Limits...
EphA3 expressed in the chicken tectum stimulates nasal retinal ganglion cell axon growth and is required for retinotectal topographic map formation.

Ortalli AL, Fiore L, Di Napoli J, Rapacioli M, Salierno M, Etchenique R, Flores V, Sanchez V, Carri NG, Scicolone G - PLoS ONE (2012)

Bottom Line: We demonstrated in vitro and in vivo that EphA3 ectodomain (which is expressed in a decreasing rostro-caudal gradient in the tectum) is necessary for topographic mapping by stimulating the nasal axon growth toward the caudal tectum and inhibiting their branching in the rostral tectum.Furthermore, the ability of EphA3 of stimulating axon growth allows understanding how optic fibers invade the tectum growing throughout this molecular gradient.Therefore, opposing tectal gradients of repellent ephrin-As and of axon growth stimulating EphA3 complement each other to map optic fibers along the rostro-caudal tectal axis.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Developmental Neurobiology, Institute of Cell Biology and Neurosciences Prof. E. De Robertis (UBA-CONICET), School of Medicine, University of Buenos Aires, Buenos Aires, Argentina.

ABSTRACT

Background: Retinotopic projection onto the tectum/colliculus constitutes the most studied model of topographic mapping and Eph receptors and their ligands, the ephrins, are the best characterized molecular system involved in this process. Ephrin-As, expressed in an increasing rostro-caudal gradient in the tectum/colliculus, repel temporal retinal ganglion cell (RGC) axons from the caudal tectum and inhibit their branching posterior to their termination zones. However, there are conflicting data regarding the nature of the second force that guides nasal axons to invade and branch only in the caudal tectum/colliculus. The predominant model postulates that this second force is produced by a decreasing rostro-caudal gradient of EphA7 which repels nasal optic fibers and prevents their branching in the rostral tectum/colliculus. However, as optic fibers invade the tectum/colliculus growing throughout this gradient, this model cannot explain how the axons grow throughout this repellent molecule.

Methodology/principal findings: By using chicken retinal cultures we showed that EphA3 ectodomain stimulates nasal RGC axon growth in a concentration dependent way. Moreover, we showed that nasal axons choose growing on EphA3-expressing cells and that EphA3 diminishes the density of interstitial filopodia in nasal RGC axons. Accordingly, in vivo EphA3 ectodomain misexpression directs nasal optic fibers toward the caudal tectum preventing their branching in the rostral tectum.

Conclusions: We demonstrated in vitro and in vivo that EphA3 ectodomain (which is expressed in a decreasing rostro-caudal gradient in the tectum) is necessary for topographic mapping by stimulating the nasal axon growth toward the caudal tectum and inhibiting their branching in the rostral tectum. Furthermore, the ability of EphA3 of stimulating axon growth allows understanding how optic fibers invade the tectum growing throughout this molecular gradient. Therefore, opposing tectal gradients of repellent ephrin-As and of axon growth stimulating EphA3 complement each other to map optic fibers along the rostro-caudal tectal axis.

Show MeSH

Related in: MedlinePlus

EphA3 ectodomain overexpression stimulates nasal optic fibers (OFs) passing throughout and inhibits termination zones (TZs) formation.After infection of the optic tectum at E2 with RCAS-BP-B-EGFPF (control) (A) or with RCAS-BP-B-EphA3ΔC-EGFPN3 (B) and DiI labeling of the naso-dorsal retina at E16 (HH42), the tectum was analyzed in whole mounts at E18 (HH44). (A, B) Microphotographs show a termination zone (TZ) formed by nasal optic fibers in an EGFPF-positive domain located in the caudal tectum (A) and nasal optic fibers (OFs) passing throughout an EphA3ΔC-EGFP- positive domain located in the caudal tectum (B). Dotted lines demarcate the overexpressed regions. Scale bars  = 50 µm. (C, D) Comparison between the proportions of temporal (C) and (D) nasal RGC axons (T RGC and N RGC) which form TZs in the areas which express EGFPF versus EphA3ΔC-EGFP. Temporal RGC axons were evaluated in the rostral tectum whereas nasal RGC axons were evaluated in the caudal tectum. (C) No significant difference is detected between the proportion of temporal RGC axons which form TZs in EphA3ΔC-EGFP-positive regions and in EGFPF-positive regions (control) in rostral tectum. (D) A significantly lower proportion of nasal axons form TZs in EphA3ΔC-EGFP-positive regions than in EGFPF-positive regions (control) in caudal tectum (Student's t test, n: 4 EphA3ΔC-EGFP-overexpressed tecta versus 7 control tecta for temporal RGCs; n: 5 EphA3ΔC-EGFP-overexpressed tecta versus 4 control tecta for nasal RGCs). Results are shown as mean +/− SE.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3369860&req=5

pone-0038566-g006: EphA3 ectodomain overexpression stimulates nasal optic fibers (OFs) passing throughout and inhibits termination zones (TZs) formation.After infection of the optic tectum at E2 with RCAS-BP-B-EGFPF (control) (A) or with RCAS-BP-B-EphA3ΔC-EGFPN3 (B) and DiI labeling of the naso-dorsal retina at E16 (HH42), the tectum was analyzed in whole mounts at E18 (HH44). (A, B) Microphotographs show a termination zone (TZ) formed by nasal optic fibers in an EGFPF-positive domain located in the caudal tectum (A) and nasal optic fibers (OFs) passing throughout an EphA3ΔC-EGFP- positive domain located in the caudal tectum (B). Dotted lines demarcate the overexpressed regions. Scale bars  = 50 µm. (C, D) Comparison between the proportions of temporal (C) and (D) nasal RGC axons (T RGC and N RGC) which form TZs in the areas which express EGFPF versus EphA3ΔC-EGFP. Temporal RGC axons were evaluated in the rostral tectum whereas nasal RGC axons were evaluated in the caudal tectum. (C) No significant difference is detected between the proportion of temporal RGC axons which form TZs in EphA3ΔC-EGFP-positive regions and in EGFPF-positive regions (control) in rostral tectum. (D) A significantly lower proportion of nasal axons form TZs in EphA3ΔC-EGFP-positive regions than in EGFPF-positive regions (control) in caudal tectum (Student's t test, n: 4 EphA3ΔC-EGFP-overexpressed tecta versus 7 control tecta for temporal RGCs; n: 5 EphA3ΔC-EGFP-overexpressed tecta versus 4 control tecta for nasal RGCs). Results are shown as mean +/− SE.

Mentions: To analyze the effects on the behavior of retinal optic fibers exerced by the overexpression of EphA3 ectodomain on the tectum, we compared the proportions of nasal and temporal axons which passed throughout or formed termination zones in contact with EphA3ΔC-EGFP versus EGFPF positive tectal regions. RGC axons were evaluated in the corresponding target area. Results were analyzed at the time point in which a mature retinotectal projection was established (between E15–HH41– and E19–HH45-) [6]. We found that a significantly higher proportion of nasal optic fibers passed through EphA3ΔC-EGFP-positive areas (75.94 %+/−12) in comparison with EGFPF-positive areas in the caudal tectum (13.33 %+/−8.16,). Conversely, a significantly lower proportion of axons formed termination zones in EphA3ΔC-EGFP-positive areas (Fig. 6A, B, D). However, temporal RGC axons did not show any significant difference in terms of proportions of axons which produce termination zones after making contact with EphA3ΔC-EGFP-positive areas (49.29%+/−3.52%) versus EGFPF-positive areas (50.68%+/−7.58%) in the rostral tectum (Fig. 6A, C). These results show that the EphA3 ectodomain stimulates axon growth and inhibits termination zones formation on nasal RGCs in vivo whereas it does not present any significant effect on temporal RGCs.


EphA3 expressed in the chicken tectum stimulates nasal retinal ganglion cell axon growth and is required for retinotectal topographic map formation.

Ortalli AL, Fiore L, Di Napoli J, Rapacioli M, Salierno M, Etchenique R, Flores V, Sanchez V, Carri NG, Scicolone G - PLoS ONE (2012)

EphA3 ectodomain overexpression stimulates nasal optic fibers (OFs) passing throughout and inhibits termination zones (TZs) formation.After infection of the optic tectum at E2 with RCAS-BP-B-EGFPF (control) (A) or with RCAS-BP-B-EphA3ΔC-EGFPN3 (B) and DiI labeling of the naso-dorsal retina at E16 (HH42), the tectum was analyzed in whole mounts at E18 (HH44). (A, B) Microphotographs show a termination zone (TZ) formed by nasal optic fibers in an EGFPF-positive domain located in the caudal tectum (A) and nasal optic fibers (OFs) passing throughout an EphA3ΔC-EGFP- positive domain located in the caudal tectum (B). Dotted lines demarcate the overexpressed regions. Scale bars  = 50 µm. (C, D) Comparison between the proportions of temporal (C) and (D) nasal RGC axons (T RGC and N RGC) which form TZs in the areas which express EGFPF versus EphA3ΔC-EGFP. Temporal RGC axons were evaluated in the rostral tectum whereas nasal RGC axons were evaluated in the caudal tectum. (C) No significant difference is detected between the proportion of temporal RGC axons which form TZs in EphA3ΔC-EGFP-positive regions and in EGFPF-positive regions (control) in rostral tectum. (D) A significantly lower proportion of nasal axons form TZs in EphA3ΔC-EGFP-positive regions than in EGFPF-positive regions (control) in caudal tectum (Student's t test, n: 4 EphA3ΔC-EGFP-overexpressed tecta versus 7 control tecta for temporal RGCs; n: 5 EphA3ΔC-EGFP-overexpressed tecta versus 4 control tecta for nasal RGCs). Results are shown as mean +/− SE.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369860&req=5

pone-0038566-g006: EphA3 ectodomain overexpression stimulates nasal optic fibers (OFs) passing throughout and inhibits termination zones (TZs) formation.After infection of the optic tectum at E2 with RCAS-BP-B-EGFPF (control) (A) or with RCAS-BP-B-EphA3ΔC-EGFPN3 (B) and DiI labeling of the naso-dorsal retina at E16 (HH42), the tectum was analyzed in whole mounts at E18 (HH44). (A, B) Microphotographs show a termination zone (TZ) formed by nasal optic fibers in an EGFPF-positive domain located in the caudal tectum (A) and nasal optic fibers (OFs) passing throughout an EphA3ΔC-EGFP- positive domain located in the caudal tectum (B). Dotted lines demarcate the overexpressed regions. Scale bars  = 50 µm. (C, D) Comparison between the proportions of temporal (C) and (D) nasal RGC axons (T RGC and N RGC) which form TZs in the areas which express EGFPF versus EphA3ΔC-EGFP. Temporal RGC axons were evaluated in the rostral tectum whereas nasal RGC axons were evaluated in the caudal tectum. (C) No significant difference is detected between the proportion of temporal RGC axons which form TZs in EphA3ΔC-EGFP-positive regions and in EGFPF-positive regions (control) in rostral tectum. (D) A significantly lower proportion of nasal axons form TZs in EphA3ΔC-EGFP-positive regions than in EGFPF-positive regions (control) in caudal tectum (Student's t test, n: 4 EphA3ΔC-EGFP-overexpressed tecta versus 7 control tecta for temporal RGCs; n: 5 EphA3ΔC-EGFP-overexpressed tecta versus 4 control tecta for nasal RGCs). Results are shown as mean +/− SE.
Mentions: To analyze the effects on the behavior of retinal optic fibers exerced by the overexpression of EphA3 ectodomain on the tectum, we compared the proportions of nasal and temporal axons which passed throughout or formed termination zones in contact with EphA3ΔC-EGFP versus EGFPF positive tectal regions. RGC axons were evaluated in the corresponding target area. Results were analyzed at the time point in which a mature retinotectal projection was established (between E15–HH41– and E19–HH45-) [6]. We found that a significantly higher proportion of nasal optic fibers passed through EphA3ΔC-EGFP-positive areas (75.94 %+/−12) in comparison with EGFPF-positive areas in the caudal tectum (13.33 %+/−8.16,). Conversely, a significantly lower proportion of axons formed termination zones in EphA3ΔC-EGFP-positive areas (Fig. 6A, B, D). However, temporal RGC axons did not show any significant difference in terms of proportions of axons which produce termination zones after making contact with EphA3ΔC-EGFP-positive areas (49.29%+/−3.52%) versus EGFPF-positive areas (50.68%+/−7.58%) in the rostral tectum (Fig. 6A, C). These results show that the EphA3 ectodomain stimulates axon growth and inhibits termination zones formation on nasal RGCs in vivo whereas it does not present any significant effect on temporal RGCs.

Bottom Line: We demonstrated in vitro and in vivo that EphA3 ectodomain (which is expressed in a decreasing rostro-caudal gradient in the tectum) is necessary for topographic mapping by stimulating the nasal axon growth toward the caudal tectum and inhibiting their branching in the rostral tectum.Furthermore, the ability of EphA3 of stimulating axon growth allows understanding how optic fibers invade the tectum growing throughout this molecular gradient.Therefore, opposing tectal gradients of repellent ephrin-As and of axon growth stimulating EphA3 complement each other to map optic fibers along the rostro-caudal tectal axis.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Developmental Neurobiology, Institute of Cell Biology and Neurosciences Prof. E. De Robertis (UBA-CONICET), School of Medicine, University of Buenos Aires, Buenos Aires, Argentina.

ABSTRACT

Background: Retinotopic projection onto the tectum/colliculus constitutes the most studied model of topographic mapping and Eph receptors and their ligands, the ephrins, are the best characterized molecular system involved in this process. Ephrin-As, expressed in an increasing rostro-caudal gradient in the tectum/colliculus, repel temporal retinal ganglion cell (RGC) axons from the caudal tectum and inhibit their branching posterior to their termination zones. However, there are conflicting data regarding the nature of the second force that guides nasal axons to invade and branch only in the caudal tectum/colliculus. The predominant model postulates that this second force is produced by a decreasing rostro-caudal gradient of EphA7 which repels nasal optic fibers and prevents their branching in the rostral tectum/colliculus. However, as optic fibers invade the tectum/colliculus growing throughout this gradient, this model cannot explain how the axons grow throughout this repellent molecule.

Methodology/principal findings: By using chicken retinal cultures we showed that EphA3 ectodomain stimulates nasal RGC axon growth in a concentration dependent way. Moreover, we showed that nasal axons choose growing on EphA3-expressing cells and that EphA3 diminishes the density of interstitial filopodia in nasal RGC axons. Accordingly, in vivo EphA3 ectodomain misexpression directs nasal optic fibers toward the caudal tectum preventing their branching in the rostral tectum.

Conclusions: We demonstrated in vitro and in vivo that EphA3 ectodomain (which is expressed in a decreasing rostro-caudal gradient in the tectum) is necessary for topographic mapping by stimulating the nasal axon growth toward the caudal tectum and inhibiting their branching in the rostral tectum. Furthermore, the ability of EphA3 of stimulating axon growth allows understanding how optic fibers invade the tectum growing throughout this molecular gradient. Therefore, opposing tectal gradients of repellent ephrin-As and of axon growth stimulating EphA3 complement each other to map optic fibers along the rostro-caudal tectal axis.

Show MeSH
Related in: MedlinePlus