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Iguchi T, Oka Y, Yasumura M, Omi M, Kuroda K, Yagi H, Xie MJ, Taniguchi M, Bastmeyer M, Sato M. Mutually Repulsive EphA7-EfnA5 Organize Region-to-Region Corticopontine Projection by Inhibiting Collateral Extension. J Neurosci 2021; 41:4795-4808. [PMID: 33906900 PMCID: PMC8260171 DOI: 10.1523/jneurosci.0367-20.2021] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Revised: 03/31/2021] [Accepted: 04/14/2021] [Indexed: 11/21/2022] Open
Abstract
Coordination of skilled movements and motor planning relies on the formation of regionally restricted brain circuits that connect cortex with subcortical areas during embryonic development. Layer 5 neurons that are distributed across most cortical areas innervate the pontine nuclei (basilar pons) by protrusion and extension of collateral branches interstitially along their corticospinal extending axons. Pons-derived chemotropic cues are known to attract extending axons, but molecules that regulate collateral extension to create regionally segregated targeting patterns have not been identified. Here, we discovered that EphA7 and EfnA5 are expressed in the cortex and the basilar pons in a region-specific and mutually exclusive manner, and that their repulsive activities are essential for segregating collateral extensions from corticospinal axonal tracts in mice. Specifically, EphA7 and EfnA5 forward and reverse inhibitory signals direct collateral extension such that EphA7-positive frontal and occipital cortical areas extend their axon collaterals into the EfnA5-negative rostral part of the basilar pons, whereas EfnA5-positive parietal cortical areas extend their collaterals into the EphA7-negative caudal part of the basilar pons. Together, our results provide a molecular basis that explains how the corticopontine projection connects multimodal cortical outputs to their subcortical targets.SIGNIFICANCE STATEMENT Our findings put forward a model in which region-to-region connections between cortex and subcortical areas are shaped by mutually exclusive molecules to ensure the fidelity of regionally restricted circuitry. This model is distinct from earlier work showing that neuronal circuits within individual cortical modalities form in a topographical manner controlled by a gradient of axon guidance molecules. The principle that a shared molecular program of mutually repulsive signaling instructs regional organization-both within each brain region and between connected brain regions-may well be applicable to other contexts in which information is sorted by converging and diverging neuronal circuits.
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Affiliation(s)
- Tokuichi Iguchi
- Department of Anatomy and Neuroscience, Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan
- Division of Cell Biology and Neuroscience, Department of Morphological and Physiological Sciences, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan
- Department of Nursing, Faculty of Health Science, Fukui Health Science University, Fukui 910-3190, Japan
| | - Yuichiro Oka
- Department of Anatomy and Neuroscience, Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan
- Division of Cell Biology and Neuroscience, Department of Morphological and Physiological Sciences, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan
- United Graduate School of Child Development, Osaka University, Kanazawa University, Hamamatsu University School of Medicine, Chiba University, and University of Fukui (UGSCD), Osaka University, Osaka 565-0871, Japan
| | - Misato Yasumura
- Department of Anatomy and Neuroscience, Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan
| | - Minoru Omi
- Division of Cell Biology and Neuroscience, Department of Morphological and Physiological Sciences, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan
| | - Kazuki Kuroda
- Division of Cell Biology and Neuroscience, Department of Morphological and Physiological Sciences, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan
| | - Hideshi Yagi
- Division of Cell Biology and Neuroscience, Department of Morphological and Physiological Sciences, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan
| | - Min-Jue Xie
- Division of Cell Biology and Neuroscience, Department of Morphological and Physiological Sciences, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan
- United Graduate School of Child Development, Osaka University, Kanazawa University, Hamamatsu University School of Medicine, Chiba University, and University of Fukui (UGSCD), Osaka University, Osaka 565-0871, Japan
| | - Manabu Taniguchi
- Department of Anatomy and Neuroscience, Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan
| | - Martin Bastmeyer
- Department of Cell and Neurobiology, Zoological Institute, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
| | - Makoto Sato
- Department of Anatomy and Neuroscience, Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan
- Division of Cell Biology and Neuroscience, Department of Morphological and Physiological Sciences, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan
- United Graduate School of Child Development, Osaka University, Kanazawa University, Hamamatsu University School of Medicine, Chiba University, and University of Fukui (UGSCD), Osaka University, Osaka 565-0871, Japan
- Graduate School of Frontier Biosciences, Osaka University, Osaka 565-0871, Japan
- Research Center for Child Mental Development, University of Fukui, Fukui 910-1193, Japan
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Abstract
Axonal guidance factors play a central role in neural development and regeneration. The ability of cell surface adhesive proteins and extracellular matrix components to promote axonal outgrowth has been documented for some time. Recently, the existence and the importance of molecules that repulse axons and of soluble factors that attract axons have been appreciated. By virtue of their long-range diffusible action, the netrins are now well- defined, soluble axonal guidance molecules. The physiological role of repulsive mecha nisms has been best documented in the development of the retinotectal map and in the ability of CNS myelin to inhibit axonal regeneration. The collapsin/semaphorin family of axonal growth inhibitors has been characterized at the molecular level. It is now clear that an understanding of axonal guidance mechanisms must include soluble cell-surface and matrix-bound factors, which are both attractive and repulsive for axonal growth cones. The Neuroscientist 1:255-258, 1995
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Chalmers K, Kita EM, Scott EK, Goodhill GJ. Quantitative Analysis of Axonal Branch Dynamics in the Developing Nervous System. PLoS Comput Biol 2016; 12:e1004813. [PMID: 26998842 PMCID: PMC4801415 DOI: 10.1371/journal.pcbi.1004813] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Accepted: 02/15/2016] [Indexed: 11/18/2022] Open
Abstract
Branching is an important mechanism by which axons navigate to their targets during neural development. For instance, in the developing zebrafish retinotectal system, selective branching plays a critical role during both initial pathfinding and subsequent arborisation once the target zone has been reached. Here we show how quantitative methods can help extract new information from time-lapse imaging about the nature of the underlying branch dynamics. First, we introduce Dynamic Time Warping to this domain as a method for automatically matching branches between frames, replacing the effort required for manual matching. Second, we model branch dynamics as a birth-death process, i.e. a special case of a continuous-time Markov process. This reveals that the birth rate for branches from zebrafish retinotectal axons, as they navigate across the tectum, increased over time. We observed no significant change in the death rate for branches over this time period. However, blocking neuronal activity with TTX slightly increased the death rate, without a detectable change in the birth rate. Third, we show how the extraction of these rates allows computational simulations of branch dynamics whose statistics closely match the data. Together these results reveal new aspects of the biology of retinotectal pathfinding, and introduce computational techniques which are applicable to the study of axon branching more generally. The complex morphologies of neurons present challenges for analysis. Large data sets can be gathered, but extracting meaningful data from the hundreds of branches from one axon over a few hundred time points can be difficult. One problem in particular is matching a single unique branch through several images, when the branches can extend, retract, or be removed entirely. In addition, if the imaging is done in vivo, the environment itself can grow and shift. Here we introduce Dynamic Time Warping (DTW) analysis to follow the complex structures of neurons through time. DTW identifies individual branches and therefore allows the determination of branch lifetimes. Using this approach we find that for retinal ganglion cell axons, the branch birth rate increases over time as axons navigate to their targets, and that blocking neural activity slightly increases the branch death rate without impacting the birth rate. From the estimated birth and death rate parameters we create simulations based on a continuous-time Markov chain process. These tools expand the techniques available to study the development of neuronal structures and provide more information from large time-lapse imaging datasets.
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Affiliation(s)
- Kelsey Chalmers
- Queensland Brain Institute, The University of Queensland, Brisbane, Queensland, Australia
| | - Elizabeth M. Kita
- Queensland Brain Institute, The University of Queensland, Brisbane, Queensland, Australia
| | - Ethan K. Scott
- School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia
| | - Geoffrey J. Goodhill
- Queensland Brain Institute, The University of Queensland, Brisbane, Queensland, Australia
- School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland, Australia
- * E-mail:
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Penazzi L, Bakota L, Brandt R. Microtubule Dynamics in Neuronal Development, Plasticity, and Neurodegeneration. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2015; 321:89-169. [PMID: 26811287 DOI: 10.1016/bs.ircmb.2015.09.004] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Neurons are the basic information-processing units of the nervous system. In fulfilling their task, they establish a structural polarity with an axon that can be over a meter long and dendrites with a complex arbor, which can harbor ten-thousands of spines. Microtubules and their associated proteins play important roles during the development of neuronal morphology, the plasticity of neurons, and neurodegenerative processes. They are dynamic structures, which can quickly adapt to changes in the environment and establish a structural scaffold with high local variations in composition and stability. This review presents a comprehensive overview about the role of microtubules and their dynamic behavior during the formation and maturation of processes and spines in the healthy brain, during aging and under neurodegenerative conditions. The review ends with a discussion of microtubule-targeted therapies as a perspective for the supportive treatment of neurodegenerative disorders.
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Affiliation(s)
- Lorène Penazzi
- Department of Neurobiology, University of Osnabrück, Osnabrück, Germany
| | - Lidia Bakota
- Department of Neurobiology, University of Osnabrück, Osnabrück, Germany
| | - Roland Brandt
- Department of Neurobiology, University of Osnabrück, Osnabrück, Germany
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Hara S, Kaneyama T, Inamata Y, Onodera R, Shirasaki R. Interstitial branch formation within the red nucleus by deep cerebellar nuclei-derived commissural axons during target recognition. J Comp Neurol 2015; 524:999-1014. [DOI: 10.1002/cne.23888] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 07/29/2015] [Accepted: 08/21/2015] [Indexed: 11/08/2022]
Affiliation(s)
- Satoshi Hara
- Cellular and Molecular Neurobiology Laboratory, Graduate School of Frontier Biosciences; Osaka University; Suita Osaka 565-0871 Japan
| | - Takeshi Kaneyama
- Cellular and Molecular Neurobiology Laboratory, Graduate School of Frontier Biosciences; Osaka University; Suita Osaka 565-0871 Japan
| | - Yasuyuki Inamata
- Cellular and Molecular Neurobiology Laboratory, Graduate School of Frontier Biosciences; Osaka University; Suita Osaka 565-0871 Japan
| | - Ryota Onodera
- Cellular and Molecular Neurobiology Laboratory, Graduate School of Frontier Biosciences; Osaka University; Suita Osaka 565-0871 Japan
| | - Ryuichi Shirasaki
- Cellular and Molecular Neurobiology Laboratory, Graduate School of Frontier Biosciences; Osaka University; Suita Osaka 565-0871 Japan
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Kim N, Min KW, Kang KH, Lee EJ, Kim HT, Moon K, Choi J, Le D, Lee SH, Kim JW. Regulation of retinal axon growth by secreted Vax1 homeodomain protein. eLife 2014; 3:e02671. [PMID: 25201875 PMCID: PMC4178304 DOI: 10.7554/elife.02671] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Accepted: 09/03/2014] [Indexed: 11/25/2022] Open
Abstract
Retinal ganglion cell (RGC) axons of binocular animals cross the midline at the optic chiasm (OC) to grow toward their synaptic targets in the contralateral brain. Ventral anterior homeobox 1 (Vax1) plays an essential role in the development of the OC by regulating RGC axon growth in a non-cell autonomous manner. In this study, we identify an unexpected function of Vax1 that is secreted from ventral hypothalamic cells and diffuses to RGC axons, where it promotes axonal growth independent of its transcription factor activity. We demonstrate that Vax1 binds to extracellular sugar groups of the heparan sulfate proteoglycans (HSPGs) located in RGC axons. Both Vax1 binding to HSPGs and subsequent penetration into the axoplasm, where Vax1 activates local protein synthesis, are required for RGC axonal growth. Together, our findings demonstrate that Vax1 possesses a novel RGC axon growth factor activity that is critical for the development of the mammalian binocular visual system. DOI:http://dx.doi.org/10.7554/eLife.02671.001 We see the world around us when light bounces off of objects and hits the retina at the back of our eyes. This triggers electrical signals in neurons called retinal ganglion cells (RGCs), which have long structures called axons that extend out from the retina and into the parts of the brain where the signals are interpreted. As the axons grow, various ‘guidance’ molecules direct the axons to the correct part of the brain. One molecule that is important for the growth of retinal ganglion cells' axons is a protein called Vax1. This protein is a transcription factor and binds to DNA to control how and when the molecular templates used to make proteins are made—a process called transcription. Vax1 is not produced in retinal ganglion cells, but it does control the extension of these cells' axons into part of the brain called the ventral hypothalamus. In this study, the axons cross to the other side of the brain by forming a structure called optic chiasm. Humans and mice lacking Vax1 are unable to develop the optic chiasm, and the axons of their retinal ganglion cells do not reach their targets in the brain. These defects were thought to occur because the guidance molecules whose transcription is normally controlled by Vax1 were not produced in the correct amounts when Vax1 is absent. Kim et al. now challenge this view by creating a mutant version of Vax1 that cannot bind to DNA or regulate the transcription of other proteins. Retinal ganglion cell axons could still grow correctly when they were put close to cells expressing this version of the Vax1 protein. This contradicts a hypothesis that Vax1 supports axonal growth by transcribing guidance molecules. Kim et al. followed up these results by examining developing mice and reached the unexpected conclusion that Vax1 is secreted from cells in the ventral hypothalamus and binds to a type of sugar molecule found on the surface of the axons. Once bound, Vax1 can enter the axons where it appears to stimulate the production of proteins inside axons, which helps the axons to grow. These findings reveal unconventional functions for Vax1 that occur in addition to its role as a transcription factor. Vax1 is known to regulate the development of several structures in the brain, so the work of Kim et al. also raises new questions about how Vax1 controls these processes. DOI:http://dx.doi.org/10.7554/eLife.02671.002
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Affiliation(s)
- Namsuk Kim
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
| | - Kwang Wook Min
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
| | - Kyung Hwa Kang
- KAIST Institute of BioCentury, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
| | - Eun Jung Lee
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
| | - Hyoung-Tai Kim
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
| | - Kyunghwan Moon
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
| | - Jiheon Choi
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
| | - Dai Le
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
| | - Sang-Hee Lee
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
| | - Jin Woo Kim
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
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Lewis TL, Courchet J, Polleux F. Cell biology in neuroscience: Cellular and molecular mechanisms underlying axon formation, growth, and branching. ACTA ACUST UNITED AC 2013; 202:837-48. [PMID: 24043699 PMCID: PMC3776347 DOI: 10.1083/jcb.201305098] [Citation(s) in RCA: 114] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Proper brain wiring during development is pivotal for adult brain function. Neurons display a high degree of polarization both morphologically and functionally, and this polarization requires the segregation of mRNA, proteins, and lipids into the axonal or somatodendritic domains. Recent discoveries have provided insight into many aspects of the cell biology of axonal development including axon specification during neuronal polarization, axon growth, and terminal axon branching during synaptogenesis.
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Affiliation(s)
- Tommy L Lewis
- The Scripps Research Institute, Dorris Neuroscience Center, Department of Molecular and Cellular Neuroscience, La Jolla, CA 92037
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Gallo G. Mechanisms underlying the initiation and dynamics of neuronal filopodia: from neurite formation to synaptogenesis. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 301:95-156. [PMID: 23317818 DOI: 10.1016/b978-0-12-407704-1.00003-8] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Filopodia are finger-like cellular protrusions found throughout the metazoan kingdom and perform fundamental cellular functions during development and cell migration. Neurons exhibit a wide variety of extremely complex morphologies. In the nervous system, filopodia underlie many major morphogenetic events. Filopodia have roles spanning the initiation and guidance of neuronal processes, axons and dendrites to the formation of synaptic connections. This chapter addresses the mechanisms of the formation and dynamics of neuronal filopodia. Some of the major lessons learned from the study of neuronal filopodia are (1) there are multiple mechanisms that can regulate filopodia in a context-dependent manner, (2) that filopodia are specialized subcellular domains, (3) that filopodia exhibit dynamic membrane recycling which also controls aspects of filopodial dynamics, (4) that neuronal filopodia contain machinery for the orchestration of the actin and microtubule cytoskeleton, and (5) localized protein synthesis contributes to neuronal filopodial dynamics.
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Affiliation(s)
- Gianluca Gallo
- Shriners Hospitals Pediatric Research Center, Center for Neural Repair and Rehabilitation, Department of Anatomy and Cell Biology, Temple University, Philadelphia, PA, USA.
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Joosten EAJ. Biodegradable biomatrices and bridging the injured spinal cord: the corticospinal tract as a proof of principle. Cell Tissue Res 2012; 349:375-95. [PMID: 22411698 PMCID: PMC3375422 DOI: 10.1007/s00441-012-1352-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Accepted: 01/27/2012] [Indexed: 12/12/2022]
Abstract
Important advances in the development of smart biodegradable implants for axonal regeneration after spinal cord injury have recently been reported. These advances are evaluated in this review with special emphasis on the regeneration of the corticospinal tract. The corticospinal tract is often considered the ultimate challenge in demonstrating whether a repair strategy has been successful in the regeneration of the injured mammalian spinal cord. The extensive know-how of factors and cells involved in the development of the corticospinal tract, and the advances made in material science and tissue engineering technology, have provided the foundations for the optimization of the biomatrices needed for repair. Based on the findings summarized in this review, the future development of smart biodegradable bridges for CST regrowth and regeneration in the injured spinal cord is discussed.
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Affiliation(s)
- Elbert A J Joosten
- Department of Anesthesiology, Pain Management and Research Center, Maastricht University Medical Hospital, Maastricht, The Netherlands.
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Abstract
During development, axons are guided to their appropriate targets by a variety of guidance factors. On arriving at their synaptic targets, or while en route, axons form branches. Branches generated de novo from the main axon are termed collateral branches. The generation of axon collateral branches allows individual neurons to make contacts with multiple neurons within a target and with multiple targets. In the adult nervous system, the formation of axon collateral branches is associated with injury and disease states and may contribute to normally occurring plasticity. Collateral branches are initiated by actin filament– based axonal protrusions that subsequently become invaded by microtubules, thereby allowing the branch to mature and continue extending. This article reviews the current knowledge of the cellular mechanisms of the formation of axon collateral branches. The major conclusions of this review are (1) the mechanisms of axon extension and branching are not identical; (2) active suppression of protrusive activity along the axon negatively regulates branching; (3) the earliest steps in the formation of axon branches involve focal activation of signaling pathways within axons, which in turn drive the formation of actin-based protrusions; and (4) regulation of the microtubule array by microtubule-associated and severing proteins underlies the development of branches. Linking the activation of signaling pathways to specific proteins that directly regulate the axonal cytoskeleton underlying the formation of collateral branches remains a frontier in the field.
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Affiliation(s)
- Gianluca Gallo
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, Pennsylvania 19129, USA.
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Ruthazer ES, Bachleda AR, Olavarria JF. Role of interstitial branching in the development of visual corticocortical connections: a time-lapse and fixed-tissue analysis. J Comp Neurol 2011; 518:4963-79. [PMID: 21031561 DOI: 10.1002/cne.22502] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We combined fixed-tissue and time-lapse analyses to investigate the axonal branching phenomena underlying the development of topographically organized ipsilateral projections from area 17 to area 18a in the rat. These complementary approaches allowed us to relate static, large-scale information provided by traditional fixed-tissue analysis to highly dynamic, local, small-scale branching phenomena observed with two-photon time-lapse microscopy in acute slices of visual cortex. Our fixed-tissue data revealed that labeled area 17 fibers invaded area 18a gray matter at topographically restricted sites, reaching superficial layers in significant numbers by postnatal day 6 (P6). Moreover, most parental axons gave rise to only one or occasionally a small number of closely spaced interstitial branches beneath 18a. Our time-lapse data showed that many filopodium-like branches emerged along parental axons in white matter or deep layers in area 18a. Most of these filopodial branches were transient, often disappearing after several minutes to hours of exploratory extension and retraction. These dynamic behaviors decreased significantly from P4, when the projection is first forming, through the second postnatal week, suggesting that the expression of, or sensitivity to, cortical cues promoting new branch addition in the white matter is developmentally down-regulated coincident with gray matter innervation. Together, these data demonstrate that the development of topographically organized corticocortical projections in rats involves extensive exploratory branching along parental axons and invasion of cortex by only a small number of interstitial branches, rather than the widespread innervation of superficial cortical layers by an initially exuberant population of branches.
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Affiliation(s)
- Edward S Ruthazer
- Montreal Neurological Institute, McGill University, Montréal, Québec, Canada
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Ueno M, Yamashita T. Strategies for regenerating injured axons after spinal cord injury - insights from brain development. Biologics 2011; 2:253-64. [PMID: 19707358 PMCID: PMC2721354 DOI: 10.2147/btt.s2715] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Axonal regeneration does not occur easily after an adult central nervous system (CNS) injury. Various attempts have partially succeeded in promoting axonal regeneration after the spinal cord injury (SCI). Interestingly, several recent therapeutic concepts have emerged from or been tightly linked to the researches on brain development. In a developing brain, remarkable and dynamic axonal elongation and sprouting occur even after the injury; this finding is essential to the development of a therapy for SCI. In this review, we overview the revealed mechanism of axonal tract formation and plasticity in the developing brain and compare the differences between a developing brain and a lesion site in an adult brain. One of the differences is that mature glial cells participate in the repair process in the case of adult injuries. Interestingly, these cells express inhibitory molecules that impede axonal regeneration such as myelin-associated proteins and the repulsive guidance molecules found originally in the developing brain for navigating axons to specific routes. Some reports have clearly elucidated that any treatment designed to suppress these inhibitory cues is beneficial for promoting regeneration and plasticity after an injury. Thus, understanding the developmental process will provide us with an important clue for designing therapeutic strategies for recovery from SCI.
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Affiliation(s)
- Masaki Ueno
- Department of Molecular Neuroscience, Graduate School of Medicine, Osaka University, 2-2, Yamadaoka, Suita-shi, Osaka 565-0871, Japan
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Szabó NE, Zhao T, Çankaya M, Stoykova A, Zhou X, Alvarez-Bolado G. Interaction between axons and specific populations of surrounding cells is indispensable for collateral formation in the mammillary system. PLoS One 2011; 6:e20315. [PMID: 21625468 PMCID: PMC3098884 DOI: 10.1371/journal.pone.0020315] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Accepted: 04/29/2011] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND An essential phenomenon during brain development is the extension of long collateral branches by axons. How the local cellular environment contributes to the initial sprouting of these branches in specific points of an axonal shaft remains unclear. METHODOLOGY/PRINCIPAL FINDINGS The principal mammillary tract (pm) is a landmark axonal bundle connecting ventral diencephalon to brainstem (through the mammillotegmental tract, mtg). Late in development, the axons of the principal mammillary tract sprout collateral branches at a very specific point forming a large bundle whose target is the thalamus. Inspection of this model showed a number of distinct, identified cell populations originated in the dorsal and the ventral diencephalon and migrating during development to arrange themselves into several discrete groups around the branching point. Further analysis of this system in several mouse lines carrying mutant alleles of genes expressed in defined subpopulations (including Pax6, Foxb1, Lrp6 and Gbx2) together with the use of an unambiguous genetic marker of mammillary axons revealed: 1) a specific group of Pax6-expressing cells in close apposition with the prospective branching point is indispensable to elicit axonal branching in this system; and 2) cooperation of transcription factors Foxb1 and Pax6 to differentially regulate navigation and fasciculation of distinct branches of the principal mammillary tract. CONCLUSIONS/SIGNIFICANCE Our results define for the first time a model system where interaction of the axonal shaft with a specific group of surrounding cells is essential to promote branching. Additionally, we provide insight on the cooperative transcriptional regulation necessary to promote and organize an intricate axonal tree.
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Affiliation(s)
- Nora-Emöke Szabó
- Brain Development Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany
| | - Tianyu Zhao
- Brain Development Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany
| | - Murat Çankaya
- Department of Biology, Faculty of Sciences and Art, Erzincan University, Erzincan, Turkey
| | - Anastassia Stoykova
- Department of Molecular Cell Biology, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany
| | - Xunlei Zhou
- Brain Development Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany
| | - Gonzalo Alvarez-Bolado
- Brain Development Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany
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14
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Gibson DA, Ma L. Developmental regulation of axon branching in the vertebrate nervous system. Development 2011; 138:183-95. [PMID: 21177340 DOI: 10.1242/dev.046441] [Citation(s) in RCA: 135] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
During nervous system development, axons generate branches to connect with multiple synaptic targets. As with axon growth and guidance, axon branching is tightly controlled in order to establish functional neural circuits, yet the mechanisms that regulate this important process are less well understood. Here, we review recent advances in the study of several common branching processes in the vertebrate nervous system. By focusing on each step in these processes we illustrate how different types of branching are regulated by extracellular cues and neural activity, and highlight some common principles that underlie the establishment of complex neural circuits in vertebrate development.
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Affiliation(s)
- Daniel A Gibson
- Zilkha Neurogenetic Institute, Department of Cell and Neurobiology, Keck School of Medicine, Neuroscience Graduate Program, University of Southern California, 1501 San Pablo Street, Los Angeles, CA 90089, USA
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15
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Liu X, Hawkes E, Ishimaru T, Tran T, Sretavan DW. EphB3: an endogenous mediator of adult axonal plasticity and regrowth after CNS injury. J Neurosci 2006; 26:3087-101. [PMID: 16554460 PMCID: PMC6674090 DOI: 10.1523/jneurosci.4797-05.2006] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Endogenous mechanisms underlying the remodeling of neuronal circuitry after mammalian CNS injury or disease remain primarily unknown. Here, we investigated axonal plasticity after optic nerve injury and found that macrophages recruited into the injury site and adult retinal ganglion cell (RGC) axons, which undergo injury-induced sprouting and terminal remodeling, were linked by their respective expression of a ligand and receptor pair active in axon guidance. Recruited macrophages specifically upregulated mRNA encoding the guidance molecule EphB3 and expressed EphB proteins capable of binding Ephrin B molecules in vivo and in vitro. Injured adult RGC axons in turn expressed EphrinB3, a known receptor for EphB3, and RGC axons bound recombinant EphB3 protein injected into the optic nerve. In vitro, EphB3 supported adult RGC axon outgrowth, and axons turned toward a source of this guidance molecule. In vivo, both reduction of EphB3 function in adult heterozygous animals and loss of function in homozygous animals greatly decreased RGC axon re-extension or sprouting after optic nerve injury. Comparisons of axon re-extension in EphB3 null and wild-type littermates showed that this loss of axonal plasticity was not attributable to a difference in intrinsic axon growth potential. Rather, the results indicated an essential role for local optic nerve-derived EphB3 in regulating adult RGC axon plasticity after optic nerve injury. Of note, the loss of EphB3 did not affect the ability of injured RGC axons to elaborate complex terminal branching, suggesting that additional EphB3-independent mechanisms governed adult axon branching triggered by CNS damage.
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16
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Erzurumlu RS, Chen ZF, Jacquin MF. Molecular determinants of the face map development in the trigeminal brainstem. THE ANATOMICAL RECORD. PART A, DISCOVERIES IN MOLECULAR, CELLULAR, AND EVOLUTIONARY BIOLOGY 2006; 288:121-34. [PMID: 16432893 PMCID: PMC3556733 DOI: 10.1002/ar.a.20285] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The perception of external sensory information by the brain requires highly ordered synaptic connectivity between peripheral sensory neurons and their targets in the central nervous system. Since the discovery of the whisker-related barrel patterns in the mouse cortex, the trigeminal system has become a favorite model for study of how its connectivity and somatotopic maps are established during development. The trigeminal brainstem nuclei are the first CNS regions where whisker-specific neural patterns are set up by the trigeminal afferents that innervate the whiskers. In particular, barrelette patterns in the principal sensory nucleus of the trigeminal nerve provide the template for similar patterns in the face representation areas of the thalamus and subsequently in the primary somatosensory cortex. Here, we describe and review studies of neurotrophins, multiple axon guidance molecules, transcription factors, and glutamate receptors during early development of trigeminal connections between the whiskers and the brainstem that lead to emergence of patterned face maps. Studies from our laboratories and others' showed that developing trigeminal ganglion cells and their axons depend on a variety of molecular signals that cooperatively direct them to proper peripheral and central targets and sculpt their synaptic terminal fields into patterns that replicate the organization of the whiskers on the muzzle. Similar mechanisms may also be used by trigeminothalamic and thalamocortical projections in establishing patterned neural modules upstream from the trigeminal brainstem.
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Affiliation(s)
- Reha S Erzurumlu
- Department of Cell Biology and Anatomy, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA.
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17
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Bai W, Ishida M, Okabe M, Arimatsu Y. Role of the Protomap and Target-derived Signals in the Development of Intrahemispheric Connections. Cereb Cortex 2005; 16:124-35. [PMID: 15843629 DOI: 10.1093/cercor/bhi092] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Mechanisms intrinsic to the early cerebral cortex have been implicated in the establishment of cortical area identity. However, the extent to which the cortical protomap contributes to the formation of highly complex intrahemispheric connections remains obscure. Mechanisms by which postmitotic neurons establish correct corticocortical connections later in corticogenesis also remain to be elucidated. Here, we used a new transplantation method, employing donor tissue harvested from enhanced green fluorescent protein-expressing rats, to show that cortical progenitors are regionally specified for connectional potential and that this controls the development of specific intrahemispheric projections. The acquisition of connectional capacity relies on positional cues within the cortical primordium, but is independent of thalamic inputs. In addition, since cortical neurons developing in organotypic slice culture extended axons more prominently into their normal cortical target tissues than into non-target tissues, we suggest that cortical neurons respond to specific signals derived from their cortical targets.
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Affiliation(s)
- Wanzhu Bai
- Mitsubishi Kagaku Institute of Life Sciences, 11 Minamiooya, Machida, Tokyo 194-8511, Japan
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18
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Litwack ED, Babey R, Buser R, Gesemann M, O'Leary DDM. Identification and characterization of two novel brain-derived immunoglobulin superfamily members with a unique structural organization. Mol Cell Neurosci 2004; 25:263-74. [PMID: 15019943 DOI: 10.1016/j.mcn.2003.10.016] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2003] [Revised: 10/02/2003] [Accepted: 10/21/2003] [Indexed: 11/28/2022] Open
Abstract
We recently used a differential display PCR screen to identify secreted and transmembrane proteins that are highly expressed in the developing rat basilar pons, a prominent ventral hindbrain nucleus used as a model for studies of neuronal migration, axon outgrowth, and axon-target recognition. Here we describe cloning and characterization of one of these molecules, now called MDGA1, and a closely related homologue, MDGA2. Analyses of the full-length coding region of MDGA1 and MDGA2 indicate that they encode proteins that comprise a novel subgroup of the Ig superfamily and have a unique structural organization consisting of six immunoglobulin (Ig)-like domains followed by a single MAM domain. Biochemical characterization demonstrates that MDGA1 and MDGA2 proteins are highly glycosylated, and that MDGA1 is tethered to the cell membrane by a GPI anchor. The MDGAs are differentially expressed by subpopulations of neurons in both the central and peripheral nervous systems, including neurons of the basilar pons, inferior olive, cerebellum, cerebral cortex, olfactory bulb, spinal cord, and dorsal root and trigeminal ganglia. Little or no MDGA expression is detected outside of the nervous system of developing rats. The similarity of MDGAs to other Ig-containing molecules and their temporal-spatial patterns of expression within restricted neuronal populations, for example migrating pontine neurons and D1 spinal interneurons, suggest a role for these novel proteins in regulating neuronal migration, as well as other aspects of neural development, including axon guidance.
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Affiliation(s)
- E David Litwack
- Molecular Neurobiology Laboratory, The Salk Institute, San Diego, CA 92037, USA
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19
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Kubota C, Nagano T, Baba H, Sato M. Netrin‐1 is crucial for the establishment of the dorsal column‐medial lemniscal system. J Neurochem 2004; 89:1547-54. [PMID: 15189358 DOI: 10.1111/j.1471-4159.2004.02460.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The dorsal column-medial lemniscal system is a significant sensory pathway that mediates touch and limb position sense. In this system, axons from the second-order neurons in the dorsal column nuclei form the internal arcuate fibers, cross the ventral midline (floor plate) within the medulla oblongata, and then project to the thalamus as the medial lemniscus. Here we demonstrate that Netrin-1, which is secreted from the floor plate in the medulla oblongata, is indispensable to the formation of the dorsal column-medial lemniscal system. Axons from the dorsal column nuclei cross the midline at around embryonic day 11 in mice. Concurrently, Netrin-1 mRNA and its receptor DCC (deleted in colorectal cancer) were expressed in the floor plate and commissural axons there, respectively. In our explant culture experiments, the floor plates of the embryonic 11-day-old mutant Netrin-1 homozygous mice did not attract axons from the dorsal column nuclei of ICR mice, while those from the wild type littermates did. Moreover, we observed that although the dorsal column nuclei developed in situ in mutant mice, their axons were not attracted toward the floor plate: they did not cross midline and remained ipsilaterally, without forming the internal arcuate fibers, in embryonic 17-day-old mutant Netrin-1 homozygous mice.
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Affiliation(s)
- Chikara Kubota
- Division of Cell Biology and Neuroscience, Department of Morphological and Physiological Sciences, Faculty of Medical Sciences, University of Fukui, 23 Shimoaizuki, Matsuoka, Fukui 910-1193, Japan
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20
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Koyama R, Yamada MK, Nishiyama N, Matsuki N, Ikegaya Y. Developmental switch in axon guidance modes of hippocampal mossy fibers in vitro. Dev Biol 2004; 267:29-42. [PMID: 14975715 DOI: 10.1016/j.ydbio.2003.11.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2003] [Revised: 10/07/2003] [Accepted: 11/11/2003] [Indexed: 10/26/2022]
Abstract
Hippocampal mossy fibers (MFs), axons of dentate granule cells, run through a narrow strip, called the stratum lucidum, and make synaptic contacts with CA3 pyramidal cells. This stereotyped pathfinding is assumed to require a tightly controlled guidance system, but the responsible mechanisms have not been proven directly. To clarify the cellular basis for the MF pathfinding, microslices of the dentate gyrus (DG) and Ammon's horn (AH) were topographically arranged in an organotypic explant coculture system. When collagen gels were interposed between DG and AH slices prepared from postnatal day 6 (P6) rats, the MFs passed across this intervening gap and reached CA3 stratum lucidum. Even when the recipient AH was chemically pre-fixed with paraformaldehyde, the axons were still capable of accessing their normal target area only if the DG and AH slices were directly juxtaposed without a collagen bridge. The data imply that diffusible and contact cues are both involved in MF guidance. To determine how these different cues contribute to MF pathfinding during development, a P6 DG slice was apposed simultaneously to two AH slices prepared from P0 and P13 rats. MFs projected normally to both the host slices, whereas they rarely invaded P0 AH when the two hosts were fixed. Early in development, therefore, the MFs are guided mainly by a chemoattractant gradient, and thereafter, they can find their trajectories by a contact factor, probably via fasciculation with pre-established MFs. The present study proposes a dynamic paradigm in CNS axon pathfinding, that is, developmental changes in axon guidance cues.
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Affiliation(s)
- Ryuta Koyama
- Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan
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21
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Tonge DA, Pountney DJ, Leclere PG, Zhu N, Pizzey JA. Neurotrophin-independent attraction of growing sensory and motor axons towards developing Xenopus limb buds in vitro. Dev Biol 2004; 265:169-80. [PMID: 14697361 DOI: 10.1016/j.ydbio.2003.09.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The mechanisms for directing axons to their targets in developing limbs remain largely unknown though recent studies in mice have demonstrated the importance of neurotrophins in this process. We now report that in co-cultures of larval Xenopus laevis limb buds with spinal cords and dorsal root ganglia of Xenopus and axolotl (Ambystoma mexicanum) axons grow directly to the limb buds over distances of up to 800 microm and in particular to sheets of epidermal cells which migrate away from the limb buds and also tail segments in culture. This directed axonal growth persists in the presence of trk-IgG chimeras, which sequester neurotrophins, and k252a, which blocks their actions mediated via trk receptors. These findings indicate that developing limb buds in Xenopus release diffusible factors other than neurotrophins, able to attract growth of sensory and motor axons over long distances.
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Affiliation(s)
- David A Tonge
- GKT School of Biomedical Sciences, King's College London, Guy's Hospital Campus, London Bridge, London SE1 1UL, UK.
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22
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Abstract
During development of the central nervous system, growth cones navigate along specific pathways, recognize their targets and then form synaptic connections by elaborating terminal arbors. To date, a number of developmental and in vitro studies have characterized the nature of the guidance cues that underlie various types of axonal behavior, from initial outgrowth to synapse formation, including pathway selection, polarized growth, orientated growth, termination and branching. New approaches in molecular biology have identified several types of guidance cues, most of which are likely to act as local cues. Moreover, recent studies have indicated that axonal responsiveness to guidance cues changes dynamically, which appears to be elicited by environmental factors encountered by the navigating growth cones. This article addresses what molecular cues are responsible for guidance mechanisms including axonal responsiveness, focusing on axonal behavior in the developmental stages.
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Affiliation(s)
- Nobuhiko Yamamoto
- Laboratory of Neuroscience, Graduate School of Frontier Biosciences, Osaka University, Toyonaka, Osaka 560-8531, Japan
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23
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Abstract
Axons that carry information from the sensory periphery first elongate unbranched and form precisely ordered tracts within the CNS. Later, they begin collateralizing into their proper targets and form terminal arbors. Target-derived factors that govern sensory axon elongation and branching-arborization are not well understood. Here we report that Slit2 is a major player in branching-arborization of central trigeminal axons in the brainstem. Embryonic trigeminal axons initially develop unbranched as they form the trigeminal tract within the lateral brainstem; later, they emit collateral branches into the brainstem trigeminal nuclei and form terminal arbors therein. In whole-mount explant cultures of this pathway, embryonic day 15 (E15) rat central trigeminal axons retain their unbranched growth within the tract, whereas E17 trigeminal axons show branching and arborization in the brainstem trigeminal nuclei, much like that seen in vivo. Similar observations were made in E13 and E15 mouse embryos. We cocultured Slit2-expressing tissues or cells with the whole-mount explant cultures of the central trigeminal pathway derived from embryonic rats or mice. When central trigeminal axons are exposed to ectopic Slit2 during their elongation phase, they show robust and premature branching and arborization. Blocking available Slit2 reverses this effect on axon growth. Spatiotemporal expression of Slit2 and Robo receptor mRNAs within the brainstem trigeminal nuclei and the trigeminal ganglion during elongation and branching-arborization further corroborates our experimental results.
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Woodring PJ, Litwack ED, O'Leary DDM, Lucero GR, Wang JYJ, Hunter T. Modulation of the F-actin cytoskeleton by c-Abl tyrosine kinase in cell spreading and neurite extension. J Cell Biol 2002; 156:879-92. [PMID: 11864995 PMCID: PMC2173320 DOI: 10.1083/jcb.200110014] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The nonreceptor tyrosine kinase encoded by the c-Abl gene has the unique feature of an F-actin binding domain (FABD). Purified c-Abl tyrosine kinase is inhibited by F-actin, and this inhibition can be relieved through mutation of its FABD. The c-Abl kinase is activated by physiological signals that also regulate the actin cytoskeleton. We show here that c-Abl stimulated the formation of actin microspikes in fibroblasts spreading on fibronectin. This function of c-Abl is dependent on kinase activity and is not shared by c-Src tyrosine kinase. The Abl-dependent F-actin microspikes occurred under conditions where the Rho-family GTPases were inhibited. The FABD-mutated c-Abl, which is active in detached fibroblasts, stimulated F-actin microspikes independent of cell attachment. Moreover, FABD-mutated c-Abl stimulated the formation of F-actin branches in neurites of rat embryonic cortical neurons. The reciprocal regulation between F-actin and the c-Abl tyrosine kinase may provide a self-limiting mechanism in the control of actin cytoskeleton dynamics.
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25
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Yamamoto N. Cellular and molecular basis for the formation of lamina-specific thalamocortical projections. Neurosci Res 2002; 42:167-73. [PMID: 11900826 DOI: 10.1016/s0168-0102(01)00324-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The neocortex is composed of a characteristic layered structure, which is a basis of extrinsic and intrinsic cortical connections. In recent years the cellular and molecular mechanisms, which are responsible for the formation of lamina-specific connections, have been explored by extensive molecular and in vitro studies. This article attempts to address what cell-cell interactions are required for axonal targeting and what molecules regulate cellular events, focusing upon the development of the thalamocortical projection.
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Affiliation(s)
- Nobuhiko Yamamoto
- Division of Biophysical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
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26
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Wang J, Zugates CT, Liang IH, Lee CHJ, Lee T. Drosophila Dscam is required for divergent segregation of sister branches and suppresses ectopic bifurcation of axons. Neuron 2002; 33:559-71. [PMID: 11856530 DOI: 10.1016/s0896-6273(02)00570-6] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Axon bifurcation results in the formation of sister branches, and divergent segregation of the sister branches is essential for efficient innervation of multiple targets. From a genetic mosaic screen, we find that a lethal mutation in the Drosophila Down syndrome cell adhesion molecule (Dscam) specifically perturbs segregation of axonal branches in the mushroom bodies. Single axon analysis further reveals that Dscam mutant axons generate additional branches, which randomly segregate among the available targets. Moreover, when only one target remains, branching is suppressed in wild-type axons while Dscam mutant axons still form multiple branches at the original bifurcation point. Taken together, we conclude that Dscam controls axon branching and guidance such that a neuron can innervate multiple targets with minimal branching.
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Affiliation(s)
- Jian Wang
- Department of Cell and Structural Biology, University of Illinois, Urbana, IL 61801, USA
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27
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Ourednik J, Ourednik V, Bastmeyer M, Schachner M. Ectopic expression of the neural cell adhesion molecule L1 in astrocytes leads to changes in the development of the corticospinal tract. Eur J Neurosci 2001; 14:1464-74. [PMID: 11722608 DOI: 10.1046/j.0953-816x.2001.01773.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The cell recognition molecule L1, of the immunoglobulin superfamily, participates in the formation of the nervous system and has been shown to enhance cell migration and neurite outgrowth in vitro. To test whether ectopic expression of L1 would influence axonal outgrowth in vivo, we studied the development of the corticospinal tract in transgenic mice expressing L1 in astrocytes under the control of the GFAP-promoter. Corticospinal axons innervate their targets by extending collateral branches interstitially along the axon shaft following a precise spatio-temporal pattern. Using DiI as an anterograde tracer, we found that in the transgenic animals, corticospinal axons appear to be defasciculated, reach their targets sooner and form collateral branches innervating the basilar pons at earlier developmental stages and more diffusely than in wild type littermates. Collateral branches in the transgenic mice did not start out as distinct rostral and caudal sets, but they branched from the axon segments in a continuous rostrocaudal direction across the entire region of the corticospinal tract overlying the basilar pons. The ectopic branches are transient and no longer present at postnatal day 22. The earlier outgrowth and altered branching pattern of corticospinal axons in the transgenics is accompanied by an earlier differentiation of astrocytes. Taken together, our observations provide evidence that the ectopic expression of L1 on astrocytes causes an earlier differentiation of these cells, results in faster progression of corticospinal axons and influences the branching pattern of corticospinal axons innervating the basilar pons.
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Affiliation(s)
- J Ourednik
- Department of Neurobiology, Swiss Federal Institute of Technology, Hönggerberg, CH-8093 Zürich, Switzerland.
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28
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Gesemann M, Litwack ED, Yee KT, Christen U, O'Leary DD. Identification of candidate genes for controlling development of the basilar pons by differential display PCR. Mol Cell Neurosci 2001; 18:1-12. [PMID: 11461149 DOI: 10.1006/mcne.2001.0996] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The basilar pons, a major hindbrain nucleus involved in sensory-motor integration, has become a model system for studying long-distance neuronal migration, axon-target recognition by collateral branching, and the formation of patterned axonal projections. To identify genes potentially involved in these developmental events, we have performed a differential display PCR screen comparing RNA isolated from the developing basilar pons with RNA obtained from developing cerebellum and olfactory bulb, as well as the mature basilar pons. Using 400 different combinations of primers, we screened more than 11,000 labeled DNA fragments and identified 201 that exhibited higher expression in the basilar pons than in the control tissues. From these, 138 distinct gene fragments were cloned. The differential expression of a large subset of these fragments was confirmed using RNase protection assays. In situ hybridization analysis revealed that the expression of many of these genes is limited to the basilar pons and only a few other brain regions, suggesting that they may play specific roles in pontine development.
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Affiliation(s)
- M Gesemann
- Molecular Neurobiology Laboratory, The Salk Institute, 10010 North Torrey Pines Road, San Diego, California 92037, USA
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29
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Raineteau O, Fouad K, Noth P, Thallmair M, Schwab ME. Functional switch between motor tracts in the presence of the mAb IN-1 in the adult rat. Proc Natl Acad Sci U S A 2001; 98:6929-34. [PMID: 11381120 PMCID: PMC34455 DOI: 10.1073/pnas.111165498] [Citation(s) in RCA: 125] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Fine finger and hand movements in humans, monkeys, and rats are under the direct control of the corticospinal tract (CST). CST lesions lead to severe, long-term deficits of precision movements. We transected completely both CSTs in adult rats and treated the animals for 2 weeks with an antibody that neutralized the central nervous system neurite growth inhibitory protein Nogo-A (mAb IN-1). Anatomical studies of the rubrospinal tracts showed that the number of collaterals innervating the cervical spinal cord doubled in the mAb IN-1- but not in the control antibody-treated animals. Precision movements of the forelimb and fingers were severely impaired in the controls, but almost completely recovered in the mAb IN-1-treated rats. Low threshold microstimulation of the motor cortex induced a rapid forelimb electromyography response that was mediated by the red nucleus in the mAb IN-1 animals but not in the controls. These findings demonstrate an unexpectedly high capacity of the adult central nervous system motor system to sprout and reorganize in a targeted and functionally meaningful way.
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Affiliation(s)
- O Raineteau
- Brain Research Institute, University and Swiss Federal Institute of Technology (ETH) Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
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30
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Abstract
Neural geometry is the major factor that determines connectivity and, possibly, functional output from a nervous system. Recently some of the proteins and pathways involved in specific modes of branch formation or maintenance, or both, have been described. To a variable extent, dendrites and axon collaterals can be viewed as dynamic structures subject to fine modulation that can result either in further growth or retraction. Each form of branching results from specific molecular mechanisms. Cell-internal, substrate-derived factors and functional activity, however, can often differ in their effect according to cell type and physiological context at the site of branch formation. Neural branching is not a linear process but an integrative one that takes place in a microenvironment where we have only a limited experimental access. To attain a coherent mechanism for this phenomenon, quantitative in situ data on the proteins involved and their interactions will be required.
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Affiliation(s)
- A Acebes
- The Instituto Cajal (CSIC), 28002, Madrid, Spain
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31
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Kingsbury MA, Graf ER, Finlay BL. Altered development of visual subcortical projections following neonatal thalamic ablation in the hamster. J Comp Neurol 2000; 424:165-78. [PMID: 10888746 DOI: 10.1002/1096-9861(20000814)424:1<165::aid-cne12>3.0.co;2-u] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Previous research has demonstrated that precise patterns of axonal connectivity often develop during a series of stages characterized by pathfinding, target recognition, and address selection. This last stage involves the focusing of projections to a precisely defined region within the target. Because thalamic projections begin to innervate cortex before the latter stages are reached, these projections may be important in the establishment of adult-like patterns of cortical connectivity. To address this issue, we examined the mature corticopontine and corticospinal projections of visual cortex deprived of early thalamic input by visual thalamic ablation. Although ablations on the day of birth in hamsters did not disrupt the targeting of appropriate subcortical structures by visual cortical axons, they did alter the organization of projections within the basilar pons and spinal cord. The density and spread of visual corticopontine connections in lesioned animals was greatly increased relative to unlesioned animals, suggesting that thalamic afferents are required during address selection, when the topographic specificity of projections is established. To determine whether early visual thalamic ablation increases connectivity by stabilizing an exuberant developmental projection, we examined the normal development of visual corticopontine connections in hamsters ages postnatal days 1-17 (P1-P17). From the earliest ages, visual cortical axons innervate the pontine nucleus in regions specific to their adult projection zones and show progressive growth within these zones. At no time during development do projections exist that are equivalent to the projections found after thalamic ablation, suggesting that removal of thalamic input does not simply stabilize a developmental projection.
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Affiliation(s)
- M A Kingsbury
- Department of Psychology, Cornell University, Ithaca, New York 14853, USA
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32
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Abstract
Generally, it is assumed that growth cones respond to a specific guidance cue with a single, specific, and stereotyped behavior. However, there is evidence to suggest that previous exposure to a given cue might alter subsequent responses to that cue (Snow and Letourneau, 1992; Shirasaki et al., 1998). We therefore tested the hypothesis that growth cone responses to stimuli are dependent on the history of previous stimulation. Growth cones of chick dorsal root ganglion neurons were exposed to well characterized stimuli: (1) contact with a laminin-coated bead, which causes growth cone turning, or (2) electrical stimulation, which causes growth cone collapse. Although the expected behavioral responses were observed after the initial stimulation, strikingly different responses to a subsequent stimulation were observed. Growth cones that had recovered from electrical stimulation-induced collapse rapidly developed insensitivity to a second identical electrical stimulation. Growth cones that previously turned in response to contact with a laminin-coated bead responded to a second bead with a "stall" or cessation in outgrowth. This stimulus history dependence of growth cone behavior could be generalized across dissimilar stimuli: after contact with a laminin-coated bead, growth cones failed to collapse in response to electrical stimulation. The calcium/calmodulin-dependent protein kinase II (CaMKII) was implicated in this history dependence by pharmacological experiments. Together, these results demonstrate that growth cones can alter their behavioral response rapidly to a given stimulus in a manner dependent on previous history and that knowledge of past events in growth cone navigation may be required to predict future growth cone behavior.
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Zheng M, Kuffler DP. Guidance of regenerating motor axonsin vivo by gradients of diffusible peripheral nerve-derived factors. ACTA ACUST UNITED AC 2000. [DOI: 10.1002/(sici)1097-4695(20000205)42:2<212::aid-neu5>3.0.co;2-c] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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34
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35
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Hill ES, Latalladi G, Kuffler DP. Dissociated adult Rana pipiens motoneuron growth cones turn up concentration gradients of denervated peripheral nerve-released factors. Neurosci Lett 1999; 277:87-90. [PMID: 10624816 DOI: 10.1016/s0304-3940(99)00868-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
During development of the central nervous system neuronal growth cones are attracted or repelled by concentration gradients of specific target-derived factors. Although evidence suggests that gradients of target-derived factors are chemotropic for adult motoneuron growth cones, a conclusive demonstration has remained elusive. Further, no preparation has been available on which to rapidly and reliably test candidate factors. The present results demonstrate that in vitro adult frog motoneuron growth cones consistently turn and grow up diffusible concentration gradients of denervated peripheral nerve-released factors over distances of almost 200 microm, and that the responsible factor/s are larger than 30 kDa. This preparation provides an excellent bioassay on which the factor/s responsible for this influence can be tested as they are isolated and characterized.
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Affiliation(s)
- E S Hill
- Institute of Neurobiology, School of Medicine, University of Puerto Rico, San Juan 00901, USA
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Bertuzzi S, Hindges R, Mui SH, O'Leary DD, Lemke G. The homeodomain protein vax1 is required for axon guidance and major tract formation in the developing forebrain. Genes Dev 1999; 13:3092-105. [PMID: 10601035 PMCID: PMC317177 DOI: 10.1101/gad.13.23.3092] [Citation(s) in RCA: 121] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The homeodomain protein Vax1 is expressed in a highly circumscribed set of cells at the ventral anterior midline of the embryonic CNS. These cells populate the choroid fissure of the optic disk, the body of the optic stalk and nerve, the optic chiasm and ventral diencephalon, and the anterior midline zones that abut developing commissural tracts. We have generated mutant mice that lack Vax1. In these mice (1) the optic disks fail to close, leading to coloboma and loss of the eye-nerve boundary; (2) optic nerve glia fail to associate with and appear to repulse ingrowing retinal axons, resulting in a fascicle of axons that are completely segregated from optic nerve astrocytes; (3) retinal axons fail to penetrate the brain in significant numbers and fail to form an optic chiasm; and (4) axons in multiple commissural tracts of the anterior CNS, including the corpus callosum and the hippocampal and anterior commissures, fail to cross the midline. These axon guidance defects do not result from the death of normally Vax1(+) midline cells but, instead, correlate with markedly diminished expression of attractive guidance cues in these cells. Vax1 therefore regulates the guidance properties of a set of anterior midline cells that orchestrate axon trajectories in the developing mammalian forebrain.
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Affiliation(s)
- S Bertuzzi
- Molecular Neurobiology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA
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37
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Miller MW, Astley SJ, Clarren SK. Number of axons in the corpus callosum of the mature Macaca nemestrina: Increases caused by prenatal exposure to ethanol. J Comp Neurol 1999. [DOI: 10.1002/(sici)1096-9861(19990913)412:1<123::aid-cne9>3.0.co;2-f] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Castellani V, Bolz J. Opposing roles for neurotrophin-3 in targeting and collateral formation of distinct sets of developing cortical neurons. Development 1999; 126:3335-45. [PMID: 10393113 DOI: 10.1242/dev.126.15.3335] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Neurotrophin-3 and its receptor TrkC are expressed during the development of the mammalian cerebral cortex. To examine whether neurotrophin-3 might play a role in the elaboration of layer-specific cortical circuits, slices of layer 6 and layers 2/3 neurons were cultured in the presence of exogenously applied neurotrophin-3. Results indicate that neurotrophin-3 promotes axonal branching of layer 6 axons, which target neurotrophin-3-expressing layers in vivo, and that it inhibits branching of layers 2/3 axons, which avoid neurotrophin-3-expressing layers. Such opposing effects of neurotrophin-3 on axonal branching were also observed with embryonic cortical neurons, indicating that the response to neurotrophin-3 is specified at early developmental stages, prior to cell migration. In addition to its effects on fiber branching, axonal guidance assays also indicate that neurotrophin-3 is an attractive signal for layer 6 axons and a repellent guidance cue for layers 2/3 axons. Experiments with specific antibodies to neutralize neurotrophin-3 in cortical membranes revealed that endogenous levels of neurotrophin-3 are sufficient to regulate branching and targeting of cortical axons. These opposing effects of neurotrophin-3 on specific populations of axons demonstrate that it could serve as one of the signals for the elaboration of local cortical circuits.
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Affiliation(s)
- V Castellani
- INSERM Unité 371 'Cerveau et Vision' 18, Avenue du Doyen Lépine, France
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39
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Different contributions of microtubule dynamics and transport to the growth of axons and collateral sprouts. J Neurosci 1999. [PMID: 10234018 DOI: 10.1523/jneurosci.19-10-03860.1999] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Axonal growth is believed to depend on microtubule transport and microtubule dynamic instability. We now report that the growth of axon collateral branches can occur independent of microtubule dynamic instability and can rely mostly on the transport of preassembled polymer. Raising embryonic sensory neurons in concentrations of either taxol or nocodazole (NOC) that largely inhibit microtubule dynamics significantly inhibited growth of main axonal shafts but had only minor effects on collateral branch growth. The collaterals of axons raised in taxol or nocodazole often contained single microtubules with both ends clearly visible within the collateral branch ("floating" microtubules), which we interpret as microtubules undergoing transport. Furthermore, in these collaterals there was a distoproximal gradient in microtubule mass, indicating the distal accumulation of transported polymer. Treatment of cultures with a high dose of nocodazole to deplete microtubules from collaterals, followed by treatment with 4-20 nM vinblastine to inhibit microtubule repolymerization, resulted in the time-dependent reappearance and subsequent distal accumulation of floating microtubules in collaterals, providing further evidence for microtubule transport into collateral branches. Our data show that, surprisingly, the contribution of microtubule dynamics to collateral branch growth is minor compared with the important role of microtubule dynamics in growth cone migration, and they indicate that the transport of microtubules may provide sufficient cytoskeletal material for the initial growth of collateral branches.
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Wang KH, Brose K, Arnott D, Kidd T, Goodman CS, Henzel W, Tessier-Lavigne M. Biochemical purification of a mammalian slit protein as a positive regulator of sensory axon elongation and branching. Cell 1999; 96:771-84. [PMID: 10102266 DOI: 10.1016/s0092-8674(00)80588-7] [Citation(s) in RCA: 378] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Many neurons in both vertebrates and invertebrates innervate multiple targets by sprouting secondary axon collaterals (or branches) from a primary axon shaft. To begin to identify molecular regulators of axon branch initiation or extension, we studied the growth of single sensory axons in an in vitro collagen assay system and identified an activity in extracts of embryonic spinal cord and of postnatal and adult brain that promotes the elongation and formation of extensive branches by these axons. Biochemical purification of the activity from calf brain extracts led to the identification of an amino-terminal fragment of Slit2 as the main active component and to the discovery of a distinct activity that potentiates its effects. These results indicate that Slit proteins may function as positive regulators of axon collateral formation during the establishment or remodeling of neural circuits.
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Affiliation(s)
- K H Wang
- Department of Anatomy, Howard Hughes Medical Institute, University of California, San Francisco 94143-0452, USA
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41
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The establishment of peripheral sensory arbors in the leech: in vivo time-lapse studies reveal a highly dynamic process. J Neurosci 1999. [PMID: 9065502 DOI: 10.1523/jneurosci.17-07-02408.1997] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Pressure-sensitive (P) neurons located in the leech CNS form elaborate terminal arbors in the body wall of the animal during mid-embryogenesis. In the experiments discussed here, arbor development in the target region was studied in intact, unanesthetized leech embryos using time-lapse video microscopy of individual, fluorescently stained P neurons. Analysis of time-lapse recordings made over a period of several days revealed that arbor formation is a very dynamic process. At any particular time, most high-order terminal branches were either extending or retracting, in approximately equal numbers and at very similar rates. Many branches underwent several rounds of extension and retraction every hour. Net arbor growth occurred at a much lower rate than the extension and retraction rates of individual branches. Process retraction sometimes resulted in an apparent change in the topological order of processes. Significantly, the initiation of new branches was restricted to a few locations along the parent process, which were termed "hot spots." Moreover, the capacity to generate high-order branches correlated with parent process stability. The target region of the growing P cell arbor in the body wall was subsequently examined using confocal microscopy in fixed preparations. The arbor expanded between the longitudinal and circular muscle layers, a region occupied by small unidentified cells. Simultaneous imaging of the dye-labeled terminal arbor and the surrounding tissue at two different wavelengths suggested that the high-order processes were navigating around these cells, which sometimes forced the growing processes to assume a bent form. These observations suggest that the formation of the P cell arbor can be best described as a "dynamically unstable" process that is constrained by interactions with its environment.
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Directed growth of early cortical axons is influenced by a chemoattractant released from an intermediate target. J Neurosci 1999. [PMID: 9065505 DOI: 10.1523/jneurosci.17-07-02445.1997] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Projection neurons throughout the mature mammalian neocortex extend efferent axons either through the ventrolaterally positioned internal capsule to subcortical targets or through the dorsally located midline corpus callosum to the contralateral cortex. In rats, the internal capsule is pioneered on E14, but the corpus callosum is not pioneered until E17, even though these two types of projection neurons are generated at the same time. Here we use axonal markers to demonstrate that early cortical axon growth is directed toward the nascent internal capsule, which could account for the timing difference in the development of the two efferent pathways. This directed axon growth may be due to a chemoattractant and/or a chemorepellent secreted by intermediate targets of cortical efferent axons, the nascent internal capsule, or the medial wall of the dorsal telencephalon (MDT), respectively. To test for these soluble activities, explants of E15 rat neocortex and intermediate targets were cocultured in collagen gels. Cortical axon outgrowth was directed toward the internal capsule, but outgrowth was nondirected and suppressed when cocultured with MDT, suggesting that the internal capsule releases a chemoattractant for cortical axons, whereas the MDT releases a chemosuppressant. Because the chemoattractant Netrin-1 is expressed in the internal capsule, we cocultured cortical explants with E13 rat floor plate, which expresses Netrin-1, or with Netrin-1-transfected or control-transfected 293T cells. Cortical axon growth was directed toward both floor plate and Netrin-1-transfected 293T cells, as it had been toward the internal capsule, but not toward control-transfected 293T cells. These findings suggest that early events in cortical axon pathfinding may be controlled by a soluble activity which attracts initial axon growth toward the internal capsule and that this activity may be due to Netrin-1.
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Matheson SF, Levine RB. Steroid hormone enhancement of neurite outgrowth in identified insect motor neurons involves specific effects on growth cone form and function. ACTA ACUST UNITED AC 1999. [DOI: 10.1002/(sici)1097-4695(199901)38:1<27::aid-neu3>3.0.co;2-u] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Angelucci A, Clascá F, Sur M. Brainstem inputs to the ferret medial geniculate nucleus and the effect of early deafferentation on novel retinal projections to the auditory thalamus. J Comp Neurol 1998; 400:417-39. [PMID: 9779945 DOI: 10.1002/(sici)1096-9861(19981026)400:3<417::aid-cne10>3.0.co;2-o] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Following specific neonatal brain lesions in rodents and ferrets, retinal axons have been induced to innervate the medial geniculate nucleus (MGN). Previous studies have suggested that reduction of normal retinal targets along with deafferentation of the MGN are two concurrent factors required for the induction of novel retino-MGN projections. We have examined, in ferrets, the relative influence of these two factors on the extent of the novel retinal projection. We first characterized the inputs to the normal MGN, and the most effective combination of neonatal lesions to deafferent this nucleus, by injecting retrograde tracers into the MGN of normal and neonatally operated adult ferrets, respectively. In a second group of experiments, newborn ferrets received different combinations of lesions of normal retinal targets and MGN afferents. The resulting extent of retino-MGN projections was estimated for each case at adulthood, by using intraocular injections of anterograde tracers. We found that the extent of retino-MGN projections correlates well with the extent of MGN deafferentation, but not with extent of removal of normal retinal targets. Indeed, the presence of at least some normal retinal targets seems necessary for the formation of retino-MGN connections. The diameters of retino-MGN axons suggest that more than one type of retinal ganglion cells innervate the MGN under a lesion paradigm that spares the visual cortex and lateral geniculate nucleus. We also found that, after extensive deafferentation of MGN, other axonal systems in addition to retinal axons project ectopically to the MGN. These data are consistent with the idea that ectopic retino-MGN projections develop by sprouting of axon collaterals in response to signals arising from the deafferented nucleus, and that these axons compete with other sets of axons for terminal space in the MGN.
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Affiliation(s)
- A Angelucci
- Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge 02139, USA
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45
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Interstitial branches develop from active regions of the axon demarcated by the primary growth cone during pausing behaviors. J Neurosci 1998. [PMID: 9742160 DOI: 10.1523/jneurosci.18-19-07930.1998] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Interstitial branches arise from the axon shaft, sometimes at great distances behind the primary growth cone. After a waiting period that can last for days after extension of the primary growth cone past the target, branches elongate toward their targets. Delayed interstitial branching is an important but little understood mechanism for target innervation in the developing CNS of vertebrates. One possible mechanism of collateral branch formation is that the axon shaft responds to target-derived signals independent of the primary growth cone. Another possibility is that the primary growth cone recognizes the target and demarcates specific regions of the axon for future branching. To address whether behaviors of the primary growth cone and development of interstitial branches are related, we performed high-resolution time-lapse imaging on dissociated sensorimotor cortical neurons that branch interstitially in vivo. Imaging of entire cortical neurons for periods of days revealed that the primary growth cone pauses in regions in which axon branches later develop. Pausing behaviors involve repeated cycles of collapse, retraction, and extension during which growth cones enlarge and reorganize. Remnants of reorganized growth cones are left behind on the axon shaft as active filopodial or lamellar protrusions, and axon branches subsequently emerge from these active regions of the axon shaft. In this study we propose a new model to account for target innervation in vivo by interstitial branching. Our model suggests that delayed interstitial branching results directly from target recognition by the primary growth cone.
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Houweling DA, Lankhorst AJ, Gispen WH, Bär PR, Joosten EA. Collagen containing neurotrophin-3 (NT-3) attracts regrowing injured corticospinal axons in the adult rat spinal cord and promotes partial functional recovery. Exp Neurol 1998; 153:49-59. [PMID: 9743566 DOI: 10.1006/exnr.1998.6867] [Citation(s) in RCA: 159] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
During development, neurotrophic factors play an important role in the guidance and outgrowth of axons. Our working hypothesis is that neurotrophic factors involved in the development of axons of a particular CNS tract are among the most promising candidates for stimulating and directing the regrowth of fibers of this tract in the lesioned adult animal. The neurotrophin NT-3 is known to be involved in the target selection of outgrowing corticospinal tract (CST) fibers. We studied the capacity of locally applied NT-3 to stimulate and direct the regrowth of axons of the CST in the lesioned adult rat spinal cord. We also studied the effect of NT-3 application on the functional recovery of rats after spinal cord injury, using the gridwalk test. NT-3 was applied at the site of the lesion dissolved into rat tail collagen type I. Four weeks after spinal cord injury and collagen implantation, significantly more CST fibers had regrown into the collagen matrix containing NT-3 (22 +/- 6%, mean +/- SEM) than into the control collagen matrix without NT-3 (7 +/- 2%). No CST fibers grew into areas caudal to the collagen implant. Despite the absence of regrowth of corticospinal axons into host tissue caudal to the lesion area, functional recovery was observed in rats with NT-3 containing collagen implants.
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Affiliation(s)
- D A Houweling
- Department of Neurology, Rudolf Magnus Institute for Neurosciences, Utrecht University, Utrecht, 3508 GA, The Netherlands
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Oland LA, Pott WM, Higgins MR, Tolbert LP. Targeted ingrowth and glial relationships of olfactory receptor axons in the primary olfactory pathway of an insect. J Comp Neurol 1998. [DOI: 10.1002/(sici)1096-9861(19980817)398:1<119::aid-cne8>3.0.co;2-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Abstract
The sprouting of axon collateral branches is important in the establishment and refinement of neuronal connections during both development and regeneration. Collateral branches are initiated by the appearance of localized filopodial activity along quiescent axonal shafts. We report here that sensory neuron axonal shafts rapidly sprout filopodia at sites of contact with nerve growth factor-coated polystyrene beads. Some sprouts can extend up to at least 60 micro(m) through multiple bead contacts. Axonal filopodial sprouts often contained microtubules and exhibited a debundling of axonal microtubules at the site of bead-axon contact. Cytochalasin treatment abolished the filopodial sprouting, but not the accumulation of actin filaments at sites of bead-axon contact. The axonal sprouting response is mediated by the trkA receptor and likely acts through a phosphoinositide-3 kinase-dependent pathway, in a manner independent of intracellular Ca2+ fluctuations. These findings implicate neurotrophins as local cues that directly stimulate the formation of collateral axon branches.
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49
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Bastmeyer M, Daston MM, Possel H, O'Leary DD. Collateral branch formation related to cellular structures in the axon tract during corticopontine target recognition. J Comp Neurol 1998; 392:1-18. [PMID: 9482229 DOI: 10.1002/(sici)1096-9861(19980302)392:1<1::aid-cne1>3.0.co;2-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The corticopontine projection develops exclusively by collateral branches that form along the length of corticospinal axons days after they have passed their hindbrain target, the basilar pons. In vitro evidence suggests that the basilar pons releases a diffusible activity that initiates and directs the growth of collateral branches. This study investigates whether contact-dependent mechanisms may also influence the formation of collateral branches. By using immunocytochemistry, electron microscopy, and neuronal tracing techniques, we examined the region of the axon tract, the cerebral peduncle, overlying the basilar pons for cellular structures that correlate spatially and temporally with collateral branch formation. We found that radial glia are excluded from the tract. Oligodendrocyte precursors are found only at low density. Although mature astrocytes are absent, immature astrocytes are present throughout the tract. However, our evidence does not suggest a direct role for glial cell types in collateral branch formation. In contrast, dendrites of basilar pontine neurons are transiently present in the tract during the time of collateral branch formation. Although collateral branches are observed in regions of the tract devoid of dendrites, the orientation and location of most collateral branches correlates at the light microscopic level with dendrites. Electron microscopy reveals sites of increased collateral branch formation near neuronal cell bodies or dendrites. However, cell processes, whether dendritic or otherwise, are rarely found in direct contact with collateral branch points. A common and unexpected feature is the bundles of corticopontine collateral branches, oriented transversely to their parent corticospinal axons and directed across the tract to the basilar pons. Dendrites were often apposed to or embedded within the transverse bundles. These findings suggest that dendrites are not essential for collateral branch formation but that they may enhance this process and define discrete preferred locations for collateral branch initiation and elongation within the cerebral peduncle.
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Affiliation(s)
- M Bastmeyer
- Molecular Neurobiology Laboratory, The Salk Institute, La Jolla, California 92037, USA
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