Osmotic avoidance in Caenorhabditis elegans: synaptic function of two genes, orthologues of human NRXN1 and NLGN1, as candidates for autism.
ABSTRACT Neurexins 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 pathways.
Full-textDOI: · Available from: Manuel Ruiz-Rubio, Jun 02, 2015
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ABSTRACT: The Nrf family of transcription factors mediates adaptive responses to stress and longevity, but the identities of the crucial Nrf targets, and the tissues in which they function in multicellular organisms to promote survival, are not known. Here, we use whole transcriptome RNA sequencing to identify 810 genes whose expression is controlled by the SKN-1/Nrf2 negative regulator WDR-23 in the nervous system of Caenorhabditis elegans. Among the genes identified is the synaptic cell adhesion molecule nlg-1/neuroligin. We find that the synaptic abundance of NLG-1 protein increases following pharmacological treatments that generate oxidative stress or by the genetic activation of skn-1. Increasing nlg-1 dosage correlates with increased survival in response to oxidative stress, whereas genetic inactivation of nlg-1 reduces survival and impairs skn-1-mediated stress resistance. We identify a canonical SKN-1 binding site in the nlg-1 promoter that binds to SKN-1 in vitro and is necessary for SKN-1 and toxin-mediated increases in nlg-1 expression in vivo. Together, our results suggest that SKN-1 activation in the nervous system can confer protection to organisms in response to stress by directly regulating nlg-1/neuroligin expression.PLoS Genetics 01/2014; 10(1):e1004100. DOI:10.1371/journal.pgen.1004100 · 8.17 Impact Factor
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ABSTRACT: The study of autism spectrum disorder (ASD) is diffi cult because of the heterogeneous phenotypic manifestation of the disease and because of the complexity of its etiology. The estimated genetic heritability of ASD is high, about 80 %. The identifi cation of individual genes involved in this syndrome is essential for advancing in the understanding of the mechanisms involved in the development of the disease. Until now, more than 600 genes have been reported in human that could be related to ASDs, and over 70 % of them are orthologs to genes present in the genome of invertebrate animal models. This particular scenario is where invertebrate animals acquire special relevance as biological models, given the relative simplicity of their nervous system compared it to that of mammals. Moreover, many of the molecular mechanisms operating in neuronal synapses are evolutionarily conserved among vertebrates and invertebrates. Invertebrates are also easy to handle, and most of them are reproduced rapidly in the laboratory, which allows obtaining many individuals to study the effect of mutations and/or environmental factors in behavior. In this chapter, we review the features that make Drosophila melanogaster , Aplysia californica , and Caenorhabditis elegans exceptional models for the study of particular genes related to ASDs. We present some examples of the functional analysis of genes associated with these disorders in these organisms and discuss molecular basis of behaviors that might be signifi cant in the etiology of ASDs.Organism Models of Autism Spectrum Disorders., Edited by Pierre Roubertoux, 01/2015: chapter Invertebrate models of synaptic transmission in autism spectrum disorders.: pages 157-182; Humana Press, Springer Science, New York.
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ABSTRACT: Current research indicates that the causes of autism spectrum disorders (ASDs) are multifactorial and include both genetic and environmental factors. To date, several works have associated ASDs with mutations in genes that encode proteins involved in neuronal synapses; however other factors and the way they can interact with the development of the nervous system remain largely unknown. Some studies have established a direct relationship between risk for ASDs and the exposure of the fetus to high testosterone levels during the prenatal stage. In this work, in order to explain possible mechanisms by which this androgenic hormone may interact with the nervous system, C. elegans was used as an experimental model. We observed that testosterone was able to alter the behavioral pattern of the worm, including the gentle touch response and the pharyngeal pumping rate. This impairment of the behavior was abolished using specific RNAi against genes orthologous to the human androgen receptor gene. The effect of testosterone was eliminated in the nhr-69 (ok1926) deficient mutant, a putative ortholog of human AR gene, suggesting that this gene encodes a receptor able to interact with the hormone. On the other hand the testosterone effect remained in the gentle touch response during four generations in the absence of the hormone, indicating that some epigenetic mechanisms could be involved. Sodium butyrate, a histone deacetylase inhibitor, was able to abolish the effect of testosterone. In addition, the lasting effect of testosterone was eliminated after the dauer stage. These results suggest that testosterone may impair the nervous system function generating transgenerational epigenetic marks in the genome. This work may provide new paradigms for understanding biological mechanisms involved in ASDs traits.Frontiers in Cellular Neuroscience 01/2014; 8:69. DOI:10.3389/fncel.2014.00069 · 4.18 Impact Factor