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Thomas M Jessell - One of the best experts on this subject based on the ideXlab platform.
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The when and where of Floor Plate induction
Science (New York N.Y.), 1998Co-Authors: Jane Dodd, Thomas M Jessell, Marysia PlaczekAbstract:Floor Plate induction is a well-studied early step in the development of the nervous system. Here Dodd, Jessell, and Placzek review recent work on the mechanism of that induction, including some controversial suggestions that part of the Floor Plate is derived from notochord.
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Induction of motor neurons by Sonic hedgehog is independent of Floor Plate differentiation
Current biology : CB, 1995Co-Authors: Yasuto Tanabe, Henk Roelink, Thomas M JessellAbstract:Abstract Background: The differentiation of Floor Plate cells and motor neurons in the vertebrate neural tube appears to be induced by signals from the notochord. The secreted protein encoded by the Sonic hedgehog (Shh) gene is expressed by axial midline cells and can induce Floor Plate cells in vivo and in vitro. Motor neurons can also be induced in vitro by cells that synthesize Sonic hedgehog protein (Shh). It remains unclear, however, if the motor-neuron-inducing activity of Shh depends on the synthesis of a distinct signaling molecule by Floor Plate cells. To resolve this issue, we have developed an in vitro assay which uncouples the notochord-mediated induction of motor neurons from Floor Plate differentiation, and have used this assay to examine whether Shh induces motor neurons in the absence of Floor Plate differentiation. Results Floor Plate cells and motor neurons were induced in neural Plate explants grown in contact with the notochord, but only motor neurons were induced when explants were separated from the notochord. COS cells transfected with Shh induced both Floor Plate cells and motor neurons when grown in contact with neural Plate explants, whereas only motor neurons were induced when the explants were grown at a distance from Shh -transfected COS cells. Direct transfection of neural Plate cells with an Shh -expression construct induced both Floor Plate cells and motor neurons, with motor neuron differentiation occurring prior to, or coincidentally with, Floor Plate differentiation. The induction of motor neurons appears, therefore, not to depend on Floor Plate differentiation. Conclusion The induction of motor neurons by Shh does not depend on distinct Floor-Plate-derived signaling molecules. Shh can, therefore, initiate the differentiation of two cell types that are generated in the ventral region of the neural tube. These results show that the early development of motor neurons involves the inductive action of Shh, whereas the survival of motor neurons at later stages of embryonic development requires neurotrophic factors.
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Floor Plate and motor neuron induction by different concentrations of the amino terminal cleavage product of sonic hedgehog autoproteolysis
Cell, 1995Co-Authors: Henk Roelink, Yasuto Tanabe, Jeffery A Porter, C Chiang, D T Chang, Philip A Beachy, Thomas M JessellAbstract:Abstract The differentiation of Floor Plate cells and motor neurons can be induced by Sonic hedgehog (SHH), a secreted signaling protein that undergoes autoproteolytic cleavage to generate amino- and carboxy-terminal products. We have found that both Floor Plate cells and motor neurons are induced by the aminoterminal cleavage product of SHH (SHH-N). The threshold concentration of SHH-N required for motor neuron induction is about 5-fold lower than that required for Floor Plate induction. Higher concentrations of SHH-N can induce Floor Plate cells at the expense of motor neuron differentiation. Our results suggest that the induction of Floor Plate cells and motor neurons by the notochord in vivo is mediated by exposure of neural Plate cells to different concentrations of the amino-terminal product of SHH autoproteolytic cleavage.
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Restrictions to Floor Plate induction by hedgehog and winged-helix genes in the neural tube of frog embryos.
Molecular and cellular neurosciences, 1995Co-Authors: A. Ruiz I Altaba, Thomas M Jessell, Henk RoelinkAbstract:Abstract Intercellular signaling molecules of the vertebrate hedgehog family and transcription factors of the winged-helix family have been implicated in Floor Plate development. We have examined the consequences of misexpressing the vertebrate hedgehog gene vhh-1 (sonic hedgehog, shh) and the winged-helix gene HNF-3β in the neural Plate and neural tube of frog embryos. Misexpression of either of these genes induces Floor Plate differentiation at ectopic locations. However, ectopic Floor Plate induction in response to both vhh-1 and HNF-3β was temporally and spatially restricted. At neural Plate stages, ectopic Floor Plate differentiation was not detected. After neural tube closure, ectopic Floor Plate differentiation was detected but was restricted predominantly to the dorsal region of the neural tube. The ability of winged-helix and vertebrate hedgehog genes to induce Floor Plate differentiation in vivo may, therefore, be constrained by additional signals that specify the time and position of Floor Plate differentiation.
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Early Stages of Notochord and Floor Plate Development in the Chick Embryo Defined by Normal and Induced Expression of HNF-3β
Developmental biology, 1995Co-Authors: A. Ruiz I Altaba, Mark Baldassare, J. Dodd, M. Placzek, Thomas M JessellAbstract:Abstract We have cloned a cDNA encoding the chick HNF-3 β gene and have used RNA and antibody probes that detect HNF-3β to monitor the normal and induced expression of the gene in early embryos. HNF-3 β is expressed in Koller's sickle, at the onset of primitive streak formation, and later in Hensen's node. At neural Plate and neural tube stages, HNF-3 β is expressed transiently in the notochord and is then expressed by Floor Plate cells. Prospective Floor Plate cells that are located in the epiblast immediately anterior to Hensen's node prior to its regression do not express HNF-3 β, providing evidence that Floor Plate fate is normally determined only after these cells populate the midline of the neural Plate and overlie the notechord. Removal of the notochord in vivo prevents Floor Plate development and in this condition HNF-3 β is not expressed by cells at the ventral midline of the neural tube. Notochord grafts induce ectopic Floor Plate development and ectopic neural expression of HNF-3 β. In vitro , neural Plate explants are induced to express HNF-3 β by notochord cells in a contact-dependent but cycloheximide-resistant manner, providing evidence that expression of HNF-3 β is a direct response of neural Plate cells to notochord-derived inducing signals.
Marysia Placzek - One of the best experts on this subject based on the ideXlab platform.
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The Floor Plate: multiple cells, multiple signals
Nature Reviews Neuroscience, 2005Co-Authors: Marysia Placzek, James BriscoeAbstract:The Floor Plate is a small group of cells located at the ventral midline of the neural tube that profoundly influences the development of the vertebrate nervous system by specifying cellular identities and directing axonal trajectories. This review focuses on evidence that the Floor Plate is not composed of a uniform population of cells along the anteroposterior (AP) axis, and discusses the implications of this finding for resolving recent controversies about the embryological origin of the Floor Plate and the inductive mechanisms that control its development. In the classic Floor Plate induction model, Floor Plate cells differentiate from neuroepithelial cells that occupy a ventral midline position, and are induced to a Floor Plate fate under the influence of signals from the underlying notochord. However, a second model proposes that some Floor Plate cells are induced early, during gastrulation, by prechordal mesoderm. There are three main lines of evidence for AP differences in Floor Plate cells. First, there are molecular and morphological differences along the AP axis. Second, the Floor Plate seems to have separate embryological origins and ontogeny at different AP levels. Last, distinct inductive processes seem to be involved in the specification of the Floor Plate at different AP levels. The initial evidence for AP differences in Floor Plate cells came from experiments in chick embryos, and promoter/enhancer studies in the mouse and zebrafish are beginning to indicate that Floor Plate-specific genes are regulated in distinct ways along the AP axis in these organisms. Studies in amniotes indicate that sonic hedgehog is required for Floor Plate induction, whereas studies in zebrafish emphasize a requirement for the transforming growth factor-β family member Nodal. However, this distinction between zebrafish and amniotes might not be as clear-cut as was initially thought. One possibility is that Nodal has a pivotal role in the induction of the early-induced, predominantly anterior Floor Plate population, whereas hedgehog functions primarily to induce the later-arising posterior Floor Plate cells. One of the key organizers in the CNS is the Floor Plate — a group of cells that is responsible for instructing neural cells to acquire distinctive fates, and that has an important role in establishing the elaborate neuronal networks that underlie the function of the brain and spinal cord. In recent years, considerable controversy has arisen over the mechanism by which Floor Plate cells form. Here, we describe recent evidence that indicates that discrete populations of Floor Plate cells, with characteristic molecular properties, form in different regions of the neuraxis, and we discuss data that imply that the mode of Floor Plate induction varies along the anteroposterior axis.
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The Floor Plate: multiple cells, multiple signals.
Nature reviews. Neuroscience, 2005Co-Authors: Marysia Placzek, James BriscoeAbstract:One of the key organizers in the CNS is the Floor Plate - a group of cells that is responsible for instructing neural cells to acquire distinctive fates, and that has an important role in establishing the elaborate neuronal networks that underlie the function of the brain and spinal cord. In recent years, considerable controversy has arisen over the mechanism by which Floor Plate cells form. Here, we describe recent evidence that indicates that discrete populations of Floor Plate cells, with characteristic molecular properties, form in different regions of the neuraxis, and we discuss data that imply that the mode of Floor Plate induction varies along the anteroposterior axis.
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Distinct modes of Floor Plate induction in the chick embryo
Development (Cambridge England), 2003Co-Authors: Iain Patten, Paul M. Kulesa, Michael M. Shen, Scott E. Fraser, Marysia PlaczekAbstract:To begin to reconcile models of Floor Plate formation in the vertebrate neural tube, we have performed experiments aimed at understanding the development of the early Floor Plate in the chick embryo. Using real-time analyses of cell behaviour, we provide evidence that the principal contributor to the early neural midline, the future anterior Floor Plate, exists as a separate population of Floor Plate precursor cells in the epiblast of the gastrula stage embryo, and does not share a lineage with axial mesoderm. Analysis of the tissue interactions associated with differentiation of these cells to a Floor Plate fate reveals a role for the nascent prechordal mesoderm, indicating that more than one inductive event is associated with Floor Plate formation along the length of the neuraxis. We show that Nr1, a chick nodal homologue, is expressed in the nascent prechordal mesoderm and we provide evidence that Nodal signalling can cooperate with Shh to induce the epiblast precursors to a Floor-Plate fate. These results indicate that a shared lineage with axial mesoderm cells is not a pre-requisite for Floor Plate differentiation and suggest parallels between the development of the Floor Plate in amniote and anamniote embryos.
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Opponent Activities of Shh and BMP Signaling during Floor Plate Induction In Vivo
Current Biology, 2002Co-Authors: Iain Patten, Marysia PlaczekAbstract:We performed in vivo experiments in chick embryos that examined whether application of an exogenous source of Shh protein mimics the ability of the notochord to induce ectopic Floor Plate cells in the neural tube. Shh cannot act alone to induce a Floor Plate. However, coapplication of Shh and chordin, a BMP antagonist normally coexpressed with Shh in the notochord, results in a marked switch from dorsal to ventral cell fate, including a dramatic and widespread induction of Floor Plate cells. These data provide in vivo evidence that notochord-derived BMP antagonists may normally generate a permissive environment for the Shh-mediated induction of Floor Plate. Further experiments performed to address the source of BMPs that are inhibited by the action of chordin suggest that they derive specifically from the surface ectoderm and dorsal-most neuroepithelium. These data indicate that, at neural groove stages, dorsally derived BMPs affect ventral-most regions of the neural Plate, suggesting a novel long-range action of BMPs. Together, these studies suggest that the balance of dorsally derived signals and notochord-derived signals determines the extent of Floor Plate cell induction.
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The when and where of Floor Plate induction
Science (New York N.Y.), 1998Co-Authors: Jane Dodd, Thomas M Jessell, Marysia PlaczekAbstract:Floor Plate induction is a well-studied early step in the development of the nervous system. Here Dodd, Jessell, and Placzek review recent work on the mechanism of that induction, including some controversial suggestions that part of the Floor Plate is derived from notochord.
Alain Chédotal - One of the best experts on this subject based on the ideXlab platform.
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Synergistic Activity of Floor-Plate- and Ventricular-Zone-Derived Netrin-1 in Spinal Cord Commissural Axon Guidance
Neuron, 2019Co-Authors: Juan Moreno-bravo, Sergi Roig Puiggros, Patrick Mehlen, Alain ChédotalAbstract:In vertebrates, commissural axons extend ventrally toward the Floor Plate in the spinal cord and hindbrain. Netrin-1, secreted by Floor Plate cells, was proposed to attract commissural axons at a distance. However, recent genetic studies in mice have shown that netrin-1 is also produced by ventricular zone (VZ) progenitors and that in the hindbrain, it represents the main source of netrin-1 for commissural axons. Here, we show that genetically deleting netrin-1 either from the VZ or the Floor Plate does not prevent midline crossing in the spinal cord, although axon pathfinding and fasciculation are perturbed. Strikingly, the VZ and Floor Plate act synergistically, as the simultaneous ablation of netrin-1 from these two sources severely impedes crossing. These results suggest that Floor-Plate-derived netrin-1 has a distinct impact on commissural axons in the spinal cord and hindbrain.
Nikoloz Tsikolia - One of the best experts on this subject based on the ideXlab platform.
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Divergent axial morphogenesis and early shh expression in vertebrate prospective Floor Plate
EvoDevo, 2018Co-Authors: Stanislav Kremnyov, Kristine Henningfeld, Christoph Viebahn, Nikoloz TsikoliaAbstract:Background The notochord has organizer properties and is required for Floor Plate induction and dorsoventral patterning of the neural tube. This activity has been attributed to sonic hedgehog (shh) signaling, which originates in the notochord, forms a gradient, and autoinduces shh expression in the Floor Plate. However, reported data are inconsistent and the spatiotemporal development of the relevant shh expression domains has not been studied in detail. We therefore studied the expression dynamics of shh in rabbit, chicken and Xenopus laevis embryos (as well as indian hedgehog and desert hedgehog as possible alternative functional candidates in the chicken). Results Our analysis reveals a markedly divergent pattern within these vertebrates: whereas in the rabbit shh is first expressed in the notochord and its Floor Plate domain is then induced during subsequent somitogenesis stages, in the chick embryo shh is expressed in the prospective neuroectoderm prior to the notochord formation and, interestingly, prior to mesoderm immigration. Neither indian hedgehog nor desert hedgehog are expressed in these midline structures although mRNA of both genes was detected in other structures of the early chick embryo. In X . laevis , shh is expressed at the beginning of gastrulation in a distinct area dorsal to the dorsal blastopore lip and adjacent to the prospective neuroectoderm, whereas the Floor Plate expresses shh at the end of gastrulation. Conclusions While shh expression patterns in rabbit and X . laevis embryos are roughly compatible with the classical view of “ventral to dorsal induction” of the Floor Plate, the early shh expression in the chick Floor Plate challenges this model. Intriguingly, this alternative sequence of domain induction is related to the asymmetrical morphogenesis of the primitive node and other axial organs in the chick. Our results indicate that the Floor Plate in X . laevis and chick embryos may be initially induced by planar interaction within the ectoderm or epiblast. Furthermore, we propose that the mode of the Floor Plate induction adapts to the variant topography of interacting tissues during gastrulation and notochord formation and thereby reveals evolutionary plasticity of early embryonic induction.
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Divergent axial morphogenesis and early shh expression in vertebrate prospective Floor Plate
EvoDevo, 2018Co-Authors: Stanislav Kremnyov, Kristine Henningfeld, Christoph Viebahn, Nikoloz TsikoliaAbstract:The notochord has organizer properties and is required for Floor Plate induction and dorsoventral patterning of the neural tube. This activity has been attributed to sonic hedgehog (shh) signaling, which originates in the notochord, forms a gradient, and autoinduces shh expression in the Floor Plate. However, reported data are inconsistent and the spatiotemporal development of the relevant shh expression domains has not been studied in detail. We therefore studied the expression dynamics of shh in rabbit, chicken and Xenopus laevis embryos (as well as indian hedgehog and desert hedgehog as possible alternative functional candidates in the chicken). Our analysis reveals a markedly divergent pattern within these vertebrates: whereas in the rabbit shh is first expressed in the notochord and its Floor Plate domain is then induced during subsequent somitogenesis stages, in the chick embryo shh is expressed in the prospective neuroectoderm prior to the notochord formation and, interestingly, prior to mesoderm immigration. Neither indian hedgehog nor desert hedgehog are expressed in these midline structures although mRNA of both genes was detected in other structures of the early chick embryo. In X. laevis, shh is expressed at the beginning of gastrulation in a distinct area dorsal to the dorsal blastopore lip and adjacent to the prospective neuroectoderm, whereas the Floor Plate expresses shh at the end of gastrulation. While shh expression patterns in rabbit and X. laevis embryos are roughly compatible with the classical view of “ventral to dorsal induction” of the Floor Plate, the early shh expression in the chick Floor Plate challenges this model. Intriguingly, this alternative sequence of domain induction is related to the asymmetrical morphogenesis of the primitive node and other axial organs in the chick. Our results indicate that the Floor Plate in X. laevis and chick embryos may be initially induced by planar interaction within the ectoderm or epiblast. Furthermore, we propose that the mode of the Floor Plate induction adapts to the variant topography of interacting tissues during gastrulation and notochord formation and thereby reveals evolutionary plasticity of early embryonic induction.
Jane Dodd - One of the best experts on this subject based on the ideXlab platform.
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The when and where of Floor Plate induction
Science (New York N.Y.), 1998Co-Authors: Jane Dodd, Thomas M Jessell, Marysia PlaczekAbstract:Floor Plate induction is a well-studied early step in the development of the nervous system. Here Dodd, Jessell, and Placzek review recent work on the mechanism of that induction, including some controversial suggestions that part of the Floor Plate is derived from notochord.
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Induction of Floor Plate Differentiation by Contact-Dependent, Homeogenetic Signals
Development (Cambridge England), 1993Co-Authors: Marysia Placzek, Thomas M Jessell, Jane DoddAbstract:The Floor Plate is located at the ventral midline of the neural tube and has been implicated in neural cell patterning and axon guidance. To address the cellular mechanisms involved in Floor Plate differentiation, we have used an assay that monitors the expression of Floor-Plate-specific antigens in neural Plate explants cultured in the presence of inducing tissues. Contact-mediated signals from both the notochord and the Floor Plate act directly on neural Plate cells to induce Floor Plate differentiation. Floor Plate induction is initiated medially by a signal from the notochord, but appears to be propagated to more lateral cells by homeogenetic signals that derive from medial Floor Plate cells. The response of neural Plate cells to inductive signals declines with embryonic age, suggesting that the mediolateral extent of the Floor Plate is limited by a loss of competence of neural cells. The rostral boundary of the Floor Plate at the midbrain-forebrain junction appears to result from the lack of inducing activity in prechordal mesoderm and the inability of rostral neural Plate cells to respond to inductive signals.
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control of cell pattern in the developing nervous system polarizing activity of the Floor Plate and notochord
Cell, 1991Co-Authors: Marysia Placzek, Thomas M Jessell, Jane Dodd, Toshiya Yamada, H TanakaAbstract:Abstract Individual classes of neural cells differentiate at distinct locations in the developing vertebrate nervous system. We provide evidence that the pattern of cell differentiation along the dorsoventral axis of the chick neural tube is regulated by signals derived from two ventral midline cell groups, the notochord and Floor Plate. Grafting an additional notochord or Floor Plate to ectopic positions, or deleting both cell groups, resulted in changes in the fate and position of neural cell types, defined by expression of specific antigens. These results suggest that the differentiation of neural cells is controlled, in part, by their position with respect to the notochord and Floor Plate.
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Control of dorsoventral pattern in vertebrate neural development: induction and polarizing properties of the Floor Plate.
Development, 1991Co-Authors: Marysia Placzek, Marc Tessier-lavigne, Thomas M Jessell, Toshiya Yamada, Jane DoddAbstract:Distinct classes of neural cells differentiate at specific locations within the embryonic vertebrate nervous system. To define the cellular mechanisms that control the identity and pattern of neural cells we have used a combination of functional assays and antigenic markers to examine the differentiation of cells in the developing spinal cord and hindbrain in vivo and in vitro. Our results suggest that a critical step in the dorsoventral patterning of the embryonic CNS is the differentiation of a specialized group of midline neural cells, termed the Floor Plate, in response to local inductive signals from the underlying notochord. The Floor Plate and notochord appear to control the pattern of cell types that appear along the dorsoventral axis of the neural tube. The fate of neuroepithelial cells in the ventral neural tube may be defined by cell position with respect to the ventral midline and controlled by polarizing signals that originate from the Floor Plate and notochord.
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Perturbation of neuronal differentiation and axon guidance in the spinal cord of mouse embryos lacking a Floor Plate: analysis of Danforth's short-tail mutation.
Development (Cambridge England), 1991Co-Authors: Paola Bovolenta, Jane DoddAbstract:The Floor Plate of the vertebrate nervous system has been implicated in the guidance of commissural axons at the ventral midline. Experiments in chick have also suggested that at earlier stages of development the Floor Plate induces the differentiation of motor neurons and other neurons of the ventral spinal cord. Here we have examined the development of the spinal cord in a mouse mutant, Danforth's short-tail, in which the Floor Plate is absent from caudal regions of the neuraxis. In affected regions of the spinal cord, commissural axons exhibited aberrant projection patterns as they reached and crossed the ventral midline. In addition, motor neurons were absent or markedly reduced in number in regions of the spinal cord lacking a Floor Plate. Our results suggest that the Floor Plate is indeed an intermediate target in the projection of commissural axons and support the idea that several different mechanisms operate in concert in the guidance of axons to their cellular targets in the developing nervous system. In addition, these experiments suggest that the mechanisms that govern the differentiation of the Floor Plate and other ventral cell types in the neural tube are common to mammals and lower vertebrates.