The Experts below are selected from a list of 618 Experts worldwide ranked by ideXlab platform
John G Flanagan - One of the best experts on this subject based on the ideXlab platform.
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Topographically specific effects of ELF-1 on retinal axon guidance in vitro and retinal axon mapping in vivo
Cell, 1996Co-Authors: Masaru Nakamoto, Cliff H. Yoon, Todd Mclaughlin, Glenn C Friedman, Dennis D.m. O'leary, Hwai-jong Cheng, Michael J Hansen, John G FlanaganAbstract:Topographic maps, which maintain the spatial order of neurons in the order of their axonal connections, are found throughout the nervous system. In the visual Retinotectal Projection, ELF-1, a ligand in the tectum, and its receptors in the retina show complementary gradients in expression and binding, indicating they may be positional labels for map development. Here we show that ELF-1 acts as a repellent axon guidance factor in vitro. In vivo, when the tectal ELF-1 pattern is modified by retroviral overexpression, retinal axons avoid ectopic ELF-1 patches and map to abnormally anterior positions. All these effects were seen on axons from temporal but not nasal retina, indicating that ELF-1 could determine nasal versus temporal Retinotectal specificity, and providing a direct demonstration of a cell recognition molecule with topographically specific effects on neural map development.
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complementary gradients in expression and binding of elf 1 and mek4 in development of the topographic Retinotectal Projection map
Cell, 1995Co-Authors: Hwai-jong Cheng, Masaru Nakamoto, Andrew D Bergemann, John G FlanaganAbstract:Topographic maps with a defined spatial ordering of neuronal connections are a key feature of brain organization. Such maps are believed to develop in response to complementary position-specific labels in presynaptic and postsynaptic fields. However, the complementary labeling molecules are not known. In the well-studied visual map of retinal axons projecting to the tectum, the labels are hypothesized to be in gradients, without needing large numbers of cell-specific molecules. We recently cloned ELF-1 as a ligand for Eph family receptors. Here, RNA hybridization shows matching expression gradients for ELF-1 in the tectum and its receptor Mek4 in the retina. Binding activity detected with alkaline phosphatase fusions of ELF-1 and Mek4 also reveals gradients and provides direct evidence for molecular complementarity of gradients in reciprocal fields. ELF-1 and Mek4 may therefore play roles in Retinotectal development and have properties predicted of topographic mapping labels.
Christine E Holt - One of the best experts on this subject based on the ideXlab platform.
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Brief Communications NF-Protocadherin and TAF1 Regulate Retinal Axon Initiation and Elongation In Vivo
2020Co-Authors: Michael Piper, Asha Dwivedy, Louis Leung, Roger S Bradley, Christine E HoltAbstract:NF-protocadherin (NFPC)-mediated cell-cell adhesion plays a critical role in vertebrate neural tube formation. NFPC is also expressed during the period of axon tract formation, but little is known about its function in axonogenesis. Here we have tested the role of NFPC and its cytosolic cofactor template-activating factor 1 (TAF1) in the emergence of the Xenopus Retinotectal Projection. NFPC is expressed in the developing retina and optic pathway and is abundant in growing retinal axons. Inhibition of NFPC function in developing retinal ganglion cells (RGCs) severely reduces axon initiation and elongation and suppresses dendrite genesis. Furthermore, an identical phenotype occurs when TAF1 function is blocked. These data provide evidence that NFPC regulates axon initiation and elongation and indicate a conserved role for TAF1, a transcriptional regulator, as a downstream cytosolic effector of NFPC in RGCs
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nf protocadherin and taf1 regulate retinal axon initiation and elongation in vivo
The Journal of Neuroscience, 2008Co-Authors: Roger Bradley, Michael Piper, Asha Dwivedy, Louis C Leung, Christine E HoltAbstract:NF-protocadherin (NFPC)-mediated cell–cell adhesion plays a critical role in vertebrate neural tube formation. NFPC is also expressed during the period of axon tract formation, but little is known about its function in axonogenesis. Here we have tested the role of NFPC and its cytosolic cofactor template-activating factor 1 (TAF1) in the emergence of the Xenopus Retinotectal Projection. NFPC is expressed in the developing retina and optic pathway and is abundant in growing retinal axons. Inhibition of NFPC function in developing retinal ganglion cells (RGCs) severely reduces axon initiation and elongation and suppresses dendrite genesis. Furthermore, an identical phenotype occurs when TAF1 function is blocked. These data provide evidence that NFPC regulates axon initiation and elongation and indicate a conserved role for TAF1, a transcriptional regulator, as a downstream cytosolic effector of NFPC in RGCs.
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a critical window for cooperation and competition among developing Retinotectal synapses
Nature, 1998Co-Authors: Li I Zhang, Christine E Holt, Huizhong W Tao, William A Harris, Muming PooAbstract:In the developing frog visual system, topographic refinement of the Retinotectal Projection depends on electrical activity. In vivo whole-cell recording from developing Xenopus tectal neurons shows that convergent Retinotectal synapses undergo activity-dependent cooperation and competition following correlated pre- and postsynaptic spiking within a narrow time window. Synaptic inputs activated repetitively within 20 ms before spiking of the tectal neuron become potentiated, whereas subthreshold inputs activated within 20 ms after spiking become depressed. Thus both the initial synaptic strength and the temporal order of activation are critical for heterosynaptic interactions among convergent synaptic inputs during activity-dependent refinement of developing neural networks.
Friedrich Bonhoeffer - One of the best experts on this subject based on the ideXlab platform.
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RGM is a repulsive guidance molecule for retinal axons
Nature, 2002Co-Authors: Philippe P. Monnier, Ana Sierra, Paolo Macchi, Lutz Deitinghoff, Jens S. Andersen, Matthias Mann, Manuela Flad, Martin Hornberger, Bernd Stahl, Friedrich BonhoefferAbstract:Axons rely on guidance cues to reach remote targets during nervous system development1. A well-studied model system for axon guidance is the Retinotectal Projection. The retina can be divided into halves; the nasal half, next to the nose, and the temporal half. A subset of retinal axons, those from the temporal half, is guided by repulsive cues expressed in a graded fashion in the optic tectum2,3, part of the midbrain. Here we report the cloning and functional characterization of a membrane-associated glycoprotein, which we call RGM (repulsive guidance molecule). This molecule shares no sequence homology with known guidance cues, and its messenger RNA is distributed in a gradient with increasing concentration from the anterior to posterior pole of the embryonic tectum. Recombinant RGM at low nanomolar concentration induces collapse of temporal but not of nasal growth cones and guides temporal retinal axons in vitro, demonstrating its repulsive and axon-specific guiding activity.
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Differential Withdrawal of Retinal Axons Induced by a Secreted Factor
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1998Co-Authors: Hiroyuki Ichijo, Friedrich BonhoefferAbstract:To understand the development of the topographic map in the chick Retinotectal Projection, we studied the long-term interactions between retinal axons and tectal cell processes using a novel coculture system, the ryomen chamber. Both nasal and temporal retinal axons initially grew equally well on a substrate consisting of posterior tectal cell processes; however, subsequently most temporal axons withdrew from this surface, whereas most nasal axons did not. Experiments using conditioned media indicate that posterior tectal cells induced withdrawal of the temporal axons by secreting a soluble factor. This withdrawal seems to be distinct from the immediate repulsive effect of ephrin-A2 (ELF-1) and ephrin-A5 (RAGS) seen in the stripe assay because (1) the withdrawal-inducing factor was diffusible, whereas ephrin-A2 and -A5 are membrane-bound, and (2) the withdrawal-inducing factor appeared later in development than ephrin-A2 and -A5. Furthermore, sensitivity to the withdrawal-inducing factor decreased continuously from the temporal to nasal retina. These results suggest that target cell-induced axonal withdrawal may be involved during a late stage of the development of the Retinotectal map.
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Differential withdrawal of retinal axons induced by a secreted factor
1998Co-Authors: Hiroyuki Ichijo, Friedrich BonhoefferAbstract:To understand the development of the topographic map in the chick Retinotectal Projection, we studied the long-term interac-tions between retinal axons and tectal cell processes using a novel coculture system, the ryomen chamber. Both nasal and temporal retinal axons initially grew equally well on a substrate consisting of posterior tectal cell processes; however, subse-quently most temporal axons withdrew from this surface, whereas most nasal axons did not. Experiments using condi-tioned media indicate that posterior tectal cells induced with-drawal of the temporal axons by secreting a soluble factor. This withdrawal seems to be distinct from the immediate repulsive effect of ephrin-A2 (ELF-1) and ephrin-A5 (RAGS) seen in the stripe assay because (1) the withdrawal-inducing factor was diffusible, whereas ephrin-A2 and-A5 are membrane-bound, and (2) the withdrawal-inducing factor appeared later in devel
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in vitro guidance of retinal ganglion cell axons by rags a 25 kda tectal protein related to ligands for eph receptor tyrosine kinases
Cell, 1995Co-Authors: Uwe Drescher, Claudia Handwerker, Claus Kremoser, Jurgen Loschinger, Masaharu Noda, Friedrich BonhoefferAbstract:The results of previous in vitro experiments indicate that a glycosylphosphatidylinositol (GPI)-anchored protein may play an important role in the guidance of temporal retinal axons during the formation of the topographically ordered Retinotectal Projection. We have purified and cloned a GPI-anchored, 25 kDa glycoprotein that is a good candidate for a molecule involved in this process. During the time of innervation by retinal ganglion cells, this protein is gradedly expressed in the posterior part of the developing tectum. In two different in vitro assay systems, the recombinant protein induces growth cone collapse and repulsion of retinal ganglion cell axons. These phenomena are observed for axons of temporal as well as nasal origin, indicating that an additional activity may be necessary to confer the nasotemporal specificity observed in previous assays. We named the protein RAGS (for repulsive axon guidance signal). The sequence of RAGS shows significant homology to recently identified ligands for receptor tyrosine kinases of the Eph subfamily.
Masaharu Noda - One of the best experts on this subject based on the ideXlab platform.
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visual Projection map specified by topographic expression of transcription factors in the retina
Nature, 1996Co-Authors: Junichi Yuasa, Shinji Hirano, Masahito Yamagata, Masaharu NodaAbstract:TOPOGRAPHICAL maps of neuronal connectivity occur in various brain regions1. In the visual system of birds, retinal ganglion-cell axons from the anterior retina connect to a posterior part of the optic tectum, and posterior retinal axons connect to the anterior part, thereby establishing a point-to-point Projection map2,3. The chemoaffinity theory4 predicts that the orderly Retinotectal Projection is generated by a topographical arrangement of molecules. We report here that we have found several genes topographically expressed along the nasotemporal (anterior–posterior) axis in the embryonic chicken retina. Among these, two transcriptional regulators, belonging to the winged-helix family5 are expressed in a mutually exclusive manner in either the nasal or temporal part of the retina. Misexpression of each factor causes misProjection on the tectum along the rostrocaudal axis, showing that topographical expression of these transcription factors controls formation of the Retinotectal map.
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in vitro guidance of retinal ganglion cell axons by rags a 25 kda tectal protein related to ligands for eph receptor tyrosine kinases
Cell, 1995Co-Authors: Uwe Drescher, Claudia Handwerker, Claus Kremoser, Jurgen Loschinger, Masaharu Noda, Friedrich BonhoefferAbstract:The results of previous in vitro experiments indicate that a glycosylphosphatidylinositol (GPI)-anchored protein may play an important role in the guidance of temporal retinal axons during the formation of the topographically ordered Retinotectal Projection. We have purified and cloned a GPI-anchored, 25 kDa glycoprotein that is a good candidate for a molecule involved in this process. During the time of innervation by retinal ganglion cells, this protein is gradedly expressed in the posterior part of the developing tectum. In two different in vitro assay systems, the recombinant protein induces growth cone collapse and repulsion of retinal ganglion cell axons. These phenomena are observed for axons of temporal as well as nasal origin, indicating that an additional activity may be necessary to confer the nasotemporal specificity observed in previous assays. We named the protein RAGS (for repulsive axon guidance signal). The sequence of RAGS shows significant homology to recently identified ligands for receptor tyrosine kinases of the Eph subfamily.
Masaru Nakamoto - One of the best experts on this subject based on the ideXlab platform.
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Topographically specific effects of ELF-1 on retinal axon guidance in vitro and retinal axon mapping in vivo
Cell, 1996Co-Authors: Masaru Nakamoto, Cliff H. Yoon, Todd Mclaughlin, Glenn C Friedman, Dennis D.m. O'leary, Hwai-jong Cheng, Michael J Hansen, John G FlanaganAbstract:Topographic maps, which maintain the spatial order of neurons in the order of their axonal connections, are found throughout the nervous system. In the visual Retinotectal Projection, ELF-1, a ligand in the tectum, and its receptors in the retina show complementary gradients in expression and binding, indicating they may be positional labels for map development. Here we show that ELF-1 acts as a repellent axon guidance factor in vitro. In vivo, when the tectal ELF-1 pattern is modified by retroviral overexpression, retinal axons avoid ectopic ELF-1 patches and map to abnormally anterior positions. All these effects were seen on axons from temporal but not nasal retina, indicating that ELF-1 could determine nasal versus temporal Retinotectal specificity, and providing a direct demonstration of a cell recognition molecule with topographically specific effects on neural map development.
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complementary gradients in expression and binding of elf 1 and mek4 in development of the topographic Retinotectal Projection map
Cell, 1995Co-Authors: Hwai-jong Cheng, Masaru Nakamoto, Andrew D Bergemann, John G FlanaganAbstract:Topographic maps with a defined spatial ordering of neuronal connections are a key feature of brain organization. Such maps are believed to develop in response to complementary position-specific labels in presynaptic and postsynaptic fields. However, the complementary labeling molecules are not known. In the well-studied visual map of retinal axons projecting to the tectum, the labels are hypothesized to be in gradients, without needing large numbers of cell-specific molecules. We recently cloned ELF-1 as a ligand for Eph family receptors. Here, RNA hybridization shows matching expression gradients for ELF-1 in the tectum and its receptor Mek4 in the retina. Binding activity detected with alkaline phosphatase fusions of ELF-1 and Mek4 also reveals gradients and provides direct evidence for molecular complementarity of gradients in reciprocal fields. ELF-1 and Mek4 may therefore play roles in Retinotectal development and have properties predicted of topographic mapping labels.