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Feresten AH, Bhat JM, Yu AJ, Zapf R, Safi H, Au V, Flibotte S, Doell C, Moerman DG, Hawkins N, Rankin CH, Hutter H. ccd-5, a novel cdk-5 binding partner, regulates pioneer axon guidance in the ventral nerve cord of Caenorhabditis elegans. Genetics 2022; 220:iyac024. [PMID: 35143653 PMCID: PMC8982044 DOI: 10.1093/genetics/iyac024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 01/25/2022] [Indexed: 11/14/2022] Open
Abstract
During nervous system development, axons navigate complex environments to reach synaptic targets. Early extending axons must interact with guidance cues in the surrounding tissue, while later extending axons can interact directly with earlier "pioneering" axons, "following" their path. In Caenorhabditis elegans, the AVG neuron pioneers the right axon tract of the ventral nerve cord. We previously found that aex-3, a rab-3 guanine nucleotide exchange factor, is essential for AVG axon navigation in a nid-1 mutant background and that aex-3 might be involved in trafficking of UNC-5, a receptor for the guidance cue UNC-6/netrin. Here, we describe a new gene in this pathway: ccd-5, a putative cdk-5 binding partner. ccd-5 mutants exhibit increased navigation defects of AVG pioneer as well as interneuron and motor neuron follower axons in a nid-1 mutant background. We show that ccd-5 acts in a pathway with cdk-5, aex-3, and unc-5. Navigation defects of follower interneuron and motoneuron axons correlate with AVG pioneer axon defects. This suggests that ccd-5 mostly affects pioneer axon navigation and that follower axon defects are largely a secondary consequence of pioneer navigation defects. To determine the consequences for nervous system function, we assessed various behavioral and movement parameters. ccd-5 single mutants have no significant movement defects, and nid-1 ccd-5 double mutants are less responsive to mechanosensory stimuli compared with nid-1 single mutants. These surprisingly minor defects indicate either a high tolerance for axon guidance defects within the motor circuit and/or an ability to maintain synaptic connections among commonly misguided axons.
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Affiliation(s)
- Abigail H Feresten
- Department of Biological Sciences, Centre for Cell Biology, Development, and Disease, Simon Fraser University, Burnaby, BC V5A1S6, Canada
| | - Jaffar M Bhat
- Department of Biological Sciences, Centre for Cell Biology, Development, and Disease, Simon Fraser University, Burnaby, BC V5A1S6, Canada
| | - Alex J Yu
- Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, BC V6T2B5, Canada
| | - Richard Zapf
- Department of Biological Sciences, Centre for Cell Biology, Development, and Disease, Simon Fraser University, Burnaby, BC V5A1S6, Canada
| | - Hamida Safi
- Department of Molecular Biology and Biochemistry, Centre for Cell Biology, Development, and Disease, Simon Fraser University, Burnaby, BC V5A1S6, Canada
| | - Vinci Au
- Department of Zoology, University of British Columbia, Vancouver, BC V6T1Z4, Canada
| | - Stephane Flibotte
- UBC/LSI Bioinformatics Facility, University of British Columbia, Vancouver, BC V6T1Z4, Canada
| | - Claudia Doell
- Department of Zoology, University of British Columbia, Vancouver, BC V6T1Z4, Canada
| | - Donald G Moerman
- Department of Zoology, University of British Columbia, Vancouver, BC V6T1Z4, Canada
| | - Nancy Hawkins
- Department of Molecular Biology and Biochemistry, Centre for Cell Biology, Development, and Disease, Simon Fraser University, Burnaby, BC V5A1S6, Canada
| | - Catharine H Rankin
- Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, BC, V6T2B5, Canada
- Department of Psychology, University of British Columbia, Vancouver, BC V6T1Z4, Canada
| | - Harald Hutter
- Department of Biological Sciences, Centre for Cell Biology, Development, and Disease, Simon Fraser University, Burnaby, BC V5A1S6, Canada
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2
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The transmembrane collagen COL-99 guides longitudinally extending axons in C. elegans. Mol Cell Neurosci 2018; 89:9-19. [DOI: 10.1016/j.mcn.2018.03.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 02/27/2018] [Accepted: 03/09/2018] [Indexed: 11/23/2022] Open
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Alqadah A, Hsieh YW, Morrissey ZD, Chuang CF. Asymmetric development of the nervous system. Dev Dyn 2017; 247:124-137. [PMID: 28940676 DOI: 10.1002/dvdy.24595] [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: 05/30/2017] [Revised: 09/09/2017] [Accepted: 09/18/2017] [Indexed: 12/13/2022] Open
Abstract
The human nervous system consists of seemingly symmetric left and right halves. However, closer observation of the brain reveals anatomical and functional lateralization. Defects in brain asymmetry correlate with several neurological disorders, yet our understanding of the mechanisms used to establish lateralization in the human central nervous system is extremely limited. Here, we review left-right asymmetries within the nervous system of humans and several model organisms, including rodents, Zebrafish, chickens, Xenopus, Drosophila, and the nematode Caenorhabditis elegans. Comparing and contrasting mechanisms used to develop left-right asymmetry in the nervous system can provide insight into how the human brain is lateralized. Developmental Dynamics 247:124-137, 2018. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- Amel Alqadah
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois
| | - Yi-Wen Hsieh
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois
| | - Zachery D Morrissey
- Graduate Program in Neuroscience, University of Illinois at Chicago, Chicago, Illinois
| | - Chiou-Fen Chuang
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois.,Graduate Program in Neuroscience, University of Illinois at Chicago, Chicago, Illinois
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Sharma V, Roy S, Sekler I, O'Halloran DM. The NCLX-type Na +/Ca 2+ Exchanger NCX-9 Is Required for Patterning of Neural Circuits in Caenorhabditis elegans. J Biol Chem 2017; 292:5364-5377. [PMID: 28196860 DOI: 10.1074/jbc.m116.758953] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Revised: 02/13/2017] [Indexed: 12/22/2022] Open
Abstract
NCLX is a Na+/Ca2+ exchanger that uses energy stored in the transmembrane sodium gradient to facilitate the exchange of sodium ions for ionic calcium. Mammals have a single NCLX, which has been shown to function primarily at the mitochondrion and is an important regulator of neuronal physiology by contributing to neurotransmission and synaptic plasticity. The role of NCLX in developmental cell patterning (e.g. in neural circuits) is largely unknown. Here we describe a novel role for the Caenorhabditis elegans NCLX-type protein, NCX-9, in neural circuit formation. NCX-9 functions in hypodermal seam cells that secrete the axon guidance cue UNC-129/BMP, and our data revealed that ncx-9-/- mutant animals exhibit development defects in stereotyped left/right axon guidance choices within the GABAergic motor neuron circuit. Our data also implicate NCX-9 in a LON-2/heparan sulfate and UNC-6/netrin-mediated, RAC-dependent signaling pathway to guide left/right patterning within this circuit. Finally, we also provide in vitro physiology data supporting the role for NCX-9 in handling calcium exchange at the mitochondrion. Taken together, our work reveals the specificity by which the handling by NCLX of calcium exchange can map to neural circuit patterning and axon guidance decisions during development.
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Affiliation(s)
- Vishal Sharma
- From the Department of Biological Sciences and.,the Institute for Neuroscience, George Washington University, Washington, D. C. 20052 and
| | - Soumitra Roy
- the Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 8499000, Israel
| | - Israel Sekler
- the Department of Physiology and Cell Biology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 8499000, Israel
| | - Damien M O'Halloran
- From the Department of Biological Sciences and .,the Institute for Neuroscience, George Washington University, Washington, D. C. 20052 and
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5
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Blanchette CR, Thackeray A, Perrat PN, Hekimi S, Bénard CY. Functional Requirements for Heparan Sulfate Biosynthesis in Morphogenesis and Nervous System Development in C. elegans. PLoS Genet 2017; 13:e1006525. [PMID: 28068429 PMCID: PMC5221758 DOI: 10.1371/journal.pgen.1006525] [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: 04/11/2016] [Accepted: 12/06/2016] [Indexed: 12/28/2022] Open
Abstract
The regulation of cell migration is essential to animal development and physiology. Heparan sulfate proteoglycans shape the interactions of morphogens and guidance cues with their respective receptors to elicit appropriate cellular responses. Heparan sulfate proteoglycans consist of a protein core with attached heparan sulfate glycosaminoglycan chains, which are synthesized by glycosyltransferases of the exostosin (EXT) family. Abnormal HS chain synthesis results in pleiotropic consequences, including abnormal development and tumor formation. In humans, mutations in either of the exostosin genes EXT1 and EXT2 lead to osteosarcomas or multiple exostoses. Complete loss of any of the exostosin glycosyltransferases in mouse, fish, flies and worms leads to drastic morphogenetic defects and embryonic lethality. Here we identify and study previously unavailable viable hypomorphic mutations in the two C. elegans exostosin glycosyltransferases genes, rib-1 and rib-2. These partial loss-of-function mutations lead to a severe reduction of HS levels and result in profound but specific developmental defects, including abnormal cell and axonal migrations. We find that the expression pattern of the HS copolymerase is dynamic during embryonic and larval morphogenesis, and is sustained throughout life in specific cell types, consistent with HSPGs playing both developmental and post-developmental roles. Cell-type specific expression of the HS copolymerase shows that HS elongation is required in both the migrating neuron and neighboring cells to coordinate migration guidance. Our findings provide insights into general principles underlying HSPG function in development. During animal development, cells and neurons navigate long distances to reach their final target destinations. Migrating cells are guided by extracellular molecular cues, and cellular responses to these cues are regulated by heparan sulfate proteoglycans. Heparan sulfate proteoglycans are proteins with long heparan sulfate polysaccharide chains attached. Here we identify and study previously unavailable viable mutants that disrupt the elongation of the heparan sulfate chains in the nematode C. elegans. Our analysis shows that these HS-chain-elongation mutations affect the development of the nervous system as they result in misguided migrations of neurons and axons. Furthermore, we find that heparan sulfate chain elongation occurs in numerous cell types during development and that the coordinated production of heparan sulfate proteoglycans, in both the migrating cell and neighboring tissues, ensures proper migration. Our findings highlight the critical roles of heparan sulfate proteoglycans in nervous system development and the evolutionary conservation of the molecular mechanisms driving guided migrations.
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Affiliation(s)
- Cassandra R. Blanchette
- Department of Neurobiology, UMass Medical School, Worcester, Massachusetts, United States of America
| | - Andrea Thackeray
- Department of Neurobiology, UMass Medical School, Worcester, Massachusetts, United States of America
| | - Paola N. Perrat
- Department of Neurobiology, UMass Medical School, Worcester, Massachusetts, United States of America
| | | | - Claire Y. Bénard
- Department of Neurobiology, UMass Medical School, Worcester, Massachusetts, United States of America
- Department of Biological Sciences, University of Quebec at Montreal, Montreal, Canada
- * E-mail: ,
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6
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Chisholm AD, Hutter H, Jin Y, Wadsworth WG. The Genetics of Axon Guidance and Axon Regeneration in Caenorhabditis elegans. Genetics 2016; 204:849-882. [PMID: 28114100 PMCID: PMC5105865 DOI: 10.1534/genetics.115.186262] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Accepted: 09/06/2016] [Indexed: 11/18/2022] Open
Abstract
The correct wiring of neuronal circuits depends on outgrowth and guidance of neuronal processes during development. In the past two decades, great progress has been made in understanding the molecular basis of axon outgrowth and guidance. Genetic analysis in Caenorhabditis elegans has played a key role in elucidating conserved pathways regulating axon guidance, including Netrin signaling, the slit Slit/Robo pathway, Wnt signaling, and others. Axon guidance factors were first identified by screens for mutations affecting animal behavior, and by direct visual screens for axon guidance defects. Genetic analysis of these pathways has revealed the complex and combinatorial nature of guidance cues, and has delineated how cues guide growth cones via receptor activity and cytoskeletal rearrangement. Several axon guidance pathways also affect directed migrations of non-neuronal cells in C. elegans, with implications for normal and pathological cell migrations in situations such as tumor metastasis. The small number of neurons and highly stereotyped axonal architecture of the C. elegans nervous system allow analysis of axon guidance at the level of single identified axons, and permit in vivo tests of prevailing models of axon guidance. C. elegans axons also have a robust capacity to undergo regenerative regrowth after precise laser injury (axotomy). Although such axon regrowth shares some similarities with developmental axon outgrowth, screens for regrowth mutants have revealed regeneration-specific pathways and factors that were not identified in developmental screens. Several areas remain poorly understood, including how major axon tracts are formed in the embryo, and the function of axon regeneration in the natural environment.
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Affiliation(s)
| | - Harald Hutter
- Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, V5A 1S6, Canada
| | - Yishi Jin
- Section of Neurobiology, Division of Biological Sciences, and
- Department of Cellular and Molecular Medicine, School of Medicine, University of California, San Diego, La Jolla, California 92093
- Department of Pathology and Laboratory Medicine, Howard Hughes Medical Institute, Chevy Chase, Maryland, and
| | - William G Wadsworth
- Department of Pathology, Rutgers Robert Wood Johnson Medical School, Piscataway, New Jersey 08854
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Reid A, Sherry TJ, Yücel D, Llamosas E, Nicholas HR. The C-terminal binding protein (CTBP-1) regulates dorsal SMD axonal morphology in Caenorhabditis elegans. Neuroscience 2015; 311:216-30. [PMID: 26480814 DOI: 10.1016/j.neuroscience.2015.10.026] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Revised: 10/09/2015] [Accepted: 10/13/2015] [Indexed: 12/31/2022]
Abstract
C-terminal binding proteins (CtBPs) are transcriptional co-repressors which cooperate with a variety of transcription factors to repress gene expression. Caenorhabditis elegans CTBP-1 expression has been observed in the nervous system and hypodermis. In C. elegans, CTBP-1 regulates several processes including Acute Functional Tolerance to ethanol and functions in the nervous system to modulate both lifespan and expression of a lipase gene called lips-7. Incorrect structure and/or function of the nervous system can lead to behavioral changes. Here, we demonstrate reduced exploration behavior in ctbp-1 mutants. Our examination of a subset of neurons involved in regulating locomotion revealed that the axonal morphology of dorsal SMD (SMDD) neurons is altered in ctbp-1 mutants at the fourth larval (L4) stage. Expressing CTBP-1 under the control of the endogenous ctbp-1 promoter rescued both the exploration behavior phenotype and defective SMDD axon structure in ctbp-1 mutants at the L4 stage. Interestingly, the pre-synaptic marker RAB-3 was found to localize to the mispositioned portion of SMDD axons in a ctbp-1 mutant. Further analysis of SMDD axonal morphology at days 1, 3 and 5 of adulthood revealed that the number of ctbp-1 mutants showing an SMDD axonal morphology defect increases in early adulthood and the observed defect appears to be qualitatively more severe. CTBP-1 is prominently expressed in the nervous system with weak expression detected in the hypodermis. Surprisingly, solely expressing CTBP-1a in the nervous system or hypodermis did not restore correct SMDD axonal structure in a ctbp-1 mutant. Our results demonstrate a role for CTBP-1 in exploration behavior and the regulation of SMDD axonal morphology in C. elegans.
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Affiliation(s)
- A Reid
- School of Molecular Bioscience, The University of Sydney, Sydney, NSW 2006, Australia
| | - T J Sherry
- School of Molecular Bioscience, The University of Sydney, Sydney, NSW 2006, Australia
| | - D Yücel
- School of Molecular Bioscience, The University of Sydney, Sydney, NSW 2006, Australia
| | - E Llamosas
- School of Molecular Bioscience, The University of Sydney, Sydney, NSW 2006, Australia
| | - H R Nicholas
- School of Molecular Bioscience, The University of Sydney, Sydney, NSW 2006, Australia.
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8
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Steimel A, Suh J, Hussainkhel A, Deheshi S, Grants JM, Zapf R, Moerman DG, Taubert S, Hutter H. The C. elegans CDK8 Mediator module regulates axon guidance decisions in the ventral nerve cord and during dorsal axon navigation. Dev Biol 2013; 377:385-98. [PMID: 23458898 DOI: 10.1016/j.ydbio.2013.02.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Revised: 01/21/2013] [Accepted: 02/14/2013] [Indexed: 11/30/2022]
Abstract
Receptors expressed on the growth cone of outgrowing axons detect cues required for proper navigation. The pathway choices available to an axon are in part defined by the set of guidance receptors present on the growth cone. Regulated expression of receptors and genes controlling the localization and activity of receptors ensures that axons respond only to guidance cues relevant for reaching their targets. In genetic screens for axon guidance mutants, we isolated an allele of let-19/mdt-13, a component of the Mediator, a large ~30 subunit protein complex essential for gene transcription by RNA polymerase II. LET-19/MDT-13 is part of the CDK8 module of the Mediator. By testing other Mediator components, we found that all subunits of the CDK8 module as well as some other Mediator components are required for specific axon navigation decisions in a subset of neurons. Expression profiling demonstrated that let-19/mdt-13 regulates the expression of a large number of genes in interneurons. A mutation in the sax-3 gene, encoding a receptor for the repulsive guidance cue SLT-1, suppresses the commissure navigation defects found in cdk-8 mutants. This suggests that the CDK8 module specifically represses the SAX-3/ROBO pathway to ensure proper commissure navigation.
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Affiliation(s)
- Andreas Steimel
- Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada
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9
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Abstract
Fluorescent proteins such as the "green fluorescent protein" (GFP) are popular tools in Caenorhabditis elegans, because as genetically encoded markers they are easy to introduce. Furthermore, they can be used in a living animal without the need for extensive sample preparation, because C. elegans is transparent and small enough so that entire animals can be imaged directly. Consequently, fluorescent proteins have emerged as the method of choice to study gene expression in C. elegans and reporter constructs for thousands of genes are currently available. When fused to a protein of interest, fluorescent proteins allow the imaging of its subcellular localization in vivo, offering a powerful alternative to antibody staining techniques. Fluorescent proteins can be employed to label cellular and subcellular structures and as indicators for cell physiological parameters like calcium concentration. Genetic screens relying on fluorescent proteins to visualize anatomical structures and recent progress in automation techniques have tremendously expanded their potential uses. This chapter presents tools and techniques related to the use of fluorescent proteins, discusses their advantages and shortcomings, and provides practical considerations for various applications.
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Affiliation(s)
- Harald Hutter
- Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada
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Siehr MS, Koo PK, Sherlekar AL, Bian X, Bunkers MR, Miller RM, Portman DS, Lints R. Multiple doublesex-related genes specify critical cell fates in a C. elegans male neural circuit. PLoS One 2011; 6:e26811. [PMID: 22069471 PMCID: PMC3206049 DOI: 10.1371/journal.pone.0026811] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Accepted: 10/04/2011] [Indexed: 11/18/2022] Open
Abstract
Background In most animal species, males and females exhibit differences in behavior and morphology that relate to their respective roles in reproduction. DM (Doublesex/MAB-3) domain transcription factors are phylogenetically conserved regulators of sexual development. They are thought to establish sexual traits by sex-specifically modifying the activity of general developmental programs. However, there are few examples where the details of these interactions are known, particularly in the nervous system. Methodology/Principal Findings In this study, we show that two C. elegans DM domain genes, dmd-3 and mab-23, regulate sensory and muscle cell development in a male neural circuit required for mating. Using genetic approaches, we show that in the circuit sensory neurons, dmd-3 and mab-23 establish the correct pattern of dopaminergic (DA) and cholinergic (ACh) fate. We find that the ETS-domain transcription factor gene ast-1, a non-sex-specific, phylogenetically conserved activator of dopamine biosynthesis gene transcription, is broadly expressed in the circuit sensory neuron population. However, dmd-3 and mab-23 repress its activity in most cells, promoting ACh fate instead. A subset of neurons, preferentially exposed to a TGF-beta ligand, escape this repression because signal transduction pathway activity in these cells blocks dmd-3/mab-23 function, allowing DA fate to be established. Through optogenetic and pharmacological approaches, we show that the sensory and muscle cell characteristics controlled by dmd-3 and mab-23 are crucial for circuit function. Conclusions/Significance In the C. elegans male, DM domain genes dmd-3 and mab-23 regulate expression of cell sub-type characteristics that are critical for mating success. In particular, these factors limit the number of DA neurons in the male nervous system by sex-specifically regulating a phylogenetically conserved dopamine biosynthesis gene transcription factor. Homologous interactions between vertebrate counterparts could regulate sex differences in neuron sub-type populations in the brain.
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Affiliation(s)
- Meagan S. Siehr
- Department of Biology, Texas A & M University, College Station, Texas, United States of America
| | - Pamela K. Koo
- Department of Biology, Texas A & M University, College Station, Texas, United States of America
| | - Amrita L. Sherlekar
- Department of Biology, Texas A & M University, College Station, Texas, United States of America
| | - Xuelin Bian
- Department of Biology, Texas A & M University, College Station, Texas, United States of America
| | - Meredith R. Bunkers
- Department of Biology, Texas A & M University, College Station, Texas, United States of America
| | - Renee M. Miller
- Department of Biomedical Genetics, Center for Neural Development and Disease, University of Rochester, Rochester, New York, United States of America
| | - Douglas S. Portman
- Department of Biomedical Genetics, Center for Neural Development and Disease, University of Rochester, Rochester, New York, United States of America
| | - Robyn Lints
- Department of Biology, Texas A & M University, College Station, Texas, United States of America
- * E-mail:
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11
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Steimel A, Wong L, Najarro EH, Ackley BD, Garriga G, Hutter H. The Flamingo ortholog FMI-1 controls pioneer-dependent navigation of follower axons in C. elegans. Development 2010; 137:3663-73. [PMID: 20876647 DOI: 10.1242/dev.054320] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Development of a functional neuronal network during embryogenesis begins with pioneer axons creating a scaffold along which later-outgrowing axons extend. The molecular mechanism used by these follower axons to navigate along pre-existing axons remains poorly understood. We isolated loss-of-function alleles of fmi-1, which caused strong axon navigation defects of pioneer and follower axons in the ventral nerve cord (VNC) of C. elegans. Notably follower axons, which exclusively depend on pioneer axons for correct navigation, frequently separated from the pioneer. fmi-1 is the sole C. elegans ortholog of Drosophila flamingo and vertebrate Celsr genes, and this phenotype defines a new role for this important molecule in follower axon navigation. FMI-1 has a unique and strikingly conserved structure with cadherin and C-terminal G-protein coupled receptor domains and could mediate cell-cell adhesion and signaling functions. We found that follower axon navigation depended on the extracellular but not on the intracellular domain, suggesting that FMI-1 mediates primarily adhesion between pioneer and follower axons. By contrast, pioneer axon navigation required the intracellular domain, suggesting that FMI-1 acts as receptor transducing a signal in this case. Our findings indicate that FMI-1 is a cell-type dependent axon guidance factor with different domain requirements for its different functions in pioneers and followers.
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Affiliation(s)
- Andreas Steimel
- Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada
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12
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Seifert M, Schmidt E, Baumeister R. The genetics of synapse formation and function in Caenorhabditis elegans. Cell Tissue Res 2006; 326:273-85. [PMID: 16896949 DOI: 10.1007/s00441-006-0277-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2006] [Accepted: 06/08/2006] [Indexed: 01/17/2023]
Abstract
The aim of this review is to introduce the reader to Caenorhabditis elegans as a model system, especially with respect to studies of synapse formation and function. We begin by giving a short description of the structure of the nervous system of C. elegans. As most of the findings that are reviewed here have emerged from studies of neuromuscular junctions (NMJs), two prominent NMJs of C. elegans will be outlined briefly. In addition, we summarize new findings that have added to our understanding of NMJs during the last few years.
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Affiliation(s)
- Mark Seifert
- Bio 3, Bioinformatics and Molecular Genetics, University of Freiburg, Schaenzlestrasse 1, 79104 Freiburg (Brsg.), Germany
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Jia L, Emmons SW. Genes that control ray sensory neuron axon development in the Caenorhabditis elegans male. Genetics 2006; 173:1241-58. [PMID: 16624900 PMCID: PMC1526702 DOI: 10.1534/genetics.106.057000] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2006] [Accepted: 04/13/2006] [Indexed: 11/18/2022] Open
Abstract
We have studied how a set of male-specific sensory neurons in Caenorhabditis elegans establish axonal connections during postembryonic development. In the adult male, 9 bilateral pairs of ray sensory neurons innervate an acellular fan that serves as a presumptive tactile and olfactory organ during copulation. We visualized ray axon commissures with a ray neuron-specific reporter gene and studied both known and new mutations that affect the establishment of connections to the pre-anal ganglion. We found that the UNC-6/netrin-UNC-40/DCC pathway provides the primary dorsoventral guidance cue to ray axon growth cones. Some axon growth cones also respond to an anteroposterior cue, following a segmented pathway, and most or all also have a tendency to fasciculate. Two newly identified genes, rax-1 and rax-4, are highly specific to the ray neurons and appear to be required for ray axon growth cones to respond to the dorsoventral cue. Among other genes we identified, rax-2 and rax-3 affect anteroposterior signaling or fate specification and rax-5 and rax-6 affect ray identities. We identified a mutation in sax-2 and show that the sax-2/Furry and sax-1/Tricornered pathway affects ectopic neurite outgrowth and establishment of normal axon synapses. Finally, we identified mutations in genes for muscle proteins that affect axon pathways by distorting the conformation of the body wall. Thus ray axon pathfinding relies on a variety of general and more ray neuron-specific genes and provides a potentially fruitful system for further studies of how migrating axon growth cones locate their targets. This system is applicable to the study of mechanisms underlying topographic mapping of sensory neurons into target circuitry where the next stage of information processing is carried out.
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Affiliation(s)
- Lingyun Jia
- Department of Molecular Genetics, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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14
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Schmid C, Schwarz V, Hutter H. AST-1, a novel ETS-box transcription factor, controls axon guidance and pharynx development in C. elegans. Dev Biol 2006; 293:403-13. [PMID: 16584723 DOI: 10.1016/j.ydbio.2006.02.042] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2005] [Revised: 12/16/2005] [Accepted: 02/06/2006] [Indexed: 02/01/2023]
Abstract
Neurons send out axons and dendrites over large distances into target areas where they eventually form synapses with selected target cells. Axonal navigation is controlled by a variety of extracellular signals and neurons express receptors only for that subset of signals they need to navigate to their own target area. How the expression of axon guidance receptors is regulated is not understood. In genetic screens for mutants with axon guidance defects, we identified an ETS-domain transcription factor, AST-1, specifically required for axon navigation in certain classes of interneurons. In addition, ast-1 has a role in the differentiation of the ventral cord pioneer neuron AVG. Outside the nervous system, ast-1 is essential for morphogenesis of the pharynx. Ast-1 is transiently expressed in several classes of neurons (including AVG) during neuronal differentiation with a peak expression during late stages of neuronal differentiation and axon outgrowth. Ast-1 genetically interacts with other transcription factors controlling neuronal differentiation like lin-11 and zag-1 as well as components of the netrin pathway suggesting that ast-1 might control the expression of components of the netrin signal transduction machinery.
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Affiliation(s)
- Christina Schmid
- Max Planck Institute for Medical Research, Jahnstr. 29, 69120 Heidelberg, Germany
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Chisholm AD, Jin Y. Neuronal differentiation in C. elegans. Curr Opin Cell Biol 2005; 17:682-9. [PMID: 16242313 DOI: 10.1016/j.ceb.2005.10.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2005] [Accepted: 10/03/2005] [Indexed: 02/04/2023]
Abstract
The small size and defined connectivity of the C. elegans nervous system and the amenability of this species to systematic functional screens have continued to yield new insights into neuronal differentiation. Many aspects of C. elegans neuronal development resemble those of other more complex neurons. The basic cellular machinery of synaptic transmission is highly conserved. Recent work has begun to unveil the roles of proteoglycans in axon guidance and branching, and of the extracellular matrix in neuronal process maintenance. The importance of ubiquitin-mediated protein turnover in neuronal differentiation is revealed by the identification of new and conserved pathways that promote the organization and function of the synapse.
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Affiliation(s)
- Andrew D Chisholm
- Department of Molecular, Cell and Development Biology, Sinsheimer Laboratories, University of California, Santa Cruz, California 95064, USA.
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