Choline transport and de novo choline synthesis support acetylcholine biosynthesis in Caenorhabditis elegans cholinergic neurons

Vitamin B12 produced by gut bacteria modulates cholinergic signalling

A growing body of evidence indicates that gut microbiota influence brain function and behaviour. 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 cholinergic signalling and behaviour in the host Caenorhabditis elegans. Here we demonstrate that vitamin B12 reduces cholinergic signalling in the nervous system through rewiring of the methionine (Met)/S-adenosylmethionine cycle in the intestine. We identify a conserved metabolic crosstalk between the methionine/S-adenosylmethionine cycle and the choline-oxidation pathway. In addition, we show that metabolic rewiring of these pathways by vitamin B12 reduces cholinergic signalling 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 behaviour and may affect neurological health.

baz-2 enhances systemic proteostasis in vivo by regulating acetylcholine metabolism

Neurodegenerative disorders, such as Alzheimer's disease (AD) or Huntington's disease (HD), are linked to protein aggregate neurotoxicity. According to the "cholinergic hypothesis," loss of acetylcholine (ACh) signaling contributes to the AD pathology, and therapeutic restoration of ACh signaling is a common treatment strategy. How disease causation and the effect of ACh are linked to protein aggregation and neurotoxicity remains incompletely understood, thus limiting the development of more effective therapies. Here, we show that BAZ-2, the Caenorhabditis elegans ortholog of human BAZ2B, limits ACh signaling. baz-2 mutations reverse aggregation and toxicity of amyloid-beta as well as polyglutamine peptides, thereby restoring health and lifespan in nematode models of AD and HD, respectively. The neuroprotective effect of Δbaz-2 is mediated by choline acetyltransferase, phenocopied by ACh-esterase depletion, and dependent on ACh receptors. baz-2 reduction or ectopic ACh treatment augments proteostasis via induction of the endoplasmic reticulum unfolded protein response and the ubiquitin proteasome system.

Competitive inhibition of the high-affinity choline transporter by tetrahydropyrimidine anthelmintics

The high-affinity choline transporter CHT1 mediates choline uptake, the rate-limiting and regulatory step in acetylcholine synthesis at cholinergic presynaptic terminals. CHT1-medated choline uptake is specifically inhibited by hemicholinium-3, which is a type of choline analog that acts as a competitive inhibitor. Although the substrate choline and the inhibitor hemicholinium-3 are well-established ligands of CHT1, few potent ligands other than choline analogs have been reported. Here we show that tetrahydropyrimidine anthelmintics, known as nicotinic acetylcholine receptor agonists, act as competitive inhibitors of CHT1. A ligand-dependent trafficking assay in cell lines expressing human CHT1 was designed to search for CHT1 ligands from a collection of biologically active compounds. We found that morantel as well as other tetrahydropyrimidines, pyrantel and oxantel, potently inhibits the high-affinity choline uptake activity of CHT1 in a competitive manner similar to the inhibitor hemicholinium-3. They also inhibit the high-affinity choline transporter from the nematode Caenorhabditis elegans. Finally, tetrahydropyrimidines potently inhibit the high-affinity choline uptake in rat brain synaptosomes at a low micromolar level, resulting in the inhibition of acetylcholine synthesis. The rank order of potency in synaptosomes is as follows: morantel > pyarantel > oxantel (K_i = 1.3, 5.7, and 8.3 μM, respectively). Our results reveal that tetrahydropyrimidine anthelmintics are novel CHT1 ligands that inhibit the high-affinity choline uptake for acetylcholine synthesis in cholinergic neurons.

Cholinergic transmission in C. elegans: Functions, diversity, and maturation of ACh-activated ion channels

Acetylcholine is an abundant neurotransmitter in all animals. Effects of acetylcholine are excitatory, inhibitory, or modulatory depending on the receptor and cell type. Research using the nematode C. elegans has made ground-breaking contributions to the mechanistic understanding of cholinergic transmission. Powerful genetic screens for behavioral mutants or for responses to pharmacological reagents identified the core cellular machinery for synaptic transmission. Pharmacological reagents that perturb acetylcholine-mediated processes led to the discovery and also uncovered the composition and regulators of acetylcholine-activated channels and receptors. From a combination of electrophysiological and molecular cellular studies, we have gained a profound understanding of cholinergic signaling at the levels of synapses, neural circuits, and animal behaviors. This review will begin with a historical overview, then cover in-depth current knowledge on acetylcholine-activated ionotropic receptors, mechanisms regulating their functional expression and their functions in regulating locomotion.

Modular Organization of Cis-regulatory Control Information of Neurotransmitter Pathway Genes in Caenorhabditis elegans

We explore here the cis-regulatory logic that dictates gene expression in specific cell types in the nervous system. We focus on a set of eight genes involved in the synthesis, transport, and breakdown of three neurotransmitter systems: acetylcholine (unc-17 /VAChT, cha-1 /ChAT, cho-1 /ChT, and ace-2 /AChE), glutamate (eat-4 /VGluT), and γ-aminobutyric acid (unc-25 /GAD, unc-46 /LAMP, and unc-47 /VGAT). These genes are specifically expressed in defined subsets of cells in the nervous system. Through transgenic reporter gene assays, we find that the cellular specificity of expression of all of these genes is controlled in a modular manner through distinct cis-regulatory elements, corroborating the previously inferred piecemeal nature of specification of neurotransmitter identity. This modularity provides the mechanistic basis for the phenomenon of "phenotypic convergence," in which distinct regulatory pathways can generate similar phenotypic outcomes (i.e., the acquisition of a specific neurotransmitter identity) in different neuron classes. We also identify cases of enhancer pleiotropy, in which the same cis-regulatory element is utilized to control gene expression in distinct neuron types. We engineered a cis-regulatory allele of the vesicular acetylcholine transporter, unc-17 /VAChT, to assess the functional contribution of a "shadowed" enhancer. We observed a selective loss of unc-17 /VAChT expression in one cholinergic pharyngeal pacemaker motor neuron class and a behavioral phenotype that matches microsurgical removal of this neuron. Our analysis illustrates the value of understanding cis-regulatory information to manipulate gene expression and control animal behavior.

Blockade and reversal of swimming-induced paralysis in C. elegans by the antipsychotic and D2-type dopamine receptor antagonist azaperone

The catecholamine neurotransmitter dopamine (DA) exerts powerful modulatory control of physiology and behavior across phylogeny. Perturbations of DA signaling in humans are associated with multiple neurodegenerative and behavioral disorders, including Parkinson's disease, attention-deficit/hyperactivity disorder, addiction and schizophrenia. In the nematode C. elegans, DA signaling regulates mating behavior, learning, food seeking and locomotion. Previously, we demonstrated that loss of function mutations in the dat-1 gene that encodes the presynaptic DA transporter (DAT-1) results in a rapid cessation of movement when animals are placed in water, termed Swimming Induced Paralysis (Swip). Loss of function mutations in genes that support DA biosynthesis, DA vesicular packaging and DA action at the extrasynaptic D2-type DA receptor DOP-3 suppress Swip in dat-1 animals, consistent with paralysis as arising from excessive DA signaling. Although animals grown on the vesicular monoamine transporter antagonist reserpine diminish Swip, the drug must be applied chronically, can impact the signaling of multiple biogenic amines, and has been reported to have penetrant, off-target actions. Here, we demonstrate that the antipsychotic drug azaperone potently and rapidly suppresses Swip behavior in either dat-1 mutants, as well as in wildtype animals treated with the DAT-1 antagonist nisoxetine, with genetic experiments consistent with DOP-3 antagonism as the mechanism of Swip suppression. Reversal of Swip in previously paralyzed dat-1 animals by azaperone application demonstrates an otherwise functionally-intact swimming circuit in these mutants. Finally, whereas azaperone suppresses DA-dependent Swip, the drug fails to attenuate the DA-independent paralysis induced by βPEA, aldicarb or genetic disruption of γ-aminobutyric acid (GABA) signaling. We discuss our findings with respect to the use of azaperone as a potent and selective tool in the identification and analysis of presynaptic mechanisms that regulate DA signaling.

Acute blockade of the Caenorhabditis elegans dopamine transporter DAT-1 by the mammalian norepinephrine transporter inhibitor nisoxetine reveals the influence of genetic modifications of dopamine signaling in vivo

Modulation of neurotransmission by the catecholamine dopamine (DA) is conserved across phylogeny. In the nematode Caenorhabditis elegans, excess DA signaling triggers Swimming-Induced Paralysis (Swip), a phenotype first described in animals with loss of function mutations in the presynaptic DA transporter (dat-1). Swip has proven to be a phenotype suitable for the identification of novel dat-1 mutations as well as the identification of novel genes that impact DA signaling. Pharmacological manipulations can also induce Swip, though the reagents employed to date lack specificity and potency, limiting their use in evaluation of dat-1 expression and function. Our lab previously established the mammalian norepinephrine transporter (NET) inhibitor nisoxetine to be a potent antagonist of DA uptake conferred by DAT-1 following heterologous expression. Here we demonstrate the ability of low (μM) concentrations of nisoxetine to trigger Swip within minutes of incubation, with paralysis dependent on DA release and signaling, and non-additive with Swip triggered by dat-1 deletion. Using nisoxetine in combination with genetic mutations that impact DA release, we further demonstrate the utility of the drug for demonstrating contributions of presynaptic DA receptors and ion channels to Swip. Together, these findings reveal nisoxetine as a powerful reagent for monitoring multiple dimensions of DA signaling in vivo, thus providing a new resource that can be used to evaluate contributions of dat-1 and other genes linked to DA signaling without the potential for compensations that attend constitutive genetic mutations.

Circuit mechanisms encoding odors and driving aging-associated behavioral declines in Caenorhabditis elegans

Chemosensory neurons extract information about chemical cues from the environment. How is the activity in these sensory neurons transformed into behavior? Using Caenorhabditis elegans, we map a novel sensory neuron circuit motif that encodes odor concentration. Primary neurons, AWC^ON and AWA, directly detect the food odor benzaldehyde (BZ) and release insulin-like peptides and acetylcholine, respectively, which are required for odor-evoked responses in secondary neurons, ASEL and AWB. Consistently, both primary and secondary neurons are required for BZ attraction. Unexpectedly, this combinatorial code is altered in aged animals: odor-evoked activity in secondary, but not primary, olfactory neurons is reduced. Moreover, experimental manipulations increasing neurotransmission from primary neurons rescues aging-associated neuronal deficits. Finally, we correlate the odor responsiveness of aged animals with their lifespan. Together, these results show how odors are encoded by primary and secondary neurons and suggest reduced neurotransmission as a novel mechanism driving aging-associated sensory neural activity and behavioral declines.

DOI:http://dx.doi.org/10.7554/eLife.10181.001

A sense of smell can help animals to find food and detect danger. Odor molecules activate so-called olfactory neurons that relay signals to the brain in the form of nerve impulses. This information is then processed, and the appropriate response is triggered; for example, an animal might move towards the smell of food, or away from the scent of a predator. But how can the activity of olfactory neurons trigger the right behavioral response?

Leinwand et al. have now explored the activity of olfactory neurons in a roundworm called C. elegans. The experiments revealed that a food odor activated two olfactory neurons directly, and that each of these ‘primary’ neurons then in turn activated another ‘secondary’ olfactory neuron. This communication between primary and secondary olfactory neurons was essential for worms to respond to the food odor. Further experiments revealed that the primary olfactory neurons send chemical signals, called neurotransmitters and neuropeptides, to communicate with the secondary neurons. Importantly, mutations that blocked this chemical signaling prevented the worms from responding appropriately to the smell of food.

Aging animals, including people, often have impaired senses and can therefore find it difficult to identify and respond to odors. Leinwand et al. found that aged worms were no different. Further experiments suggested that aging worms' responses to odor decline because the communication between the primary and secondary olfactory neurons may be impaired with age. When Leinwand et al. strengthened this communication it reversed the effects of aging on the worms' sense of smell. Moreover, the experiments also showed that an animal's performance on the odor task was correlated with its longevity, such that the better performers also lived longer. A challenge for the future is to understand the precise changes that occur at early stages of aging to impair the sense of smell. Future studies could also test if similar combinations of olfactory neurons are needed to trigger certain behavioral responses to odors in young and old mammals.

DOI:http://dx.doi.org/10.7554/eLife.10181.002

Transcriptional coordination of synaptogenesis and neurotransmitter signaling

During nervous system development, postmitotic neurons face the challenge of generating and structurally organizing specific synapses with appropriate synaptic partners. An important unexplored question is whether the process of synaptogenesis is coordinated with the adoption of specific signaling properties of a neuron. Such signaling properties are defined by the neurotransmitter system that a neuron uses to communicate with postsynaptic partners, the neurotransmitter receptor type used to receive input from presynaptic neurons, and, potentially, other sensory receptors that activate a neuron. Elucidating the mechanisms that coordinate synaptogenesis, neuronal activation, and neurotransmitter signaling in a postmitotic neuron represents one key approach to understanding how neurons develop as functional units. Using the SAB class of Caenorhabditis elegans motor neurons as a model system, we show here that the phylogenetically conserved COE-type transcription factor UNC-3 is required for synaptogenesis. UNC-3 directly controls the expression of the ADAMTS-like protein MADD-4/Punctin, a presynaptically secreted synapse-organizing molecule that clusters postsynaptic receptors. UNC-3 also controls the assembly of presynaptic specializations and ensures the coordinated expression of enzymes and transporters that define the cholinergic neurotransmitter identity of the SAB neurons. Furthermore, synaptic output properties of the SAB neurons are coordinated with neuronal activation and synaptic input, as evidenced by UNC-3 also regulating the expression of ionotropic neurotransmitter receptors and putative stretch receptors. Our study shows how synaptogenesis and distinct, function-defining signaling features of a postmitotic neuron are hardwired together through coordinated transcriptional control.

CHOLINE TRANSPORTER-LIKE1 is required for sieve plate development to mediate long-distance cell-to-cell communication

Phloem, a plant tissue responsible for long-distance molecular transport, harbours specific junctions, sieve areas, between the conducting cells. To date, little is known about the molecular framework related to the biogenesis of these sieve areas. Here we identify mutations at the CHER1/AtCTL1 locus of Arabidopsis thaliana. The mutations cause several phenotypic abnormalities, including reduced pore density and altered pore structure in the sieve areas associated with impaired phloem function. CHER1 encodes a member of a poorly characterized choline transporter-like protein family in plants and animals. We show that CHER1 facilitates choline transport, localizes to the trans-Golgi network, and during cytokinesis is associated with the phragmoplast. Consistent with its function in the elaboration of the sieve areas, CHER1 has a sustained, polar localization in the forming sieve plates. Our results indicate that the regulation of choline levels is crucial for phloem development and conductivity in plants.

Molecular identification and functional characterization of the human colonic thiamine pyrophosphate transporter

Colonic microbiota synthesize a considerable amount of thiamine in the form of thiamine pyrophosphate (TPP). Recent functional studies from our laboratory have shown the existence of a specific, high-affinity, and regulated carrier-mediated uptake system for TPP in human colonocytes. Nothing, however, is known about the molecular identity of this system. Here we report on the molecular identification of the colonic TPP uptake system as the product of the SLC44A4 gene. We cloned the cDNA of SLC44A4 from human colonic epithelial NCM460 cells, which, upon expression in ARPE19 cells, led to a significant (p < 0.01, >5-fold) induction in [(3)H]TPP uptake. Uptake by the induced system was also found to be temperature- and energy-dependent; Na(+)-independent, slightly higher at acidic buffer pH, and highly sensitive to protonophores; saturable as a function of TPP concentration, with an apparent Km of 0.17 ± 0.064 μM; and highly specific for TPP and not affected by free thiamine, thiamine monophosphate, or choline. Expression of the human TPP transporter was found to be high in the colon and negligible in the small intestine. A cell surface biotinylation assay and live cell confocal imaging studies showed the human TPP transporter protein to be expressed at the apical membrane domain of polarized epithelia. These results show, for the first time, the molecular identification and characterization of a specific and high-affinity TPP uptake system in human colonocytes. The findings further support the hypothesis that the microbiota-generated TPP is absorbable and could contribute toward host thiamine homeostasis, especially toward cellular nutrition of colonocytes.

Extrasynaptic muscarinic acetylcholine receptors on neuronal cell bodies regulate presynaptic function in Caenorhabditis elegans

Acetylcholine (ACh) is a potent neuromodulator in the brain, and its effects on cognition and memory formation are largely performed through muscarinic acetylcholine receptors (mAChRs). mAChRs are often preferentially distributed on specialized membrane regions in neurons, but the significance of mAChR localization in modulating neuronal function is not known. Here we show that the Caenorhabditis elegans homolog of the M1/M3/M5 family of mAChRs, gar-3, is expressed in cholinergic motor neurons, and GAR-3-GFP fusion proteins localize to cell bodies where they are enriched at extrasynaptic regions that are in contact with the basal lamina. The GAR-3 N-terminal extracellular domain is necessary and sufficient for this asymmetric distribution, and mutation of a predicted N-linked glycosylation site within the N-terminus disrupts GAR-3-GFP localization. In transgenic animals expressing GAR-3 variants that are no longer asymmetrically localized, synaptic transmission at neuromuscular junctions is impaired and there is a reduction in the abundance of the presynaptic protein sphingosine kinase at release sites. Finally, GAR-3 can be activated by endogenously produced ACh released from neurons that do not directly contact cholinergic motor neurons. Together, our results suggest that humoral activation of asymmetrically localized mAChRs by ACh is an evolutionarily conserved mechanism by which ACh modulates neuronal function.

The choline transporter-like family SLC44: properties and roles in human diseases

The Na(+)-independent, high affinity choline carrier system proposed to supply choline for the synthesis of cell membrane phospholipids was recently associated with SLC44 family members (SLC44A1-5) also called choline-like transporter family. SLC44A1 is widely expressed throughout the nervous system in both neurons and oligodendrocytes, while SLC44A2-4 are mainly detected in peripheral tissues. The subcellular localization of the proteins was mainly addressed for SLC44A1 through the development of specific antibodies. SLC44A1 is detected in both the plasma and mitochondrial membranes where the protein is able to transport choline at high affinity and in a Na(+)-independent manner. The physiological relevance of SLC44A1 as a choline carrier is indicated by its likely involvement in membrane synthesis for cell growth or repair, and also by its role in phospholipid production for the generation of lung surfactant. Moreover, an autoimmune disease has been related to the blockade of SLC44A2 function, which results in the alteration of hair cells in the inner ear and leads to autoimmune hearing loss. In the alloimmune syndrome called transfusion-related acute lung injury, antibodies to SLC44A2 cause a deleterious aggregation of granulocytes. Therefore transporters of the SLC44 family represent attractive and promising targets for therapeutic and diagnostic applications regarding both immune and degenerative diseases.

Global analysis of fission yeast mating genes reveals new autophagy factors

Macroautophagy (autophagy) is crucial for cell survival during starvation and plays important roles in animal development and human diseases. Molecular understanding of autophagy has mainly come from the budding yeast Saccharomyces cerevisiae, and it remains unclear to what extent the mechanisms are the same in other organisms. Here, through screening the mating phenotype of a genome-wide deletion collection of the fission yeast Schizosaccharomyces pombe, we obtained a comprehensive catalog of autophagy genes in this highly tractable organism, including genes encoding three heretofore unidentified core Atg proteins, Atg10, Atg14, and Atg16, and two novel factors, Ctl1 and Fsc1. We systematically examined the subcellular localization of fission yeast autophagy factors for the first time and characterized the phenotypes of their mutants, thereby uncovering both similarities and differences between the two yeasts. Unlike budding yeast, all three Atg18/WIPI proteins in fission yeast are essential for autophagy, and we found that they play different roles, with Atg18a uniquely required for the targeting of the Atg12–Atg5·Atg16 complex. Our investigation of the two novel factors revealed unforeseen autophagy mechanisms. The choline transporter-like protein Ctl1 interacts with Atg9 and is required for autophagosome formation. The fasciclin domain protein Fsc1 localizes to the vacuole membrane and is required for autophagosome-vacuole fusion but not other vacuolar fusion events. Our study sheds new light on the evolutionary diversity of the autophagy machinery and establishes the fission yeast as a useful model for dissecting the mechanisms of autophagy.

Autophagy is a eukaryotic cellular process that transports cytoplasmic contents into lysosomes/vacuoles for degradation. It has been linked to multiple human diseases, including cancer and neurodegenerative disorders. The molecular machinery of autophagy was first identified and has been best characterized in the budding yeast Saccharomyces cerevisiae, but little is known about the autophagy machinery in another important unicellular model organism, the fission yeast Schizosaccharomyces pombe. In this study, we performed an unbiased and comprehensive screening of the fission yeast autophagy genes by profiling the mating phenotypes of nearly 3000 deletion strains. Following up on the screening results, we systematically characterized both previously known and newly identified fission yeast autophagy factors by examining their localization and the phenotype of their mutants. Our analysis increased the number of experimentally defined fission yeast autophagy factors from 14 to 23, including two novel factors that act in ways different from all previously known autophagy proteins. Together, our data reveal unexpected evolutionary divergence of autophagy mechanisms and establish a new model system for unraveling the molecular details of the autophagy process.

Metal-induced neurodegeneration in C. elegans

The model species, Caenorhabditis elegans, has been used as a tool to probe for mechanisms underlying numerous neurodegenerative diseases. This use has been exploited to study neurodegeneration induced by metals. The allure of the nematode comes from the ease of genetic manipulation, the ability to fluorescently label neuronal subtypes, and the relative simplicity of the nervous system. Notably, C. elegans have approximately 60-80% of human genes and contain genes involved in metal homeostasis and transport, allowing for the study of metal-induced degeneration in the nematode. This review discusses methods to assess degeneration as well as outlines techniques for genetic manipulation and presents a comprehensive survey of the existing literature on metal-induced degeneration studies in the worm.

Genetic interactions between UNC-17/VAChT and a novel transmembrane protein in Caenorhabditis elegans

The unc-17 gene encodes the vesicular acetylcholine transporter (VAChT) in Caenorhabditis elegans. unc-17 reduction-of-function mutants are small, slow growing, and uncoordinated. Several independent unc-17 alleles are associated with a glycine-to-arginine substitution (G347R), which introduces a positive charge in the ninth transmembrane domain (TMD) of UNC-17. To identify proteins that interact with UNC-17/VAChT, we screened for mutations that suppress the uncoordinated phenotype of UNC-17(G347R) mutants. We identified several dominant allele-specific suppressors, including mutations in the sup-1 locus. The sup-1 gene encodes a single-pass transmembrane protein that is expressed in a subset of neurons and in body muscles. Two independent suppressor alleles of sup-1 are associated with a glycine-to-glutamic acid substitution (G84E), resulting in a negative charge in the SUP-1 TMD. A sup-1 null mutant has no obvious deficits in cholinergic neurotransmission and does not suppress unc-17 mutant phenotypes. Bimolecular fluorescence complementation (BiFC) analysis demonstrated close association of SUP-1 and UNC-17 in synapse-rich regions of the cholinergic nervous system, including the nerve ring and dorsal nerve cords. These observations suggest that UNC-17 and SUP-1 are in close proximity at synapses. We propose that electrostatic interactions between the UNC-17(G347R) and SUP-1(G84E) TMDs alter the conformation of the mutant UNC-17 protein, thereby restoring UNC-17 function; this is similar to the interaction between UNC-17/VAChT and synaptobrevin.

A network of G-protein signaling pathways control neuronal activity in C. elegans

The Caenorhabditis elegans neuromuscular junction (NMJ) is one of the best studied synapses in any organism. A variety of genetic screens have identified genes required both for the essential steps of neurotransmitter release from motorneurons as well as the signaling pathways that regulate rates of neurotransmitter release. A number of these regulatory genes encode proteins that converge to regulate neurotransmitter release. In other cases genes are known to regulate signaling at the NMJ but how they act remains unknown. Many of the proteins that regulate activity at the NMJ participate in a network of heterotrimeric G-protein signaling pathways controlling the release of synaptic vesicles and/or dense-core vesicles (DCVs). At least four heterotrimeric G-proteins (Galphaq, Galpha12, Galphao, and Galphas) act within the motorneurons to control the activity of the NMJ. The Galphaq, Galpha12, and Galphao pathways converge to control production and destruction of the lipid-bound second messenger diacylglycerol (DAG) at sites of neurotransmitter release. DAG acts via at least two effectors, MUNC13 and PKC, to control the release of both neurotransmitters and neuropeptides from motorneurons. The Galphas pathway converges with the other three heterotrimeric G-protein pathways downstream of DAG to regulate neuropeptide release. Released neurotransmitters and neuropeptides then act to control contraction of the body-wall muscles to control locomotion. The lipids and proteins involved in these networks are conserved between C. elegans and mammals. Thus, the C. elegans NMJ acts as a model synapse to understand how neuronal activity in the human brain is regulated.