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Chen L. Microtubules and axon regeneration in C. elegans. Mol Cell Neurosci 2018; 91:160-166. [PMID: 29551667 DOI: 10.1016/j.mcn.2018.03.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Revised: 03/14/2018] [Accepted: 03/15/2018] [Indexed: 11/28/2022] Open
Abstract
Axon regeneration is a fundamental and conserved process that allows the nervous system to repair circuits after trauma. Due to its conserved genome, transparent body, and relatively simple neuroanatomy, C. elegans has become a powerful model organism for studying the cellular and molecular mechanisms underlying axon regeneration. Various studies from different model organisms have found microtubule dynamics to be pivotal to axon regrowth. In this review, we will discuss the latest findings on how microtubule dynamics are regulated during axon regeneration in C. elegans. Understanding the mechanisms of axon regeneration will aid in the development of more effective therapeutic strategies for treatments of diseases involving disconnection of axons, such as spinal cord injury and stroke.
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Affiliation(s)
- Lizhen Chen
- Barshop Institute for Longevity and Aging Studies, Department of Cell Systems and Anatomy, Department of Molecular Medicine, University of Texas Health Science Center San Antonio, San Antonio, TX, USA.
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52
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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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53
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Kim KW, Tang NH, Andrusiak MG, Wu Z, Chisholm AD, Jin Y. A Neuronal piRNA Pathway Inhibits Axon Regeneration in C. elegans. Neuron 2018; 97:511-519.e6. [PMID: 29395906 PMCID: PMC5866297 DOI: 10.1016/j.neuron.2018.01.014] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2017] [Revised: 11/19/2017] [Accepted: 01/04/2018] [Indexed: 11/29/2022]
Abstract
The PIWI-interacting RNA (piRNA) pathway has long been thought to function solely in the germline, but evidence for its functions in somatic cells is emerging. Here we report an unexpected role for the piRNA pathway in Caenorhabditis elegans sensory axon regeneration after injury. Loss of function in a subset of components of the piRNA pathway results in enhanced axon regrowth. Two essential piRNA factors, PRDE-1 and PRG-1/PIWI, inhibit axon regeneration in a gonad-independent and cell-autonomous manner. By smFISH analysis we find that prde-1 transcripts are present in neurons, as well as germ cells. The piRNA pathway inhibits axon regrowth independent of nuclear transcriptional silencing but dependent on the slicer domain of PRG-1/PIWI, suggesting that post-transcriptional gene silencing is involved. Our results reveal the neuronal piRNA pathway as a novel intrinsic repressor of axon regeneration.
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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, USA
| | - Ngang Heok Tang
- Section of Neurobiology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA
| | - Matthew G Andrusiak
- Section of Neurobiology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA
| | - Zilu Wu
- 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
| | - Yishi Jin
- Section of Neurobiology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA; Department of Cellular and Molecular Medicine, School of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
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54
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Lai AG, Aboobaker AA. EvoRegen in animals: Time to uncover deep conservation or convergence of adult stem cell evolution and regenerative processes. Dev Biol 2018; 433:118-131. [PMID: 29198565 DOI: 10.1016/j.ydbio.2017.10.010] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Revised: 10/09/2017] [Accepted: 10/10/2017] [Indexed: 01/08/2023]
Abstract
How do animals regenerate specialised tissues or their entire body after a traumatic injury, how has this ability evolved and what are the genetic and cellular components underpinning this remarkable feat? While some progress has been made in understanding mechanisms, relatively little is known about the evolution of regenerative ability. Which elements of regeneration are due to lineage specific evolutionary novelties or have deeply conserved roots within the Metazoa remains an open question. The renaissance in regeneration research, fuelled by the development of modern functional and comparative genomics, now enable us to gain a detailed understanding of both the mechanisms and evolutionary forces underpinning regeneration in diverse animal phyla. Here we review existing and emerging model systems, with the focus on invertebrates, for studying regeneration. We summarize findings across these taxa that tell us something about the evolution of adult stem cell types that fuel regeneration and the growing evidence that many highly regenerative animals harbor adult stem cells with a gene expression profile that overlaps with germline stem cells. We propose a framework in which regenerative ability broadly evolves through changes in the extent to which stem cells generated through embryogenesis are maintained into the adult life history.
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Affiliation(s)
- Alvina G Lai
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, United Kingdom
| | - A Aziz Aboobaker
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, United Kingdom.
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55
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Vibert L, Daulny A, Jarriault S. Wound healing, cellular regeneration and plasticity: the elegans way. THE INTERNATIONAL JOURNAL OF DEVELOPMENTAL BIOLOGY 2018; 62:491-505. [PMID: 29938761 PMCID: PMC6161810 DOI: 10.1387/ijdb.180123sj] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Regeneration and wound healing are complex processes that allow organs and tissues to regain their integrity and functionality after injury. Wound healing, a key property of epithelia, involves tissue closure that in some cases leads to scar formation. Regeneration, a process rather limited in mammals, is the capacity to regrow (parts of) an organ or a tissue, after damage or amputation. What are the properties of organs and the features of tissue permitting functional regrowth and repair? What are the cellular and molecular mechanisms underlying these processes? These questions are crucial both in fundamental and applied contexts, with important medical implications. The mechanisms and cells underlying tissue repair have thus been the focus of intense investigation. The last decades have seen rapid progress in the domain and new models emerging. Here, we review the fundamental advances and the perspectives that the use of C. elegans as a model have brought to the mechanisms of wound healing and cellular plasticity, axon regeneration and transdifferentiation in vivo.
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Affiliation(s)
- Laura Vibert
- Department of Development and Stem Cells, IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), CNRS UMR 7104/INSERM U1258, Université de Strasbourg, Strasbourg, France
| | - Anne Daulny
- Department of Development and Stem Cells, IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), CNRS UMR 7104/INSERM U1258, Université de Strasbourg, Strasbourg, France
| | - Sophie Jarriault
- Department of Development and Stem Cells, IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), CNRS UMR 7104/INSERM U1258, Université de Strasbourg, Strasbourg, France
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56
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Gordon T, Shenkar N. Solitary Ascidians as Model Organisms in Regenerative Biology Studies. Results Probl Cell Differ 2018; 65:321-336. [PMID: 30083926 DOI: 10.1007/978-3-319-92486-1_15] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
Regeneration, the process of replacing lost or damaged body parts, has long captured human imagination and is a key feature among all animal phyla. Due to their close phylogenetic relationship to vertebrates and their high regenerative abilities, ascidians (Chordata, Ascidiacea) are often used as models to shed light on the cellular and genetic process involved in tissue regeneration. Surprisingly, ascidian regeneration studies are based on only a few model species. In this chapter, we point out the important potential of solitary ascidians in regenerative and stem cell studies. We review recent studies of regeneration among solitary ascidians and discuss the cellular mechanism of tissue regeneration and the possible involvement of circulating cells in these processes. New data regarding the relationship between age and regeneration abilities of the solitary ascidian Polycarpa mytiligera (Stolidobranchia, Styelidae) are presented. The unique regeneration abilities found in P. mytiligera following evisceration of its digestive system and following amputation of its neural complex and siphon-associated structures and nerves imply on its potential to serve as a novel model system for understanding tissue regeneration.
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Affiliation(s)
- Tal Gordon
- School of Zoology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv, Israel.
| | - Noa Shenkar
- School of Zoology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv, Israel.,The Steinhardt Museum of Natural History, Israel National Center for Biodiversity Studies, Tel-Aviv University, Tel-Aviv, Israel
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57
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Basu A, Dey S, Puri D, Das Saha N, Sabharwal V, Thyagarajan P, Srivastava P, Koushika SP, Ghosh-Roy A. let-7 miRNA controls CED-7 homotypic adhesion and EFF-1-mediated axonal self-fusion to restore touch sensation following injury. Proc Natl Acad Sci U S A 2017; 114:E10206-E10215. [PMID: 29109254 PMCID: PMC5703274 DOI: 10.1073/pnas.1704372114] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neuronal injury often leads to devastating consequences such as loss of senses or locomotion. Restoration of function after injury relies on whether the injured axons can find their target cells. Although fusion between injured proximal axon and distal fragment has been observed in many organisms, its functional significance is not clear. Here, using Caenorhabditis elegans mechanosensory neurons, we address this question. Using two femtosecond lasers simultaneously, we could scan and sever posterior lateral microtubule neurons [posterior lateral microtubules (PLMs)] on both sides of the worm. We showed that axotomy of both PLMs leads to a dramatic loss of posterior touch sensation. During the regenerative phase, only axons that fuse to their distal counterparts contribute to functional recovery. Loss of let-7 miRNA promotes functional restoration in both larval and adult stages. In the L4 stage, loss of let-7 increases fusion events by increasing the mRNA level of one of the cell-recognition molecules, CED-7. The ability to establish cytoplasmic continuity between the proximal and distal ends declines with age. Loss of let-7 overcomes this barrier by promoting axonal transport and enrichment of the EFF-1 fusogen at the growing tip of cut processes. Our data reveal the functional property of a regenerating neuron.
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Affiliation(s)
- Atrayee Basu
- National Brain Research Centre, Manesar, Nainwal Mode, Gurgaon, Haryana 122051, India
| | - Shirshendu Dey
- Bruker India Scientific Private Ltd, New Delhi 110019, India
| | - Dharmendra Puri
- National Brain Research Centre, Manesar, Nainwal Mode, Gurgaon, Haryana 122051, India
| | - Nilanjana Das Saha
- National Brain Research Centre, Manesar, Nainwal Mode, Gurgaon, Haryana 122051, India
| | - Vidur Sabharwal
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai 400 005, India
| | - Pankajam Thyagarajan
- National Brain Research Centre, Manesar, Nainwal Mode, Gurgaon, Haryana 122051, India
| | - Prerna Srivastava
- National Brain Research Centre, Manesar, Nainwal Mode, Gurgaon, Haryana 122051, India
| | | | - Anindya Ghosh-Roy
- National Brain Research Centre, Manesar, Nainwal Mode, Gurgaon, Haryana 122051, India;
- Wellcome Trust-Department of Biotechnology India Alliance, Banjara Hills, Hyderabad, Telangana 500034, India
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58
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Phosphatidylserine save-me signals drive functional recovery of severed axons in Caenorhabditis elegans. Proc Natl Acad Sci U S A 2017; 114:E10196-E10205. [PMID: 29109263 PMCID: PMC5703272 DOI: 10.1073/pnas.1703807114] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Nervous system injury can cause lifelong disability, because repair rarely leads to reconnection with the target tissue. In the nematode Caenorhabditis elegans and in several other species, regeneration can proceed through a mechanism of axonal fusion, whereby regrowing axons reconnect and fuse with their own separated fragments, rapidly and efficiently restoring the original axonal tract. We have found that the process of axonal fusion restores full function to damaged neurons. In addition, we show that injury-induced changes to the axonal membrane that result in exposure of lipid “save-me” signals mediate the level of axonal fusion. Thus, our results establish axonal fusion as a complete regenerative mechanism that can be modulated by changing the level of save-me signals exposed after injury. Functional regeneration after axonal injury requires transected axons to regrow and reestablish connection with their original target tissue. The spontaneous regenerative mechanism known as axonal fusion provides a highly efficient means of achieving targeted reconnection, as a regrowing axon is able to recognize and fuse with its own detached axon segment, thereby rapidly reestablishing the original axonal tract. Here, we use behavioral assays and fluorescent reporters to show that axonal fusion enables full recovery of function after axotomy of Caenorhabditis elegans mechanosensory neurons. Furthermore, we reveal that the phospholipid phosphatidylserine, which becomes exposed on the damaged axon to function as a “save-me” signal, defines the level of axonal fusion. We also show that successful axonal fusion correlates with the regrowth potential and branching of the proximal fragment and with the retraction length and degeneration of the separated segment. Finally, we identify discrete axonal domains that vary in their propensity to regrow through fusion and show that the level of axonal fusion can be genetically modulated. Taken together, our results reveal that axonal fusion restores full function to injured neurons, is dependent on exposure of phospholipid signals, and is achieved through the balance between regenerative potential and level of degeneration.
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59
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Abstract
In this issue of Neuron, Tedeschi et al. (2016) describe the voltage-gated calcium channel subunit alpha2delta2 as a developmental switch from axon elongation to synapse formation and transmission that doubles as a suppressor of axon regeneration, providing a molecular clue for the synaptic stabilization hypothesis of CNS regeneration failure.
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Affiliation(s)
- Jessica M Meves
- Neurosciences Graduate Program and Department of Neurosciences, University of California San Diego, School of Medicine, 9500 Gilman Drive, MC 0691, La Jolla, CA 92093, USA
| | - Binhai Zheng
- Neurosciences Graduate Program and Department of Neurosciences, University of California San Diego, School of Medicine, 9500 Gilman Drive, MC 0691, La Jolla, CA 92093, USA.
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60
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Rao KS, Rolls MM. Two Drosophila model neurons can regenerate axons from the stump or from a converted dendrite, with feedback between the two sites. Neural Dev 2017; 12:15. [PMID: 28818097 PMCID: PMC5561650 DOI: 10.1186/s13064-017-0092-3] [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: 05/26/2017] [Accepted: 08/09/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND After axon severing, neurons recover function by reinitiating axon outgrowth. New outgrowth often originates from the remaining axon stump. However, in many mammalian neurons, new axons initiate from a dendritic site when the axon is injured close to the cell body. METHODS Drosophila sensory neurons are ideal for studying neuronal injury responses because they can be injured reproducibly in a variety of genetic backgrounds. In Drosophila, it has been shown that a complex sensory neuron, ddaC, can regenerate an axon from a stump, and a simple sensory neuron, ddaE, can regenerate an axon from a dendrite. To provide a more complete picture of axon regeneration in these cell types, we performed additional injury types. RESULTS We found that ddaE neurons can initiate regeneration from an axon stump when a stump remains. We also showed that ddaC neurons regenerate from the dendrite when the axon is severed close to the cell body. We next demonstrated if a stump remains, new axons can originate from this site and a dendrite at the same time. Because cutting the axon close to the cell body results in growth of the new axon from a dendrite, and cutting further out may not, we asked whether the initial response in the cell body was similar after both types of injury. A transcriptional reporter for axon injury signaling, puc-GFP, increased with similar timing and levels after proximal and distal axotomy. However, changes in dendritic microtubule polarity differed in response to the two types of injury, and were influenced by the presence of a scar at the distal axotomy site. CONCLUSIONS We conclude that both ddaE and ddaC can regenerate axons either from the stump or a dendrite, and that there is some feedback between the two sites that modulates dendritic microtubule polarity.
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Affiliation(s)
- Kavitha S Rao
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Melissa M Rolls
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA.
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61
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Noma K, Goncharov A, Ellisman MH, Jin Y. Microtubule-dependent ribosome localization in C. elegans neurons. eLife 2017; 6:26376. [PMID: 28767038 PMCID: PMC5577916 DOI: 10.7554/elife.26376] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 08/01/2017] [Indexed: 01/23/2023] Open
Abstract
Subcellular localization of ribosomes defines the location and capacity for protein synthesis. Methods for in vivo visualizing ribosomes in multicellular organisms are desirable in mechanistic investigations of the cell biology of ribosome dynamics. Here, we developed an approach using split GFP for tissue-specific visualization of ribosomes in Caenorhabditis elegans. Labeled ribosomes are detected as fluorescent puncta in the axons and synaptic terminals of specific neuron types, correlating with ribosome distribution at the ultrastructural level. We found that axonal ribosomes change localization during neuronal development and after axonal injury. By examining mutants affecting axonal trafficking and performing a forward genetic screen, we showed that the microtubule cytoskeleton and the JIP3 protein UNC-16 exert distinct effects on localization of axonal and somatic ribosomes. Our data demonstrate the utility of tissue-specific visualization of ribosomes in vivo, and provide insight into the mechanisms of active regulation of ribosome localization in neurons.
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Affiliation(s)
- Kentaro Noma
- Division of Biological Sciences, Neurobiology Section, University of California, San Diego, San Diego, United States.,Howard Hughes Medical Institute, University of California, San Diego, San Diego, United States
| | - Alexandr Goncharov
- Division of Biological Sciences, Neurobiology Section, University of California, San Diego, San Diego, United States.,Howard Hughes Medical Institute, University of California, San Diego, San Diego, United States
| | - Mark H Ellisman
- National Center for Research in Biological Systems, Department of Neurosciences, School of Medicine, University of California, San Diego, San Diego, United States
| | - Yishi Jin
- Division of Biological Sciences, Neurobiology Section, 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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62
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Chaudhury AR, Insolera R, Hwang RD, Fridell YW, Collins C, Chronis N. On chip cryo-anesthesia of Drosophila larvae for high resolution in vivo imaging applications. LAB ON A CHIP 2017; 17:2303-2322. [PMID: 28613308 PMCID: PMC5559736 DOI: 10.1039/c7lc00345e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
We present a microfluidic chip for immobilizing Drosophila melanogaster larvae for high resolution in vivo imaging. The chip creates a low-temperature micro-environment that anaesthetizes and immobilizes the larva in under 3 minutes. We characterized the temperature distribution within the chip and analyzed the resulting larval body movement using high resolution fluorescence imaging. Our results indicate that the proposed method minimizes submicron movements of internal organs and tissue without affecting the larva physiology. It can be used to continuously immobilize larvae for short periods of time (minutes) or for longer periods (several hours) if used intermittently. The same chip can be used to accommodate and immobilize arvae across all developmental stages (1st instar to late 3rd instar), and loading larvae onto the chip does not require any specialized skills. To demonstrate the usability of the chip, we observed mitochondrial trafficking in neurons from the cell bodies to the axon terminals along with mitochondrial fusion and neuro-synaptic growth through time in intact larvae. Besides studying sub-cellular processes and cellular development, we envision the use of on chip cryo-anesthesia in a wide variety of biological in vivo imaging applications, including observing organ development of the salivary glands, fat bodies and body-wall muscles.
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Affiliation(s)
- Amrita Ray Chaudhury
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
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63
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Thompson-Peer KL, DeVault L, Li T, Jan LY, Jan YN. In vivo dendrite regeneration after injury is different from dendrite development. Genes Dev 2017; 30:1776-89. [PMID: 27542831 PMCID: PMC5002981 DOI: 10.1101/gad.282848.116] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Accepted: 07/25/2016] [Indexed: 12/22/2022]
Abstract
Thompson-Peer et al. show that, in intact Drosophila larvae, a discrete injury that removes all dendrites induces robust dendritic growth that recreates many features of uninjured dendrites. However, the growth and patterning of injury-induced dendrites is significantly different from uninjured dendrites. Neurons receive information along dendrites and send signals along axons to synaptic contacts. The factors that control axon regeneration have been examined in many systems, but dendrite regeneration has been largely unexplored. Here we report that, in intact Drosophila larvae, a discrete injury that removes all dendrites induces robust dendritic growth that recreates many features of uninjured dendrites, including the number of dendrite branches that regenerate and responsiveness to sensory stimuli. However, the growth and patterning of injury-induced dendrites is significantly different from uninjured dendrites. We found that regenerated arbors cover much less territory than uninjured neurons, fail to avoid crossing over other branches from the same neuron, respond less strongly to mechanical stimuli, and are pruned precociously. Finally, silencing the electrical activity of the neurons specifically blocks injury-induced, but not developmental, dendrite growth. By elucidating the essential features of dendrites grown in response to acute injury, our work builds a framework for exploring dendrite regeneration in physiological and pathological conditions.
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Affiliation(s)
- Katherine L Thompson-Peer
- Howard Hughes Medical Institute, Department of Physiology, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA
| | - Laura DeVault
- Howard Hughes Medical Institute, Department of Physiology, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA
| | - Tun Li
- Howard Hughes Medical Institute, Department of Physiology, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA
| | - Lily Yeh Jan
- Howard Hughes Medical Institute, Department of Physiology, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA
| | - Yuh Nung Jan
- Howard Hughes Medical Institute, Department of Physiology, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA
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64
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Knowlton WM, Hubert T, Wu Z, Chisholm AD, Jin Y. A Select Subset of Electron Transport Chain Genes Associated with Optic Atrophy Link Mitochondria to Axon Regeneration in Caenorhabditis elegans. Front Neurosci 2017; 11:263. [PMID: 28539870 PMCID: PMC5423972 DOI: 10.3389/fnins.2017.00263] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Accepted: 04/24/2017] [Indexed: 12/13/2022] Open
Abstract
The role of mitochondria within injured neurons is an area of active interest since these organelles are vital for the production of cellular energy in the form of ATP. Using mechanosensory neurons of the nematode Caenorhabditis elegans to test regeneration after neuronal injury in vivo, we surveyed genes related to mitochondrial function for effects on axon regrowth after laser axotomy. Genes involved in mitochondrial transport, calcium uptake, mitophagy, or fission and fusion were largely dispensable for axon regrowth, with the exception of eat-3/Opa1. Surprisingly, many genes encoding components of the electron transport chain were dispensable for regrowth, except for the iron-sulfur proteins gas-1, nduf-2.2, nduf-7, and isp-1, and the putative oxidoreductase rad-8. In these mutants, axonal development was essentially normal and axons responded normally to injury by forming regenerative growth cones, but were impaired in subsequent axon extension. Overexpression of nduf-2.2 or isp-1 was sufficient to enhance regrowth, suggesting that mitochondrial function is rate-limiting in axon regeneration. Moreover, loss of function in isp-1 reduced the enhanced regeneration caused by either a gain-of-function mutation in the calcium channel EGL-19 or overexpression of the MAP kinase DLK-1. While the cellular function of RAD-8 remains unclear, our genetic analyses place rad-8 in the same pathway as other electron transport genes in axon regeneration. Unexpectedly, rad-8 regrowth defects were suppressed by altered function in the ubiquinone biosynthesis gene clk-1. Furthermore, we found that inhibition of the mitochondrial unfolded protein response via deletion of atfs-1 suppressed the defective regrowth in nduf-2.2 mutants. Together, our data indicate that while axon regeneration is not significantly affected by general dysfunction of cellular respiration, it is sensitive to the proper functioning of a select subset of electron transport chain genes, or to the cellular adaptations used by neurons under conditions of injury.
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Affiliation(s)
- Wendy M Knowlton
- Section of Neurobiology, Division of Biological Sciences, University of CaliforniaSan Diego, CA, USA
| | - Thomas Hubert
- Section of Neurobiology, Division of Biological Sciences, University of CaliforniaSan Diego, CA, USA
| | - Zilu Wu
- Howard Hughes Medical Institute, University of CaliforniaSan Diego, CA, USA
| | - Andrew D Chisholm
- Section of Neurobiology, Division of Biological Sciences, University of CaliforniaSan Diego, CA, USA
| | - Yishi Jin
- Section of Neurobiology, Division of Biological Sciences, University of CaliforniaSan Diego, CA, USA.,Howard Hughes Medical Institute, University of CaliforniaSan Diego, CA, USA.,Department of Cellular and Molecular Medicine, School of Medicine, University of CaliforniaSan Diego, CA, USA
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Oren-Suissa M, Gattegno T, Kravtsov V, Podbilewicz B. Extrinsic Repair of Injured Dendrites as a Paradigm for Regeneration by Fusion in Caenorhabditis elegans. Genetics 2017; 206:215-230. [PMID: 28283540 PMCID: PMC5419471 DOI: 10.1534/genetics.116.196386] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Accepted: 03/07/2017] [Indexed: 11/18/2022] Open
Abstract
Injury triggers regeneration of axons and dendrites. Research has identified factors required for axonal regeneration outside the CNS, but little is known about regeneration triggered by dendrotomy. Here, we study neuronal plasticity triggered by dendrotomy and determine the fate of complex PVD arbors following laser surgery of dendrites. We find that severed primary dendrites grow toward each other and reconnect via branch fusion. Simultaneously, terminal branches lose self-avoidance and grow toward each other, meeting and fusing at the tips via an AFF-1-mediated process. Ectopic branch growth is identified as a step in the regeneration process required for bypassing the lesion site. Failure of reconnection to the severed dendrites results in degeneration of the distal end of the neuron. We discover pruning of excess branches via EFF-1 that acts to recover the original wild-type arborization pattern in a late stage of the process. In contrast, AFF-1 activity during dendritic auto-fusion is derived from the lateral seam cells and not autonomously from the PVD neuron. We propose a model in which AFF-1-vesicles derived from the epidermal seam cells fuse neuronal dendrites. Thus, EFF-1 and AFF-1 fusion proteins emerge as new players in neuronal arborization and maintenance of arbor connectivity following injury in Caenorhabditis elegans Our results demonstrate that there is a genetically determined multi-step pathway to repair broken dendrites in which EFF-1 and AFF-1 act on different steps of the pathway. EFF-1 is essential for dendritic pruning after injury and extrinsic AFF-1 mediates dendrite fusion to bypass injuries.
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Affiliation(s)
- Meital Oren-Suissa
- Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Tamar Gattegno
- Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Veronika Kravtsov
- Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Benjamin Podbilewicz
- Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
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66
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Tedeschi A, Bradke F. Spatial and temporal arrangement of neuronal intrinsic and extrinsic mechanisms controlling axon regeneration. Curr Opin Neurobiol 2016; 42:118-127. [PMID: 28039763 DOI: 10.1016/j.conb.2016.12.005] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 12/07/2016] [Accepted: 12/08/2016] [Indexed: 01/30/2023]
Abstract
Axon regeneration and neuronal tissue repair varies across animal lineages as well as in the mammalian central and peripheral nervous systems. While the peripheral nervous system retains the ability to self-repair, the majority of axons in the adult mammalian central nervous system (CNS) fail to reactivate intrinsic growth programs after injury. Recent findings, however, suggest that long-distance axon regeneration, neuronal circuit assembly and recovery of functions in the adult mammalian CNS are possible. Here, we discuss our current knowledge of the cell signaling pathways and networks controlling axon regeneration. In addition, we outline a number of combinatorial strategies that include among others microtubule-based treatments to foster regeneration and functional connectivity after CNS trauma.
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Affiliation(s)
- Andrea Tedeschi
- German Center for Neurodegenerative Diseases (DZNE), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.
| | - Frank Bradke
- German Center for Neurodegenerative Diseases (DZNE), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.
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Kim KW, Thakur N, Piggott CA, Omi S, Polanowska J, Jin Y, Pujol N. Coordinated inhibition of C/EBP by Tribbles in multiple tissues is essential for Caenorhabditis elegans development. BMC Biol 2016; 14:104. [PMID: 27927209 PMCID: PMC5141650 DOI: 10.1186/s12915-016-0320-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 10/19/2016] [Indexed: 01/15/2023] Open
Abstract
Background Tribbles proteins are conserved pseudokinases that function to control kinase signalling and transcription in diverse biological processes. Abnormal function in human Tribbles has been implicated in a number of diseases including leukaemia, metabolic syndromes and cardiovascular diseases. Caenorhabditis elegans Tribbles NIPI-3 was previously shown to activate host defense upon infection by promoting the conserved PMK-1/p38 mitogen-activated protein kinase (MAPK) signalling pathway. Despite the prominent role of Tribbles proteins in many species, our knowledge of their mechanism of action is fragmented, and the in vivo functional relevance of their interactions with other proteins remains largely unknown. Results Here, by characterizing nipi-3 null mutants, we show that nipi-3 is essential for larval development and viability. Through analyses of genetic suppressors of nipi-3 null mutant lethality, we show that NIPI-3 negatively controls PMK-1/p38 signalling via transcriptional repression of the C/EBP transcription factor CEBP-1. We identified CEBP-1’s transcriptional targets by ChIP-seq analyses and found them to be enriched in genes involved in development and stress responses. Unlike its cell-autonomous role in innate immunity, NIPI-3 is required in multiple tissues to control organismal development. Conclusions Together, our data uncover an unprecedented crosstalk involving multiple tissues, in which NIPI-3 acts as a master regulator to inhibit CEBP-1 and the PMK-1/p38 MAPK pathway. In doing so, it keeps innate immunity in check and ensures proper organismal development. Electronic supplementary material The online version of this article (doi:10.1186/s12915-016-0320-z) contains supplementary material, which is available to authorized users.
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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, USA.
| | - Nishant Thakur
- Centre d'Immunologie de Marseille-Luminy, Aix Marseille Université, Inserm, CNRS, Marseille, France
| | - Christopher A Piggott
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, CA, 92093, USA
| | - Shizue Omi
- Centre d'Immunologie de Marseille-Luminy, Aix Marseille Université, Inserm, CNRS, Marseille, France
| | - Jolanta Polanowska
- Centre d'Immunologie de Marseille-Luminy, Aix Marseille Université, Inserm, CNRS, Marseille, France
| | - Yishi Jin
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, CA, 92093, USA. .,Howard Hughes Medical Institute, University of California San Diego, La Jolla, CA, 92093, USA.
| | - Nathalie Pujol
- Centre d'Immunologie de Marseille-Luminy, Aix Marseille Université, Inserm, CNRS, Marseille, France.
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68
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Kalichamy SS, Lee TY, Yoon KH, Lee JI. Hypergravity hinders axonal development of motor neurons in Caenorhabditis elegans. PeerJ 2016; 4:e2666. [PMID: 27833821 PMCID: PMC5101602 DOI: 10.7717/peerj.2666] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Accepted: 10/08/2016] [Indexed: 12/29/2022] Open
Abstract
As space flight becomes more accessible in the future, humans will be exposed to gravity conditions other than our 1G environment on Earth. Our bodies and physiology, however, are adapted for life at 1G gravity. Altering gravity can have profound effects on the body, particularly the development of muscles, but the reasons and biology behind gravity’s effect are not fully known. We asked whether increasing gravity had effects on the development of motor neurons that innervate and control muscle, a relatively unexplored area of gravity biology. Using the nematode model organism Caenorhabditis elegans, we examined changes in response to hypergravity in the development of the 19 GABAergic DD/VD motor neurons that innervate body muscle. We found that a high gravity force above 10G significantly increases the number of animals with defects in the development of axonal projections from the DD/VD neurons. We showed that a critical period of hypergravity exposure during the embryonic/early larval stage was sufficient to induce defects. While characterizing the nature of the axonal defects, we found that in normal 1G gravity conditions, DD/VD axonal defects occasionally occurred, with the majority of defects occurring on the dorsal side of the animal and in the mid-body region, and a significantly higher rate of error in the 13 VD axons than the 6 DD axons. Hypergravity exposure increased the rate of DD/VD axonal defects, but did not change the distribution or the characteristics of the defects. Our study demonstrates that altering gravity can impact motor neuron development.
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Affiliation(s)
| | - Tong Young Lee
- Division of Biological Science and Technology, Yonsei University , Wonju , South Korea
| | - Kyoung-Hye Yoon
- Division of Biological Science and Technology, Yonsei University , Wonju , South Korea
| | - Jin Il Lee
- Division of Biological Science and Technology, Yonsei University , Wonju , South Korea
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69
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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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70
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Tedeschi A, Dupraz S, Laskowski CJ, Xue J, Ulas T, Beyer M, Schultze JL, Bradke F. The Calcium Channel Subunit Alpha2delta2 Suppresses Axon Regeneration in the Adult CNS. Neuron 2016; 92:419-434. [PMID: 27720483 DOI: 10.1016/j.neuron.2016.09.026] [Citation(s) in RCA: 168] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Revised: 07/21/2016] [Accepted: 09/01/2016] [Indexed: 12/22/2022]
Abstract
Injuries to the adult CNS often result in permanent disabilities because neurons lose the ability to regenerate their axon during development. Here, whole transcriptome sequencing and bioinformatics analysis followed by gain- and loss-of-function experiments identified Cacna2d2, the gene encoding the Alpha2delta2 subunit of voltage-gated calcium channels (VGCCs), as a developmental switch that limits axon growth and regeneration. Cacna2d2 gene deletion or silencing promoted axon growth in vitro. In vivo, Alpha2delta2 pharmacological blockade through Pregabalin (PGB) administration enhanced axon regeneration in adult mice after spinal cord injury (SCI). As PGB is already an established treatment for a wide range of neurological disorders, our findings suggest that targeting Alpha2delta2 may be a novel treatment strategy to promote structural plasticity and regeneration following CNS trauma.
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Affiliation(s)
- Andrea Tedeschi
- Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases, 53175 Bonn, Germany
| | - Sebastian Dupraz
- Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases, 53175 Bonn, Germany
| | - Claudia J Laskowski
- Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases, 53175 Bonn, Germany
| | - Jia Xue
- Genomics and Immunoregulation, LIMES-Institute, University of Bonn, 53115 Bonn, Germany
| | - Thomas Ulas
- Genomics and Immunoregulation, LIMES-Institute, University of Bonn, 53115 Bonn, Germany
| | - Marc Beyer
- Genomics and Immunoregulation, LIMES-Institute, University of Bonn, 53115 Bonn, Germany
| | - Joachim L Schultze
- Genomics and Immunoregulation, LIMES-Institute, University of Bonn, 53115 Bonn, Germany; Platform for Single Cell Genomics and Epigenomics, German Center for Neurodegenerative Diseases, 53175 Bonn, Germany
| | - Frank Bradke
- Axonal Growth and Regeneration, German Center for Neurodegenerative Diseases, 53175 Bonn, Germany.
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71
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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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72
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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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73
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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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74
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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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75
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Nichols ALA, Meelkop E, Linton C, Giordano-Santini R, Sullivan RK, Donato A, Nolan C, Hall DH, Xue D, Neumann B, Hilliard MA. The Apoptotic Engulfment Machinery Regulates Axonal Degeneration in C. elegans Neurons. Cell Rep 2016; 14:1673-1683. [PMID: 26876181 PMCID: PMC4821572 DOI: 10.1016/j.celrep.2016.01.050] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Revised: 12/23/2015] [Accepted: 01/13/2016] [Indexed: 01/31/2023] Open
Abstract
Axonal degeneration is a characteristic feature of neurodegenerative disease and nerve injury. Here, we characterize axonal degeneration in Caenorhabditis elegans neurons following laser-induced axotomy. We show that this process proceeds independently of the WLD(S) and Nmnat pathway and requires the axonal clearance machinery that includes the conserved transmembrane receptor CED-1/Draper, the adaptor protein CED-6, the guanine nucleotide exchange factor complex Crk/Mbc/dCed-12 (CED-2/CED-5/CED-12), and the small GTPase Rac1 (CED-10). We demonstrate that CED-1 and CED-6 function non-cell autonomously in the surrounding hypodermis, which we show acts as the engulfing tissue for the severed axon. Moreover, we establish a function in this process for CED-7, an ATP-binding cassette (ABC) transporter, and NRF-5, a lipid-binding protein, both associated with release of lipid-vesicles during apoptotic cell clearance. Thus, our results reveal the existence of a WLD(S)/Nmnat-independent axonal degeneration pathway, conservation of the axonal clearance machinery, and a function for CED-7 and NRF-5 in this process.
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Affiliation(s)
- Annika L A Nichols
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Ellen Meelkop
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Casey Linton
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Rosina Giordano-Santini
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Robert K Sullivan
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Alessandra Donato
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Cara Nolan
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - David H Hall
- Center for C. elegans Anatomy, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Ding Xue
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309, USA
| | - Brent Neumann
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
| | - Massimo A Hilliard
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
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76
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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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77
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Ballesteros C, Tritten L, O’Neill M, Burkman E, Zaky WI, Xia J, Moorhead A, Williams SA, Geary TG. The Effect of In Vitro Cultivation on the Transcriptome of Adult Brugia malayi. PLoS Negl Trop Dis 2016; 10:e0004311. [PMID: 26727204 PMCID: PMC4699822 DOI: 10.1371/journal.pntd.0004311] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 11/29/2015] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Filarial nematodes cause serious and debilitating infections in human populations of tropical countries, contributing to an entrenched cycle of poverty. Only one human filarial parasite, Brugia malayi, can be maintained in rodents in the laboratory setting. It has been a widely used model organism in experiments that employ culture systems, the impact of which on the worms is unknown. METHODOLOGY/PRINCIPAL FINDINGS Using Illumina RNA sequencing, we characterized changes in gene expression upon in vitro maintenance of adult B. malayi female worms at four time points: immediately upon removal from the host, immediately after receipt following shipment, and after 48 h and 5 days in liquid culture media. The dramatic environmental change and the 24 h time lapse between removal from the host and establishment in culture caused a globally dysregulated gene expression profile. We found a maximum of 562 differentially expressed genes based on pairwise comparison between time points. After an initial shock upon removal from the host and shipping, a few stress fingerprints remained after 48 h in culture and until the experiment was stopped. This was best illustrated by a strong and persistent up-regulation of several genes encoding cuticle collagens, as well as serpins. CONCLUSIONS/SIGNIFICANCE These findings suggest that B. malayi can be maintained in culture as a valid system for pharmacological and biological studies, at least for several days after removal from the host and adaptation to the new environment. However, genes encoding several stress indicators remained dysregulated until the experiment was stopped.
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Affiliation(s)
- Cristina Ballesteros
- Institute of Parasitology, Centre for Host-Parasite Interactions, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada
| | - Lucienne Tritten
- Institute of Parasitology, Centre for Host-Parasite Interactions, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada
| | - Maeghan O’Neill
- Institute of Parasitology, Centre for Host-Parasite Interactions, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada
| | - Erica Burkman
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, Georgia, United States of America
- Filariasis Research Reagent Resource Center, Northampton, Massachusetts, United States of America
| | - Weam I. Zaky
- Filariasis Research Reagent Resource Center, Northampton, Massachusetts, United States of America
- Department of Biological Sciences, Smith College, Northampton, Massachusetts, United States of America
| | - Jianguo Xia
- Institute of Parasitology, Centre for Host-Parasite Interactions, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada
| | - Andrew Moorhead
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, Georgia, United States of America
- Filariasis Research Reagent Resource Center, Northampton, Massachusetts, United States of America
| | - Steven A. Williams
- Filariasis Research Reagent Resource Center, Northampton, Massachusetts, United States of America
- Department of Biological Sciences, Smith College, Northampton, Massachusetts, United States of America
| | - Timothy G. Geary
- Institute of Parasitology, Centre for Host-Parasite Interactions, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada
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78
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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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A surviving intact branch stabilizes remaining axon architecture after injury as revealed by in vivo imaging in the mouse spinal cord. Neuron 2015; 86:947-954. [PMID: 25937174 DOI: 10.1016/j.neuron.2015.03.061] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2014] [Revised: 02/17/2015] [Accepted: 03/24/2015] [Indexed: 01/21/2023]
Abstract
The complex morphology of axons presents a challenge in understanding axonal responses to injury and disease. By in vivo two-photon imaging of spinal dorsal column sensory axons, we systematically examined the effect of injury location relative to the main bifurcation point on axon degeneration and regeneration following highly localized laser injuries. Retrograde but not anterograde degeneration was strongly blocked at the bifurcation point at both the acute and subacute phases. Eliminating either the ascending or descending branch led to a poor regenerative response, while eliminating both led to a strong regenerative response. Thus, a surviving intact branch suppresses both retrograde degeneration and regeneration of the injured branch, thereby preserving the remaining axon architecture. Regenerating axons exhibited a dynamic pattern with alternating phases of regeneration and pruning over a chronic period. In vivo imaging continues to reveal new insights on axonal responses to injury in the mammalian spinal cord.
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80
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Chin MR, Zlotkowski K, Han M, Patel S, Eliasen AM, Axelrod A, Siegel D. Expedited access to vinaxanthone and chemically edited derivatives possessing neuronal regenerative effects through ynone coupling reactions. ACS Chem Neurosci 2015; 6:542-50. [PMID: 25615693 DOI: 10.1021/cn500237z] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The natural product vinaxanthone has demonstrated a remarkable capability to promote nerve growth following injury or transplantation. In rats following total transection of the spinal cord delivery of vinaxanthone enhanced axonal regeneration, remyelination and angiogenesis at the site of injury all leading to an improved reinstatement of motor function. Through the development of a new ynone coupling reaction, chemically edited derivatives of vinaxanthone have been prepared and studied for improved activity. The coupling reaction allows rapid access to new derivatives, wherein n ynone precursors provide n(2) vinaxanthone analogues. These compounds have been tested for their ability to promote neuronal regrowth using laser axotomy, severing axonal connections in Caenorhabditis elegans. This precise microsurgery using C. elegans allows a new in vivo approach for medicinal chemistry based optimization of neuronal growth promoting compounds.
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Affiliation(s)
- Matthew R. Chin
- Department
of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
- Skaggs
School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92039, United States
| | - Katherine Zlotkowski
- Department
of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
- Skaggs
School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92039, United States
| | - Michelle Han
- Department
of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Saagar Patel
- Department
of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Anders M. Eliasen
- Department
of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
- Skaggs
School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92039, United States
| | - Abram Axelrod
- Department
of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Dionicio Siegel
- Department
of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
- Skaggs
School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92039, United States
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81
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Xu S, Chisholm AD. C. elegans epidermal wounding induces a mitochondrial ROS burst that promotes wound repair. Dev Cell 2015; 31:48-60. [PMID: 25313960 DOI: 10.1016/j.devcel.2014.08.002] [Citation(s) in RCA: 148] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 06/10/2014] [Accepted: 08/04/2014] [Indexed: 12/17/2022]
Abstract
Reactive oxygen species (ROS) such as hydrogen peroxide are generated at wound sites and act as long-range signals in wound healing. The roles of other ROS in wound repair are little explored. Here, we reveal a cytoprotective role for mitochondrial ROS (mtROS) in Caenorhabditis elegans skin wound healing. We show that skin wounding causes local production of mtROS superoxide at the wound site. Inhibition of mtROS levels by mitochondrial superoxide-specific antioxidants blocks actin-based wound closure, whereas elevation of mtROS promotes wound closure and enhances survival of mutant animals defective in wound healing. mtROS act downstream of wound-triggered Ca(2+) influx. We find that the mitochondrial calcium uniporter MCU-1 is essential for rapid mitochondrial Ca(2+) uptake and mtROS production after wounding. mtROS can promote wound closure by local inhibition of Rho GTPase activity via a redox-sensitive motif. These findings delineate a pathway acting via mtROS that promotes cytoskeletal responses in wound healing.
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Affiliation(s)
- Suhong Xu
- Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Andrew D Chisholm
- Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA.
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82
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Selfridge A, Hyun N, Chiang CC, Reyna SM, Weissmiller AM, Shi LZ, Preece D, Mobley WC, Berns MW. Rat embryonic hippocampus and induced pluripotent stem cell derived cultured neurons recover from laser-induced subaxotomy. NEUROPHOTONICS 2015; 2:015006. [PMID: 26157985 PMCID: PMC4487718 DOI: 10.1117/1.nph.2.1.015006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2014] [Accepted: 01/12/2015] [Indexed: 06/04/2023]
Abstract
Axonal injury and stress have long been thought to play a pathogenic role in a variety of neurodegenerative diseases. However, a model for studying single-cell axonal injury in mammalian cells and the processes of repair has not been established. The purpose of this study was to examine the response of neuronal growth cones to laser-induced axonal damage in cultures of embryonic rat hippocampal neurons and induced pluripotent stem cell (iPSC) derived human neurons. A 532-nm pulsed [Formula: see text] picosecond laser was focused to a diffraction limited spot at a precise location on an axon using a laser energy/power that did not rupture the cell membrane (subaxotomy). Subsequent time series images were taken to follow axonal recovery and growth cone dynamics. After laser subaxotomy, axons thinned at the damage site and initiated a dynamic cytoskeletal remodeling process to restore axonal thickness. The growth cone was observed to play a role in the repair process in both hippocampal and iPSC-derived neurons. Immunofluorescence staining confirmed structural tubulin damage and revealed initial phases of actin-based cytoskeletal remodeling at the damage site. The results of this study indicate that there is a repeatable and cross-species repair response of axons and growth cones after laser-induced damage.
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Affiliation(s)
- Aaron Selfridge
- University of California, San Diego, Department of Bioengineering, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Nicholas Hyun
- University of California, San Diego, Department of Bioengineering, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Chai-Chun Chiang
- University of California, San Diego, Department of Neurosciences, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Sol M. Reyna
- University of California, San Diego, Department of Biomedical Sciences, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - April M. Weissmiller
- University of California, San Diego, Department of Neurosciences, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Linda Z. Shi
- University of California, San Diego, Institute of Engineering in Medicine, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Daryl Preece
- University of California, San Diego, Department of NanoEngineering, 9500 Gilman Drive La Jolla, California 92093, United States
| | - William C. Mobley
- University of California, San Diego, Department of Neurosciences, 9500 Gilman Drive, La Jolla, California 92093, United States
| | - Michael W. Berns
- University of California, San Diego, Department of Bioengineering, 9500 Gilman Drive, La Jolla, California 92093, United States
- University of California, San Diego, Institute of Engineering in Medicine, 9500 Gilman Drive, La Jolla, California 92093, United States
- University of California, Irvine, Beckman Laser Institute, 1002 Health Sciences Road, Irvine, California 92612, United States
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83
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Gruner M, Nelson D, Winbush A, Hintz R, Ryu L, Chung SH, Kim K, Gabel CV, van der Linden AM. Feeding state, insulin and NPR-1 modulate chemoreceptor gene expression via integration of sensory and circuit inputs. PLoS Genet 2014; 10:e1004707. [PMID: 25357003 PMCID: PMC4214617 DOI: 10.1371/journal.pgen.1004707] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Accepted: 08/26/2014] [Indexed: 12/24/2022] Open
Abstract
Feeding state and food availability can dramatically alter an animals' sensory response to chemicals in its environment. Dynamic changes in the expression of chemoreceptor genes may underlie some of these food and state-dependent changes in chemosensory behavior, but the mechanisms underlying these expression changes are unknown. Here, we identified a KIN-29 (SIK)-dependent chemoreceptor, srh-234, in C. elegans whose expression in the ADL sensory neuron type is regulated by integration of sensory and internal feeding state signals. We show that in addition to KIN-29, signaling is mediated by the DAF-2 insulin-like receptor, OCR-2 TRPV channel, and NPR-1 neuropeptide receptor. Cell-specific rescue experiments suggest that DAF-2 and OCR-2 act in ADL, while NPR-1 acts in the RMG interneurons. NPR-1-mediated regulation of srh-234 is dependent on gap-junctions, implying that circuit inputs regulate the expression of chemoreceptor genes in sensory neurons. Using physical and genetic manipulation of ADL neurons, we show that sensory inputs from food presence and ADL neural output regulate srh-234 expression. While KIN-29 and DAF-2 act primarily via the MEF-2 (MEF2) and DAF-16 (FOXO) transcription factors to regulate srh-234 expression in ADL neurons, OCR-2 and NPR-1 likely act via a calcium-dependent but MEF-2- and DAF-16-independent pathway. Together, our results suggest that sensory- and circuit-mediated regulation of chemoreceptor genes via multiple pathways may allow animals to precisely regulate and fine-tune their chemosensory responses as a function of internal and external conditions. Animals dramatically modify their chemosensory behaviors to attractive and noxious chemical stimuli when starved. This could allow them to alter and optimize their food-search strategies to increase their survival and reproduction. Changes in the gene expression of chemoreceptors specialized in detecting environmental stimuli is observed in fish, insects and nematodes, and may be a general mechanism underlying the changes in chemosensory behaviors observed in starved animals. To elucidate this mechanism, we have developed an in vivo reporter assay in C. elegans for monitoring the expression of a candidate chemoreceptor gene in a single sensory neuron type, called ADL, as a function of feeding state. Using this reporter assay, we show that sensory inputs into ADL and neural outputs from ADL, as well as inputs from the RMG interneuron, which is electrically connected to ADL, are required to fine-tune expression of chemoreceptor genes in ADL. Sensory and circuit-mediated regulation of chemoreceptor gene expression is dependent on multiple pathways, including the neuropeptide receptor, NPR-1, and the DAF-2 insulin-like receptor. Our results reveal mechanisms underlying chemoreceptor gene expression, and provide insight into how expression changes in chemoreceptor genes may contribute to changes in chemosensory behavior as a function of feeding state.
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Affiliation(s)
- Matthew Gruner
- Department of Biology, University of Nevada, Reno, Nevada, United States of America
| | - Dru Nelson
- Department of Biology, University of Nevada, Reno, Nevada, United States of America
| | - Ari Winbush
- Department of Biology, University of Nevada, Reno, Nevada, United States of America
| | - Rebecca Hintz
- Department of Agriculture, Nutrition and Veterinary Sciences, University of Nevada, Reno, Nevada, United States of America
| | - Leesun Ryu
- Department of Brain Science, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, Korea
| | - Samuel H. Chung
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts, United States of America
- Boston University Photonics Center, Boston, Massachusetts, United States of America
| | - Kyuhyung Kim
- Department of Brain Science, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, Korea
| | - Chrisopher V. Gabel
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts, United States of America
- Boston University Photonics Center, Boston, Massachusetts, United States of America
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84
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Chuang M, Goncharov A, Wang S, Oegema K, Jin Y, Chisholm AD. The microtubule minus-end-binding protein patronin/PTRN-1 is required for axon regeneration in C. elegans. Cell Rep 2014; 9:874-83. [PMID: 25437544 DOI: 10.1016/j.celrep.2014.09.054] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2014] [Revised: 09/15/2014] [Accepted: 09/29/2014] [Indexed: 11/17/2022] Open
Abstract
Precise regulation of microtubule (MT) dynamics is increasingly recognized as a critical determinant of axon regeneration. In contrast to developing neurons, mature axons exhibit noncentrosomal microtubule nucleation. The factors regulating noncentrosomal MT architecture in axon regeneration remain poorly understood. We report that PTRN-1, the C. elegans member of the Patronin/Nezha/calmodulin- and spectrin-associated protein (CAMSAP) family of microtubule minus-end-binding proteins, is critical for efficient axon regeneration in vivo. ptrn-1-null mutants display generally normal developmental axon outgrowth but significantly impaired regenerative regrowth after laser axotomy. Unexpectedly, mature axons in ptrn-1 mutants display elevated numbers of dynamic axonal MTs before and after injury, suggesting that PTRN-1 inhibits MT dynamics. The CKK domain of PTRN-1 is necessary and sufficient for its functions in axon regeneration and MT dynamics and appears to stabilize MTs independent of minus-end localization. Whereas in developing neurons, PTRN-1 inhibits activity of the DLK-1 mitogen-activated protein kinase (MAPK) cascade, we find that, in regeneration, PTRN-1 and DLK-1 function together to promote axonal regrowth.
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Affiliation(s)
- Marian Chuang
- Section of Neurobiology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA
| | - Alexandr Goncharov
- Howard Hughes Medical Institute, University of California, San Diego, La Jolla, CA 92093, USA
| | - Shaohe Wang
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093, USA; Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, CA 92093, USA; Biomedical Sciences Graduate Program, University of California, San Diego, La Jolla, CA 92093, USA
| | - Karen Oegema
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093, USA; Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, CA 92093, USA
| | - Yishi Jin
- Section of Neurobiology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA; Howard Hughes Medical Institute, University of California, San Diego, La Jolla, CA 92093, USA; Department of Cellular and Molecular Medicine, 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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85
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Donaldson K, Höke A. Studying axonal degeneration and regeneration using in vitro and in vivo models: the translational potential. FUTURE NEUROLOGY 2014. [DOI: 10.2217/fnl.14.29] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
ABSTRACT: Since the initial studies by Cajal, multiple models of peripheral nerve degeneration and regeneration have been developed to address the ever-increasing complexity of the mechanisms involved in regeneration. In vitro models offer the principal benefit of a system that can be readily manipulated to address specific mechanistic questions in a deconstructed system. However, in vitro models can be overly simplified and intricacies of the interactions between neurons and glia can be lost. In vivo animal models seek to remedy some of these shortcomings, but most in vivo animal systems fail to precisely model human nerve regeneration. Rodent models of chronic nerve regeneration have been developed to better recapitulate human nerve regeneration, but are not widely used. An important development in the field has been the establishment of experimental nerve regeneration in humans, involving the reinnervation of the epidermis after cutaneous axotomy or topical capsaicin application. Use of such human models will likely accelerate the development and evaluation of new drugs that enhance peripheral nerve regeneration.
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Affiliation(s)
- Katelyn Donaldson
- Departments of Neurology & Neuroscience, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA
| | - Ahmet Höke
- Departments of Neurology & Neuroscience, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA
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86
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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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87
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S6 kinase inhibits intrinsic axon regeneration capacity via AMP kinase in Caenorhabditis elegans. J Neurosci 2014; 34:758-63. [PMID: 24431434 DOI: 10.1523/jneurosci.2886-13.2014] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The ability of axons to regrow after injury is determined by the complex interplay of intrinsic growth programs and external cues. In Caenorhabditis elegans mechanosensory neuron, axons exhibit robust regenerative regrowth following laser axotomy. By surveying conserved metabolic signaling pathways, we have identified the ribosomal S6 kinase RSKS-1 as a new cell-autonomous inhibitor of axon regeneration. RSKS-1 is not required for axonal development but inhibits axon regrowth after injury in multiple neuron types. Loss of function in rsks-1 results in more rapid growth cone formation after injury and accelerates subsequent axon extension. The enhanced regrowth of rsks-1 mutants is partly dependent on the DLK-1 MAPK cascade. An essential output of RSKS-1 in axon regrowth is the metabolic sensor AMP kinase, AAK-2. We further show that the antidiabetic drug phenformin, which activates AMP kinase, can promote axon regrowth. Our data reveal a new function for an S6 kinase acting through an AMP kinase in regenerative growth of injured axons.
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88
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Rawson RL, Yam L, Weimer RM, Bend EG, Hartwieg E, Horvitz HR, Clark SG, Jorgensen EM. Axons degenerate in the absence of mitochondria in C. elegans. Curr Biol 2014; 24:760-5. [PMID: 24631238 DOI: 10.1016/j.cub.2014.02.025] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Revised: 01/07/2014] [Accepted: 02/11/2014] [Indexed: 01/21/2023]
Abstract
Many neurodegenerative disorders are associated with mitochondrial defects [1-3]. Mitochondria can play an active role in degeneration by releasing reactive oxygen species and apoptotic factors [4-7]. Alternatively, mitochondria can protect axons from stress and insults, for example by buffering calcium [8]. Recent studies manipulating mitochondria lend support to both of these models [9-13]. Here, we identify a C. elegans mutant, ric-7, in which mitochondria are unable to exit the neuron cell bodies, similar to the kinesin-1/unc-116 mutant. When axons lacking mitochondria are cut with a laser, they rapidly degenerate. Some neurons even spontaneously degenerate in ric-7 mutants. Degeneration can be suppressed by forcing mitochondria into the axons of the mutants. The protective effect of mitochondria is also observed in the wild-type: a majority of axon fragments containing a mitochondrion survive axotomy, whereas those lacking mitochondria degenerate. Thus, mitochondria are not required for axon degeneration and serve a protective role in C. elegans axons.
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Affiliation(s)
- Randi L Rawson
- Department of Biology and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Lung Yam
- Molecular Neurobiology Program, Department of Pharmacology, Skirball Institute, NYU School of Medicine, New York, NY 10016, USA
| | - Robby M Weimer
- Department of Biology and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Eric G Bend
- Department of Biology and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Erika Hartwieg
- Howard Hughes Medical Institute and Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - H Robert Horvitz
- Howard Hughes Medical Institute and Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Scott G Clark
- Molecular Neurobiology Program, Department of Pharmacology, Skirball Institute, NYU School of Medicine, New York, NY 10016, USA
| | - Erik M Jorgensen
- Department of Biology and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT 84112-0840, USA.
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89
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Abstract
Axons of the mammalian CNS lose the ability to regenerate soon after development due to both an inhibitory CNS environment and the loss of cell-intrinsic factors necessary for regeneration. The complex molecular events required for robust regeneration of mature neurons are not fully understood, particularly in vivo. To identify genes affecting axon regeneration in Caenorhabditis elegans, we performed both an RNAi-based screen for defective motor axon regeneration in unc-70/β-spectrin mutants and a candidate gene screen. From these screens, we identified at least 50 conserved genes with growth-promoting or growth-inhibiting functions. Through our analysis of mutants, we shed new light on certain aspects of regeneration, including the role of β-spectrin and membrane dynamics, the antagonistic activity of MAP kinase signaling pathways, and the role of stress in promoting axon regeneration. Many gene candidates had not previously been associated with axon regeneration and implicate new pathways of interest for therapeutic intervention.
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90
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Abstract
The ability of injured axons to regenerate declines with age, yet the mechanisms that regulate axon regeneration in response to age are not known. Here we show that axon regeneration in aging C. elegans motor neurons is inhibited by the conserved insulin/IGF1 receptor DAF-2. DAF-2's function in regeneration is mediated by intrinsic neuronal activity of the forkhead transcription factor DAF-16/FOXO. DAF-16 regulates regeneration independently of lifespan, indicating that neuronal aging is an intrinsic, neuron-specific, and genetically regulated process. In addition, we found that DAF-18/PTEN inhibits regeneration independently of age and FOXO signaling via the TOR pathway. Finally, DLK-1, a conserved regulator of regeneration, is downregulated by insulin/IGF1 signaling, bound by DAF-16 in neurons, and required for both DAF-16- and DAF-18-mediated regeneration. Together, our data establish that insulin signaling specifically inhibits regeneration in aging adult neurons and that this mechanism is independent of PTEN and TOR.
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91
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Chen CH, Chen YC, Jiang HC, Chen CK, Pan CL. Neuronal aging: learning from C. elegans. J Mol Signal 2013; 8:14. [PMID: 24325838 PMCID: PMC3895751 DOI: 10.1186/1750-2187-8-14] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Accepted: 12/03/2013] [Indexed: 12/21/2022] Open
Abstract
The heterogeneity and multigenetic nature of nervous system aging make modeling of it a formidable task in mammalian species. The powerful genetics, simple anatomy and short life span of the nematode Caenorhabditis elegans offer unique advantages in unraveling the molecular genetic network that regulates the integrity of neuronal structures and functions during aging. In this review, we first summarize recent breakthroughs in the morphological and functional characterization of C. elegans neuronal aging. Age-associated morphological changes include age-dependent neurite branching, axon beading or swelling, axon defasciculation, progressive distortion of the neuronal soma, and early decline in presynaptic release function. We then discuss genetic pathways that modulate the speed of neuronal aging concordant with alteration in life span, such as insulin signaling, as well as cell-autonomous factors that promote neuronal integrity during senescence, including membrane activity and JNK/MAPK signaling. As a robust genetic model for aging, insights from C. elegans neuronal aging studies will contribute to our mechanistic understanding of human brain aging.
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Affiliation(s)
| | | | | | | | - Chun-Liang Pan
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, No, 7, Chung-Shan South Rd, Taipei 100, Taiwan.
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92
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Siddique R, Thakor N. Investigation of nerve injury through microfluidic devices. J R Soc Interface 2013; 11:20130676. [PMID: 24227311 DOI: 10.1098/rsif.2013.0676] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Traumatic injuries, both in the central nervous system (CNS) and peripheral nervous system (PNS), can potentially lead to irreversible damage resulting in permanent loss of function. Investigating the complex dynamics involved in these processes may elucidate the biological mechanisms of both nerve degeneration and regeneration, and may potentially lead to the development of new therapies for recovery. A scientific overview on the biological foundations of nerve injury is presented. Differences between nerve regeneration in the central and PNS are discussed. Advances in microtechnology over the past several years have led to the development of invaluable tools that now facilitate investigation of neurobiology at the cellular scale. Microfluidic devices are explored as a means to study nerve injury at the necessary simplification of the cellular level, including those devices aimed at both chemical and physical injury, as well as those that recreate the post-injury environment.
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Affiliation(s)
- Rezina Siddique
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, , Baltimore, MD, USA
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93
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Reina CP, Driscoll M, Gabel CV. Neuronal repair: Apoptotic proteins make good. WORM 2013; 2:e22285. [PMID: 24058867 PMCID: PMC3704441 DOI: 10.4161/worm.22285] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Accepted: 09/18/2012] [Indexed: 11/25/2022]
Abstract
The potential of the central nervous system (CNS) to regenerate is regulated by a complex interaction of neuronal intrinsic and extrinsic factors that remain poorly understood. Significant research has been dedicated to identifying these factors to facilitate design of therapies that will treat the functional impairment associated with CNS injuries. Over the last decade, the development of in vivo laser severing of single axons in C. elegans has established an invaluable model for the genetic identification of novel regeneration factors. In a recent study we report the unexpected identification of the core apoptotic proteins CED-4/Apaf-1 and the executioner caspase CED-3 as important factors that promote early events in regeneration in C. elegans. Other upstream regulators of apoptosis do not influence regeneration, indicating the existence of a novel mechanism for activation of CED-4 and CED-3 in neuronal repair. CED-4 and CED-3 function downstream of injury-induced calcium transients and appear to act through the conserved DLK-1 pathway to promote regeneration. We propose a working model for calcium-dependent localized activation of CED-4 and CED-3 caspase and discuss questions raised including mechanisms for spatially regulating activated CED-3 and the possible substrates that it might cleave to initiate regeneration.
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Affiliation(s)
- Christopher P Reina
- Department of Molecular Biology and Biochemistry; Rutgers University; Piscataway, NJ USA
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94
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Kurup N, Sharifnia P, Jin Y. Spatial and temporal dynamics of neurite regrowth. Curr Opin Neurobiol 2013; 23:1011-7. [PMID: 23856616 DOI: 10.1016/j.conb.2013.06.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Revised: 06/19/2013] [Accepted: 06/20/2013] [Indexed: 11/26/2022]
Abstract
Injury to mature neurites triggers a series of events that have both growth promoting and inhibitory roles. Recent evidence from a variety of experimental models has revealed new neuronal re-growth modulators. The action of these modulators must be precisely regulated both in time and space, and involves multiple cellular processes including retrograde signaling and local translation in the injured neurite. New genetic techniques, in combination with pharmacological approaches, have served to advance mechanistic dissection of neuronal response to injury. Better understanding of the spatio-temporal cues would greatly aid in the development of effective regenerative therapies.
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Affiliation(s)
- Naina Kurup
- Division of Biological Sciences, Section of Neurobiology, University of California, San Diego, La Jolla, CA 92093, USA; Biology Graduate Program, University of California, San Diego, La Jolla, CA 92093, USA
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95
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Abstract
Axon regeneration after damage is widespread in the animal kingdom, and the nematode Caenorhabditis elegans has recently emerged as a tractable model in which to study the genetics and cell biology of axon regrowth in vivo. A key early step in axon regrowth is the conversion of part of a mature axon shaft into a growth cone-like structure, involving coordinated alterations in the microtubule, actin, and neurofilament systems. Recent attention has focused on microtubule dynamics as a determinant of axon-regrowth ability in several organisms. Live imaging studies have begun to reveal how the microtubule cytoskeleton is remodeled after axon injury, as well as the regulatory pathways involved. The dual leucine zipper kinase family of mixed-lineage kinases has emerged as a critical sensor of axon damage and plays a key role in regulating microtubule dynamics in the damaged axon.
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Affiliation(s)
- Andrew D Chisholm
- Division of Biological Sciences, Section of Neurobiology, University of California, San Diego, La Jolla, California 92093;
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96
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Tedeschi A, Bradke F. The DLK signalling pathway--a double-edged sword in neural development and regeneration. EMBO Rep 2013; 14:605-14. [PMID: 23681442 DOI: 10.1038/embor.2013.64] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Accepted: 04/23/2013] [Indexed: 01/08/2023] Open
Abstract
Dual leucine zipper kinase (DLK), a mitogen-activated protein kinase kinase kinase, controls axon growth, apoptosis and neuron degeneration during neural development, as well as neurodegeneration after various insults to the adult nervous system. Interestingly, recent studies have also highlighted a role of DLK in promoting axon regeneration in diverse model systems. Invertebrates and vertebrates, cold- and warm-blooded animals, as well as central and peripheral mammalian nervous systems all differ in their ability to regenerate injured axons. Here, we discuss how DLK-dependent signalling regulates apparently contradictory functions during neural development and regeneration in different species. In addition, we outline strategies to fine-tune DLK function, either alone or together with other approaches, to promote axon regeneration in the adult mammalian central nervous system.
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Affiliation(s)
- Andrea Tedeschi
- Laboratory for Axon Growth & Regeneration, German Center for Neurodegenerative Diseases (DZNE), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany
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97
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Zou Y, Chiu H, Zinovyeva A, Ambros V, Chuang CF, Chang C. Developmental decline in neuronal regeneration by the progressive change of two intrinsic timers. Science 2013; 340:372-376. [PMID: 23599497 PMCID: PMC4074024 DOI: 10.1126/science.1231321] [Citation(s) in RCA: 117] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Like mammalian neurons, Caenorhabditis elegans neurons lose axon regeneration ability as they age, but it is not known why. Here, we report that let-7 contributes to a developmental decline in anterior ventral microtubule (AVM) axon regeneration. In older AVM axons, let-7 inhibits regeneration by down-regulating LIN-41, an important AVM axon regeneration-promoting factor. Whereas let-7 inhibits lin-41 expression in older neurons through the lin-41 3' untranslated region, lin-41 inhibits let-7 expression in younger neurons through Argonaute ALG-1. This reciprocal inhibition ensures that axon regeneration is inhibited only in older neurons. These findings show that a let-7-lin-41 regulatory circuit, which was previously shown to control timing of events in mitotic stem cell lineages, is reutilized in postmitotic neurons to control postdifferentiation events.
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Affiliation(s)
- Yan Zou
- Division of Developmental Biology, Cincinnati Children's Hospital Research Foundation, Cincinnati, Ohio 45229
| | - Hui Chiu
- Division of Developmental Biology, Cincinnati Children's Hospital Research Foundation, Cincinnati, Ohio 45229
| | - Anna Zinovyeva
- RNA Therapeutics Institute and Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605
| | - Victor Ambros
- RNA Therapeutics Institute and Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605
| | - Chiou-Fen Chuang
- Division of Developmental Biology, Cincinnati Children's Hospital Research Foundation, Cincinnati, Ohio 45229
| | - Chieh Chang
- Division of Developmental Biology, Cincinnati Children's Hospital Research Foundation, Cincinnati, Ohio 45229
- Dept. of Neurology and Neurosurgery, McGill University, Montreal, Quebec H3A 1B1, Canada
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98
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Yan D, Jin Y. Regulation of DLK-1 kinase activity by calcium-mediated dissociation from an inhibitory isoform. Neuron 2013; 76:534-48. [PMID: 23141066 DOI: 10.1016/j.neuron.2012.08.043] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/31/2012] [Indexed: 01/19/2023]
Abstract
MAPKKK dual leucine zipper-bearing kinases (DLKs) are regulators of synaptic development and axon regeneration. The mechanisms underlying their activation are not fully understood. Here, we show that C. elegans DLK-1 is activated by a Ca(2+)-dependent switch from inactive heteromeric to active homomeric protein complexes. We identify a DLK-1 isoform, DLK-1S, that shares identical kinase and leucine zipper domains with the previously described long isoform DLK-1L but acts to inhibit DLK-1 function by binding to DLK-1L. The switch between homo- or heteromeric DLK-1 complexes is influenced by Ca(2+) concentration. A conserved hexapeptide in the DLK-1L C terminus is essential for DLK-1 activity and is required for Ca(2+) regulation. The mammalian DLK-1 homolog MAP3K13 contains an identical C-terminal hexapeptide and can functionally complement dlk-1 mutants, suggesting that the DLK activation mechanism is conserved. The DLK activation mechanism is ideally suited for rapid and spatially controlled signal transduction in response to axonal injury and synaptic activity.
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Affiliation(s)
- Dong Yan
- Neurobiology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA
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99
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Kirszenblat L, Neumann B, Coakley S, Hilliard MA. A dominant mutation in mec-7/β-tubulin affects axon development and regeneration in Caenorhabditis elegans neurons. Mol Biol Cell 2012; 24:285-96. [PMID: 23223572 PMCID: PMC3564523 DOI: 10.1091/mbc.e12-06-0441] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Microtubules are the basic elements of the cytoskeleton. This study demonstrates that a specific mutation in mec-7/β-tubulin is necessary for the correct number of neurites a neuron extends in vivo and the neuron’s capacity for axonal regeneration following injury. Microtubules have been known for decades to be basic elements of the cytoskeleton. They form long, dynamic, rope-like structures within the cell that are essential for mitosis, maintenance of cell shape, and intracellular transport. More recently, in vitro studies have implicated microtubules as signaling molecules that, through changes in their stability, have the potential to trigger growth of axons and dendrites in developing neurons. In this study, we show that specific mutations in the Caenorhabditis elegans mec-7/β-tubulin gene cause ectopic axon formation in mechanosensory neurons in vivo. In mec-7 mutants, the ALM mechanosensory neuron forms a long ectopic neurite that extends posteriorly, a phenotype that can be mimicked in wild-type worms with a microtubule-stabilizing drug (paclitaxel), and suppressed by mutations in unc-33/CRMP2 and the kinesin-related gene, vab-8. Our results also reveal that these ectopic neurites contain RAB-3, a marker for presynaptic loci, suggesting that they have axon-like properties. Interestingly, in contrast with the excessive axonal growth observed during development, mec-7 mutants are inhibited in axonal regrowth and remodeling following axonal injury. Together our results suggest that MEC-7/β-tubulin integrity is necessary for the correct number of neurites a neuron generates in vivo and for the capacity of an axon to regenerate.
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Affiliation(s)
- Leonie Kirszenblat
- Queensland Brain Institute, The University of Queensland, Brisbane 4072, Australia
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100
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Miller MA, Chin-Sang ID. Eph receptor signaling in C. elegans. WORMBOOK : THE ONLINE REVIEW OF C. ELEGANS BIOLOGY 2012. [PMID: 23197476 DOI: 10.1895/wormbook.1.151.1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Eph receptor protein-tyrosine kinases are among the oldest known animal receptors and have greatly expanded in number during vertebrate evolution. Their complex transduction mechanisms are capable of bidirectional and bimodal (multi-response) signaling. Eph receptors are expressed in almost every cell type in the human body, yet their roles in development, physiology, and disease are incompletely understood. Studies in C. elegans have helped identify biological functions of these receptors, as well as transduction mechanisms. Here we review advances in our understanding of Eph receptor signaling made using the C. elegans model system.
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Affiliation(s)
- Michael A Miller
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham School of Medicine, Birmingham, AL, USA.
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