1,720,974 research outputs found
Analysis of splice variants for the C.-elegans orthologue of human neuroligin reveals a developmentally regulated transcript
No full textNeuroligins are synaptic adhesion molecules and important determinants of synaptic function. They are expressed at postsynaptic sites and involved in synaptic organization through key extracellular and intracellular protein interactions. They undergo trans-synaptic interaction with presynaptic neurexins. Distinct neuroligins use differences in their intracellular domains to selectively recruit synaptic scaffolds and this plays an important role in how they encode specialization of synaptic function. Several levels of regulation including gene expression, splicing, protein translation and processing regulate the expression of neuroligin function. We have used in silico and cDNA analyses to investigate the mRNA splicing of the Caenorhabditis-elegans orthologue nlg-1. Transcript analysis highlights the potential for gene regulation with respect to both temporal expression and splicing. We found nlg-1 splice variants with all the predicted exons are a minor species relative to major splice variants lacking exons 13 and 14, or 14 alone. These major alternatively spliced variants change the intracellular domain of the gene product NLG-1. Interestingly, exon 14 encodes a cassette with two distinct potential functional domains. One is a polyproline SH3 binding domain and the other has homology to a region encoding the binding site for the scaffolding protein gephyrin in mammalian neuroligins. This suggests differential splicing impacts on NLG-1 competence to recruit intracellular binding partners. This may have developmental relevance as nlg-1 exon 14 containing transcripts are selectively expressed in L2-L3 larvae. These results highlight a developmental regulation of C.-elegans nlg-1 that could play a key role in the assembly of synaptic protein complexes during the early stages of nervous system development
Osmotic avoidance in Caenorhabditis elegans: synaptic function of two genes, orthologues of human NRXN1 and NLGN1, as candidates for autism
No full textNeurexins and neuroligins are cell adhesion molecules present in excitatory and inhibitory synapses, and they are required for correct neuron network function. These proteins are found at the presynaptic and postsynaptic membranes. Studies in mice indicate that neurexins and neurologins have an essential role in synaptic transmission. Recent reports have shown that altered neuronal connections during the development of the human nervous system could constitute the basis of the etiology of numerous cases of autism spectrum disorders. Caenorhabditis elegans could be used as an experimental tool to facilitate the study of the functioning of synaptic components, because of its simplicity for laboratory experimentation, and given that its nervous system and synaptic wiring has been fully characterized. In C. elegans nrx-1 and nlg-1 genes are orthologous to human NRXN1 and NLGN1 genes which encode alpha-neurexin-1 and neuroligin-1 proteins, respectively. In humans and nematodes, the organization of neurexins and neuroligins is similar in respect to functional domains. The head of the nematode contains the amphid, a sensory organ of the nematode, which mediates responses to different stimuli, including osmotic strength. The amphid is made of 12 sensory bipolar neurons with ciliated dendrites and one presynaptic terminal axon. Two of these neurons, named ASHR and ASHL are particularly important in osmotic sensory function, detecting water-soluble repellents with high osmotic strength. The dendrites of these two neurons lengthen to the tip of the mouth and the axons extend to the nerve ring, where they make synaptic connections with other neurons determining the behavioral response. To evaluate the implications of neurexin and neuroligin in high osmotic strength avoidance, we show the different response of C. elegans mutants defective in nrx-1 and nlg-1 genes, using a method based on a 4M fructose ring. The behavioral phenotypes were confirmed using specific RNAi clones. In C. elegans, the dsRNA required to trigger RNAi can be administered by feeding. The delivery of dsRNA through food induces the RNAi interference of the gene of interest thus allowing the identification of genetic components and network pathway
Caenorhabditis elegans as an experimental tool for the study of complex neurological diseases: Parkinson's disease, Alzheimer's disease and autism spectrum disorder
No full textThe nematode Caenorhabditis elegans has a very well-defined and genetically tractable nervous system which offers an effective model to explore basic mechanistic pathways that might be underpin complex human neurological diseases. Here, the role C. elegans is playing in understanding two neurodegenerative conditions, Parkinson's and Alzheimer's disease (AD), and a complex neurological condition, autism, is used as an exemplar of the utility of this model system. C. elegans is an imperfect model of Parkinson's disease because it lacks orthologues of the human disease-related genes PARK1 and LRRK2 which are linked to the autosomal dominant form of this disease. Despite this fact, the nematode is a good model because it allows transgenic expression of these human genes and the study of the impact on dopaminergic neurons in several genetic backgrounds and environmental conditions. For AD, C. elegans has orthologues of the amyloid precursor protein and both human presenilins, PS1 and PS2. In addition, many of the neurotoxic properties linked with A? amyloid and tau peptides can be studied in the nematode. Autism spectrum disorder is a complex neurodevelopmental disorder characterised by impairments in human social interaction, difficulties in communication, and restrictive and repetitive behaviours. Establishing C. elegans as a model for this complex behavioural disorder is difficult; however, abnormalities in neuronal synaptic communication are implicated in the aetiology of the disorder. Numerous studies have associated autism with mutations in several genes involved in excitatory and inhibitory synapses in the mammalian brain, including neuroligin, neurexin and shank, for which there are C. elegans orthologues. Thus, several molecular pathways and behavioural phenotypes in C. elegans have been related to autism. In general, the nematode offers a series of advantages that combined with knowledge from other animal models and human research, provides a powerful complementary experimental approach for understanding the molecular mechanisms and underlying aetiology of complex neurological diseases
Neuroligin modulates the locomotory dopaminergic and serotonergic neuronal pathways of C. elegans.
No full textNeuroligins are neuronal and neuromuscular transmembrane proteins that have been implicated in autism spectrum disorder and other cognitive diseases. The nlg-1 gene from Caenorhabditis elegans is orthologous to human neuroligin genes. In the nematode, the locomotory rate is mediated by dopaminergic and serotonergic pathways, which result in two different behavioral responses known as basal slowing response (BSR) and enhanced slowing response (ESR), respectively. We report that nlg-1-deficient mutants are defective in both the BSR and ESR behaviors. In addition, we demonstrate that methylphenidate (a dopamine reuptake inhibitor) and fluoxetine (a serotonin reuptake inhibitor), two drugs widely used for the treatment of behavioral disorders in humans, are able to restore the BSR and ESR wild type phenotypes, respectively, in nlg-1 defective mutant nematodes. The abnormal locomotory behavior patterns were rescued in nlg-1-deficient mutant by expressing a cDNA from the human NLGN1 gene under the C. elegans nlg-1 promoter. However, human NLGN1 (R453C) and NLGN1 (D432X) mutant alleles did not rescue any of the two mutant phenotypes. The results indicate that neuroligin is involved in modulating the action of dopamine and serotonin in the nematode and suggest that the functional mechanism underpinning both methylphenidate and fluoxetine in C. elegans might be comparable to that in humans. The neuroligin-deficient mutants may undergo inefficient synaptic transmissions which could affect different traits in the nervous system. In particular, neuroligin might be required for normal neurotransmitters release. The understanding of the mechanisms by which methylphenidate and fluoxetine are able to restore the behavior of these mutants could help to explain the etiology of some human neurological diseases
Na<sup>+</sup>/K<sup>+</sup>-pump and neurotransmitter membrane receptors
No full textNa+/K+-pump is an electrogenic transmembrane ATPase located in the outer plasma membrane of cells. The Na+/K+-ATPase pumps 3 sodium ions out of cells while pumping 2 potassium ions into cells. Both cations move against their concentration gradients. This enzyme’s electrogenic nature means that it has a chronic role in stabilizing the resting membrane potential of the cell, in regulating the cell volume and in the signal transduction of the cell. This review will mainly consider the role of the Na+/K+-pump in neurons, with an emphasis on its role in modulating neurotransmitter receptor. Most of the literature on the modulation of neurotransmitter receptors refers to the situation in the mammalian nervous system, but the position is likely to be similar in most, if not all, invertebrate nervous systems.</p
Neurexin mediates the assembly of presynaptic terminals
No full textNeurexins are a large family of proteins that act as neuronal cell-surface receptors. The function and localization of the various neurexins, however, have not yet been clarified. Beta-neurexins are candidate receptors for neuroligin-1, a postsynaptic membrane protein that can trigger synapse formation at axon contacts. Here we report that neurexins are concentrated at synapses and that purified neuroligin is sufficient to cluster neurexin and to induce presynaptic differentiation. Oligomerization of neuroligin is required for its function, and we find that beta-neurexin clustering is sufficient to trigger the recruitment of synaptic vesicles through interactions that require the cytoplasmic domain of neurexin. We propose a two-step model in which postsynaptic neuroligin multimers initially cluster axonal neurexins. In response to this clustering, neurexins nucleate the assembly of a cytoplasmic scaffold to which the exocytotic apparatus is recruited
PharmacoGenetic targeting of a C. elegans essential neuron provides an in vivo screening for novel modulators of nematode ion channel function
No full textChemical or drug treatments are successfully used to treat parasitic nematode infections that impact human, animal and plant health. Many of these exert their effects through modifying neural function underpinning behaviours essential for parasite viability. Selectivity against the parasite may be achieved through distinct pharmacological properties of the parasite nervous system, as exemplified by the success of the ivermectin which target a glutamate-gated chloride channel found only in invertebrates. Despite the success of the ivermectins, emerging resistance and concerns around eco-toxicity are driving the search for new nematocidal chemicals or drugs. Here, we describe the potential of a 5-HT-gated chloride channel MOD-1, which is involved in vital parasite behaviours with constrained distribution in the invertebrate phyla. This ion channel has potential pharmacophores that could be targeted by new nematocidal chemicals and drugs. We have developed a microtiter based bioassay for MOD-1 pharmacology based on its ectopic expression in the Caenorhabditis elegans essential neuron M4. We have termed this technology ‘PhaGeM4’ for ‘Pharmacogenetic targeting of M4 neuron’. Exposure of transgenic worms harbouring ectopically expressed MOD-1 to 5-HT results in developmental arrest. By additional expression of a fluorescence marker in body wall muscle to monitor growth we demonstrate that this assay is suitable for the identification of receptor agonists and antagonists. Indeed, the developmental progression is a robustly quantifiable bioassay that resolves MOD-1 activation by quipazine, 5-carboxyamidotryptamine and fluoxetine and highlight methiothepin as a potent antagonist. This assay has the intrinsic ability to highlight compounds with optimal bioavailability and furthermore to filter out off-target effects. It can be extended to the investigation of other classes of membrane receptors and modulators of neuronal excitation. This approach based on heterologous modulation of the essential M4 neuron function offers a route to discover new effective and selective anthelmintics potentially less confounded by disruptive environmental impact
Binding Affinity Ranking at the Molecular Initiating Event (BARMIE): an open- source computational pipeline for ecological hazard ranking of endocrine disrupting chemicals
No full textOne of the key challenges in ecological risk assessment lies in identifying the chemicals that pose the greatest threat and determining the species that are most vulnerable to their effects. Computational prediction of protein binding affinity can help in assessing the risk of chemicals to species. In this study we developed and validated an open-source tool called BARMIE (Binding Affinity Ranking at the Molecular Initiating Event) to rank chemical hazards and identify species that are most susceptible based on the binding affinity of the chemical to steroid receptor proteins. As an exemplar of BARMIE’s output we focus on 163 teleost fish glucocorticoid receptors (GRs) and the natural ligand cortisol and 10 synthetic glucocorticoid (GCs) drugs and five other potential chemical GR agonists. The hazard ranking is based on the likelihood that the chemicals with the highest binding affinity are likely to outcompete cortisol at the receptor binding site. In this analysis, halcinonide, a GC, was predicted to be the most hazardous based on its binding affinity and the superorder Protacanthopterygii species, including the Esociformes and Salmoniformes, were identified as the most vulnerable. This computational pipeline can be expanded to evaluate more chemicals, species, and proteins as part of an in silico chemical hazard assessment tool
Neuroligin tuning of pharyngeal pumping reveals an extrapharyngeal modulation of Caenorhabditis elegans feeding
No full textThe integration of distinct sensory modalities is essential for behavioural decision making. In C. elegans this process is coordinated by neural circuits that integrate sensory cues from the environment to generate an appropriate behaviour at the appropriate output muscles. Food is a multimodal cue that impacts on the microcircuits to modulating feeding and foraging drivers at the level of the pharyngeal and body wall muscle respectively. When food triggers an upregulation in pharyngeal pumping it allows the effective ingestion of food. Here we show that a C. elegans mutant in the single orthologous gene of human neuroligins, nlg-1, is defective in food induced pumping. This is not explained by an inability to sense food, as nlg-1 mutants are not defective in chemotaxis towards bacteria. In addition, we show that neuroligin is widely expressed in the nervous system including AIY, ADE, ALA, URX and HSN neurones. Interestingly, despite the deficit in pharyngeal pumping neuroligin is not expressed within the pharyngeal neuromuscular network, which suggests an extrapharyngeal regulation of this circuit. We resolve electrophysiologically the neuroligin contribution to the pharyngeal circuit by mimicking a food-dependent pumping, and show that the nlg-1 phenotype is similar to mutants impaired in GABAergic and/or glutamatergic signalling. We suggest that neuroligin organizes extrapharyngeal circuits that regulate the pharynx. These observations based on the molecular and cellular determinants of feeding are consistent with the emerging role of neuroligin in discretely impacting functional circuits underpinning complex behaviours
In vivo and in vitro studies of the role of lyophilised blond Lager beer and some bioactive components in the modulation of degenerative processes
No full textThe aim of the present study was to examine the nutraceutic potential of lyophilised blond Lager beer, as well as two of its bioactive components: xanthohumol and folic acid. Several toxicity, antitoxicity, genotoxicity, antigenotoxicity and longevity endpoints were checked in the SMART in vivo Drosophila system. Cytotoxicity in HL-60 promyelocytic and NIH3T3 mouse fibroblasts cells, proapototic DNA fragmentation, comet assay, macroautophagy activity and methylation status were tested in in vitro assays. Lyophilised blond Lager beer could be proposed as a substance with an important nutraceutical value, because of its hopeful results as a lifespan promoter, DNA protection against free radicals in the animal model and its chemopreventive activity in HL-60 cells and enhacer of macroautophagy at moderate doses in NIH3T3 inmortal cells. Only xanthohumol mimics the biological activities found in lyophilised beer
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