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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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52
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Byrne AB, Hammarlund M. Axon regeneration in C. elegans: Worming our way to mechanisms of axon regeneration. Exp Neurol 2016; 287:300-309. [PMID: 27569538 DOI: 10.1016/j.expneurol.2016.08.015] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Revised: 08/19/2016] [Accepted: 08/24/2016] [Indexed: 12/12/2022]
Abstract
How axons repair themselves after injury is a fundamental question in neurobiology. With its conserved genome, relatively simple nervous system, and transparent body, C. elegans has recently emerged as a productive model to uncover the cellular mechanisms that regulate and execute axon regeneration. In this review, we discuss the strengths and weaknesses of the C. elegans model of regeneration. We explore the technical advances that enable the use of C. elegans for in vivo regeneration studies, review findings in C. elegans that have contributed to our understanding of the regeneration response across species, discuss the potential of C. elegans research to provide insight into mechanisms that function in the injured mammalian nervous system, and present potential future directions of axon regeneration research using C. elegans.
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Affiliation(s)
- Alexandra B Byrne
- Department of Genetics, Yale University School of Medicine, New Haven, CT, United States; Department of Neuroscience, Yale University School of Medicine, New Haven, CT, United States
| | - Marc Hammarlund
- Department of Genetics, Yale University School of Medicine, New Haven, CT, United States; Department of Neuroscience, Yale University School of Medicine, New Haven, CT, United States.
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53
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Munkácsy E, Khan MH, Lane RK, Borror MB, Park JH, Bokov AF, Fisher AL, Link CD, Rea SL. DLK-1, SEK-3 and PMK-3 Are Required for the Life Extension Induced by Mitochondrial Bioenergetic Disruption in C. elegans. PLoS Genet 2016; 12:e1006133. [PMID: 27420916 PMCID: PMC4946786 DOI: 10.1371/journal.pgen.1006133] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Accepted: 05/27/2016] [Indexed: 12/17/2022] Open
Abstract
Mitochondrial dysfunction underlies numerous age-related pathologies. In an effort to uncover how the detrimental effects of mitochondrial dysfunction might be alleviated, we examined how the nematode C. elegans not only adapts to disruption of the mitochondrial electron transport chain, but in many instances responds with extended lifespan. Studies have shown various retrograde responses are activated in these animals, including the well-studied ATFS-1-dependent mitochondrial unfolded protein response (UPRmt). Such processes fall under the greater rubric of cellular surveillance mechanisms. Here we identify a novel p38 signaling cascade that is required to extend life when the mitochondrial electron transport chain is disrupted in worms, and which is blocked by disruption of the Mitochondrial-associated Degradation (MAD) pathway. This novel cascade is defined by DLK-1 (MAP3K), SEK-3 (MAP2K), PMK-3 (MAPK) and the reporter gene Ptbb-6::GFP. Inhibition of known mitochondrial retrograde responses does not alter induction of Ptbb-6::GFP, instead induction of this reporter often occurs in counterpoint to activation of SKN-1, which we show is under the control of ATFS-1. In those mitochondrial bioenergetic mutants which activate Ptbb-6::GFP, we find that dlk-1, sek-3 and pmk-3 are all required for their life extension.
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Affiliation(s)
- Erin Munkácsy
- The Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
- Department of Cellular & Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Maruf H. Khan
- The Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
- Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
- Department of Medicine (Division of Geriatrics, Gerontology, and Palliative Medicine), University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Rebecca K. Lane
- The Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Megan B. Borror
- The Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Jae H. Park
- The Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Alex F. Bokov
- Department of Epidemiology and Biostatistics, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Alfred L. Fisher
- Department of Medicine (Division of Geriatrics, Gerontology, and Palliative Medicine), University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
- Geriatric Research, Education and Clinical Center, South Texas VA Health Care System, San Antonio, Texas, United States of America
- Center for Healthy Aging, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
| | - Christopher D. Link
- Institute for Behavioral Genetics & Department of Integrative Physiology, University of Colorado at Boulder, Boulder, Colorado, United States of America
| | - Shane L. Rea
- The Barshop Institute for Longevity and Aging Studies, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
- Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America
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54
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Miller KG. Keeping Neuronal Cargoes on the Right Track: New Insights into Regulators of Axonal Transport. Neuroscientist 2016; 23:232-250. [PMID: 27154488 DOI: 10.1177/1073858416648307] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In neurons, a single motor (dynein) transports large organelles as well as synaptic and dense core vesicles toward microtubule minus ends; however, it is unclear why dynein appears more active on organelles, which are generally excluded from mature axons, than on synaptic and dense core vesicles, which are maintained at high levels. Recent studies in Zebrafish and Caenorhabditis elegans have shown that JIP3 promotes dynein-mediated retrograde transport to clear some organelles (lysosomes, early endosomes, and Golgi) from axons and prevent their potentially harmful accumulation in presynaptic regions. A JIP3 mutant suppressor screen in C. elegans revealed that JIP3 promotes the clearance of organelles from axons by blocking the action of the CSS system (Cdk5, SAD Kinase, SYD-2/Liprin). A synthesis of results in vertebrates with the new findings suggests that JIP3 blocks the CSS system from disrupting the connection between dynein and organelles. Most components of the CSS system are enriched at presynaptic active zones where they normally contribute to maintaining optimal levels of captured synaptic and dense core vesicles, in part by inhibiting dynein transport. The JIP3-CSS system model explains how neurons selectively regulate a single minus-end motor to exclude specific classes of organelles from axons, while at the same time ensuring optimal levels of synaptic and dense core vesicles.
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Affiliation(s)
- Kenneth G Miller
- 1 Genetic Models of Disease Laboratory, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
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55
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He Z, Jin Y. Intrinsic Control of Axon Regeneration. Neuron 2016; 90:437-51. [DOI: 10.1016/j.neuron.2016.04.022] [Citation(s) in RCA: 337] [Impact Index Per Article: 42.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Revised: 03/10/2016] [Accepted: 04/13/2016] [Indexed: 01/12/2023]
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Abstract
The capacity of an axon to regenerate is regulated by its external environment and by cell-intrinsic factors. Studies in a variety of organisms suggest that alterations in axonal microtubule (MT) dynamics have potent effects on axon regeneration. We review recent findings on the regulation of MT dynamics during axon regeneration, focusing on the nematode Caenorhabditis elegans. In C. elegans the dual leucine zipper kinase (DLK) promotes axon regeneration, whereas the exchange factor for Arf6 (EFA-6) inhibits axon regeneration. Both DLK and EFA-6 respond to injury and control axon regeneration in part via MT dynamics. How the DLK and EFA-6 pathways are related is a topic of active investigation, as is the mechanism by which EFA-6 responds to axonal injury. We evaluate potential candidates, such as the MT affinity-regulating kinase PAR-1/MARK, in regulation of EFA-6 and axonal MT dynamics in regeneration.
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Affiliation(s)
- Ngang Heok Tang
- Section of Neurobiology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA, 92093, USA
| | - Andrew D Chisholm
- Section of Neurobiology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA, 92093, USA
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57
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Novel DLK-independent neuronal regeneration in Caenorhabditis elegans shares links with activity-dependent ectopic outgrowth. Proc Natl Acad Sci U S A 2016; 113:E2852-60. [PMID: 27078101 DOI: 10.1073/pnas.1600564113] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
During development, a neuron transitions from a state of rapid growth to a stable morphology, and neurons within the adult mammalian CNS lose their ability to effectively regenerate in response to injury. Here, we identify a novel form of neuronal regeneration, which is remarkably independent of DLK-1/DLK, KGB-1/JNK, and other MAPK signaling factors known to mediate regeneration in Caenorhabditis elegans, Drosophila, and mammals. This DLK-independent regeneration in C. elegans has direct genetic and molecular links to a well-studied form of endogenous activity-dependent ectopic axon outgrowth in the same neuron type. Both neuron outgrowth types are triggered by physical lesion of the sensory dendrite or mutations disrupting sensory activity, calcium signaling, or genes that restrict outgrowth during neuronal maturation, such as SAX-1/NDR kinase or UNC-43/CaMKII. These connections suggest that ectopic outgrowth represents a powerful platform for gene discovery in neuronal regeneration. Moreover, we note numerous similarities between C. elegans DLK-independent regeneration and lesion conditioning, a phenomenon producing robust regeneration in the mammalian CNS. Both regeneration types are triggered by lesion of a sensory neurite via reduction of neuronal activity and enhanced by disrupting L-type calcium channels or elevating cAMP. Taken as a whole, our study unites disparate forms of neuronal outgrowth to uncover fresh molecular insights into activity-dependent control of the adult nervous system's intrinsic regenerative capacity.
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58
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Andrusiak MG, Jin Y. Context Specificity of Stress-activated Mitogen-activated Protein (MAP) Kinase Signaling: The Story as Told by Caenorhabditis elegans. J Biol Chem 2016; 291:7796-804. [PMID: 26907690 DOI: 10.1074/jbc.r115.711101] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Stress-associated p38 and JNK mitogen-activated protein (MAP) kinase signaling cascades trigger specific cellular responses and are involved in multiple disease states. At the root of MAP kinase signaling complexity is the differential use of common components on a context-specific basis. The roundwormCaenorhabditis eleganswas developed as a system to study genes required for development and nervous system function. The powerful genetics ofC. elegansin combination with molecular and cellular dissections has led to a greater understanding of how p38 and JNK signaling affects many biological processes under normal and stress conditions. This review focuses on the studies revealing context specificity of different stress-activated MAPK components inC. elegans.
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Affiliation(s)
| | - Yishi Jin
- From the Howard Hughes Medical Institute and the Neurobiology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, California 92093
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59
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Alam T, Maruyama H, Li C, Pastuhov SI, Nix P, Bastiani M, Hisamoto N, Matsumoto K. Axotomy-induced HIF-serotonin signalling axis promotes axon regeneration in C. elegans. Nat Commun 2016; 7:10388. [PMID: 26790951 PMCID: PMC4735912 DOI: 10.1038/ncomms10388] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 12/05/2015] [Indexed: 12/28/2022] Open
Abstract
The molecular mechanisms underlying the ability of axons to regenerate after injury remain poorly understood. Here we show that in Caenorhabditis elegans, axotomy induces ectopic expression of serotonin (5-HT) in axotomized non-serotonergic neurons via HIF-1, a hypoxia-inducible transcription factor, and that 5-HT subsequently promotes axon regeneration by autocrine signalling through the SER-7 5-HT receptor. Furthermore, we identify the rhgf-1 and rga-5 genes, encoding homologues of RhoGEF and RhoGAP, respectively, as regulators of axon regeneration. We demonstrate that one pathway initiated by SER-7 acts upstream of the C. elegans RhoA homolog RHO-1 in neuron regeneration, which functions via G12α and RHGF-1. In this pathway, RHO-1 inhibits diacylglycerol kinase, resulting in an increase in diacylglycerol. SER-7 also promotes axon regeneration by activating the cyclic AMP (cAMP) signalling pathway. Thus, HIF-1-mediated activation of 5-HT signalling promotes axon regeneration by activating both the RhoA and cAMP pathways.
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Affiliation(s)
- Tanimul Alam
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
| | - Hiroki Maruyama
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
| | - Chun Li
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
| | - Strahil Iv. Pastuhov
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
| | - Paola Nix
- Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, Utah 84112-0840, USA
| | - Michael Bastiani
- Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, Utah 84112-0840, USA
| | - Naoki Hisamoto
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
| | - Kunihiro Matsumoto
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
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60
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Isaacman-Beck J, Schneider V, Franzini-Armstrong C, Granato M. The lh3 Glycosyltransferase Directs Target-Selective Peripheral Nerve Regeneration. Neuron 2015; 88:691-703. [PMID: 26549330 PMCID: PMC4655140 DOI: 10.1016/j.neuron.2015.10.004] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2015] [Revised: 08/16/2015] [Accepted: 09/28/2015] [Indexed: 12/26/2022]
Abstract
Functional PNS regeneration requires injured axons to return to their original synaptic targets, yet the mechanisms underlying target-selective regeneration have remained elusive. Using live-cell imaging in zebrafish we find that regenerating motor axons exhibit a strong preference for their original muscle territory and that axons probe both correct and incorrect trajectories extensively before selecting their original path. We show that this process requires the glycosyltransferase lh3 and that post-injury expression of lh3 in Schwann cells is sufficient to restore target-selective regeneration. Moreover, we demonstrate that Schwann cells neighboring the transection site express the lh3 substrate collagen4a5 and that during regeneration collagen4a5 destabilizes axons probing inappropriate trajectories to ensure target-selective regeneration, possibly through the axonal repellant slit1a. Our results demonstrate that selective ECM components match subpopulations of regenerating axons with their original targets and reveal a previously unappreciated mechanism that conveys synaptic target selection to regenerating axons in vivo. VIDEO ABSTRACT.
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Affiliation(s)
- Jesse Isaacman-Beck
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104-6058, USA
| | - Valerie Schneider
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104-6058, USA
| | - Clara Franzini-Armstrong
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104-6058, USA
| | - Michael Granato
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104-6058, USA.
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61
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Cho Y, Shin JE, Ewan EE, Oh YM, Pita-Thomas W, Cavalli V. Activating Injury-Responsive Genes with Hypoxia Enhances Axon Regeneration through Neuronal HIF-1α. Neuron 2015; 88:720-34. [PMID: 26526390 DOI: 10.1016/j.neuron.2015.09.050] [Citation(s) in RCA: 109] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 08/24/2015] [Accepted: 09/22/2015] [Indexed: 02/07/2023]
Abstract
Injured peripheral neurons successfully activate a proregenerative transcriptional program to enable axon regeneration and functional recovery. How transcriptional regulators coordinate the expression of such program remains unclear. Here we show that hypoxia-inducible factor 1α (HIF-1α) controls multiple injury-induced genes in sensory neurons and contribute to the preconditioning lesion effect. Knockdown of HIF-1α in vitro or conditional knock out in vivo impairs sensory axon regeneration. The HIF-1α target gene Vascular Endothelial Growth Factor A (VEGFA) is expressed in injured neurons and contributes to stimulate axon regeneration. Induction of HIF-1α using hypoxia enhances axon regeneration in vitro and in vivo in sensory neurons. Hypoxia also stimulates motor neuron regeneration and accelerates neuromuscular junction re-innervation. This study demonstrates that HIF-1α represents a critical transcriptional regulator in regenerating neurons and suggests hypoxia as a tool to stimulate axon regeneration.
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Affiliation(s)
- Yongcheol Cho
- Department of Anatomy and Neurobiology, School of Medicine, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Jung Eun Shin
- Department of Developmental Biology, School of Medicine, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Eric Edward Ewan
- Department of Anatomy and Neurobiology, School of Medicine, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Young Mi Oh
- Department of Anatomy and Neurobiology, School of Medicine, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Wolfgang Pita-Thomas
- Department of Anatomy and Neurobiology, School of Medicine, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Valeria Cavalli
- Department of Anatomy and Neurobiology, School of Medicine, Washington University in St. Louis, St. Louis, MO 63110, USA.
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62
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Abstract
Food availability determines developmental rate, behavior, and survival of animals. Animals that enter diapause or hibernate in response to lack of food have a double advantage: they are able to adapt to environmental and cellular challenges and survive to these challenges for a prolonged time. The metabolic and physiological adaptations that make possible diapause and hibernation also provide a favorable cellular environment for tissue protection. This review highlights the benefits of dormancy on neuronal protection in the model organism Caenorhabditis elegans and small mammals such as squirrels. Additionally, I discuss the link between metabolic restructuring occurring in diapause and changes in gene expression with the increased capacity of diapausing animals to protect neurons from degeneration and potentially foster their regeneration.
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Affiliation(s)
- Andrea Calixto
- Center for Genomics and Bioinformatics, Faculty of Sciences, Universidad Mayor, Santiago, Chile.
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63
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Edwards SL, Morrison LM, Yorks RM, Hoover CM, Boominathan S, Miller KG. UNC-16 (JIP3) Acts Through Synapse-Assembly Proteins to Inhibit the Active Transport of Cell Soma Organelles to Caenorhabditis elegans Motor Neuron Axons. Genetics 2015; 201:117-41. [PMID: 26354976 PMCID: PMC4566257 DOI: 10.1534/genetics.115.177345] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Accepted: 06/24/2015] [Indexed: 12/31/2022] Open
Abstract
The conserved protein UNC-16 (JIP3) inhibits the active transport of some cell soma organelles, such as lysosomes, early endosomes, and Golgi, to the synaptic region of axons. However, little is known about UNC-16's organelle transport regulatory function, which is distinct from its Kinesin-1 adaptor function. We used an unc-16 suppressor screen in Caenorhabditis elegans to discover that UNC-16 acts through CDK-5 (Cdk5) and two conserved synapse assembly proteins: SAD-1 (SAD-A Kinase), and SYD-2 (Liprin-α). Genetic analysis of all combinations of double and triple mutants in unc-16(+) and unc-16(-) backgrounds showed that the three proteins (CDK-5, SAD-1, and SYD-2) are all part of the same organelle transport regulatory system, which we named the CSS system based on its founder proteins. Further genetic analysis revealed roles for SYD-1 (another synapse assembly protein) and STRADα (a SAD-1-interacting protein) in the CSS system. In an unc-16(-) background, loss of the CSS system improved the sluggish locomotion of unc-16 mutants, inhibited axonal lysosome accumulation, and led to the dynein-dependent accumulation of lysosomes in dendrites. Time-lapse imaging of lysosomes in CSS system mutants in unc-16(+) and unc-16(-) backgrounds revealed active transport defects consistent with the steady-state distributions of lysosomes. UNC-16 also uses the CSS system to regulate the distribution of early endosomes in neurons and, to a lesser extent, Golgi. The data reveal a new and unprecedented role for synapse assembly proteins, acting as part of the newly defined CSS system, in mediating UNC-16's organelle transport regulatory function.
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Affiliation(s)
- Stacey L Edwards
- Genetic Models of Disease Laboratory, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
| | - Logan M Morrison
- Genetic Models of Disease Laboratory, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
| | - Rosalina M Yorks
- Genetic Models of Disease Laboratory, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
| | - Christopher M Hoover
- Genetic Models of Disease Laboratory, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
| | - Soorajnath Boominathan
- Genetic Models of Disease Laboratory, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
| | - Kenneth G Miller
- Genetic Models of Disease Laboratory, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
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64
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Abstract
Activity of the RNA ligase RtcB has only two known functions: tRNA ligation after intron removal and XBP1 mRNA ligation during activation of the unfolded protein response. Here, we show that RtcB acts in neurons to inhibit axon regeneration after nerve injury. This function of RtcB is independent of its basal activities in tRNA ligation and the unfolded protein response. Furthermore, inhibition of axon regeneration is independent of the RtcB cofactor archease. Finally, RtcB is enriched at axon termini after nerve injury. Our data indicate that neurons have co-opted an ancient RNA modification mechanism to regulate specific and dynamic functions and identify neuronal RtcB activity as a critical regulator of neuronal growth potential.
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65
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Kim KW, Jin Y. Neuronal responses to stress and injury in C. elegans. FEBS Lett 2015; 589:1644-52. [PMID: 25979176 DOI: 10.1016/j.febslet.2015.05.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2015] [Revised: 04/30/2015] [Accepted: 05/04/2015] [Indexed: 12/22/2022]
Abstract
The nervous system plays critical roles in the stress response. Animals can survive and function under harsh conditions, and resist and recover from injuries because neurons perceive and respond to various stressors through specific regulatory mechanisms. Caenorhabditis elegans has served as an excellent model to discover fundamental mechanisms underlying the neuronal response to stress. The basic physiological processes that C. elegans exhibits under stress conditions are similar to those observed in higher organisms. Many molecular pathways activated by environmental and cellular stresses are also conserved. In this review, we summarize major findings in examining neuronal responses to hypoxia, oxidative stress, osmotic stress, and traumatic injury. These studies from C. elegans have provided novel insights into our understanding of neuronal responses to stress at the molecular, cellular, and circuit levels.
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Affiliation(s)
- Kyung Won Kim
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093, United States.
| | - Yishi Jin
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093, United States; Howard Hughes Medical Institute, University of California San Diego, La Jolla, CA 92093, United States.
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66
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Song Y, Sretavan D, Salegio EA, Berg J, Huang X, Cheng T, Xiong X, Meltzer S, Han C, Nguyen TT, Bresnahan JC, Beattie MS, Jan LY, Jan YN. Regulation of axon regeneration by the RNA repair and splicing pathway. Nat Neurosci 2015; 18:817-25. [PMID: 25961792 PMCID: PMC4446171 DOI: 10.1038/nn.4019] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 04/07/2015] [Indexed: 12/15/2022]
Abstract
Mechanisms governing a neuron’s regenerative ability are important but not well understood. We identified Rtca, RNA 3′-terminal phosphate cyclase, as an inhibitor for axon regeneration. Removal of dRtca cell-autonomously enhanced axon regrowth in the Drosophila central nervous system, whereas its overexpression reduced axon regeneration in the periphery. Rtca along with the RNA ligase Rtcb and its catalyst Archease operate in the RNA repair/splicing pathway important for stress induced mRNA splicing, including that of Xbp1, a cellular stress sensor. dRtca and dArchease had opposing effects on Xbp1 splicing, and deficiency of dArchease or Xbp1 impeded axon regeneration in Drosophila. Moreover, overexpressing mammalian Rtca in cultured rodent neurons reduced axonal complexity in vitro, whereas reducing its function promoted retinal ganglion cell axon regeneration after optic nerve crush in mice. Our study thus links axon regeneration to cellular stress and RNA metabolism, revealing new potential therapeutic targets for treating nervous system trauma.
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Affiliation(s)
- Yuanquan Song
- 1] Howard Hughes Medical Institute, University of California, San Francisco, California, USA. [2] Department of Physiology, University of California, San Francisco, California, USA
| | - David Sretavan
- Department of Ophthalmology, University of California, San Francisco, San Francisco, California, USA
| | - Ernesto A Salegio
- Brain and Spinal Injury Center, University of California, San Francisco, California, USA
| | - Jim Berg
- 1] Howard Hughes Medical Institute, University of California, San Francisco, California, USA. [2] Department of Physiology, University of California, San Francisco, California, USA
| | - Xi Huang
- 1] Howard Hughes Medical Institute, University of California, San Francisco, California, USA. [2] Department of Physiology, University of California, San Francisco, California, USA
| | - Tong Cheng
- 1] Howard Hughes Medical Institute, University of California, San Francisco, California, USA. [2] Department of Physiology, University of California, San Francisco, California, USA
| | - Xin Xiong
- Howard Hughes Medical Institute, University of California, San Francisco, California, USA
| | - Shan Meltzer
- 1] Howard Hughes Medical Institute, University of California, San Francisco, California, USA. [2] Department of Physiology, University of California, San Francisco, California, USA
| | - Chun Han
- 1] Howard Hughes Medical Institute, University of California, San Francisco, California, USA. [2] Department of Physiology, University of California, San Francisco, California, USA
| | - Trong-Tuong Nguyen
- Department of Ophthalmology, University of California, San Francisco, San Francisco, California, USA
| | - Jacqueline C Bresnahan
- Brain and Spinal Injury Center, University of California, San Francisco, California, USA
| | - Michael S Beattie
- Brain and Spinal Injury Center, University of California, San Francisco, California, USA
| | - Lily Yeh Jan
- 1] Howard Hughes Medical Institute, University of California, San Francisco, California, USA. [2] Department of Physiology, University of California, San Francisco, California, USA
| | - Yuh Nung Jan
- 1] Howard Hughes Medical Institute, University of California, San Francisco, California, USA. [2] Department of Physiology, University of California, San Francisco, California, USA
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RTCB-1 mediates neuroprotection via XBP-1 mRNA splicing in the unfolded protein response pathway. J Neurosci 2015; 34:16076-85. [PMID: 25429148 DOI: 10.1523/jneurosci.1945-14.2014] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Parkinson's disease (PD), the second most prevalent neurodegenerative disorder, is characterized by the degeneration of dopamine (DA) neurons and age-dependent formation of protein inclusions that contain the α-synuclein (α-syn) protein. RNA interference (RNAi) screening using Caenorhabditis elegans identified RTCB-1, an uncharacterized gene product, as one of several significant modifiers of α-syn protein misfolding. RTCB-1 is the worm ortholog of the human HSPC117 protein, a component of RNA trafficking granules in mammalian neurons. Here we show that RTCB-1 protects C. elegans DA neurons from age-dependent degeneration induced by human α-syn. Moreover, neuronal-specific RNAi depletion of rtcb-1 enhanced α-syn-induced degeneration. Similar results were obtained when worms were exposed to the DA neurotoxin 6-hydroxydopamine. HSPC117 has been characterized recently as an essential subunit of the human tRNA splicing ligase complex. tRNA ligases have alternative functions in RNA repair and nonconventional mRNA splicing events. For example, in yeast, unconventional splicing of HAC1, a transcription factor that controls the unfolded protein response (UPR), is mediated by a tRNA ligase. In C. elegans, we demonstrate that RTCB-1 is necessary for xbp-1 (worm homolog of HAC1) mRNA splicing. Moreover, using a RNA ligase-dead mutant, we determine that the ligase activity of worm RTCB-1 is required for its neuroprotective role, which, in turn, is mediated through XBP-1 in the UPR pathway. Collectively, these studies highlight the mechanistic intersection of RNA processing and proteostasis in mediating neuroprotection.
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PASTUHOV SI, HISAMOTO N, MATSUMOTO K. MAP kinase cascades regulating axon regeneration in C. elegans. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2015; 91:63-75. [PMID: 25792136 PMCID: PMC4410086 DOI: 10.2183/pjab.91.63] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/24/2014] [Accepted: 01/13/2015] [Indexed: 06/04/2023]
Abstract
Mitogen-activated protein kinase (MAPK) signaling cascades are activated by diverse stimuli such as growth factors, cytokines, neurotransmitters and various types of cellular stress. Our evolving understanding of these signal cascades has been facilitated by genetic analyses and physiological characterization in model organisms such as the nematode Caenorhabditis elegans. Genetic and biochemical studies in C. elegans have shed light on the physiological roles of MAPK cascades in the control of cell fate decision, neuronal function and immunity. Recently it was demonstrated that MAPK signaling is also important for axon regeneration in C. elegans, and the use of C. elegans as a model system has significantly advanced our understanding of the largely conserved molecular mechanisms underlying axon regeneration. This review summarizes our current understanding of the role and regulation of MAPK signaling in C. elegans axon regeneration.
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Affiliation(s)
- Strahil Iv. PASTUHOV
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, Japan
| | - Naoki HISAMOTO
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, Japan
| | - Kunihiro MATSUMOTO
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, Japan
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69
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Levi-Ferber M, Salzberg Y, Safra M, Haviv-Chesner A, Bülow HE, Henis-Korenblit S. It's all in your mind: determining germ cell fate by neuronal IRE-1 in C. elegans. PLoS Genet 2014; 10:e1004747. [PMID: 25340700 PMCID: PMC4207656 DOI: 10.1371/journal.pgen.1004747] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Accepted: 09/11/2014] [Indexed: 01/26/2023] Open
Abstract
The C. elegans germline is pluripotent and mitotic, similar to self-renewing mammalian tissues. Apoptosis is triggered as part of the normal oogenesis program, and is increased in response to various stresses. Here, we examined the effect of endoplasmic reticulum (ER) stress on apoptosis in the C. elegans germline. We demonstrate that pharmacological or genetic induction of ER stress enhances germline apoptosis. This process is mediated by the ER stress response sensor IRE-1, but is independent of its canonical downstream target XBP-1. We further demonstrate that ire-1-dependent apoptosis in the germline requires both CEP-1/p53 and the same canonical apoptotic genes as DNA damage-induced germline apoptosis. Strikingly, we find that activation of ire-1, specifically in the ASI neurons, but not in germ cells, is sufficient to induce apoptosis in the germline. This implies that ER stress related germline apoptosis can be determined at the organism level, and is a result of active IRE-1 signaling in neurons. Altogether, our findings uncover ire-1 as a novel cell non-autonomous regulator of germ cell apoptosis, linking ER homeostasis in sensory neurons and germ cell fate.
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Affiliation(s)
- Mor Levi-Ferber
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
| | - Yehuda Salzberg
- Department of Genetics, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York, New York, United States of America
| | - Modi Safra
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
| | - Anat Haviv-Chesner
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
| | - Hannes E. Bülow
- Department of Genetics, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York, New York, United States of America
| | - Sivan Henis-Korenblit
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
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70
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Soares L, Parisi M, Bonini NM. Axon injury and regeneration in the adult Drosophila. Sci Rep 2014; 4:6199. [PMID: 25160612 PMCID: PMC4145289 DOI: 10.1038/srep06199] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Accepted: 08/04/2014] [Indexed: 01/09/2023] Open
Abstract
Neural regeneration is a fascinating process with profound impact on human health, such that defining biological and genetic pathways is of interest. Here we describe an in vivo preparation for neuronal regeneration in the adult Drosophila. The nerve along the anterior margin of the wing is comprised of ~225 neurons that send projections into the central neuropil (thorax). Precise ablation can be induced with a pulsed laser to sever the entire axonal tract. The animal can be recovered, and response to injury assessed over time. Upon ablation, there is local loss of axons near the injury site, scar formation, a rapid impact on the cytoskeleton, and stimulation of hemocytes. By 7d, ~50% of animals show nerve regrowth, with axons from the nerve cells extending down towards the injury or re-routing. Inhibition of JNK signaling promotes regrowth through the injury site, enabling regeneration of the axonal tract.
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Affiliation(s)
- Lorena Soares
- Department of Biology, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Michael Parisi
- Department of Biology, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Nancy M Bonini
- Department of Biology, University of Pennsylvania, Philadelphia, PA, 19104, USA
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71
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Syndecan promotes axon regeneration by stabilizing growth cone migration. Cell Rep 2014; 8:272-83. [PMID: 25001284 DOI: 10.1016/j.celrep.2014.06.008] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 04/29/2014] [Accepted: 06/05/2014] [Indexed: 01/22/2023] Open
Abstract
Growth cones facilitate the repair of nervous system damage by providing the driving force for axon regeneration. Using single-neuron laser axotomy and in vivo time-lapse imaging, we show that syndecan, a heparan sulfate (HS) proteoglycan, is required for growth cone function during axon regeneration in C. elegans. In the absence of syndecan, regenerating growth cones form but are unstable and collapse, decreasing the effective growth rate and impeding regrowth to target cells. We provide evidence that syndecan has two distinct functions during axon regeneration: (1) a canonical function in axon guidance that requires expression outside the nervous system and depends on HS chains and (2) an intrinsic function in growth cone stabilization that is mediated by the syndecan core protein, independently of HS. Thus, syndecan is a regulator of a critical choke point in nervous system repair.
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Axon regeneration in C. elegans. Curr Opin Neurobiol 2014; 27:199-207. [PMID: 24794753 DOI: 10.1016/j.conb.2014.04.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Revised: 04/01/2014] [Accepted: 04/01/2014] [Indexed: 11/22/2022]
Abstract
Single axon transection by laser surgery has made Caenorhabditis elegans a new model for axon regeneration. Multiple conserved molecular signaling modules have been discovered through powerful genetic screening. In vivo imaging with single cell and axon resolution has revealed unprecedented cellular dynamics in regenerating axons. Information from C. elegans has greatly expanded our knowledge of the molecular and cellular mechanisms of axon regeneration.
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