QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online 11 October 2006
doi: 10.1242/dev.02623

This Article Summary Figures Only Full Text (PDF) All Versions of this Article: dev.02623v1 133/22/4415    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dufour, A. Articles by Vanderhaeghen, P. Search for Related Content PubMed PubMed Citation Articles by Dufour, A. Articles by Vanderhaeghen, P. Social Bookmarking                         What's this?

Genetic analysis of EphA-dependent signaling mechanisms controlling topographic mapping in vivo

¹ Institut de Recherches en Biologie Humaine et Moléculaire (IRIBHM), University of Brussels (U.L.B.), Campus Erasme, 808 Route de Lennik, B-1070 Brussels, Belgium.
² Max Planck Institute of Neurobiology, 82152 Martinsried, Germany.
³ Department of Neuroscience, Unit of Developmental Genetics, Uppsala University, Box 587, 751 23 Uppsala, Sweden.

^* Author for correspondence (e-mail: pvdhaegh{at}ulb.ac.be)

Accepted 11 September 2006

SUMMARY

Ephrin/Eph ligands and receptors are best known for their prominent role in topographic mapping of neural connectivity. Despite the large amount of work centered on ephrin/Eph-dependent signaling pathways in various cellular contexts, the molecular mechanisms of action of Eph receptors in neural mapping, requiring dynamic interactions between complementary gradients of ephrins and Eph receptors, remain largely unknown. Here, we investigated in vivo the signaling mechanisms of neural mapping mediated by the EphA4 receptor, previously shown to control topographic specificity of thalamocortical axons in the mouse somatosensory system. Using axon tracing analyses of knock-in mouse lines displaying selective mutations for the Epha4 gene, we determined for the first time which intracellular domains of an Eph receptor are required for topographic mapping. We provide direct in vivo evidence that the tyrosine kinase domain of EphA4, as well as a tight regulation of its activity, are required for topographic mapping of thalamocortical axons, whereas non-catalytic functional modules, such as the PDZ-binding motif (PBM) and the Sterile- motif (SAM) domain, are dispensable. These data provide a novel insight into the molecular mechanisms of topographic mapping, and constitute a physiological framework for the dissection of the downstream signaling cascades involved.

Key words: Topographic mapping, Ephrin, Eph, Thalamocortical

INTRODUCTION

Ephrin/Eph genes have been shown to play a prominent role in topographic mapping of neural connectivity in several sensory and motor systems (reviewed by Flanagan, 2006; Flanagan and Vanderhaeghen, 1998; McLaughlin and O'Leary, 2005).

Most of what is known about topographic mapping mediated by ephrin/Eph genes was learnt from studies on the retinotectal system; however, recently it has also been studied in other contexts, in particular in neuronal networks from higher brain structures, such as the thalamus and cerebral cortex. For example, several ephrin/Eph genes have been shown to control the patterning of thalamocortical (TC) maps in the primary somatosensory and visual areas of the neocortex (Cang et al., 2005; Dufour et al., 2003; Prakash et al., 2000; Vanderhaeghen et al., 2000; Vanderhaeghen and Polleux, 2004), as well as the mapping of somatosensory cortico-thalamic efferents (Torii and Levitt, 2005).

The molecular mechanisms of signaling downstream of Eph receptors have been intensively investigated over the past few years (reviewed by Klein, 2004; Kullander and Klein, 2002; Pasquale, 2005). Eph receptors are receptor tyrosine kinases (RTKs) that show ligand-induced autophosphorylation and kinase activation, and many in vivo functions mediated by Eph signaling are thought to require an intact kinase activity (Egea et al., 2005; Kullander et al., 2001; Kullander and Klein, 2002). Like other RTKs, they are kept in an autoinhibited state by their juxtamembrane region, which interacts intramolecularly with the kinase domain, thereby maintaining it in an inactive conformation. Phosphorylation of specific tyrosine residues within the juxtamembrane region relieves this autoinhibition (Kullander et al., 2001; Kullander and Klein, 2002). Recent work also demonstrated the paramount importance of receptor clustering in triggering ephrin-dependent responses, aside of tyrosine kinase activation (Egea et al., 2005).

In addition to juxtamembrane tyrosines and the kinase domain, the cytoplasmic region of Eph receptors contains other functional modules, including a Sterile- motif (SAM) and a PDZ-binding motif (PBM). So far no obvious role has been assigned to the SAM domain, either in vitro or in vivo (Kullander et al., 2001). Similarly, although the PBM of ephrin-B ligands is thought to be important for neural migration and lymphangiogenesis (Lu et al., 2001; Makinen et al., 2005), the functional relevance of this domain in Eph receptors remains poorly understood.

By contrast, a number of potential intracellular interactors for Eph receptors have been identified, including MAP kinases, Src family kinases (SFK), PI 3-kinase, phopholipase C and small G-protein regulators (Kullander and Klein, 2002; Pasquale, 2005). Among the G-protein regulators, ephexins (Shamah et al., 2001) have been shown to be phosphorylated by SFKs upon ephrin stimulation (Knoll and Drescher, 2004), and to play a key role in Eph-mediated growth cone collapse, although their function in vivo remains partially unknown as a result of genetic redundancy (Sahin et al., 2005).

In contrast to the knowledge accumulated on ephrin/Eph-dependent signaling, the molecular mechanisms of action of Eph receptors in the context of neural topographic mapping remain much less characterized, although their major role as axon guidance factors has been uncovered in this biological context. The main reason for this discrepancy is that ephrin/Eph-dependent neural mapping is a complex system. In particular it relies on dynamic interactions between complementary gradients of ephrins and Eph receptors that influence several aspects of axon guidance, including repulsion and differential adhesion/attraction of the growth cone, as well as collateral branching (Flanagan, 2006; McLaughlin and O'Leary, 2005). Because of this complexity, it has been exceedingly difficult, if not impossible, to recapitulate mapping by using in vitro systems that are amenable to signal transduction pathway dissection. For the same reason, it is conceivable that distinct ephrin/Eph signaling mechanisms may be used specifically to achieve topographic mapping, but nothing is known about these.

We have previously shown that EphA4, which is expressed in a graded fashion in the somatosensory thalamic ventrobasal nucleus (VB), is required to generate proper topography of TC axons within the somatosensory cortex S1, which expresses a complementary gradient of ephrin A5 (Dufour et al., 2003). The somatosensory TC system thus constitutes an attractive system of topographic mapping that is dependent upon EphA4 signaling.

To try to gain insight into the signaling mechanisms of Eph-dependent mapping, we analyzed EphA4-dependent TC mapping in several mouse knock-in lines displaying distinct targeted mutations for EphA4 (Egea et al., 2005; Grunwald et al., 2004; Kullander et al., 2001). This set of mouse models had previously enabled the demonstration of distinct signaling mechanisms involved in EphA4-dependent midline pathfinding (Kullander et al., 2001), and suggested a differential requirement of EphA4 kinase regulation for repulsion at the midline and TC mapping (Egea et al., 2005). Here, we extended the analysis of TC mapping to all EphA4 alleles available and determined for the first time which intracellular domains of an Eph receptor are required for topographic mapping in vivo. We provide direct in vivo evidence that the tyrosine kinase domain of EphA4, as well as dynamic regulation of its activity, are required for the mapping of TC axons, whereas non-catalytic modules, such as the PBM and the SAM domain, are dispensable. Our data provide an in vivo framework of the signaling mechanisms downstream of Eph receptors that mediate topographic mapping in vivo.

MATERIALS AND METHODS

Generation of EphA4 mutant mice
Mutant EphA4^KO, EphA4^SAM, EphA4^KD, EphA4^GFP and EphA4^EE mice have been described previously (Egea et al., 2005; Grunwald et al., 2004; Kullander et al., 2001). The mutant EphA4^PBM allele was generated in the same way and encoded EphA4 lacking the last 12 amino acids, including the PDZ-binding domain. The loxP flanked neo cassette was removed in vivo by crossbreeding to a Cre recombinase-expressing transgenic mouse strain. All mutant phenotypes were analyzed in littermates from a comparable mixed 129/SvevxC57Bl/6 background. Western blot analyses of EphA4 protein content in neonatal thalamic extracts of wild-type and mutant mice were performed as described previously (Egea et al., 2005).

Axon tracing
Axon tracing was performed by focally injecting a carbocyanin dye [1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), 3% in dimethyl-formamide, Molecular Probes] into the cortex of living mice anesthetized by avertin (aged P13-P18, the time where all aspects of thalamocortical connectivity have been well established), using capillary micropipettes hooked up to a PicospritzerII (Dufour et al., 2003). Animals were sacrificed 1 to 2 days later, fixed by perfusion, and forebrain was vibratome sectioned at 200 µm. After examination of the sections using fluorescence microscopy, only cases in which the injections were restricted to the cortex without encompassing the white matter were further analyzed, to preclude artefacts due to dye uptake by fibers `en passant'. We focused our analysis to the topography of the VPM (ventro-postero-medial) part of the VB to the barrel cortex, which corresponds to the upper levels of the trigeminal representation. The position of the VB nucleus and its boundaries with respect to neighbouring nuclei in the thalamus was determined by inspection of the bright-field image, as well as by nuclear stain and a comparison of atlas data, and by cytochrome oxidase staining in some cases (Dufour et al., 2003). The phenotype was considered to be abnormal only when more than 10 cells were found outside the normal cluster of retrogradely labeled cells. Indeed, in a few cases, a few (less than 10) cells were found occasionally outside of the normal cluster irrespective of their genotype (including in wild type).

RESULTS AND DISCUSSION

To determine the distinct requirements of the signaling modules of the intracellular domain of EphA4 involved in mediating mapping function in vivo, we focused on the thalamocortical (TC) system (Fig. 1A) and performed axon-tracing analyses of mice with targeted mutations of EphA4 (Fig. 1E). These included mice displaying a full disruption of the gene (EphA4^KO) (Kullander et al., 2001), mice lacking the whole intracellular domain (EphA4^GFP mice, where GFP replaced the whole intracellular domain) (Grunwald et al., 2004) or mutated within the kinase catalytic domain (EphA4^KD) (Kullander et al., 2001), and mice lacking the SAM domain (EphA4^SAM) (Kullander et al., 2001) or the PBM (EphA4^PBM; this study). Phenotypes observed in these loss-of-function mutants were also compared with the ones observed in a previously described mutant, in which the juxtamembrane tyrosines are replaced by two glutamic acid residues (EphA4^EE), thereby resulting in constitutive activation of the tyrosine kinase domain (Egea et al., 2005). Importantly, none of these mutations altered the level of expression of EphA4 in the thalamus at relevant perinatal stages (Fig. 1F) (see also Egea et al., 2005).

In wild-type (EphA4^WT/WT) animals (n=17 in this study), a single injection of DiI in the S1 cortex (Fig. 1B,C) systematically results in a robust retrograde labeling of a single cluster of cells in the ventro-posterior-medial (VPM) part of the VB that corresponds to barreloids, the thalamic counterparts of cortical barrels (Fig. 1A-C) (see also Dufour et al., 2003). We have previously shown that in EphA4^KO/KO mutants, in spite of a grossly normal thalamocortical barreloid to barrel topography, some animals (43%, n=7/16) (Dufour et al., 2003) have retrogradely labeled cells located at ectopic positions with respect to the normal barreloid cluster (arrows in Fig. 1D).

Importantly, the same phenotype was observed in EphA4^GFP/GFP mutants (penetrance 83%, n=5/6), providing direct evidence that TC mapping requires the intracellular domain of EphA4 (Fig. 2A) (Egea et al., 2005). This indicates that forward signaling is the most important component required for EphA4 in this system, although EphA-dependent reverse signaling is known to be involved in mapping of the visual or olfactory systems (Cutforth et al., 2003; Knoll et al., 2001; Rashid et al., 2005).

Given the involvement of the EphA4 intracellular domain, we next analyzed EphA4^KD/KD mutants, in which the kinase catalytic domain was disrupted (Fig. 2C). Strikingly, these mutants displayed a similar loss-of-function phenotype (penetrance 55%, n=5/9; Fig. 2C). This phenotype was also reminiscent of the phenotype observed for the EphA4^EE/EE mutants in which EphA4 kinase is constitutively activated [penetrance 61%, n=8/13; Fig. 2B) (see also Egea et al., 2005). In all cases, the phenotypes appeared to be grossly the same in severity (Fig. 2A-C), but, interestingly, the penetrance tended to be higher for mutants in which the EphA4 variants are still capable of interacting with other Eph receptors (Fig. 2F).

Overall, these data indicate that regulation of kinase activity is crucial for the ability of EphA4 to mediate mapping of TC axons, as either a disruption (this study), or a constitutive activation [this study and Egea et al. (Egea et al., 2005)], of the kinase domain result in a similar disruption of TC mapping.

This situation is different from EphA4-dependent repulsion of cortical axons at the midline, which is dependent on an intact tyrosine kinase activity (Kullander et al., 2001), but is seemingly normal in EphA4^EE/EE mutants (Egea et al., 2005). This interesting dissociation somehow suggests that Eph-dependent mapping is particularly sensitive to the regulation of kinase activity. Indeed, it is likely that EphA4 kinase activity acts as a sensor for ephrin gradients during mapping, which requires a normal basal level and a normal capacity to be activated or inhibited. Such a hypothesis would be compatible with current models of topographic mapping in the retinotectal system, where different concentrations of ephrins have qualitatively different effects on retinal axons, depending on their relative expression of Eph receptors (Flanagan, 2006; Hansen et al., 2004). It is also in line with a recent report describing the crucial role of tyrosine phosphatase receptor O in controlling the level of phosphorylation of EphA receptors and, hence, the sensitivity of retinal axons to ephrin ligands, both in vitro and in vivo (Shintani et al., 2006). This could help to explain how the molecular mechanisms of EphA4 receptor-dependent mapping may be distinct from other guidance decisions, such as midline repulsion (Egea et al., 2005): the ability to sense a smooth gradient, as for TC mapping, may require a tighter or more dynamic range of regulation of Eph kinase-dependent signaling than repulsion at the midline, for instance, which is thought to rely on sensing a single-step boundary of cues (Egea et al., 2005; Kullander et al., 2001). In this context it would be interesting to test the qualitative responsiveness of TC axons from the various EphA4 mutants to graded concentrations of ephrin ligands using dedicated in vitro systems (Rosoff et al., 2004).

View larger version (71K): [in this window] [in a new window]   Fig. 1. EphA4 mutants and the thalamocortical somatosensory map. (A,B) The point-to-point topography of projections between the thalamic primay somatosensory nucleus VB [subdivided into a medial and a lateral part, ventro-postero-medial (VPM) and ventro-postero-lateral (VPL), respectively) and the primary somatosensory area S1, and its relation to ephrin/Eph gradients. Schematic drawings and a low-power view are shown. In control wild-type (WT) mice (B,C), focal injection of DiI in S1 resulted in the retrograde labeling of a single cluster of cells in the thalamic nucleus VPM (asterisk in C). In addition, labeling of the postero-medial nucleus (PoM), a secondary somatosensory nucleus, can be detected in some cases outside the VB, but its diffuse and variable pattern was not analyzed in this study. (D) By contrast, the EphA4KO/KO mutants show, in addition to the normal cluster, ectopic cells that are located more medially than their normal location (arrows), indicating that thalamocortical projections are not properly organized. Scale bar in C: 400 µm for B-D. (E) Schematic model of the intracellular domains of wild-type and mutant forms of EphA4 encoded by the mutant alleles examined in this study. In KD, EphA4 lysine residue K653 (K) in the kinase catalytic domain was replaced by a methionine (M), rendering the receptor kinase domain completely inactive. In EE mutants, the two juxtamembrane residues (Y) are replaced by two glutamic acid residues (E), rendering the receptor kinase activity constitutively active. In SAM mutants, the entire SAM domain (gray oval) is deleted. In PBM mutants, the entire PBM (black oval) is deleted. In GFP alleles, the entire intracellular domain is replaced by GFP (large gray oval). (F) Expression of wild-type and mutant EphA4 protein in the thalamus of the indicated mutant mice. Protein (50 µg) from thalamic extracts of the indicated mutant mice was resolved by SDS-PAGE and analyzed by western blot using an anti-EphA4 antibody raised against the extracellular domain of the protein (upper panels); the blot was reprobed with an anti-tubulin antibody for loading control (lower panels). EphA4 expression was analyzed in at least two independent animals per genotype. The lanes are representative expression examples of the different genotypes, and all of them belong to the same gel and the same western blot analysis.

Although these data highlight the paramount importance of Eph tyrosine kinase activity in neural mapping, they do not exclude the possibility that other signaling mechanisms may be involved. To address this issue, we therefore turned to mouse lines displaying mutations in other signaling modules of the cytoplasmic domain of EphA4 to evaluate their importance in TC mapping. Interestingly, mutants for either the PBM (EphA4^PBM/PBM; n=7) or the SAM domain (EphA4^SAM/SAM, n=5) displayed normal TC projections from VPM to S1 (Fig. 2D-F).

These data thus suggest that these domains, although largely conserved among Eph receptor subtypes between and within species, do not seem to be important for topographic mapping. A subtle regulation of neural mapping by these domains cannot be excluded at this stage, however, and could be revealed in a sensitized background. This could be achieved, for instance, by crossing these mutants with other mutants of the ephrin/Eph genes involved in TC mapping, such as ephrin-A5 or other EphA receptors, or by looking at compound mutants for different domains of EphA4. In any case, although the PBM of ephrin Bs is known to be crucial for lymphangiogenesis and neural migration (Lu et al., 2001; Makinen et al., 2005), these results illustrate the modular organization of ephrin/Eph factors, where unique sets of functional modules are required for distinct biological processes, depending on the cellular context or the ephrin/Eph factor considered.

View larger version (63K): [in this window] [in a new window]   Fig. 2. Analysis of somatosensory TC projections in EphA4 mutants. (A-C) Analysis of somatosensory TC projections in mutants displaying abnormal EphA4 kinase activity. In EphA4GFP/GFP (A), EphA4EE/EE (B) and EphA4KD/KD (C) mutants, similar arrays of ectopic cells can be found in the medial part of the VPM (arrows). (D,E) Analysis of somatosensory TC projections in mutants displaying EphA4 lacking non-catalytic functional domains. EphA4PBM (D) and EphA4SAM (E) mutants display a normal pattern of TC projections. Scale bar in A: 400 µm for A-E. In A,C,D,E, left panels show corresponding DiI injection sites in S1. (F) Summary of the penetrance of TC topographic defects found in the various EphA4 mutants analyzed. The first line shows the number of affected animals/number of tested animals. The second line shows the percentage of animals displaying defective TC mapping in the VB.

WT/SAM

WT/PBM

View larger version (56K): [in this window] [in a new window]   Fig. 3. Analysis of somatosensory TC projections in EphA4 heterozygote animals. (A-C) In some EphA4WT/GFP (A), EphA4WT/KD (B) and EphA4WT/KO (C) mutants, arrays of ectopic cells can be found in the medial part of the VPM (arrows), as in corresponding homozygous mutants. Scale bar in C: 400 µm for A-C. (D) Expression of EphA4 in the thalamus of heterozygous EphA4 mutant mice. Protein (50 µg) from thalamic extracts of the indicated mutant mice was resolved by SDS-PAGE and analyzed by western blot using an anti-EphA4 antibody raised against the extracellular domain of the protein (upper panels); the blot was reprobed with an anti-tubulin antibody for loading control (lower panels). (E) Summary of the penetrance of TC topographic defects found in the various EphA4 heterozygote mutants analyzed. The first line shows the number of affected animals/number of tested animals. The second line shows the percentage of animals displaying defective TC mapping in the VB.

In conclusion, we demonstrate that neural mapping is particularly dependent on the tight regulation of EphA4 kinase activity, whereas the other signaling modules of this receptor appear to be dispensable for the same function. The level of EphA4-dependent signaling in thalamic axons, which perhaps allows the right signal combination with other thalamic EphA receptors of the system, also seems to be important. These data provide a physiological framework for further dissection of the intracellular signaling cascades, downstream of Eph receptors, that mediate the graded responsiveness of axons to ephrin labels, thereby controlling neural topographic mapping.

ACKNOWLEDGMENTS

We thank G. Vassart for continuous support and interest, members of the lab and of IRIBHM for helpful discussions and advice, and Mélanie Degraeve for expert assistance. This work was funded by grants from the Belgian FNRS, the Belgian FRSM, the Belgian Queen Elizabeth Medical Foundation and the Interuniversity Attraction Poles Programme, Belgian State, Federal Office for Scientific, Technical and Cultural Affairs to P.V.; and the Swedish Research Council (K2004-32P-15230-01A, K2005-33X-15327-01A), and the foundation of Knut and Alice Wallenberg to K.K. P.V. is a Research Associate of the FNRS. A.D. is a Fellow from the Belgian FRIA. The authors declare they have no competing financial interests.

REFERENCES

Brown, A., Yates, P. A., Burrola, P., Ortuno, D., Vaidya, A., Jessell, T. M., Pfaff, S. L., O'Leary, D. D. and Lemke, G. (2000). Topographic mapping from the retina to the midbrain is controlled by relative but not absolute levels of EphA receptor signaling. Cell 102,77 -88.[CrossRef][Medline]

Cang, J., Kaneko, M., Yamada, J., Woods, G., Stryker, M. P. and Feldheim, D. A. (2005). Ephrin-as guide the formation of functional maps in the visual cortex. Neuron 48,577 -589.[CrossRef][Medline]

Cutforth, T., Moring, L., Mendelsohn, M., Nemes, A., Shah, N. M., Kim, M. M., Frisen, J. and Axel, R. (2003). Axonal ephrin-As and odorant receptors: coordinate determination of the olfactory sensory map. Cell 114,311 -322.[CrossRef][Medline]

Dufour, A., Seibt, J., Passante, L., Depaepe, V., Ciossek, T., Frisen, J., Kullander, K., Flanagan, J. G., Polleux, F. and Vanderhaeghen, P. (2003). Area specificity and topography of thalamocortical projections are controlled by ephrin/Eph genes. Neuron 39,453 -465.[CrossRef][Medline]

Egea, J., Nissen, U. V., Dufour, A., Sahin, M., Greer, P., Kullander, K., Mrsic-Flogel, T. D., Greenberg, M. E., Kiehn, O., Vanderhaeghen, P. et al. (2005). Regulation of EphA4 kinase activity is required for a subset of axon guidance decisions suggesting a key role for receptor clustering in Eph function. Neuron 47,515 -528.[CrossRef][Medline]

Feldheim, D. A., Kim, Y. I., Bergemann, A. D., Frisen, J., Barbacid, M. and Flanagan, J. G. (2000). Genetic analysis of ephrin-A2 and ephrin-A5 shows their requirement in multiple aspects of retinocollicular mapping. Neuron 25,563 -574.[CrossRef][Medline]

Feldheim, D. A., Nakamoto, M., Osterfiel, M., Gale, N. W., DeChiara, T. M., Rohatgi, R., Yancopoulos, G. D. and Flanagan, J. G. (2004). Loss-of-function analysis of EphA receptors in retinotectal mapping. J. Neurosci. 24,2542 -2550.[Abstract/Free Full Text]

Flanagan, J. G. (2006). Neural map specification by gradients. Curr. Opin. Neurobiol. 16, 1-8.[CrossRef][Medline]

Flanagan, J. G. and Vanderhaeghen, P. (1998). The ephrins and Eph receptors in neural development. Annu. Rev. Neurosci. 21,309 -345.[CrossRef][Medline]

Grunwald, I. C., Korte, M., Adelmann, G., Plueck, A., Kullander, K., Adams, R. H., Frotscher, M., Bonhoeffer, T. and Klein, R. (2004). Hippocampal plasticity requires postsynaptic ephrinBs. Nat. Neurosci. 7,33 -40.[CrossRef][Medline]

Hansen, M. J., Dallal, G. E. and Flanagan, J. G. (2004). Retinal axon response to ephrin-as shows a graded, concentration-dependent transition from growth promotion to inhibition. Neuron 42,717 -730.[CrossRef][Medline]

Klein, R. (2004). Eph/ephrin signaling in morphogenesis, neural development and plasticity. Curr. Opin. Cell Biol. 16,580 -589.[CrossRef][Medline]

Knoll, B. and Drescher, U. (2004). Src family kinases are involved in EphA receptor-mediated retinal axon guidance. J. Neurosci. 24,6248 -6257.[Abstract/Free Full Text]

Knoll, B., Zarbalis, K., Wurst, W. and Drescher, U. (2001). A role for the EphA family in the topographic targeting of vomeronasal axons. Development 128,895 -906.[Abstract]

Kullander, K. and Klein, R. (2002). Mechanisms and functions of Eph and ephrin signalling. Nat. Rev. Mol. Cell Biol. 3,475 -486.[CrossRef][Medline]

Kullander, K., Mather, N. K., Diella, F., Dottori, M., Boyd, A. W. and Klein, R. (2001). Kinase-dependent and kinase-independent functions of EphA4 receptors in major axon tract formation in vivo. Neuron 29,73 -84.[CrossRef][Medline]

Kullander, K., Butt, S. J., Lebret, J. M., Lundfald, L., Restrepo, C. E., Rydstrom, A., Klein, R. and Kiehn, O. (2003). Role of EphA4 and EphrinB3 in local neuronal circuits that control walking. Science 299,1889 -1892.[Abstract/Free Full Text]

Lu, Q., Sun, E. E., Klein, R. S. and Flanagan, J. G. (2001). Ephrin-B reverse signaling is mediated by a novel PDZ-RGS protein and selectively inhibits G protein-coupled chemoattraction. Cell 105,69 -79.[CrossRef][Medline]

Makinen, T., Adams, R. H., Bailey, J., Lu, Q., Ziemiecki, A., Alitalo, K., Klein, R. and Wilkinson, G. A. (2005). PDZ interaction site in ephrinB2 is required for the remodeling of lymphatic vasculature. Genes Dev. 19,397 -410.[Abstract/Free Full Text]

McLaughlin, T. and O'Leary, D. D. (2005). Molecular gradients and development of retinotopic maps. Annu. Rev. Neurosci. 28,327 -355.[CrossRef][Medline]

Pasquale, E. B. (2005). Eph receptor signalling casts a wide net on cell behaviour. Nat. Rev. Mol. Cell Biol. 6,462 -475.[CrossRef][Medline]

Prakash, N., Vanderhaeghen, P., Cohen-Cory, S., Frisen, J., Flanagan, J. G. and Frostig, R. D. (2000). Malformation of the functional organization of somatosensory cortex in adult ephrin-A5 knock-out mice revealed by in vivo functional imaging. J. Neurosci. 20,5841 -5847.[Abstract/Free Full Text]

Rashid, T., Upton, A. L., Blentic, A., Ciossek, T., Knoll, B., Thompson, I. D. and Drescher, U. (2005). Opposing gradients of Ephrin-As and EphA7 in the superior colliculus are essential for topographic mapping in the mammalian visual system. Neuron 47,57 -69.[CrossRef][Medline]

Rosoff, W. J., Urbach, J. S., Esrick, M. A., McAllister, R. G., Richards, L. J. and Goodhill, G. J. (2004). A new chemotaxis assay shows the extreme sensitivity of axons to molecular gradients. Nat. Neurosci. 7,678 -682.[CrossRef][Medline]

Sahin, M., Greer, P. L., Lin, M. Z., Poucher, H., Eberhart, J., Schmidt, S., Wright, T. M., Shamah, S. M., O'Connell, S., Cowan, C. W. et al. (2005). Eph-dependent tyrosine phosphorylation of ephexin1 modulates growth cone collapse. Neuron 46,191 -204.[CrossRef][Medline]

Shamah, S. M., Lin, M. Z., Goldberg, J. L., Estrach, S., Sahin, M., Hu, L., Bazalakova, M., Neve, R. L., Corfas, G., Debant, A. et al. (2001). EphA receptors regulate growth cone dynamics through the novel guanine nucleotide exchange factor ephexin. Cell 105,233 -244.[CrossRef][Medline]

Shintani, T., Ihara, M., Sakuta, H., Takahashi, H., Watakabe, I. and Noda, M. (2006). Eph receptors are negatively controlled by protein tyrosine phosphatase receptor type O. Nat. Neurosci. 9,761 -769.[CrossRef][Medline]

Torii, M. and Levitt, P. (2005). Dissociation of corticothalamic and thalamocortical axon targeting by an EphA7-mediated mechanism. Neuron 48,563 -575.[CrossRef][Medline]

Vanderhaeghen, P. and Polleux, F. (2004). Developmental mechanisms patterning thalamocortical projections: intrinsic, extrinsic and in between. Trends Neurosci. 27,384 -391.[CrossRef][Medline]

Vanderhaeghen, P., Lu, Q., Prakash, N., Frisen, J., Walsh, C. A., Frostig, R. D. and Flanagan, J. G. (2000). A mapping label required for normal scale of body representation in the cortex. Nat. Neurosci. 3,358 -365.[CrossRef][Medline]

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

Twitter

This article has been cited by other articles:

				T. J. Petros, B. R. Shrestha, and C. Mason Specificity and Sufficiency of EphB1 in Driving the Ipsilateral Retinal Projection J. Neurosci., March 18, 2009; 29(11): 3463 - 3474. [Abstract] [Full Text] [PDF]

				S. Shim, Y. Kim, J. Shin, J. Kim, and S. Park Regulation of EphA8 Gene Expression by TALE Homeobox Transcription Factors during Development of the Mesencephalon Mol. Cell. Biol., March 1, 2007; 27(5): 1614 - 1630. [Abstract] [Full Text] [PDF]

This Article Summary Figures Only Full Text (PDF) All Versions of this Article: dev.02623v1 133/22/4415    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dufour, A. Articles by Vanderhaeghen, P. Search for Related Content PubMed PubMed Citation Articles by Dufour, A. Articles by Vanderhaeghen, P. Social Bookmarking                         What's this?