A Transparent Window into Biology: A Primer on Caenorhabditis elegans

Toxicological assessment of photoactivated tetra-cationic porphyrin molecules under white light exposure in a Caenorhabditis elegans model

Photodynamic therapy (PDT) utilizes the potential of photosensitizing substances to absorb light energy and produce reactive oxygen species. Tetra-cationic porphyrins, which have organic or coordination compounds attached to their periphery, are heterocyclic derivatives with well-described antimicrobial and antitumoral properties. This is due to their ability to produce reactive oxygen species and their photobiological properties in solution. Consequently, these molecules are promising candidates as new and more effective photosensitizers with biomedical, environmental, and other biomedical applications. Prior to human exposure, it is essential to establish the toxicological profile of these molecules using in vivo models. In this study, we used Caenorhabditis elegans, a small free-living nematode, as a model for assessing toxic effects and predicting toxicity in preclinical research. We evaluated the toxic effects of porphyrins (neutral and tetra-cationic) on nematodes under dark/light conditions. Our findings demonstrate that tetra-methylated porphyrins (3TMeP and 4TMeP) at a concentration of 3.3 µg/mL (1.36 and 0.93 µM) exhibit high toxicity (as evidenced by reduced survival, development, and locomotion) under dark conditions. Moreover, photoactivated tetra-methylated porphyrins induce higher ROS levels compared to neutral (3TPyP and 4TPyP), tetra-palladated (3PdTPyP and 4PdTPyP), and tetra-platinated (3PtTPyP and 4PtTPyP) porphyrins, which may be responsible for the observed toxic effects.

Anti-aging effects of medicinal plants and their rapid screening using the nematode Caenorhabditis elegans

BACKGROUND

Aging is the primary risk factor of most chronic diseases in humans, including cardiovascular diseases, osteoporosis and neurodegenerative diseases, which extensively damage the quality of life for elderly individuals. Aging is a multifaceted process with numerous factors affecting it. Efficient model organisms are essential for the research and development of anti-aging agents, particularly when investigating pharmacological mechanisms are needed.

PURPOSE

This review discusses the application of Caenorhabditis elegans for studying aging and its related signaling pathways, and presents an overview of studies exploring the mechanism and screening of anti-aging agents in C. elegans. Additionally, the review summarizes related clinical trials of anti-aging agents to inspire the development of new medications.

METHOD

Literature was searched, analyzed, and collected using PubMed, Web of Science, and Science Direct. The search terms used were "anti-aging", "medicinal plants", "synthetic compounds", "C. elegans", "signal pathway", etc. Several combinations of these keywords were used. Studies conducted in C. elegans or humans were included. Articles were excluded, if they were on studies conducted in silico or in vitro or could not offer effective data.

RESULTS

Four compounds mainly derived through synthesis (metformin, rapamycin, nicotinamide mononucleotide, alpha-ketoglutarate) and four active ingredients chiefly obtained from plants (resveratrol, quercetin, Astragalus polysaccharide, ginsenosides) are introduced emphatically. These compounds and active ingredients exhibit potential anti-aging effects in preclinical and clinical studies. The screening of these anti-aging agents and the investigation of their pharmacological mechanisms can benefit from the use of C. elegans.

CONCLUSION

Medicinal plants provide valuable resource for the treatment of diseases. A wide source of raw materials for the particular plant medicinal compounds having anti-aging effects meet diverse pharmaceutical requirements, such as immunomodulatory, anti-inflammation and alleviating oxidative stress. C. elegans possesses advantages in scientific research including short life cycle, small size, easy maintenance, genetic tractability and conserved biological processes related to aging. C. elegans can be used for the efficient and rapid evaluation of compounds with the potential to slow down aging.

How neurobehavior and brain development in alternative whole-organism models can contribute to prediction of developmental neurotoxicity

Developmental neurotoxicity (DNT) is not routinely evaluated in chemical risk assessment because current test paradigms for DNT require the use of mammalian models which are ethically controversial, expensive, and resource demanding. Consequently, efforts have focused on revolutionizing DNT testing through affordable novel alternative methods for risk assessment. The goal is to develop a DNT in vitro test battery amenable to high-throughput screening (HTS). Currently, the DNT in vitro test battery consists primarily of human cell-based assays because of their immediate relevance to human health. However, such cell-based assays alone are unable to capture the complexity of a developing nervous system. Whole organismal systems that qualify as 3 R (Replace, Reduce and Refine) models are urgently needed to complement cell-based DNT testing. These models can provide the necessary organismal context and be used to explore the impact of chemicals on brain function by linking molecular and/or cellular changes to behavioural readouts. The nematode Caenorhabditis elegans, the planarian Dugesia japonica, and embryos of the zebrafish Danio rerio are all suited to low-cost HTS and each has unique strengths for DNT testing. Here, we review the strengths and the complementarity of these organisms in a novel, integrative context and highlight how they can augment current cell-based assays for more comprehensive and robust DNT screening of chemicals. Considering the limitations of all in vitro test systems, we discuss how a smart combinatory use of these systems will contribute to a better human relevant risk assessment of chemicals that considers the complexity of the developing brain.

Pathogenicity of enterotoxigenic Escherichia coli in Caenorhabditis elegans as an alternative model host

Enterotoxigenic Escherichia coli (ETEC), one of the diarrheagenic E. coli, is the most common cause of diarrhea in developing country and in travelers to those areas. In this study, Caenorhabditis elegans was used as an alternative model host to evaluate ETEC infections. The ETEC strain ETEC1, which was isolated from a patient with diarrhea, possessed enterotoxins STh, LT1, and EAST1 and colonization factors CS2 and CS3. Live ETEC1 shortened the life span and body size of C. elegans in association with increased expression of enterotoxin genes and intestinal colonization. In contrast, heat-killed ETEC1 did not affect the life span of C. elegans. Caenorhabditis elegans infected with ETEC1 showed upregulated expression of genes related to insulin-like peptides and host defense responses. These results suggest that ETEC1 exhibits pathogenicity through intestinal colonization and enterotoxin production in C. elegans. This system is useful as an ETEC infection model.

The polyglutamine domain is the primary driver of seeding in huntingtin aggregation

Huntington's Disease (HD) is a fatal, neurodegenerative disease caused by aggregation of the huntingtin protein (htt) with an expanded polyglutamine (polyQ) domain into amyloid fibrils. Htt aggregation is modified by flanking sequences surrounding the polyQ domain as well as the binding of htt to lipid membranes. Upon fibrillization, htt fibrils are able to template the aggregation of monomers into fibrils in a phenomenon known as seeding, and this process appears to play a critical role in cell-to-cell spread of HD. Here, exposure of C. elegans expressing a nonpathogenic N-terminal htt fragment (15-repeat glutamine residues) to preformed htt-exon1 fibrils induced inclusion formation and resulted in decreased viability in a dose dependent manner, demonstrating that seeding can induce toxic aggregation of nonpathogenic forms of htt. To better understand this seeding process, the impact of flanking sequences adjacent to the polyQ stretch, polyQ length, and the presence of model lipid membranes on htt seeding was investigated. Htt seeding readily occurred across polyQ lengths and was independent of flanking sequence, suggesting that the structured polyQ domain within fibrils is the key contributor to the seeding phenomenon. However, the addition of lipid vesicles modified seeding efficiency in a manner suggesting that seeding primarily occurs in bulk solution and not at the membrane interface. In addition, fibrils formed in the presence of lipid membranes displayed similar seeding efficiencies. Collectively, this suggests that the polyQ domain that forms the amyloid fibril core is the main driver of seeding in htt aggregation.

Nanoplastics exacerbate Parkinson's disease symptoms in C. elegans and human cells

The increasing prevalence of nanoplastics in our environment due to the widespread use of plastics poses potential health risks that are not yet fully understood. This study examines the physiological and neurotoxic effects of these minuscule nanoplastic particles on the nematode Caenorhabditis elegans as well as on human cells. Here, we find that 25 nm polystyrene nanoplastic particles can inhibit animal growth and movement at very low concentrations, with varying effects on their surface groups. Furthermore, these nanoplastic particles not only accumulate in the digestive tract but also penetrate further into extraintestinal tissues. Such nanoplastics significantly compromise the integrity of the intestinal barrier, leading to "leaky gut" conditions and cause mitochondrial fragmentation in muscles, which possibly explains the observed movement impairments. A striking discovery was that these nanoplastics exacerbate symptoms similar to those of Parkinson's disease (PD), including dopaminergic neuronal degeneration, locomotor dysfunction, and accumulation of α-Synuclein aggregates. Importantly, our study demonstrates that the detrimental effects of nanoplastics on the aggregation of α-Synuclein extend to both C. elegans and human cell models of PD. In conclusion, our research highlights the potential health hazards linked to the physicochemical properties of nanoplastics, underlining the urgency of understanding their interactions with biological systems. ENVIRONMENTAL IMPLICATION: The escalating prevalence of nanoplastics in the environment due to widespread plastic usage raises potential health risks. Studies conducted on C. elegans indicate that even low concentrations of 25 nm polystyrene nanoplastics can impair growth and movement. These particles accumulate in the digestive system, compromising the intestinal barrier, causing "leaky gut", as well as inducing Parkinson's-like symptoms. Importantly, in both C. elegans and human cell models of Parkinson's disease, such nanoplastics penetrate tissues or cells and increase α-Synuclein aggregates. This underscores the urgent need to understand the interactions of nanoplastics with biological systems and highlights potential environmental and health consequences.

Feeding-structure morphogenesis in "rhabditid" and diplogastrid nematodes is not controlled by a conserved genetic module

Disentangling the evolution of the molecular processes and genetic networks that facilitate the emergence of morphological novelties is one of the main objectives in evolutionary developmental biology. Here, we investigated the evolutionary history of a gene regulatory network controlling the development of novel tooth-like feeding structures in diplogastrid nematodes. Focusing on NHR-1 and NHR-40, the two transcription factors that regulate the morphogenesis of these feeding structures in Pristionchus pacificus, we sought to determine whether they have a similar function in Caenorhabditis elegans, an outgroup species to the Diplogastridae which has typical "rhabditid" flaps instead of teeth. Contrary to our initial expectations, we found that they do not have a similar function. While both receptors are co-expressed in the tissues that produce the feeding structures in the two nematodes, genetic inactivation of either receptor had no impact on feeding-structure morphogenesis in C. elegans. Transcriptomic experiments revealed that NHR-1 and NHR-40 have highly species-specific regulatory targets. These results suggest two possible evolutionary scenarios: either the genetic module responsible for feeding-structure morphogenesis in Diplogastridae already existed in the last common ancestor of C. elegans and P. pacificus, and subsequently disintegrated in the former as NHR-1 and NHR-40 acquired new targets, or it evolved in conjunction with teeth in Diplogastridae. These findings indicate that feeding-structure morphogenesis is regulated by different genetic programs in P. pacificus and C. elegans, hinting at developmental systems drift during the flap-to-tooth transformation. Further research in other "rhabditid" species is needed to fully reconstruct the developmental genetic changes which facilitated the evolution of novel feeding structures in Diplogastridae.

Synthetic Communities of Gut Microbes for Basic Research and Translational Approaches in Animal Health and Nutrition

Microbes and animals have a symbiotic relationship that greatly influences nutrient uptake and animal health. This relationship can be studied using selections of microbes termed synthetic communities, or SynComs. SynComs are used in many different animal hosts, including agricultural animals, to investigate microbial interactions with nutrients and how these affect animal health. The most common host focuses for SynComs are currently mouse and human, from basic mechanistic research through to translational disease models and live biotherapeutic products (LBPs) as treatments. We discuss SynComs used in basic research models and findings that relate to human and animal health and nutrition. Translational use cases of SynComs are discussed, followed by LBPs, especially within the context of agriculture. SynComs still face challenges, such as standardization for reproducibility and contamination risks. However, the future of SynComs is hopeful, especially in the areas of genome-guided SynCom design and custom SynCom-based treatments.

Anti-aging activities of neutral and acidic polysaccharides from Polygonum multiflorum Thunb in Caenorhabditis elegans

Polygonum multiflorum Thunb (PM) is used to slow the aging process. Although polysaccharides are a major constituent of PM, their anti-aging properties have not been thoroughly investigated. Therefore, this study aimed to examine the anti-aging effects of polysaccharides extracted from PM using the Caenorhabditis elegans (C. elegans) model. Two types of water-soluble heteropolysaccharides, namely a neutral polysaccharide (RPMP-N) and an acidic polysaccharide (RPMP-A), were obtained from PM. Their structures were elucidated by various methods. The effects of these polysaccharides on the lifespan, levels of antioxidants, and activities of antioxidant-related enzymes in C. elegans were also evaluated. The results showed that RPMP-A had higher GalA content compared with RPMP-N. The average molecular weights of RPMP-N and RPMP-A were 245.30 and 28.45 kDa, respectively. RPMP-N is a α-1,4-linked dextran as the main chain, and contains a small amount of branched dextran with O-6 as the branched linkage site；RPMP-A may be a complex of α-1,4-linked dextran, HG and RG-I. Treatment with RPMP-N and RPMP-A increased the mean lifespan of C. elegans, and significantly regulated oxidative stress. RPMP-A exhibited stronger anti-aging effects compared with RPMP-N. These findings suggest that RPMP-A may be a potent antioxidant and anti-aging component that can be used for developing functional food products and effective dietary supplements.

Patterns of Genomic Diversity in a Fig-Associated Close Relative of Caenorhabditis elegans

The evolution of reproductive mode is expected to have profound impacts on the genetic composition of populations. At the same time, ecological interactions can generate close associations among species, which can in turn generate a high degree of overlap in their spatial distributions. Caenorhabditis elegans is a hermaphroditic nematode that has enabled extensive advances in developmental genetics. Caenorhabditis inopinata, the sister species of C. elegans, is a gonochoristic nematode that thrives in figs and obligately disperses on fig wasps. Here, we describe patterns of genomic diversity in C. inopinata. We performed RAD-seq on individual worms isolated from the field across three Okinawan island populations. C. inopinata is about five times more diverse than C. elegans. Additionally, C. inopinata harbors greater differences in diversity among functional genomic regions (such as between genic and intergenic sequences) than C. elegans. Conversely, C. elegans harbors greater differences in diversity between high-recombining chromosome arms and low-recombining chromosome centers than C. inopinata. FST is low among island population pairs, and clear population structure could not be easily detected among islands, suggesting frequent migration of wasps between islands. These patterns of population differentiation appear comparable with those previously reported in its fig wasp vector. These results confirm many theoretical population genetic predictions regarding the evolution of reproductive mode and suggest C. inopinata population dynamics may be driven by wasp dispersal. This work sets the stage for future evolutionary genomic studies aimed at understanding the evolution of sex as well as the evolution of ecological interactions.

Structure activity relationship and target prediction for ABX464 analogues in Caenorhabditis elegans

Global challenges with treatment failures and/or widespread resistance in parasitic worms against commercially available anthelmintics lend impetus to the development of new anthelmintics with novel mechanism(s) of action. The free-living nematode Caenorhabditis elegans is an important model organism used for drug discovery, including the screening and structure-activity investigation of new compounds, and target deconvolution. Previously, we conducted a whole-organism phenotypic screen of the 'Pandemic Response Box' (from Medicines for Malaria Venture, MMV) and identified a hit compound, called ABX464, with activity against C. elegans and a related, parasitic nematode, Haemonchus contortus. Here, we tested a series of 44 synthesized analogues to explore the pharmacophore of activity on C. elegans and revealed five compounds whose potency was similar or greater than that of ABX464, but which were not toxic to human hepatoma (HepG2) cells. Subsequently, we employed thermal proteome profiling (TPP), protein structure prediction and an in silico-docking algorithm to predict ABX464-target candidates. Taken together, the findings from this study contribute significantly to the early-stage drug discovery of a new nematocide based on ABX464. Future work is aimed at validating the ABX464-protein interactions identified here, and at assessing ABX464 and associated analogues against a panel of parasitic nematodes, towards developing a new anthelmintic with a mechanism of action that is distinct from any of the compounds currently-available commercially.

Behavioral Tests for Associative Learning in Caenorhabditis elegans

Learning is critical for survival as it provides the capacity to adapt to a changing environment. At the molecular and cellular level, learning leads to alterations within neural circuits that include synaptic rewiring, synaptic plasticity, and protein level/gene expression changes. There has been substantial progress in recent years on dissecting how learning and memory is regulated at the molecular and cellular level, including the use of compact invertebrate nervous systems as experimental models. This progress has been facilitated by the establishment of robust behavioral assays that generate a quantifiable readout of the extent to which animals learn and remember. This chapter will focus on protocols of behavioral tests for associative learning using the nematode Caenorhabditis elegans, with its unparalleled genetic tractability, compact nervous system of ~300 neurons, high level of conservation with mammalian systems, and amenability to a suite of behavioral tools and analyses. Specifically, we will provide a detailed description of the methods for two behavioral assays that model associative learning, one measuring appetitive olfactory learning and the other assaying aversive gustatory learning.

Neural mechanisms of dopamine function in learning and memory in Caenorhabditis elegans

Research into learning and memory over the past decades has revealed key neurotransmitters that regulate these processes, many of which are evolutionarily conserved across diverse species. The monoamine neurotransmitter dopamine is one example of this, with countless studies demonstrating its importance in regulating behavioural plasticity. However, dopaminergic neural networks in the mammalian brain consist of hundreds or thousands of neurons, and thus cannot be studied at the level of single neurons acting within defined neural circuits. The nematode Caenorhabditis elegans (C. elegans) has an experimentally tractable nervous system with a completely characterized synaptic connectome. This makes it an advantageous system to undertake mechanistic studies into how dopamine encodes lasting yet flexible behavioural plasticity in the nervous system. In this review, we synthesize the research to date exploring the importance of dopaminergic signalling in learning, memory formation, and forgetting, focusing on research in C. elegans. We also explore the potential for dopamine-specific fluorescent biosensors in C. elegans to visualize dopaminergic neural circuits during learning and memory formation in real-time. We propose that the use of these sensors in C. elegans, in combination with optogenetic and other light-based approaches, will further illuminate the detailed spatiotemporal requirements for encoding behavioural plasticity in an accessible experimental system. Understanding the key molecules and circuit mechanisms that regulate learning and forgetting in more compact invertebrate nervous systems may reveal new druggable targets for enhancing memory storage and delaying memory loss in bigger brains.

Development Features on the Selection of Animal Models for Teratogenic Testing

Today, the use of animal models from different species continues to represent a fundamental step in teratogenic testing, despite the increase in alternative solutions that provide an important screening to the enormous quantity of new substances that aim to enter the market every year. The maintenance of these models is due to the sharing of similar development processes with humans, and in this way they represent an important contribution to the safety in the use of the compounds tested. Furthermore, the application of advances in embryology to teratology, although hampered by the complexity of reproductive processes, continues to prove the importance of sensitivity during embryonic and fetal development to detect potential toxicity, inducing mortality/abortion and malformations.In this chapter, essential periods of development in different models are outlined, highlighting the similarities and differences between species, the advantages and disadvantages of each group, and specific sensitivities for teratogenic testing. Models can be divided into invertebrate species such as earthworms of the species Eisenia fetida/Eisenia andrei, Caenorhabditis elegans, and Drosophila melanogaster, allowing for rapid results and minor ethical concerns. Vertebrate nonmammalian species Xenopus laevis and Danio rerio are important models to assess teratogenic potential later in development with fewer ethical requirements. Finally, the mammalian species Mus musculus, Rattus norvegicus, and Oryctolagus cuniculus, phylogenetically closer to humans, are essential for the assessment of complex specialized processes, occurring later in development.Regulations for the development of toxicology tests require the use of mammalian species. Although ethical concerns and costs limit their use in large-scale screening. On the other hand, invertebrate and vertebrate nonmammalian species are increasing as alternative animal models, as these organisms combine low cost, less ethical requirements, and culture conditions compatible with large-scale screening. Their main advantage is to allow high-throughput screening in a whole-animal context, in contrast to the in vitro techniques, not dependent on the prior identification of a target. Better knowledge of the development pathways of animal models will allow to maximize human translation and reduce the number of animals used, leading to a selection of compounds with an improved safety profile and reduced time to market for new drugs.

Indian Almond (Terminalia catappa Linn.) Leaf Extract Extends Lifespan by Improving Lipid Metabolism and Antioxidant Activity Dependent on AMPK Signaling Pathway in Caenorhabditis elegans under High-Glucose-Diet Conditions

This study aimed to evaluate the antioxidant and antiaging effects of Indian almond (Terminalia catappa Linn.) leaf extract (TCE) on high-glucose (GLU)-induced obese Caenorhabditis elegans. Since TCE contains high contents of flavonoids and phenolics, strong radical scavenging activity was confirmed in vitro. The stress-resistance effect of TCE was confirmed under thermal and oxidative stress conditions at nontoxic tested concentrations (6.25, 12.5, and 25 μg/mL). GLU at 2% caused lipid and reactive oxygen species (ROS) accumulation in C. elegans, and TCE inhibited lipid and ROS accumulation under both normal and 2% GLU conditions in a concentration-dependent manner. In addition, TCE proved to be effective in prolonging the lifespan of C. elegans under normal and 2% GLU conditions. The ROS reduction effect of TCE was abolished in mutants deficient in daf-16/FOXO and skn-1/Nrf-2. In addition, the lifespan-extending effect of TCE in these two mutants disappeared. The lifespan-extending effect was abolished even in atgl-1/ATGL-deficiency mutants. The TCE effect was reduced in aak-1/AMPK-deficient mutants and completely abolished under 2% GLU conditions. Therefore, the effect of prolonging lifespan by inhibiting lipid and ROS accumulation under the high GLU conditions of TCE is considered to be the result of atgl-1, daf-16, and skn-1 being downregulated by aak-1. These results suggest that the physiological potential of TCE contributes to antiaging under metabolic disorders.

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.

TRPM2 as a conserved gatekeeper determines the vulnerability of DA neurons by mediating ROS sensing and calcium dyshomeostasis

Different dopaminergic (DA) neuronal subgroups exhibit distinct vulnerability to stress, while the underlying mechanisms are elusive. Here we report that the transient receptor potential melastatin 2 (TRPM2) channel is preferentially expressed in vulnerable DA neuronal subgroups, which correlates positively with aging in Parkinson's Disease (PD) patients. Overexpression of human TRPM2 in the DA neurons of C. elegans resulted in selective death of ADE but not CEP neurons in aged worms. Mechanistically, TRPM2 activation mediates FZO-1/CED-9-dependent mitochondrial hyperfusion and mitochondrial permeability transition (MPT), leading to ADE death. In mice, TRPM2 knockout reduced vulnerable substantia nigra pars compacta (SNc) DA neuronal death induced by stress. Moreover, the TRPM2-mediated vulnerable DA neuronal death pathway is conserved from C. elegans to toxin-treated mice model and PD patient iPSC-derived DA neurons. The vulnerable SNc DA neuronal loss is the major symptom and cause of PD, and therefore the TRPM2-mediated pathway serves as a promising therapeutic target against PD.

Cadmium-induced reproductive toxicity combined with a correlation to the oogenesis process and competing endogenous RNA networks based on a Caenorhabditis elegans model

Accumulation of the heavy metal Cadmium (Cd) in the ovaries and placenta can affect the structure and function of these organs and induce female reproductive toxicity. This toxicity may be due to Cd's similarity to estrogen and its ability to disrupt endocrine systems. However, the exact molecular mechanism by which Cd causes reproductive toxicity at the transcriptome level remains poorly understood. Hence, this study aimed to observe Cd-induced reproductive damage at the gene level, scrutinize the repercussions of Cd exposure on oogenesis, and explicate the putative pathogenesis of Cd-induced oogenesis based on Caenorhabditis elegans (C. elegans) as an in vivo model. The results showed that Cd exposure significantly decreased the number of offspring and prolonged the reproductive span of C. elegans. Cd exposure also reduced the number of cells in mitosis and the pachytene and diakinesis stages of meiosis, thereby disrupting oogenesis. Combined with transcriptional sequencing and bioinformatics analysis, a total of 3167 DEmRNAs were identified. Regarding gene expression, cul-6, mum-2, and vang-1 were found to be related to Cd-induced reproductive toxicity, and their competing endogenous RNA networks were constructed. We observed that mutations of mom-2 and vang-1 in the Wnt pathway could induce susceptibility to Cd-caused meiosis injury. In conclusion, the results indicated that Cd could impair the oogenesis of C. elegans and the Wnt pathway might serve as a protective mechanism against Cd reproductive toxicity. These findings contribute to a better understanding of the damaging effects and molecular biological mechanisms of Cd on the human reproductive system.

Use of fine capillaries for cryopreservation of Caenorhabditis elegans by vitrification

Caenorhabditis elegans is an exceptional model organism. More than twenty thousand different strains have been developed, increasing knowledge on countless topics. However, the traditional method to cryopreserve this nematode, based on slow freezing, usually reaches recovery rates of around 35% for the L1 and L2 larval stages. Here, we propose two alternative methods to cryopreserve this nematode based on vitrification that are applicable in common laboratories and allow the selective individual cryopreservation of this organism. These new methods require ultra-high warming rates, which are achieved by employing very thin capillaries as the nematode container, and a very low final concentration of cryoprotectants, which, as compared to slow freezing, reduce toxicity damage. The recovery rate was 98.5% for larvae (L1 - L4) and 84.3% for adults. Given these results, our procedures offer an alternative to cryopreserve this nematode (larvae and adults) with higher recovery rates, avoiding expensive requirements. Indeed, it only needed a container with liquid nitrogen and a warming bath for water at 37 °C. The high performance of this approach has been revealed by preserving the long-term memory and, probably, the connectome of this nematode.

Life-Cycle-Dependent Toxicities of Mono- and Bifunctional Alkylating Agents in the 3R-Compliant Model Organism C. elegans

Caenorhabditis elegans (C. elegans) is gaining recognition and importance as an organismic model for toxicity testing in line with the 3Rs principle (replace, reduce, refine). In this study, we explored the use of C. elegans to examine the toxicities of alkylating sulphur mustard analogues, specifically the monofunctional agent 2-chloroethyl-ethyl sulphide (CEES) and the bifunctional, crosslinking agent mechlorethamine (HN2). We exposed wild-type worms at different life cycle stages (from larvae L1 to adulthood day 10) to CEES or HN2 and scored their viability 24 h later. The susceptibility of C. elegans to CEES and HN2 paralleled that of human cells, with HN2 exhibiting higher toxicity than CEES, reflected in LC50 values in the high µM to low mM range. Importantly, the effects were dependent on the worms' developmental stage as well as organismic age: the highest susceptibility was observed in L1, whereas the lowest was observed in L4 worms. In adult worms, susceptibility to alkylating agents increased with advanced age, especially to HN2. To examine reproductive effects, L4 worms were exposed to CEES and HN2, and both the offspring and the percentage of unhatched eggs were assessed. Moreover, germline apoptosis was assessed by using ced-1p::GFP (MD701) worms. In contrast to concentrations that elicited low toxicities to L4 worms, CEES and HN2 were highly toxic to germline cells, manifesting as increased germline apoptosis as well as reduced offspring number and percentage of eggs hatched. Again, HN2 exhibited stronger effects than CEES. Compound specificity was also evident in toxicities to dopaminergic neurons-HN2 exposure affected expression of dopamine transporter DAT-1 (strain BY200) at lower concentrations than CEES, suggesting a higher neurotoxic effect. Mechanistically, nicotinamide adenine dinucleotide (NAD+) has been linked to mustard agent toxicities. Therefore, the NAD+-dependent system was investigated in the response to CEES and HN2 treatment. Overall NAD+ levels in worm extracts were revealed to be largely resistant to mustard exposure except for high concentrations, which lowered the NAD+ levels in L4 worms 24 h post-treatment. Interestingly, however, mutant worms lacking components of NAD+-dependent pathways involved in genome maintenance, namely pme-2, parg-2, and sirt-2.1 showed a higher and compound-specific susceptibility, indicating an active role of NAD+ in genotoxic stress response. In conclusion, the present results demonstrate that C. elegans represents an attractive model to study the toxicology of alkylating agents, which supports its use in mechanistic as well as intervention studies with major strength in the possibility to analyze toxicities at different life cycle stages.

Ancient diversity in host-parasite interaction genes in a model parasitic nematode

Host-parasite interactions exert strong selection pressures on the genomes of both host and parasite. These interactions can lead to negative frequency-dependent selection, a form of balancing selection that is hypothesised to explain the high levels of polymorphism seen in many host immune and parasite antigen loci. Here, we sequence the genomes of several individuals of Heligmosomoides bakeri, a model parasite of house mice, and Heligmosomoides polygyrus, a closely related parasite of wood mice. Although H. bakeri is commonly referred to as H. polygyrus in the literature, their genomes show levels of divergence that are consistent with at least a million years of independent evolution. The genomes of both species contain hyper-divergent haplotypes that are enriched for proteins that interact with the host immune response. Many of these haplotypes originated prior to the divergence between H. bakeri and H. polygyrus, suggesting that they have been maintained by long-term balancing selection. Together, our results suggest that the selection pressures exerted by the host immune response have played a key role in shaping patterns of genetic diversity in the genomes of parasitic nematodes.

Widespread changes in gene expression accompany body size evolution in nematodes

Body size is a fundamental trait that drives multiple evolutionary and ecological patterns. Caenorhabditis inopinata is a fig-associated nematode that is exceptionally large relative to other members of the genus, including C. elegans. We previously showed that C. inopinata is large primarily due to postembryonic cell size expansion that occurs during the larval-to-adult transition. Here, we describe gene expression patterns in C. elegans and C. inopinata throughout this developmental period to understand the transcriptional basis of body size change. We performed RNA-seq in both species across the L3, L4, and adult stages. Most genes are differentially expressed across all developmental stages, consistent with C. inopinata's divergent ecology and morphology. We also used a model comparison approach to identify orthologs with divergent dynamics across this developmental period between the two species. This included genes connected to neurons, behavior, stress response, developmental timing, and small RNA/chromatin regulation. Multiple hypodermal collagens were also observed to harbor divergent developmental dynamics across this period, and genes important for molting and body morphology were also detected. Genes associated with TGF-β signaling revealed idiosyncratic and unexpected transcriptional patterns given their role in body size regulation in C. elegans. Widespread transcriptional divergence between these species is unexpected and may be a signature of the ecological and morphological divergence of C. inopinata. Alternatively, transcriptional turnover may be the rule in the Caenorhabditis genus, indicative of widespread developmental system drift among species. This work lays the foundation for future functional genetic studies interrogating the bases of body size evolution in this group.

The stage-specific toxicity of per- and polyfluoroalkyl substances (PFAS) in nematode Caenorhabditis elegans

Per- and Polyfluoroalkyl Substances (PFAS) are a diverse class of industrial chemicals that have been used for decades in industrial and commercial applications. Due to their widespread usages, persistence in the environment, and bioaccumulation in animals and humans, great public health concerns have been raised on adverse health risks of PFAS. In this study, ten PFAS were selected according to their occurrence in different water bodies. The wild-type worms were exposed to individual PFAS at 0, 0.1, 1,10, 100, and 200 μM, and the toxic effects of PFAS on growth, development, fecundity, and behavior at different life stages were investigated using a high-throughput screening (HTS) platform. Our results showed that perfluorooctanesulfonic acid (PFOS), 1H,1H, 2H, 2H-perfluorooctanesulfonamidoacetic acid (NEtFOSAA), perfluorobutanesulfonic (PFBS), and perfluorohexanesulfonic acid (PFHxS) exhibited significant inhibitive effects on the growth in the L4 larva and later stages of worms with concentrations ranging from 0.1 to 200 μmol/L. PFOS and PFBS significantly decreased the brood size of worms across all tested concentrations (p < 0.05), and the most potent PFAS is PFOS with BMC of 0.02013 μM (BMCL, 1.6e-06 μM). During adulthood, all PFAS induced a significant reduction in motility (p < 0.01), while only PFOS can significantly induce behavior alteration at the early larvae stage. Furthermore, the adverse effects occurred in larval stages were found to be the most susceptible to the PFAS exposure. These findings provide valuable insights into the potential adverse effects associated with PFAS exposure and show the importance of considering developmental stages in toxicity assessments.

Similarities in the induction of the intracellular pathogen response in Caenorhabditis elegans and the type I interferon response in mammals

Although the type-I interferon (IFN-I) response is considered vertebrate-specific, recent findings about the Intracellular Pathogen Response (IPR) in nematode Caenorhabditis elegans indicate that there are similarities between these two transcriptional immunological programs. The IPR is induced during infection with natural intracellular fungal and viral pathogens of the intestine and promotes resistance against these pathogens. Similarly, the IFN-I response is induced by viruses and other intracellular pathogens and promotes resistance against infection. Whether the IPR and the IFN-I response evolved in a divergent or convergent manner is an unanswered and exciting question, which could be addressed by further studies of immunity against intracellular pathogens in C. elegans and other simple host organisms. Here we highlight similar roles played by RIG-I-like receptors, purine metabolism enzymes, proteotoxic stressors, and transcription factors to induce the IPR and IFN-I response, as well as the similar consequences of these defense programs on organismal development.

Signaling circuits and the apical extracellular matrix in aging: connections identified in the nematode Caenorhabditis elegans

Numerous conserved signaling pathways play critical roles in aging, including insulin/IGF-1, TGF-β, and Wnt pathways. Some of these pathways also play prominent roles in the formation and maintenance of the extracellular matrix. The nematode Caenorhabditis elegans has been an enduringly productive system for the identification of conserved mechanisms of biological aging. Recent studies in C. elegans highlight the regulatory circuits between conserved signaling pathways and the extracellular matrix, revealing a bidirectional relationship between these factors and providing a platform to address how regulation of and by the extracellular matrix can impact lifespan and organismal health during aging. These discoveries provide new opportunities for clinical advances and novel therapeutic strategies.

Grape juice reduces the effects of amyloid β aggregation phenotype and extends the longevity in Caenorhabditis elegans

OBJECTIVES

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence of aggregated amyloid-β (Aβ) peptides. Several natural compounds have been proposed against this disease and grape products are among these. However, little is known about grape juice potential. Transgenic Caenorhabditis elegans (C. elegans) strains that express human Aβ have been used as an in vivo model for AD.

METHODS

In this study, we have exposed CL2006 worms to nine different juices obtained from different cultivars.

RESULTS

Cora, Bordo, Isabel, Isabel Precoce, BRS-Magna, BRS-Rubea and BRS-Violeta juices improved the behavioral phenotype (paralysis) that is caused by Aβ aggregation in the transgenic animals at the concentrations tested and no toxic effects were found. Some juices were also able to increase the worm's lifespan. We could not attribute lifespan increase and paralysis reduction with any specific compound found in the phytochemical analysis.

DISCUSSION

Our data indicate that the rich constitution of the juices is responsible for attenuating the phenotype caused by Aβ aggregation in C. elegans.

Macrocephaly and developmental delay caused by missense variants in RAB5C

Rab GTPases are important regulators of intracellular vesicular trafficking. RAB5C is a member of the Rab GTPase family that plays an important role in the endocytic pathway, membrane protein recycling and signaling. Here we report on 12 individuals with nine different heterozygous de novo variants in RAB5C. All but one patient with missense variants (n = 9) exhibited macrocephaly, combined with mild-to-moderate developmental delay. Patients with loss of function variants (n = 2) had an apparently more severe clinical phenotype with refractory epilepsy and intellectual disability but a normal head circumference. Four missense variants were investigated experimentally. In vitro biochemical studies revealed that all four variants were damaging, resulting in increased nucleotide exchange rate, attenuated responsivity to guanine exchange factors and heterogeneous effects on interactions with effector proteins. Studies in C. elegans confirmed that all four variants were damaging in vivo and showed defects in endocytic pathway function. The variant heterozygotes displayed phenotypes that were not observed in null heterozygotes, with two shown to be through a dominant negative mechanism. Expression of the human RAB5C variants in zebrafish embryos resulted in defective development, further underscoring the damaging effects of the RAB5C variants. Our combined bioinformatic, in vitro and in vivo experimental studies and clinical data support the association of RAB5C missense variants with a neurodevelopmental disorder characterized by macrocephaly and mild-to-moderate developmental delay through disruption of the endocytic pathway.

Effect of altered production and storage of dopamine on development and behavior in C. elegans

The nematode, Caenorhabditis elegans, is an advantageous model for studying developmental toxicology due to its homology to humans and well-defined developmental stages. Similarly to humans, C. elegans utilize dopamine as a neurotransmitter to regulate motor behavior. We have previously reported behavioral deficits in a genetic model of C. elegans (OK411) that lack the neurotransmitter transporter necessary for packaging dopamine into synaptic vesicles. Anecdotally, we observed these C. elegans appeared to have a smaller body size, which is supported by prior studies that observed a larger body size in C. elegans that lack the enzyme that catalyzes dopamine synthesis, suggesting a complex regulatory system in which dopamine mediates body size in C. elegans. However, the question of whether body size abnormalities apparent in C. elegans with disruptions to their dopamine system are developmental or purely based on body size remains unanswered. Here, we present data characterizing the effect of gene mutations in dopamine-related proteins on body size, development, and behavior. We analyzed C. elegans that lack the ability to sequester dopamine (OK411), that overproduce dopamine (UA57), and a novel strain (MBIA) generated through crossing OK411 and UA57, which lacks the ability to sequester dopamine into vesicles and additionally endogenously overproduces dopamine. This novel strain was generated to address the hypothesis that an endogenous increase in production of dopamine can rescue deficits caused by a lack of vesicular dopamine sequestration. Compared to wild type, OK411 have shorter body lengths and behavioral deficits in early life stages. In contrast, the MBIA strain have similar body lengths to wild-type by early adulthood and display similar behavior to wild-type by early adulthood. Our data suggests that endogenously increasing the production of dopamine is able to mitigate deficits in C. elegans lacking the ability to package dopamine into synaptic vesicles. These results provide evidence that the dopamine system impacts development, growth, and reproduction in C. elegans.

Ethyl caffeate attefnuates Aβ-induced toxicity in Caenorhabditis elegans AD models via the insulin/insulin-like growth factor-1 signaling pathway

The pathogenesis of Alzheimer's disease (AD), a multifactorial progressive neurodegenerative disease associated with aging, is unclear. Ethyl caffeate is a plant polyphenol that has been reported to have neuroprotective effects, but the mechanisms by which it acts are unclear. In this study, for the first time, we investigated the molecular mechanism of its anti-AD properties using the Caernorhabditis elegans model. The results of our experiments showed that ethyl caffeate delayed the paralysis symptoms of CL4176 to a different extent and reduced the exogenous 5-hydroxytryptophan-induced paralysis phenotype. Further studies revealed that ethyl caffeate lowered Aβ plaques and depressed the expression of Aβ monomers and oligomers, but did not influence the mRNA levels of Aβ. Moreover, it was able to bring paraquat-induced ROS levels down to near-standard conditions. Real-time quantitative PCR experiment showed a significant upregulation of the transcript abundance of daf-16, skn-1 and hsf-1, key factors associated with the insulin/insulin-like growth factor 1 (IGF-1) signaling pathway (IIS), and their downstream genes sod-3, gst-4 and hsp-16.2. It was further shown that ethyl caffeate activated the translocation of DAF-16 and SKN-1 from the cytoplasm to the nucleus and enhanced the expression of sod-3::GFP, gst-4::GFP and hsp-16.2::GFP in transgenic nematodes. This meant that the protection against Aβ toxicity by ethyl caffeate may be partly through the IIS signaling pathway. In addition, ethyl caffeate suppressed the aggregation of polyglutamine proteins in AM141, which indicated a potential protective effect against neurodegenerative diseases based on abnormal folding and aggregation of amyloid proteins. Taken together, ethyl caffeate is expected to develop as a potential drug for the management of AD.

Pathogen infection induces specific transgenerational modifications to gene expression and fitness in Caenorhabditis elegans

How pathogen infection in a parental generation affects response in future generations to the same pathogen via epigenetic modifications has been the topic of recent studies. These studies focused on changes attributed to transgenerational epigenetic inheritance and how these changes cause an observable difference in behavior or immune response in a population. However, we questioned if pathogen infection causes hidden epigenetic changes to fitness that are not observable at the population level. Using the nematode Caenorhabditis elegans as a model organism, we examined the generation-to-generation differences in survival of both an unexposed and primed lineage of animals against a human opportunistic pathogen Salmonella enterica. We discovered that training a lineage of C. elegans against a specific pathogen does not cause a significant change to overall survival, but rather narrows survival variability between generations. Quantification of gene expression revealed reduced variation of a specific member of the TFEB lipophagic pathway. We also provided the first report of a repeating pattern of survival times over the course of 12 generations in the control lineage of C. elegans. This repeating pattern indicates that the variability in survival between generations of the control lineage is not random but may be regulated by unknown mechanisms. Overall, our study indicates that pathogen infection can cause specific phenotypic changes due to epigenetic modifications, and a possible system of epigenetic regulation between generations.

Periodic ethanol supply as a path toward unlimited lifespan of Caenorhabditis elegans dauer larvae

The dauer larva is a specialized stage of worm development optimized for survival under harsh conditions that have been used as a model for stress resistance, metabolic adaptations, and longevity. Recent findings suggest that the dauer larva of Caenorhabditis elegans may utilize external ethanol as an energy source to extend their lifespan. It was shown that while ethanol may serve as an effectively infinite source of energy, some toxic compounds accumulating as byproducts of its metabolism may lead to the damage of mitochondria and thus limit the lifespan of larvae. A minimal mathematical model was proposed to explain the connection between the lifespan of a dauer larva and its ethanol metabolism. To explore theoretically if it is possible to extend even further the lifespan of dauer larvae, we incorporated two natural mechanisms describing the recovery of damaged mitochondria and elimination of toxic compounds, which were previously omitted in the model. Numerical simulations of the revised model suggested that while the ethanol concentration is constant, the lifespan still stays limited. However, if ethanol is supplied periodically, with a suitable frequency and amplitude, the dauer could survive as long as we observe the system. Analytical methods further help to explain how feeding frequency and amplitude affect lifespan extension. Based on the comparison of the model with experimental data for fixed ethanol concentration, we proposed the range of feeding protocols that could lead to even longer dauer survival and it can be tested experimentally.

Comparative Analysis of Muscle Atrophy During Spaceflight, Nutritional Deficiency and Disuse in the Nematode Caenorhabditis elegans

While spaceflight is becoming more common than before, the hazards spaceflight and space microgravity pose to the human body remain relatively unexplored. Astronauts experience muscle atrophy after spaceflight, but the exact reasons for this and solutions are unknown. Here, we take advantage of the nematode C. elegans to understand the effects of space microgravity on worm body wall muscle. We found that space microgravity induces muscle atrophy in C. elegans from two independent spaceflight missions. As a comparison to spaceflight-induced muscle atrophy, we assessed the effects of acute nutritional deprivation and muscle disuse on C. elegans muscle cells. We found that these two factors also induce muscle atrophy in the nematode. Finally, we identified clp-4, which encodes a calpain protease that promotes muscle atrophy. Mutants of clp-4 suppress starvation-induced muscle atrophy. Such comparative analyses of different factors causing muscle atrophy in C. elegans could provide a way to identify novel genetic factors regulating space microgravity-induced muscle atrophy.

LINKIN-associated proteins necessary for tissue integrity during collective cell migration

Cell adhesion plays essential roles in almost every aspect of metazoan biology. LINKIN (Human: ITFG1, Caenorhabditis elegans: lnkn-1) is a conserved transmembrane protein that has been identified to be necessary for tissue integrity during migration. In C. elegans, loss of lnkn-1 results in the detachment of the lead migratory cell from the rest of the developing male gonad. Previously, three interactors of ITFG1/lnkn-1 - RUVBL1/ruvb-1, RUVBL2/ruvb-2, and alpha-tubulin - were identified by immunoprecipitation-mass spectrometry (IP-MS) analysis using human HEK293T cells and then validated in the nematode male gonad. The ITFG1-RUVBL1 interaction has since been independently validated in a breast cancer cell line model that also implicates the involvement of the pair in metastasis. Here, we showed that epitope-tagged ITFG1 localized to the cell surface of MDA-MB-231 breast cancer cells. Using IP-MS analysis, we identified a new list of potential interactors of ITFG1. Loss-of-function analysis of their C. elegans orthologs found that three of the interactors - ATP9A/tat-5, NME1/ndk-1, and ANAPC2/apc-2 - displayed migratory detachment phenotypes similar to that of lnkn-1. Taken together with the other genes whose reduction-of-function phenotype is similar to that of lnkn-1 (notably cohesion and condensin), suggests the involvement of membrane remodeling and chromosome biology in LINKIN-dependent cell adhesion and supports the hypothesis for a structural role of chromosomes in post-mitotic cells.

Genomic diversity landscapes in outcrossing and selfing Caenorhabditis nematodes

Caenorhabditis nematodes form an excellent model for studying how the mode of reproduction affects genetic diversity, as some species reproduce via outcrossing whereas others can self-fertilize. Currently, chromosome-level patterns of diversity and recombination are only available for self-reproducing Caenorhabditis, making the generality of genomic patterns across the genus unclear given the profound potential influence of reproductive mode. Here we present a whole-genome diversity landscape, coupled with a new genetic map, for the outcrossing nematode C. remanei. We demonstrate that the genomic distribution of recombination in C. remanei, like the model nematode C. elegans, shows high recombination rates on chromosome arms and low rates toward the central regions. Patterns of genetic variation across the genome are also similar between these species, but differ dramatically in scale, being tenfold greater for C. remanei. Historical reconstructions of variation in effective population size over the past million generations echo this difference in polymorphism. Evolutionary simulations demonstrate how selection, recombination, mutation, and selfing shape variation along the genome, and that multiple drivers can produce patterns similar to those observed in natural populations. The results illustrate how genome organization and selection play a crucial role in shaping the genomic pattern of diversity whereas demographic processes scale the level of diversity across the genome as a whole.

The diverse family of Cys-loop receptors in Caenorhabditis elegans: insights from electrophysiological studies

Cys-loop receptors integrate a large family of pentameric ligand-gated ion channels that mediate fast ionotropic responses in vertebrates and invertebrates. Their vital role in converting neurotransmitter recognition into an electrical impulse makes these receptors essential for a great variety of physiological processes. In vertebrates, the Cys-loop receptor family includes the cation-selective channels, nicotinic acetylcholine and 5-hydroxytryptamine type 3 receptors, and the anion-selective channels, GABAA and glycine receptors, whereas in invertebrates, the repertoire is significantly larger. The free-living nematode Caenorhabditis elegans has the largest known Cys-loop receptor family as well as unique receptors that are absent in vertebrates and constitute attractive targets for anthelmintic drugs. Given the large number and variety of Cys-loop receptor subunits and the multiple possible ways of subunit assembly, C. elegans offers a large diversity of receptors although only a limited number of them have been characterized to date. C. elegans has emerged as a powerful model for the study of the nervous system and human diseases as well as a model for antiparasitic drug discovery. This nematode has also shown promise in the pharmaceutical industry search for new therapeutic compounds. C. elegans is therefore a powerful model organism to explore the biology and pharmacology of Cys-loop receptors and their potential as targets for novel therapeutic interventions. In this review, we provide a comprehensive overview of what is known about the function of C. elegans Cys-loop receptors from an electrophysiological perspective.

Caenorhabditis elegans in microgravity: An omics perspective

The application of omics to study Caenorhabditis elegans (C. elegans) in the context of spaceflight is increasing, illuminating the wide-ranging biological impacts of spaceflight on physiology. In this review, we highlight the application of omics, including transcriptomics, genomics, proteomics, multi-omics, and integrated omics in the study of spaceflown C. elegans, and discuss the impact, use, and future direction of this branch of research. We highlight the variety of molecular alterations that occur in response to spaceflight, most notably changes in metabolic and neuromuscular gene regulation. These transcriptional features are reproducible and evident across many spaceflown species (e.g., mice and astronauts), supporting the use of C. elegans as a model organism to study spaceflight physiology with translational capital. Integrating tissue-specific, spatial, and multi-omics approaches, which quantitatively link molecular responses to phenotypic adaptations, will facilitate the identification of candidate regulatory molecules for therapeutic intervention and thus represents the next frontiers in C. elegans space omics research.

Notes from the Underground: Heme Homeostasis in C. elegans

Heme is an iron-containing tetrapyrrole that plays a critical role in various biological processes, including oxygen transport, electron transport, signal transduction, and catalysis. However, free heme is hydrophobic and potentially toxic to cells. Organisms have evolved specific pathways to safely transport this essential but toxic macrocycle within and between cells. The bacterivorous soil-dwelling nematode Caenorhabditis elegans is a powerful animal model for studying heme-trafficking pathways, as it lacks the ability to synthesize heme but instead relies on specialized trafficking pathways to acquire, distribute, and utilize heme. Over the past 15 years, studies on this microscopic animal have led to the identification of a number of heme-trafficking proteins, with corresponding functional homologs in vertebrates. In this review, we provide a comprehensive overview of the heme-trafficking proteins identified in C. elegans and their corresponding homologs in related organisms.

Integrated Analysis of Transcriptome and Metabolome Provides Insight into Camellia oleifera Oil Alleviating Fat Accumulation in High-Fat Caenorhabditis elegans

Camellia oil (CO) is a high medicinal and nutritional value edible oil. However, its ability to alleviate fat accumulation in high-fat Caenorhabditis elegans has not been well elucidated. Therefore, this study aimed to investigate the effect of CO on fat accumulation in high-fat C. elegans via transcriptome and metabolome analysis. The results showed that CO significantly reduced fat accumulation in high-fat C. elegans by 10.34% (Oil Red O method) and 11.54% (TG content method), respectively. Furthermore, CO primarily altered the transcription levels of genes involved in longevity regulating pathway. Specifically, CO decreased lipid storage in high-fat C. elegans by inhibiting fat synthesis. In addition, CO supplementation modulated the abundance of metabolic biomarkers related to pyrimidine metabolism and riboflavin metabolism. The integrated transcriptome and metabolome analyses indicated that CO supplementation could alleviate fat accumulation in high-fat C. elegans by regulating retinol metabolism, drug metabolism-cytochrome P450, metabolism of xenobiotics by cytochrome P450, ascorbate and aldarate metabolism, and pentose and glucuronate interconversions. Overall, these findings highlight the potential health benefits of CO that could potentially be used as a functional edible oil.

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.

Evolutionary Change in Gut Specification in Caenorhabditis Centers on the GATA Factor ELT-3 in an Example of Developmental System Drift

Cells in a developing animal embryo become specified by the activation of cell-type-specific gene regulatory networks. The network that specifies the gut in the nematode Caenorhabditis elegans has been the subject of study for more than two decades. In this network, the maternal factors SKN-1/Nrf and POP-1/TCF activate a zygotic GATA factor cascade consisting of the regulators MED-1,2 → END-1,3 → ELT-2,7, leading to the specification of the gut in early embryos. Paradoxically, the MED, END, and ELT-7 regulators are present only in species closely related to C. elegans, raising the question of how the gut can be specified without them. Recent work found that ELT-3, a GATA factor without an endodermal role in C. elegans, acts in a simpler ELT-3 → ELT-2 network to specify gut in more distant species. The simpler ELT-3 → ELT-2 network may thus represent an ancestral pathway. In this review, we describe the elucidation of the gut specification network in C. elegans and related species and propose a model by which the more complex network might have formed. Because the evolution of this network occurred without a change in phenotype, it is an example of the phenomenon of Developmental System Drift.

Difference in Intestine Content of Caenorhabditis elegans When Fed on Non-Pathogenic or Pathogenic Bacteria

We investigated the bacterial food digestion and accumulation in wild-type adult Caenorhabditis elegans (C. elegans) worms that have fed on either non-pathogenic RFP-expressing Escherichia coli (E. coli) OP50 or pathogenic-RFP-expressing Pseudomonas aeruginosa (P. aeruginosa) PAO1 during the first 4 days of adulthood. Once the worms had completed their planned feeding cycles, they were loaded on microfluidic chips, where they were fixed to allow high-resolution z-stack fluorescence imaging of their intestines utilizing a Spinning Disk Confocal Microscope (SDCM) equipped with a high-resolution oil-immersion objective (60×). IMARIS software was used to visualize and analyze the obtained images, resulting in the production of three-dimensional constructs of the intestinal bacterial load. We discovered two distinct patterns for the bacteria-derived fluorescence signal in the intestine: (i) individual fluorescent spots, originating from intact bacteria, were present in the fluorescent E. coli-OP50-fed worms, and (ii) individual fluorescent spots (originating from intact bacteria) were dispersed in large regions of diffuse fluorescence (RDF), originating from disrupted bacteria, in fluorescent P. aeruginosa-PAO1-fed worms. We performed a semi-automated single-worm-resolution quantitative analysis of the intestinal bacterial load, which showed that the intestinal bacterial load generally increases with age of the worms, but more rapidly for the fluorescent P. aeruginosa-PAO1-fed worms.

A robotic system for automated genetic manipulation and analysis of Caenorhabditis elegans

The nematode Caenorhabditis elegans is one of the most widely studied organisms in biology due to its small size, rapid life cycle, and manipulable genetics. Research with C. elegans depends on labor-intensive and time-consuming manual procedures, imposing a major bottleneck for many studies, especially for those involving large numbers of animals. Here, we describe a general-purpose tool, WormPicker, a robotic system capable of performing complex genetic manipulations and other tasks by imaging, phenotyping, and transferring C. elegans on standard agar media. Our system uses a motorized stage to move an imaging system and a robotic arm over an array of agar plates. Machine vision tools identify animals and assay developmental stage, morphology, sex, expression of fluorescent reporters, and other phenotypes. Based on the results of these assays, the robotic arm selectively transfers individual animals using an electrically self-sterilized wire loop, with the aid of machine vision and electrical capacitance sensing. Automated C. elegans manipulation shows reliability and throughput comparable with standard manual methods. We developed software to enable the system to autonomously carry out complex protocols. To validate the effectiveness and versatility of our methods, we used the system to perform a collection of common C. elegans procedures, including genetic crossing, genetic mapping, and genomic integration of a transgene. Our robotic system will accelerate C. elegans research and open possibilities for performing genetic and pharmacological screens that would be impractical using manual methods.

Learning the Biochemical Basis of Axonal Guidance: Using Caenorhabditis elegans as a Model

AIM

Experimental models are a powerful aid in visualizing molecular phenomena. This work reports how the worm Caenorhabditis elegans (C. elegans) can be effectively explored for students to learn how molecular cues dramatically condition axonal guidance and define nervous system structure and behavior at the organism level. Summary of work: A loosely oriented observational activity preceded detailed discussions on molecules implied in axonal migration. C. elegans mutants were used to introduce second-year medical students to the deleterious effects of gene malfunctioning in neuron response to extracellular biochemical cues and to establish links between molecular function, nervous system structure, and animal behavior. Students observed C. elegans cultures and associated animal behavior alterations with the lack of function of specific axon guidance molecules (the soluble cue netrin/UNC-6 or two receptors, DCC/UNC-40 and UNC-5H). Microscopical observations of these strains, in combination with pan-neuronal GFP expression, allowed optimal visualization of severely affected neurons. Once the list of mutated genes in each strain was displayed, students could also relate abnormal patterns in axon migration/ventral and dorsal nerve cord neuron formation in C. elegans with mutated molecular components homologous to those in humans.

SUMMARY OF RESULTS

Students rated the importance and effectiveness of the activity very highly. Ninety-three percent found it helpful to grasp human axonal migration, and all students were surprised with the power of the model in helping to visualize the phenomenon.

Age-associated anatomical and physiological alterations in Caenorhabditis elegans

Since its introduction by Sydney Brenner, Caenorhabditis elegans has become a widely studied organism. Given its highly significant properties, including transparency, short lifespan, self-fertilization, high reproductive yield and ease in manipulation and genetic modifications, the nematode has contributed to the elucidation of several fundamental aspects of biology, such as development and ageing. Moreover, it has been extensively used as a platform for the modelling of ageing-associated human disorders, especially those related to neurodegeneration. The use of C. elegans for such purposes requires, and at the same time promotes the investigation of its normal ageing process. In this review we aim to summarize the major organismal alterations during normal worm ageing, in terms of morphology and functionality.

Multi-generation reproductive toxicity of RDX and the involved signal pathways in Caenorhabditis elegans

As one of the most frequently used explosives, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) can cause persistent pollution in the environment, leading to the potential ecological threat crossing the generations. In this study, we employed Caenorhabditis elegans to explore the toxic effects of RDX on the parental and offspring worms and the involved signaling pathways. Exposure up to 1000 ng/mL of RDX produced a significant increase in reactive oxygen species (ROS) production, germ cell apoptosis, and decrease in eggs laid. Various mutants were used to demonstrate the RDX-induced apoptosis signaling pathway, and the metabolism of RDX in the nematodes was found related to cytochrome P450 and GST through RNA sequencing. Exposure of parental worms to RDX produced significant reproductive toxicity in F1 and F2, but was recovered in F3 and F4. The transgenerational effects were associated with the decreased expression of met-2, spr-5, and set-2. Our findings revealed the signaling pathways related to the reproductive toxicity caused by RDX in C. elegans and their future generations, which provided the basis for further exploration of the ecological risks of energetic compounds in the environment.

An Undergraduate Laboratory Series Using C. elegans That Prepares Students for Independent Inquiry

Undergraduate neuroscience laboratories provide valuable opportunities for students to learn about neurobiological systems through active learning. Caenorhabditis elegans (C. elegans) is a valuable model for teaching students how to use a reductionist approach to neuroscientific inquiry. This series of lab modules trains students to utilize foundational laboratory techniques such as worm handling and maintenance, fluorescence imaging, behavioral assays, and Western blot. Upon completing this series of laboratory exercises, students are well prepared to engage in independent research projects using these research techniques. As supported by student survey results, this series of C. elegans laboratory exercises leads to the development of essential research skills, which students may be able to apply to a wide range of future scientific endeavors.

Microfluidic-Assisted Caenorhabditis elegans Sorting: Current Status and Future Prospects

Caenorhabditis elegans (C. elegans) has been a popular model organism for several decades since its first discovery of the huge research potential for modeling human diseases and genetics. Sorting is an important means of providing stage- or age-synchronized worm populations for many worm-based bioassays. However, conventional manual techniques for C. elegans sorting are tedious and inefficient, and commercial complex object parametric analyzer and sorter is too expensive and bulky for most laboratories. Recently, the development of lab-on-a-chip (microfluidics) technology has greatly facilitated C. elegans studies where large numbers of synchronized worm populations are required and advances of new designs, mechanisms, and automation algorithms. Most previous reviews have focused on the development of microfluidic devices but lacked the summaries and discussion of the biological research demands of C. elegans, and are hard to read for worm researchers. We aim to comprehensively review the up-to-date microfluidic-assisted C. elegans sorting developments from several angles to suit different background researchers, i.e., biologists and engineers. First, we highlighted the microfluidic C. elegans sorting devices' advantages and limitations compared to the conventional commercialized worm sorting tools. Second, to benefit the engineers, we reviewed the current devices from the perspectives of active or passive sorting, sorting strategies, target populations, and sorting criteria. Third, to benefit the biologists, we reviewed the contributions of sorting to biological research. We expect, by providing this comprehensive review, that each researcher from this multidisciplinary community can effectively find the needed information and, in turn, facilitate future research.

Translational Neuroscience Approaches to Understanding Autism

While autism spectrum disorder affects nearly 2% of children in the United States, little is known with certainty concerning the etiologies and brain systems involved. This is due, in part, to the substantial heterogeneity in the presentation of the core symptoms of autism as well as the great number of co-occurring conditions that are common in autistic individuals. Understanding the neurobiology of autism is further hampered by the limited availability of postmortem brain tissue to determine the cellular and molecular alterations that take place in the autistic brain. Animal models therefore provide great translational value in helping to define the neural systems that constitute the social brain and mediate repetitive behaviors or interests. If they are based on genetic or environmental factors that contribute to autism, organisms from flies to nonhuman primates may serve as models of the neural structure or function of the autistic brain. Ultimately, successful models can also be employed to test the safety and effectiveness of potential therapeutics. This is an overview of the major animal species that are currently used as models of autism, including an appraisal of the advantages and limitations of each.

Saccharomyces cerevisiae: a patulin degradation candidate both in vitro and in vivo

Patulin is one of the mycotoxins that exists in abundance in fruits and derivative products and is easily exposed in daily life, leading to various toxicities such as genotoxicity, teratogenicity, immunotoxicity, and carcinogenicity in the human body, while the efficient removal or degradation measures are still in urgent demand. In this work, Saccharomyces cerevisiae, a natural yeast with both patulin degradation and intestine damage protection abilities, was first applied to prevent and decrease the hazard after patulin intake. In vitro, Saccharomyces cerevisiae KD (S. cerevisiae KD) could efficiently degrade patulin at high concentrations. In a Canenorhabditis elegans (C. elegans) model fed on S. cerevisiae KD, locomotion, oxidative stress, patulin residual, intestine damage, and gene expression were investigated after exposure to 50 μg mL^-1 patulin. The results demonstrated that S. cerevisiae KD could efficiently degrade patulin, as well as weaken the oxidative stress and intestinal damage caused by patulin. Moreover, S. cerevisiae KD could regulate the gene expression levels of daf-2 and daf-16 through the IGF-1 signaling pathway to control the ROS level and glutathione (GSH) content, thus decreasing intestinal damage. In summary, this work uncovers the outstanding characteristic of an edible probiotic S. cerevisiae KD in patulin degradation and biotoxicity alleviation and provides enlightenment toward solving the hazards caused by the accumulation of patulin.