosensation in the Javanese root-knot nematode Meloidogyne javanica, RNA-sequencing of the second-stage juveniles (J2s) treated with tomato root exudate (TRE) for 1 h and 6 h was performed. Genes related to chemosensation in M. javanica mainly responded to TRE treatment at 1 h. Moreover, a gene ontology (GO) analysis underscored the significance of the neuropeptide G protein-coupled receptor signaling pathway. Consequently, the repertoire of putative neuropeptides in M. javanica, including FMRFamide-like peptides (FLPs), insulin-like peptides (ILPs), and neuropeptide-like peptides (NLPs), were outlined based on a homology analysis. The gene Mjflp-14a, harboring two neuropeptides, was significantly up-regulated at 1 h TRE treatment. Through peptide synthesis and J2 treatment, one of the two neuropeptides (MjFLP-14-2) was proven to influence the J2 chemotaxis towards tomato root tips. Overall, our study reinforces the potential of nematode neuropeptides as novel targets and tools for root-knot nematode control.

Dendrite morphogenesis in Caenorhabditis elegans

Since the days of Ramón y Cajal, the vast diversity of neuronal and particularly dendrite morphology has been used to catalog neurons into different classes. Dendrite morphology varies greatly and reflects the different functions performed by different types of neurons. Significant progress has been made in our understanding of how dendrites form and the molecular factors and forces that shape these often elaborately sculpted structures. Here, we review work in the nematode Caenorhabditis elegans that has shed light on the developmental mechanisms that mediate dendrite morphogenesis with a focus on studies investigating ciliated sensory neurons and the highly elaborated dendritic trees of somatosensory neurons. These studies, which combine time-lapse imaging, genetics, and biochemistry, reveal an intricate network of factors that function both intrinsically in dendrites and extrinsically from surrounding tissues. Therefore, dendrite morphogenesis is the result of multiple tissue interactions, which ultimately determine the shape of dendritic arbors.

Differential modulation of sensory response dynamics by cilia structure and intraflagellar transport within and across chemosensory neurons

Sensory neurons contain morphologically diverse primary cilia that are built by intraflagellar transport (IFT) and house sensory signaling molecules. Since both ciliary structural and signaling proteins are trafficked via IFT, it has been challenging to decouple the contributions of IFT and cilia structure to neuronal responses. By acutely inhibiting IFT without altering cilia structure and vice versa , here we describe the differential roles of ciliary trafficking and sensory ending morphology in shaping chemosensory responses in C. elegans. We show that a minimum cilium length but not continuous IFT is necessary for a subset of responses in the ASH nociceptive neurons. In contrast, neither cilia nor continuous IFT are necessary for odorant responses in the AWA olfactory neurons. Instead, continuous IFT differentially modulates response dynamics in AWA. Upon acute inhibition of IFT, cilia-destined odorant receptors are shunted to ectopic branches emanating from the cilia base. Spatial segregation of receptors in these branches from a cilia-restricted regulatory kinase results in odorant desensitization defects, highlighting the importance of precise organization of signaling molecules at sensory endings in regulating response dynamics. We also find that adaptation of AWA responses upon repeated exposure to an odorant is mediated by IFT-driven removal of its cognate receptor, whereas adaptation to a second odorant is regulated via IFT-independent mechanisms. Our results reveal unexpected complexity in the contribution of IFT and cilia organization to the regulation of responses even within a single chemosensory neuron type, and establish a critical role for these processes in the precise modulation of olfactory behaviors.

Neuronal basis and diverse mechanisms of pathogen avoidance in Caenorhabditis elegans

Pathogen avoidance behaviour has been observed across animal taxa as a vital host-microbe interaction mechanism. The nematode Caenorhabditis elegans has evolved multiple diverse mechanisms for pathogen avoidance under natural selection pressure. We summarise the current knowledge of the stimuli that trigger pathogen avoidance, including alterations in aerotaxis, intestinal bloating, and metabolites. We then survey the neural circuits involved in pathogen avoidance, transgenerational epigenetic inheritance of pathogen avoidance, signalling crosstalk between pathogen avoidance and innate immunity, and C. elegans avoidance of non-Pseudomonas bacteria. In this review, we highlight the latest advances in understanding host-microbe interactions and the gut-brain axis.

Functional implications of NHR-210 enrichment in C. elegans cephalic sheath glia: insights into metabolic and mitochondrial disruptions in Parkinson's disease models

Glial cells constitute nearly half of the mammalian nervous system's cellular composition. The glia in C. elegans perform majority of tasks comparable to those conducted by their mammalian equivalents. The cephalic sheath (CEPsh) glia, which are known to be the counterparts of mammalian astrocytes, are enriched with two nuclear hormone receptors (NHRs)-NHR-210 and NHR-231. This unique enrichment makes the CEPsh glia and these NHRs intriguing subjects of study concerning neuronal health. We endeavored to assess the role of these NHRs in neurodegenerative diseases and related functional processes, using transgenic C. elegans expressing human alpha-synuclein. We employed RNAi-mediated silencing, followed by behavioural, functional, and metabolic profiling in relation to suppression of NHR-210 and 231. Our findings revealed that depleting nhr-210 changes dopamine-associated behaviour and mitochondrial function in human alpha synuclein-expressing strains NL5901 and UA44, through a putative target, pgp-9, a transmembrane transporter. Considering the alteration in mitochondrial function and the involvement of a transmembrane transporter, we performed metabolomics study via HR-MAS NMR spectroscopy. Remarkably, substantial modifications in ATP, betaine, lactate, and glycine levels were seen upon the absence of nhr-210. We also detected considerable changes in metabolic pathways such as phenylalanine, tyrosine, and tryptophan biosynthesis metabolism; glycine, serine, and threonine metabolism; as well as glyoxalate and dicarboxylate metabolism. In conclusion, the deficiency of the nuclear hormone receptor nhr-210 in alpha-synuclein expressing strain of C. elegans, results in altered mitochondrial function, coupled with alterations in vital metabolite levels. These findings underline the functional and physiological importance of nhr-210 enrichment in CEPsh glia.

An efficient behavioral screening platform classifies natural products and other chemical cues according to their chemosensory valence in C. elegans

Throughout history, humans have relied on plants as a source of medication, flavoring, and food. Plants synthesize large chemical libraries and release many of these compounds into the rhizosphere and atmosphere where they affect animal and microbe behavior. To survive, nematodes must have evolved the sensory capacity to distinguish plant-made small molecules (SMs) that are harmful and must be avoided from those that are beneficial and should be sought. This ability to classify chemical cues as a function of their value is fundamental to olfaction, and represents a capacity shared by many animals, including humans. Here, we present an efficient platform based on multi-well plates, liquid handling instrumentation, inexpensive optical scanners, and bespoke software that can efficiently determine the valence (attraction or repulsion) of single SMs in the model nematode, Caenorhabditis elegans. Using this integrated hardware-wetware-software platform, we screened 90 plant SMs and identified 37 that attracted or repelled wild-type animals, but had no effect on mutants defective in chemosensory transduction. Genetic dissection indicates that for at least 10 of these SMs, response valence emerges from the integration of opposing signals, arguing that olfactory valence is often determined by integrating chemosensory signals over multiple lines of information. This study establishes that C. elegans is an effective discovery engine for determining chemotaxis valence and for identifying natural products detected by the chemosensory nervous system.

Pheromone-based communication influences the production of somatic extracellular vesicles in C. elegans

Extracellular vesicles (EVs) are integral to numerous biological processes, yet it is unclear how environmental factors or interactions among individuals within a population affect EV-regulated systems. In Caenorhabditis elegans, the evolutionarily conserved large EVs, known as exophers, are part of a maternal somatic tissue resource management system. Consequently, the offspring of individuals exhibiting active exopher biogenesis (exophergenesis) develop faster. Our research focuses on unraveling the complex inter-tissue and social dynamics that govern exophergenesis. We found that ascr#10, the primary male pheromone, enhances exopher production in hermaphrodites, mediated by the G-protein-coupled receptor STR-173 in ASK sensory neurons. In contrast, pheromone produced by other hermaphrodites, ascr#3, diminishes exophergenesis within the population. This process is regulated via the neuropeptides FLP-8 and FLP-21, which originate from the URX and AQR/PQR/URX neurons, respectively. Our results reveal a regulatory network that controls the production of somatic EV by the nervous system in response to social signals.

Polymodal sensory perception drives settlement and metamorphosis of Ciona larvae

The Earth's oceans brim with an incredible diversity of microscopic lifeforms, including motile planktonic larvae, whose survival critically depends on effective dispersal in the water column and subsequent exploration of the seafloor to identify a suitable settlement site. How their nervous systems mediate sensing of diverse multimodal cues remains enigmatic. Here, we uncover that the tunicate Ciona intestinalis larvae employ ectodermal sensory cells to sense various mechanical and chemical cues. Combining whole-brain imaging and chemogenetics, we demonstrate that stimuli encoded at the periphery are sufficient to drive global brain-state changes to promote or impede both larval attachment and metamorphosis behaviors. The ability of C. intestinalis larvae to leverage polymodal sensory perception to support information coding and chemotactile behaviors may explain how marine larvae make complex decisions despite streamlined nervous systems.

Sensory integration of food availability and population density during the diapause exit decision involves insulin-like signaling in Caenorhabditis elegans

Decisions made over long time scales, such as life cycle decisions, require coordinated interplay between sensory perception and sustained gene expression. The Caenorhabditis elegans dauer (or diapause) exit developmental decision requires sensory integration of population density and food availability to induce an all-or-nothing organismal-wide response, but the mechanism by which this occurs remains unknown. Here, we demonstrate how the ASJ chemosensory neurons, known to be critical for dauer exit, perform sensory integration at both the levels of gene expression and calcium activity. In response to favorable conditions, dauers rapidly produce and secrete the dauer exit-promoting insulin-like peptide INS-6. Expression of ins-6 in the ASJ neurons integrate population density and food level and can reflect decision commitment since dauers committed to exiting have higher ins-6 expression levels than those of non-committed dauers. Calcium imaging in dauers reveals that the ASJ neurons are activated by food, and this activity is suppressed by pheromone, indicating that sensory integration also occurs at the level of calcium transients. We find that ins-6 expression in the ASJ neurons depends on neuronal activity in the ASJs, cGMP signaling, a CaM-kinase pathway, and the pheromone components ascr#8 and ascr#2. We propose a model in which decision commitment to exit the dauer state involves an autoregulatory feedback loop in the ASJ neurons that promotes high INS-6 production and secretion. These results collectively demonstrate how insulin-like peptide signaling helps animals compute long-term decisions by bridging sensory perception to decision execution.

Induced knockdown of Mg-odr-1 and Mg-odr-3 perturbed the host seeking behavior of Meloidogyne graminicola in rice

Root-knot nematode Meloidogyne graminicola is one of the most destructive plant parasites in upland as well as direct seeded rice. As an integral part of nematode biology, host finding behavior involves perceiving and responding to different chemical cues originating from the rhizosphere. A sustainable management tactic may include retardation of nematode chemoreception that would impair them to detect and discriminate the host stimuli. Deciphering the molecular basis of nematode chemoreception is vital to identify chokepoints for chemical or genetic interventions. However, compared to the well-characterized chemoreception mechanism in model nematode Caenorhabditis elegans, plant nematode chemoreception is yet underexplored. Herein, the full-length cDNA sequences of two chemotaxis-related genes (Mg-odr-1 and Mg-odr-3) were cloned from M. graminicola. Both the genes were markedly upregulated in the early developmental stages of M. graminicola suggesting their involvement in host finding processes. RNAi-induced independent knockdown of Mg-odr-1 and Mg-odr-3 caused behavioral aberration in second-stage juveniles of M. graminicola which in turn perturbed the nematodes' host finding ability and parasitic success inside rice roots. Additionally, nematodes' chemotactic response to different host root exudates, volatile and nonvolatile compounds was affected. Our results demonstrating the role of specific chemosensory genes in modulating M. graminicola host seeking behavior can enrich the existing knowledge of plant nematode chemoreception mechanism, and these genes can be targeted for novel nematicide development or in planta RNAi screens.

Legacies of salient environmental experiences-insights from chemosensation

Evidence for parental environments profoundly influencing the physiology, biology, and neurobiology of future generations has been accumulating in the literature. Recent efforts to understand this phenomenon and its underlying mechanisms have sought to use species like rodents and insects to model multi-generational legacies of parental experiences like stress and nutritional exposures. From these studies, we have come to appreciate that parental exposure to salient environmental experiences impacts the cadence of brain development, hormonal responses to stress, and the expression of genes that govern cellular responses to stress in offspring. Recent studies using chemosensory exposure have emerged as a powerful tool to shed new light on how future generations come to be influenced by environments to which parents are exposed. With a specific focus on studies that have leveraged such use of salient chemosensory experiences, this review synthesizes our current understanding of the concept, causes, and consequences of the inheritance of chemosensory legacies by future generations and how this field of inquiry informs the larger picture of how parental experiences can influence offspring biology.

A cGAL-UAS bipartite expression toolkit for Caenorhabditis elegans sensory neurons

Animals integrate sensory information from the environment and display various behaviors in response to external stimuli. In Caenorhabditis elegans hermaphrodites, 33 types of sensory neurons are responsible for chemosensation, olfaction, and mechanosensation. However, the functional roles of all sensory neurons have not been systematically studied due to the lack of facile genetic accessibility. A bipartite cGAL-UAS system has been previously developed to study tissue- or cell-specific functions in C. elegans. Here, we report a toolkit of new cGAL drivers that can facilitate the analysis of a vast majority of the 60 sensory neurons in C. elegans hermaphrodites. We generated 37 sensory neuronal cGAL drivers that drive cGAL expression by cell-specific regulatory sequences or intersection of two distinct regulatory regions with overlapping expression (split cGAL). Most cGAL-drivers exhibit expression in single types of cells. We also constructed 28 UAS effectors that allow expression of proteins to perturb or interrogate sensory neurons of choice. This cGAL-UAS sensory neuron toolkit provides a genetic platform to systematically study the functions of C. elegans sensory neurons.

Dissecting the genetic landscape of GPCR signaling through phenotypic profiling in C. elegans

G protein-coupled receptors (GPCRs) mediate responses to various extracellular and intracellular cues. However, the large number of GPCR genes and their substantial functional redundancy make it challenging to systematically dissect GPCR functions in vivo. Here, we employ a CRISPR/Cas9-based approach, disrupting 1654 GPCR-encoding genes in 284 strains and mutating 152 neuropeptide-encoding genes in 38 strains in C. elegans. These two mutant libraries enable effective deorphanization of chemoreceptors, and characterization of receptors for neuropeptides in various cellular processes. Mutating a set of closely related GPCRs in a single strain permits the assignment of functions to GPCRs with functional redundancy. Our analyses identify a neuropeptide that interacts with three receptors in hypoxia-evoked locomotory responses, unveil a collection of regulators in pathogen-induced immune responses, and define receptors for the volatile food-related odorants. These results establish our GPCR and neuropeptide mutant libraries as valuable resources for the C. elegans community to expedite studies of GPCR signaling in multiple contexts.

Molecular and functional characterization of chemosensory genes from the root-knot nematode Meloidogyne graminicola

BACKGROUND

Root-knot nematode Meloidogyne graminicola has emerged as a major threat in rice agroecosystems owing to climate change-induced changes in cultivation practices. Synthetic nematicides are continually being withdrawn from the nematode management toolbox because of their ill effects on the environment. A sustainable strategy would be to develop novel nematicides or resistant plants that would target nematode sensory perception, which is a key step in the host finding biology of plant-parasitic nematodes (PPNs). However, compared to the extensive literature on the free-living nematode Caenorhabditis elegans, negligible research has been performed on PPN chemosensory biology.

RESULTS

The present study characterizes the five chemosensory genes (Mg-odr-7, Mg-tax-4, Mg-tax-4.1, Mg-osm-9, and Mg-ocr-2) from M. graminicola that are putatively associated with nematode host-finding biology. All the genes were highly transcribed in the early life stages, and RNA interference (RNAi)-induced downregulation of each candidate gene perturbed the normal behavioural phenotypes of M. graminicola, as determined by examining the tracking pattern of juveniles on Pluronic gel medium, attraction to and penetration in rice root tip, and developmental progression in rice root. In addition, a detrimental effect on nematode chemotaxis towards different volatile and nonvolatile organic compounds and host root exudates was documented.

CONCLUSION

Our findings enrich the existing literature on PPN chemosensory biology and can supplement future research aimed at identifying a comprehensive chemosensory signal transduction pathway in PPNs.

The G protein alpha chaperone and guanine-nucleotide exchange factor RIC-8 regulates cilia morphogenesis in Caenorhabditis elegans sensory neurons

Heterotrimeric G (αβγ) proteins are canonical transducers of G-protein-coupled receptor (GPCR) signaling and play critical roles in communication between cells and their environment. Many GPCRs and heterotrimeric G proteins localize to primary cilia and modulate cilia morphology via mechanisms that are not well understood. Here, we show that RIC-8, a cytosolic guanine nucleotide exchange factor (GEF) and chaperone for Gα protein subunits, shapes cilia membrane morphology in a subset of Caenorhabditis elegans sensory neurons. Consistent with its role in ciliogenesis, C. elegans RIC-8 localizes to cilia in different sensory neuron types. Using domain mutagenesis, we demonstrate that while the GEF function alone is not sufficient, both the GEF and Gα-interacting chaperone motifs of RIC-8 are required for its role in cilia morphogenesis. We identify ODR-3 as the RIC-8 Gα client and demonstrate that RIC-8 functions in the same genetic pathway with another component of the non-canonical G protein signaling AGS-3 to shape cilia morphology. Notably, despite defects in AWC cilia morphology, ags-3 null mutants exhibit normal chemotaxis toward benzaldehyde unlike odr-3 mutant animals. Collectively, our findings describe a novel function for the evolutionarily conserved protein RIC-8 and non-canonical RIC-8-AGS-3-ODR-3 signaling in cilia morphogenesis and uncouple Gα ODR-3 functions in ciliogenesis and olfaction.

A single neuron in C. elegans orchestrates multiple motor outputs through parallel modes of transmission

Animals generate a wide range of highly coordinated motor outputs, which allows them to execute purposeful behaviors. Individual neurons in the circuits that generate behaviors have a remarkable capacity for flexibility as they exhibit multiple axonal projections, transmitter systems, and modes of neural activity. How these multi-functional properties of neurons enable the generation of adaptive behaviors remains unknown. Here, we show that the HSN neuron in C. elegans evokes multiple motor programs over different timescales to enable a suite of behavioral changes during egg laying. Using HSN activity perturbations and in vivo calcium imaging, we show that HSN acutely increases egg laying and locomotion while also biasing the animals toward low-speed dwelling behavior over minutes. The acute effects of HSN on egg laying and high-speed locomotion are mediated by separate sets of HSN transmitters and different HSN axonal compartments. The long-lasting effects on dwelling are mediated in part by HSN release of serotonin, which is taken up and re-released by NSM, another serotonergic neuron class that directly evokes dwelling. Our results show how the multi-functional properties of a single neuron allow it to induce a coordinated suite of behaviors and also reveal that neurons can borrow serotonin from one another to control behavior.

Integration of spatially opposing cues by a single interneuron guides decision-making in C. elegans

The capacity of animals to respond to hazardous stimuli in their surroundings is crucial for their survival. In mammals, complex evaluations of the environment require large numbers and different subtypes of neurons. The nematode C. elegans avoids hazardous chemicals they encounter by reversing their direction of movement. How does the worms' compact nervous system process the spatial information and direct motion change? We show here that a single interneuron, AVA, receives glutamatergic excitatory and inhibitory signals from head and tail sensory neurons, respectively. AVA integrates the spatially distinct and opposing cues, whose output instructs the animal's behavioral decision. We further find that the differential activation of AVA stems from distinct localization of inhibitory and excitatory glutamate-gated receptors along AVA's process and from different threshold sensitivities of the sensory neurons. Our results thus uncover a cellular mechanism that mediates spatial computation of nociceptive cues for efficient decision-making in C. elegans.

Pancreatic Cancer and Detection Methods

The pancreas is a vital organ with exocrine and endocrine functions. Pancreatitis is an inflammation of the pancreas caused by alcohol consumption and gallstones. This condition can heighten the risk of pancreatic cancer (PC), a challenging disease with a high mortality rate. Genetic and epigenetic factors contribute significantly to PC development, along with other risk factors. Early detection is crucial for improving PC outcomes. Diagnostic methods, including imagining modalities and tissue biopsy, aid in the detection and analysis of PC. In contrast, liquid biopsy (LB) shows promise in early tumor detection by assessing biomarkers in bodily fluids. Understanding the function of the pancreas, associated diseases, risk factors, and available diagnostic methods is essential for effective management and early PC detection. The current clinical examination of PC is challenging due to its asymptomatic early stages and limitations of highly precise diagnostics. Screening is recommended for high-risk populations and individuals with potential benign tumors. Among various PC screening methods, the N-NOSE plus pancreas test stands out with its high AUC of 0.865. Compared to other commercial products, the N-NOSE plus pancreas test offers a cost-effective solution for early detection. However, additional diagnostic tests are required for confirmation. Further research, validation, and the development of non-invasive screening methods and standardized scoring systems are crucial to enhance PC detection and improve patient outcomes. This review outlines the context of pancreatic cancer and the challenges for early detection.

The G protein alpha Chaperone and Guanine-Nucleotide Exchange Factor RIC-8 Regulates Cilia Morphogenesis in Caenorhabditis elegans Sensory Neurons

Heterotrimeric G (αβγ) proteins are canonical transducers of G-protein-coupled receptor (GPCR) signaling and play critical roles in communication between cells and their environment. Many GPCRs and heterotrimeric G proteins localize to primary cilia and modulate cilia morphology via mechanisms that are not well understood. Here, we show that RIC-8, a cytosolic guanine nucleotide exchange factor (GEF) and chaperone for Gα protein subunits, shapes cilia membrane morphology in a subset of Caenorhabditis elegans sensory neurons. Consistent with its role in ciliogenesis, C. elegans RIC-8 localizes to cilia in different sensory neuron types. Using domain mutagenesis, we demonstrate that while the GEF function alone is not sufficient, both the GEF and Gα-interacting chaperone motifs of RIC-8 are required for its role in cilia morphogenesis. We identify ODR-3 as the RIC-8 Gα client and demonstrate that RIC-8 functions in the same genetic pathway with another component of the non-canonical G protein signaling AGS-3 to shape cilia morphology. Notably, despite severe defects in AWC cilia morphology, ags-3 null mutants exhibit normal chemotaxis toward benzaldehyde unlike odr-3 mutant animals. Collectively, our findings describe a novel function for the evolutionarily conserved protein RIC-8 and non-canonical RIC-8-AGS-3-ODR-3 signaling in cilia morphogenesis and uncouple Gα ODR-3 functions in ciliogenesis and olfaction.

Synthetic biology in multicellular organisms: Opportunities in nematodes

Synthetic biology has mainly focused on introducing new or altered functionality in single cell systems: primarily bacteria, yeast, or mammalian cells. Here, we describe the extension of synthetic biology to nematodes, in particular the well-studied model organism Caenorhabditis elegans, as a convenient platform for developing applications in a multicellular setting. We review transgenesis techniques for nematodes, as well as the application of synthetic biology principles to construct nematode gene switches and genetic devices to control motility. Finally, we discuss potential applications of engineered nematodes.

Sleep is required to consolidate odor memory and remodel olfactory synapses

Animals with complex nervous systems demand sleep for memory consolidation and synaptic remodeling. Here, we show that, although the Caenorhabditis elegans nervous system has a limited number of neurons, sleep is necessary for both processes. In addition, it is unclear if, in any system, sleep collaborates with experience to alter synapses between specific neurons and whether this ultimately affects behavior. C. elegans neurons have defined connections and well-described contributions to behavior. We show that spaced odor-training and post-training sleep induce long-term memory. Memory consolidation, but not acquisition, requires a pair of interneurons, the AIYs, which play a role in odor-seeking behavior. In worms that consolidate memory, both sleep and odor conditioning are required to diminish inhibitory synaptic connections between the AWC chemosensory neurons and the AIYs. Thus, we demonstrate in a living organism that sleep is required for events immediately after training that drive memory consolidation and alter synaptic structures.

Full-Length Transcriptome Analysis of Soybean Cyst Nematode (Heterodera glycines) Reveals an Association of Behaviors in Response to Attractive pH and Salt Solutions with Activation of Transmembrane Receptors, Ion Channels, and Ca2+ Transporters

Soybean cyst nematode (Heterodera glycines Ichinohe), a devastating pathogen in soybean, was chosen as a model system to investigate nematode behavior and gene expression changes in response to acidic and basic pH and salt signals (pH 4.5, 5.25, 8.6, and 10 and NaCl) through full-length transcriptome sequencing of 18 samples. An average of 4.36 Gbp of clean reads per sample were generated, and 3972 novel genes and 29,529 novel transcripts were identified. Sequence structural variation during or after transcription may be associated with the nematode's behavioral response. The functional analysis of 1817/4962 differentially expressed genes/transcripts showed that signal transduction pathways, including transmembrane receptors, ion channels, and Ca²⁺ transporters, were activated, but pathways involved in nematode development (e.g., ribosome) and energy production (e.g., oxidative phosphorylation) were inhibited. A corresponding model was established. Our findings suggest that these receptors and ion channels might be potential targets for nematicides or drug discovery.

A high-throughput nematode sensory assay reveals an inhibitory effect of ivermectin on parasite gustation

Sensory pathways first elucidated in Caenorhabditis elegans are conserved across free-living and parasitic nematodes, even though each species responds to a diverse array of compounds. Most nematode sensory assays are performed by tallying observations of worm behavior on two-dimensional planes using agarose plates. These assays have been successful in the study of volatile sensation but are poorly suited for investigation of water-soluble gustation or parasitic nematodes without a free-living stage. In contrast, gustatory assays tend to be tedious, often limited to the manipulation of a single individual at a time. We have designed a nematode sensory assay using a microfluidics device that allows for the study of gustation in a 96-well, three-dimensional environment. This device is suited for free-living worms and parasitic worms that spend their lives in an aqueous environment, and we have used it to show that ivermectin inhibits the gustatory ability of vector-borne parasitic nematodes.

The Caenorhabditis elegans innexin INX-20 regulates nociceptive behavioral sensitivity

Organisms rely on chemical cues in their environment to indicate the presence or absence of food, reproductive partners, predators, or other harmful stimuli. In the nematode Caenorhabditis elegans, the bilaterally symmetric pair of ASH sensory neurons serves as the primary nociceptors. ASH activation by aversive stimuli leads to backward locomotion and stimulus avoidance. We previously reported a role for guanylyl cyclases in dampening nociceptive sensitivity that requires an innexin-based gap junction network to pass cGMP between neurons. Here, we report that animals lacking function of the gap junction component INX-20 are hypersensitive in their behavioral response to both soluble and volatile chemical stimuli that signal through G protein-coupled receptor pathways in ASH. We find that expressing inx-20 in the ADL and AFD sensory neurons is sufficient to dampen ASH sensitivity, which is supported by new expression analysis of endogenous INX-20 tagged with mCherry via the CRISPR-Cas9 system. Although ADL does not form gap junctions directly with ASH, it does so via gap junctions with the interneuron RMG and the sensory neuron ASK. Ablating either ADL or RMG and ASK also resulted in nociceptive hypersensitivity, suggesting an important role for RMG/ASK downstream of ADL in the ASH modulatory circuit. This work adds to our growing understanding of the repertoire of ways by which ASH activity is regulated via its connectivity to other neurons and identifies a previously unknown role for ADL and RMG in the modulation of aversive behavior.

A single neuron in C. elegans orchestrates multiple motor outputs through parallel modes of transmission

Animals generate a wide range of highly coordinated motor outputs, which allows them to execute purposeful behaviors. Individual neuron classes in the circuits that generate behavior have a remarkable capacity for flexibility, as they exhibit multiple axonal projections, transmitter systems, and modes of neural activity. How these multi-functional properties of neurons enable the generation of highly coordinated behaviors remains unknown. Here we show that the HSN neuron in C. elegans evokes multiple motor programs over different timescales to enable a suite of behavioral changes during egg-laying. Using HSN activity perturbations and in vivo calcium imaging, we show that HSN acutely increases egg-laying and locomotion while also biasing the animals towards low-speed dwelling behavior over longer timescales. The acute effects of HSN on egg-laying and high-speed locomotion are mediated by separate sets of HSN transmitters and different HSN axonal projections. The long-lasting effects on dwelling are mediated by HSN release of serotonin that is taken up and re-released by NSM, another serotonergic neuron class that directly evokes dwelling. Our results show how the multi-functional properties of a single neuron allow it to induce a coordinated suite of behaviors and also reveal for the first time that neurons can borrow serotonin from one another to control behavior.

Disexcitation in the ASH/RIM/ADL negative feedback circuit fine-tunes hyperosmotic sensation and avoidance in Caenorhabditis elegans

Sensations, especially nociception, are tightly controlled and regulated by the central and peripheral nervous systems. Osmotic sensation and related physiological and behavioral reactions are essential for animal well-being and survival. In this study, we find that interaction between secondary nociceptive ADL and primary nociceptive ASH neurons upregulates Caenorhabditis elegans avoidance of the mild and medium hyperosmolality of 0.41 and 0.88 Osm but does not affect avoidance of high osmolality of 1.37 and 2.29 Osm. The interaction between ASH and ADL is actualized through a negative feedback circuit consisting of ASH, ADL, and RIM interneurons. In this circuit, hyperosmolality-sensitive ADL augments the ASH hyperosmotic response and animal hyperosmotic avoidance; RIM inhibits ADL and is excited by ASH; thus, ASH exciting RIM reduces ADL augmenting ASH. The neuronal signal integration modality in the circuit is disexcitation. In addition, ASH promotes hyperosmotic avoidance through ASH/RIC/AIY feedforward circuit. Finally, we find that in addition to ASH and ADL, multiple sensory neurons are involved in hyperosmotic sensation and avoidance behavior.

A Conserved Role for Stomatin Domain Genes in Olfactory Behavior

The highly-conserved stomatin domain has been identified in genes throughout all classes of life. In animals, different stomatin domain-encoding genes have been implicated in the function of the kidney, red blood cells, and specific neuron types, although the underlying mechanisms remain unresolved. In one well-studied example of stomatin domain gene function, the Caenorhabditis elegans gene mec-2 and its mouse homolog Stoml3 are required for the function of mechanosensory neurons, where they modulate the activity of mechanosensory ion channels on the plasma membrane. Here, we identify an additional shared function for mec-2 and Stoml3 in a very different sensory context, that of olfaction. In worms, we find that a subset of stomatin domain genes are expressed in olfactory neurons, but only mec-2 is strongly required for olfactory behavior. mec-2 acts cell-autonomously and multiple alternatively-spliced isoforms of mec-2 can be substituted for each other. We generate a Stoml3 knock-out (KO) mouse and demonstrate that, like its worm homolog mec-2, it is required for olfactory behavior. In mice, Stoml3 is not required for odor detection, but is required for odor discrimination. Therefore, in addition to their shared roles in mechanosensory behavior, mec-2 and Stoml3 also have a shared role in olfactory behavior.

Quantitative description of neuronal calcium dynamics in C. elegans' thermoreception

The dynamical mechanisms underlying thermoreception in the nematode C. elegans are studied with a mathematical model for the amphid finger-like ciliated (AFD) neurons. The equations, equipped with Arrhenius temperature factors, account for the worm's thermotaxis when seeking environments at its cultivation temperature, and for the AFD's calcium dynamics when exposed to both linearly ramping and oscillatory temperature stimuli. Calculations of the peak time for calcium responses during simulations of pulse-like temperature inputs are consistent with known behavioral time scales of C. elegans.