1
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Liu J, Wang Y, Liu X, Han J, Tian Y. Spatiotemporal changes in Netrin/Dscam1 signaling dictate axonal projection direction in Drosophila small ventral lateral clock neurons. eLife 2024; 13:RP96041. [PMID: 39052321 PMCID: PMC11272162 DOI: 10.7554/elife.96041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/27/2024] Open
Abstract
Axon projection is a spatial- and temporal-specific process in which the growth cone receives environmental signals guiding axons to their final destination. However, the mechanisms underlying changes in axonal projection direction without well-defined landmarks remain elusive. Here, we present evidence showcasing the dynamic nature of axonal projections in Drosophila's small ventral lateral clock neurons (s-LNvs). Our findings reveal that these axons undergo an initial vertical projection in the early larval stage, followed by a subsequent transition to a horizontal projection in the early-to-mid third instar larvae. The vertical projection of s-LNv axons correlates with mushroom body calyx expansion, while the s-LNv-expressed Down syndrome cell adhesion molecule (Dscam1) interacts with Netrins to regulate the horizontal projection. During a specific temporal window, locally newborn dorsal clock neurons secrete Netrins, facilitating the transition of axonal projection direction in s-LNvs. Our study establishes a compelling in vivo model to probe the mechanisms of axonal projection direction switching in the absence of clear landmarks. These findings underscore the significance of dynamic local microenvironments in the complementary regulation of axonal projection direction transitions.
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Affiliation(s)
- Jingjing Liu
- School of Life Science and Technology, the Key Laboratory of Developmental Genes and Human Disease, Southeast UniversityNanjingChina
| | - Yuedong Wang
- School of Life Science and Technology, the Key Laboratory of Developmental Genes and Human Disease, Southeast UniversityNanjingChina
| | - Xian Liu
- School of Life Science and Technology, the Key Laboratory of Developmental Genes and Human Disease, Southeast UniversityNanjingChina
| | - Junhai Han
- School of Life Science and Technology, the Key Laboratory of Developmental Genes and Human Disease, Southeast UniversityNanjingChina
- Co-innovation Center of Neuroregeneration, Nantong UniversityNantongChina
| | - Yao Tian
- School of Life Science and Technology, the Key Laboratory of Developmental Genes and Human Disease, Southeast UniversityNanjingChina
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2
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Marsh APL, Edwards TJ, Galea C, Cooper HM, Engle EC, Jamuar SS, Méneret A, Moutard ML, Nava C, Rastetter A, Robinson G, Rouleau G, Roze E, Spencer-Smith M, Trouillard O, Billette de Villemeur T, Walsh CA, Yu TW, Heron D, Sherr EH, Richards LJ, Depienne C, Leventer RJ, Lockhart PJ. DCC mutation update: Congenital mirror movements, isolated agenesis of the corpus callosum, and developmental split brain syndrome. Hum Mutat 2017; 39:23-39. [PMID: 29068161 DOI: 10.1002/humu.23361] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2017] [Revised: 10/08/2017] [Accepted: 10/11/2017] [Indexed: 12/12/2022]
Abstract
The deleted in colorectal cancer (DCC) gene encodes the netrin-1 (NTN1) receptor DCC, a transmembrane protein required for the guidance of commissural axons. Germline DCC mutations disrupt the development of predominantly commissural tracts in the central nervous system (CNS) and cause a spectrum of neurological disorders. Monoallelic, missense, and predicted loss-of-function DCC mutations cause congenital mirror movements, isolated agenesis of the corpus callosum (ACC), or both. Biallelic, predicted loss-of-function DCC mutations cause developmental split brain syndrome (DSBS). Although the underlying molecular mechanisms leading to disease remain poorly understood, they are thought to stem from reduced or perturbed NTN1 signaling. Here, we review the 26 reported DCC mutations associated with abnormal CNS development in humans, including 14 missense and 12 predicted loss-of-function mutations, and discuss their associated clinical characteristics and diagnostic features. We provide an update on the observed genotype-phenotype relationships of congenital mirror movements, isolated ACC and DSBS, and correlate this to our current understanding of the biological function of DCC in the development of the CNS. All mutations and their associated phenotypes were deposited into a locus-specific LOVD (https://databases.lovd.nl/shared/genes/DCC).
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Affiliation(s)
- Ashley P L Marsh
- Bruce Lefroy Centre for Genetic Health Research, Murdoch Children's Research Institute, Royal Children's Hospital, Parkville, Victoria, Australia.,Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia
| | - Timothy J Edwards
- Queensland Brain Institute, The University of Queensland, St Lucia, Brisbane, Australia.,Faculty of Medicine, The University of Queensland, Herston, Brisbane, Australia
| | - Charles Galea
- Drug Delivery, Disposition and Dynamics (D4), Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - Helen M Cooper
- Queensland Brain Institute, The University of Queensland, St Lucia, Brisbane, Australia
| | - Elizabeth C Engle
- Division of Genetics and Genomics, Boston Children's Hospital, Boston, Massachusetts.,Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, Massachusetts.,Howard Hughes Medical Institute, Boston Children's Hospital, Boston, Massachusetts.,Department of Neurology, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts.,Department of Ophthalmology, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts.,Program in Medical and Population Genetics, Broad Institute of Massachusetts Institute of Technology (MIT) and Harvard, Cambridge, Massachusetts
| | - Saumya S Jamuar
- Division of Genetics and Genomics, Boston Children's Hospital, Boston, Massachusetts.,Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, Massachusetts.,Howard Hughes Medical Institute, Boston Children's Hospital, Boston, Massachusetts.,Department of Pediatrics, Harvard Medical School, Boston, Massachusetts.,Department of Paediatrics, KK Women's and Children's Hospital, Paediatric Academic Clinical Programme, Duke-NUS Medical School, Singapore, Singapore
| | - Aurélie Méneret
- INSERM, U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, Paris, France.,Département de Neurologie, AP-HP, Hôpital de la Pitié-Salpêtrière, Paris, France
| | - Marie-Laure Moutard
- Service de Neuropédiatrie, AP-HP, Hôpital Trousseau, Paris, France.,UPMC, GRC ConCer-LD, Sorbonne Université, Paris, France.,Centre de référence "Neurogénétique", Paris, France
| | - Caroline Nava
- INSERM, U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, Paris, France.,Département de Génétique, AP-HP, Hôpital de la Pitié-Salpêtrière, Paris, France
| | - Agnès Rastetter
- INSERM, U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, Paris, France
| | - Gail Robinson
- Neuropsychology Research Unit, School of Psychology, The University of Queensland, Brisbane, Queensland, Australia
| | - Guy Rouleau
- Department of Neurology and Neurosurgery, McGill University Health Center, Montreal, Quebec, Canada.,Montreal Neurological Institute and Hospital, McGill University, Montréal, Quebec, Canada
| | - Emmanuel Roze
- INSERM, U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, Paris, France.,Département de Neurologie, AP-HP, Hôpital de la Pitié-Salpêtrière, Paris, France
| | - Megan Spencer-Smith
- Clinical Sciences, Murdoch Children's Research Institute, Parkville, Victoria, Australia.,School of Psychological Sciences and Monash Institute of Cognitive and Clinical Neurosciences, Monash University, Clayton Campus, Clayton, Victoria, Australia
| | - Oriane Trouillard
- INSERM, U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, Paris, France
| | - Thierry Billette de Villemeur
- Service de Neuropédiatrie, AP-HP, Hôpital Trousseau, Paris, France.,UPMC, GRC ConCer-LD, Sorbonne Université, Paris, France.,Centre de Référence "déficiences intellectuelles de causes rares", Paris, France.,INSERM U1141, Paris, France
| | - Christopher A Walsh
- Division of Genetics and Genomics, Boston Children's Hospital, Boston, Massachusetts.,Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, Massachusetts.,Howard Hughes Medical Institute, Boston Children's Hospital, Boston, Massachusetts.,Department of Neurology, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts.,Program in Medical and Population Genetics, Broad Institute of Massachusetts Institute of Technology (MIT) and Harvard, Cambridge, Massachusetts.,Department of Pediatrics, Harvard Medical School, Boston, Massachusetts
| | - Timothy W Yu
- Division of Genetics and Genomics, Boston Children's Hospital, Boston, Massachusetts.,Program in Medical and Population Genetics, Broad Institute of Massachusetts Institute of Technology (MIT) and Harvard, Cambridge, Massachusetts.,Department of Pediatrics, Harvard Medical School, Boston, Massachusetts
| | | | - Delphine Heron
- UPMC, GRC ConCer-LD, Sorbonne Université, Paris, France.,Département de Génétique, AP-HP, Hôpital de la Pitié-Salpêtrière, Paris, France
| | - Elliott H Sherr
- Department of Neurology, UCSF Benioff Children's Hospital, San Francisco, California
| | - Linda J Richards
- Queensland Brain Institute, The University of Queensland, St Lucia, Brisbane, Australia.,The University of Queensland, School of Biomedical Sciences, St Lucia, Brisbane, Australia
| | - Christel Depienne
- INSERM, U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, Paris, France.,Département de Génétique, AP-HP, Hôpital de la Pitié-Salpêtrière, Paris, France.,Département de Médicine translationnelle et Neurogénétique, IGBMC, CNRS UMR 7104, INSERM U964, Université de Strasbourg, Illkirch, France.,Laboratoires de génétique, Institut de génétique médicale d'Alsace, Hôpitaux Universitaires de Strasbourg, Strasbourg, France
| | - Richard J Leventer
- Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia.,Neuroscience Research Group, Murdoch Children's Research Institute, Parkville, Victoria, Australia.,Department of Neurology, University of Melbourne, Royal Children's Hospital, Parkville, Victoria, Australia
| | - Paul J Lockhart
- Bruce Lefroy Centre for Genetic Health Research, Murdoch Children's Research Institute, Royal Children's Hospital, Parkville, Victoria, Australia.,Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia
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3
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Commissural axonal corridors instruct neuronal migration in the mouse spinal cord. Nat Commun 2015; 6:7028. [DOI: 10.1038/ncomms8028] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Accepted: 03/25/2015] [Indexed: 12/24/2022] Open
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4
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Sloan TFW, Qasaimeh MA, Juncker D, Yam PT, Charron F. Integration of shallow gradients of Shh and Netrin-1 guides commissural axons. PLoS Biol 2015; 13:e1002119. [PMID: 25826604 PMCID: PMC4380419 DOI: 10.1371/journal.pbio.1002119] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Accepted: 03/03/2015] [Indexed: 11/19/2022] Open
Abstract
During nervous system development, gradients of Sonic Hedgehog (Shh) and Netrin-1 attract growth cones of commissural axons toward the floor plate of the embryonic spinal cord. Mice defective for either Shh or Netrin-1 signaling have commissural axon guidance defects, suggesting that both Shh and Netrin-1 are required for correct axon guidance. However, how Shh and Netrin-1 collaborate to guide axons is not known. We first quantified the steepness of the Shh gradient in the spinal cord and found that it is mostly very shallow. We then developed an in vitro microfluidic guidance assay to simulate these shallow gradients. We found that axons of dissociated commissural neurons respond to steep but not shallow gradients of Shh or Netrin-1. However, when we presented axons with combined Shh and Netrin-1 gradients, they had heightened sensitivity to the guidance cues, turning in response to shallower gradients that were unable to guide axons when only one cue was present. Furthermore, these shallow gradients polarized growth cone Src-family kinase (SFK) activity only when Shh and Netrin-1 were combined, indicating that SFKs can integrate the two guidance cues. Together, our results indicate that Shh and Netrin-1 synergize to enable growth cones to sense shallow gradients in regions of the spinal cord where the steepness of a single guidance cue is insufficient to guide axons, and we identify a novel type of synergy that occurs when the steepness (and not the concentration) of a guidance cue is limiting.
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Affiliation(s)
- Tyler F. W. Sloan
- Molecular Biology of Neural Development, Institut de Recherches Cliniques de Montréal (IRCM), Montreal, Quebec, Canada
- Division of Experimental Medicine, McGill University, Montreal, Quebec, Canada
- Program in Neuroengineering, McGill University, Montreal, Quebec, Canada
| | - Mohammad A. Qasaimeh
- Program in Neuroengineering, McGill University, Montreal, Quebec, Canada
- Division of Engineering, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
| | - David Juncker
- Program in Neuroengineering, McGill University, Montreal, Quebec, Canada
- Department of Biomedical Engineering, McGill University, Montreal, Quebec, Canada
- McGill University and Genome Quebec Innovation Centre, McGill University, Montreal, Quebec, Canada
| | - Patricia T. Yam
- Molecular Biology of Neural Development, Institut de Recherches Cliniques de Montréal (IRCM), Montreal, Quebec, Canada
| | - Frédéric Charron
- Molecular Biology of Neural Development, Institut de Recherches Cliniques de Montréal (IRCM), Montreal, Quebec, Canada
- Division of Experimental Medicine, McGill University, Montreal, Quebec, Canada
- Program in Neuroengineering, McGill University, Montreal, Quebec, Canada
- Department of Anatomy and Cell Biology, Department of Biology, McGill University, Quebec, Canada
- Department of Medicine, University of Montreal, Montreal, Quebec, Canada
- * E-mail:
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5
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Martinez E, Tran TS. Vertebrate spinal commissural neurons: a model system for studying axon guidance beyond the midline. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2015; 4:283-97. [PMID: 25619385 DOI: 10.1002/wdev.173] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Revised: 11/27/2014] [Accepted: 12/04/2014] [Indexed: 12/21/2022]
Abstract
For bilaterally symmetric organisms, the transfer of information between the left and right side of the nervous system is mediated by commissures formed by neurons that project their axons across the body midline to the contralateral side of the central nervous system (CNS). After crossing the midline, many of these axons must travel long distances to reach their targets, including those that extend from spinal commissural neurons. Owing to the highly stereotyped trajectories of spinal commissural neurons that can be divided into several segments as these axons project to their targets, it is an ideal system for investigators to ask fundamental questions related to mechanisms of short- and long-range axon guidance, fasciculation, and choice point decisions at the midline intermediate target. In addition, studies of patterning genes of the nervous system have revealed complex transcription factor codes that function in a combinatorial fashion to specify individual classes of spinal neurons including commissural neurons. Despite these advances and the functional importance of spinal commissural neurons in mediating the transfer of external sensory information from the peripheral nervous system (PNS) to the CNS, only a handful of studies have begun to elucidate the mechanistic logic underlying their long-range pathfinding and the characterization of their synaptic targets. Using in vitro assays, in vivo labeling methodologies, in combination with both loss- and gain-of-function experiments, several studies have revealed that the molecular mechanisms of long-range spinal commissural axon pathfinding involve an interplay between classical axon guidance cues, morphogens and cell adhesion molecules. For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Edward Martinez
- Department of Biological Sciences, Rutgers University, Newark, NJ, USA
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6
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Bilaterally symmetric populations of chicken dI1 (commissural) axons cross the floor plate independently of each other. PLoS One 2013; 8:e62977. [PMID: 23646165 PMCID: PMC3639936 DOI: 10.1371/journal.pone.0062977] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Accepted: 03/28/2013] [Indexed: 12/19/2022] Open
Abstract
Axons use temporal and directional guidance cues at intermediate targets to set the rate and direction of growth towards their synaptic targets. Our recent studies have shown that disrupting the temporal guidance process, by unilaterally accelerating the rate at which spinal dI1 (commissural) axons grow, resulted in turning errors both in the ventral spinal cord and after crossing the floor plate. Here we investigate a mechanistic explanation for these defects: the accelerated dI1 axons arrive in the ventral spinal cord before necessary fasciculation cues from incoming dI1 axons from the opposite side of the spinal cord. The identification of such an interaction would support a model of selective fasciculation whereby the pioneering dI1 axons serve as guides for the processes of the bilaterally symmetrical population of dI1 neurons. To test this model, we first developed the ability to “double” in ovo electroporate the embryonic chicken spinal cord to independently manipulate the rate of growth of the two bilateral populations of dI1 axons. Second, we examined the requirement for a putative bilateral interaction by unilaterally ablating the dI1 population in cultured explants of chicken embryonic spinal cord. Surprisingly, we find no evidence for a bilateral dI1 axon interaction, rather dI1 axons appear to project independently of each other.
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7
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Phan KD, Croteau LP, Kam JWK, Kania A, Cloutier JF, Butler SJ. Neogenin may functionally substitute for Dcc in chicken. PLoS One 2011; 6:e22072. [PMID: 21779375 PMCID: PMC3133656 DOI: 10.1371/journal.pone.0022072] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Accepted: 06/14/2011] [Indexed: 11/22/2022] Open
Abstract
Dcc is the key receptor that mediates attractive responses of axonal growth cones to netrins, a family of axon guidance cues used throughout evolution. However, a Dcc homolog has not yet been identified in the chicken genome, raising the possibility that Dcc is not present in avians. Here we show that the closely related family member neogenin may functionally substitute for Dcc in the developing chicken spinal cord. The expression pattern of chicken neogenin in the developing spinal cord is a composite of the distribution patterns of both rodent Dcc and neogenin. Moreover, whereas the loss of mouse neogenin has no effect on the trajectory of commissural axons, removing chicken neogenin by RNA interference results in a phenotype similar to the functional inactivation of Dcc in mouse. Taken together, these data suggest that the chick neogenin is functionally equivalent to rodent Dcc.
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Affiliation(s)
- Keith Dai Phan
- Department of Biological Sciences, University of Southern California, Los Angeles, California, United States of America
| | | | - Joseph Wai Keung Kam
- Montreal Neurological Institute, McGill University, Montréal, Québec, Canada
- Department of Neurology and Neurosurgery, McGill University, Montréal, Québec, Canada
| | - Artur Kania
- Institut de Recherches Cliniques de Montréal, Montréal, Québec, Canada
- Faculté de Médecine, Université de Montréal, Montréal, Québec, Canada
- Departments of Anatomy and Cell Biology and Biology, McGill University, Montréal, Québec, Canada
| | - Jean-François Cloutier
- Montreal Neurological Institute, McGill University, Montréal, Québec, Canada
- Department of Neurology and Neurosurgery, McGill University, Montréal, Québec, Canada
| | - Samantha Joanna Butler
- Department of Biological Sciences, University of Southern California, Los Angeles, California, United States of America
- * E-mail:
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8
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Schell-Apacik CC, Wagner K, Bihler M, Ertl-Wagner B, Heinrich U, Klopocki E, Kalscheuer VM, Muenke M, von Voss H. Agenesis and dysgenesis of the corpus callosum: clinical, genetic and neuroimaging findings in a series of 41 patients. Am J Med Genet A 2008; 146A:2501-11. [PMID: 18792984 PMCID: PMC2774850 DOI: 10.1002/ajmg.a.32476] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Agenesis of the corpus callosum (ACC) is among the most frequent human brain malformations with an incidence of 0.5-70 in 10,000. It is a heterogeneous condition, for which several different genetic causes are known, for example, ACC as part of monogenic syndromes or complex chromosomal rearrangements. We systematically evaluated the data of 172 patients with documented corpus callosum abnormalities in the records, and 23 patients with chromosomal rearrangements known to be associated with corpus callosum changes. All available neuroimaging data, including CT and MRI, were re-evaluated following a standardized protocol. Whenever feasible chromosome and subtelomere analyses as well as molecular genetic testing were performed in patients with disorders of the corpus callosum in order to identify a genetic diagnosis. Our results showed that 41 patients with complete absence (agenesis of the corpus callosum-ACC) or partial absence (dysgenesis of the corpus callosum-DCC) were identified. Out of these 28 had ACC, 13 had DCC. In 11 of the 28 patients with ACC, the following diagnoses could be established: Mowat-Wilson syndrome (n = 2), Walker-Warburg syndrome (n = 1), oro-facial-digital syndrome type 1 (n = 1), and chromosomal rearrangements (n = 7), including a patient with an apparently balanced reciprocal translocation, which led to the disruption and a predicted loss of function in the FOXG1B gene. The cause of the ACC in 17 patients remained unclear. In 2 of the 13 patients with DCC, unbalanced chromosomal rearrangements could be detected (n = 2), while the cause of DCC in 11 patients remained unclear. In our series of cases a variety of genetic causes of disorders of the corpus callosum were identified with cytogenetic anomalies representing the most common underlying etiology.
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Affiliation(s)
- Chayim Can Schell-Apacik
- Institute of Social Pediatrics and Adolescent Medicine of the University of Munich, München, Germany.
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9
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Yamauchi K, Phan KD, Butler SJ. BMP type I receptor complexes have distinct activities mediating cell fate and axon guidance decisions. Development 2008; 135:1119-28. [DOI: 10.1242/dev.012989] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The finding that morphogens, signalling molecules that specify cell identity, also act as axon guidance molecules has raised the possibility that the mechanisms that establish neural cell fate are also used to assemble neuronal circuits. It remains unresolved, however, how cells differentially transduce the cell fate specification and guidance activities of morphogens. To address this question, we have examined the mechanism by which the Bone morphogenetic proteins (BMPs) guide commissural axons in the developing spinal cord. In contrast to studies that have suggested that morphogens direct axon guidance decisions using non-canonical signal transduction factors, our results indicate that canonical components of the BMP signalling pathway, the type I BMP receptors (BMPRs), are both necessary and sufficient to specify the fate of commissural neurons and guide their axonal projections. However,whereas the induction of cell fate is a shared property of both type I BMPRs,axon guidance is chiefly mediated by only one of the type I BMPRs, BMPRIB. Taken together, these results indicate that the diverse activities of BMP morphogens can be accounted for by the differential use of distinct components of the canonical BMPR complex.
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Affiliation(s)
- Ken Yamauchi
- Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089, USA
| | - Keith D. Phan
- Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089, USA
| | - Samantha J. Butler
- Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089, USA
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10
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Kennedy TE, Wang H, Marshall W, Tessier-Lavigne M. Axon guidance by diffusible chemoattractants: a gradient of netrin protein in the developing spinal cord. J Neurosci 2006; 26:8866-74. [PMID: 16928876 PMCID: PMC6674364 DOI: 10.1523/jneurosci.5191-05.2006] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Gradients of diffusible long-range attractant and repellent proteins have been proposed to guide growing axons during nervous system development, but such gradients have never been visualized directly. In the embryonic spinal cord, commissural axons pioneer a circumferential trajectory to the floor plate at the ventral midline directed by secreted proteins of the netrin family. In the embryonic chick spinal cord netrin-1 mRNA is expressed by floor plate cells and netrin-2 mRNA by neural epithelial cells. Antibodies to the two netrins reveal a gradient of netrin protein directly in the path of commissural axons. The netrin-1 gradient itself extends many cell diameters dorsal to the floor plate, the site of netrin-1 expression. A similar distribution of netrin-1 protein has been detected in embryonic rat and mouse spinal cord. The detection of a gradient of netrin-1 protein supports the operation of long-range chemotropic mechanisms in the developing nervous system.
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Affiliation(s)
- Timothy E. Kennedy
- Departments of Anatomy and Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California 94143
- Departments of Neurology and Neurosurgery and Anatomy and Cell Biology, Center for Neuronal Survival, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4, and
| | - Hao Wang
- Departments of Anatomy and Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California 94143
| | - Wallace Marshall
- Departments of Anatomy and Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California 94143
| | - Marc Tessier-Lavigne
- Departments of Anatomy and Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California 94143
- Division of Research, Genentech, South San Francisco, California 94080
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11
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Mihrshahi R. The corpus callosum as an evolutionary innovation. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2006; 306:8-17. [PMID: 16116611 DOI: 10.1002/jez.b.21067] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The corpus callosum (CC) is the major interhemispheric fibre bundle in the eutherian brain and has been described as a true evolutionary innovation. This paper reviews the current literature with regard to functional, developmental and genetic concepts that may help elucidate the evolutionary origin of this structure. It has been suggested that the CC arose in the eutherian brain as a more direct and, therefore, more effective system for the interhemispheric integration of topographically organized sensory cortices than the anterior commissure (AC) and hippocampal commissure (HC) already present in nonplacental mammals. It can also be argued, however, that the ability of the CC to integrate the newly evolving motor cortices of placental mammals may have played a role in the evolutionary fixation of this structure. Investigations into the developmental mechanism involved in the formation of the CC and their underlying patterns of gene expression make it possible to formulate a tentative hypothesis about the evolutionary origin of this commissure. This paper suggests that changes in the developmental patterns of the expression of certain regulatory genes may have allowed a first group of callosal pioneering axons to cross the cortical midline. These pioneering fibres may have used the axons of the HC to find their way across the midline. Additional callosal fibres may then have fasciculated with these pioneers. Once the CC had formed in this way, more complex systems of axonal guidance may have evolved over time, thus enabling a gradual increase in the size and complexity of the CC.
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Affiliation(s)
- Robin Mihrshahi
- Department of Biological Sciences, Macquarie University, Sydney, North Ryde 2109, Australia.
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12
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Abstract
The protein products of both of the identified chick engrailed-like (En) genes, chick En-1 and chick En-2, are localized in cells of the developing brain, mandibular arch, spinal cord, dermatome, and ventral limb bud ectoderm, as demonstrated by labeling with the polyclonal antiserum alpha Enhb-1 developed by Davis et al. (Development 111:281-298, 1991). A subpopulation of cephalic neural crest cells is also En-protein-positive. The monoclonal antibody 4D9 recognizes the chick En-2 gene product exclusively (Patel et al.: Cell 58:955-968, 1989; Davis et al., 1991) and colocalizes with chick En-2 mRNA in the developing head region of the chick embryo as shown by in situ hybridization (Gardner et al.: J. Neurosci. Res. 21:426-437, 1988). In the present study we examine the pattern of alpha Enhb-1 and 4D9 localization throughout the chick embryo from the first appearance of antibody (Ab)-positive cells at stage 8 (Hamburger and Hamilton: J. Morphol. 88:49-92, 1951) through stage 28 (1-5.5 days). We compare the localization patterns of the two Abs to each other, as well as to the localization of the monoclonal Ab, HNK-1, which recognizes many neural crest cells, using double- and triple-label fluorescence immunohistochemistry. Most En protein-positive cells in the path of neural crest cell migration are not HNK-1 positive. In detailed examination of alpha Enhb-1 and 4D9 localization, we find previously undetected patterns of En protein localization in the prechordal plate, hindbrain, myotome, ventral body-wall mesoderm, and extraembryonic membranes. Based upon these observations we propose: 1) that En expression in the mesoderm may be induced through interaction with En expressing cells in the neuroectoderm; 2) that En expression in the head mesenchyme is associated with somitomere 4; and 3) that En expression may be involved in epithelial-mesenchymal cell transformations.
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Affiliation(s)
- C A Gardner
- Department of Anatomy and Cell Biology, University of Michigan Medical School, Ann Arbor 48109
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13
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Abstract
The human brain assembles an incredible network of over a billion neurons. Understanding how these connections form during development in order for the brain to function properly is a fundamental question in biology. Much of this wiring takes place during embryonic development. Neurons are generated in the ventricular zone, migrate out, and begin to differentiate. However, neurons are often born in locations some distance from the target cells with which they will ultimately form connections. To form connections, neurons project long axons tipped with a specialized sensing device called a growth cone. The growing axons interact directly with molecules within the environment through which they grow. In order to find their targets, axonal growth cones use guidance molecules that can either attract or repel them. Understanding what these guidance cues are, where they are expressed, and how the growth cone is able to transduce their signal in a directionally specific manner is essential to understanding how the functional brain is constructed. In this chapter, we review what is known about the mechanisms involved in axonal guidance. We discuss how the growth cone is able to sense and respond to its environment and how it is guided by pioneering cells and axons. As examples, we discuss current models for the development of the spinal cord, the cerebral cortex, and the visual and olfactory systems.
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Affiliation(s)
- Céline Plachez
- Department of Anatomy and Neurobiology, University of Maryland, School of Medicine, Baltimore, Maryland 21201, USA
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14
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Tran TS, Cohen-Cory S, Phelps PE. Embryonic GABAergic spinal commissural neurons project rostrally to mesencephalic targets. J Comp Neurol 2004; 475:327-39. [PMID: 15221949 DOI: 10.1002/cne.20166] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Although spinal commissural neurons serve as a model system for studying the mechanisms that underlie axonal pathfinding during development, little is known about their synaptic targets. Previously we identified a group of ventromedially located commissural neurons in rat spinal cord that are gamma-aminobutyric acid (GABA)-ergic and express L1 CAM on their axons. In this study, serial sagittal sections of embryos (E12-15) were processed for glutamic acid decarboxylase (GAD)-65 and L1 immunocytochemistry and showed labeled commissural axons coursing rostrally within the ventral marginal zone. Both GAD65- and L1-positive axons extended rostrally out of the spinal cord into the central part of the medulla and then into the midbrain. GAD65-positive axons branched and ended abruptly within the lateral midbrain. To determine the targets of these ventral commissural neurons, embryos (E13-15) were injected with DiI into the ventromedial spinal cord. At all three ages, DiI-labeled axons projected rostrally in the contralateral ventral marginal zone, turned into the central medulla, and then traveled to the midbrain. DiI-labeled axons appeared to terminate in the lateral midbrain by branching into small, punctate structures. In reciprocal experiments, DiI injected into the lateral midbrain identified an axon pathway that coursed through the brainstem, into the spinal cord ventral marginal zone, and then filled cell bodies in the contralateral ventromedial spinal cord. A spatial and temporal coincidence was apparent between the GAD65/L1- and the DiI-labeled pathways. Together these findings suggest that some GABAergic commissural neurons are early projection neurons to midbrain targets and most likely represent a spinomesencephalic pathway to the midbrain reticular formation.
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Affiliation(s)
- Tracy S Tran
- Department of Physiological Science, University of California, Los Angeles, Los Angeles, California 90095, USA
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15
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Abstract
During spinal cord development, commissural neurons extend their axons ventrally, away from the roof plate. The roof plate is the source of a diffusible repellent that orients commissural axons in vitro and, thus, may regulate the trajectory of commissural axons in vivo. Of three Bmps expressed in the roof plate, BMP7, but not BMP6 or GDF7, mimics the roof plate activity in vitro. We show here that expression of both Bmp7 and Gdf7 by roof plate cells is required for the fidelity of commissural axon growth in vivo. We also demonstrate that BMP7 and GDF7 heterodimerize in vitro and that, under these conditions, GDF7 enhances the axon-orienting activity of BMP7. Our findings suggest that a GDF7:BMP7 heterodimer functions as a roof plate-derived repellent that establishes the initial ventral trajectory of commissural axons.
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Affiliation(s)
- Samantha J Butler
- Department of Physiology and Cellular Biophysics, Center for Neurobiology and Behavior, Columbia University, New York, NY 10032, USA
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16
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Gross MK, Dottori M, Goulding M. Lbx1 specifies somatosensory association interneurons in the dorsal spinal cord. Neuron 2002; 34:535-49. [PMID: 12062038 DOI: 10.1016/s0896-6273(02)00690-6] [Citation(s) in RCA: 301] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Association and relay neurons that are generated in the dorsal spinal cord play essential roles in transducing somatosensory information. During development, these two major neuronal classes are delineated by the expression of the homeodomain transcription factor Lbx1. Lbx1 is expressed in and required for the correct specification of three early dorsal interneuron populations and late-born neurons that form the substantia gelatinosa. In mice lacking Lbx1, cells types that arise in the ventral alar plate acquire more dorsal identities. This results in the loss of dorsal horn association interneurons, excess production of commissural neurons, and disrupted sensory afferent innervation of the dorsal horn. Lbx1, therefore, plays a critical role in the development of sensory pathways in the spinal cord that relay pain and touch.
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Affiliation(s)
- Michael K Gross
- Molecular Neurobiology Laboratory, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA
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17
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Rash BG, Richards LJ. A role for cingulate pioneering axons in the development of the corpus callosum. J Comp Neurol 2001; 434:147-57. [PMID: 11331522 DOI: 10.1002/cne.1170] [Citation(s) in RCA: 112] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In many vertebrate and invertebrate systems, pioneering axons play a crucial role in establishing large axon tracts. Previous studies have addressed whether the first axons to cross the midline to from the corpus callosum arise from neurons in either the cingulate cortex (Koester and O'Leary [1994] J. Neurosci. 11:6608-6620) or the rostrolateral neocortex (Ozaki and Wahlsten [1998] J. Comp. Neurol. 400:197-206). However, these studies have not provided a consensus on which populations pioneer the corpus callosum. We have found that neurons within the cingulate cortex project axons that cross the midline and enter the contralateral hemisphere at E15.5. By using different carbocyanine dyes injected into either the cingulate cortex or the neocortex of the same brain, we found that cingulate axons crossed the midline before neocortical axons and projected into the contralateral cortex. Furthermore, the first neocortical axons to reach the midline crossed within the tract formed by these cingulate callosal axons, and appeared to fasciculate with them as they crossed the midline. These data indicate that axons from the cingulate cortex might pioneer a pathway for later arriving neocortical axons that form the corpus callosum. We also found that a small number of cingulate axons project to the septum as well as to the ipsilateral hippocampus via the fornix. In addition, we found that neurons in the cingulate cortex projected laterally to the rostrolateral neocortex at least 1 day before the neocortical axons reach the midline. Because the rostrolateral neocortex is the first neocortical region to develop, it sends the first neocortical axons to the midline to form the corpus callosum. We postulate that, together, both laterally and medially projecting cingulate axons may pioneer a path for the medially directed neocortical axons, thus helping to guide these axons toward and across the midline during the formation of the corpus callosum.
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Affiliation(s)
- B G Rash
- The University of Maryland, Baltimore, School of Medicine, Department of Anatomy and Neurobiology, and the Program in Neuroscience, Baltimore, Maryland 21201, USA
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18
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Orlino EN, Wong CM, Phelps PE. L1 and GAD65 are expressed on dorsal commissural axons in embryonic rat spinal cord. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2000; 125:117-30. [PMID: 11154767 DOI: 10.1016/s0165-3806(00)00087-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Using immunocytochemical methods, the cell adhesion molecule L1 was detected on axons crossing in the dorsal commissure of developing rat spinal cord. Immunoreactive axons were found in locations similar to fiber bundles illustrated by Ramón y Cajal and designated the anterior, middle and posterior bundles of the dorsal commissure. L1-immunoreactive dorsal commissural axons were first observed on embryonic day 17 (E17), appeared more numerous by E19, and remained detectable in early postnatal ages. The massive middle axon bundles extended bilaterally from the dorsolateral funiculi towards the midline and crossed in the central part of the commissure. In horizontal sections, bundles of L1-labeled middle axons were observed to traverse the dorsal commissure in a periodic pattern along the entire rostrocaudal extent of the spinal cord. Bundles of glutamic acid decarboxylase (GAD65)-positive axons were detected crossing in the middle and posterior regions of the dorsal commissure between E17 and E20. Results from double-labeling experiments demonstrated that GAD65-positive fibers were embedded in larger bundles of L1-labeled axons and that some dorsal commissural axons were double-labeled. To determine if there were axons crossing in the dorsal commissure that did not express L1, double-labeling experiments were conducted using neurofilament and L1 antibodies. Results indicated that bundles of axons identified with anti-neurofilament antibodies were also L1-positive, whereas individually coursing axons within the commissure were L1-negative. The predominance of L1 on fiber bundles traversing the dorsal commissure adds to the growing evidence that this molecule may play a role in axon outgrowth and fasciculation.
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Affiliation(s)
- E N Orlino
- Department of Physiological Science, UCLA, Box 951527, Los Angeles, CA 90095-1527, USA
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19
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Augsburger A, Schuchardt A, Hoskins S, Dodd J, Butler S. BMPs as mediators of roof plate repulsion of commissural neurons. Neuron 1999; 24:127-41. [PMID: 10677032 DOI: 10.1016/s0896-6273(00)80827-2] [Citation(s) in RCA: 206] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
During spinal cord development, commissural (C) neurons, located near the dorsal midline, send axons ventrally and across the floor plate (FP). The trajectory of these axons toward the FP is guided in part by netrins. The mechanisms that guide the early phase of C axon extension, however, have not been resolved. We show that the roof plate (RP) expresses a diffusible activity that repels C axons and orients their growth within the dorsal spinal cord. Bone morphogenetic proteins (BMPs) appear to act as RP-derived chemorepellents that guide the early trajectory of the axons of C neurons in the developing spinal cord: BMP7 mimics the RP repellent activity for C axons in vitro, can act directly to collapse C growth cones, and appears to serve an essential function in RP repulsion of C axons.
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Affiliation(s)
- A Augsburger
- Department of Physiology and Cellular Biophysics, Columbia University, New York, New York 10032, USA
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20
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Phelps PE, Alijani A, Tran TS. Ventrally located commissural neurons express the GABAergic phenotype in developing rat spinal cord. J Comp Neurol 1999. [DOI: 10.1002/(sici)1096-9861(19990628)409:2<285::aid-cne9>3.0.co;2-7] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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21
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Ohyama K, Kawano H, Kawamura K. Localization of extracellular matrix molecules, integrins and their regulators, TGF betas, is correlated with axon pathfinding in the spinal cord of normal and Danforth's short tail mice. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1997; 103:143-54. [PMID: 9427478 DOI: 10.1016/s0165-3806(97)81790-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
To clarify the roles of extracellular matrix molecules (ECMs) and their receptors, integrins, in axonal pathfinding, their spatiotemporal localization was studied immunohistochemically in the developing mouse spinal cord. Immunoreactivities for collagen type IV (Col IV), laminin, integrins (alpha2, alpha3 and beta1 subunits), and transforming growth factor (TGF) betas (TGF beta2 and TGF beta3), putative regulators of gene expression of these molecules, were localized on the midline of the ventral spinal cord, or the 'floor plate', in normal ICR mice. These immunoreactions appeared at embryonic day 9 (E9), when commissural axons began to cross the floor plate, and peaked at E13-E14 when more axons crossed, turned rostrally, and projected longitudinally. At this stage, TAG-1-immunopositive commissural axons passed through the floor plate region. Longitudinal axons, on the other hand, projected ipsilaterally parallel to the midline. Immunoreactions for ECMs, integrins and TGF betas were weakly positive at the midline until postnatal day 0 (P0), after which they decreased markedly. In Danforth's short tail (Sd) heterozygous mutants with discontinuous floor plates, immunoreactions for ECMs, integrins, and TGF betas were not detected at P0. Few crossing axons were seen at this stage, and longitudinally ascending axons crossed via aberrant paths in these regions. These results suggest that the restricted localization of ECMs, integrins, and TGF betas at the floor plate is involved in the pathfinding of commissural and longitudinal axons.
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Affiliation(s)
- K Ohyama
- Department of Anatomy, School of Medicine, Keio University, Tokyo, Japan.
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22
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Keller-Peck CR, Mullen RJ. Altered cell proliferation in the spinal cord of mouse neural tube mutants curly tail and Pax3 splotch-delayed. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1997; 102:177-88. [PMID: 9352100 DOI: 10.1016/s0165-3806(97)00095-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The mutant mouse strains splotch-delayed (Pax3Sp-d) and curly tail (ct) develop neural tube defects (NTDs) in the lumbosacral region of the neuraxis. Some research has focused on cell proliferation around the time of posterior neuropore closure in these mutants; however, there are little data on the effects of NTDs on cell birth at later stages of development. To investigate the role neural tube closure might play in cytogenesis of the spinal cord, the thymidine analog 5-bromo-2'-deoxyuridine (BrdU) was injected into pregnant splotch-delayed and curly tail mice at various stages of gestation. The mean number of labelled cells in the dorsal and ventral halves of spina bifida and control embryos was then calculated per section and per mm2. Mutagenically separated PCR (MS-PCR), was used to ascertain the genotype of splotch-delayed embryos. Our data indicate that the peak proliferation dates, for both the dorsal and ventral regions of the cord, are similar in spina bifida and control embryos. However, the quantity of proliferation is significantly different between affected and unaffected embryos. In general, there are markedly fewer cells born in spina bifida embryos in early neural tube development, followed by a short period of equal proliferation, and culminating in a significant increase in cell proliferation later in gestation. This increase in proliferation results in a greater number of cells being born in spina bifida embryos compared to controls. Several possible explanations for this phenomenon are considered, including the hypothesis that the roof plate, or other factors induced by neural tube closure, might have an anti-mitotic activity.
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Affiliation(s)
- C R Keller-Peck
- Department of Neurobiology and Anatomy, University of Utah School of Medicine, Salt Lake City 84132, USA
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23
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Abstract
Netrin-1 has profound in vitro effects on the growth properties of vertebrate embryonic axons. In addition, netrin-1 mRNA is found in the floor plate of the embryonic nervous system, an intermediate target of many axons, including commissural axons that are affected by netrin-1 in vitro. Moreover, genetic studies of netrin-1 homologs in Caenorhabditis elegans and Drosophila implicate these proteins in commissure formation. We raised polyclonal antisera that recognize chick netrin-1 in fixed tissue sections. The antisera were used to immunohistochemically map netrin-1 in the embryonic spinal cord, brain, and retina. The relationship between netrin-1 localization and the growth of pioneering axons suggests roles for netrin-1 in the regulation of circumferential, commissural, and longitudinal axon growth in the spinal cord and brain. The data also suggest that the primary or sole effect of netrin-1 on pioneering spinal cord commissural axons is haptotactic. Furthermore, the pattern of netrin-1 localization raises the possibility that this protein helps mediate neuronal migration in the spinal cord, brain, and retina.
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24
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Jungbluth S, Koentges G, Lumsden A. Coordination of early neural tube development by BDNF/trkB. Development 1997; 124:1877-85. [PMID: 9169835 DOI: 10.1242/dev.124.10.1877] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Neurotrophins signal through members of the trk family of tyrosine kinase receptors and are known to regulate several neuronal properties. Although initially characterized by their ability to prevent naturally occurring cell death of subsets of neurons during development, neurotrophins can also regulate the proliferation and differentiation of precursor cells. Here we report a novel involvement of neurotrophins in early development of the neural tube. We demonstrate that a functional trkB receptor is expressed by motor neuron progenitors in the ventral neural tube and that treatment of ventral neural tube explants with the trkB ligand Brain-Derived Neurotrophic Factor (BDNF) leads to a significant increase in the number of motor neurons. The only BDNF expression detectable at this stage is by a subset of ventrally projecting interneurons in the dorsal neural tube; ablating this region in vivo leads to a reduction of motor neuron numbers. This loss can be prevented by simultaneous treatment with BDNF. We propose that BDNF produced by dorsal interneurons stimulates proliferation and/or differentiation of motor neuron progenitors after anterograde axonal transport and release in proximity to the trkB-expressing motor neuron precursors, thereby coordinating development between dorsal and ventral regions of the neural tube.
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Affiliation(s)
- S Jungbluth
- Department of Developmental Neurobiology, United Medical and Dental School, Guy's Hospital, London, UK
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25
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Abstract
A battery of antibodies was used to assess development of the spinal cord and its neurons in mouse embryos with neural tube defects (NTDs). The two mutant strains examined, curly tail (ct) and splotch-delayed (Pax3Sp-d), develop an open neural tube for unrelated reasons, and thus provided for a complementary analysis. Five percent of embryos homozygous for the ct gene and 89% of embryos homozygous for the Pax3Sp-d gene develop spina bifida in the lumbosacral region of the neuraxis. Expression of several neuronal antigens, including Islet-1/2, polysialylated neural cell adhesion molecule (NCAM), neurofilaments, and a neuronal-specific nuclear protein (Neu-N) recognized by monoclonal antibody A60, were used as indicators of the level of differentiation of neuronal tissue. Immunohistochemical labeling suggests that early (embryonic days 12-15) neuronal differentiation in the dorsal and ventral region of the dysraphic neural tube occurs remarkably normally in both of the mutants. Similarly, labeling with antibodies to NCAM and neuroafilaments indicate that axonal development during early neurogenesis is unperturbed. Later stages of neuronal maturation, however, do not occur in the usual manner. Instead, the neuronal tissue begins a prodigious degeneration at embryonic day 17 (E17), so that by E18 only a rudimentary tissue remains. These results suggest that the aberrant morphology of the neural tube does not affect neuronal differentiation. However, the anomalous morphological and chemical environment may contribute to the neuronal degeneration observed at later stages.
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Affiliation(s)
- C R Keller-Peck
- Department of Neurobiology and Anatomy, University of Utah School of Medicine, Salt Lake City 84132, USA
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26
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Berki AC, O'Donovan MJ, Antal M. Developmental expression of glycine immunoreactivity and its colocalization with GABA in the embryonic chick lumbosacral spinal cord. J Comp Neurol 1995; 362:583-96. [PMID: 8636469 DOI: 10.1002/cne.903620411] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The development of immunoreactivity for the putative inhibitory amino acid neurotransmitter glycine was investigated in the embryonic and posthatched chick lumbosacral spinal cord by using postembedding immunocytochemical methods. Glycine immunoreactive perikarya were first observed at embryonic day 8 (E8) both in the dorsal and ventral gray matters. The number of immunostained neurons sharply increased by E10 and was gradually augmented further at later developmental stages. The general pattern of glycine immunoreactivity characteristic of mature animals had been achieved by E12 and was only slightly altered afterward. Most of the immunostained neurons were located in the presumptive deep dorsal horn (laminae IV-VI) and lamina VII, although glycine-immunoreactive neurons were scattered throughout the entire extent of the spinal gray matter. By using some of our previously obtained and published data concerning the development of gamma-aminobutyric acid (GABA)-ergic neurons in the embryonic chick lumbosacral spinal cord, we have compared the numbers, sizes, and distribution of glycine- and GABA-immunoreactive spinal neurons at various developmental stages and found the following marked differences in the developmental characteristics of these two populations of putative inhibitory interneurons. (i) GABA immunoreactivity was expressed very early (E4), whereas immunoreactivity for glycine appeared relatively late (E8) in embryonic development. (ii) In the ventral horn, GABA immunoreactivity declined, whereas immunoreactivity for glycine gradually increased from E8 onward in such a manner that the sum of glycinergic and GABAergic perikarya remained constant during the second half of embryonic development. (iii) Glycinergic and GABAergic neurons showed different distribution patterns in the spinal gray matter throughout the entire course of embryogenesis as well as in the posthatched animal. When investigating the colocalization of glycine and GABA immunoreactivities, perikarya immunostained for both amino acids were revealed at all developmental stages from E8 onward, and the proportions of glycine- and GABA-immunoreactive neurons that were also immunostained for the other amino acid were remarkably constant during development. The characteristic features of the development of the investigated putative inhibitory spinal interneurons are discussed and correlated with previous neuroanatomical and physiological studies.
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Affiliation(s)
- A C Berki
- Department of Anatomy, University Medical School, Debrecen, Hungary
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27
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Phelps PE, Vaughn JE. Commissural fibers may guide cholinergic neuronal migration in developing rat cervical spinal cord. J Comp Neurol 1995; 355:38-50. [PMID: 7636012 DOI: 10.1002/cne.903550107] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The present investigation examines the role of intercellular relationships in the guidance of neuronal migration in embryonic rat cervical spinal cord. A "U-shaped" group of cholinergic neurons, was first detected on embryonic days (E) 15.5-16 surrounding the ventral proliferative zone. At these stages, no cholinergic cells were observed in the dorsal spinal cord, but by E17, many of the "U-shaped" group of cholinergic cells appeared to have translocated dorsally, to become the cholinergic dorsal horn cells seen in older animals. Between E16 and E17, these choline acetyltransferase (ChAT)-immunoreactive cells displayed primitive processes oriented dorsoventrally, suggesting migration along that axis. Two early forming substrates present in embryonic spinal cord have been implicated in the guidance of other populations of migrating neurons: glial cells organized in radial arrays and commissural axons aligned along the dorsoventral axis. Involvement of the commissural fibers with cholinergic cell migration seems more likely because the fibers and the translocation pathway have similar orientations. In double-labeling immunocytochemical studies of E15.5-17 spinal cord, some immature ChAT-containing neurons were directly adjacent to commissural fibers, as identified by SNAP/TAG-1 immunoreactivity. The temporal and spatial coincidence of developing cholinergic neurons and commissural axons is consistent with the hypothesis that these neurons could use commissural fibers as migratory guides. In addition, conventional electron micrographs were examined to determine if immature neuronal profiles were physically apposed to commissural axons. Immature neurons with leading and trailing processes oriented dorsally and ventrally, respectively, were embedded within and aligned along bundles of commissural fibers or along other similarly oriented neurons. This direct apposition of immature cells to the surfaces of commissural axons and other bipolar neurons is consistent with the hypothesis that the "U-shaped" group of cholinergic neurons may use commissural axons and other cohort neurons for guidance during their dorsal migration.
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Affiliation(s)
- P E Phelps
- Division of Neurosciences, Beckman Research Institute of the City of Hope, Duarte, California 91010-0269, USA
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28
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Abstract
The early development of the uncrossed tectobulbar and the crossed tectospinal tracts was studied. These two projections arise from the same structure, the mesencephalon, and develop during the same time period, but follow divergent courses. We have traced the pathways followed by these projections and identified the positions at which axon guidance decisions are made. The first neurons differentiate either side of the entire rostrocaudal extent of the dorsal midline and initiate axons that extend dorsoventrally across the surface of the tectum. At the ventral edge of the tectum these axons turn abruptly and fasciculate to form a caudal descending projection to the hindbrain. These axons extend to the caudal hindbrain and do not project to the periphery along cranial nerve roots. We therefore consider this tract to be the tectobular, rather than the mesencephalic division of the trigeminal. While the tectobulbar projection is still developing, a second wave of axons is initiated, which arises from only the rostral part of the tectum. These axons grow beyond the tectobulbar turn point and continue toward the ventral midline, where they cross the floor plate, before turning caudally at the lateral edge of the main descending hindbrain tract, the ventrolateral tract. We discuss the development of these tracts with reference to possible guidance cues mediating their course.
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Affiliation(s)
- I T Shepherd
- Department of Human Anatomy, University of Oxford, United Kingdom
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29
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Drenhaus U, Rager G. Formation of alternating tiers in the optic chiasm of the chick embryo. Anat Rec (Hoboken) 1994; 240:555-71. [PMID: 7879907 DOI: 10.1002/ar.1092400413] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
BACKGROUND When the fibers of the two optic nerves of the chick cross to the contralateral side at the prospective chiasmatic region, they segregate into clearly defined bundles. These bundles form horizontally oriented tiers which alternate between the right and the left optic nerve. METHODS We have analyzed the development of these tiers qualitatively and quantitatively using light and electron microscopy between embryonic days (E) 4 and E19. RESULTS The formation of the chiasm begins on E4. In the course of E4, tiers become visible for the first time. Their number increases rapidly until E7. Then the increase is slowed down and the final value (32 +/- 1) is approximated by E18/19. Growing axons allow one to distinguish three different segments: the growth cone, the distal, and the proximal segment. The latter originates in the perikaryon. Growth cones and distal segments are found predominantly in the ventralmost tiers. Their frequency decreases from ventral to dorsal. Proximal segments which indicate the presence of older axons appear first in the dorsal tiers and later also in more ventrally located tiers. CONCLUSION Based on these criteria it is concluded that newly formed axons contribute primarily but not exclusively to the ventral tiers. There is a gradient of maturity of axons from ventral to dorsal whose slope becomes steeper with age until the last growth cones have arrived by E18. Thus, the formation of the chiasm corresponds to the spatiotemporal pattern of ganglion cell formation in the retina. The process of cell death of retinal ganglion cells is also seen in the chiasm but probably does not lead to a transitory diminution in the number of tiers.
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Affiliation(s)
- U Drenhaus
- Institut für Anatomie und Spezielle Embryologie, Fribourg, Switzerland
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Bush MS, Gordon-Weeks PR. Distribution and expression of developmentally regulated phosphorylation epitopes on MAP 1B and neurofilament proteins in the developing rat spinal cord. JOURNAL OF NEUROCYTOLOGY 1994; 23:682-98. [PMID: 7532215 DOI: 10.1007/bf01181643] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The distribution and expression of developmentally regulated phosphorylation epitopes on the microtubule-associated protein 1B and on neurofilament proteins recognized by monoclonal antibody (mAb) 150 and mAb SMI-31 was investigated in the developing rat spinal cord. In the embryonic day 11 spinal cord, mAb 150 stained the first axons to appear, whereas mAb SMI-31 staining did not appear until embryonic day 12. At the start of axonogenesis, mAb 150 stained neuronal cell bodies and axons whereas at later times only the distal axon was stained, this is the first demonstration in vivo of a mAb 150 axonal gradient similar to that seen previously in vitro (Mansfield et al., 1991). During the postnatal period, axonal staining by mAb 150 dramatically declined so that by the third postnatal week, only the corticospinal tract, which contains axons that are still growing, was labelled. There was no evidence of dendritic staining except of adult primary motoneurons. In contrast, mAb SMI-31 staining of axons was not present as a gradient. Instead, mAb SMI-31 staining increased progressively throughout this period, persisted into adulthood and was shown by immunoblotting to be related to the increased phosphorylation of the medium and heavy neurofilament proteins. Axonal staining by mAb 150 re-appears in a sub-population of the SMI-31-labelled myelinated axons in the adult spinal cord and PNS and in the perikarya and dendrites of primary motoneurons, where it probably recognizes a phosphorylation epitope on heavy neurofilament proteins. This late appearing epitope has some similarities to that recognized by mAb SMI-31 on neurofilaments, but it is not identical. These cross-reactivities of mAbs that recognize phosphorylation epitopes on otherwise unrelated proteins dictate caution in interpreting immunohistochemical data. It may now be necessary in some cases to re-appraise published studies using these two antibodies.
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Affiliation(s)
- M S Bush
- Developmental Biology Research Centre, Randall Institute, King's College, London, UK
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Yaginuma H, Shiga T, Oppenheim RW. Early developmental patterns and mechanisms of axonal guidance of spinal interneurons in the chick embryo spinal cord. Prog Neurobiol 1994; 44:249-78. [PMID: 7886227 DOI: 10.1016/0301-0082(94)90041-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- H Yaginuma
- Department of Anatomy, University of Tsukuba, Japan
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Hirano S, Tanaka H. Immunohistochemical Analysis of the Development of the Floor Plate- and Notochord-Deprived Neural Tube. (basement membrane/immunohistochemistry/motoneuron development/alar plate/basal plate/chick embryo). Dev Growth Differ 1994. [DOI: 10.1111/j.1440-169x.1994.00481.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Kennedy TE, Serafini T, de la Torre JR, Tessier-Lavigne M. Netrins are diffusible chemotropic factors for commissural axons in the embryonic spinal cord. Cell 1994; 78:425-35. [PMID: 8062385 DOI: 10.1016/0092-8674(94)90421-9] [Citation(s) in RCA: 1030] [Impact Index Per Article: 34.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The guidance of axons to their targets in the developing nervous system is believed to involve diffusible chemotropic factors secreted by target cells. Floor plate cells at the ventral midline of the spinal cord secrete a diffusible factor or factors that promotes the outgrowth of spinal commissural axons and attracts these axons in vitro. Two membrane-associated proteins isolated from brain, netrin-1 and netrin-2, possess commissural axon outgrowth-promoting activity. We show here that netrin-1 RNA is expressed by floor plate cells, whereas netrin-2 RNA is detected at lower levels in the ventral two-thirds of the spinal cord, but not the floor plate. Heterologous cells expressing recombinant netrin-1 or netrin-2 secrete diffusible forms of the proteins and can attract commissural axons at a distance. These results show that netrin-1 is a chemotropic factor expressed by floor plate cells and suggest that the two netrin proteins guide commissural axons in the developing spinal cord.
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Affiliation(s)
- T E Kennedy
- Howard Hughes Medical Institute, Department of Anatomy, University of California, San Francisco 94143-0452
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Serafini T, Kennedy TE, Galko MJ, Mirzayan C, Jessell TM, Tessier-Lavigne M. The netrins define a family of axon outgrowth-promoting proteins homologous to C. elegans UNC-6. Cell 1994; 78:409-24. [PMID: 8062384 DOI: 10.1016/0092-8674(94)90420-0] [Citation(s) in RCA: 1042] [Impact Index Per Article: 34.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
In vertebrates, commissural axons pioneer a circumferential pathway to the floor plate at the ventral midline of the embryonic spinal cord. Floor plate cells secrete a diffusible factor that promotes the outgrowth of commissural axons in vitro. We have purified from embryonic chick brain two proteins, netrin-1 and netrin-2, that each possess commissural axon outgrowth-promoting activity, and we have also identified a distinct activity that potentiates their effects. Cloning of cDNAs encoding the two netrins shows that they are homologous to UNC-6, a laminin-related protein required for the circumferential migration of cells and axons in C. elegans. This homology suggests that growth cones in the vertebrate spinal cord and the nematode are responsive to similar molecular cues.
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Affiliation(s)
- T Serafini
- Howard Hughes Medical Institute, Department of Anatomy, University of California, San Francisco 94143-0452
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35
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Antal M, Berki AC, Horváth L, O'Donovan MJ. Developmental changes in the distribution of gamma-aminobutyric acid-immunoreactive neurons in the embryonic chick lumbosacral spinal cord. J Comp Neurol 1994; 343:228-36. [PMID: 8027440 DOI: 10.1002/cne.903430204] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The development of gamma-aminobutyric acid (GABA)-immunoreactive neurons was investigated in the embryonic and posthatch chick lumbosacral spinal cord by using pre- and postembedding immunostaining with an anti-GABA antiserum. The first GABA-immunoreactive cells were detected in the ventral one-half of the spinal cord dorsal to the lateral motor column at E4. GABAergic neurons in this location sharply increased in number and, with the exception of the lateral motor column, appeared throughout the entire extent of the ventral one-half of the spinal gray matter by E6. Thereafter, GABA-immunoreactive neurons extended from ventral to dorsal regions. Stained perikarya first appeared at E8 and then progressively accumulated in the dorsal horn, while immunoreactive neurons gradually declined in the ventral horn. The general pattern of GABA immunoreactivity characteristic of mature animals had been achieved by E12 and was only slightly altered afterwards. In the dorsal horn, most of the stained neurons were observed in laminae I-III, both at the upper (LS 1-3) and at the lower (LS 5-7) segments of the lumbosacral spinal cord. In the ventral horn, the upper and lower lumbosacral segments showed marked differences in the distribution of stained perikarya. GABAergic neurons were scattered in a relatively large region dorsomedial to the lateral motor column at the level of the upper lumbosacral segments, whereas they were confined to the dorsalmost region of lamina VII at the lower segments. The early expression of GABA immunoreactivity may indicate a trophic and synaptogenetic role for GABA in early phases of spinal cord development.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Antal
- Department of Anatomy, University Medical School, Debrecen, Hungary
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36
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Campbell RM, Peterson AC. Expression of a lacZ transgene reveals floor plate cell morphology and macromolecular transfer to commissural axons. Development 1993; 119:1217-28. [PMID: 8306884 DOI: 10.1242/dev.119.4.1217] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The floor plate is situated at the ventral midline of the neural tube and is an important intermediate target for commissural axons. During elongation, these axons converge bilaterally on the ventral midline neural tube and after crossing the floor plate make an abrupt rostral turn. Ample evidence indicates that the initial projection of commissural axons to the floor plate is guided by a chemotropic factor secreted by floor plate cells. However, the way in which the subsequent interaction of these axons with the floor plate leads them to make further trajectory changes remains undefined. In an effort to gain further understanding of the structure and function of floor plate cells, we have taken advantage of a line of transgenic mice in which these cells express beta-galactosidase and thus can be stained by histochemical means. In this line, a genomic imprinting mechanism restricts the expression of the lacZ transgene to only a proportion of the floor plate cells, allowing their morphology to be appreciated with particular clarity. Our analysis revealed that the basal processes of floor plate cells are flattened in their rostrocaudal dimension and possess fine lateral branches which are aligned with commissural axons. Unexpectedly, beta-galactosidase activity was also detected within longer transverse linear profiles traversing the floor plate whose ultrastructural appearance was not that of floor plate cells but instead corresponded to that of commissural axons. Enzyme activity was not detected in more proximal axonal segments or in the neuronal cell bodies from which these axons originated. Therefore, we propose that the transgene product, and potentially other proteins synthesized by floor plate cells, can be transferred to decussating axons.
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Affiliation(s)
- R M Campbell
- Division of Experimental Medicine, Faculty of Medicine, McGill University, Montreal, Quebec, Canada
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37
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Phelps PE, Barber RP, Vaughn JE. Embryonic development of rat sympathetic preganglionic neurons: possible migratory substrates. J Comp Neurol 1993; 330:1-14. [PMID: 8468397 DOI: 10.1002/cne.903300102] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Spinal somatic and autonomic (sympathetic preganglionic) motor neurons are generated synchronously and, subsequently, migrate from the ventricular zone together to form a common primitive motor column. However, these two subsets of motor neurons ultimately express several phenotypic differences, including somal size, peripheral targets, and spinal cord locations. While somatic motor neurons remain ventrally, autonomic motor neurons (AMNs) move both dorsally and medially between embryonic days 14 and 18, when they approximate their final locations in spinal cord. The goal of the present investigation was to determine the potential guidance substrates available to AMNs during these movements. The dorsal translocation was studied in developing upper thoracic spinal cord, because, at this level, the majority of AMNs are located dorsolaterally. Sections were double-labeled by ChAT (choline acetyltransferase) and SNAP/TAG-1 (stage-specific neurite associated protein/transiently expressed axonal surface glycoprotein) immunocytochemistry to visualize motor neurons and the axons of early forming circumferential interneurons, respectively. Results showed that during the developmental stage when AMNs translocated dorsally, SNAP/TAG-1 immunoreactive lateral circumferential axons were physically located along the borders of the AMN region, as well as among its constituent cells. These findings indicate that lateral circumferential axons, as well as the SNAP/TAG-1 molecules contained upon their surfaces, are in the correct spatial and temporal position to serve as guidance substrates for AMNs. The medial translocation was studied in developing lower thoracic-upper lumbar spinal cord, because, at this level, more than half of the AMNs are medially located. Sections were double-labeled by ChAT and vimentin immunocytochemistry to visualize motor neurons and radial glial fibers, respectively. Observations on consecutive developmental days of the medial translocation revealed that AMNs were aligned with parallel arrays of radial glial fibers. Thus, the glial processes could serve as guides for the AMN medial movement. Future experimental analyses will examine whether circumferential axons and radial glial fibers are in fact functioning as migratory guides during AMN development, and, if so, whether specific surface molecules on these guides trigger the subsequent differentiation of AMNs.
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Affiliation(s)
- P E Phelps
- Division of Neurosciences, Beckman Research Institute of City of Hope, Duarte, California 91010-0269
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38
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Goulding MD, Lumsden A, Gruss P. Signals from the notochord and floor plate regulate the region-specific expression of two Pax genes in the developing spinal cord. Development 1993; 117:1001-16. [PMID: 8100762 DOI: 10.1242/dev.117.3.1001] [Citation(s) in RCA: 269] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Members of the paired box (Pax) gene family are expressed in discrete regions of the developing central nervous system, suggesting a role in neural patterning. In this study, we describe the isolation of the chicken homologues of Pax-3 and Pax-6. Both genes are very highly conserved and share extensive homology with the mouse Pax-3 and Pax-6 genes. Pax-3 is expressed in the primitive streak and in two bands of cells at the lateral extremity of the neural plate. In the spinal cord, Pax-6 is expressed later than Pax-3 with the first detectable expression preceding closure of the neural tube. When the neural tube closes, transcripts of both genes become dorsoventrally restricted in the undifferentiated mitotic neuroepithelium. We show that the removal of the notochord, or implantation of an additional notochord, dramatically alter the dorsoventral (DV) expression patterns of Pax-3 and Pax-6. These manipulations suggest that signals from the notochord and floor plate regulate the establishment of the dorsoventrally restricted expression domains of Pax-3 and Pax-6 in the spinal cord. The rapid changes to Pax gene expression that occur in neural progenitor cells following the grafting of an ectopic notochord suggest that changes to Pax gene expression are an early effect of the notochord on spinal cord patterning.
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Affiliation(s)
- M D Goulding
- Department of Molecular Cell Biology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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39
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Abstract
In the hatched chick the fibers of the two optic nerves segregate into clearly defined bundles when they cross to the other side. These bundles run in horizontally oriented tiers. The tiers are demarcated by blood vessels and pial tissue. The organization of these tiers was investigated qualitatively and quantitatively using light and electron microscopy as well as tracer techniques. The fibers within the tiers cross to the contralateral optic tract without leaving their respective tier. The mean total number of tiers is 34 with a great individual variation. A preference in the superposition of one side over the other could not be observed. Comparing these data with our earlier study (Rager et al.: Anat. Embryol., 179:135-148, 1988) it can be concluded that neither the segregation of fibers into discrete bundles nor the variability in the number of alternating tiers seem to disturb the topography of fibers as it is achieved in the optic nerve. The pattern of vascularization correlates with the order of crossing axon bundles and contributes to the demarcation of the tiers. The chiasm is vascularized by the Aa. preopticae and the A. infundibularis.
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Affiliation(s)
- U Drenhaus
- Institut für Anatomie und Spezielle Embryologie, Fribourg, Switzerland
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40
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McCabe CF, Cole GJ. Expression of the barrier-associated proteins EAP-300 and claustrin in the developing central nervous system. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1992; 70:9-24. [PMID: 1473281 DOI: 10.1016/0165-3806(92)90099-i] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Immunohistochemistry of embryonic chick central nervous system (CNS) and immunocytochemistry of retinal cells were performed to compare and map the expression of two barrier-associated molecules. EAP-300 (embryonic avian polypeptide of 300 kDa) and claustrin (a 320 kDa extracellular matrix keratan sulfate proteoglycan) were both transiently expressed in CNS regions that are considered non-permissive to either neuron migration or axon growth. In the developing spinal cord, EAP-300 and claustrin were both expressed by the marginal zone early in development and by the roof plate later in embryogenesis. In the developing rhombencephalon, immunoreactivity for both molecules was also observed first in the marginal zone, and later expression was restricted mostly to the midline. In the mesencephalon, EAP-300 and claustrin were also localized to the midline, and this expression represented a continuation of the expression observed in the spinal cord roof plate and hindbrain ventral midline. In the developing retina and cerebellum, EAP-300 and claustrin were differentially expressed. In retina, EAP-300 and claustrin were expressed by Müller cells and the optic fiber layer, respectively. In cerebellum at embryonic day 12 (E12), EAP-300 was expressed by Bergman glia, but claustrin was not expressed until E15. Immunocytochemical staining of retinal and cerebellar cultures indicated that EAP-300 was expressed by a subset of radial astrocytes, as confirmed by double labeling experiments with a specific marker for radial astrocytes. These data indicate that in the absence of claustrin expression, EAP-300 was expressed specifically by radial astrocytes during developmental periods of neuron migration. Also, the coexpression of EAP-300 and claustrin in CNS regions considered to be non-permissive to neurite extension suggests that these two developmentally regulated proteins may be associated with barrier function in the developing CNS.
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Affiliation(s)
- C F McCabe
- Department of Anatomy and Cell Biology, Medical University of South Carolina, Charleston 29425
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41
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Sumi Y, Dent MA, Owen DE, Seeley PJ, Morris RJ. The expression of tissue and urokinase-type plasminogen activators in neural development suggests different modes of proteolytic involvement in neuronal growth. Development 1992; 116:625-37. [PMID: 1289056 DOI: 10.1242/dev.116.3.625] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Tissue and urokinase-type plasminogen activators are serine proteases with highly restricted specificity, their best characterised role being to release the broad specificity protease plasmin from inactive plasminogen. It has frequently been suggested that these, and similar proteases, are involved in axonal growth and tissue remodelling associated with neural development. To help define what this role might be, we have studied the expression of the plasminogen activators in developing rat nervous tissue. Urokinase-type plasminogen activator mRNA is strongly expressed by many classes of neurons in peripheral and central nervous system. We have analysed its appearance in spinal cord and sensory ganglia, and found the mRNA is detectable by in situ hybridisation very early in neuronal development (by embryonic day 12.5), at a stage compatible with it playing a role in axonal or dendritic growth. Tissue plasminogen activator mRNA, on the other hand, is expressed only by cells of the floor plate in the developing nervous system, from embryonic day 10.5 and thereafter. Immunohistochemical and enzymatic analysis showed that active tissue plasminogen activator is produced by, and retained within, the floor plate. A mechanism is suggested by which high levels of tissue plasminogen activator produced by the stationary cells of the floor plate could influence the direction of growth of commissural axons as they pass through this midline structure.
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Affiliation(s)
- Y Sumi
- Norman and Sadie Lee Centre, Laboratory of Neurobiology, National Institute for Medical Research, London, UK
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42
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Phelan P, Gordon-Weeks PR. Widespread Distribution of Synaptophysin, a Synaptic Vesicle Glycoprotein, in Growing Neurites and Growth Cones. Eur J Neurosci 1992; 4:1180-1190. [PMID: 12106422 DOI: 10.1111/j.1460-9568.1992.tb00143.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Synaptophysin, a 38-kD glycoprotein, is one of the most abundant of the integral membrane proteins of small synaptic vesicles. The protein is widely distributed at synapses throughout the nervous system, where it is believed to be involved in the exocytosis of stored neurotransmitter. We show here that synaptophysin is also widely expressed in growing neurites and growth cones both in vitro and in vivo. In dissociated rat cerebral cortical cultures anti-synaptophysin antiserum (G-95) stains growth cones punctately as soon as they emerge from the cell body. In early cultures all neurites are immunoreactive. Later, synaptophysin is redistributed to become concentrated in axonal varicosities. In developing rat embryos, synaptophysin is expressed in the growing axons of, for instance, the spinal commissural interneurons and the parallel fibres of the cerebellar granule cells long before these neurons have established synaptic connections. These observations suggest that synaptic vesicle proteins like synaptophysin are functionally important in neuronal development.
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Affiliation(s)
- Pauline Phelan
- Developmental Biology Research Centre, Division of Biomedical Sciences, King's College London, 26 - 29 Drury Lane, London WC2B 5RL, UK
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43
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Vaughn JE, Phelps PE, Yamamoto M, Barber RP. Association interneurons of embryonic rat spinal cord transiently express the cell surface glycoprotein SNAP/TAG-1. Dev Dyn 1992; 194:43-51. [PMID: 1421519 DOI: 10.1002/aja.1001940106] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
SNAP/TAG-1 is a 135 kDa glycoprotein of the immunoglobulin superfamily that is transiently expressed upon the surfaces of developing axons. In the embryonic rodent spinal cord, this molecule is expressed by motor neurons, dorsal root ganglion cells, and commissural neurons (Yamamoto et al.: J. Neurosci. 6:3576-3594, 1986; Dodd et al.: Neuron 1:105-116, 1988). The commissural cells are a subset of early-forming dorsal horn interneurons whose axons follow a circumferential course in the embryonic spinal cord. The axons of commissural neurons cross the developing ventral commissure to terminate on contralateral synaptic targets, whereas those of the other subset of circumferential cells, the association interneurons, remain on the same side of the spinal cord to form ipsilateral, terminal synaptic fields. The difference between the axonal trajectories of these two subsets of nerve cells raised the question of whether or not association interneurons would also express the SNAP/TAG-1 epitope and, if so, how would this expression be related to that of the commissural cells. Immunocytochemistry for SNAP/TAG-1 and choline acetyltransferase (ChAT) was used to answer these questions. The results indicated that association interneurons expressed SNAP/TAG-1 epitopes and that this expression began later and lasted longer than that of the commissural neurons. Other new findings of this study included the identification of a lateral subgroup of commissural fibers that expressed SNAP/TAG-1 later than their more medially located counterparts, and these lateral fibers were more pronounced in the thoracic spinal cord than at cervical levels.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J E Vaughn
- Division of Neurosciences, Beckman Research Institute, City of Hope, Duarte, California 91010
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44
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Shiga T, Oppenheim RW. Immunolocalization studies of putative guidance molecules used by axons and growth cones of intersegemental interneurons in the chick embryo spinal cord. J Comp Neurol 1991; 310:234-52. [PMID: 1720141 DOI: 10.1002/cne.903100208] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The earliest developing interneurons in the chick spinal cord can be divided into two groups: neurons in the ventral region whose axons pioneer the primitive longitudinal pathway (PL-cells) and neurons whose axons project circumferentially (C-cells) along the lateral marginal zone and join the ipsilateral or contralateral ventrolateral longitudinal pathways. To begin to examine the molecular cues for axonal pathway formation of these interneurons, we screened a variety of molecules from embryonic day (E) 2 to E6.5 [stage 14-30 of Hamburger and Hamilton (1951) J. Morphol. 88:49-92]. These include cell adhesion and related molecules (G4, F11, neurofascin, N-cadherin, TAG-1-like molecule), extracellular matrix (ECM) molecules (laminin, fibronectin, heparan sulfate proteoglycan, laminin-heparan sulfate proteoglycan complex, and collagen type IV), and receptors for ECM molecules (beta 1-class integrin). PL-cells first expressed neurofascin at stage 14+ before the onset of axonogenesis. When the PL-cells began to extend their axons at stage 15, they expressed G4 and avian TAG-1-like molecules, as well as neurofascin, on both cell bodies and longitudinal axons. In the following stages, PL-cells continued to strongly express neurofascin and G4 on their fasciculating axons, suggesting the involvement of these glycoproteins in growth and fasciculation. C-cells began to express G4 and TAG-1-like molecules on cell bodies and axons at stage 15-16 shortly after axonal growth. In the following stages, C-cells expressed several cell adhesion molecules differentially on their axonal segments. The proximal segment of C-axons in the circumferential pathway strongly expressed a TAG-1-like molecule, whereas the distal segment in the longitudinal pathway strongly expressed G4 and neurofascin. The commissural axonal segment in the floor plate expressed TAG-1-like molecule, neurofascin, N-cadherin, and beta 1-class integrin. The basement membrane around the spinal cord was enriched with ECM glycoproteins (laminin, fibronectin, heparan sulfate proteoglycan, and collagen type IV) during the stages examined (stage 15-27), and commissural C-cell axons became strongly integrin positive in the floor plate where they contacted the basement membrane. These data indicate that interneurons may use multiple molecules during axonal pathway formation, depending on cell type, pathway position, and developmental stage.
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Affiliation(s)
- T Shiga
- Department of Neurobiology and Anatomy, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27157
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45
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Shiga T, Künzi R, Oppenheim RW. Axonal projections and synaptogenesis by supraspinal descending neurons in the spinal cord of the chick embryo. J Comp Neurol 1991; 305:83-95. [PMID: 1709651 DOI: 10.1002/cne.903050109] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Following the injection of horeseradish peroxidase (HRP) into the brachial spinal cord of the chick on embryonic day (E)4.5, retrogradely labeled neurons can be found in the brainstem (Okado and Oppenheim: Journal of Comparative Neurology 232: 143-161, 1985). By contrast, following high cervical spinal transection, functional (behavioral) deficits are not observed until E10 (Oppenheim: Journal of Comparative Neurology 160: 37-50, 1975). To determine whether this temporal difference between projections and function reflects a delay in synaptogenesis, we looked for the presence of anterogradely HRP-labeled pre-synaptic terminals in brachial cord following injection of HRP into the boundary between brainstem and spinal cord at ages between E3.5 and E7. HRP-labeled fibers were observed in the branchial cord by E4.5 and were diffusely distributed in the ventral and lateral marginal zones (presumptive ventral and lateral funiculi, respectively). Although some axo-dendritic and axo-somatic synapses were observed in the brachial cord prior to E6, the presynaptic profiles were always unlabeled by HRP and thus must originate from propriospinal sources. The first HRP-labeled supraspinal synapses were found in the ventral and lateral funiculi on E6. They contained several clear spherical synaptic vesicles and were axo-dendritic in nature. The cells of origin of the postsynaptic dendrites were determined by injecting HRP into the wing-bud to label the brachial motoneurons retrogradely and the presynaptic component was identified as supraspinal by HRP injections into the brainstem/spinal cord boundary to orthogradely label the descending fibers. Several double-labeled axo-dendritic synapses were found in the ventral and lateral funiculi of E6 brachial cord. Therefore, at least some descending supraspinal fibers make synapses directly onto motoneuron dendrites. We conclude that 1) there is a delay of about 1.5 days between the arrival of supraspinal fibers and synapse formation in the brachial cord, 2) the earliest synapses are axo-dendritic in nature, 3) at least some supraspinal fibers make direct contact with motoneuron dendrites as early as E6, and 4) synaptogenesis from propriospinal sources precedes that from supraspinal descending axons. These observations provide evidence indicating that the temporal difference between the onset of projections of supraspinal descending fibers and the onset of their function may be partly owing to delayed synaptogenesis.
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Affiliation(s)
- T Shiga
- Department of Neurobiology and Anatomy, Wake Forest University, Bowman Gray School of Medicine, Winston-Salem, North Carolina 27103
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46
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Abstract
Among the various types of membrane molecules involved in cell-cell interactions in the nervous system, we have focused in this review upon membrane proteins belonging to the immunoglobulin superfamily (IgSF). IgSF molecules are distinctive in that: (1) a large percentage of known neural adhesion molecules belongs to the IgSF; (2) they are homologous in structure (Ig domain), yet exhibit large variation of function in cell-cell interactions. The structure of IgSF molecules is briefly summarized in Section II, and each member of the IgSF which has been found in the nervous system is reviewed in Section III. In Section IV, we have discussed possible properties of yet-unknown nervous system IgSF molecules, on the assumption that nervous system IgSF molecules thus far discovered comprise only a small portion of those existing. Discussion is based upon an analogy with the immune system and upon knowledge of cell-cell interactions in the development of the nervous system. Our principal aims in this review are to summarize knowledge of neural IgSF molecules and to discuss the possibility that some IgSF molecules may encode in their structures instructions for recognizing, or for being recognized by, target neural cells. Further growth of knowledge of IgSF molecules may yield insights into the patterns of cell-cell interactions underlying the formation of neuronal circuits during development.
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Affiliation(s)
- Y Yoshihara
- Department of Neuroscience, Osaka Bioscience Institute, Japan
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47
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Yaginuma H, Homma S, Künzi R, Oppenheim RW. Pathfinding by growth cones of commissural interneurons in the chick embryo spinal cord: a light and electron microscopic study. J Comp Neurol 1991; 304:78-102. [PMID: 2016414 DOI: 10.1002/cne.903040107] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
To investigate putative axonal guidance mechanisms used by commissural interneurons in the chick embryo spinal cord, we have examined growth cone morphology, the microenvironment through which the growth cones advance, and interactions between growth cones and their surroundings. Growth cones of both early and late developing commissural interneurons were examined. The growth cones were visualized by injection of either horseradish peroxidase (HRP) or the fluorescent dye Di-I. Unlabelled growth cones as well as HRP-labelled growth cones were also examined by electron microscopy. The early developing growth cones project circumferentially without fasciculation until they reach the region of the longitudinal pathway in the contralateral ventral funiculus (CVF). In their trajectory towards the floor plate, axons exhibited elaborate growth cones with filopodia and lamellipodia. They projected between processes of neuroepithelial cells within abundant extracellular spaces. Upon arrival at the ipsilateral ventral funiculus, growth cones did not appear to contact preexisting longitudinal axons. Within the floor plate, the growth cones were less complex and lacked long filopodia and exhibited bulbous or varicose shapes with short processes. Electron microscopic observations of the floor plate at this stage revealed that there was only a small amount of extracellular space and that the basal portion of the floor plate cells were directionally oriented (polarized) in the transverse plane. It is of particular interest that contacts between growth cones and the basement membrane in the floor plate were often observed. When the growth cones reached the contralateral ventrolateral region, they again exhibited an elaborate morphology. Close contacts between growth cones and the preexisting contralateral longitudinal axons were observed. Growth cones advancing in the contralateral longitudinal pathway exhibited various shapes and were observed to contact other axons and processes of neuroepithelial cells. Most of the later developing growth cones of commissural cells exhibited lamellipodial shapes irrespective of their location along the circumferential trajectory. Electron microscopic observations revealed that these late developing growth cones always contacted or fasciculated with preexisting axons and that the cellular environment through which they grow is oriented in such a way that the growth cones appear to be guided in specific directions. Growth cones entering the CVF exhibited more elaborated shapes with ramified lamellipodia that made multiple contacts with preexisting longitudinal axons. The present results indicate that differential axonal guidance mechanisms may be employed along the pathway followed by spinal commissural interneurons and that axons and growth cones projecting along this pathway at different developmental stages employ different mechanisms for pathfinding and guidance.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- H Yaginuma
- Department of Neurobiology and Anatomy, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27103
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Jostes B, Walther C, Gruss P. The murine paired box gene, Pax7, is expressed specifically during the development of the nervous and muscular system. Mech Dev 1990; 33:27-37. [PMID: 1982921 DOI: 10.1016/0925-4773(90)90132-6] [Citation(s) in RCA: 311] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Eight murine paired box-containing (Pax) genes have been isolated so far. The gene described here, Pax7, contains not only a paired box, but also an octapeptide and a paired-type homeobox. As shown by Northern and in situ analysis, Pax7 is expressed from day 8 to 17 p.c. during embryogenesis. At early stages Pax7 transcripts are present in a subset of cells throughout the entire brain, but later in development expression is limited to the mesencephalon. In the developing neural tube Pax7 is restricted to the dorsal ventricular zone along the entire antero-posterior axis, suggesting a role for Pax7 in the formation of certain parts of the CNS. Additionally Pax7 expression can be followed during myogenesis from the dermamyotome of the somites to the skeletal muscle tissues.
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Affiliation(s)
- B Jostes
- Department of Molecular Cell Biology, Max Planck Institute of Biophysical Chemistry, Göttingen, F.R.G
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49
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Kröger S, Niehörster L. Isolation, characterization, and substrate properties of the external limiting membrane from the avian embryonic optic tectum. J Neurosci Res 1990; 27:169-83. [PMID: 2254962 DOI: 10.1002/jnr.490270207] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The external limiting membrane of the avian embryonic optic tectum is isolated by mechanically separating the neuronal mesencephalon from the overlying mesenchymal tissue. The preparation consists of a basal lamina which is covered on its neural side by endfeet of neuroepithelial cells and has attached to it on its meningeal side a collageneous stroma, containing blood vessels. The external limiting membrane can be flat-mounted on a piece of nitrocellulose filter as mechanical support. It covers an area between 0.3 and 1 cm2, depending on the age of the donor embryo. The endfeet can be removed together with all cellular components of the meninges by treatment with 2% Triton-X-100 or with distilled water. The basal lamina itself is approximately 80 nm thick and consists of two laminae rarae and a central lamina densa. Immunohistochemical staining reveals that the basal lamina in the embryo, after isolation and after detergent extraction of the isolated preparation, contains type IV collagen, nidogen, laminin, and low density heparan sulfate proteoglycan as do other basement membranes. Antibodies against the neural cell adhesion molecule (N-CAM), chondroitin sulfate proteoglycan, and fibronectin fail to stain the external limiting membrane, but these proteins were clearly identified in the blood vessel-containing meninges or in the optic tectum. The flat-mounted external limiting membrane preparation was used as substrate to culture several different neural tissues of central and peripheral origin. Explants of neural crest cells, dorsal root ganglia, and sympathetic ganglia can be cultured on the external limiting membrane. All explants grow well on the basal lamina preparations whether the endfeet are attached or detergent-extracted prior to explantation; however, neurite outgrowth from sympathetic ganglia is reduced in the presence of the endfeet. Although the endfoot-lined external limiting membrane represents at least part of the immediate environment encountered by retinal axons as they invade the optic tectum and despite its excellent properties as a substrate for retinal axons in vitro, cues guiding the orientation of axons were not detected in the flat-mounted preparation.
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Affiliation(s)
- S Kröger
- Abteilung Biochemie, Max-Planck-Institut für Entwicklungsbiologie, Tübingen, Federal Republic of Germany
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von Langsdorff D, Ali SS, Nürnberger F. An improved silver staining technique as an alternative nuclear or combined nuclear nerve-fiber impregnation for comparative light-, secondary and backscattered electron scanning microscopy. J Neurosci Methods 1990; 35:3-8. [PMID: 1703613 DOI: 10.1016/0165-0270(90)90088-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Slices of rat brain were stained by a new silver impregnation technique. This method takes into consideration the pH-dependent differences of silver stain affinity of nerve tissues and can be used alternatively as a stain for nuclei or as a method for combined demonstration of nuclei nerves fibers. The slices were studied at the light microscopical (LM) level and subsequently with a scanning electron microscope, using secondary (SSEM = classical SEM), and backscattered electron detectors (BSEM). This new silver staining technique offers the opportunity of comparative studies with regard to different information acquired with LM, SSEM and BSEM. The described method allows to distinguish between nervous and glial tissue without necessarily damaging the glial tissue surrounding the nerve fibers. Specifically, scanning electron microscopy with backscattered electron detector of in situ preparations provides a higher contrast of stained and unstained tissue and increased depth of focus as compared to secondary electron detectors.
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Affiliation(s)
- D von Langsdorff
- Department of Anatomy and Cytobiology, University of Giessen, F.R.G
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