Guidance Cues (guidance + cue)

Distribution by Scientific Domains

Selected Abstracts

Comparison of the effects of HGF, BDNF, CT-1, CNTF, and the branchial arches on the growth of embryonic cranial motor neurons

Arifa Naeem
Abstract In the developing embryo, axon growth and guidance depend on cues that include diffusible molecules. We have shown previously that the branchial arches and hepatocyte growth factor (HGF) are growth-promoting and chemoattractant for young embryonic cranial motor axons. HGF is produced in the branchial arches of the embryo, but a number of lines of evidence suggest that HGF is unlikely to be the only factor involved in the growth and guidance of these axons. Here we investigate whether other neurotrophic factors could be involved in the growth of young cranial motor neurons in explant cultures. We find that brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) and cardiotrophin-1 (CT-1) all promote the outgrowth of embryonic cranial motor neurons, while glial cell line-derived neurotrophic factor (GDNF) and neurotrophin-3 (NT-3) fail to affect outgrowth. We next examined whether HGF and the branchial arches had similar effects on motor neuron subpopulations at different axial levels. Our results show that HGF acts as a generalized rather than a specific neurotrophic factor and guidance cue for cranial motor neurons. Although the branchial arches also had general growth-promoting effects on all motor neuron subpopulations, they chemoattracted different axial levels differentially, with motor neurons from the caudal hindbrain showing the most striking response. 2002 Wiley Periodicals, Inc. J Neurobiol 51: 101,114, 2002 [source]

Semaphorin 3A-Neuropilin-1 signaling regulates peripheral axon fasciculation and pathfinding but not developmental cell death patterns

Corinna Haupt
Abstract In early development, an excess of neurons is generated, of which later about half will be lost by cell death due to a limited supply of trophic support by their respective target areas. However, some of the neurons die when their axons have not yet reached their target, thus suggesting that additional causes of developmental cell death exist. Semaphorin 3A (Sema3A), in addition to its function as a guidance cue and mediator of timing and fasciculation of motor and sensory axon outgrowth, can also induce death of sensory neurons in vitro. However, it is unknown whether Neuropilin-1 (Npn-1), its binding receptor in axon guidance, also mediates the death-inducing activity. We show here that abolished Sema3A-Npn-1 signaling does not influence the cell death patterns of motor or sensory neurons in mouse during the developmental wave of programmed cell death. The number of motor and sensory neurons was unchanged at embryonic day 15.5 when this wave is concluded. Interestingly, the defasciculation of early motor and sensory projections that is observed in the absence of Sema3A or Npn-1 persists to postnatal stages. Thus, Sema3A-Npn-1 signaling plays an important role in the guidance and fasciculation of motor and sensory axons but does not contribute to the developmental elimination of these neurons. [source]

Spatially patterned gene expression for guided neurite extension

Tiffany Houchin-Ray
Abstract Axon pathfinding by localized expression of guidance molecules is critical for the proper development of the nervous system. In this report, we present a well-defined spatially patterned gene expression system to investigate neurite guidance in vitro. Nonviral gene delivery was patterned by combining substrate-mediated gene delivery with soft lithography techniques, and the amount of protein produced at the region of localized expression was varied by altering the vector concentration and the width of the pattern, highlighting the flexibility of the system. A neuronal coculture model was used to investigate responses to spatial patterns of nerve growth factor (NGF) expression. The soluble NGF gradient elicited a guidance cue, and the degree of guidance was governed by the distance a neuron was cultured from the pattern and the time between accessory cell and neuron seedings. A portion of the diffusible NGF bound to the culture surface in the extracellular space, and the surface-associated NGF supported neuron survival and neurite outgrowth. However, the surface-bound NGF gradient alone did not elicit a guidance signal, and in fact masked the guidance cue by soluble NGF gradients. Mathematical modeling of NGF diffusion was used to predict the concentration gradients, and both the absolute and fractional gradients capable of guiding neurites produced by patterned gene expression differed substantially from the values obtained with existing engineered protein gradients. Spatially patterned gene expression provides a versatile tool to investigate the factors that may promote neurite guidance. 2008 Wiley-Liss, Inc. [source]

Zebrafish notch signalling pathway mutants exhibit trunk vessel patterning anomalies that are secondary to somite misregulation

Christina Therapontos
Abstract The Notch signalling pathway mutants, after-eight (aei), beamter (bea), and deadly-seven (des) have previously been used to study somitogenesis and neurogenesis. Notch signalling has also been shown to have roles in vascular development. However, vascular development in each of these three Notch mutants has not been described, and so their potential usefulness for further understanding the role of Notch signalling in angiogenesis is unknown. Here we demonstrate each of the mutants also exhibit vascular defects in inter-somitic vessel (ISV) positioning and patterning. Ectopic filopodia were also observed on the ISVs of the mutants. Ectopic filopodia are not due to loss of dll4. Somite expression of known vascular guidance cues, efnb2, sema3a2, and plexinD1 are disrupted, suggesting that the ISV vascular phenotype is due to disruption of these cues. Developmental Dynamics 239:2761,2768, 2010. 2010 Wiley-Liss, Inc. [source]

Semaphorin and neuropilin expression during early morphogenesis of Xenopus laevis

Ulrich Koestner
Abstract Semaphorins are major regulators of morphogenesis and are involved in a variety of processes ranging from the guidance of cell migration to the development of cancer. Since semaphorins were first characterized as repulsive neuronal guidance cues, their expression has been best documented in the nervous system. However, broader studies are lacking. Here, we describe the expression of 13 members of the semaphorin family and two neuropilin receptors during early Xenopus laevis development. No particular expression pattern defines any of the semaphorin classes, but many are dynamically expressed in distinct areas undergoing morphogenetic cell movements like the developing mesoderm and the migrating neural crest. Furthermore, the complementary expression patterns of Sema3A/Nrp1 and Sema3F/Nrp2 are maintained across hundreds of millions of years, possibly indicating a conserved role in the guidance of migrating neural crest cells. Developmental Dynamics 237:3853,3863, 2008. 2008 Wiley-Liss, Inc. [source]

Activation of ADF/cofilin mediates attractive growth cone turning toward nerve growth factor and netrin-1

Bonnie M. Marsick
Abstract Proper neural circuitry requires that growth cones, motile tips of extending axons, respond to molecular guidance cues expressed in the developing organism. However, it is unclear how guidance cues modify the cytoskeleton to guide growth cone pathfinding. Here, we show acute treatment with two attractive guidance cues, nerve growth factor (NGF) and netrin-1, for embryonic dorsal root ganglion and temporal retinal neurons, respectively, results in increased growth cone membrane protrusion, actin polymerization, and filamentous actin (F-actin). ADF/cofilin (AC) family proteins facilitate F-actin dynamics, and we found the inactive phosphorylated form of AC is decreased in NGF- or netrin-1-treated growth cones. Directly increasing AC activity mimics addition of NGF or netrin-1 to increase growth cone protrusion and F-actin levels. Extracellular gradients of NGF, netrin-1, and a cell-permeable AC elicit attractive growth cone turning and increased F-actin barbed ends, F-actin accumulation, and active AC in growth cone regions proximal to the gradient source. Reducing AC activity blunts turning responses to NGF and netrin. Our results suggest that gradients of NGF and netrin-1 locally activate AC to promote actin polymerization and subsequent growth cone turning toward the side containing higher AC activity. 2010 Wiley Periodicals, Inc. Develop Neurobiol 70: 565,588, 2010 [source]

Laminin and fibronectin modulate inner ear spiral ganglion neurite outgrowth in an in vitro alternate choice assay

Amaretta R. Evans
Abstract Extracellular matrix (ECM) molecules have been shown to function as cues for neurite guidance in various populations of neurons. Here we show that laminin (LN) and fibronectin (FN) presented in stripe micro-patterns can provide guidance cues to neonatal (P5) inner ear spiral ganglion (SG) neurites. The response to both ECM molecules was dose-dependent. In a LN versus poly- L -lysine (PLL) assay, neurites were more often observed on PLL at low coating concentrations (5 and 10 ,g/mL), while they were more often on LN at a high concentration (80 ,g/mL). In a FN versus PLL assay, neurites were more often on PLL than on FN stripes at high coating concentrations (40 and 80 ,g/mL). In a direct competition between LN and FN, neurites were observed on LN significantly more often than on FN at both 10 and 40 ,g/mL. The data suggest a preference by SG neurites for LN at high concentrations, as well as avoidance of both LN at low and FN at high concentrations. The results also support a potential model for neurite guidance in the developing inner ear in vivo. LN, in the SG and osseus spiral lamina may promote SG dendrite growth toward the organ of Corti. Within the organ of Corti, lower concentrations of LN may slow neurite growth, with FN beneath each row of hair cells providing a stop or avoidance signal. This could allow growth cone filopodia increased time to sample their cellular targets, or direct the fibers upward toward the hair cells. 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007 [source]

Netrin-1 receptor-deficient mice show enhanced mesocortical dopamine transmission and blunted behavioural responses to amphetamine

Alanna Grant
Abstract The mesocorticolimbic dopamine (DA) system is implicated in neurodevelopmental psychiatric disorders including schizophrenia but it is unknown how disruptions in brain development modify this system and increase predisposition to cognitive and behavioural abnormalities in adulthood. Netrins are guidance cues involved in the proper organization of neuronal connectivity during development. We have hypothesized that variations in the function of DCC (deleted in colorectal cancer), a netrin-1 receptor highly expressed by DA neurones, may result in altered development and organization of mesocorticolimbic DA circuitry, and influence DA function in the adult. To test this hypothesis, we assessed the effects of reduced DCC on several indicators of DA function. Using in-vivo microdialysis, we showed that adult mice that develop with reduced DCC display increased basal DA levels in the medial prefrontal cortex and exaggerated DA release in response to the indirect DA agonist amphetamine. In contrast, these mice exhibit normal levels of DA in the nucleus accumbens but significantly blunted amphetamine-induced DA release. Concomitantly, using conditioned place preference, locomotor activity and prepulse inhibition paradigms, we found that reduced DCC diminishes the rewarding and behavioural-activating effects of amphetamine and protects against amphetamine-induced deficits in sensorimotor gating. Furthermore, we found that adult DCC-deficient mice exhibit altered dendritic spine density in layer V medial prefrontal cortex pyramidal neurones but not in nucleus accumbens medium spiny neurones. These findings demonstrate that reduced DCC during development results in a behavioural phenotype opposite to that observed in developmental models of schizophrenia and identify DCC as a critical factor in the development of DA function. [source]

Membrane-associated guidance cues direct the innervation of forebrain and midbrain by dorsal raphe-derived serotonergic axons

Audrey Petit
Abstract Unlike many neurons that extend an axon precisely to a single target, individual dorsal raphe 5-HT neurons project to multiple brain regions and their axon terminals often lack classical synaptic specializations. It is not known how 5-HT axon collaterals select between multiple target fields, or even if 5-HT axons require specific guidance cues to innervate their targets. Nor is it known how these axon collaterals are restrained within specific innervation target regions. To investigate this, we challenged explants of dorsal raphe with co-explants, or cell membrane preparations of ventral midbrain, striatum or cerebral cortex. We provide evidence for membrane-associated cues that promote 5-HT axon growth into each of these three target regions. The axon growth-promoting activity was heat-, protease- and phosphatidylinositol-phospholipase-C (PI-PLC)-sensitive. Interestingly, 5-HT axons specifically lost the ability to grow in heterotypic explants, or membrane carpets, following contact with ventral midbrain or striatal, but not cortical, explants or membranes. This inductive activity associated with striatal and ventral midbrain membranes was sensitive to both high salt extraction and PI-PLC treatment. By contrast, the activity that inhibited 5-HT axon growth onto heterotypic membranes was sensitive only to high salt extraction. These results provide evidence that a glycosylphosphatidylinositol (GPI)-linked membrane protein promotes 5-HT axon growth, and that short-range membrane-bound, as well as GPI-linked, molecules contribute to the guidance of 5-HT axon collaterals. These findings suggest that 5-HT axon collaterals acquire a target-induced growth-inhibitory response to alternative targets, increasing their selectivity for the newly innervated field. [source]

Dynamic changes in glypican-1 expression in dorsal root ganglion neurons after peripheral and central axonal injury

Stefan Bloechlinger
Abstract Glypican-1, a glycosyl phosphatidyl inositol (GPI)-anchored heparan sulphate proteoglycan expressed in the developing and mature cells of the central nervous system, acts as a coreceptor for diverse ligands, including slit axonal guidance proteins, fibroblast growth factors and laminin. We have examined its expression in primary sensory dorsal root ganglion (DRG) neurons and spinal cord after axonal injury. In noninjured rats, glypican-1 mRNA and protein are constitutively expressed at low levels in lumbar DRGs. Sciatic nerve transection results in a two-fold increase in mRNA and protein expression. High glypican-1 expression persists until the injured axons reinnervate their peripheral targets, as in the case of a crushed nerve. Injury to the central axons of DRG neurons by either a dorsal column injury or a dorsal root transection also up-regulates glypican-1, a feature that differs from most DRG axonal injury-induced genes, whose regulation changes only after peripheral and not central axonal injury. After axonal injury, the cellular localization of glypican-1 changes from a nuclear pattern restricted to neurons in noninjured DRGs, to the cytoplasm and membrane of injured neurons, as well as neighbouring non-neuronal cells. Sciatic nerve transection also leads to an accumulation of glypican-1 in the proximal nerve segment of injured axons. Glypican-1 is coexpressed with robo 2 and its up-regulation after axonal injury may contribute to an altered sensitivity to axonal growth or guidance cues. [source]

Spatiotemporal properties of cytoplasmic cyclic AMP gradients can alter the turning behaviour of neuronal growth cones

Sebastian Munck
Abstract Growth cones, the terminal structures of elongating neurites, use extracellular guidance information in order to navigate to appropriate target cells. The directional information of guidance cues is transduced to a cytoplasmic gradient of messenger molecules across the growth cone leading to rearrangements of the cytoskeleton. One messenger molecule regulating growth cone turning is cAMP, which is also known to be sufficient to direct growth cone attraction. Cytoplasmic cAMP gradients have been generated in the present study by photolysing caged cAMP with UV light focused on one side of growth cones of chick sensory neurons. Using this method we show that only specific time patterns of pulsed cAMP release are capable of inducing growth cone turning whereas others, which release the same amount of cAMP, are ineffective. Theoretical calculations show that diverse time patterns produce different intracellular gradients, which were visualized directly in HeLa cells expressing cAMP-sensitive ion channels as a reporter system. Together these data indicate that the spatiotemporal properties of the intracellular gradient are crucial for growth cone turning. [source]

Cell Migration: Guided Cell Migration on Microtextured Substrates with Variable Local Density and Anisotropy (Adv. Funct.

A novel microtextured cell substrate with variable local density and anisotropy as a platform for guided cell migration is presented by A. Levchenko, K.-Y. Suh, et al. on page 1579. A simple, scalable, and cost-effective technique, capillary force lithography, is used to fabricate precise microtopographic features on an optically transparent glass coverslip. Live cell motility is found to be extremely sensitive to variation in the local density and anisotropy of rectangular lattices, with cell elongation and speed decreasing on a symmetric lattice. Cells integrate orthogonal contact guidance cues when determining the direction of their orientation and movement. [source]

Netrin induces down-regulation of its receptor, Deleted in Colorectal Cancer, through the ubiquitin,proteasome pathway in the embryonic cortical neuron

Tae-Hong Kim
Abstract The proper regulation of temporal and spatial expression of the axon guidance cues and their receptors is critical for the normal wiring of nervous system during development. Netrins, a family of secreted guidance cues, are involved in the midline crossing of spinal commissural axons and in the guidance of cortical efferents. Axons normally lose the responsiveness to their attractants when they arrive at their targets, where the attractant is produced. However the molecular mechanism is still unknown. We investigated the molecular mechanism of down-regulation of netrin-1 signaling in the embryonic cortical neurons. Netrin-1 induced the ubiquitination and proteolytic cleavage of Deleted in Colorectal Cancer (DCC), a transmembrane receptor for netrin, in dissociated cortical neurons. A dramatic decrease of DCC level particularly on the cell surface was also observed after netrin-1 stimulation. Specific ubiquitin,proteasome inhibitors prevented the netrin-induced DCC cleavage and decrease of cell surface DCC. We suggest that the ligand-mediated down-regulation of DCC might participate in the loss of netrin-responsiveness in the developing nervous system. [source]

Impaired postnatal development of hippocampal neurons and axon projections in the Emx2,/, mutants

Nicolai E. Savaskan
Abstract The specification and innervation of cerebral subregions is a complex layer-specific process, primed by region-specific transcription factor expression and axonal guidance cues. In Emx2,/, mice, the hippocampus fails to form a normal dentate gyrus as well as the normal layering of principal neurons in the hippocampus proper. Here, we analyzed the late embryonic and postnatal development of the hippocampal formation and its axonal projections in mice lacking Emx2 expression in vitro. As these mutants die perinatally, we used slice cultures of Emx2 mutant hippocampus to circumvent this problem. In late embryonic Emx2,/, cultivated hippocampi, both the perforant path as well as the distribution of calretinin-positive cells are affected. Traced entorhinal afferents in co-cultures with hippocampus from embryonic Emx2,/, mice terminate diffusely in the prospective dentate gyrus in contrast to the layer-specific termination of co-cultures from wild-type littermates. In addition, in brain slice cultures from null mutants the presumptive dentate gyrus failed to develop its normal cytoarchitecture and mature dentate granule cells, including the lack of their mossy fiber projection. Our data indicate that Emx2 is essential for the terminal differentiation of granular cells and the correct formation of extrinsic and intrinsic hippocampal connections. [source]

Signaling mechanisms that regulate actin-based motility processes in the nervous system

Gary Meyer
Abstract Actin-based motility is critical for nervous system development. Both the migration of neurons and the extension of neurites require organized actin polymerization to push the cell membrane forward. Numerous extracellular stimulants of motility and axon guidance cues regulate actin-based motility through the rho GTPases (rho, rac, and cdc42). The rho GTPases reorganize the actin cytoskeleton, leading to stress fiber, filopodium, or lamellipodium formation. The activity of the rho GTPases is regulated by a variety of proteins that either stimulate GTP uptake (activation) or hydrolysis (inactivation). These proteins potentially link extracellular signals to the activation state of rho GTPases. Effectors downstream of the rho GTPases that directly influence actin polymerization have been identified and are involved in neurite development. The Arp2/3 complex nucleates the formation of new actin branches that extend the membrane forward. Ena/VASP proteins can cause the formation of longer actin filaments, characteristic of growth cone actin morphology, by preventing the capping of barbed ends. Actin-depolymerizing factor (ADF)/cofilin depolymerizes and severs actin branches in older parts of the actin meshwork, freeing monomers to be re-incorporated into actively growing filaments. The signaling mechanisms by which extracellular cues that guide axons to their targets lead to direct effects on actin filament dynamics are becoming better understood. [source]

Olfactory axon guidance: The modified rules

Gerald A. Schwarting
Abstract The olfactory system represents a complex model for the investigation of factors that influence the guidance of sensory axon populations to specific targets in the CNS. In the mouse, the projections of approximately 1,000 neuronal subsets, each defined by expression of a distinct odorant receptor (OR), converge at unique glomerular loci in the olfactory bulb (OB). Unlike the case in other sensory systems, proper guidance is achieved without benefit of any known cues in the target itself that are capable of attracting or repelling specific axons. It has long been argued that OR proteins are the critical molecules orchestrating guidance. However, recent studies suggest that axon identity may be dependent on the graded expression of a variety of unique olfactory axon guidance cues. This review focuses attention on these non-OR factors and their roles in olfactory axon guidance. 2007 Wiley-Liss, Inc. [source]

Statistical morphological analysis of hippocampal principal neurons indicates cell-specific repulsion of dendrites from their own cell

Alexei V. Samsonovich
Abstract Traditionally, the sources of guidance cues for dendritic outgrowth are mainly associated with external bodies (A) rather than with the same neuron from which dendrites originate (B). To quantify the relationship between factors A and B as determinants of the adult dendritic shape, the morphology of 83 intracellularly characterized, stained, completely reconstructed, and digitized principal neurons of the rat hippocampus was statistically analyzed using Bayesian optimization. It was found that the dominant directional preference (tropism) manifested in dendritic turns is to grow away from the soma rather than toward the incoming fibers or in any other fixed direction; therefore, B is predominant. Results are robust and consistent for all examined morphological classes (dentate gyrus granule cells, basal and apical trees of CA3 and CA1 pyramidal cells). In addition, computer remodeling of neurons based on the measured parameters produced virtual structures consistent with real morphologies, as confirmed by measurement of several global emergent parameters. Thus, the simple description of dendritic shape based on dendrites' tendency to grow straight, away from their own soma, and with additional random deflections, proves remarkably accurate and complete. Although based on adult neurons, these results suggest that dendritic guidance during development may be associated primarily with the host cell. This possibility challenges the traditional concept of dendritic guidance: in that hippocampal cells are densely packed and have highly overlapping dendritic fields, the somatodendritic repulsion must be cell specific. Plausible mechanisms involving extracellular effects of spikes are discussed, together with feasible experimental tests and predicted results. 2002 Wiley-Liss, Inc. [source]

Thermodynamic characterization of two homologous protein complexes: Associations of the semaphorin receptor plexin-B1 RhoGTPase binding domain with Rnd1 and active Rac1

Prasanta K. Hota
Abstract Plexin receptors function in response to semaphorin guidance cues in a variety of developmental processes involving cell motility. Interactions with Rho, as well as Ras family small GTPases are critical events in the cell signaling mechanism. We have recently determined the structure of a cytoplasmic domain (RBD) of plexin-B1 and mapped its binding interface with several Rho-GTPases, Rac1, Rnd1, and RhoD. All three GTPases associate with a similar region of this plexin domain, but show different functional behavior in cells. To understand whether thermodynamic properties of the GTPase,RBD interaction contribute to such different behavior, we have examined the interaction at different temperatures, buffer, and pH conditions. Although the binding affinity of both Rnd1 and Rac1 with the plexin-B1 RBD is similar, the detailed thermodynamic properties of the interactions are considerably different. These data suggest that on Rac1 binding to the plexin-B1 RBD, the proteins become more rigid in the complex. By contrast, Rnd1 binding is consistent with unchanged or slightly increased flexibility in one or both proteins. Both GTPases show an appreciable reduction in affinity for the dimeric plexin-B1 RBD indicating that GTPase binding is not cooperative with dimer formation, but that a partial steric hindrance destabilizes the dimer. However, a reduced affinity binding mode to a disulphide stabilized model for the dimeric RBD is also possible. Consistent with cellular studies, the interaction thermodynamics imply that further levels of regulation involving additional binding partners and/or regions outside of the RhoGTPase binding domain are required for receptor activation. [source]

Analysis of Gene Expression in Parkinson's Disease: Possible Involvement of Neurotrophic Support and Axon Guidance in Dopaminergic Cell Death

Koen Bossers
Abstract Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra. We have studied alterations in gene expression in the substantia nigra, the caudate nucleus and putamen of four PD patients and four matched controls using custom designed Agilent microarrays. To gain insight into changes in gene expression during early stages of dopaminergic neurodegeneration, we selectively investigated the relatively spared parts of the PD substantia nigra, and correlated gene expression changes with alterations in neuronal density. We identified changes in the expression of 287 transcripts in the substantia nigra, 16 transcripts in the caudate nucleus and four transcripts in the putamen. For selected transcripts, transcriptional alterations were confirmed with qPCR on a larger set of seven PD cases and seven matched controls. We detected concerted changes in functionally connected groups of genes. In the PD substantia nigra, we observed strong evidence for a reduction in neurotrophic support and alterations in axon guidance cues. As the changes occur in relatively spared parts of the PD substantia nigra, they suggest novel disease mechanisms involving neurotrophic support and axon guidance in early stages of cellular stress events, ultimately leading to dopaminergic cell death in PD. [source]