RIC-3 expression and splicing regulate nAChR functional expression

Effects of FL human RIC-3 vs. mouse FL on α7 nAChR functional expression in X. leavis oocytes. Results were normalized to currents recorded in oocytes expressing the respective receptors in the absence of RIC-3 in the same experiment. Each bar represents 10–20 oocytes from 2 to 3 independent X. laevis. The y-axis ordinates are on a log scale. * indicates a p value of less than 0.05; ** indicates a p value of less than 0.01. (PDF 714 kb

Time-lapse imaging and cell-specific expression profiling reveal dynamic branching and molecular determinants of a multi-dendritic nociceptor in C. elegans

AbstractNociceptive neurons innervate the skin with complex dendritic arbors that respond to pain-evoking stimuli such as harsh mechanical force or extreme temperatures. Here we describe the structure and development of a model nociceptor, the PVD neuron of C. elegans, and identify transcription factors that control morphogenesis of the PVD dendritic arbor. The two PVD neuron cell bodies occupy positions on either the right (PVDR) or left (PVDL) sides of the animal in posterior–lateral locations. Imaging with a GFP reporter revealed a single axon projecting from the PVD soma to the ventral cord and an elaborate, highly branched arbor of dendritic processes that envelop the animal with a web-like array directly beneath the skin. Dendritic branches emerge in a step-wise fashion during larval development and may use an existing network of peripheral nerve cords as guideposts for key branching decisions. Time-lapse imaging revealed that branching is highly dynamic with active extension and withdrawal and that PVD branch overlap is prevented by a contact-dependent self-avoidance, a mechanism that is also employed by sensory neurons in other organisms. With the goal of identifying genes that regulate dendritic morphogenesis, we used the mRNA-tagging method to produce a gene expression profile of PVD during late larval development. This microarray experiment identified>2,000 genes that are 1.5X elevated relative to all larval cells. The enriched transcripts encode a wide range of proteins with potential roles in PVD function (e.g., DEG/ENaC and Trp channels) or development (e.g., UNC-5 and LIN-17/frizzled receptors). We used RNAi and genetic tests to screen 86 transcription factors from this list and identified eleven genes that specify PVD dendritic structure. These transcription factors appear to control discrete steps in PVD morphogenesis and may either promote or limit PVD branching at specific developmental stages. For example, time-lapse imaging revealed that MEC-3 (LIM homeodomain) is required for branch initiation in early larval development whereas EGL-44 (TEAD domain) prevents ectopic PVD branching in the adult. A comparison of PVD-enriched transcripts to a microarray profile of mammalian nociceptors revealed homologous genes with potentially shared nociceptive functions. We conclude that PVD neurons display striking structural, functional and molecular similarities to nociceptive neurons from more complex organisms and can thus provide a useful model system in which to identify evolutionarily conserved determinants of nociceptor fate

The brain is a DJ using neuropeptides as sensory crossfaders

Sensory loss induces cross-modal plasticity, often resulting in altered performance in remaining sensory modalities. Whereas much is known about the macroscopic mechanisms underlying cross-modal plasticity, only scant information exists about its cellular and molecular underpinnings. We found that Caenorhabditis elegans nematodes deprived of a sense of body touch exhibit various changes in behavior, associated with other unimpaired senses. We focused on one such behavioral alteration, enhanced odor sensation, and sought to reveal the neuronal and molecular mechanisms that translate mechanosensory loss into improved olfactory acuity. To this end, we analyzed in mechanosensory mutants food-dependent locomotion patterns that are associated with olfactory responses and found changes that are consistent with enhanced olfaction. The altered locomotion could be reversed in adults by optogenetic stimulation of the touch receptor (mechanosensory) neurons. Furthermore, we revealed that the enhanced odor response is related to a strengthening of inhibitory AWC→AIY synaptic transmission in the olfactory circuit. Consistently, inserting in this circuit an engineered electrical synapse that diminishes AWC inhibition of AIY counteracted the locomotion changes in touch-deficient mutants. We found that this cross-modal signaling between the mechanosensory and olfactory circuits is mediated by neuropeptides, one of which we identified as FLP-20. Our results indicate that under normal function, ongoing touch receptor neuron activation evokes FLP-20 release, suppressing synaptic communication and thus dampening odor sensation. In contrast, in the absence of mechanosensory input, FLP-20 signaling is reduced, synaptic suppression is released, and this enables enhanced olfactory acuity; these changes are long lasting and do not represent ongoing modulation, as revealed by optogenetic experiments. Our work adds to a growing literature on the roles of neuropeptides in cross-modal signaling, by showing how activity-dependent neuropeptide signaling leads to specific cross-modal plastic changes in neural circuit connectivity, enhancing sensory performance.status: publishe

The Blueprint for Life

A living cell is the product of complex interactions between DNA and the cellular environment. Can researchers recreate the environment based on the information contained in the DNA alone

Neuroinflammation Modulation via α7 Nicotinic Acetylcholine Receptor and Its Chaperone, RIC-3

Nicotinic acetylcholine receptors (nAChRs) are widely expressed in or on various cell types and have diverse functions. In immune cells nAChRs regulate proliferation, differentiation and cytokine release. Specifically, activation of the α7 nAChR reduces inflammation as part of the cholinergic anti-inflammatory pathway. Here we review numerous effects of α7 nAChR activation on immune cell function and differentiation. Further, we also describe evidence implicating this receptor and its chaperone RIC-3 in diseases of the central nervous system and in neuroinflammation, focusing on multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Deregulated neuroinflammation due to dysfunction of α7 nAChR provides one explanation for involvement of this receptor and of RIC-3 in neurodegenerative diseases. In this review, we also provide evidence implicating α7 nAChRs and RIC-3 in neurodegenerative diseases such as Alzheimer’s disease (AD) and Parkinson’s disease (PD) involving neuroinflammation. Besides, we will describe the therapeutic implications of activating the cholinergic anti-inflammatory pathway for diseases involving neuroinflammation

The C.elegans ric-3 gene is required for maturation of nicotinic acetylcholine receptors

Mutations in ric-3 (resistant to inhibitors of cholinesterase) suppress the neuronal degenerations caused by a gain of function mutation in the Caenorhabditis elegans DEG-3 acetylcholine receptor. RIC-3 is a novel protein with two transmembrane domains and extensive coiled-coil domains. It is expressed in both muscles and neurons, and the protein is concentrated within the cell bodies. We demonstrate that RIC-3 is required for the function of at least four nicotinic acetylcholine receptors. However, GABA and glutamate receptors expressed in the same cells are unaffected. In ric-3 mutants, the DEG-3 receptor accumulates in the cell body instead of in the cell processes. Moreover, co-expression of ric-3 in Xenopus laevis oocytes enhances the activity of the C.elegans DEG-3/DES-2 and of the rat α-7 acetylcholine receptors. Together, these data suggest that RIC-3 is specifically required for the maturation of acetylcholine receptors

Conservation within the RIC-3 gene family: Effectors of mammalian nicotinic acetylcholine receptor expression

In Caenorhabditis elegans, the ric-3 gene is required for the maturation of multiple nicotinic acetylcholine receptors (nAChRs), whereas other neurotransmittergated channels expressed within the same cells are unaffected by the presence of RIC-3. Here we show that RIC-3 is a member of a conserved gene family with representatives in both vertebrates and invertebrates. All members of this family have two transmembrane domains followed by a coiled-coil domain. Expression of the human ric-3 homolog, hric3, like the C. elegans ric-3, enhances C. elegans DEG-3/DES-2, rat α7, and human α7 nAChR-dependent whole-cell current amplitudes in Xenopus leavis oocytes, thus demonstrating functional conservation. However, hric3 also reduces human α4β2 and α3β4 nAChR-dependent whole-cell current amplitudes. Thus, hric3 shows differential effects on human nAChRs unlike the observed uniform effect of ric-3 on C. elegans nAChRs. Moreover, hric3 totally abolished currents evoked by 5-HT3 serotonin receptors, whereas it barely modified α1 glycine receptor currents. With this caveat, RIC-3 belongs to a conserved family of genes likely to regulate nAChR-mediated transmission throughout evolution. Analysis of transcripts encoded by the hric3 locus shows that it encodes for multiple transcripts, likely to produce multiple hric3 isoforms, and that hric3 is expressed in neurons and muscles, thus enabling its interactions with nAChRs in vivo.This work was supported by a U. S.-Israel Binational Science Foundation Grant 1999-074-01 and grants from the Ministry of Education of Spain (Grants PM98-0097 and PM98-0104) and Generalitat Valenciana (Grant CTIDIB/2002/138).Peer reviewe