Biology subjects

Fox, B. W.

Publications and source records attributed to Fox, B. W..

9 recordsLinked to original sources

bioRxiv2025

Serotonergic signaling governs C. elegans sensory response to conflicting olfactory stimuli

Neural circuits that consolidate sensory cues are essential for neurological functioning. Neural circuits that perform sensory integration can vary greatly because the sensory processing regions of the brain employ various neural motifs. Here, we investigate a neural circuit that mediates the response to conflicting olfactory stimuli in C. elegans. We concurrently expose animals to an aversive dispersal pheromone, osas#9, and an attractive bacterial extract. While worms usually avoid osas#9 alone, they suppress this avoidance behavior in the presence of a bacterial extract. Loss-of-function mutants and cell-specific rescues reveal that serotonergic signaling from the ADF neuron is essential for bacterial extract-induced osas#9 avoidance attenuation. The inhibitory serotonin receptor, MOD-1, which is widely expressed on interneurons and motor neurons, is required for this sensory integration, suggesting that serotonin acts in an inhibitory manner. By performing calcium imaging on the ADF neurons in synaptic signaling (unc-13) and peptidergic (unc-31) signaling mutant backgrounds, we show that the ADF neurons require input from other neurons, likely the ASK neurons, to respond to food extracts. We reveal a cue integration neural circuit in which serotonergic signaling at the sensory neuron level silences an aversive neural signal. SignificanceAnimals use sensory cues to make behavioral choices and sometimes, these cues convey opposite information. The nervous system consolidates competing sensory cues to create a coherent response to external stimuli. The neural circuits that govern this process are important, and still largely unknown. We use C. elegans, a soil-dwelling nematode, to uncover a neural circuit governing the consolidation of competing cues by concurrently exposing worms to positive and negative stimuli . We find that the neurotransmitter serotonin can suppress aversive neural signals created by negative stimuli. These results show the important neurological role that serotonin plays in modulating neural signals.

neuroscience↗

bioRxiv2024

Naturally occurring variation in a cytochrome P450 modifies thiabendazole responses independent of beta-tubulin

Widespread anthelmintic resistance has complicated the management of parasitic nematodes. Resistance to the benzimidazole (BZ) drug class is nearly ubiquitous in many species and is associated with mutations in beta-tubulin genes. However, mutations in beta-tubulin alone do not fully explain all BZ resistance. We performed a genome-wide association study using a genetically diverse panel of Caenorhabditis elegans strains to identify loci that contribute to resistance to the BZ drug thiabendazole (TBZ). We identified a quantitative trait locus (QTL) on chromosome V independent of all beta-tubulin genes and overlapping with two promising candidate genes, the cytochrome P450 gene cyp-35d1 and the nuclear hormone receptor nhr-176, identified by another mapping technique. Both genes were previously demonstrated to play a role in TBZ metabolism. NHR-176 binds TBZ and induces the expression of CYP-35D1, which metabolizes TBZ. We generated single gene deletions of nhr-176 and cyp-35d1 and found that both genes play a role in TBZ response. A predicted high-impact lysine-to-glutamate substitution at position 267 (K267E) in CYP-35D1 was identified in a sensitive parental strain, and reciprocal allele replacement strains in both genetic backgrounds were used to show that the lysine allele conferred increased TBZ resistance. Using competitive fitness assays, we found that neither allele is deleterious, but the lysine allele is selected in the presence of TBZ. Additionally, we found that the lysine allele significantly increased the rate of TBZ metabolism compared to the glutamate allele. Moreover, yeast expression assays showed that the lysine version of CYP-35D1 had twice the enzymatic activity of the glutamate allele. To connect our results to parasitic nematodes, we analyzed four Haemonchus contortus cytochrome P450 orthologs but did not find variation at the 267 position in fenbendazole-resistant populations. Overall, we confirmed that variation in this cytochrome P450 gene is the first locus independent of beta-tubulin to play a role in BZ resistance. Author SummaryBenzimidazoles (BZs) are the most common drug class used to control parasitic nematodes, but because of overuse, resistance is widespread. The known genetic causes of BZ resistance are associated with mutations in beta-tubulin and are the most well understood of any anthelmintic class. However, BZ response varies significantly and differential levels of resistance likely require mutations in genes independent of beta-tubulin. We used the free-living model nematode Caenorhabditis elegans to identify and characterize a novel cytochrome P450 gene, cyp-35d1, associated with natural resistance to the BZ drug thiabendazole (TBZ). We demonstrated that a lysine at position 267 confers TBZ resistance and is selected over multiple generations after TBZ treatment. This allele significantly increased the rate of TBZ metabolism in both C. elegans and yeast. In conclusion, we have characterized the role of variation in a cytochrome P450 that contributes to TBZ resistance, independent of mutations in beta-tubulin.

genetics↗

bioRxiv2023

ATP-release pannexin channels are gated by lysophospholipids

In addition to its role as cellular energy currency, adenosine triphosphate (ATP) serves as an extracellular messenger that mediates diverse cell-to-cell communication. Compelling evidence supports that ATP is released from cells through pannexins, a family of membrane proteins that form heptameric large-pore channels. However, the activation mechanisms that trigger ATP release by pannexins remain poorly understood. Here, we discover lysophospholipids as endogenous pannexin activators, using activity-guided fractionation of mouse tissue extracts combined with untargeted metabolomics and electrophysiology. We show that lysophospholipids directly and reversibly activate pannexins in the absence of other proteins. Secretomics experiments reveal that lysophospholipid-activated pannexin 1 leads to the release of not only ATP but also other signaling metabolites, such as 5-methylthioadenosine, which is important for immunomodulation. We also demonstrate that lysophospholipids activate endogenous pannexin 1 in human monocytes, leading to the release of IL-1{beta} through inflammasome activation. Our results provide a connection between lipid metabolism and purinergic signaling, both of which play major roles in immune responses.

biophysics↗

bioRxiv2022

Natural genetic variation in the pheromone production of C. elegans

From bacterial quorum sensing to human language, communication is essential for social interactions. Nematodes produce and sense pheromones to communicate among individuals and respond to environmental changes. These signals are encoded by different types and mixtures of ascarosides, whose modular structures further enhance the diversity of this nematode pheromone language. Interspecific and intraspecific differences in this ascaroside pheromone language have been described previously, but the genetic basis and molecular mechanisms underlying the variation remain largely unknown. Here, we analyzed natural variation in the production of 44 ascarosides across 95 wild Caenorhabditis elegans strains using high-performance liquid chromatography coupled to high-resolution mass spectrometry (HPLC-HRMS). By cross-analyzing genomes and exo-metabolomes of wild strains, we discovered quantitative trait loci (QTL) that underlie the natural differences in pheromone bouquet composition. Fine mapping of the QTL further uncovered associations between mitochondrial metabolism and pheromone production. Our findings demonstrate how natural genetic variation in core metabolic pathways can affect the production of social signals.

evolutionary biology↗

bioRxiv2022

Vitamin B12 produced by gut bacteria modulates excitatory neurotransmission

A growing body of evidence indicates that gut microbiota influence brain function and behavior. However, the molecular basis of how gut bacteria modulate host nervous system function is largely unknown. Here we show that vitamin B12-producing bacteria that colonize the intestine can modulate excitatory synaptic transmission and behavior in the host Caenorhabditis elegans. We find that vitamin B12 reduces cholinergic signaling in the nervous system through rewiring of the methionine (Met)/S-Adenosylmethionine (SAM) cycle in the intestine. We identify a conserved metabolic crosstalk between the Met/SAM cycle and the choline oxidation pathway. We show that metabolic rewiring of these pathways by vitamin B12 reduces cholinergic transmission by limiting the availability of free choline required by neurons to synthesize acetylcholine. Our study reveals a gut-brain communication pathway by which enteric bacteria modulate host behavior and may affect mental health.

neuroscience↗

bioRxiv2022

Sex-specificity of the C. elegans metabolome

Recent studies of animal metabolism have revealed large numbers of novel metabolites that are involved in all aspects of organismal biology, but it is unclear to what extent metabolomes differ between sexes. Here, using untargeted comparative metabolomics for the analysis of wildtype animals and a series of germline mutants, we show that C. elegans hermaphrodites and males exhibit pervasive metabolomic differences. Several hundred small molecules are produced exclusively or in much larger amounts in one sex, including a host of previously unreported metabolites that incorporate building blocks from nucleoside, carbohydrate, lipid, and amino acid metabolism. A subset of male-enriched metabolites is specifically associated with the presence of a male germline, whereas enrichment of other compounds requires a male soma. Further, we show that one of the male germline-dependent metabolites, an unusual dipeptide incorporating N,N-dimethyltryptophan, accelerates the last stage of larval development in hermaphrodites. Our results serve as a foundation for mechanistic studies of how the genetic sex of soma and germline shape the C. elegans metabolome and provides a blueprint for the discovery of sex-dependent metabolites in other animals.

bioinformatics↗

bioRxiv2022

D-2-Hydroxyglutarate dehydrogenase connects the propionate shunt to ketone body metabolism in Caenorhabditis elegans

In humans, mutations in D-2-hydroxyglutarate (D-2HG) dehydrogenase (D2HGDH) result in D-2HG accumulation, delayed development, seizures, and ataxia. While the mechanisms of 2HG-associated diseases have been studied extensively, the endogenous metabolism of D-2HG remains unclear in any organism. Here, we find that, in Caenorhabditis elegans, D-2HG is produced in the propionate shunt, which is transcriptionally activated when flux through the canonical, vitamin B12-dependent propionate breakdown pathway is perturbed. Deletion of the D2HGDH ortholog, dhgd-1, results in embryonic lethality, mitochondrial defects, and the upregulation of ketone body metabolism genes. Viability can be rescued by RNAi of hphd-1, which encodes the enzyme that produces D-2HG, or by supplementing either vitamin B12 or the ketone body 3-hydroxybutyrate (3HB). Altogether, our findings support a model in which C. elegans relies on ketone bodies for energy when vitamin B12 levels are low, and in which a loss of dhgd-1 causes lethality by limiting ketone body production. HIGHLIGHTS- D-2-hydroxyglutarate is produced by HPHD-1 in the propionate shunt pathway - DHGD-1 recycles 2-hydroxyglutarate to sustain flux through the propionate shunt - dhgd-1 loss perturbs ketone body metabolism and causes embryonic lethality - 3-Hydroxybutyrate, vitamin B12 or hphd-1 RNAi rescue dhgd-1 mutant lethality

biochemistry↗

bioRxiv2019

Modulation of sensory behavior and food choice by an enteric bacteria-produced neurotransmitter

Animals coexist in commensal, pathogenic or mutualistic relationships with complex communities of diverse organisms including microbes1. Some bacteria produce bioactive neurotransmitters which have been proposed to modulate host nervous system activity and behaviors2. However, the mechanistic basis of this microbiota-brain modulation and its physiological relevance is largely unknown. Here we show that in C. elegans, the neuromodulator tyramine (TA) produced by gut-colonizing commensal Providencia bacteria can bypass the requirement for host TA biosynthesis to manipulate a host sensory decision. Bacterially-produced TA is likely converted to octopamine (OA) by the host tyramine beta-hydroxylase enzyme. OA, in turn, targets the OCTR-1 receptor on the ASH/ASI sensory neurons to modulate an aversive olfactory response. We identify genes required for TA biosynthesis in Providencia, and show that these genes are necessary for modulation of host behavior. We further find that C. elegans colonized by Providencia preferentially select these bacteria in food choice assays, and that this selection bias requires bacterially-produced TA. Our results demonstrate that a neurotransmitter produced by gut microbiota mimics the functions of the cognate host molecule to override host control of a sensory decision, thereby promoting fitness of both host and microbe.

neuroscience↗

bioRxiv2018

Natural variation in arsenic toxicity is explained by differences in branched chain amino acid catabolism

We find that variation in the dbt-1 gene underlies natural differences in Caenorhabditis elegans responses to the toxin arsenic. This gene encodes the E2 subunit of the branched-chain -keto acid dehydrogenase (BCKDH) complex, a core component of branched-chain amino acid (BCAA) metabolism. We causally linked a non-synonymous variant in the conserved lipoyl domain of DBT-1 to differential arsenic responses. Using targeted metabolomics and chemical supplementation, we demonstrate that differences in responses to arsenic are caused by variation in iso-branched chain fatty acids. Additionally, we show that levels of branched chain fatty acids in human cells are perturbed by arsenic treatment. This finding has broad implications for arsenic toxicity and for arsenic-focused chemotherapeutics across human populations. Our study implicates the BCKDH complex and BCAA metabolism in arsenic responses, demonstrating the power of C. elegans natural genetic diversity to identify novel mechanisms by which environmental toxins affect organismal physiology.

genetics↗