Retinal axon growth cones respond to EphB extracellular domains as inhibitory axon guidance cues

Development ◽  
2001 ◽  
Vol 128 (15) ◽  
pp. 3041-3048 ◽  
Author(s):  
Eric Birgbauer ◽  
Stephen F. Oster ◽  
Christophe G. Severin ◽  
David W. Sretavan
Keyword(s):  
Axon Guidance ◽  
Optic Disc ◽  
Growth Cone ◽  
Axon Growth ◽  
Growth Cones ◽  
Axon Pathfinding ◽  
Guidance Cues ◽  
Extracellular Domains ◽  
Retinal Axons ◽  
Retinal Axon

Axon pathfinding relies on cellular signaling mediated by growth cone receptor proteins responding to ligands, or guidance cues, in the environment. Eph proteins are a family of receptor tyrosine kinases that govern axon pathway development, including retinal axon projections to CNS targets. Recent examination of EphB mutant mice, however, has shown that axon pathfinding within the retina to the optic disc is dependent on EphB receptors, but independent of their kinase activity. Here we show a function for EphB1, B2 and B3 receptor extracellular domains (ECDs) in inhibiting mouse retinal axons when presented either as substratum-bound proteins or as soluble proteins directly applied to growth cones via micropipettes. In substratum choice assays, retinal axons tended to avoid EphB-ECDs, while time-lapse microscopy showed that exposure to soluble EphB-ECD led to growth cone collapse or other inhibitory responses. These results demonstrate that, in addition to the conventional role of Eph proteins signaling as receptors, EphB receptor ECDs can also function in the opposite role as guidance cues to alter axon behavior. Furthermore, the data support a model in which dorsal retinal ganglion cell axons heading to the optic disc encounter a gradient of inhibitory EphB proteins which helps maintain tight axon fasciculation and prevents aberrant axon growth into ventral retina. In conclusion, development of neuronal connectivity may involve the combined activity of Eph proteins serving as guidance receptors and as axon guidance cues.

scholarly journals Glial insulin regulates cooperative or antagonistic Golden goal/Flamingo interactions during photoreceptor axon guidance

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Hiroki Takechi ◽  
Satoko Hakeda-Suzuki ◽  
Yohei Nitta ◽  
Yuichi Ishiwata ◽  
Riku Iwanaga ◽  
...  
Keyword(s):  
Visual System ◽  
Axon Guidance ◽  
Growth Cone ◽  
Short Range ◽  
Transmembrane Protein ◽  
Axon Growth ◽  
Growth Cones ◽  
Axon Targeting ◽  
Stepwise Manner ◽  
Photoreceptor Axon Guidance

Transmembrane protein Golden goal (Gogo) interacts with atypical cadherin Flamingo to direct R8 photoreceptor axons in the Drosophila visual system. However, the precise mechanisms underlying Gogo regulation during columnar- and layer-specific R8 axon targeting are unknown. Our studies demonstrated that the insulin secreted from surface and cortex glia switches the phosphorylation status of Gogo, thereby regulating its two distinct functions. Non-phosphorylated Gogo mediates the initial recognition of the glial protrusion in the center of the medulla column, whereas phosphorylated Gogo suppresses radial filopodia extension by counteracting Flamingo to maintain a one axon to one column ratio. Later, Gogo expression ceases during the midpupal stage, thus allowing R8 filopodia to extend vertically into the M3 layer. These results demonstrate that the long- and short-range signaling between the glia and R8 axon growth cones regulates growth cone dynamics in a stepwise manner, and thus shape the entire organization of the visual system.

scholarly journals Retinal axon guidance by region-specific cues in diencephalon

Development ◽  
1998 ◽  
Vol 125 (5) ◽  
pp. 791-801 ◽  
Author(s):  
R. Tuttle ◽  
J.E. Braisted ◽  
L.J. Richards ◽  
D.D. O'Leary
Keyword(s):  
Extracellular Matrix ◽  
Axon Guidance ◽  
Axon Growth ◽  
Floor Plate ◽  
Retinal Axons ◽  
Stimulatory Activity ◽  
Extracellular Matrix Molecules ◽  
Retinal Axon

Retinal axons show region-specific patterning along the dorsal-ventral axis of diencephalon: retinal axons grow in a compact bundle over hypothalamus, dramatically splay out over thalamus, and circumvent epithalamus as they continue toward the dorsal midbrain. In vitro, retinal axons are repulsed by substrate-bound and soluble activities in hypothalamus and epithalamus, but invade thalamus. The repulsion is mimicked by a soluble floor plate activity. Tenascin and neurocan, extracellular matrix molecules that inhibit retinal axon growth in vitro, are enriched in hypothalamus and epithalamus. Within thalamus, a stimulatory activity is specifically upregulated in target nuclei at the time that retinal axons invade them. These findings suggest that region-specific, axon repulsive and stimulatory activities control retinal axon patterning in the embryonic diencephalon.

Integrating Chemistry and Mechanics: The Forces Driving Axon Growth

2020 ◽  
Vol 36 (1) ◽  
pp. 61-83 ◽  
Author(s):  
Kristian Franze
Keyword(s):  
Axon Growth ◽  
Growth Cones ◽  
Chemical Signals ◽  
Current Understanding ◽  
Axon Pathfinding ◽  
Chemical Signaling ◽  
Guidance Cues ◽  
Cellular Forces ◽  
The Brain ◽  
Complex Organ

The brain is our most complex organ. During development, neurons extend axons, which may grow over long distances along well-defined pathways to connect to distant targets. Our current understanding of axon pathfinding is largely based on chemical signaling by attractive and repulsive guidance cues. These cues instruct motile growth cones, the leading tips of growing axons, where to turn and where to stop. However, it is not chemical signals that cause motion—motion is driven by forces. Yet our current understanding of the mechanical regulation of axon growth is very limited. In this review, I discuss the origin of the cellular forces controlling axon growth and pathfinding, and how mechanical signals encountered by growing axons may be integrated with chemical signals. This mechanochemical cross talk is an important but often overlooked aspect of cell motility that has major implications for many physiological and pathological processes involving neuronal growth.

scholarly journals CRMP2 and CRMP4 Are Differentially Required for Axon Guidance and Growth in Zebrafish Retinal Neurons

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Zhi-Zhi Liu ◽  
Jian Zhu ◽  
Chang-Ling Wang ◽  
Xin Wang ◽  
Ying-Ying Han ◽  
...  
Keyword(s):  
Axon Guidance ◽  
Retinal Ganglion ◽  
Guidance Cues ◽  
Retinal Axons ◽  
Neuropilin 1 ◽  
Axon Development ◽  
Intracellular Proteins ◽  
Retinal Axon

Axons are directed to their correct targets by guidance cues during neurodevelopment. Many axon guidance cues have been discovered; however, much less known is about how the growth cones transduce the extracellular guidance cues to intracellular responses. Collapsin response mediator proteins (CRMPs) are a family of intracellular proteins that have been found to mediate growth cone behavior in vitro; however, their roles in vivo in axon development are much less explored. In zebrafish embryos, we find that CRMP2 and CRMP4 are expressed in the retinal ganglion cell layer when retinal axons are crossing the midline. Knocking down CRMP2 causes reduced elongation and premature termination of the retinal axons, while knocking down CRMP4 results in ipsilateral misprojections of retinal axons that would normally project to the contralateral brain. Furthermore, CRMP4 synchronizes with neuropilin 1 in retinal axon guidance, suggesting that CRMP4 might mediate the semaphorin/neuropilin signaling pathway. These results demonstrate that CRMP2 and CRMP4 function differentially in axon development in vivo.

The metalloproteinase ADAM10 is required for retinal ganglion cell axon guidance in the developing visual systems

2007 ◽  
Vol 30 (4) ◽  
pp. 77
Author(s):  
Y. Y. Chen ◽  
C. L. Hehr ◽  
K. Atkinson-Leadbeater ◽  
J. C. Hocking ◽  
S. McFarlane
Keyword(s):  
Ganglion Cell ◽  
Axon Guidance ◽  
Retinal Ganglion Cell ◽  
Growth Cone ◽  
Expression Patterns ◽  
Optic Tract ◽  
Axon Growth ◽  
Proteolytic Processing ◽  
Retinal Ganglion

Background: The growth cone interprets cues in its environment in order to reach its target. We want to identify molecules that regulate growth cone behaviour in the developing embryo. We investigated the role of A disintegrin and metalloproteinase 10 (ADAM10) in axon guidance in the developing visual system of African frog, Xenopus laevis. Methods: We first examined the expression patterns of adam10 mRNA by in situ hybridization. We then exposed the developing optic tract to an ADAM10 inhibitor, GI254023X, in vivo. Lastly, we inhibited ADAM10 function in diencephalic neuroepithelial cells (through which retinal ganglion cell (RGC) axons extend) or RGCs by electroporating or transfecting an ADAM10 dominant negative (dn-adam10). Results: We show that adam10 mRNA is expressed in the dorsal neuroepithelium over the time RGC axons extend towards their target, the optic tectum. Second, pharmacological inhibition of ADAM10 in an in vivo exposed brain preparation causes the failure of RGC axons to recognize their target at low concentrations (0.5, 1 μM), and the failure of the axons to make a caudal turn in the mid-diencephalon at higher concentration (5 μM). Thus, ADAM10 function is required for RGC axon guidance at two key guidance decisions. Finally, molecular inhibition of ADAM10 function by electroporating dn-adam10 in the brain neuroepithelium causes defects in RGC axon target recognition (57%) and/or defects in caudal turn (12%), as seen with the pharmacological inhibitor. In contrast, molecular inhibition of ADAM10 within the RGC axons has no effect. Conclusions: These data argue strongly that ADAM10 acts cell non-autonomously within the neuroepithelium to regulate the guidance of RGC axons. This study shows for the first time that a metalloproteinase acts in a cell non-autonomous fashion to direct vertebrate axon growth. It will provide important insights into candidate molecules that could be used to reform nerve connections if destroyed because of injury or disease. References Hattori M, Osterfield M, Flanagan JG. Regulated cleavage of a contact-mediated axon repellent. Science 2000; 289(5483):1360-5. Janes PW, Saha N, Barton WA, Kolev MV, Wimmer-Kleikamp SH, Nievergall E, Blobel CP, Himanen JP, Lackmann M, Nikolov DB. Adam meets Eph: an ADAM substrate recognition module acts as a molecular switch for ephrin cleavage in trans. Cell 2005; 123(2):291-304. Pan D, Rubin GM. Kuzbanian controls proteolytic processing of Notch and mediates lateral inhibition during Drosophila and vertebrate neurogenesis. Cell 1997; 90(2):271-80.

scholarly journals Axon growth regulation by a bistable molecular switch

2018 ◽  
Vol 285 (1877) ◽  
pp. 20172618 ◽  
Author(s):  
Pranesh Padmanabhan ◽  
Geoffrey J. Goodhill
Keyword(s):  
Growth Cone ◽  
Neural Development ◽  
Growth Regulation ◽  
Axon Growth ◽  
Interaction Network ◽  
Growth Cones ◽  
Extrinsic Factors ◽  
Environmental Signals ◽  
Switching Behaviour ◽  
The Right

For the brain to function properly, its neurons must make the right connections during neural development. A key aspect of this process is the tight regulation of axon growth as axons navigate towards their targets. Neuronal growth cones at the tips of developing axons switch between growth and paused states during axonal pathfinding, and this switching behaviour determines the heterogeneous axon growth rates observed during brain development. The mechanisms controlling this switching behaviour, however, remain largely unknown. Here, using mathematical modelling, we predict that the molecular interaction network involved in axon growth can exhibit bistability, with one state representing a fast-growing growth cone state and the other a paused growth cone state. Owing to stochastic effects, even in an unchanging environment, model growth cones reversibly switch between growth and paused states. Our model further predicts that environmental signals could regulate axon growth rate by controlling the rates of switching between the two states. Our study presents a new conceptual understanding of growth cone switching behaviour, and suggests that axon guidance may be controlled by both cell-extrinsic factors and cell-intrinsic growth regulatory mechanisms.

scholarly journals A pair of E3 ubiquitin ligases compete to regulate filopodial dynamics and axon guidance

2019 ◽  
Vol 219 (1) ◽  
Author(s):  
Nicholas P. Boyer ◽  
Laura E. McCormick ◽  
Shalini Menon ◽  
Fabio L. Urbina ◽  
Stephanie L. Gupton
Keyword(s):  
Axon Guidance ◽  
Growth Cone ◽  
Ubiquitin Ligases ◽  
Critical Element ◽  
E3 Ubiquitin Ligases ◽  
Related Protein ◽  
Guidance Cues ◽  
Guidance Cue ◽  
Neuronal Connections ◽  
Novel Model

Appropriate axon guidance is necessary to form accurate neuronal connections. Axon guidance cues that stimulate cytoskeletal reorganization within the growth cone direct axon navigation. Filopodia at the growth cone periphery have long been considered sensors for axon guidance cues, yet how they respond to extracellular cues remains ill defined. Our previous work found that the filopodial actin polymerase VASP and consequently filopodial stability are negatively regulated via nondegradative TRIM9-dependent ubiquitination. Appropriate VASP ubiquitination and deubiquitination are required for axon turning in response to the guidance cue netrin-1. Here we show that the TRIM9-related protein TRIM67 outcompetes TRIM9 for interacting with VASP and antagonizes TRIM9-dependent VASP ubiquitination. The surprising antagonistic roles of two closely related E3 ubiquitin ligases are required for netrin-1–dependent filopodial responses, axon turning and branching, and fiber tract formation. We suggest a novel model in which coordinated regulation of VASP ubiquitination by a pair of interfering ligases is a critical element of VASP dynamics, filopodial stability, and axon guidance.

scholarly journals The role of microtubules in growth cone turning at substrate boundaries.

1995 ◽  
Vol 128 (1) ◽  
pp. 127-137 ◽  
Author(s):  
E Tanaka ◽  
M W Kirschner
Keyword(s):  
Growth Cone ◽  
Collagen Type ◽  
Axon Growth ◽  
Growth Cones ◽  
Collagen Type Iv ◽  
Early Step ◽  
Growth Cone Collapse ◽  
Type Iv ◽  
And Behaviors

To understand the role of microtubules in growth cone turning, we observed fluorescently labeled microtubules in neurons as they encountered a substrate boundary. Neurons growing on a laminin-rich substrate avoided growing onto collagen type IV. Turning growth cones assumed heterogeneous morphologies and behaviors that depended primarily in their extent of adhesion to the substrate. We grouped these behaviors into three categories-sidestepping, motility, and growth-mediated reorientation. In sidestepping and motility-mediated reorientation, the growth cone and parts of the axon were not well attached to the substrate so the acquisition of an adherent lamella caused the entire growth cone to move away from the border and consequently reoriented the axon. In these cases, since the motility of the growth cone dominates its reorientation, the microtubules were passive, and reorientation occurred without significant axon growth. In growth-mediated reorientation, the growth cone and axon were attached to the substrate. In this case, microtubules reoriented within the growth cone to stabilize a lamella. Bundling of the reoriented microtubules was followed by growth cone collapse to form new axon, and further, polarized lamellipodial extension. These observations indicate that when the growth cone remains adherent to the substrate during turning, the reorientation and bundling of microtubules is an important, early step in growth cone turning.

scholarly journals A requirement for filopodia extension toward Slit during Robo-mediated axon repulsion

2016 ◽  
Vol 213 (2) ◽  
pp. 261-274 ◽  
Author(s):  
Russell E. McConnell ◽  
J. Edward van Veen ◽  
Marina Vidaki ◽  
Adam V. Kwiatkowski ◽  
Aaron S. Meyer ◽  
...  
Keyword(s):  
Axon Guidance ◽  
Actin Polymerization ◽  
Growth Cones ◽  
Guidance Cues ◽  
Guidance Cue ◽  
3D Environments ◽  
Direct Binding ◽  
Mouse Dorsal Root Ganglion ◽  
Axon Repulsion

Axons navigate long distances through complex 3D environments to interconnect the nervous system during development. Although the precise spatiotemporal effects of most axon guidance cues remain poorly characterized, a prevailing model posits that attractive guidance cues stimulate actin polymerization in neuronal growth cones whereas repulsive cues induce actin disassembly. Contrary to this model, we find that the repulsive guidance cue Slit stimulates the formation and elongation of actin-based filopodia from mouse dorsal root ganglion growth cones. Surprisingly, filopodia form and elongate toward sources of Slit, a response that we find is required for subsequent axonal repulsion away from Slit. Mechanistically, Slit evokes changes in filopodium dynamics by increasing direct binding of its receptor, Robo, to members of the actin-regulatory Ena/VASP family. Perturbing filopodium dynamics pharmacologically or genetically disrupts Slit-mediated repulsion and produces severe axon guidance defects in vivo. Thus, Slit locally stimulates directional filopodial extension, a process that is required for subsequent axonal repulsion downstream of the Robo receptor.

scholarly journals RHO-1 and the Rho GEF RHGF-1 interact with UNC-6/Netrin signaling to regulate growth cone protrusion and microtubule organization in C. elegans

2019 ◽  
Author(s):  
Mahekta R. Gujar ◽  
Aubrie M. Stricker ◽  
Erik A. Lundquist
Keyword(s):  
Axon Guidance ◽  
Growth Cone ◽  
Neural Circuit ◽  
Growth Cones ◽  
Negative Regulator ◽  
Microtubule Organization ◽  
C Elegans ◽  
Guidance Cue ◽  
Rho Gef

AbstractUNC-6/Netrin is a conserved axon guidance cue that directs growth cone migrations in the dorsal-ventral axis of C. elegans and in the vertebrate spinal cord. UNC-6/Netrin is expressed in ventral cells, and growth cones migrate ventrally toward or dorsally away from UNC-6/Netrin. Recent studies of growth cone behavior during outgrowth in vivo in C. elegans have led to a polarity/protrusion model in directed growth cone migration away from UNC-6/Netrin. In this model, UNC-6/Netrin first polarizes the growth cone via the UNC-5 receptor, leading to dorsally biased protrusion and F-actin accumulation. UNC-6/Netrin then regulates protrusion based on this polarity. The receptor UNC-40/DCC drives protrusion dorsally, away from the UNC-6/Netrin source, and the UNC-5 receptor inhibits protrusion ventrally, near the UNC-6/Netrin source, resulting in dorsal migration. UNC-5 inhibits protrusion in part by excluding microtubules from the growth cone, which are pro-protrusive. Here we report that the RHO-1/RhoA GTPase and its activator GEF RHGF-1 inhibit growth cone protrusion and MT accumulation in growth cones, similar to UNC-5. However, growth cone polarity of protrusion and F-actin were unaffected by RHO-1 and RHGF-1. Thus, RHO-1 signaling acts specifically as a negative regulator of protrusion and MT accumulation, and not polarity. Genetic interactions suggest that RHO-1 and RHGF-1 act with UNC-5, as well as with a parallel pathway, to regulate protrusion. The cytoskeletal interacting molecule UNC-33/CRMP was required for RHO-1 activity to inhibit MT accumulation, suggesting that UNC-33/CRMP might act downstream of RHO-1. In sum, these studies describe a new role of RHO-1 and RHGF-1 in regulation of growth cone protrusion by UNC-6/Netrin.Author SummaryNeural circuits are formed by precise connections between axons. During axon formation, the growth cone leads the axon to its proper target in a process called axon guidance. Growth cone outgrowth involves asymmetric protrusion driven by extracellular cues that stimulate and inhibit protrusion. How guidance cues regulate growth cone protrusion in neural circuit formation is incompletely understood. This work shows that the signaling molecule RHO-1 acts downstream of the UNC-6/Netrin guidance cue to inhibit growth cone protrusion in part by excluding microtubules from the growth cone, which are structural elements that drive protrusion.

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