Pharyngeal pumping in Caenorhabditis elegans depends on tonic and phasic signaling from the nervous system

An unusual potassium conductance protects Caenorhabditis elegans pharyngeal muscle rhythms against environmental noise

The nematode Caenorhabditis elegans feeds by rhythmic contraction and relaxation of a neuromuscular organ called the pharynx, which draws in and filters water and bacterial food. This behavior is driven by myogenic plateau potentials, long-lasting depolarizations of the pharyngeal muscle, which are timed by neuronal input from a dedicated pharyngeal nervous system. While the timing of these plateaus' initiation has received significant attention, their mechanisms of termination remain incompletely understood. In particular, it is unclear how plateaus resist early termination by hyperpolarizing current noise. Here, we present a computational model of pharyngeal plateaus against a noisy background. We propose that an unusual, rapidly inactivating potassium conductance confers exceptional noise robustness on the system. We further investigate the possibility that a similar mechanism in other systems permits switching between plateau and spiking behavior under noisy conditions.

A comprehensive assessment of immunomodulatory potentials of Korean antler velvet extract in mouse and neurodegenerative Caenorhabditis elegans models

This study conducts a comprehensive analysis of deer antler velvet's impact, with a specific emphasis on mouse models and in vitro experiments. The study navigates the intricacies of antler velvet's variability, encompassing considerations of drying methods, extraction techniques, and anatomical regions of antlers. Employing a diverse array of processing methods, this study prioritizes both food safety and the consistent intake of deer antler velvet extracts. The study scrupulously evaluates toxicity and immune-boosting properties through exhaustive assessments, utilizing Caenorhabditis elegans, immunosuppressive mouse models, and immune cells. The study unfolds the repercussions of deer antler velvet extract on the lifespan, neuromuscular functions, and cognitive abilities of C. elegans. Additionally, this study explores the extract's potential to alleviate toxicity induced by cyclophosphamide (CPA) in a mouse model, with a focus on inflammation, metabolic disorders, and gut microbiota composition. The antler velvet extract prevents immune dysregulation caused by CPA treatment by ameliorating systemic inflammation and restoring energy metabolism. Furthermore, antler velvet extract treatment significantly transforms the gut microbiota of an immunosuppressive mouse model by fostering the proliferation of commensal bacteria such as Lactobacillus, Akkermansia, and Lachnospiraceae at the genus level. Moreover, antler velvet treatment enhances the activity of natural killer cells against YAC-1 lymphoma while tempering overactivity among immune cells to baseline levels. In conclusion, this study provides nuanced insights into the diverse benefits of antler velvet extract, encouraging sustained research to unveil its complete potential in the realms of mouse models and in vitro experiments.

Tolerance to a Diet of Toxic Microcystis aeruginosa in Caenorhabditis elegans

Reported incidences of cyanobacterial harmful algal blooms (CHABs) are increasing across the world due to climate change and nutrient loading, dominating freshwater ecosystems and producing dangerous cyanotoxins that cause ecological damage. Microcystis aeruginosa is one of the most common species of cyanobacteria; it produces hepatotoxic and neurotoxic microcystin-LR. The ecological and human impact of algal blooms is immense, and traditional CHAB remediation methods are not always adequate in eutrophic regions such as Lake Erie in North America. As a result, a proactive, targeted approach is needed to bioremediate cyanobacteria in their pre-colonial stages. Nematodes, such as the model organism Caenorhabditis elegans, are potential candidates for bioremediating cyanobacteria such as M. aeruginosa. C. elegans have metabolic pathways that could detoxify microcystin-LR and enable tolerance to cyanobacteria in nature. We analyzed C. elegans health and fat accumulation on a diet of toxic M. aeruginosa and found that C. elegans can ingest, digest, metabolize, and survive off of this diet. The mean lifespans of the worm populations were only slightly different at 20.68 ± 0.35 (mean ± S.E.M) and 17.89 ± 0.40 when fed E. coli and toxic M. aeruginosa, respectively. In addition, a diet of toxic M. aeruginosa compared to E. coli did not have any significant impact on C. elegans pharyngeal pumping (304.2 ± 9.3 versus 330.0 ± 10.4 pumps/min), dauer response (86.3 ± 1.0 versus 83.65 ± 1.0% in dauer), mobility (209.25 ± 7.0 versus 210.15 ± 4.4 thrashes/min), or SKN-1 expression based on SKN1::GFP fluorescence measurements. Overall, a diet of toxic M. aeruginosa was able to sustain C. elegans development, and C. elegans was tolerant of it. These results suggest that C. elegans and similar nematodes could be viable candidates for cyanobacterial bioremediation.

Blue-shifted ancyromonad channelrhodopsins for multiplex optogenetics

Light-gated ion channels from protists (channelrhodopsins or ChRs) are optogenetic tools widely used for controlling neurons and cardiomyocytes. Multiplex optogenetic applications require spectrally separated molecules that must be found in nature, as they are difficult to engineer without disrupting channel function. Scanning numerous sequence databases, we identified three robust naturally blue-shifted ChRs from ancyromonads. They form a separate branch on the phylogenetic tree and contain residue motifs characteristic of anion ChRs (ACRs). However, only two conduct chloride, whereas the close Nutomonas longa homolog (peak absorption at ~440 nm) generates inward cation currents in mammalian cells under physiological conditions, significantly exceeding those by previously known tools. Measurements of transient absorption changes and pH titration of purified Ancyromonas sigmoides ACR (AnsACR) combined with mutant analysis revealed the roles of the residues in the photoactive site. Both ancyromonad ACRs allowed optogenetic silencing of mouse cortical neurons in brain slices. AnsACR expression in the cholinergic neurons enabled photoinhibition of pharyngeal muscle contraction in live worms. AnsACR could be activated by near-infrared two-photon illumination, which is required to control specific neurons in thick tissue. Our results improved the mechanistic understanding of light-gated channel function and expanded the optogenetic toolkit.

Impact statement

Ancyromonad channelrhodopsins advance our understanding of ionic selectivity and wavelength regulation in light-gated ion channels and also expand the toolkit for all-optical electrophysiology.

Gamma-Decanolactone Increases Stress Resistance and Improves Toxicity Parameters on the Caenorhabditis elegans Alternative Model

Gamma-decanolactone (GD) is a monoterpene compound with anticonvulsant, antiparkinsonian, and neuroprotective effects in preclinical trials. This study aimed to evaluate the toxicity and antioxidant profile of GD in silico and in the Caenorhabditis elegans (C. elegans) experimental model. The C. elegans was used to determine the median lethal concentration (LC50) of GD, as well as its effect on survival, development, reproduction, pharyngeal pumping, and stress resistance assays. The in silico study did not indicate hepatotoxic, cardiotoxic, or mutagenic potential to GD. It reduced the worms' survival, both at the L1 and L4 stages, in a concentration-dependent manner with an LC50 value of 212.16 ± 5.56 μmol/mL. GD did not alter the development, reproduction, and pharyngeal pumping under normal experimental conditions in the three concentrations tested (25, 50, and 100 μmol/mL). In the thermal stress assay, GD did not change the survival pattern of the worms. Hydrogen peroxide (H2O2) reduced the survival of C. elegans and decreased the number of pharyngeal pumping, with these effects being reversed by GD. Also, GD presents an antioxidant activity by modulation the expression of the stress response genes such as sod-3, ctl-1,2,3, and gst-4. In conclusion, GD showed low toxicity in the C. elegans model and antioxidant profile both in the in silico study and in vivo assays.

Transcriptomic Approaches to Investigate the Anti-Aging Effects of Blueberry Anthocyanins in a Caenorhabditis Elegans Aging Model

This study investigates the anti-aging effects of various concentrations of blueberry anthocyanins (BA) on the lifespan and health-related phenotypes of Caenorhabditis elegans. Blueberry anthocyanins were administered at concentrations of 50.0 μg/mL, 200.0 μg/mL, and 500.0 μg/mL, and their effects on nematode lifespan, locomotion, pharyngeal pumping rate, and the accumulation of lipofuscin and reactive oxygen species (ROS) were examined. Transcriptomic analysis was conducted to explore the regulatory effects of BA on anti-aging molecular pathways and key genes in C. elegans. Results showed a significant, dose-dependent extension of lifespan, improvement in locomotion and pharyngeal pumping rate, and reduction in lipofuscin and ROS accumulation. Transcriptomic analysis revealed that BA activated anti-aging pathways such as FOXO, IIS, and PI3K/Akt, upregulating critical genes like daf-16. These findings highlight the potential of blueberry anthocyanins as promising anti-aging agents through multiple physiological and molecular mechanisms.

The Effect of glna Loss on the Physiological and Pathological Phenotype of Parkinson's Disease C. elegans

BACKGROUND

Parkinson's disease (PD) is a common neurodegenerative disease. Glutamate(Glu) excitotoxicity is one of the main pathogenesis of PD. Glutaminase (Gls) is an enzyme primarily responsible for catalyzing the hydrolysis and deamidation of glutamine (Gln) to produce Glu and ammonia. Inhibiting the function of Gls may have a beneficial effect on the treatment of PD by reducing the production of Glu. The homologous gene of Gls in C. elegans is glna.

AIMS

To explore the effects of glna loss on physiological and pathological phenotype of PD C. elegans, and to provide new ideas and references for the research and treatment of PD.

MATERIALS & METHODS

We used PD C. elegans UA44 and QIN27 to detect development and lifespan, behavior, degeneration of dopaminergic neurons, lipid levels, ROS levels, expression levels of common amino acids.

RESULTS

Glna loss had no significant impact on the development and lifespan of PD C. elegans. Glna loss saved part of the decline of motor function, including the head thrash frequency and the body bend frequency, and the difference was significant. There was a trend of improvement in some motor behaviors, such as the ethanol avoidance experiment, while no improvement was observed in other experiments. Glna loss slowed down the degeneration of dopaminergic neurons. Glna loss increased the lipid levels and ROS levels in C. elegans. Glna loss decreased Glu content and increased Gln content in C. elegans.

DISCUSSION

The effect of glna loss on PD C. elegans may be the result of multiple factors, such as the tissue types of α-syn expression in C. elegans, the PD C. elegans model used, the adverse effects of glna loss on other systems, and the changes in ROS levels in C. elegans. The specific mechanisms causing these phenomena are still unclear and need to be further explored.

CONCLUSION

Glna loss has a certain protective effect on dopaminergic neurons in PD C. elegans, while the improvement effect on movement and behavior is limited.

Adapting and optimizing GCaMP8f for use in Caenorhabditis elegans

Improved genetically encoded calcium indicators (GECIs) are essential for capturing intracellular dynamics of both muscle and neurons. A novel set of GECIs with ultrafast kinetics and high sensitivity was recently reported by Zhang et al. (2023). While these indicators, called jGCaMP8, were demonstrated to work in Drosophila and mice, data for Caenorhabditis elegans were not reported. Here, we present an optimized construct for C. elegans and use this to generate several strains expressing GCaMP8f (fast variant of the indicator). Utilizing the myo-2 promoter, we compare pharyngeal muscle activity measured with GCaMP7f and GCaMP8f and find that GCaMP8f is brighter upon binding to calcium, shows faster kinetics, and is not disruptive to the intrinsic contraction dynamics of the pharynx. Additionally, we validate its application for detecting neuronal activity in touch receptor neurons which reveals robust calcium transients even at small stimulus amplitudes. As such, we establish GCaMP8f as a potent tool for C. elegans research which is capable of extracting fast calcium dynamics at very low magnifications across multiple cell types.

Segmentation-free measurement of locomotor frequency in Caenorhabditis elegans using image invariants

An animal's locomotor rate is an important indicator of its motility. In studies of the nematode Caenorhabditis elegans (C. elegans), assays of the frequency of body bending waves have often been used to discern the effects of mutations, drugs, or aging. Traditional manual methods for measuring locomotor frequency are low in throughput and subject to human error. Most current automated methods depend on image segmentation, which requires high image quality and is prone to errors. Here, we describe an algorithm for automated estimation of C. elegans locomotor frequency using image invariants, i.e. shape-based parameters that are independent of object translation, rotation, and scaling. For each video frame, the method calculates a combination of 8 Hu's moment invariants and a set of maximally stable extremal regions (MSER) invariants. The algorithm then calculates the locomotor frequency by computing the autocorrelation of the time sequence of the invariant ensemble. Results of our method show excellent agreement with manual or segmentation-based results over a wide range of frequencies. We show that compared to a segmentation-based method that analyzes a worm's shape and a method based on video covariance, our technique is more robust to low image quality and background noise. We demonstrate the system's capabilities by testing the effects of serotonin and serotonin pathway mutations on C. elegans locomotor frequency.

Deciphering the underlying mechanisms of the pharyngeal pumping motions in Caenorhabditis elegans

The pharynx of the nematode Caenorhabditis elegans is a neuromuscular organ that exhibits typical pumping motions, which result in the intake of food particles from the environment. In-depth inspection reveals slightly different dynamics at the various pharyngeal areas, rather than synchronous pumping motions of the whole organ, which are important for its effective functioning. While the different pumping dynamics are well characterized, the underlying mechanisms that generate them are not known. In this study, the C. elegans pharynx was modeled in a bottom-up fashion, including all of the underlying biological processes that lead to, and including, its end function, food intake. The mathematical modeling of all processes allowed performing comprehensive, quantitative analyses of the system as a whole. Our analyses provided detailed explanations for the various pumping dynamics generated at the different pharyngeal areas; a fine-resolution description of muscle dynamics, both between and within different pharyngeal areas; a quantitative assessment of the values of many parameters of the system that are unavailable in the literature; and support for a functional role of the marginal cells, which are currently assumed to mainly have a structural role in the pharynx. In addition, our model predicted that in tiny organisms such as C. elegans, the generation of long-lasting action potentials must involve ions other than calcium. Our study exemplifies the power of mathematical models, which allow a more accurate, higher-resolution inspection of the studied system, and an easier and faster execution of in silico experiments than feasible in the lab.

Neuroprotective effect of biogenically synthesized ZnO nanoparticles against oxidative stress and β-amyloid toxicity in transgenic Caenorhabditis elegans

Amyloid β (Aβ) plaque accumulation-mediated neuronal toxicity has been suggested to cause synaptic damage and consequent degeneration of brain cells in Alzheimer's disease (AD). With the increasing prerequisite of eco-friendly nanoparticles (NPs), research investigators are utilizing green approaches for the synthesis of zinc oxide (ZnO) NPs for pharmaceutical applications. In this present study, ZnO NPs were synthesized from Acanthus ilicifolius to assess the neuroprotective properties in the AD model of transgenic Caenorhabditis elegans strains CL2006 and CL4176 expressing Aβ aggregation. Our findings revealed that the therapeutic effect of green-synthesized ZnO NPs is associated with antioxidant activity. We also found that ZnO NPs significantly enhance the C. elegan's lifespan, locomotion, pharyngeal pumping, chemotaxis behavior also diminish the ROS deposition and intracellular productionMoreover, thioflavin T staining demonstrated that ZnO NPs substantially attenuated the Aβ deposition in the C. elegans strain as compared to untreated worms. With their antioxidant properties, the greenly synthesized ZnO NPs had a significant neuroprotective efficiency on Aβ-induced toxicity by reducing Aβ aggregation and specifically reducing the progression of paralysis in the C. elegans AD model. Our findings suggested that the biosynthesized ZnO NPs could be thought-provoking candidates for age-associated neurodegenerative disorders accompanied by oxidative stress.

Uncovering the essential roles of glutamate carboxypeptidase 2 orthologs in Caenorhabditis elegans

Human glutamate carboxypeptidase 2 (GCP2) from the M28B metalloprotease group is an important target for therapy in neurological disorders and an established tumor marker. However, its physiological functions remain unclear. To better understand general roles, we used the model organism Caenorhabditis elegans to genetically manipulate its three existing orthologous genes and evaluate the impact on worm physiology. The results of gene knockout studies showed that C. elegans GCP2 orthologs affect the pharyngeal physiology, reproduction, and structural integrity of the organism. Promoter-driven GFP expression revealed distinct localization for each of the three gene paralogs, with gcp-2.1 being most abundant in muscles, intestine, and pharyngeal interneurons, gcp-2.2 restricted to the phasmid neurons, and gcp-2.3 located in the excretory cell. The present study provides new insight into the unique phenotypic effects of GCP2 gene knockouts in C. elegans, and the specific tissue localizations. We believe that elucidation of particular roles in a non-mammalian organism can help to explain important questions linked to physiology of this protease group and in extension to human GCP2 involvement in pathophysiological processes.

Early-life caffeine exposure induces morphological changes and altered physiology in Caenorhabditiselegans

Caffeine, a widely consumed stimulant, is known for its effects on alertness and fatigue reduction by blockade of adenosine receptors. While it holds therapeutic potential, its diverse impacts pose risks, particularly in early development. This study explores the developmental effects of caffeine exposure using Caenorhabditis elegans (C. elegans) as a model organism. We investigated morphological and behavioral changes induced by caffeine exposure at the L1 stage and assessed their impact at the L4 stage, which roughly corresponds to human infancy and adolescence, respectively. Caffeine-exposed worms displayed increased body length, body bends, and pharyngeal pumping rates compared to control worms. These findings indicate heightened food-seeking behavior and greater food intake, leading to the observed morphological changes. While caffeine did not affect other locomotor behaviors, its stimulatory effect on growth and development highlights its significance. This study provides insights into the potential impact of early-life caffeine exposure on long-term health and development, offering a foundation for future research in vertebrates to uncover its implications on metabolism and other metrics of health.

Glia in Invertebrate Models: Insights from Caenorhabditis elegans

Glial cells modulate brain development, function, and health across all bilaterian animals, and studies in the past two decades have made rapid strides to uncover the underlying molecular mechanisms of glial functions. The nervous system of the invertebrate genetic model Caenorhabditis elegans (C. elegans) has small cell numbers with invariant lineages, mapped connectome, easy genetic manipulation, and a short lifespan, and the animal is also optically transparent. These characteristics are revealing C. elegans to be a powerful experimental platform for studying glial biology. This chapter discusses studies in C. elegans that add to our understanding of how glia modulate adult neural functions, and thereby animal behaviors, as well as emerging evidence of their roles as autonomous sensory cells. The rapid molecular and cellular advancements in understanding C. elegans glia in recent years underscore the utility of this model in studies of glial biology. We conclude with a perspective on future research avenues for C. elegans glia that may readily contribute molecular mechanistic insights into glial functions in the nervous system.

Forward genetic screen of Caenorhabditis elegans mutants with impaired sleep reveals a crucial role of neuronal diacylglycerol kinase DGK-1 in regulating sleep

The sleep state is widely observed in animals. The molecular mechanisms underlying sleep regulation, however, remain largely unclear. In the nematode Caenorhabditis elegans, developmentally timed sleep (DTS) and stress-induced sleep (SIS) are 2 types of quiescent behaviors that fulfill the definition of sleep and share conserved sleep-regulating molecules with mammals. To identify novel sleep-regulating molecules, we conducted an unbiased forward genetic screen based on DTS phenotypes. We isolated 2 mutants, rem8 and rem10, that exhibited significantly disrupted DTS and SIS. The causal gene of the abnormal sleep phenotypes in both mutants was mapped to dgk-1, which encodes diacylglycerol kinase. Perhaps due to the diminished SIS, dgk-1 mutant worms exhibited decreased survival following exposure to a noxious stimulus. Pan-neuronal and/or cholinergic expression of dgk-1 partly rescued the dgk-1 mutant defects in DTS, SIS, and post-stress survival. Moreover, we revealed that pkc-1/nPKC participates in sleep regulation and counteracts the effect of dgk-1; the reduced DTS, SIS, and post-stress survival rate were partly suppressed in the pkc-1; dgk-1 double mutant compared with the dgk-1 single mutant. Excessive sleep observed in the pkc-1 mutant was also suppressed in the pkc-1; dgk-1 double mutant, implying that dgk-1 has a complicated mode of action. Our findings indicate that neuronal DGK-1 is essential for normal sleep and that the counterbalance between DGK-1 and PKC-1 is crucial for regulating sleep and mitigating post-stress damage.

Methylglyoxal-derived hydroimidazolone, MG-H1, increases food intake by altering tyramine signaling via the GATA transcription factor ELT-3 in Caenorhabditis elegans

The Maillard reaction, a chemical reaction between amino acids and sugars, is exploited to produce flavorful food ubiquitously, from the baking industry to our everyday lives. However, the Maillard reaction also occurs in all cells, from prokaryotes to eukaryotes, forming advanced glycation end-products (AGEs). AGEs are a heterogeneous group of compounds resulting from the irreversible reaction between biomolecules and α-dicarbonyls (α-DCs), including methylglyoxal (MGO), an unavoidable byproduct of anaerobic glycolysis and lipid peroxidation. We previously demonstrated that Caenorhabditis elegans mutants lacking the glod-4 glyoxalase enzyme displayed enhanced accumulation of α-DCs, reduced lifespan, increased neuronal damage, and touch hypersensitivity. Here, we demonstrate that glod-4 mutation increased food intake and identify that MGO-derived hydroimidazolone, MG-H1, is a mediator of the observed increase in food intake. RNAseq analysis in glod-4 knockdown worms identified upregulation of several neurotransmitters and feeding genes. Suppressor screening of the overfeeding phenotype identified the tdc-1-tyramine-tyra-2/ser-2 signaling as an essential pathway mediating AGE (MG-H1)-induced feeding in glod-4 mutants. We also identified the elt-3 GATA transcription factor as an essential upstream regulator for increased feeding upon accumulation of AGEs by partially controlling the expression of tdc-1 gene. Furthermore, the lack of either tdc-1 or tyra-2/ser-2 receptors suppresses the reduced lifespan and rescues neuronal damage observed in glod-4 mutants. Thus, in C. elegans, we identified an elt-3 regulated tyramine-dependent pathway mediating the toxic effects of MG-H1 AGE. Understanding this signaling pathway may help understand hedonistic overfeeding behavior observed due to modern AGE-rich diets.

A Reliable Method Based on Liquid Chromatography-Tandem Mass Spectrometry for the Simultaneous Quantification of Neurotransmitters in Caenorhabditis elegans

Neurotransmitters like dopamine (DA), serotonin (SRT), γ-aminobutyric acid (GABA) and acetylcholine (ACh) are messenger molecules that play a pivotal role in transmitting excitation between neurons across chemical synapses, thus enabling complex processes in the central nervous system (CNS). Balance in neurotransmitter homeostasis is essential, and altered neurotransmitter levels are associated with various neurological disorders, e.g., loss of dopaminergic neurons (Parkinson's disease) or altered ACh synthesis (Alzheimer's disease). Therefore, it is crucial to possess adequate tools to assess precise neurotransmitter levels, and to apply targeted therapies. An established in vivo model to study neurotoxicity is the model organism Caenorhabditis elegans (C. elegans), as its neurons have been well characterized and functionally are analogous to mammals. We have developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method including a sample preparation assuring neurotransmitter stability, which allows a simultaneous neurotransmitter quantification of DA, SRT, GABA and ACh in C. elegans, but can easily be applied to other matrices. LC-MS/MS combined with isotope-labeled standards is the tool of choice, due to its otherwise unattainable sensitivity and specificity. Using C. elegans together with our analytically validated and verified method provides a powerful tool to evaluate mechanisms of neurotoxicity, and furthermore to identify possible therapeutic approaches.

Serotonin-induced stereospecific formation and bioactivity of the eicosanoid 17,18-epoxyeicosatetraenoic acid in the regulation of pharyngeal pumping of C. elegans

17,18-Epoxyeicosatetraenoic acid (17,18-EEQ), the most abundant eicosanoid generated by cytochrome P450 (CYP) enzymes in C. elegans, is a potential signaling molecule in the regulation of pharyngeal pumping activity of this nematode. As a chiral molecule, 17,18-EEQ can exist in two stereoisomers, the 17(R),18(S)- and 17(S),18(R)-EEQ enantiomers. Here we tested the hypothesis that 17,18-EEQ may function as a second messenger of the feeding-promoting neurotransmitter serotonin and stimulates pharyngeal pumping and food uptake in a stereospecific manner. Serotonin treatment of wildtype worms induced a more than twofold increase of free 17,18-EEQ levels. As revealed by chiral lipidomics analysis, this increase was almost exclusively due to an enhanced release of the (R,S)-enantiomer of 17,18-EEQ. In contrast to the wildtype strain, serotonin failed to induce 17,18-EEQ formation as well as to accelerate pharyngeal pumping in mutant strains defective in the serotonin SER-7 receptor. However, the pharyngeal activity of the ser-7 mutant remained fully responsive to exogenous 17,18-EEQ administration. Short term incubations of well-fed and starved wildtype nematodes showed that both racemic 17,18-EEQ and 17(R),18(S)-EEQ were able to increase pharyngeal pumping frequency and the uptake of fluorescence-labeled microspheres, while 17(S),18(R)-EEQ and also 17,18-dihydroxyeicosatetraenoic acid (17,18-DHEQ, the hydrolysis product of 17,18-EEQ) were ineffective. Taken together, these results show that serotonin induces 17,18-EEQ formation in C. elegans via the SER-7 receptor and that both the formation of this epoxyeicosanoid and its subsequent stimulatory effect on pharyngeal activity proceed with high stereospecificity confined to the (R,S)-enantiomer.

Caenorhabditis elegans as a Promising Model Organism in Chronobiology

Circadian rhythms represent an adaptive feature, ubiquitously found in nature, which grants living beings the ability to anticipate daily variations in their environment. They have been found in a multitude of organisms, ranging from bacteria to fungi, plants, and animals. Circadian rhythms are generated by endogenous clocks that can be entrained daily by environmental cycles such as light and temperature. The molecular machinery of circadian clocks includes a transcriptional-translational feedback loop that takes approximately 24 h to complete. Drosophila melanogaster has been a model organism of choice to understand the molecular basis of circadian clocks. However, alternative animal models are also being adopted, each offering their respective experimental advantages. The nematode Caenorhabditis elegans provides an excellent model for genetics and neuro-behavioral studies, which thanks to its ease of use and manipulation, as well as availability of genetic data and mutant strains, is currently used as a novel model for circadian research. Here, we aim to evaluate C. elegans as a model for chronobiological studies, focusing on its strengths and weaknesses while reviewing the available literature. Possible zeitgebers (including light and temperature) are also discussed. Determining the molecular bases and the neural circuitry involved in the central pacemaker of the C. elegans' clock will contribute to the understanding of its circadian system, becoming a novel model organism for the study of diseases due to alterations of the circadian cycle.

C. elegans as a test system to study relevant compounds that contribute to the specific health-related effects of different cannabis varieties

Background

The medicinal effects of cannabis varieties on the market cannot be explained solely by the presence of the major cannabinoids Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD). Evidence for putative entourage effects caused by other compounds present in cannabis is hard to obtain due to the subjective nature of patient experience data. Caenorhabditis elegans (C. elegans) is an objective test system to identify cannabis compounds involved in claimed health and entourage effects.

Methods

From a medicinal cannabis breeding program by MariPharm BV, the Netherlands a set of 12 varieties were selected both THC rich varieties as well as CBD rich varieties. A consecutive extraction process was applied resulting in a non-polar (cannabinoid-rich) and polar (cannabinoid-poor) extract of each variety. The test model C. elegans was exposed to these extracts in a broad set of bioassays for appetite control, body oscillation, motility, and nervous system function.

Results

Exposing C. elegans to extracts with a high concentration of cannabinoids (> 1 μg/mL) reduces the life span of C. elegans dramatically. Exposing the nematodes to the low-cannabinoid (< 0.005 μg/mL) polar extracts, however, resulted in significant effects with respect to appetite control, body oscillation, motility, and nervous system-related functions in a dose-dependent and variety-dependent manner.

Discussion

C. elegans is a small, transparent organism with a complete nervous system, behavior and is due to its genetic robustness and short life cycle highly suitable to unravel entourage effects of Cannabis compounds. Although C. elegans lacks an obvious CB1 and CB2 receptor it has orthologs of Serotonin and Vanilloid receptor which are also involved in (endo)cannabinoid signaling.

Conclusion

By using C. elegans, we were able to objectively distinguish different effects of different varieties despite the cannabinoid content. C. elegans seems a useful test system for studying entourage effects, for targeted medicinal cannabis breeding programs and product development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42238-022-00162-9.

Early-life perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) exposure cause obesity by disrupting fatty acids metabolism and enhancing triglyceride synthesis in Caenorhabditis elegans

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are widely used and considered as emerging persistent pollutants, posing a potential threat to the aquatic ecosystem due to their metabolic toxicity. However, the effects of early-life PFOA and PFOS exposure on metabolic disruption and underlying mechanisms are not fully understood. Therefore, we investigated the effects of early-life PFOA or PFOS exposure on lipid accumulation, feeding behaviors, fatty acids composition, and possible genetic regulation using the nematode Caenorhabditis elegans as an in vivo model. Our results showed that low concentrations of PFOA and PFOS (0.1 and 1 μM) induced obesity in C. elegans, which was not due to the increased feeding rate. The altered fatty acid composition illustrated the decrease of saturated fatty acids and the increase of polyunsaturated fatty acids. Furthermore, the mutant assay and mRNA levels revealed that fatty acid desaturation related genes mdt-15, nhr-49, fat-6 as well as fatty acid (fasn-1) and triglyceride (TG) (dgat-2) synthesis related genes, were associated with the increased body fat, TG, and lipid droplet (LD) contents in C. elegans exposed to PFOA and PFOS. Hence, this present study provides the genetic regulatory information of PFOA and PFOS induced metabolic disruption of lipid metabolism and obesity.

Automatically tracking feeding behavior in populations of foraging C. elegans

Caenorhabditis elegans feeds on bacteria and other small microorganisms which it ingests using its pharynx, a neuromuscular pump. Currently, measuring feeding behavior requires tracking a single animal, indirectly estimating food intake from population-level metrics, or using restrained animals. To enable large throughput feeding measurements of unrestrained, crawling worms on agarose plates at a single worm resolution, we developed an imaging protocol and a complementary image analysis tool called PharaGlow. We image up to 50 unrestrained crawling worms simultaneously and extract locomotion and feeding behaviors. We demonstrate the tool's robustness and high-throughput capabilities by measuring feeding in different use-case scenarios, such as through development, with genetic and chemical perturbations that result in faster and slower pumping, and in the presence or absence of food. Finally, we demonstrate that our tool is capable of long-term imaging by showing behavioral dynamics of mating animals and worms with different genetic backgrounds. The low-resolution fluorescence microscopes required are readily available in C. elegans laboratories, and in combination with our python-based analysis workflow makes this methodology easily accessible. PharaGlow therefore enables the observation and analysis of the temporal dynamics of feeding and locomotory behaviors with high-throughput and precision in a user-friendly system.

Lactobacillus brevis MTCC 1750 enhances oxidative stress resistance and lifespan extension with improved physiological and functional capacity in Caenorhabditis elegans via the DAF-16 pathway

Redox imbalance plays a crucial role in the development of age-related diseases, and resistance to oxidative stress is crucial for optimum longevity and healthy aging. Using the wild-type, mutant and transgenic strains, this study explored the antioxidative potential and lifespan extension benefits of different Lactobacillus strains in Caenorhabditis elegans (C. elegans). We observed that Lactobacillus brevis MTCC 1750 could enhance the resistance of C. elegans against juglone induced oxidative stress by reducing its intracellular reactive oxygen species (ROS) accumulation. Also, live L. brevis MTCC 1750 could prolong the worm's lifespan. These effects are dependent on transcription factor DAF-16 evident with significant upregulation of its target gene sod-3. This also explained the significant improvements in different age-associated changes in physiological and mechanical parameters of the worm by L. brevis MTCC 1750. Further investigations revealed that DAF-16 activation and, its enhanced translocation in the nucleus is independent of DAF-2 or JNK pathway. These findings highlighted L. brevis MTCC 1750 as a potent anti-oxidant source for complementing current antioxidant therapeutic strategies. Nonetheless, the findings showed how different signaling events are regulated based on an organism's diet component, and their consequences on the aging process in multiple species.

Pharyngeal timing and particle transport defects in Caenorhabditis elegans feeding mutants

The nematode C. elegans uses rhythmic muscle contractions (pumps) of the pharynx, a tubular feeding organ, to filter, transport, and crush food particles. A number of feeding mutants have been identified, including those with slow pharyngeal pumping rate, weak muscle contraction, defective muscle relaxation, and defective grinding of bacteria. Many aspects of these pharyngeal behavioral defects and how they affect pharyngeal function are not well understood. For example, the behavioral deficits underlying inefficient particle transport in 'slippery' mutants have been unclear. Here we use high speed video microscopy to describe pharyngeal pumping behaviors and particle transport in wild-type animals and in feeding mutants. Different 'slippery' mutants exhibit distinct defects including weak isthmus contraction, failure to trap particles in the anterior isthmus, and abnormal timing of contraction and relaxation in pharyngeal compartments. Our results show that multiple deficits in pharyngeal timing or contraction can cause defects in particle transport.

Acute, Sublethal, and Developmental Toxicity of Kratom (Mitragyna speciosa Korth.) Leaf Preparations on Caenorhabditis elegans as an Invertebrate Model for Human Exposure

Kratom (Mitragyna speciosa Korth.) is a tree native to Southeast Asia with stimulant and opioid-like effects which has seen increased use in Europe and North America in recent years. Its safety and pharmacological effects remain under investigation, especially in regard to developmental and generational toxicity. In the current study, we investigated commercial kratom preparations using the nematode Caenorhabditis elegans as a translational model for toxicity and pharmacological effects. The pure alkaloids mitragynine and 7-hydroxymitragynine as well as aqueous, ethanolic, and methanolic extracts of three commercial kratom products were evaluated using a battery of developmental, genotoxic, and opioid-related experiments. As determined previously, the mitragynine and 7-hydroxymitragynine content in kratom samples was higher in the alcoholic extracts than the aqueous extracts. Above the human consumption range equivalent of 15-70 µg/mL, kratom dose-dependently reduced brood size and health of parent worms and their progeny. 7-hydroxymitragynine, but not mitragynine, presented with toxic and developmental effects at very high concentrations, while the positive control, morphine, displayed toxic effects at 0.5 mM. Kratom and its alkaloids did not affect pumping rate or interpump interval in the same way as morphine, suggesting that kratom is unlikely to act primarily via the opioid-signalling pathway. Only at very high doses did kratom cause developmental and genotoxic effects in nematodes, indicating its relative safety.

C. elegans PEZO-1 is a mechanosensitive ion channel involved in food sensation

PIEZO channels are force sensors essential for physiological processes, including baroreception and proprioception. The Caenorhabditis elegans genome encodes an orthologue gene of the Piezo family, pezo-1, which is expressed in several tissues, including the pharynx. This myogenic pump is an essential component of the C. elegans alimentary canal, whose contraction and relaxation are modulated by mechanical stimulation elicited by food content. Whether pezo-1 encodes a mechanosensitive ion channel and contributes to pharyngeal function remains unknown. Here, we leverage genome editing, genetics, microfluidics, and electropharyngeogram recording to establish that pezo-1 is expressed in the pharynx, including in a proprioceptive-like neuron, and regulates pharyngeal function. Knockout (KO) and gain-of-function (GOF) mutants reveal that pezo-1 is involved in fine-tuning pharyngeal pumping frequency, as well as sensing osmolarity and food mechanical properties. Using pressure-clamp experiments in primary C. elegans embryo cultures, we determine that pezo-1 KO cells do not display mechanosensitive currents, whereas cells expressing wild-type or GOF PEZO-1 exhibit mechanosensitivity. Moreover, infecting the Spodoptera frugiperda cell line with a baculovirus containing the G-isoform of pezo-1 (among the longest isoforms) demonstrates that pezo-1 encodes a mechanosensitive channel. Our findings reveal that pezo-1 is a mechanosensitive ion channel that regulates food sensation in worms.

Optogenetic Perturbation of Individual C. elegans Pharyngeal Neurons While Monitoring Feeding Behavior

Optogenetic approaches have proven to be powerful for examining the roles of specific neurons in generating behaviors, especially in systems where electrophysiological manipulation is not possible. Here we describe a method for optogenetically manipulating single pharyngeal neurons in intact C. elegans while monitoring pharyngeal behavior. This approach provides bidirectional and dynamic control of pharyngeal neural activity while quantitatively assessing behavior and has allowed us to test hypotheses about the roles of individual pharyngeal neurons in feeding behavior.

Cisplatin-induced neurotoxicity involves the disruption of serotonergic neurotransmission

Neurotoxicity is a frequent side effect of cisplatin (CisPt)-based anticancer therapy whose pathophysiology is largely vague. Here, we exploited C. elegans as a 3R-compliant in vivo model to elucidate molecular mechanisms contributing to CisPt-induced neuronal dysfunction. To this end, we monitored the impact of CisPt on various sensory functions as well as pharyngeal neurotransmission by recording electropharyngeograms (EPGs). CisPt neither affected food and odor sensation nor mechano-sensation, which involve dopaminergic and glutaminergic neurotransmission. However, CisPt reduced serotonin-regulated pharyngeal pumping activity independent of changes in the morphology of related neurons. CisPt-mediated alterations in EPGs were fully rescued by addition of serotonin (5-HT) (≤ 2 mM). Moreover, the CisPt-induced pharyngeal injury was prevented by co-incubation with the clinically approved serotonin re-uptake inhibitory drug duloxetine. A protective effect of 5-HT was also observed with respect to CisPt-mediated impairment of another 5-HT-dependent process, the egg laying activity. Importantly, CisPt-induced apoptosis in the gonad and learning disability were not influenced by 5-HT. Using different C. elegans mutants we found that CisPt-mediated (neuro)toxicity is independent of serotonin biosynthesis and re-uptake and likely involves serotonin-receptor subtype 7 (SER-7)-related functions. In conclusion, by measuring EPGs as a surrogate parameter of neuronal dysfunction, we provide first evidence that CisPt-induced neurotoxicity in C. elegans involves 5-HT-dependent neurotransmission and SER-7-mediated signaling mechanisms and can be prevented by the clinically approved antidepressant duloxetine. The data highlight the particular suitability of C. elegans as a 3R-conform in vivo model in molecular (neuro)toxicology and, moreover, for the pre-clinical identification of neuroprotective candidate drugs.

Application of Fluorescence Microscopy and Behavioral Assays to Demonstrating Neuronal Connectomes and Neurotransmitter Systems in C. elegans

The nematode Caenorhabditis elegans (C. elegans) is a prevailing model which is commonly utilized in a variety of biomedical research arenas, including neuroscience. Due to its transparency and simplicity, it is becoming a choice model organism for conducting imaging and behavioral assessment crucial to understanding the intricacies of the nervous system. Here, the methods required for neuronal characterization using fluorescent proteins and behavioral tasks are described. These are simplified protocols using fluorescent microscopy and behavioral assays to examine neuronal connections and associated neurotransmitter systems involved in normal physiology and aberrant pathology of the nervous system. Our aim is to make available to readers some streamlined and replicable procedures using C. elegans models as well as highlighting some of the limitations.

Methylglyoxal influences development of Caenorhabditis elegans via lin-41-dependent pathway

Methylglyoxal is a highly reactive dicarbonyl compound. It can be obtained either endogenously through biological enzymatic/non-enzymatic pathways or exogenously via the uptake of certain foods and beverages, such as Manuka honey. Studies about its biological properties are quite controversial, though the majority reported a positive association between methylglyoxal and certain pathologies. In this report, we tested if methylglyoxal can alter the development of animals using Caenorhabditis elegans as the in vivo model. Treatment of methylglyoxal at 0.1 and 1 mmol/L for 2 days significantly inhibited the development of Caenorhabditis elegans, particularly targeting the transition from L3 stage. Pharyngeal pumping rate, the food intake marker was also significantly reduced by methylglyoxal at both 0.1 and 1 mmol/L. Additionally, treatment of 0.1 mmol/L methylglyoxal increased, while 1 mmol/L methylglyoxal decreased the nematodes' average moving speed. The effect of methylglyoxal on development was in part due to the modulation of lin-41, which encodes a homolog of human TRIM71. The mutation of lin-41 could alleviate or abolish the effects of methylglyoxal on growth rate, body size, pumping rate and locomotive activity. In summary, these results suggested that methylglyoxal influenced the development of Caenorhabditis elegans, which is in part via the lin-41-dependent pathway.

Use of C. elegans as a 3R-compliant in vivo model for the chemoprevention of cisplatin-induced neurotoxicity

Anticancer therapeutics can provoke severe side effects that impair the patient's quality of life. A frequent dose-limiting side effect of platinum-based anticancer therapy is neurotoxicity. Its pathophysiology is poorly understood, and effective preventive or therapeutic measures are missing. Therefore, elucidation of the molecular mechanism of platinating drug-induced neurotoxicity and the development of preventive strategies is urgently needed. To this end, we aim to use C. elegans as a 3R-compliant in vivo model. The 3R principles were conceived for animal welfare in science concerning animal experiments, which should be replaced, reduced or refined. We can analytically demonstrate dose-dependent uptake of cisplatin (CisPt) in C. elegans, as well as genotoxic and cytotoxic effects based on DNA adduct formation (i.e., 1,2-GpG intrastrand crosslinks), induction of apoptosis, and developmental toxicity. Measuring the impairment of pharyngeal pumping as a marker of neurotoxicity, we found that especially CisPt reduces the pumping frequency at concentrations where basal and touch-provoked movement were not yet affected. CisPt causes glutathione (GSH) depletion and RNAi-mediated knockdown of the glutamate-cysteine ligase GCS-1 aggravates the CisPt-induced inhibition of pharyngeal pumping. Moreover, N-acetylcysteine (NAC) mitigated CisPt-triggered toxicity, indicating that GSH depletion contributes to the CisPt-induced pharyngeal damage. In addition to NAC, amifostine (WR1065) also protected the pharynx of C. elegans from the toxic effects of CisPt. Measuring pharyngeal activity by the electrophysiological recording of neurotransmission in the pharynx, we confirmed that CisPt is neurotoxic in C. elegans and that NAC is neuroprotective in the nematode. The data support the hypothesis that monitoring the pharyngeal activity of C. elegans is a useful surrogate marker of CisPt-induced neurotoxicity. In addition, a low GSH pool reduces the resistance of neurons to CisPt treatment, and both NAC and WR1065 are capable of attenuating platinum-induced neurotoxicity during post-incubation in C. elegans. Overall, we propose C. elegans as a 3R-compliant in vivo model to study the molecular mechanisms of platinum-induced neurotoxicity and to explore novel neuroprotective therapeutic strategies to alleviate respective side effects of platinum-based cancer therapy.

Elevated mitochondrial DNA copy number found in ubiquinone-deficient clk-1 mutants is not rescued by ubiquinone precursor 2-4-dihydroxybenzoate

Inside mitochondria reside semi-autonomous genomes, called mtDNA. mtDNA is multi-copy per cell and mtDNA copy number can vary from hundreds to thousands of copies per cell. The variability of mtDNA copy number between tissues, combined with the lack of variability of copy number within a tissue, suggest a homeostatic copy number regulation mechanism. Mutations in the gene encoding the Caenorhabditis elegans hydroxylase, CLK-1, result in elevated mtDNA. CLK-1's canonical role in ubiquinone biosynthesis results in clk-1 mutants lacking ubiquinone. Importantly, clk-1 mutants also exhibit slowed biological timing phenotypes (pharyngeal pumping, defecation, development) and an activated stress response (UPR^mt). These biological timing and stress phenotypes have been attributed to ubiquinone deficiency; however, it is unknown whether the mtDNA phenotype is also due to ubiquinone deficiency. To test this, in animals carrying the uncharacterized clk-1 (ok1247) mutant allele, we supplemented with an exogenous ubiquinone precursor 2-4-dihydroxybenzoate (DHB), which has previously been shown to restore ubiquinone biosynthesis. We measured phenotypes as a function of DHB across a log-scale range. Unlike the biological timing and stress phenotypes, the elevated mtDNA phenotype was not rescued. Since CLK-1's canonical role is in ubiquinone biosynthesis and DHB does not rescue mtDNA copy number, we infer CLK-1 has an additional function in homeostatic mtDNA copy number regulation.

DamID identifies targets of CEH-60/PBX that are associated with neuron development and muscle structure in Caenorhabditis elegans

Transcription factors govern many of the time- and tissue-specific gene expression events in living organisms. CEH-60, a homolog of the TALE transcription factor PBX in vertebrates, was recently characterized as a new regulator of intestinal lipid mobilization in Caenorhabditis elegans. Because CEH-60's orthologs and paralogs exhibit several other functions, notably in neuron and muscle development, and because ceh-60 expression is not limited to the C. elegans intestine, we sought to identify additional functions of CEH-60 through DNA adenine methyltransferase identification (DamID). DamID identifies protein-genome interaction sites through GATC-specific methylation. We here report 872 putative CEH-60 gene targets in young adult animals, and 587 in L2 larvae, many of which are associated with neuron development or muscle structure. In light of this, we investigate morphology and function of ceh-60 expressing AWC neurons, and contraction of pharyngeal muscles. We find no clear functional consequences of loss of ceh-60 in these assays, suggesting that in AWC neurons and pharyngeal muscle, CEH-60 function is likely more subtle or redundant with other factors.

Mitochondrial Ca2+ Dynamics in MCU Knockout C. elegans Worms

Mitochondrial [Ca²⁺] plays an important role in the regulation of mitochondrial function, controlling ATP production and apoptosis triggered by mitochondrial Ca²⁺ overload. This regulation depends on Ca²⁺ entry into the mitochondria during cell activation processes, which is thought to occur through the mitochondrial Ca²⁺ uniporter (MCU). Here, we have studied the mitochondrial Ca²⁺ dynamics in control and MCU-defective C. elegans worms in vivo, by using worms expressing mitochondrially-targeted YC3.60 yellow cameleon in pharynx muscle. Our data show that the small mitochondrial Ca²⁺ oscillations that occur during normal physiological activity of the pharynx were very similar in both control and MCU-defective worms, except for some kinetic differences that could mostly be explained by changes in neuronal stimulation of the pharynx. However, direct pharynx muscle stimulation with carbachol triggered a large and prolonged increase in mitochondrial [Ca²⁺] that was much larger in control worms than in MCU-defective worms. This suggests that MCU is necessary for the fast mitochondrial Ca²⁺ uptake induced by large cell stimulations. However, low-amplitude mitochondrial Ca²⁺ oscillations occurring under more physiological conditions are independent of the MCU and use a different Ca²⁺ pathway.

C. elegans pharyngeal pumping provides a whole organism bio-assay to investigate anti-cholinesterase intoxication and antidotes

Inhibition of acetylcholinesterase by either organophosphates or carbamates causes anti-cholinesterase poisoning. This arises through a wide range of neurotoxic effects triggered by the overstimulation of the cholinergic receptors at synapses and neuromuscular junctions. Without intervention, this poisoning can lead to profound toxic effects, including death, and the incomplete efficacy of the current treatments, particularly for oxime-insensitive agents, provokes the need to find better antidotes. Here we show how the non-parasitic nematode Caenorhabditis elegans offers an excellent tool for investigating the acetylcholinesterase intoxication. The C. elegans neuromuscular junctions show a high degree of molecular and functional conservation with the cholinergic transmission that operates in the autonomic, central and neuromuscular synapses in mammals. In fact, the anti-cholinesterase intoxication of the worm's body wall neuromuscular junction has been unprecedented in understanding molecular determinants of cholinergic function in nematodes and other organisms. We extend the use of the model organism's feeding behaviour as a tool to investigate carbamate and organophosphate mode of action. We show that inhibition of the cholinergic-dependent rhythmic pumping of the pharyngeal muscle correlates with the inhibition of the acetylcholinesterase activity caused by aldicarb, paraoxons and DFP exposure. Further, this bio-assay allows one to address oxime dependent reversal of cholinesterase inhibition in the context of whole organism recovery. Interestingly, the recovery of the pharyngeal function after such anti-cholinesterase poisoning represents a sensitive and easily quantifiable phenotype that is indicative of the spontaneous recovery or irreversible modification of the worm acetylcholinesterase after inhibition. These observations highlight the pharynx of C. elegans as a new tractable approach to explore anti-cholinesterase intoxication and recovery with the potential to resolve critical genetic determinants of these neurotoxins' mode of action.

The connectome of the Caenorhabditis elegans pharynx

Detailed anatomical maps of individual organs and entire animals have served as invaluable entry points for ensuing dissection of their evolution, development, and function. The pharynx of the nematode Caenorhabditis elegans is a simple neuromuscular organ with a self-contained, autonomously acting nervous system, composed of 20 neurons that fall into 14 anatomically distinct types. Using serial electron micrograph (EM) reconstruction, we re-evaluate here the connectome of the pharyngeal nervous system, providing a novel and more detailed view of its structure and predicted function. Contrasting the previous classification of pharyngeal neurons into distinct inter- and motor neuron classes, we provide evidence that most pharyngeal neurons are also likely sensory neurons and most, if not all, pharyngeal neurons also classify as motor neurons. Together with the extensive cross-connectivity among pharyngeal neurons, which is more widespread than previously realized, the sensory-motor characteristics of most neurons define a shallow network architecture of the pharyngeal connectome. Network analysis reveals that the patterns of neuronal connections are organized into putative computational modules that reflect the known functional domains of the pharynx. Compared with the somatic nervous system, pharyngeal neurons both physically associate with a larger fraction of their neighbors and create synapses with a greater proportion of their neighbors. We speculate that the overall architecture of the pharyngeal nervous system may be reminiscent of the architecture of ancestral, primitive nervous systems.

Tissue-specific isoforms of the single C. elegans Ryanodine receptor gene unc-68 control specific functions

Ryanodine receptors (RyR) are essential regulators of cellular calcium homeostasis and signaling. Vertebrate genomes contain multiple RyR gene isoforms, expressed in different tissues and executing different functions. In contrast, invertebrate genomes contain a single RyR-encoding gene and it has long been proposed that different transcripts generated by alternative splicing may diversify their functions. Here, we analyze the expression and function of alternative exons in the C. elegans RyR gene unc-68. We show that specific isoform subsets are created via alternative promoters and via alternative splicing in unc-68 Divergent Region 2 (DR2), which actually corresponds to a region of high sequence variability across vertebrate isoforms. The expression of specific unc-68 alternative exons is enriched in different tissues, such as in body wall muscle, neurons and pharyngeal muscle. In order to infer the function of specific alternative promoters and alternative exons of unc-68, we selectively deleted them by CRISPR/Cas9 genome editing. We evaluated pharyngeal function, as well as locomotor function in swimming and crawling with high-content computer-assisted postural and behavioral analysis. Our data provide a comprehensive map of the pleiotropic impact of isoform-specific mutations and highlight that tissue-specific unc-68 isoforms fulfill distinct functions. As a whole, our work clarifies how the C. elegans single RyR gene unc-68 can fulfill multiple tasks through tissue-specific isoforms, and provide a solid foundation to further develop C. elegans as a model to study RyR channel functions and malfunctions.

A New Antagonist of Caenorhabditis elegans Glutamate-Activated Chloride Channels With Anthelmintic Activity

Nematode parasitosis causes significant mortality and morbidity in humans and considerable losses in livestock and domestic animals. The acquisition of resistance to current anthelmintic drugs has prompted the search for new compounds for which the free-living nematode Caenorhabditis elegans has emerged as a valuable platform. We have previously synthetized a small library of oxygenated tricyclic compounds and determined that dibenzo[b,e]oxepin-11(6H)-one (doxepinone) inhibits C. elegans motility. Because doxepinone shows potential anthelmintic activity, we explored its behavioral effects and deciphered its target site and mechanism of action on C. elegans. Doxepinone reduces swimming rate, induces paralysis, and decreases the rate of pharyngeal pumping required for feeding, indicating a marked anthelmintic activity. To identify the main drug targets, we performed an in vivo screening of selected strains carrying mutations in Cys-loop receptors involved in worm locomotion for determining resistance to doxepinone effects. A mutant strain that lacks subunit genes of the invertebrate glutamate-gated chloride channels (GluCl), which are targets of the widely used antiparasitic ivermectin (IVM), is resistant to doxepinone effects. To unravel the molecular mechanism, we measured whole-cell currents from GluClα1/β receptors expressed in mammalian cells. Glutamate elicits macroscopic currents whereas no responses are elicited by doxepinone, indicating that it is not an agonist of GluCls. Preincubation of the cell with doxepinone produces a statistically significant decrease of the decay time constant and net charge of glutamate-elicited currents, indicating that it inhibits GluCls, which contrasts to IVM molecular actions. Thus, we identify doxepinone as an attractive scaffold with promising anthelmintic activity and propose the inhibition of GluCls as a potential anthelmintic mechanism of action.

Hemiterpene compound, 3,3-dimethylallyl alcohol promotes longevity and neuroprotection in Caenorhabditis elegans

Terpenes and their derivatives have been used conventionally as potential dietary supplements to boost the nutritional value of endless food products. Several plant-based complex terpenoid and their derivatives have been reported for a wide range of medicinal and nutritional properties. However, their simple counterparts, whose production is relatively easy, sustainable, and economic from food-grade microbial sources, have not been studied yet for any such biological activities. The present study aimed to investigate the longevity-promoting property and neuromodulatory effects of 3,3-dimethylallyl alcohol (Prenol), one of the simplest forms of terpenoid and a constituent of fruit aroma, in the animal model Caenorhabditis elegans. Prenol supplementation (0.25 mM) augmented the lifespan of wild-type nematodes by 22.8% over the non-treated worms. Moreover, a suspended amyloid-β induced paralysis and reduced α-synuclein aggregation were observed in Prenol-treated worms. The lifespan extending properties of Prenol were correlated with ameliorated physiological parameters and increased stress (heat and oxidative) tolerance in C. elegans. In silico and gene-specific mutant studies showed that pro-longevity transcription factors DAF-16, HSF-1, and SKN-1 were involved in the improved lifespan and health-span of Prenol-treated worms. Transgenic green fluorescent protein-reporter gene expression analysis and relative mRNA quantification (using real-time PCR) demonstrated an increase in the expression of DAF-16, HSF-1, and SKN-1 transcription factors and their downstream target genes in Prenol-treated worms. Together, the findings suggest that small molecules, like Prenol, could be explored as a potential alternate to develop therapeutics against aging and age-related ailments.

Prototypical pacemaker neurons interact with the resident microbiota

Pacemaker neurons exert control over neuronal circuit function by their intrinsic ability to generate rhythmic bursts of action potential. Recent work has identified rhythmic gut contractions in human, mice, and hydra to be dependent on both neurons and the resident microbiota. However, little is known about the evolutionary origin of these neurons and their interaction with microbes. In this study, we identified and functionally characterized prototypical ANO/SCN/TRPM ion channel-expressing pacemaker cells in the basal metazoan Hydra by using a combination of single-cell transcriptomics, immunochemistry, and functional experiments. Unexpectedly, these prototypical pacemaker neurons express a rich set of immune-related genes mediating their interaction with the microbial environment. Furthermore, functional experiments gave a strong support to a model of the evolutionary emergence of pacemaker cells as neurons using components of innate immunity to interact with the microbial environment and ion channels to generate rhythmic contractions.

In silico and In vivo Evaluation of Oxidative Stress Inhibitors Against Parkinson's Disease using the C. elegans Model

BACKGROUND

Parkinson's disease ranks second, after Alzheimer's as the major neurodegenerative disorder, for which no cure or disease-modifying therapies exist. Ample evidence indicate that PD manifests as a result of impaired anti-oxidative machinery leading to neuronal death wherein Cullin-3 has ascended as a potential therapeutic target for diseases involving damaged anti-oxidative machinery.

OBJECTIVE

The design of target specific inhibitors for the Cullin-3 protein might be a promising strategy to increase the Nrf2 levels and to decrease the possibility of "off-target" toxic properties.

METHODS

In the present study, an integrated computational and wet lab approach was adopted to identify small molecule inhibitors for Cullin-3. The rational drug designing process comprised homology modeling and derivation of the pharmacophore for Cullin-3, virtual screening of Zinc natural compound database, molecular docking and Molecular dynamics based screening of ligand molecules. In vivo validations of an identified lead compound were conducted in the PD model of C. elegans.

RESULTS AND DISCUSSION

Our strategy yielded a potential inhibitor; (Glide score = -12.31), which was evaluated for its neuroprotective efficacy in the PD model of C. elegans. The inhibitor was able to efficiently defend against neuronal death in PD model of C. elegans and the neuroprotective effects were attributed to its anti-oxidant activities, supported by the increase in superoxide dismutase, catalase and the diminution of acetylcholinesterase and reactive oxygen species levels. In addition, the Cullin-3 inhibitor significantly restored the behavioral deficits in the transgenic C. elegans.

CONCLUSION

Taken together, these findings highlight the potential utility of Cullin-3 inhibition to block the persistent neuronal death in PD. Further studies focusing on Cullin-3 and its mechanism of action would be interesting.

The effects of Microcystis aeruginosa cells lysate containing microcystins on physiological and molecular responses in the nematode Caenorhabditis elegans

Microcystins (MCs) are potent toxins produced by environmental cyanobacterial blooms. The present study evaluated the effects of a Microcystis aeruginosa cyanobacterial lysate containing 0.1, 1, and 10 μg L^-1 MC-LR equivalent in the C. elegans Bristol N2 wild-type and the effects caused by equivalent concentrations of a MC-LR standard. The lysate was prepared from a culture of toxic strain (RST9501) originated from the Patos Lagoon Estuary (RS, Brazil). The minimal concentration necessary to cause significant effects in C. elegans under exposure to M. aeruginosa lysate or to MC-LR standard were, respectively, 10 and 0.1 μg L^-1 MC-LR equivalent for growth and 10 and 1 μg L^-1 MC-LR equivalent for fertility. Reproduction (ie, brood size) was only affected by the exposure to 10 μg L^-1 MC-LR standard and was not affected by the lysate. The nematodes that were exposed to lysate containing 1 μg L^-1 MC-LR equivalent or MC-LR were also analyzed for pharyngeal pumping and gene expression using RT-qPCR. The worms' rhythmic contractions of the pharynx were similarly affected by the lysate containing 1 μg L^-1 of MC-LR equivalent and the MC-LR standard. The MC-LR standard caused down-regulation of genes related to growth (daf-16), fertility (spe-10), and biotransformation (gst-2). This is the first study to evaluate the effects of a toxic cyanobacterial lysate using the C. elegans model. This study suggests the organism as a potential biotest to evaluate toxicity of natural waters containing M. aeruginosa cells and to environmental risk assessment associated to cyanobacterial bloom events.

Multivariate Analysis of Increase in Life Span of Caenorhabditis elegans Through Intestinal Colonization by Indigenous Probiotic Strains

The present study aimed to analyze the colonization potential of indigenous probiotic strains and to assess their effects on physiology of Caenorhabditis elegans. The protective effect of probiotics was evaluated in terms of increase in life span of the worm through colonization in the intestine. A total of 15 probiotic cultures were evaluated for their effect on mean life span, pharyngeal pumping, and normal reproduction behavior in the worms. The chemotactic behavior in terms of binary choice index was also evaluated. The adherence and colonization of the intestine of the worm by probiotics were monitored at different time intervals by enumerating the microbial population and fluorescent microscopic observations. The survival analysis-based Kaplan-Meier method indicated that the probiotic cultures increased the survival probability as compared to control strain E. coli OP50. There was no effect of feeding probiotics on physiological responses of the worm such as pharyngeal pumping and reproduction. The principal component analysis (PCA) of the results indicated Lactobacillus plantarum K90 and L. paracasei CD4 as potential probiotics with binary choice index of 0.8 as food preference of C. elegans. The strains exhibit higher adherence and colonization in the gut of worms and increased the life span by 5 days as compared to control E. coli OP50. In conclusion, feeding with probiotic cultures is effective in extending the lifespan of C. elegans; however, the colonization ability differs among the strains.

Functional analysis of epilepsy-associated variants in STXBP1/Munc18-1 using humanized Caenorhabditis elegans

OBJECTIVE

Genetic variants in STXBP1, which encodes the conserved exocytosis protein Munc18-1, are associated with a variety of infantile epilepsy syndromes. We aimed to develop an in vivo Caenorhabditis elegans model that could be used to test the pathogenicity of such variants in a cost-effective manner.

METHODS

The CRISPR/Cas9 method was used to introduce a null mutation into the unc-18 gene (the C. elegans orthologue of STXBP1), thereby creating a paralyzed worm strain. We subsequently rescued this strain with transgenes encoding the human STXBP1/Munc18-1 protein (wild-type and eight different epilepsy-associated missense variants). The resulting humanized worm strains were then analyzed via behavioral, electrophysiological, and biochemical approaches.

RESULTS

Transgenic expression of wild-type human STXBP1 protein fully rescued locomotion in both solid and liquid media to the same level as the standard wild-type worm strain, Bristol N2. Six variant strains (E59K, V84D, C180Y, R292H, L341P, R551C) exhibited impaired locomotion, whereas two (P335L, R406H) were no different from worms expressing wild-type STXBP1. Electrophysiological recordings revealed that all eight variant strains displayed less frequent and more irregular pharyngeal pumping in comparison to wild-type STXBP1-expressing strains. Four strains (V84D, C180Y, R292H, P335L) exhibited pentylenetetrazol-induced convulsions in an acute assay of seizure-like activity, in contrast to worms expressing wild-type STXBP1. No differences were seen between wild-type and variant STXBP1 strains in terms of mRNA abundance. However, STXBP1 protein levels were reduced to 20%-30% of wild-type in all variants, suggesting that the mutations result in STXBP1 protein instability.

SIGNIFICANCE

The approach described here is a cost-effective in vivo method for establishing the pathogenicity of genetic variants in STXBP1 and potentially other conserved neuronal proteins. Furthermore, the humanized strains we created could potentially be used in the future for high-throughput drug screens to identify novel therapeutics.

Ingestion of microplastics by nematodes depends on feeding strategy and buccal cavity size

Microplastics are hardly biodegradable and thus accumulate rather than decompose in the environment. Due to sedimentation processes, meiobenthic fauna is exposed to microplastics. Within the meiofauna, nematodes are a very abundant taxon and occupy an important position in benthic food webs by connecting lower and higher trophic levels. However, the key determinants of the uptake of microplastics by freshwater nematodes are still unknown. To investigate the bioaccessibility of microplastics for nematodes, we performed single- and multi-species ingestion experiments in which the ability of seven nematode species (six bacterial and one fungal feeder), diverse in their buccal cavity morphology (1.3-10.5 μm), to ingest fluorescence-labelled polystyrene (PS) beads along with their natural diet was examined. Applied beads sizes (0.5, 1.0, 3.0 and 6.0 μm), exposure time (4, 24 and 72 h) and concentration (3 × 10⁶ PS beads ml^-1 and 10⁷ PS beads ml^-1) were varied. Ingested beads were localized and quantified via fluorescence microscopy in the nematodes. In contrast to fungal-feeding nematode species with a stylet, bacterial-feeding species ingested 0.5- and 1.0-μm PS beads with up to 249 and 255 beads after 24 h, respectively. Microplastics ≥0.5 μm could only be ingested and transported into the gastrointestinal tract, if the buccal cavities were considerably (>1.3 times) larger than the beads. At concentrations of 10⁷ PS beads ml^-1 ingestion rates were influenced by exposure time and PS bead concentration. In case of a known microplastic size distribution in the environment, predictions on the potential ingestion for nematode communities can be made based on the feeding type composition and the size of their buccal cavities.

Tensin regulates pharyngeal pumping in Caenorhabditis elegans

Tensin is a focal adhesion molecule that is known to regulate cell adhesion, migration, and proliferation. Although there are four tensin homologs (TNS1, TNS2, TNS3, and CTEN/TNS4) in mammals, only one tensin gene is found in Caenorhabditis elegans. Sequence analysis suggests that Caenorhabditis elegans tensin is slightly closer aligned with human TNS1 than with other human tensins. To establish the role of TNS1 in Caenorhabditis elegans, we have generated TNS1 knockout (KO) worms by CRISPR-Cas9 and homologous recombination directed repair approaches. Lack of TNS1 does not appear to affect the development or gross morphology of the worms. Nonetheless, defecation cycles are significantly longer in TNS1 KO worms. In addition, their pharyngeal pumping rate is markedly faster, which is likely due to a shorter pump duration in the KO worms. These findings indicate that TNS1 is not required for the development and survival of Caenorhabditis elegans but point to a critical role in modulating defecation and pharyngeal pumping rates.

Interneurons Regulate Locomotion Quiescence via Cyclic Adenosine Monophosphate Signaling During Stress-Induced Sleep in Caenorhabditis elegans

Sleep is evolutionarily conserved, thus studying simple invertebrates such as Caenorhabditis elegans can provide mechanistic insight into sleep with single cell resolution. A conserved pathway regulating sleep across phylogeny involves cyclic adenosine monophosphate (cAMP), a ubiquitous second messenger that functions in neurons by activating protein kinase A. C. elegans sleep in response to cellular stress caused by environmental insults [stress-induced sleep (SIS)], a model for studying sleep during sickness. SIS is controlled by simple neural circuitry, thus allowing for cellular dissection of cAMP signaling during sleep. We employed a red-light activated adenylyl cyclase, IlaC22, to identify cells involved in SIS regulation. We found that pan-neuronal activation of IlaC22 disrupts SIS through mechanisms independent of the cAMP response element binding protein. Activating IlaC22 in the single DVA interneuron, the paired RIF interneurons, and in the CEPsh glia identified these cells as wake-promoting. Using a cAMP biosensor, epac1-camps, we found that cAMP is decreased in the RIF and DVA interneurons by neuropeptidergic signaling from the ALA neuron. Ectopic overexpression of sleep-promoting neuropeptides coded by flp-13 and flp-24, released from the ALA, reduced cAMP in the DVA and RIFs, respectively. Overexpression of the wake-promoting neuropeptides coded by pdf-1 increased cAMP levels in the RIFs. Using a combination of optogenetic manipulation and in vivo imaging of cAMP we have identified wake-promoting neurons downstream of the neuropeptidergic output of the ALA. Our data suggest that sleep- and wake-promoting neuropeptides signal to reduce and heighten cAMP levels during sleep, respectively.

Latrophilins: A Neuro-Centric View of an Evolutionary Conserved Adhesion G Protein-Coupled Receptor Subfamily

The adhesion G protein-coupled receptors latrophilins have been in the limelight for more than 20 years since their discovery as calcium-independent receptors for α-latrotoxin, a spider venom toxin with potent activity directed at neurotransmitter release from a variety of synapse types. Latrophilins are highly expressed in the nervous system. Although a substantial amount of studies has been conducted to describe the role of latrophilins in the toxin-mediated action, the recent identification of endogenous ligands for these receptors helped confirm their function as mediators of adhesion events. Here we hypothesize a role for latrophilins in inter-neuronal contacts and the formation of neuronal networks and we review the most recent information on their role in neurons. We explore molecular, cellular and behavioral aspects related to latrophilin adhesion function in mice, zebrafish, Drosophila melanogaster and Caenorhabditis elegans, in physiological and pathophysiological conditions, including autism spectrum, bipolar, attention deficit and hyperactivity and substance use disorders.