Orientation of commissural axons in vitro in response to a floor plate-derived chemoattractant

Development ◽  
1990 ◽  
Vol 110 (1) ◽  
pp. 19-30 ◽  
Author(s):  
M. Placzek ◽  
M. Tessier-Lavigne ◽  
T. Jessell ◽  
J. Dodd
Keyword(s):  
Spinal Cord ◽  
Collagen Gel ◽  
Axon Growth ◽  
Local Environment ◽  
Floor Plate ◽  
Target Cells ◽  
Commissural Axon ◽  
Commissural Axons ◽  
Commissural Neurons

Developing axons are guided to their targets by molecular cues in their local environment. Some cues are short-range, deriving from cells along axonal pathways. There is also increasing evidence for longer-range guidance cues, in the form of gradients of diffusible chemoattractant molecules, which originate from restricted populations of target cells. The guidance of developing commissural axons within the spinal cord depends on one of their intermediate cellular targets, the floor plate. We have shown previously that floor plate cells secrete a diffusible factor(s) that can alter the direction of commissural axon growth in vitro. Here we show that the factor is an effective chemoattractant for commissural axons. It can diffuse considerable distances through a collagen gel matrix and through dorsal and ventral neural epithelium in vitro to reorient the growth of virtually all commissural axons. The orientation of axons occurs in the absence of detectable effects on the survival of commissural neurons or on the rate of commissural axon extension. The regionally restricted expression of the factor suggests that it is present in the embryonic spinal cord in a gradient with its high point at the floor plate. These observations support the idea that the guidance of commissural axons to the ventral midline of the spinal cord results in part from the secretion of a chemoattractant by the floor plate.

scholarly journals Floor plate-derived neuropilin-2 functions as a secreted semaphorin sink to facilitate commissural axon midline crossing

2015 ◽  
Vol 29 (24) ◽  
pp. 2617-2632
Author(s):  
Berenice Hernandez-Enriquez ◽  
Zhuhao Wu ◽  
Edward Martinez ◽  
Olav Olsen ◽  
Zaven Kaprielian ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Floor Plate ◽  
Axon Pathfinding ◽  
Developmentally Regulated ◽  
Commissural Axon ◽  
Commissural Axons ◽  
Receptor Complexes ◽  
Midline Crossing

Commissural axon guidance depends on a myriad of cues expressed by intermediate targets. Secreted semaphorins signal through neuropilin-2/plexin-A1 receptor complexes on post-crossing commissural axons to mediate floor plate repulsion in the mouse spinal cord. Here, we show that neuropilin-2/plexin-A1 are also coexpressed on commissural axons prior to midline crossing and can mediate precrossing semaphorin-induced repulsion in vitro. How premature semaphorin-induced repulsion of precrossing axons is suppressed in vivo is not known. We discovered that a novel source of floor plate-derived, but not axon-derived, neuropilin-2 is required for precrossing axon pathfinding. Floor plate-specific deletion of neuropilin-2 significantly reduces the presence of precrossing axons in the ventral spinal cord, which can be rescued by inhibiting plexin-A1 signaling in vivo. Our results show that floor plate-derived neuropilin-2 is developmentally regulated, functioning as a molecular sink to sequester semaphorins, preventing premature repulsion of precrossing axons prior to subsequent down-regulation, and allowing for semaphorin-mediated repulsion of post-crossing axons.

Commissural axon pathfinding on the contralateral side of the floor plate: a role for B-class ephrins in specifying the dorsoventral position of longitudinally projecting commissural axons

Development ◽  
2001 ◽  
Vol 128 (23) ◽  
pp. 4859-4871 ◽  
Author(s):  
Ralph Imondi ◽  
Zaven Kaprielian
Keyword(s):  
Spinal Cord ◽  
Late Phase ◽  
Longitudinal Axis ◽  
Contralateral Side ◽  
Floor Plate ◽  
Axon Pathfinding ◽  
Lower Vertebrate ◽  
Commissural Axon ◽  
Commissural Axons

In both invertebrate and lower vertebrate species, decussated commissural axons travel away from the midline and assume positions within distinct longitudinal tracts. We demonstrate that in the developing chick and mouse spinal cord, most dorsally situated commissural neuron populations extend axons across the ventral midline and through the ventral white matter along an arcuate trajectory on the contralateral side of the floor plate. Within the dorsal (chick) and intermediate (mouse) marginal zone, commissural axons turn at a conserved boundary of transmembrane ephrin expression, adjacent to which they form a discrete ascending fiber tract. In vitro perturbation of endogenous EphB-ephrinB interactions results in the failure of commissural axons to turn at the appropriate dorsoventral position on the contralateral side of the spinal cord; consequently, axons inappropriately invade more dorsal regions of B-class ephrin expression in the dorsal spinal cord. Taken together, these observations suggest that B-class ephrins act locally during a late phase of commissural axon pathfinding to specify the dorsoventral position at which decussated commissural axons turn into the longitudinal axis.

Complementary expression of transmembrane ephrins and their receptors in the mouse spinal cord: a possible role in constraining the orientation of longitudinally projecting axons

Development ◽  
2000 ◽  
Vol 127 (7) ◽  
pp. 1397-1410 ◽  
Author(s):  
R. Imondi ◽  
C. Wideman ◽  
Z. Kaprielian
Keyword(s):  
Spinal Cord ◽  
Floor Plate ◽  
Plate Boundaries ◽  
Eph Receptors ◽  
Axon Pathfinding ◽  
Mouse Spinal Cord ◽  
Commissural Axon ◽  
Ligand Interactions ◽  
Ventral Funiculus

In the developing spinal cord, axons project in both the transverse plane, perpendicular to the floor plate, and in the longitudinal plane, parallel to the floor plate. For many axons, the floor plate is a source of long- and short-range guidance cues that govern growth along both dimensions. We show here that B-class transmembrane ephrins and their receptors are reciprocally expressed on floor plate cells and longitudinally projecting axons in the mouse spinal cord. During the period of commissural axon pathfinding, B-class ephrin protein is expressed at the lateral floor plate boundaries, at the interface between the floor plate and the ventral funiculus. In contrast, B-class Eph receptors are expressed on decussated commissural axon segments projecting within the ventral funiculus, and on ipsilaterally projecting axons constituting the lateral funiculus. Soluble forms of all three B-class ephrins bind to, and induce the collapse of, commissural growth cones in vitro. The collapse-inducing activity associated with B-class ephrins is likely to be mediated by EphB1. Taken together, these data support a possible role for repulsive B-class Eph receptor/ligand interactions in constraining the orientation of longitudinal axon projections at the ventral midline.

Ventral midline cells are required for the local control of commissural axon guidance in the mouse spinal cord

Development ◽  
1999 ◽  
Vol 126 (16) ◽  
pp. 3649-3659
Author(s):  
M.P. Matise ◽  
M. Lustig ◽  
T. Sakurai ◽  
M. Grumet ◽  
A.L. Joyner
Keyword(s):  
Spinal Cord ◽  
Critical Role ◽  
Floor Plate ◽  
Posterior Commissure ◽  
Ventral Midline ◽  
Mouse Spinal Cord ◽  
Commissural Axons ◽  
Midline Cells

Specialized cells at the midline of the central nervous system have been implicated in controlling axon projections in both invertebrates and vertebrates. To address the requirement for ventral midline cells in providing cues to commissural axons in mice, we have analyzed Gli2 mouse mutants, which lack specifically the floor plate and immediately adjacent interneurons. We show that a Dbx1 enhancer drives tau-lacZ expression in a subpopulation of commissural axons and, using a reporter line generated from this construct, as well as DiI tracing, we find that commissural axons projected to the ventral midline in Gli2(−/−) embryos. Netrin1 mRNA expression was detected in Gli2(−/−) embryos and, although much weaker than in wild-type embryos, was found in a dorsally decreasing gradient. This result demonstrates that while the floor plate can serve as a source of long-range cues for C-axons in vitro, it is not required in vivo for the guidance of commissural axons to the ventral midline in the mouse spinal cord. After reaching the ventral midline, most commissural axons remained clustered in Gli2(−/−) embryos, although some were able to extend longitudinally. Interestingly, some of the longitudinally projecting axons in Gli2(−/−) embryos extended caudally and others rostrally at the ventral midline, in contrast to normal embryos in which virtually all commissural axons turn rostrally after crossing the midline. This finding indicates a critical role for ventral midline cells in regulating the rostral polarity choice made by commissural axons after they cross the midline. In addition, we provide evidence that interactions between commissural axons and floor plate cells are required to modulate the localization of Nr-CAM and TAG-1 proteins on axons at the midline. Finally, we show that the floor plate is not required for the early trajectory of motoneurons or axons of the posterior commissure, whose projections are directed away from the ventral midline in both WT and Gli2(−/−) embryos, although they are less well organized in Gli2(−/−)mutants.

scholarly journals Sonic Hedgehog switches on Wnt/planar cell polarity signaling in commissural axon growth cones by reducing levels of Shisa2

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Keisuke Onishi ◽  
Yimin Zou
Keyword(s):  
Cell Polarity ◽  
Sonic Hedgehog ◽  
Planar Cell Polarity ◽  
Axon Growth ◽  
Growth Cones ◽  
Floor Plate ◽  
Commissural Axon ◽  
Commissural Axons ◽  
Midline Crossing ◽  
Regulatory Link

Commissural axons switch on responsiveness to Wnt attraction during midline crossing and turn anteriorly only after exiting the floor plate. We report here that Sonic Hedgehog (Shh)-Smoothened signaling downregulates Shisa2, which inhibits the glycosylation and cell surface presentation of Frizzled3 in rodent commissural axon growth cones. Constitutive Shisa2 expression causes randomized turning of post-crossing commissural axons along the anterior–posterior (A–P) axis. Loss of Shisa2 led to precocious anterior turning of commissural axons before or during midline crossing. Post-crossing commissural axon turning is completely randomized along the A–P axis when Wntless, which is essential for Wnt secretion, is conditionally knocked out in the floor plate. This regulatory link between Shh and planar cell polarity (PCP) signaling may also occur in other developmental processes.

Guided Axon Growth by Gradients of Adhesion in Collagen Gels

2008 ◽  
Author(s):  
Harini G. Sundararaghavan ◽  
Gary A. Monteiro ◽  
David I. Shreiber
Keyword(s):  
Spinal Cord ◽  
Collagen Gel ◽  
Axon Growth ◽  
Neurite Growth ◽  
Gradient System ◽  
Spinal Cord Regeneration ◽  
Collagen Gels ◽  
Direct Growth ◽  
3D Collagen

During development, neurites are directed by gradients of attractive and repulsive soluble (chemotactic) cues and substrate-bound adhesive (haptotactic) cues. Many of these cues have been extensively researched in vitro, and incorporated into strategies for nerve and spinal cord regeneration, primarily to improve the regenerative environment. To enhance and direct growth, we have developed a system to create 1D gradients of adhesion through a 3D collagen gel using microfluidics. We test our system using collagen grafted with bioactive peptide sequences, IKVAV and YIGSR, from laminin — an extra-cellular matrix (ECM) protein known to strongly influence neurite outgrowth. Gradients are established from ∼0.37mg peptide/mg collagen – 0, and ∼0.18 mg peptide/mg collagen – 0 of each peptide and tested using chick dorsal root ganglia (DRG). Neurite growth is evaluated 5 days after gradient formation. Neurites show increased growth in the gradient system when compared to control and biased growth up the gradient of peptides. Growth in YIGSR-grafted collagen increased with steeper gradients, whereas growth in IKVAV-grafted collagen decreased with steeper gradients. These results demonstrate that neurite growth can be enhanced and directed by controlled, immobilized, haptotactic gradients through 3D scaffolds, and suggest that including these gradients in regenerative therapies may accelerate nerve and spinal cord regeneration.

scholarly journals Depolarization and electrical stimulation enhance in vitro and in vivo sensory axon growth after spinal cord injury

2018 ◽  
Vol 300 ◽  
pp. 247-258 ◽  
Author(s):  
Ioana Goganau ◽  
Beatrice Sandner ◽  
Norbert Weidner ◽  
Karim Fouad ◽  
Armin Blesch
Keyword(s):  
Spinal Cord ◽  
Spinal Cord Injury ◽  
Electrical Stimulation ◽  
Axon Growth ◽  
Sensory Axon ◽  
Cord Injury

scholarly journals miR-7b-3p Exerts a Dual Role After Spinal Cord Injury, by Supporting Plasticity and Neuroprotection at Cortical Level

2021 ◽  
Vol 8 ◽  
Author(s):  
Matilde Ghibaudi ◽  
Marina Boido ◽  
Darrell Green ◽  
Elena Signorino ◽  
Gaia Elena Berto ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Spinal Cord Injury ◽  
Axon Growth ◽  
Dual Role ◽  
Neural Regeneration ◽  
Developmental Phase ◽  
Apoptotic Pathway ◽  
Cord Injury

Spinal cord injury (SCI) affects 6 million people worldwide with no available treatment. Despite research advances, the inherent poor regeneration potential of the central nervous system remains a major hurdle. Small RNAs (sRNAs) 19–33 nucleotides in length are a set of non-coding RNA molecules that regulate gene expression and have emerged as key players in regulating cellular events occurring after SCI. Here we profiled a class of sRNA known as microRNAs (miRNAs) following SCI in the cortex where the cell bodies of corticospinal motor neurons are located. We identified miR-7b-3p as a candidate target given its significant upregulation after SCI in vivo and we screened by miRWalk PTM the genes predicted to be targets of miR-7b-3p (among which we identified Wipf2, a gene regulating neurite extension). Moreover, 16 genes, involved in neural regeneration and potential miR-7b-3p targets, were found to be downregulated in the cortex following SCI. We also analysed miR-7b-3p function during cortical neuron development in vitro: we observed that the overexpression of miR-7b-3p was important (1) to maintain neurons in a more immature and, likely, plastic neuronal developmental phase and (2) to contrast the apoptotic pathway; however, in normal conditions it did not affect the Wipf2 expression. On the contrary, the overexpression of miR-7b-3p upon in vitro oxidative stress condition (mimicking the SCI environment) significantly reduced the expression level of Wipf2, as observed in vivo, confirming it as a direct miR-7b-3p target. Overall, these data suggest a dual role of miR-7b-3p: (i) the induction of a more plastic neuronal condition/phase, possibly at the expense of the axon growth, (ii) the neuroprotective role exerted through the inhibition of the apoptotic cascade. Increasing the miR-7b-3p levels in case of SCI could reactivate in adult neurons silenced developmental programmes, supporting at the same time the survival of the axotomised neurons.

Survival in vitro of motoneurons identified or purified by novel antibody-based methods is selectively enhanced by muscle-derived factors

Development ◽  
1991 ◽  
Vol 111 (1) ◽  
pp. 221-232 ◽  
Author(s):  
E. Bloch-Gallego ◽  
M. Huchet ◽  
H. el M'Hamdi ◽  
F.K. Xie ◽  
H. Tanaka ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Monoclonal Antibody ◽  
Growth Factors ◽  
Neurotrophic Factor ◽  
Ciliary Neurotrophic Factor ◽  
Floor Plate ◽  
New Method ◽  
Motoneuron Survival ◽  
Muscle Extract

Motoneurons were identified in vitro by a new method using the SC1 monoclonal antibody. They constituted up to 30% of total neurons in cultures of whole spinal cord from 4.5-day chicken embryos, and survived for at least 5 days in the presence of muscle extract, but not in its absence. By contrast, other neurons and floor-plate cells survived without muscle-derived factors. Motoneurons were purified to homogeneity by ‘panning’ on dishes coated with SC1 antibody; they developed rapidly even in the absence of other spinal cells. Concentrations of muscle extract required for half-maximal motoneuron survival were indistinguishable in pure and mixed cultures, suggesting that muscle-derived factors act directly on motoneurons. Other purified growth factors tested, including ciliary neurotrophic factor, did not have the survival-promoting activity of muscle.

Guidance of commissural growth cones at the floor plate in embryonic rat spinal cord

Development ◽  
1990 ◽  
Vol 109 (2) ◽  
pp. 435-447 ◽  
Author(s):  
P. Bovolenta ◽  
J. Dodd
Keyword(s):  
Spinal Cord ◽  
Axon Guidance ◽  
Plate Boundary ◽  
Growth Cones ◽  
Floor Plate ◽  
Morphological Properties ◽  
Rat Spinal Cord ◽  
Commissural Axons ◽  
Carbocyanine Dye

The floor plate of the embryonic rat spinal cord has been proposed to act as an intermediate target that plays a role in the pattern of extension of commissural axons. To begin to examine the role of the floor plate in axon guidance at the midline, we have studied the precision of the commissural axon projection to and across the floor plate during development. To delineate the pathway, the fluorescent carbocyanine dye, Di-I, has been used as a probe. We show that commissural axons traverse the floor plate and turn rostrally at its contralateral border with remarkable precision. Axons were not observed to turn ipsilaterally and turned only upon reaching the contralateral edge of the floor plate. Virtually all commissural axons follow this route. The morphology of commissural growth cones was also examined. As they encountered the floor plate, commissural growth cones became larger and increased in complexity. The reorientation of axons in register with the floor plate boundary and the change in the morphological properties of commissural growth cones as they traverse the midline suggest that the floor plate may act as a guidepost with functions similar to cells that have been implicated in axon guidance in invertebrates.

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