151
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Serrano-Saiz E, Leyva-Díaz E, De La Cruz E, Hobert O. BRN3-type POU Homeobox Genes Maintain the Identity of Mature Postmitotic Neurons in Nematodes and Mice. Curr Biol 2018; 28:2813-2823.e2. [PMID: 30146154 DOI: 10.1016/j.cub.2018.06.045] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2018] [Revised: 06/08/2018] [Accepted: 06/19/2018] [Indexed: 11/28/2022]
Abstract
Many distinct regulatory factors have been shown to be required for the proper initiation of neuron-type-specific differentiation programs, but much less is known about the regulatory programs that maintain the differentiated state in the adult [1-3]. One possibility is that regulatory factors that initiate a terminal differentiation program during development are continuously required to maintain the differentiated state. Here, we test this hypothesis by investigating the function of two orthologous POU homeobox genes in nematodes and mice. The C. elegans POU homeobox gene unc-86 is a terminal selector that is required during development to initiate the terminal differentiation program of several distinct neuron classes [4-13]. Through post-developmental removal of unc-86 activity, we show here that unc-86 is also continuously required throughout the life of many neuron classes to maintain neuron-class-specific identity features. Similarly, the mouse unc-86 ortholog Brn3a/POU4F1 has been shown to control the initiation of the terminal differentiation program of distinct neuron types across the mouse brain, such as the medial habenular neurons [14-20]. By conditionally removing Brn3a in the adult mouse central nervous system, we show that, like its invertebrate ortholog unc-86, Brn3a is also required for the maintenance of terminal identity features of medial habenular neurons. In addition, Brn3a is required for the survival of these neurons, indicating that identity maintenance and survival are genetically linked. We conclude that the continuous expression of transcription factors is essential for the active maintenance of the differentiated state of a neuron across phylogeny.
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Affiliation(s)
- Esther Serrano-Saiz
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY, USA.
| | - Eduardo Leyva-Díaz
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY, USA
| | - Estanislao De La Cruz
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY, USA
| | - Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY, USA.
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152
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Knickelbine JJ, Konop CJ, Viola IR, Rogers CB, Messinger LA, Vestling MM, Stretton AOW. Different Bioactive Neuropeptides are Expressed in Two Sub-Classes of GABAergic RME Nerve Ring Motorneurons in Ascaris suum. ACS Chem Neurosci 2018; 9:2025-2040. [PMID: 29400437 DOI: 10.1021/acschemneuro.7b00450] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Neuropeptides can have significant effects on neurons and synapses, but among the ∼250 predicted peptides in nematodes, few have been characterized functionally. Here, we report new neuropeptides in the 4 RME nerve ring motorneurons of the nematode Ascaris suum. These GABAergic neurons are involved in three-dimensional head movement. Mass spectrometry (MS) of single dissected RMEs detected a total of 12 neuropeptides (encoded by five genes), nine of which are novel. None of these are expressed in the DI/VI inhibitory GABAergic motorneurons that synapse onto body wall muscle. Using peptide sequences obtained by tandem MS, we cloned the peptide-encoding transcripts and synthesized riboprobes for in situ hybridization (ISH). This complementary technique corroborated the results from single-cell MS, showing that the dissections were not contaminated with adhering tissue from other cells. We also synthesized a multiple antigenic peptide to raise a highly specific antibody against one of the endogenous peptides, which labeled the same cells detected by MS and ISH. Our results show that the RMEs can be divided into two subsets: RMED/V (expressing afp-2, afp-15, Asu-nlp-58, and high levels of afp-16) and RMEL/R (expressing afp-15 and low levels of afp-4 and afp-16). Almost all of these peptides are bioactive in A. suum.
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153
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Konstantinides N, Kapuralin K, Fadil C, Barboza L, Satija R, Desplan C. Phenotypic Convergence: Distinct Transcription Factors Regulate Common Terminal Features. Cell 2018; 174:622-635.e13. [PMID: 29909983 PMCID: PMC6082168 DOI: 10.1016/j.cell.2018.05.021] [Citation(s) in RCA: 136] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Revised: 03/28/2018] [Accepted: 05/09/2018] [Indexed: 12/25/2022]
Abstract
Transcription factors regulate the molecular, morphological, and physiological characteristics of neurons and generate their impressive cell-type diversity. To gain insight into the general principles that govern how transcription factors regulate cell-type diversity, we used large-scale single-cell RNA sequencing to characterize the extensive cellular diversity in the Drosophila optic lobes. We sequenced 55,000 single cells and assigned them to 52 clusters. We validated and annotated many clusters using RNA sequencing of FACS-sorted single-cell types and cluster-specific genes. To identify transcription factors responsible for inducing specific terminal differentiation features, we generated a "random forest" model, and we showed that the transcription factors Apterous and Traffic-jam are required in many but not all cholinergic and glutamatergic neurons, respectively. In fact, the same terminal characters often can be regulated by different transcription factors in different cell types, arguing for extensive phenotypic convergence. Our data provide a deep understanding of the developmental and functional specification of a complex brain structure.
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Affiliation(s)
| | - Katarina Kapuralin
- New York University Abu Dhabi, Saadiyat Island, Abu Dhabi, United Arab Emirates
| | - Chaimaa Fadil
- Department of Biology, New York University, New York, NY 10003, USA; New York University Abu Dhabi, Saadiyat Island, Abu Dhabi, United Arab Emirates
| | - Luendreo Barboza
- Department of Biology, New York University, New York, NY 10003, USA; Neuroscience Institute, NYU Langone Medical Center, New York, NY 10016, USA; New York Genome Center, New York, NY 10013, USA
| | - Rahul Satija
- Department of Biology, New York University, New York, NY 10003, USA; New York Genome Center, New York, NY 10013, USA
| | - Claude Desplan
- Department of Biology, New York University, New York, NY 10003, USA; New York University Abu Dhabi, Saadiyat Island, Abu Dhabi, United Arab Emirates.
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154
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Pinkas A, Lawes M, Aschner M. System-specific neurodegeneration following glucotoxicity in the C. elegans model. Neurotoxicology 2018; 68:88-90. [PMID: 30036563 DOI: 10.1016/j.neuro.2018.07.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2018] [Revised: 06/27/2018] [Accepted: 07/06/2018] [Indexed: 12/14/2022]
Abstract
Hyperglycemia-related neuropathy leads to the onset and exacerbation of several pathologies. The C. elegans model has been used to study this phenomenon and its underlying mechanisms using a broad evaluation for neurodegeneration. Here, we report a system-specific susceptibility for glucotoxicity, namely the dopaminergic, glutamatergic and cholinergic system. Under high-glucose conditions, these systems (and not the serotonergic or GABAergic) were impaired, as observed by evaluating the fluorescent signal in GFP-tagged worm strains. The significance and implications of unequal susceptibility for glucotoxicity in the nervous system is discussed.
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Affiliation(s)
- Adi Pinkas
- Albert Einstein College of Medicine, Jack and Pearl Resnick Campus, 1300 Morris Park Avenue, Forchheimer Building, Room 209, Bronx, NY 10461, United States.
| | - Michael Lawes
- Albert Einstein College of Medicine, Jack and Pearl Resnick Campus, 1300 Morris Park Avenue, Forchheimer Building, Room 209, Bronx, NY 10461, United States
| | - Michael Aschner
- Albert Einstein College of Medicine, Jack and Pearl Resnick Campus, 1300 Morris Park Avenue, Forchheimer Building, Room 209, Bronx, NY 10461, United States
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155
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Hilbert ZA, Kim DH. PDF-1 neuropeptide signaling regulates sexually dimorphic gene expression in shared sensory neurons of C. elegans. eLife 2018; 7:36547. [PMID: 30024377 PMCID: PMC6053303 DOI: 10.7554/elife.36547] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Accepted: 07/05/2018] [Indexed: 12/23/2022] Open
Abstract
Sexually dimorphic behaviors are a feature common to species across the animal kingdom, however how such behaviors are generated from mostly sex-shared nervous systems is not well understood. Building on our previous work which described the sexually dimorphic expression of a neuroendocrine ligand, DAF-7, and its role in behavioral decision-making in C. elegans (Hilbert and Kim, 2017), we show here that sex-specific expression of daf-7 is regulated by another neuroendocrine ligand, Pigment Dispersing Factor (PDF-1), which has previously been implicated in regulating male-specific behavior (Barrios et al., 2012). Our analysis revealed that PDF-1 signaling acts sex- and cell-specifically in the ASJ neurons to regulate the expression of daf-7, and we show that differences in PDFR-1 receptor activity account for the sex-specific effects of this pathway. Our data suggest that modulation of the sex-shared nervous system by a cascade of neuroendocrine signals can shape sexually dimorphic behaviors.
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Affiliation(s)
- Zoë A Hilbert
- Department of Biology, Massachusetts Institute of Technology, Cambridge, United States
| | - Dennis H Kim
- Department of Biology, Massachusetts Institute of Technology, Cambridge, United States
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156
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Zhang B, Gong J, Zhang W, Xiao R, Liu J, Xu XZS. Brain-gut communications via distinct neuroendocrine signals bidirectionally regulate longevity in C. elegans. Genes Dev 2018; 32:258-270. [PMID: 29491136 PMCID: PMC5859967 DOI: 10.1101/gad.309625.117] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 01/24/2018] [Indexed: 11/24/2022]
Abstract
Zhang et al. identified two distinct neuroendocrine signaling circuits by which the worm nervous system senses cool and warm environmental temperatures through cool- and warm-sensitive neurons and then signals the gut to extend and shorten life span, respectively. Tissue–tissue communications are integral to organismal aging, orchestrating a body-wide aging process. The brain plays a key role in this process by detecting and processing signals from the environment and then communicating them to distal tissues such as the gut to regulate longevity. How this is achieved, however, is poorly understood. Here, using Caenorhabditis elegans as a model, we identified two distinct neuroendocrine signaling circuits by which the worm nervous system senses cool and warm environmental temperatures through cool- and warm-sensitive neurons and then signals the gut to extend and shorten life span, respectively. The prolongevity “cool” circuit uses the small neurotransmitters glutamate and serotonin, whereas the anti-longevity “warm” circuit is mediated by insulin-like neuropeptides. Both types of neuroendocrine signals converge on the gut through their cognate receptors to differentially regulate the transcription factor DAF-16/FOXO, leading to opposing outcomes in longevity. Our study illustrates how the brain detects and processes environmental signals to bidirectionally regulate longevity by signaling the gut.
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Affiliation(s)
- Bi Zhang
- International Research Center for Sensory Biology and Technology of the Ministry of Science and Technology, Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China.,Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Jianke Gong
- International Research Center for Sensory Biology and Technology of the Ministry of Science and Technology, Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China.,Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Wenyuan Zhang
- International Research Center for Sensory Biology and Technology of the Ministry of Science and Technology, Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - Rui Xiao
- Department of Aging and Geriatric Research, Institute on Aging, University of Florida, Gainesville, Florida 32610, USA
| | - Jianfeng Liu
- International Research Center for Sensory Biology and Technology of the Ministry of Science and Technology, Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
| | - X Z Shawn Xu
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109, USA.,Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA
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157
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Split cGAL, an intersectional strategy using a split intein for refined spatiotemporal transgene control in Caenorhabditis elegans. Proc Natl Acad Sci U S A 2018; 115:3900-3905. [PMID: 29581308 DOI: 10.1073/pnas.1720063115] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Bipartite expression systems, such as the GAL4-UAS system, allow fine manipulation of gene expression and are powerful tools for interrogating gene function. Recently, we established cGAL, a GAL4-based bipartite expression system for transgene control in Caenorhabditis elegans, where a single promoter dictates the expression pattern of a cGAL driver, which then binds target upstream activation sequences to drive expression of a downstream effector gene. Here, we report a split strategy for cGAL using the split intein gp41-1 for intersectional control of transgene expression. Split inteins are protein domains that associate, self-excise, and covalently ligate their flanking peptides together. We split the DNA binding domain and transcriptional activation domain of cGAL and fused them to the N terminal of gp41-1-N-intein and the C terminal of gp41-1-C-intein, respectively. In cells where both halves of cGAL are expressed, a functional cGAL driver is reconstituted via intein-mediated protein splicing. This reconstitution allows expression of the driver to be dictated by two promoters for refined spatial control or spatiotemporal control of transgene expression. We apply the split cGAL system to genetically access the single pair of MC neurons (previously inaccessible with a single promoter), and reveal an important role of protein kinase A in rhythmic pharyngeal pumping in C. elegans Thus, the split cGAL system gives researchers a greater degree of spatiotemporal control over transgene expression, and will be a valuable genetic tool in C. elegans for dissecting gene function with finer cell-specific resolution.
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158
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Barr MM, García LR, Portman DS. Sexual Dimorphism and Sex Differences in Caenorhabditis elegans Neuronal Development and Behavior. Genetics 2018; 208:909-935. [PMID: 29487147 PMCID: PMC5844341 DOI: 10.1534/genetics.117.300294] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Accepted: 01/05/2018] [Indexed: 01/05/2023] Open
Abstract
As fundamental features of nearly all animal species, sexual dimorphisms and sex differences have particular relevance for the development and function of the nervous system. The unique advantages of the nematode Caenorhabditis elegans have allowed the neurobiology of sex to be studied at unprecedented scale, linking ultrastructure, molecular genetics, cell biology, development, neural circuit function, and behavior. Sex differences in the C. elegans nervous system encompass prominent anatomical dimorphisms as well as differences in physiology and connectivity. The influence of sex on behavior is just as diverse, with biological sex programming innate sex-specific behaviors and modifying many other aspects of neural circuit function. The study of these differences has provided important insights into mechanisms of neurogenesis, cell fate specification, and differentiation; synaptogenesis and connectivity; principles of circuit function, plasticity, and behavior; social communication; and many other areas of modern neurobiology.
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Affiliation(s)
- Maureen M Barr
- Department of Genetics, Rutgers University, Piscataway, New Jersey 08854-8082
| | - L Rene García
- Department of Biology, Texas A&M University, College Station, Texas 77843-3258
| | - Douglas S Portman
- Department of Biomedical Genetics, University of Rochester, New York 14642
- Department of Neuroscience, University of Rochester, New York 14642
- Department of Biology, University of Rochester, New York 14642
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159
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De Stasio EA, Mueller KP, Bauer RJ, Hurlburt AJ, Bice SA, Scholtz SL, Phirke P, Sugiaman-Trapman D, Stinson LA, Olson HB, Vogel SL, Ek-Vazquez Z, Esemen Y, Korzynski J, Wolfe K, Arbuckle BN, Zhang H, Lombard-Knapp G, Piasecki BP, Swoboda P. An Expanded Role for the RFX Transcription Factor DAF-19, with Dual Functions in Ciliated and Nonciliated Neurons. Genetics 2018; 208:1083-1097. [PMID: 29301909 PMCID: PMC5844324 DOI: 10.1534/genetics.117.300571] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Accepted: 01/02/2017] [Indexed: 02/06/2023] Open
Abstract
Regulatory Factor X (RFX) transcription factors (TFs) are best known for activating genes required for ciliogenesis in both vertebrates and invertebrates. In humans, eight RFX TFs have a variety of tissue-specific functions, while in the worm Caenorhabditis elegans, the sole RFX gene, daf-19, encodes a set of nested isoforms. Null alleles of daf-19 confer pleiotropic effects including altered development with a dauer constitutive phenotype, complete absence of cilia and ciliary proteins, and defects in synaptic protein maintenance. We sought to identify RFX/daf-19 target genes associated with neuronal functions other than ciliogenesis using comparative transcriptome analyses at different life stages of the worm. Subsequent characterization of gene expression patterns revealed one set of genes activated in the presence of DAF-19 in ciliated sensory neurons, whose activation requires the daf-19c isoform, also required for ciliogenesis. A second set of genes is downregulated in the presence of DAF-19, primarily in nonsensory neurons. The human orthologs of some of these neuronal genes are associated with human diseases. We report the novel finding that daf-19a is directly or indirectly responsible for downregulation of these neuronal genes in C. elegans by characterizing a new mutation affecting the daf-19a isoform (tm5562) and not associated with ciliogenesis, but which confers synaptic and behavioral defects. Thus, we have identified a new regulatory role for RFX TFs in the nervous system. The new daf-19 candidate target genes we have identified by transcriptomics will serve to uncover the molecular underpinnings of the pleiotropic effects that daf-19 exerts on nervous system function.
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Affiliation(s)
| | | | - Rosemary J Bauer
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | | | - Sophie A Bice
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | - Sophie L Scholtz
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | - Prasad Phirke
- Department of Biosciences and Nutrition, Karolinska Institute, 141 83 Huddinge, Sweden
| | | | - Loraina A Stinson
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | - Haili B Olson
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | - Savannah L Vogel
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | | | - Yagmur Esemen
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | - Jessica Korzynski
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | - Kelsey Wolfe
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | - Bonnie N Arbuckle
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | - He Zhang
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | | | - Brian P Piasecki
- Department of Biology, Lawrence University, Appleton, Wisconsin 54911
| | - Peter Swoboda
- Department of Biosciences and Nutrition, Karolinska Institute, 141 83 Huddinge, Sweden
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160
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Regulation of Glutamate Signaling in the Sensorimotor Circuit by CASY-1A/Calsyntenin in Caenorhabditis elegans. Genetics 2018; 208:1553-1564. [PMID: 29475851 PMCID: PMC5887148 DOI: 10.1534/genetics.118.300834] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2018] [Accepted: 02/21/2018] [Indexed: 12/02/2022] Open
Abstract
Locomotion is one of the most prominent behaviors in the nematode Caenorhabditis elegans. Neuronal circuits that ultimately produce coordinated dorso-ventral sinusoidal bends mediate this behavior. Synchronized locomotion requires an intricate balance between excitation and inhibition at the neuromuscular junctions (NMJ), the complex cellular and molecular mechanisms of which are not fully understood. Here, we describe the role of a cell adhesion molecule CASY-1, which functions to maintain this balance at the NMJ. In this study, we dissect out mechanisms by which the longer CASY-1A isoform could be affecting the excitatory cholinergic signaling at the NMJ by modulating the activity of sensory neurons. Mutants in casy-1 appear to have hyperactive sensory neurons, resulting in accelerated locomotion and motor circuit activity. These sensory neurons mediate increased motor activity via enhanced glutamate release. Using genetic, pharmacological, and optogenetic manipulations, we establish that CASY-1A is required to monitor the activity of these neurons. Our study illustrates a novel neuromodulatory role of CASY-1-mediated signaling in regulating the excitation-inhibition balance of the motor circuit.
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161
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Arnatkevic̆iūtė A, Fulcher BD, Pocock R, Fornito A. Hub connectivity, neuronal diversity, and gene expression in the Caenorhabditis elegans connectome. PLoS Comput Biol 2018; 14:e1005989. [PMID: 29432412 PMCID: PMC5825174 DOI: 10.1371/journal.pcbi.1005989] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Revised: 02/23/2018] [Accepted: 01/19/2018] [Indexed: 11/18/2022] Open
Abstract
Studies of nervous system connectivity, in a wide variety of species and at different scales of resolution, have identified several highly conserved motifs of network organization. One such motif is a heterogeneous distribution of connectivity across neural elements, such that some elements act as highly connected and functionally important network hubs. These brain network hubs are also densely interconnected, forming a so-called rich club. Recent work in mouse has identified a distinctive transcriptional signature of neural hubs, characterized by tightly coupled expression of oxidative metabolism genes, with similar genes characterizing macroscale inter-modular hub regions of the human cortex. Here, we sought to determine whether hubs of the neuronal C. elegans connectome also show tightly coupled gene expression. Using open data on the chemical and electrical connectivity of 279 C. elegans neurons, and binary gene expression data for each neuron across 948 genes, we computed a correlated gene expression score for each pair of neurons, providing a measure of their gene expression similarity. We demonstrate that connections between hub neurons are the most similar in their gene expression while connections between nonhubs are the least similar. Genes with the greatest contribution to this effect are involved in glutamatergic and cholinergic signaling, and other communication processes. We further show that coupled expression between hub neurons cannot be explained by their neuronal subtype (i.e., sensory, motor, or interneuron), separation distance, chemically secreted neurotransmitter, birth time, pairwise lineage distance, or their topological module affiliation. Instead, this coupling is intrinsically linked to the identity of most hubs as command interneurons, a specific class of interneurons that regulates locomotion. Our results suggest that neural hubs may possess a distinctive transcriptional signature, preserved across scales and species, that is related to the involvement of hubs in regulating the higher-order behaviors of a given organism.
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Affiliation(s)
- Aurina Arnatkevic̆iūtė
- Brain and Mental Health Laboratory, Monash Institute of Cognitive and Clinical Neurosciences, School of Psychological Sciences, Monash University, Clayton, VIC, Australia
| | - Ben D. Fulcher
- Brain and Mental Health Laboratory, Monash Institute of Cognitive and Clinical Neurosciences, School of Psychological Sciences, Monash University, Clayton, VIC, Australia
| | - Roger Pocock
- Development and Stem Cells Program, Monash Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash University, Clayton, VIC, Australia
| | - Alex Fornito
- Brain and Mental Health Laboratory, Monash Institute of Cognitive and Clinical Neurosciences, School of Psychological Sciences, Monash University, Clayton, VIC, Australia
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162
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Murray JI. Systems biology of embryonic development: Prospects for a complete understanding of the Caenorhabditis elegans embryo. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2018; 7:e314. [PMID: 29369536 DOI: 10.1002/wdev.314] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Revised: 12/01/2017] [Accepted: 12/12/2017] [Indexed: 01/07/2023]
Abstract
The convergence of developmental biology and modern genomics tools brings the potential for a comprehensive understanding of developmental systems. This is especially true for the Caenorhabditis elegans embryo because its small size, invariant developmental lineage, and powerful genetic and genomic tools provide the prospect of a cellular resolution understanding of messenger RNA (mRNA) expression and regulation across the organism. We describe here how a systems biology framework might allow large-scale determination of the embryonic regulatory relationships encoded in the C. elegans genome. This framework consists of two broad steps: (a) defining the "parts list"-all genes expressed in all cells at each time during development and (b) iterative steps of computational modeling and refinement of these models by experimental perturbation. Substantial progress has been made towards defining the parts list through imaging methods such as large-scale green fluorescent protein (GFP) reporter analysis. Imaging results are now being augmented by high-resolution transcriptome methods such as single-cell RNA sequencing, and it is likely the complete expression patterns of all genes across the embryo will be known within the next few years. In contrast, the modeling and perturbation experiments performed so far have focused largely on individual cell types or genes, and improved methods will be needed to expand them to the full genome and organism. This emerging comprehensive map of embryonic expression and regulatory function will provide a powerful resource for developmental biologists, and would also allow scientists to ask questions not accessible without a comprehensive picture. This article is categorized under: Invertebrate Organogenesis > Worms Technologies > Analysis of the Transcriptome Gene Expression and Transcriptional Hierarchies > Gene Networks and Genomics.
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Affiliation(s)
- John Isaac Murray
- Department of Genetics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania
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163
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Gao S, Guan SA, Fouad AD, Meng J, Kawano T, Huang YC, Li Y, Alcaire S, Hung W, Lu Y, Qi YB, Jin Y, Alkema M, Fang-Yen C, Zhen M. Excitatory motor neurons are local oscillators for backward locomotion. eLife 2018; 7:e29915. [PMID: 29360035 PMCID: PMC5780044 DOI: 10.7554/elife.29915] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 10/22/2017] [Indexed: 01/16/2023] Open
Abstract
Cell- or network-driven oscillators underlie motor rhythmicity. The identity of C. elegans oscillators remains unknown. Through cell ablation, electrophysiology, and calcium imaging, we show: (1) forward and backward locomotion is driven by different oscillators; (2) the cholinergic and excitatory A-class motor neurons exhibit intrinsic and oscillatory activity that is sufficient to drive backward locomotion in the absence of premotor interneurons; (3) the UNC-2 P/Q/N high-voltage-activated calcium current underlies A motor neuron's oscillation; (4) descending premotor interneurons AVA, via an evolutionarily conserved, mixed gap junction and chemical synapse configuration, exert state-dependent inhibition and potentiation of A motor neuron's intrinsic activity to regulate backward locomotion. Thus, motor neurons themselves derive rhythms, which are dually regulated by the descending interneurons to control the reversal motor state. These and previous findings exemplify compression: essential circuit properties are conserved but executed by fewer numbers and layers of neurons in a small locomotor network.
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Affiliation(s)
- Shangbang Gao
- Key Laboratory of Molecular Biophysics of the Ministry of EducationCollege of Life Science and Technology, Huazhong University of Science and TechnologyWuhanChina
| | - Sihui Asuka Guan
- Lunenfeld-Tanenbaum Research InstituteMount Sinai HospitalTorontoCanada
- Department of Molecular GeneticsUniversity of TorontoTorontoCanada
- Department of PhysiologyUniversity of TorontoTorontoCanada
| | - Anthony D Fouad
- Department of BioengineeringSchool of Engineering and Applied Science, University of PennsylvaniaPhiladelphiaUnited States
| | - Jun Meng
- Lunenfeld-Tanenbaum Research InstituteMount Sinai HospitalTorontoCanada
- Department of Molecular GeneticsUniversity of TorontoTorontoCanada
- Department of PhysiologyUniversity of TorontoTorontoCanada
| | - Taizo Kawano
- Lunenfeld-Tanenbaum Research InstituteMount Sinai HospitalTorontoCanada
| | - Yung-Chi Huang
- Department of NeurobiologyUniversity of Massachusetts Medical SchoolWorcesterUnited States
| | - Yi Li
- Key Laboratory of Molecular Biophysics of the Ministry of EducationCollege of Life Science and Technology, Huazhong University of Science and TechnologyWuhanChina
| | - Salvador Alcaire
- Lunenfeld-Tanenbaum Research InstituteMount Sinai HospitalTorontoCanada
- Department of Molecular GeneticsUniversity of TorontoTorontoCanada
- Department of PhysiologyUniversity of TorontoTorontoCanada
| | - Wesley Hung
- Lunenfeld-Tanenbaum Research InstituteMount Sinai HospitalTorontoCanada
| | - Yangning Lu
- Lunenfeld-Tanenbaum Research InstituteMount Sinai HospitalTorontoCanada
- Department of Molecular GeneticsUniversity of TorontoTorontoCanada
- Department of PhysiologyUniversity of TorontoTorontoCanada
| | - Yingchuan Billy Qi
- Neurobiology Section, Division of Biological SciencesUniversity of CaliforniaSan DiegoUnited States
| | - Yishi Jin
- Neurobiology Section, Division of Biological SciencesUniversity of CaliforniaSan DiegoUnited States
| | - Mark Alkema
- Department of NeurobiologyUniversity of Massachusetts Medical SchoolWorcesterUnited States
| | - Christopher Fang-Yen
- Department of BioengineeringSchool of Engineering and Applied Science, University of PennsylvaniaPhiladelphiaUnited States
- Department of NeuroscienceUniversity of PennsylvaniaPhiladelphiaUnited States
| | - Mei Zhen
- Lunenfeld-Tanenbaum Research InstituteMount Sinai HospitalTorontoCanada
- Department of Molecular GeneticsUniversity of TorontoTorontoCanada
- Department of PhysiologyUniversity of TorontoTorontoCanada
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164
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Liu H, Yang W, Wu T, Duan F, Soucy E, Jin X, Zhang Y. Cholinergic Sensorimotor Integration Regulates Olfactory Steering. Neuron 2018; 97:390-405.e3. [PMID: 29290549 PMCID: PMC5773357 DOI: 10.1016/j.neuron.2017.12.003] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Revised: 11/06/2017] [Accepted: 12/01/2017] [Indexed: 12/14/2022]
Abstract
Sensorimotor integration regulates goal-directed movements. We study the signaling mechanisms underlying sensorimotor integration in C. elegans during olfactory steering, when the sinusoidal movements of the worm generate an in-phase oscillation in the concentration of the sampled odorant. We show that cholinergic neurotransmission encodes the oscillatory sensory response and the motor state of head undulations by acting through an acetylcholine-gated channel and a muscarinic acetylcholine receptor, respectively. These signals converge on two axonal domains of an interneuron RIA, where the sensory-evoked signal suppresses the motor-encoding signal to transform the spatial information of the odorant into the asymmetry between the axonal activities. The asymmetric synaptic outputs of the RIA axonal domains generate a directional bias in the locomotory trajectory. Experience alters the sensorimotor integration to generate specific behavioral changes. Our study reveals how cholinergic neurotransmission, which can represent sensory and motor information in the mammalian brain, regulates sensorimotor integration during goal-directed locomotions.
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Affiliation(s)
- He Liu
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA; Center for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - Wenxing Yang
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA; Center for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - Taihong Wu
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA; Center for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - Fengyun Duan
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA; Center for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - Edward Soucy
- Center for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - Xin Jin
- Society of Fellows, Harvard University, Cambridge, MA 02138, USA
| | - Yun Zhang
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA; Center for Brain Science, Harvard University, Cambridge, MA 02138, USA.
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165
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Abstract
We revisit the classification of neuronal cell types in the nervous system of the nematode Caenorhabditis elegans. Based on anatomy and synaptic connectivity patterns, the 302 neurons of the nervous system of the hermaphrodite were categorized into 118 neuron classes more than 30 years ago. Analysis of all presently available neuronal gene expression patterns reveals a remarkable congruence of anatomical and molecular classification and further suggests subclassification schemes. Transcription factor expression profiles alone are sufficient to uniquely classify more than 90% of all neuron classes in the C. elegans nervous system. Neuron classification in C. elegans may be paradigmatic for neuron classification schemes in vertebrate nervous systems.
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166
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Vidal B, Aghayeva U, Sun H, Wang C, Glenwinkel L, Bayer EA, Hobert O. An atlas of Caenorhabditis elegans chemoreceptor expression. PLoS Biol 2018; 16:e2004218. [PMID: 29293491 PMCID: PMC5749674 DOI: 10.1371/journal.pbio.2004218] [Citation(s) in RCA: 64] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Accepted: 11/22/2017] [Indexed: 12/20/2022] Open
Abstract
One goal of modern day neuroscience is the establishment of molecular maps that assign unique features to individual neuron types. Such maps provide important starting points for neuron classification, for functional analysis, and for developmental studies aimed at defining the molecular mechanisms of neuron identity acquisition and neuron identity diversification. In this resource paper, we describe a nervous system-wide map of the potential expression sites of 244 members of the largest gene family in the C. elegans genome, rhodopsin-like (class A) G-protein-coupled receptor (GPCR) chemoreceptors, using classic gfp reporter gene technology. We cover representatives of all sequence families of chemoreceptor GPCRs, some of which were previously entirely uncharacterized. Most reporters are expressed in a very restricted number of cells, often just in single cells. We assign GPCR reporter expression to all but two of the 37 sensory neuron classes of the sex-shared, core nervous system. Some sensory neurons express a very small number of receptors, while others, particularly nociceptive neurons, coexpress several dozen GPCR reporter genes. GPCR reporters are also expressed in a wide range of inter- and motorneurons, as well as non-neuronal cells, suggesting that GPCRs may constitute receptors not just for environmental signals, but also for internal cues. We observe only one notable, frequent association of coexpression patterns, namely in one nociceptive amphid (ASH) and two nociceptive phasmid sensory neurons (PHA, PHB). We identified GPCRs with sexually dimorphic expression and several GPCR reporters that are expressed in a left/right asymmetric manner. We identified a substantial degree of GPCR expression plasticity; particularly in the context of the environmentally-induced dauer diapause stage when one third of all tested GPCRs alter the cellular specificity of their expression within and outside the nervous system. Intriguingly, in a number of cases, the dauer-specific alterations of GPCR reporter expression in specific neuron classes are maintained during postdauer life and in some case new patterns are induced post-dauer, demonstrating that GPCR gene expression may serve as traits of life history. Taken together, our resource provides an entry point for functional studies and also offers a host of molecular markers for studying molecular patterning and plasticity of the nervous system.
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Affiliation(s)
- Berta Vidal
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
| | - Ulkar Aghayeva
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
| | - Haosheng Sun
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
| | - Chen Wang
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
| | - Lori Glenwinkel
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
| | - Emily A. Bayer
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
| | - Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
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167
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Kalinnikova TB, Yakhina AF, Egorova AV, Shagidullin RR, Gainutdinov MH. Heat Stress and Agonists of Muscarinic Cholinergic Receptors Modulate Sensitivity of Nicotinic Cholinergic Receptors in Soil Nematode Caenorhabditis elegans. Bull Exp Biol Med 2017; 164:144-147. [PMID: 29178050 DOI: 10.1007/s10517-017-3944-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Indexed: 11/30/2022]
Abstract
We studied the effect of moderate heat stress (30oC) and muscarinic cholinergic receptor agonists arecoline and pilocarpine on sensitivity of the behavior of the nematode Caenorhabditis elegans of N2 line to the action of the agonist of nicotinic cholinergic receptor agonist levamisole. Heat stress and muscarinic cholinergic receptor agonists increased the sensitivity of swimming induced by mechanical stimulation to levamisole (32-64 μM), which manifested in dyscoordination of locomotor muscles during swimming and complete loss of ability to swim. Combined exposure to heat stress and muscarinic cholinergic receptor agonists revealed their synergism in the influence on sensitivity of swimming behavior to levamisole: heating to 30oC potentiated the effect of arecoline and arecoline potentiated the effect of heat stress. It is assumed, that the effect of heat stress on the sensitivity of nicotinic receptors is mediated by its effect on muscarinic receptors.
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Affiliation(s)
- T B Kalinnikova
- Institute of Problems of Ecology and Subsoil Use, Academy of Sciences of the Republic of Tatarstan, Kazan, Tatarstan Republic, Russia.
| | - A F Yakhina
- Institute of Problems of Ecology and Subsoil Use, Academy of Sciences of the Republic of Tatarstan, Kazan, Tatarstan Republic, Russia
| | - A V Egorova
- Institute of Problems of Ecology and Subsoil Use, Academy of Sciences of the Republic of Tatarstan, Kazan, Tatarstan Republic, Russia
| | - R R Shagidullin
- Institute of Problems of Ecology and Subsoil Use, Academy of Sciences of the Republic of Tatarstan, Kazan, Tatarstan Republic, Russia
| | - M H Gainutdinov
- Institute of Problems of Ecology and Subsoil Use, Academy of Sciences of the Republic of Tatarstan, Kazan, Tatarstan Republic, Russia
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168
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Rakowski F, Karbowski J. Optimal synaptic signaling connectome for locomotory behavior in Caenorhabditis elegans: Design minimizing energy cost. PLoS Comput Biol 2017; 13:e1005834. [PMID: 29155814 PMCID: PMC5714387 DOI: 10.1371/journal.pcbi.1005834] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Revised: 12/04/2017] [Accepted: 10/19/2017] [Indexed: 11/18/2022] Open
Abstract
The detailed knowledge of C. elegans connectome for 3 decades has not contributed dramatically to our understanding of worm's behavior. One of main reasons for this situation has been the lack of data on the type of synaptic signaling between particular neurons in the worm's connectome. The aim of this study was to determine synaptic polarities for each connection in a small pre-motor circuit controlling locomotion. Even in this compact network of just 7 neurons the space of all possible patterns of connection types (excitation vs. inhibition) is huge. To deal effectively with this combinatorial problem we devised a novel and relatively fast technique based on genetic algorithms and large-scale parallel computations, which we combined with detailed neurophysiological modeling of interneuron dynamics and compared the theory to the available behavioral data. As a result of these massive computations, we found that the optimal connectivity pattern that matches the best locomotory data is the one in which all interneuron connections are inhibitory, even those terminating on motor neurons. This finding is consistent with recent experimental data on cholinergic signaling in C. elegans, and it suggests that the system controlling locomotion is designed to save metabolic energy. Moreover, this result provides a solid basis for a more realistic modeling of neural control in these worms, and our novel powerful computational technique can in principle be applied (possibly with some modifications) to other small-scale functional circuits in C. elegans.
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Affiliation(s)
- Franciszek Rakowski
- Interdisciplinary Centre for Mathematical and Computational Modeling, University of Warsaw, Warsaw, Poland
- Mossakowski Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland
| | - Jan Karbowski
- Nalecz Institute of Biocybernetics and Biomedical Engineering, Polish Academy of Sciences, Warsaw, Poland
- Institute of Applied Mathematics and Mechanics, Department of Mathematics, Informatics and Mechanics, University of Warsaw, Warsaw, Poland
- * E-mail:
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169
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Portman DS. Sexual modulation of sex-shared neurons and circuits in Caenorhabditis elegans. J Neurosci Res 2017; 95:527-538. [PMID: 27870393 DOI: 10.1002/jnr.23912] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Revised: 08/10/2016] [Accepted: 08/10/2016] [Indexed: 12/16/2022]
Abstract
Studies using the nematode C. elegans have provided unique insights into the development and function of sex differences in the nervous system. Enabled by the relative simplicity of this species, comprehensive studies have solved the complete cellular neuroanatomy of both sexes as well as the complete neural connectomes of the entire adult hermaphrodite and the adult male tail. This work, together with detailed behavioral studies, has revealed three aspects of sex differences in the nervous system: sex-specific neurons and circuits; circuits with sexually dimorphic synaptic connectivity; and sex differences in the physiology and functions of shared neurons and circuits. At all of these levels, biological sex influences neural development and function through the activity of a well-defined genetic hierarchy that acts throughout the body to translate chromosomal sex into the state of a master autosomal regulator of sexual differentiation, the transcription factor TRA-1A. This Review focuses on the role of genetic sex in implementing sex differences in shared neurons and circuits, with an emphasis on linking the sexual modulation of specific neural properties to the specification and optimization of sexually divergent and dimorphic behaviors. An important and unexpected finding from these studies is that chemosensory neurons are a primary focus of sexual modulation, with genetic sex adaptively shaping chemosensory repertoire to guide behavioral choice. Importantly, hormone-independent functions of genetic sex are the principal drivers of all of these sex differences, making nematodes an excellent model for understanding similar but poorly understood mechanisms that likely act throughout the animal kingdom. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Douglas S Portman
- Center for Neural Development and Disease, Department of Biomedical Genetics, Neuroscience, and Biology, University of Rochester Medical Center, Rochester, New York
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170
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Topalidou I, Cooper K, Pereira L, Ailion M. Dopamine negatively modulates the NCA ion channels in C. elegans. PLoS Genet 2017; 13:e1007032. [PMID: 28968387 PMCID: PMC5638609 DOI: 10.1371/journal.pgen.1007032] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2016] [Revised: 10/12/2017] [Accepted: 09/18/2017] [Indexed: 02/07/2023] Open
Abstract
The NALCN/NCA ion channel is a cation channel related to voltage-gated sodium and calcium channels. NALCN has been reported to be a sodium leak channel with a conserved role in establishing neuronal resting membrane potential, but its precise cellular role and regulation are unclear. The Caenorhabditis elegans orthologs of NALCN, NCA-1 and NCA-2, act in premotor interneurons to regulate motor circuit activity that sustains locomotion. Recently we found that NCA-1 and NCA-2 are activated by a signal transduction pathway acting downstream of the heterotrimeric G protein Gq and the small GTPase Rho. Through a forward genetic screen, here we identify the GPCR kinase GRK-2 as a new player affecting signaling through the Gq-Rho-NCA pathway. Using structure-function analysis, we find that the GPCR phosphorylation and membrane association domains of GRK-2 are required for its function. Genetic epistasis experiments suggest that GRK-2 acts on the D2-like dopamine receptor DOP-3 to inhibit Go signaling and positively modulate NCA-1 and NCA-2 activity. Through cell-specific rescuing experiments, we find that GRK-2 and DOP-3 act in premotor interneurons to modulate NCA channel function. Finally, we demonstrate that dopamine, through DOP-3, negatively regulates NCA activity. Thus, this study identifies a pathway by which dopamine modulates the activity of the NCA channels.
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Affiliation(s)
- Irini Topalidou
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
- * E-mail: (IT); (MA)
| | - Kirsten Cooper
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
| | - Laura Pereira
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, New York, United States of America
| | - Michael Ailion
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
- * E-mail: (IT); (MA)
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171
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The role of gap junctions in the C. elegans connectome. Neurosci Lett 2017; 695:12-18. [PMID: 28886984 DOI: 10.1016/j.neulet.2017.09.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 07/12/2017] [Accepted: 09/01/2017] [Indexed: 10/18/2022]
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172
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Ohno H, Yoshida M, Sato T, Kato J, Miyazato M, Kojima M, Ida T, Iino Y. Luqin-like RYamide peptides regulate food-evoked responses in C. elegans. eLife 2017; 6:e28877. [PMID: 28847365 PMCID: PMC5576490 DOI: 10.7554/elife.28877] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Accepted: 08/08/2017] [Indexed: 12/25/2022] Open
Abstract
Peptide signaling controls many processes involving coordinated actions of multiple organs, such as hormone-mediated appetite regulation. However, the extent to which the mode of action of peptide signaling is conserved in different animals is largely unknown, because many peptides and receptors remain orphan and many undiscovered peptides still exist. Here, we identify two novel Caenorhabditis elegans neuropeptides, LURY-1-1 and LURY-1-2, as endogenous ligands for the neuropeptide receptor-22 (NPR-22). Both peptides derive from the same precursor that is orthologous to invertebrate luqin/arginine-tyrosine-NH2 (RYamide) proneuropeptides. LURY-1 peptides are secreted from two classes of pharyngeal neurons and control food-related processes: feeding, lifespan, egg-laying, and locomotory behavior. We propose that LURY-1 peptides transmit food signals to NPR-22 expressed in feeding pacemaker neurons and a serotonergic neuron. Our results identified a critical role for luqin-like RYamides in feeding-related processes and suggested that peptide-mediated negative feedback is important for satiety regulation in C. elegans.
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Affiliation(s)
- Hayao Ohno
- Department of Biological SciencesGraduate School of Science, The University of TokyoTokyoJapan
| | - Morikatsu Yoshida
- Department of BiochemistryNational Cerebral and Cardiovascular Center Research InstituteOsakaJapan
| | - Takahiro Sato
- Molecular GeneticsInstitute of Life Sciences, Kurume UniversityFukuokaJapan
| | - Johji Kato
- Department of Bioactive PeptidesFrontier Science Research Center, University of MiyazakiMiyazakiJapan
| | - Mikiya Miyazato
- Department of BiochemistryNational Cerebral and Cardiovascular Center Research InstituteOsakaJapan
| | - Masayasu Kojima
- Molecular GeneticsInstitute of Life Sciences, Kurume UniversityFukuokaJapan
| | - Takanori Ida
- Department of Bioactive PeptidesFrontier Science Research Center, University of MiyazakiMiyazakiJapan
- Center for Animal Disease ControlUniversity of MiyazakiMiyazakiJapan
| | - Yuichi Iino
- Department of Biological SciencesGraduate School of Science, The University of TokyoTokyoJapan
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173
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Diversification of C. elegans Motor Neuron Identity via Selective Effector Gene Repression. Neuron 2017; 93:80-98. [PMID: 28056346 DOI: 10.1016/j.neuron.2016.11.036] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Revised: 11/11/2016] [Accepted: 11/11/2016] [Indexed: 12/20/2022]
Abstract
A common organizational feature of nervous systems is the existence of groups of neurons that share common traits but can be divided into individual subtypes based on anatomical or molecular features. We elucidate the mechanistic basis of neuronal diversification processes in the context of C.elegans ventral cord motor neurons that share common traits that are directly activated by the terminal selector UNC-3. Diversification of motor neurons into different classes, each characterized by unique patterns of effector gene expression, is controlled by distinct combinations of phylogenetically conserved, class-specific transcriptional repressors. These repressors are continuously required in postmitotic neurons to prevent UNC-3, which is active in all neuron classes, from activating class-specific effector genes in specific motor neuron subsets via discrete cis-regulatory elements. The strategy of antagonizing the activity of broadly acting terminal selectors of neuron identity in a subtype-specific fashion may constitute a general principle of neuron subtype diversification.
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174
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Kratsios P, Kerk SY, Catela C, Liang J, Vidal B, Bayer EA, Feng W, De La Cruz ED, Croci L, Consalez GG, Mizumoto K, Hobert O. An intersectional gene regulatory strategy defines subclass diversity of C. elegans motor neurons. eLife 2017; 6. [PMID: 28677525 PMCID: PMC5498135 DOI: 10.7554/elife.25751] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Accepted: 06/13/2017] [Indexed: 01/09/2023] Open
Abstract
A core principle of nervous system organization is the diversification of neuron classes into subclasses that share large sets of features but differ in select traits. We describe here a molecular mechanism necessary for motor neurons to acquire subclass-specific traits in the nematode Caenorhabditis elegans. Cholinergic motor neuron classes of the ventral nerve cord can be subdivided into subclasses along the anterior-posterior (A-P) axis based on synaptic connectivity patterns and molecular features. The conserved COE-type terminal selector UNC-3 not only controls the expression of traits shared by all members of a neuron class, but is also required for subclass-specific traits expressed along the A-P axis. UNC-3, which is not regionally restricted, requires region-specific cofactors in the form of Hox proteins to co-activate subclass-specific effector genes in post-mitotic motor neurons. This intersectional gene regulatory principle for neuronal subclass diversification may be conserved from nematodes to mice.
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Affiliation(s)
- Paschalis Kratsios
- Department of Neurobiology, University of Chicago, Chicago, United States
| | - Sze Yen Kerk
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, United States
| | - Catarina Catela
- Department of Neurobiology, University of Chicago, Chicago, United States
| | - Joseph Liang
- Department of Zoology, The University of British Columbia, Vancouver, Canada
| | - Berta Vidal
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, United States
| | - Emily A Bayer
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, United States
| | - Weidong Feng
- Department of Neurobiology, University of Chicago, Chicago, United States
| | - Estanisla Daniel De La Cruz
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, United States
| | - Laura Croci
- Division of Neuroscience, San Raffaele Scientific Institute, Milan, Italy
| | - G Giacomo Consalez
- Division of Neuroscience, San Raffaele Scientific Institute, Milan, Italy.,Università Vita-Salute San Raffaele, Milan, Italy
| | - Kota Mizumoto
- Department of Zoology, The University of British Columbia, Vancouver, Canada
| | - Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, United States
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175
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Serrano-Saiz E, Pereira L, Gendrel M, Aghayeva U, Bhattacharya A, Howell K, Garcia LR, Hobert O. A Neurotransmitter Atlas of the Caenorhabditis elegans Male Nervous System Reveals Sexually Dimorphic Neurotransmitter Usage. Genetics 2017; 206:1251-1269. [PMID: 28684604 PMCID: PMC5500128 DOI: 10.1534/genetics.117.202127] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Accepted: 05/03/2017] [Indexed: 11/18/2022] Open
Abstract
The nervous system of most animals is sexually dimorphic but such dimorphisms are generally poorly mapped on an anatomical, cellular, and molecular level. The adult nervous system of the nematode Caenorhabditis elegans displays a number of clearly defined anatomical sexual dimorphisms, but molecular features of sexually dimorphic neurons remain sparse. In this resource paper, we provide a comprehensive atlas of neurotransmitters used in the nervous system of the male and compare it to that of the hermaphrodite. Among the three major neurotransmitter systems, acetylcholine (ACh) is the most frequently used, followed by glutamate (Glu), and lastly γ-aminobutyric acid (GABA). Many male-specific neurons utilize multiple neurotransmitter systems. Interestingly, we find that neurons that are present in both sexes alter their neurotransmitter usage depending on the sex of the animal. One neuron scales up its usage of ACh, another becomes serotonergic in males, and another one adds a new neurotransmitter (glutamate) to its nonsex-specific transmitter (ACh). In all these cases, neurotransmitter changes are correlated with substantial changes in synaptic connectivity. We assembled the neurotransmitter maps of the male-specific nervous system into a comprehensive atlas that describes the anatomical position of all the neurons of the male-specific nervous system relative to the sex-shared nervous system. We exemplify the usefulness of the neurotransmitter atlas by using it as a tool to define the expression pattern of a synaptic organizer molecule in the male tail. Taken together, the male neurotransmitter atlas provides an entry point for future functional and developmental analysis of the male nervous system.
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Affiliation(s)
- Esther Serrano-Saiz
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York 10027
| | - Laura Pereira
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York 10027
| | - Marie Gendrel
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York 10027
| | - Ulkar Aghayeva
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York 10027
| | - Abhishek Bhattacharya
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York 10027
| | - Kelly Howell
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York 10027
| | - L Rene Garcia
- Department of Biology, Texas A&M University, College Station, Texas 77843
| | - Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York 10027
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176
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Howell K, Hobert O. Morphological Diversity of C. elegans Sensory Cilia Instructed by the Differential Expression of an Immunoglobulin Domain Protein. Curr Biol 2017; 27:1782-1790.e5. [PMID: 28578929 DOI: 10.1016/j.cub.2017.05.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Revised: 04/27/2017] [Accepted: 05/03/2017] [Indexed: 01/08/2023]
Abstract
Cilia on dendritic endings of sensory neurons organize distinct types of sensory machinery [1]. Ciliated endings display neuron-type-specific patterns of membrane elaborations [1-3], but it is not well understood how such neuron-type-specific morphologies are generated and whether they are coupled to the specification of other identity aspects of a terminally differentiated sensory neuron. In the course of a genome-wide analysis of members of a small family of immunoglobulin domain proteins, we found that OIG-8, a previously uncharacterized transmembrane protein with a single immunoglobulin (Ig) domain, instructs the distinct, neuron-type-specific elaboration of ciliated endings of different olfactory neuron types in the nematode C. elegans. OIG-8 protein localizes to ciliated endings of these sensory neurons, and is transcribed at different levels in distinct olfactory neuron types. oig-8 expression levels correlate with the extent of sensory cilia growth and branching patterns. Loss of oig-8 leads to a reduction in the branching patterns of cilia, whereas raising the levels of oig-8 results in an increase in elaborations. Levels of OIG-8 expression are controlled by the specific combination of a terminal selector type of transcription factors that also specify other identity features of distinct olfactory neuron types.
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Affiliation(s)
- Kelly Howell
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY 10027, USA.
| | - Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY 10027, USA.
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177
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Hussey R, Stieglitz J, Mesgarzadeh J, Locke TT, Zhang YK, Schroeder FC, Srinivasan S. Pheromone-sensing neurons regulate peripheral lipid metabolism in Caenorhabditis elegans. PLoS Genet 2017; 13:e1006806. [PMID: 28545126 PMCID: PMC5456406 DOI: 10.1371/journal.pgen.1006806] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Revised: 06/02/2017] [Accepted: 05/05/2017] [Indexed: 12/03/2022] Open
Abstract
It is now established that the central nervous system plays an important role in regulating whole body metabolism and energy balance. However, the extent to which sensory systems relay environmental information to modulate metabolic events in peripheral tissues has remained poorly understood. In addition, it has been challenging to map the molecular mechanisms underlying discrete sensory modalities with respect to their role in lipid metabolism. In previous work our lab has identified instructive roles for serotonin signaling as a surrogate for food availability, as well as oxygen sensing, in the control of whole body metabolism. In this study, we now identify a role for a pair of pheromone-sensing neurons in regulating fat metabolism in C. elegans, which has emerged as a tractable and highly informative model to study the neurobiology of metabolism. A genetic screen revealed that GPA-3, a member of the Gα family of G proteins, regulates body fat content in the intestine, the major metabolic organ for C. elegans. Genetic and reconstitution studies revealed that the potent body fat phenotype of gpa-3 null mutants is controlled from a pair of neurons called ADL(L/R). We show that cAMP functions as the second messenger in the ADL neurons, and regulates body fat stores via the neurotransmitter acetylcholine, from downstream neurons. We find that the pheromone ascr#3, which is detected by the ADL neurons, regulates body fat stores in a GPA-3-dependent manner. We define here a third sensory modality, pheromone sensing, as a major regulator of body fat metabolism. The pheromone ascr#3 is an indicator of population density, thus we hypothesize that pheromone sensing provides a salient 'denominator' to evaluate the amount of food available within a population and to accordingly adjust metabolic rate and body fat levels. The central nervous system plays a vital role in regulating whole body metabolism and energy balance. However, the precise cellular, genetic and molecular mechanisms underlying these effects remain a major unsolved mystery. C. elegans has emerged as a tractable and highly informative model to study the neurobiology of metabolism. Previously, we have identified instructive roles for serotonin signaling as a surrogate for food availability, as well as oxygen sensing, in the control of whole body metabolism. In our current study we have identified a role for a pair of pheromone-sensing neurons in regulating fat metabolism in C. elegans. cAMP acts as a second messenger in these neurons, and regulates body fat stores via acetylcholine signaling in the nervous system. We find that the population-density-sensing pheromone detected by these neurons regulates body fat stores. Together, we define a third sensory modality, population density sensing, as a major regulator of body fat metabolism.
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Affiliation(s)
- Rosalind Hussey
- Department of Molecular Medicine and Department of Neuroscience, The Scripps Research Institute, La Jolla, California, United States of America
- Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, California, United States of America
| | - Jon Stieglitz
- Kellogg School of Science and Technology, The Scripps Research Institute, La Jolla, California, United States of America
| | - Jaleh Mesgarzadeh
- Department of Molecular Medicine and Department of Neuroscience, The Scripps Research Institute, La Jolla, California, United States of America
- Department of Biology, University of California, San Diego, La Jolla, California, United States of America
| | - Tiffany T. Locke
- Department of Biology, University of California, San Diego, La Jolla, California, United States of America
| | - Ying K. Zhang
- Boyce Thompson Institute and Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States of America
| | - Frank C. Schroeder
- Boyce Thompson Institute and Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States of America
| | - Supriya Srinivasan
- Department of Molecular Medicine and Department of Neuroscience, The Scripps Research Institute, La Jolla, California, United States of America
- Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, California, United States of America
- * E-mail:
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178
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The NCA-1 and NCA-2 Ion Channels Function Downstream of G q and Rho To Regulate Locomotion in Caenorhabditis elegans. Genetics 2017; 206:265-282. [PMID: 28325749 DOI: 10.1534/genetics.116.198820] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 03/15/2017] [Indexed: 02/07/2023] Open
Abstract
The heterotrimeric G protein Gq positively regulates neuronal activity and synaptic transmission. Previously, the Rho guanine nucleotide exchange factor Trio was identified as a direct effector of Gq that acts in parallel to the canonical Gq effector phospholipase C. Here, we examine how Trio and Rho act to stimulate neuronal activity downstream of Gq in the nematode Caenorhabditis elegans Through two forward genetic screens, we identify the cation channels NCA-1 and NCA-2, orthologs of mammalian NALCN, as downstream targets of the Gq-Rho pathway. By performing genetic epistasis analysis using dominant activating mutations and recessive loss-of-function mutations in the members of this pathway, we show that NCA-1 and NCA-2 act downstream of Gq in a linear pathway. Through cell-specific rescue experiments, we show that function of these channels in head acetylcholine neurons is sufficient for normal locomotion in C. elegans Our results suggest that NCA-1 and NCA-2 are physiologically relevant targets of neuronal Gq-Rho signaling in C. elegans.
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179
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Liu P, Chen B, Mailler R, Wang ZW. Antidromic-rectifying gap junctions amplify chemical transmission at functionally mixed electrical-chemical synapses. Nat Commun 2017; 8:14818. [PMID: 28317880 PMCID: PMC5364397 DOI: 10.1038/ncomms14818] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 02/06/2017] [Indexed: 11/09/2022] Open
Abstract
Neurons communicate through chemical synapses and electrical synapses (gap junctions). Although these two types of synapses often coexist between neurons, little is known about whether they interact, and whether any interactions between them are important to controlling synaptic strength and circuit functions. By studying chemical and electrical synapses between premotor interneurons (AVA) and downstream motor neurons (A-MNs) in the Caenorhabditis elegans escape circuit, we found that disrupting either the chemical or electrical synapses causes defective escape response. Gap junctions between AVA and A-MNs only allow antidromic current, but, curiously, disrupting them inhibits chemical transmission. In contrast, disrupting chemical synapses has no effect on the electrical coupling. These results demonstrate that gap junctions may serve as an amplifier of chemical transmission between neurons with both electrical and chemical synapses. The use of antidromic-rectifying gap junctions to amplify chemical transmission is potentially a conserved mechanism in circuit functions.
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Affiliation(s)
- Ping Liu
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut 06030, USA
| | - Bojun Chen
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut 06030, USA
| | - Roger Mailler
- Department of Computer Science, University of Tulsa, Tulsa, Oklahoma 74104, USA
| | - Zhao-Wen Wang
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut 06030, USA
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180
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Abstract
Neurotransmitter switching is the gain of one neurotransmitter and the loss of another in the same neuron in response to chronic stimulation. Neurotransmitter receptors on postsynaptic cells change to match the identity of the newly expressed neurotransmitter. Neurotransmitter switching often appears to change the sign of the synapse from excitatory to inhibitory or from inhibitory to excitatory. In these cases, neurotransmitter switching and receptor matching thus change the polarity of the circuit in which they take place. Neurotransmitter switching produces up or down reversals of behavior. It is also observed in response to disease. These findings raise the possibility that neurotransmitter switching contributes to depression, schizophrenia, and other illnesses. Many early discoveries of the single gain or loss of a neurotransmitter may have been harbingers of neurotransmitter switching.
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Affiliation(s)
- Nicholas C Spitzer
- Neurobiology Section, Division of Biological Sciences, Kavli Institute for Brain and Mind, University of California, San Diego, La Jolla, California 92093-0357;
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181
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Morris R, Wilson L, Sturrock M, Warnock ND, Carrizo D, Cox D, Maule AG, Dalzell JJ. A neuropeptide modulates sensory perception in the entomopathogenic nematode Steinernema carpocapsae. PLoS Pathog 2017; 13:e1006185. [PMID: 28253355 PMCID: PMC5333901 DOI: 10.1371/journal.ppat.1006185] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Accepted: 01/15/2017] [Indexed: 11/19/2022] Open
Abstract
Entomopathogenic nematodes (EPNs) employ a sophisticated chemosensory apparatus to detect potential hosts. Understanding the molecular basis of relevant host-finding behaviours could facilitate improved EPN biocontrol approaches, and could lend insight to similar behaviours in economically important mammalian parasites. FMRFamide-like peptides are enriched and conserved across the Phylum Nematoda, and have been linked with motor and sensory function, including dispersal and aggregating behaviours in the free living nematode Caenorhabditis elegans. The RNA interference (RNAi) pathway of Steinernema carpocapsae was characterised in silico, and employed to knockdown the expression of the FMRFamide-like peptide 21 (GLGPRPLRFamide) gene (flp-21) in S. carpocapsae infective juveniles; a first instance of RNAi in this genus, and a first in an infective juvenile of any EPN species. Our data show that 5 mg/ml dsRNA and 50 mM serotonin triggers statistically significant flp-21 knockdown (-84%***) over a 48 h timecourse, which inhibits host-finding (chemosensory), dispersal, hyperactive nictation and jumping behaviours. However, whilst 1 mg/ml dsRNA and 50 mM serotonin also triggers statistically significant flp-21 knockdown (-51%**) over a 48 h timecourse, it does not trigger the null sensory phenotypes; statistically significant target knockdown can still lead to false negative results, necessitating appropriate experimental design. SPME GC-MS volatile profiles of two EPN hosts, Galleria mellonella and Tenebrio molitor reveal an array of shared and unique compounds; these differences had no impact on null flp-21 RNAi phenotypes for the behaviours assayed. Localisation of flp-21 / FLP-21 to paired anterior neurons by whole mount in situ hybridisation and immunocytochemistry corroborates the RNAi data, further suggesting a role in sensory modulation. These data can underpin efforts to study these behaviours in other economically important parasites, and could facilitate molecular approaches to EPN strain improvement for biocontrol.
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Affiliation(s)
- Robert Morris
- School of Biological Sciences, Institute for Global Food Security, Queen’s University Belfast, Belfast, United Kingdom
| | - Leonie Wilson
- School of Biological Sciences, Institute for Global Food Security, Queen’s University Belfast, Belfast, United Kingdom
| | - Matthew Sturrock
- School of Biological Sciences, Institute for Global Food Security, Queen’s University Belfast, Belfast, United Kingdom
| | - Neil D. Warnock
- School of Biological Sciences, Institute for Global Food Security, Queen’s University Belfast, Belfast, United Kingdom
| | - Daniel Carrizo
- School of Biological Sciences, Institute for Global Food Security, Queen’s University Belfast, Belfast, United Kingdom
| | - Deborah Cox
- School of Biological Sciences, Institute for Global Food Security, Queen’s University Belfast, Belfast, United Kingdom
| | - Aaron G. Maule
- School of Biological Sciences, Institute for Global Food Security, Queen’s University Belfast, Belfast, United Kingdom
| | - Johnathan J. Dalzell
- School of Biological Sciences, Institute for Global Food Security, Queen’s University Belfast, Belfast, United Kingdom
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182
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Schwarz J, Bringmann H. Analysis of the NK2 homeobox gene ceh-24 reveals sublateral motor neuron control of left-right turning during sleep. eLife 2017; 6. [PMID: 28244369 PMCID: PMC5384828 DOI: 10.7554/elife.24846] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2017] [Accepted: 02/26/2017] [Indexed: 11/30/2022] Open
Abstract
Sleep is a behavior that is found in all animals that have a nervous system and that have been studied carefully. In Caenorhabditis elegans larvae, sleep is associated with a turning behavior, called flipping, in which animals rotate 180° about their longitudinal axis. However, the molecular and neural substrates of this enigmatic behavior are not known. Here, we identified the conserved NK-2 homeobox gene ceh-24 to be crucially required for flipping. ceh-24 is required for the formation of processes and for cholinergic function of sublateral motor neurons, which separately innervate the four body muscle quadrants. Knockdown of cholinergic function in a subset of these sublateral neurons, the SIAs, abolishes flipping. The SIAs depolarize during flipping and their optogenetic activation induces flipping in a fraction of events. Thus, we identified the sublateral SIA neurons to control the three-dimensional movements of flipping. These neurons may also control other types of motion. DOI:http://dx.doi.org/10.7554/eLife.24846.001 Although sleeping individuals do not move voluntarily, they are not completely immobile. Both people and animals regularly change position in their sleep, but it is not known why these movements occur or what regulates them. One of the simplest animals known to require sleep is the nematode worm Caenorhabditis elegans, which is often used by researchers to study the molecular basis of behavior. In common with more complex animals, worms go to sleep lying on either their left or right side and then switch periodically between the two. This “flipping” behavior is typically not seen outside of sleep. By screening worms with mutations in different genes, Schwarz and Bringmann identified one mutant that does not flip during sleep. The mutant lacked a gene called ceh-24, which is normally active in a set of four neurons known as SIAs. These are a type of motor neuron; that is, neurons that control the contraction of muscles. The body wall muscles of C. elegans run along the length of its body and are organized into “quadrants” that each cover a quarter of the worm. Schwarz and Bringmann show that unlike other C. elegans motor neurons, SIA neurons control each quadrant separately. By activating specific SIA neurons the worms can contract the muscles on each side of the body independently, and thereby flip from one side to the other. Further investigation revealed that the SIA motor neurons can also control other types of complex movement. Additional experiments are now needed to determine how the neurons support these behaviors. Another challenge will be to work out the purpose of posture changes during sleep for C. elegans and other animals. DOI:http://dx.doi.org/10.7554/eLife.24846.002
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Affiliation(s)
- Juliane Schwarz
- Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Henrik Bringmann
- Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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183
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Caenorhabditis elegans Male Copulation Circuitry Incorporates Sex-Shared Defecation Components To Promote Intromission and Sperm Transfer. G3-GENES GENOMES GENETICS 2017; 7:647-662. [PMID: 28031243 PMCID: PMC5295609 DOI: 10.1534/g3.116.036756] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Sexual dimorphism can be achieved using a variety of mechanisms, including sex-specific circuits and sex-specific function of shared circuits, though how these work together to produce sexually dimorphic behaviors requires further investigation. Here, we explore how components of the sex-shared defecation circuitry are incorporated into the sex-specific male mating circuitry in Caenorhabditis elegans to produce successful copulation. Using behavioral studies, calcium imaging, and genetic manipulation, we show that aspects of the defecation system are coopted by the male copulatory circuitry to facilitate intromission and ejaculation. Similar to hermaphrodites, male defecation is initiated by an intestinal calcium wave, but circuit activity is coordinated differently during mating. In hermaphrodites, the tail neuron DVB promotes expulsion of gut contents through the release of the neurotransmitter GABA onto the anal depressor muscle. However, in the male, both neuron and muscle take on modified functions to promote successful copulation. Males require calcium-dependent activator protein for secretion (CAPS)/unc-31, a dense core vesicle exocytosis activator protein, in the DVB to regulate copulatory spicule insertion, while the anal depressor is remodeled to promote release of sperm into the hermaphrodite. This work shows how sex-shared circuitry is modified in multiple ways to contribute to sex-specific mating.
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184
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Schröter M, Paulsen O, Bullmore ET. Micro-connectomics: probing the organization of neuronal networks at the cellular scale. Nat Rev Neurosci 2017; 18:131-146. [PMID: 28148956 DOI: 10.1038/nrn.2016.182] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Defining the organizational principles of neuronal networks at the cellular scale, or micro-connectomics, is a key challenge of modern neuroscience. In this Review, we focus on graph theoretical parameters of micro-connectome topology, often informed by economical principles that conceptually originated with Ramón y Cajal's conservation laws. First, we summarize results from studies in intact small organisms and in samples from larger nervous systems. We then evaluate the evidence for an economical trade-off between biological cost and functional value in the organization of neuronal networks. Various results suggest that many aspects of neuronal network organization are indeed the outcome of competition between these two fundamental selection pressures.
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Affiliation(s)
- Manuel Schröter
- Department of Psychiatry and Behavioural and Clinical Neuroscience Institute, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0SZ, UK.,Department of Biosystems Science and Engineering, Bio Engineering Laboratory, ETH Zurich, Mattenstrasse 26, Basel CH-4058, Switzerland
| | - Ole Paulsen
- Department of Physiology, Development and Neuroscience, University of Cambridge, Physiological Laboratory, Downing Street, Cambridge CB2 3EG, UK
| | - Edward T Bullmore
- Department of Psychiatry and Behavioural and Clinical Neuroscience Institute, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0SZ, UK.,ImmunoPsychiatry, Immuno-Inflammation Therapeutic Area Unit, GlaxoSmithKline R&D, Stevenage SG1 2NY, UK.,Cambridgeshire and Peterborough NHS Foundation Trust, Cambridge Road, Fulbourn, Cambridge CB21 5HH, UK
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185
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Hilbert ZA, Kim DH. Sexually dimorphic control of gene expression in sensory neurons regulates decision-making behavior in C. elegans. eLife 2017; 6. [PMID: 28117661 PMCID: PMC5262377 DOI: 10.7554/elife.21166] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2016] [Accepted: 12/27/2016] [Indexed: 02/07/2023] Open
Abstract
Animal behavior is directed by the integration of sensory information from internal states and the environment. Neuroendocrine regulation of diverse behaviors of Caenorhabditis elegans is under the control of the DAF-7/TGF-β ligand that is secreted from sensory neurons. Here, we show that C. elegans males exhibit an altered, male-specific expression pattern of daf-7 in the ASJ sensory neuron pair with the onset of reproductive maturity, which functions to promote male-specific mate-searching behavior. Molecular genetic analysis of the switch-like regulation of daf-7 expression in the ASJ neuron pair reveals a hierarchy of regulation among multiple inputs—sex, age, nutritional status, and microbial environment—which function in the modulation of behavior. Our results suggest that regulation of gene expression in sensory neurons can function in the integration of a wide array of sensory information and facilitate decision-making behaviors in C. elegans. DOI:http://dx.doi.org/10.7554/eLife.21166.001 For almost all species of animal, males and females will often behave differently in similar situations. Little is known about how these sex-specific differences are generated or, for example, how different the nervous system of a male is to that of a female. Moreover, it is also poorly understood how these underlying differences based on the biological sex of an animal are integrated with and influenced by its experiences and environment. The roundworm Caenorhabditis elegans has two sexes, hermaphrodites and males. The male worms behave differently to the hermaphrodites in a number of situations. This means that these animals offer the opportunity to explore and understand sex-specific differences in behavior. It is also possible to analyze the underlying factors that contribute to behavior in C. elegans, because it has a relatively simple and well-defined nervous system. Now, Hilbert and Kim show that a signal that influences how C. elegans explores in response to chemicals in its environment is expressed differently in male and hermaphrodite worms. The signal in question is molecule called DAF-7, which is released by several sensory neurons—nerve cells that are used for detecting cues from the environment. The sensory neurons that release DAF-7 are found in both sexes of C. elegans but the specific way that the male worms express this signal encourages them to search for mates. Hermaphrodites, on the other hand, do not need to search for mates because they can fertilize their own eggs. Hilbert and Kim showed that the biological sex in combination with multiple other inputs – including the animal’s past diet and age – regulate how the DAF-7 signal is expressed in C. elegans. These inputs all converge onto a single pair of sensory neurons, which integrate the inputs and enable the worm to assess its current and past experiences and alter its behavior accordingly. Moving forward the next challenge is to understand how information about both external environment and internal states, such as hunger, are communicated to and integrated by these sensory neurons. Decoding the signals behind this process may illuminate how biological sex and internal states influence behavior in other species of animals. DOI:http://dx.doi.org/10.7554/eLife.21166.002
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Affiliation(s)
- Zoë A Hilbert
- Department of Biology, Massachusetts Institute of Technology, Cambridge, United States
| | - Dennis H Kim
- Department of Biology, Massachusetts Institute of Technology, Cambridge, United States
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186
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Sexually Dimorphic Differentiation of a C. elegans Hub Neuron Is Cell Autonomously Controlled by a Conserved Transcription Factor. Curr Biol 2017; 27:199-209. [PMID: 28065609 DOI: 10.1016/j.cub.2016.11.045] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Revised: 11/16/2016] [Accepted: 11/22/2016] [Indexed: 12/27/2022]
Abstract
Functional and anatomical sexual dimorphisms in the brain are either the result of cells that are generated only in one sex or a manifestation of sex-specific differentiation of neurons present in both sexes. The PHC neuron pair of the nematode C. elegans differentiates in a strikingly sex-specific manner. In hermaphrodites the PHC neurons display a canonical pattern of synaptic connectivity similar to that of other sensory neurons, but in males PHC differentiates into a densely connected hub sensory neuron/interneuron, integrating a large number of male-specific synaptic inputs and conveying them to both male-specific and sex-shared circuitry. We show that the differentiation into such a hub neuron involves the sex-specific scaling of several components of the synaptic vesicle machinery, including the vesicular glutamate transporter eat-4/VGLUT, induction of neuropeptide expression, changes in axonal projection morphology, and a switch in neuronal function. We demonstrate that these molecular and anatomical remodeling events are controlled cell autonomously by the phylogenetically conserved Doublesex homolog dmd-3, which is both required and sufficient for sex-specific PHC differentiation. Cellular specificity of dmd-3 action is ensured by its collaboration with non-sex-specific terminal selector-type transcription factors, whereas the sex specificity of dmd-3 action is ensured by the hermaphrodite-specific transcriptional master regulator of hermaphroditic cell identity tra-1, which represses the transcription of dmd-3 in hermaphrodite PHC. Taken together, our studies provide mechanistic insights into how neurons are specified in a sexually dimorphic manner.
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187
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Bentley B, Branicky R, Barnes CL, Chew YL, Yemini E, Bullmore ET, Vértes PE, Schafer WR. The Multilayer Connectome of Caenorhabditis elegans. PLoS Comput Biol 2016; 12:e1005283. [PMID: 27984591 PMCID: PMC5215746 DOI: 10.1371/journal.pcbi.1005283] [Citation(s) in RCA: 98] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Revised: 01/04/2017] [Accepted: 12/05/2016] [Indexed: 11/17/2022] Open
Abstract
Connectomics has focused primarily on the mapping of synaptic links in the brain; yet it is well established that extrasynaptic volume transmission, especially via monoamines and neuropeptides, is also critical to brain function and occurs primarily outside the synaptic connectome. We have mapped the putative monoamine connections, as well as a subset of neuropeptide connections, in C. elegans based on new and published gene expression data. The monoamine and neuropeptide networks exhibit distinct topological properties, with the monoamine network displaying a highly disassortative star-like structure with a rich-club of interconnected broadcasting hubs, and the neuropeptide network showing a more recurrent, highly clustered topology. Despite the low degree of overlap between the extrasynaptic (or wireless) and synaptic (or wired) connectomes, we find highly significant multilink motifs of interaction, pinpointing locations in the network where aminergic and neuropeptide signalling modulate synaptic activity. Thus, the C. elegans connectome can be mapped as a multiplex network with synaptic, gap junction, and neuromodulator layers representing alternative modes of interaction between neurons. This provides a new topological plan for understanding how aminergic and peptidergic modulation of behaviour is achieved by specific motifs and loci of integration between hard-wired synaptic or junctional circuits and extrasynaptic signals wirelessly broadcast from a small number of modulatory neurons.
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Affiliation(s)
- Barry Bentley
- Neurobiology Division, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - Robyn Branicky
- Neurobiology Division, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - Christopher L. Barnes
- Neurobiology Division, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
- HHMI Janelia Research Campus, Ashburn, VA, United States of America
| | - Yee Lian Chew
- Neurobiology Division, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - Eviatar Yemini
- Department of Biological Sciences, Columbia University, New York, NY, United States of America
| | - Edward T. Bullmore
- Department of Psychiatry, University of Cambridge, Cambridge United Kingdom
- ImmunoPsychiatry, Alternative Discovery & Development, GlaxoSmithKline R&D, Cambridge United Kingdom
| | - Petra E. Vértes
- Department of Psychiatry, University of Cambridge, Cambridge United Kingdom
| | - William R. Schafer
- Neurobiology Division, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
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188
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Takayanagi-Kiya S, Zhou K, Jin Y. Release-dependent feedback inhibition by a presynaptically localized ligand-gated anion channel. eLife 2016; 5:e21734. [PMID: 27782882 PMCID: PMC5102579 DOI: 10.7554/elife.21734] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Accepted: 10/25/2016] [Indexed: 12/16/2022] Open
Abstract
Presynaptic ligand-gated ion channels (LGICs) have long been proposed to affect neurotransmitter release and to tune the neural circuit activity. However, the understanding of their in vivo physiological action remains limited, partly due to the complexity in channel types and scarcity of genetic models. Here we report that C. elegans LGC-46, a member of the Cys-loop acetylcholine (ACh)-gated chloride (ACC) channel family, localizes to presynaptic terminals of cholinergic motor neurons and regulates synaptic vesicle (SV) release kinetics upon evoked release of acetylcholine. Loss of lgc-46 prolongs evoked release, without altering spontaneous activity. Conversely, a gain-of-function mutation of lgc-46 shortens evoked release to reduce synaptic transmission. This inhibition of presynaptic release requires the anion selectivity of LGC-46, and can ameliorate cholinergic over-excitation in a C. elegans model of excitation-inhibition imbalance. These data demonstrate a novel mechanism of presynaptic negative feedback in which an anion-selective LGIC acts as an auto-receptor to inhibit SV release.
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Affiliation(s)
- Seika Takayanagi-Kiya
- Section of Neurobiology, Division of Biological Sciences, University of California, San Diego, San Diego, United States
| | - Keming Zhou
- Section of Neurobiology, Division of Biological Sciences, University of California, San Diego, San Diego, United States
- Howard Hughes Medical Institute, University of California, San Diego, San Diego, United States
| | - Yishi Jin
- Section of Neurobiology, Division of Biological Sciences, University of California, San Diego, San Diego, United States
- Howard Hughes Medical Institute, University of California, San Diego, San Diego, United States
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189
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Gendrel M, Atlas EG, Hobert O. A cellular and regulatory map of the GABAergic nervous system of C. elegans. eLife 2016; 5. [PMID: 27740909 PMCID: PMC5065314 DOI: 10.7554/elife.17686] [Citation(s) in RCA: 112] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 08/22/2016] [Indexed: 12/16/2022] Open
Abstract
Neurotransmitter maps are important complements to anatomical maps and represent an invaluable resource to understand nervous system function and development. We report here a comprehensive map of neurons in the C. elegans nervous system that contain the neurotransmitter GABA, revealing twice as many GABA-positive neuron classes as previously reported. We define previously unknown glia-like cells that take up GABA, as well as 'GABA uptake neurons' which do not synthesize GABA but take it up from the extracellular environment, and we map the expression of previously uncharacterized ionotropic GABA receptors. We use the map of GABA-positive neurons for a comprehensive analysis of transcriptional regulators that define the GABA phenotype. We synthesize our findings of specification of GABAergic neurons with previous reports on the specification of glutamatergic and cholinergic neurons into a nervous system-wide regulatory map which defines neurotransmitter specification mechanisms for more than half of all neuron classes in C. elegans. DOI:http://dx.doi.org/10.7554/eLife.17686.001
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Affiliation(s)
- Marie Gendrel
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, United States
| | - Emily G Atlas
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, United States
| | - Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, United States
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Azulay A, Itskovits E, Zaslaver A. The C. elegans Connectome Consists of Homogenous Circuits with Defined Functional Roles. PLoS Comput Biol 2016; 12:e1005021. [PMID: 27606684 PMCID: PMC5015834 DOI: 10.1371/journal.pcbi.1005021] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2016] [Accepted: 06/15/2016] [Indexed: 12/15/2022] Open
Abstract
A major goal of systems neuroscience is to decipher the structure-function relationship in neural networks. Here we study network functionality in light of the common-neighbor-rule (CNR) in which a pair of neurons is more likely to be connected the more common neighbors it shares. Focusing on the fully-mapped neural network of C. elegans worms, we establish that the CNR is an emerging property in this connectome. Moreover, sets of common neighbors form homogenous structures that appear in defined layers of the network. Simulations of signal propagation reveal their potential functional roles: signal amplification and short-term memory at the sensory/inter-neuron layer, and synchronized activity at the motoneuron layer supporting coordinated movement. A coarse-grained view of the neural network based on homogenous connected sets alone reveals a simple modular network architecture that is intuitive to understand. These findings provide a novel framework for analyzing larger, more complex, connectomes once these become available.
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Affiliation(s)
- Aharon Azulay
- Department of Genetics, The Silberman Life Science Institute, Edmond J. Safra Campus, Hebrew University, Jerusalem, Israel
- Ph.D. Program in Brain Sciences, Edmond and Lily Safra Center for Brain Sciences, Hebrew University, Jerusalem, Israel
| | - Eyal Itskovits
- Department of Genetics, The Silberman Life Science Institute, Edmond J. Safra Campus, Hebrew University, Jerusalem, Israel
| | - Alon Zaslaver
- Department of Genetics, The Silberman Life Science Institute, Edmond J. Safra Campus, Hebrew University, Jerusalem, Israel
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Hobert O. A map of terminal regulators of neuronal identity in Caenorhabditis elegans. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2016; 5:474-98. [PMID: 27136279 PMCID: PMC4911249 DOI: 10.1002/wdev.233] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/02/2016] [Revised: 02/07/2016] [Accepted: 02/21/2016] [Indexed: 12/31/2022]
Abstract
Our present day understanding of nervous system development is an amalgam of insights gained from studying different aspects and stages of nervous system development in a variety of invertebrate and vertebrate model systems, with each model system making its own distinctive set of contributions. One aspect of nervous system development that has been among the most extensively studied in the nematode Caenorhabditis elegans is the nature of the gene regulatory programs that specify hardwired, terminal cellular identities. I first summarize a number of maps (anatomical, functional, and molecular) that describe the terminal identity of individual neurons in the C. elegans nervous system. I then provide a comprehensive summary of regulatory factors that specify terminal identities in the nervous system, synthesizing these past studies into a regulatory map of cellular identities in the C. elegans nervous system. This map shows that for three quarters of all neurons in the C. elegans nervous system, regulatory factors that control terminal identity features are known. In-depth studies of specific neuron types have revealed that regulatory factors rarely act alone, but rather act cooperatively in neuron-type specific combinations. In most cases examined so far, distinct, biochemically unlinked terminal identity features are coregulated via cooperatively acting transcription factors, termed terminal selectors, but there are also cases in which distinct identity features are controlled in a piecemeal fashion by independent regulatory inputs. The regulatory map also illustrates that identity-defining transcription factors are reemployed in distinct combinations in different neuron types. However, the same transcription factor can drive terminal differentiation in neurons that are unrelated by lineage, unrelated by function, connectivity and neurotransmitter deployment. Lastly, the regulatory map illustrates the preponderance of homeodomain transcription factors in the control of terminal identities, suggesting that these factors have ancient, phylogenetically conserved roles in controlling terminal neuronal differentiation in the nervous system. WIREs Dev Biol 2016, 5:474-498. doi: 10.1002/wdev.233 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Oliver Hobert
- Department of Biological Sciences, Howard Hughes Medical Institute, Columbia University, New York, NY, USA
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192
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Roberts WM, Augustine SB, Lawton KJ, Lindsay TH, Thiele TR, Izquierdo EJ, Faumont S, Lindsay RA, Britton MC, Pokala N, Bargmann CI, Lockery SR. A stochastic neuronal model predicts random search behaviors at multiple spatial scales in C. elegans. eLife 2016; 5:12572. [PMID: 26824391 PMCID: PMC4798983 DOI: 10.7554/elife.12572] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Accepted: 01/19/2016] [Indexed: 12/20/2022] Open
Abstract
Random search is a behavioral strategy used by organisms from bacteria to humans to locate food that is randomly distributed and undetectable at a distance. We investigated this behavior in the nematode Caenorhabditis elegans, an organism with a small, well-described nervous system. Here we formulate a mathematical model of random search abstracted from the C. elegans connectome and fit to a large-scale kinematic analysis of C. elegans behavior at submicron resolution. The model predicts behavioral effects of neuronal ablations and genetic perturbations, as well as unexpected aspects of wild type behavior. The predictive success of the model indicates that random search in C. elegans can be understood in terms of a neuronal flip-flop circuit involving reciprocal inhibition between two populations of stochastic neurons. Our findings establish a unified theoretical framework for understanding C. elegans locomotion and a testable neuronal model of random search that can be applied to other organisms. An animal’s ability to rapidly and efficiently locate new sources of food in its environment can mean the difference between life and death. As a result, animals have evolved foraging strategies that are adapted to the distribution and detectability of food sources. Organisms ranging from bacteria to humans use one such strategy, called random search, to locate food that cannot be detected at a distance and that is randomly distributed in their surroundings. The biological mechanisms that underpin random search are relatively well understood in single-cell organisms such as bacteria, but this information tells us little about the mechanisms that are used by animals, which use their nervous system to control their foraging behavior. Roberts et al. have now investigated the biological basis for random search behavior in a tiny roundworm called Caenorhabditis elegans. This worm forages for pockets of bacteria in decaying plant matter and has a simple and well-understood nervous system. Roberts et al. used information on how the cells in this worm’s nervous system connect together into so-called “neural circuits” to generate a mathematical model of random searching. The model revealed that the worm’s neural circuitry for random searching can be understood in terms of two groups of neuron-like components that switch randomly between “ON” and “OFF” states. While one group promotes forward movement, the other promotes backward movement, which is associated with a change in search direction. These two groups inhibit each other so that only one group usually is active at a given time. By adjusting this model to reproduce the behavioral records of real worms searching for food, Roberts et al. could predict the key neuronal connections involved. These predictions were then confirmed by taking electrical recordings from neurons. The model could also account for the unexpected behavioral effects that are seen when a neuron in one of these groups was destroyed or altered by a genetic mutation. These findings thus reveal a biological mechanism for random search behavior in worms that might operate in other animals as well. The findings might also provide future insight into the neural circuits involved in sleep and wakefulness in mammals, which is organized in a similar way.
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Affiliation(s)
- William M Roberts
- Institute of Neuroscience, University of Oregon, Eugene, United States
| | - Steven B Augustine
- School of Nursing, University of Pennsylvania, Philadelphia, United States
| | | | - Theodore H Lindsay
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, United States
| | - Tod R Thiele
- Department of Biological Sciences, University of Toronto, Toronto, Canada
| | | | - Serge Faumont
- Institute of Neuroscience, University of Oregon, Eugene, United States
| | - Rebecca A Lindsay
- Department of Ophthalmology, The Vision Center, Children's Hospital Los Angeles, Los Angeles, United States
| | | | - Navin Pokala
- Department of Life Sciences, New York Institute of Technology, Old Westbury, United States
| | - Cornelia I Bargmann
- Howard Hughes Medical Institute, Rockefeller University, New York, United States
| | - Shawn R Lockery
- Institute of Neuroscience, University of Oregon, Eugene, United States
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