scholarly journals RACK1 is required for axon guidance and local translation at growth cone point contacts

2019 ◽  
Author(s):  
Leah Kershner ◽  
Taylor Bumbledare ◽  
Paige Cassidy ◽  
Samantha Bailey ◽  
Kristy Welshhans
Keyword(s):  
Nervous System ◽  
Growth Cone ◽  
Axon Growth ◽  
Growth Cones ◽  
Scaffolding Protein ◽  
Local Translation ◽  
Point Contacts ◽  
Adhesion Sites ◽  
Actin Mrna ◽  
Developing Nervous System

AbstractLocal translation regulates the formation of appropriate connectivity in the developing nervous system. However, the localization and molecular mechanisms underlying this translation within growth cones is not well understood. Receptor for activated C kinase 1 (RACK1) is a multi-functional ribosomal scaffolding protein that interacts with β-actin mRNA. We recently showed that RACK1 localizes to and regulates the formation of point contacts, which are adhesion sites that control growth cone motility. This suggests that local translation occurs at these adhesion sites that are important for axonal pathfinding, but this has not been investigated. Here, we show that RACK1 is required for BDNF-induced local translation of β-actin mRNA in growth cones. Furthermore, the ribosomal binding function of RACK1 regulates point contact formation, and axon growth and guidance. We also find that local translation of β-actin occurs at point contacts. Taken together, we show that adhesions are a targeted site of local translation within growth cones, and RACK1 is critical to the formation of point contacts and appropriate neural development. These data provide further insight into how and where local translation is regulated, and thereby leads to appropriate connectivity formation in the developing nervous system.

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 Neuron-specific membrane glycoproteins promoting neurite fasciculation in Aplysia californica.

1990 ◽  
Vol 111 (6) ◽  
pp. 2637-2650 ◽  
Author(s):  
F Keller ◽  
S Schacher
Keyword(s):  
Nervous System ◽  
Aplysia Californica ◽  
Axon Growth ◽  
Growth Cones ◽  
Abundant Species ◽  
Living Cells ◽  
Membrane Glycoproteins ◽  
Western Blots ◽  
Molecular Masses ◽  
Specific Membrane

We have generated a library of mouse monoclonal antibodies against membrane proteins of the nervous system of the marine snail Aplysia californica. Two of these antibodies, 4E8 and 3D9, recognize a group of membrane glycoproteins with molecular masses of 100-150 kD. We have called these proteins ap100, from the molecular mass of the most abundant species. Based on Western blots, these proteins appear to be specific for the nervous system. They are enriched in the neuropil of central nervous system ganglia, and are present on the surface of neurites and growth cones of neurons in culture. They are not expressed on the surface of nonneuronal cells. Staining of living cells with fluorescently labeled mAb demonstrates that the epitope(s) are on the outside of the cell. The antibodies against the proteins defasciculate growing axons and alter the morphology of growth cones, but affect much less adhesion between neuritic shafts. In addition, the level of expression of these molecules appears to correlate with the degree of fasciculation of neurites. These observations suggest that the ap100 proteins are cell adhesion molecules that play a role in axon growth in the nervous system of Aplysia. The fact that they are enriched in the neuropil and possibly in varicosities suggest that they may also be relevant for the structure of mature synapses.

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.

Use of calcium imaging technologies to dissect mechanisms underlying neuronal growth cone responses to environmental cues

1995 ◽  
Vol 53 ◽  
pp. 804-805
Author(s):  
C.V. Williams ◽  
S.B. Kater
Keyword(s):  
Nervous System ◽  
Growth Cone ◽  
Local Environment ◽  
Growth Cones ◽  
Neuronal Growth ◽  
Growth Inhibitory ◽  
Direct Growth ◽  
Neuronal Growth Cone ◽  
Mechanical Factors ◽  
Growth Promoting

Since calcium is a key second messenger in both the developmental formation and adult function of the nervous system, the ability to rapidly image changes in this molecule has added greatly to our understanding of how development of the nervous system is regulated. The nervous system is comprised of billions of neurons and glial cells that establish characteristic patterns of connections during development. Neurons extend processes that often must grow long distances to establish appropriate synaptic connections. Neurons perform a pathfinding behavior largely via the highly dynamic behavior of the neuronal growth cone at the distal tip of elongating processes. The motile behavior characteristic of growth cones allows the growth cone to survey the local environment, read local cues and respond to those cues with a change in behavior. A variety of cues are now known to direct growth cones (e.g. electrical activity, depolarization, growth factors, mechanical factors, neurotransmitters, substrate factors). This collection of factors includes both growth promoting and growth inhibitory influences.

scholarly journals Gradients and Growth Cone Guidance of Grasshopper Neurons

2003 ◽  
Vol 51 (4) ◽  
pp. 445-454 ◽  
Author(s):  
Arthur T. Legg ◽  
Timothy P. O'Connor
Keyword(s):  
Nervous System ◽  
Long Range ◽  
Growth Cone ◽  
Growth Cones ◽  
Path Finding ◽  
Guidance Cues ◽  
Cone Function ◽  
The Absolute ◽  
Growth Cone Guidance

The generation of a functional nervous system is dependent on precise path-finding of axons during development. This pathfinding is directed by the distribution of local and long-range guidance cues, the latter of which are believed to be distributed in gradients. Gradients of guidance cues have been associated with growth cone function for over a hundred years. However, little is known about the mechanisms used by growth cones to respond to these gradients, in part owing to the lack of identifiable gradients in vivo. In the developing grasshopper limb, two gradients of the semaphorin Sema-2a are necessary for correct neuronal pathfinding in vivo. The gradients are found in regions where growth cones make critical steering decisions. Observations of different growth cone behaviors associated with these gradients have provided some insights into how growth cones respond to them. Growth cones appear to respond more faithfully to changes in concentration, rather than absolute levels, of Sema-2a expression, whereas the absolute levels may regulate growth cone size.

scholarly journals Local Arp2/3-dependent actin assembly modulates applied traction force during apCAM adhesion site maturation

2017 ◽  
Vol 28 (1) ◽  
pp. 98-110 ◽  
Author(s):  
Kenneth B. Buck ◽  
Andrew W. Schaefer ◽  
Vincent T. Schoonderwoert ◽  
Matthew S. Creamer ◽  
Eric R. Dufresne ◽  
...  
Keyword(s):  
Growth Cone ◽  
Network Flow ◽  
Traction Force ◽  
Axon Growth ◽  
Immunoglobulin Superfamily ◽  
Retrograde Flow ◽  
Actin Assembly ◽  
Growth Responses ◽  
Mechanical Restraint ◽  
Adhesion Sites

Homophilic binding of immunoglobulin superfamily molecules such as the Aplysia cell adhesion molecule (apCAM) leads to actin filament assembly near nascent adhesion sites. Such actin assembly can generate significant localized forces that have not been characterized in the larger context of axon growth and guidance. We used apCAM-coated bead substrates applied to the surface of neuronal growth cones to characterize the development of forces evoked by varying stiffness of mechanical restraint. Unrestrained bead propulsion matched or exceeded rates of retrograde network flow and was dependent on Arp2/3 complex activity. Analysis of growth cone forces applied to beads at low stiffness of restraint revealed switching between two states: frictional coupling to retrograde flow and Arp2/3-dependent propulsion. Stiff mechanical restraint led to formation of an extensive actin cup matching the geometric profile of the bead target and forward growth cone translocation; pharmacological inhibition of the Arp2/3 complex or Rac attenuated F-actin assembly near bead binding sites, decreased the efficacy of growth responses, and blocked accumulation of signaling molecules associated with nascent adhesions. These studies introduce a new model for regulation of traction force in which local actin assembly forces buffer nascent adhesion sites from the mechanical effects of retrograde flow.

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

2020 ◽  
Author(s):  
Hiroki Takechi ◽  
Satoko Hakeda-Suzuki ◽  
Yohei Nitta ◽  
Yuichi Ishiwata ◽  
Makoto Sato ◽  
...  
Keyword(s):  
Visual System ◽  
Developmental Stage ◽  
Growth Cone ◽  
Short Range ◽  
Transmembrane Protein ◽  
Axon Growth ◽  
Growth Cones ◽  
Neuronal Circuit ◽  
Axon Targeting ◽  
Stepwise Manner

SummaryTransmembrane protein Golden goal (Gogo) interacts with the 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 in this process. Nonphosphorylated Gogo mediates the initial recognition of the glial protrusion in the center of the medulla column, whereas phosphorylated Gogo suppresses horizontal filopodia extension by counteracting Flamingo to maintain one axon to one column ratio. Later, Gogo expression ceases during the midpupal developmental 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’s functional neuronal circuit.

scholarly journals From embryonic fascicles to adult tracts: organization of neuropile from a developmental perspective

1984 ◽  
Vol 112 (1) ◽  
pp. 45-64
Author(s):  
M. Bastiani ◽  
K. G. Pearson ◽  
C. S. Goodman
Keyword(s):  
Nervous System ◽  
Embryonic Development ◽  
Growth Cone ◽  
Morphological Differentiation ◽  
Growth Cones ◽  
The Other ◽  
Developmental Perspective ◽  
Longitudinal Axon ◽  
Repeated Pattern ◽  
Thoracic And Abdominal

We discuss ideas emerging from our studies on selective axonal fasciculation in the grasshopper embryo that have implications for the organization of the adult neuropile in insects and perhaps other animals. While one of our laboratories has been studying the embryonic development of the G neurone (in the mesothoracic segment) and its lineal homologues (in other segments), the other has been studying the morphology and physiology of this same neurone and its segmental homologues in the adult nervous system. Our embryonic studies show that the growth cone of the G neurone selectively fasciculates with the A/P fascicle in preference to all other longitudinal axon fascicles at it turns anteriorly. The homologues of G in other thoracic and abdominal segments fasciculate in this same bundle. However, early in their morphological differentiation, they reveal interesting segmental differences. Our studies on the adult nervous system show that the segmental homologues of the G neurone share many properties in common (e.g. axons in the LDT: lateral dorsal tract) while other features are quite different. The notion emerging from these studies is that a basic segmentally-repeated pattern arises during embryogenesis: a stereotyped axonal scaffold upon which growth cones faithfully fasciculate. Evolutionary plasticity allows the specialization of lineally equivalent neurones in different segments within the context of the neuropilar neighbourhood that they find themselves in as a consequence of their selective fasciculation.

SRC binding to the cytoskeleton, triggered by growth cone attachment to laminin, is protein tyrosine phosphatase-dependent

1998 ◽  
Vol 111 (16) ◽  
pp. 2465-2475 ◽  
Author(s):  
S. Helmke ◽  
K. Lohse ◽  
K. Mikule ◽  
M.R. Wood ◽  
K.H. Pfenninger
Keyword(s):  
Phosphatase Activity ◽  
Growth Cone ◽  
Protein Tyrosine Phosphatase ◽  
Tyrosine Phosphatase ◽  
Protein Tyrosine Phosphatases ◽  
Growth Cones ◽  
Tyrosine Phosphatases ◽  
Protein Tyrosine ◽  
Adhesion Sites ◽  
Adhesion Site

The interaction of the non-receptor tyrosine kinase, Src, with the cytoskeleton of adhesion sites was studied in nerve growth cones isolated from fetal rat brain. Of particular interest was the role of protein tyrosine phosphatases in the regulation of Src-cytoskeleton binding. Growth cones were found to contain a high level of protein tryrosine phosphatase activity, most of it membrane-associated and forming large, multimeric and wheat germ agglutinin-binding complexes. The receptor tyrosine phosphatase PTPalpha seems to be the most prevalent species among the membrane-associated enzymes. As seen by immunofluorescence, PTPalpha is present throughout the plasmalemma of the growth cone including filopodia, and it forms a punctate pattern consistent with that of integrin beta1. For adhesion site analysis, isolated growth cones were either plated onto the neurite growth substratum, laminin, or kept in suspension. Plating growth cones on laminin triggered an 8-fold increase in Src binding to the adherent cytoskeleton. This effect was blocked completely with the protein tyrosine phosphatase inhibitor, vanadate. Growth cone plating also increased the association with adhesion sites of tyrosine phosphatase activity (14-fold) and of PTPalpha immunoreactivity (6-fold). Vanadate blocked the enzyme activity but not the recruitment of PTPalpha to the adhesion sites. In conjunction with our previous results on growth cones, these data suggest that integrin binding to laminin triggers the recruitment of PTPalpha (and perhaps other protein tyrosine phosphatases) to adhesion sites, resulting in de-phosphorylation of Src's tyr 527. As a result Src unfolds, becomes kinase-active, and its SH2 domain can bind to an adhesion site protein. This implies a critical role for protein tyrosine phosphatase activity in the earliest phases of adhesion site assembly.

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