4/13/2015

1

Developing topographically organized retino-collicular and retino-thalamo-cortical circuits

Daniel J. Felleman

Department of Neurobiology & Anatomy

Office: MSB 7.168

Telephone: 500-5629

Email: daniel.felleman@uth.tmc.edu

Superior colliculus/Optic tectum

The primary function of the optic tectum is to localize the stimulus in space and to cause the animal to orient to the stimulus by moving its body and eyes.

4/13/2015

2

Retina-to-tectum projection

Figure 23.4 Signals in embryo affect growth cones and growing axons (Part 1)

4/13/2015

3

tectum

tectum

tectum

tectum

Chemo-affinity hypothesis – by Roger Sperry-1963

Chemical markers on growing axons are matched with complementary chemical markers on their targets through attraction or repulsion to establish precise connections.

Membrane stripe assay

RGC from nasal retina show no preference for anterior or posterior colliculusRGC from temporal retina show preference foranterior colliculus

1990sDiscovery of ELF-1 (Eph ligand family 1) and RAGS (repulsive axon guidance signal)

Expressed in low to high gradient in the OT and areligands of the receptor tyrosine kinase, EphA3 (thatis expressed in a high to low temporal=-nasal gradientby RGCs).

Ephrin-A2 and Ephrin-A5 are axon repellants and serveas axonal guidance molecules.

Figure 23.6 Mechanisms of topographic mapping in the vertebrate visual system

4/13/2015

4

Visual areas in the brain are mapped topographically.

Feldheim D A , O’Leary D D M Cold Spring Harb Perspect Biol 2010;2:a001768

©2010 by Cold Spring Harbor Laboratory Press

Two Major Stages/Mechanisms Involved in Developing Topographically-organized Neural Circuits:

1. Arborization phase: P0-P3-4 in mice SCMolecular guidance cues such as EphA/ephrinA signaling

2. Dynamic phase: P3-4 to P8-9Remodeling of retino-collicular map by activity dependentarbor plasticity and competition for collicular resources

4/13/2015

5

Developmental stages in mapping temporal-nasal retinal axis on anterior-posterior axis of colliculus/tectum in mice and chicks.

Feldheim D A , O’Leary D D M Cold Spring Harb PerspectBiol 2010;2:a001768©2010 by Cold Spring Harbor Laboratory Press

4/13/2015

6

Nasal-temporal axis

Dorso-ventral axis

Polarized expression of the transcriptionfactors BF1 and BF2 begins at opticcup stage: BF1 in nasal cup and BF2 in temporal cup.

Regulatory genes SOHo1 and GH6 areexpressed in nasal retina; they repress expression ofEphA3.

D-V polarity develops after N-Tvia SHH, RA, and BMPs.Dorsalizing effect of BMPs iscounteracted by ventroptin, a BMP antagonist.The D-V axis may be divided into 4developmental compartments.

Vax2 and Tbx5 act on expressions of EphBs and ephrin-Bs.

Substantial size differences in midbrain targets and distinct mechanisms of map development exhibited by model systems.

Feldheim D A , O’LearyCold Spring Harb Persp2010;2:a001768

(B) In mouse and chick RGC axons enter the OT/SC over a broad LM extent and significantly overshoot their future termination zone (TZ, circle).

Interstitial branches form de novo from the axon shaft around the correct anterior–posterior (A–P) position of their future TZ.

Branches are directed along the lateral–medial (L–M) axis of the OT/SC toward the position of the future TZ, in which they arborize in a domain encompassing the forming TZ.

The broad, loose array of arbors is refined to a dense TZ in the topographically appropriate location.

(C) In frogs and fish the RGC growth cone extends to the TZ in which it forms a terminal arbor through a process of terminal branching of the growth cone and backbranching immediately behind the growth cone. The tectum expands as terminal arborizations elaborate and refine into a mature TZ

4/13/2015

7

Functional imaging of adult SC in wild type and mutant mice

Feldheim D A , O’Leary D D M Cold Spring Harb Perspect Biol 2010;2:a001768

©2010 by Cold Spring Harbor Laboratory Press

4/13/2015

8

Regulation of topographic-specific interstitial branching along anterior–posterior axis of tectum/colliculus: the critical determinant of retinotopic mapping.

Feldheim D A , O’Leary D D M Cold Spring Harb PerspectBiol 2010;2:a001768©2010 by Cold Spring Harbor Laboratory Press

All models have as recurring theme the gradedrepellent activity that preferentially affects temporalRGC axons and is achieved by EphA forward signaling.

EphA is expressed in a high to low temporal (T) to nasal (N) gradient by RGCs, and ephrin—As in a low to high anterior (A) to posterior (P) gradient in the optic tectum (OT)/superior colliculus (SC).

This receptor-legend pairing generates through EphAforward signaling a high to low AP gradient of repellent activity that preferential affects temporal RGC axons, and is in principle sufficient to topographically guide RGC axonal growth cones along the AP axis to their appropriate terminal zone (TZ). This mapping mechanism is adequate in lower vertebrates.

However, a single repulsive gradient cannot generate the topographic interstitial branching of RGC axons along the AP axis observed in chicks and rodents, because branching would occur at a greater frequency more anterior to the TZ. This is not observed in vivo—branching is focused on the AP position of the TZ and is lower both anterior and posterior it.

(C) In principal, topographic-specific interstitial branching could be achieved by a model with a gradient of molecules with branch promoting activities that cooperate with the EphA forward signaling inhibition of branching. Branching is prevented posterior to the correct TZ by ephrin-A repellent activity mediated by EphA forward signaling, and does not occur anterior to the correct TZ because the branch promoting activity is subthreshold.

Branching occurs at the AP position in which the branch promoter is suprathreshold and the branch inhibitor is subthreshold.

TrkB, in a similar distribution to EphAs in the retina (and/or, if TrkB were graded along each RGC axon), and BDNF in the OT/SC have the appropriate activities to act as the graded branch promoter, and cooperate with the graded branch inhibitor generated by EphA/ephrin-A forward signaling.

(D) topographic-specific interstitial branching in the chick OT and mouse SC Topographic-specific branching is generated by opposing gradients of branch inhibiting molecules combined with a branch promoting activity.

In this model, the repellent gradient because of EphA/ephrin-A forward signaling inhibits branching posterior to the TZ and the repellent gradient because ephrin-A/EphA reverse signaling inhibits branching anterior to the TZ.

Branching occurs preferentially at a trough in the opposing repellent gradients that is subthreshold for branch inhibition and is located at the correct AP position of the TZ. At the position of this trough, the activity of a branch promoter (such as BDNF signaling through TrkB) is suprathreshold for branch inhibition and generates branching at this topographically correct location for the TZ. (Modified from McLaughlin and O’Leary 2005 [© Annual Reviews].)

4/13/2015

9

Overexpression of A5 via KIresults in separate pop. of ganglion cells that form second map

Triplett and Feldheim 2012 Seminar Cell Dev Biol. 23:7-15.

4/13/2015

10

Retinal Waves

4/13/2015

11

Functional imaging of adult SC in wild type and mutant mice

Feldheim D A , O’Leary D D M Cold Spring Harb Perspect Biol 2010;2:a001768

©2010 by Cold Spring Harbor Laboratory Press

4/13/2015

12

Duplicated mapsMultiple aberrantterminal zones

Forward and reverse signaling through ephrin-As and Bs

Forward: in Eph containing cells—binding to EphA receptors results in activation of GTPase— leading to growth cone collapse (also regulation of Tsc2).

Reverse: in the ephrin-bearing cells—mediated by co-receptors TrkB and p75NTR –resulting in axonal branching and axon repulsion.

Forward signaling through EphB –growth cone attraction or repulsion.

Reverse signaling through eprinBs is important for synapse maturation

4/13/2015

13

Paradox: In eprinA/EphA repulsion model,Cell-cell contact is required for signaling toOccur, but contact must be terminated forRepulsion to occur. ???

Solutions: cleavage of the extracellular domainof either proteinorEndocytosis of receptor-ligand complex (via GTPaseRAC)

Interactions between molecular cues and structured retinal activityIn the development of cortical topographic maps

Cang et al. (2008) Neuron 57: 511-523.

1. Disruption of azimuthal maps in Ephrin-A2/A5/beta2 KO2. Receptive fields of cortical neurons—enlarged in the azimuthal direction3. LGN RFs.4. LGN topography

4/13/2015

14

Defect in azimuth maps in triple KO

Activation by restricted stimulus vs. full screenTopographic maps to restricted stimuli

4/13/2015

15

LGN-V1 projections: Disrupted order in azimuth but not elevation axis

RF structure in V1 from 2 WT vs. 2 triple KO V1 neurons

4/13/2015

16

RF topography in cortical column inWT vs. triple KOAzimuth but not elevation errors

LGN RFs: simultaneous recorded cells:disruption in azimuth not elevation

4/13/2015

17

Disrupted topography in LGN: increased azimuth scatter

Further readings

1. Fundamental Neuroscience. 3rd edition. Edited by L.R. Squire et al. Chapter 18.2. Neuroscience: exploring the brain. 3rd edition. Edited by M.F. Bear et al. Chapter 23.3. Neuroscience. 4th edition. Edited by D. Purves et al. Chapter 24.4. Torborg, C.L and Feller, M.B. 2005 Spontaneous patterned retinal activity and the

refinement of retinal projections. Prog. Neurobiology 76:213-235.5. McLaughlin, T., Hinges, R., and O’Leary, D. 2003 Regulation of axial patterning of the

retina and its topographic mapping in the brain. Current Opinion in Neurobiology 13; 57-69.

6. Feldheim, D.A. and O’Leary, D.M.D. (2010) Visual map development: bidirectional signaling, bifunctional guidance molecules, and competition. Cold Spring Harbor Perspect Biol. 2: a001768.

7. Klein R. (2012) Eph/ephrin signaling during development. Development 139: 4105-4109.

8. Cang, J, Niell CM, Liu X, Pfeiffenberger C, Feldheim DA, and Stryker MP (2008) Selective disruption of one Cartesian axis of cortical maps and receptive fields by deficiency in Ephrin-As and structured activity. Neuron 57: 511-523.

9. Grimbert F and Cang J (2012) New model of retino-collicular mapping predicts the mechanisms of axonal competition and explains the role of reverse molecular signaling during development. J. Neuroscience 32: 9755-9768.

10. Triplett JW and Feldheim DA (2012) Eph and ephrin signaling in the formation of topographic maps. Semin. Cell Dev Biol. 23: 7-15.

11. Arvanitis D and Davy A (2008) Eph/ephrin signaling networks. Genes and Development22: 416-429.

4/13/2015

18

4/13/2015

19

Structure and action of growth cones

Non-diffusible signals for axon guidance

Extracellular matrix molecules and integrin receptors

Ca+2-independent cell adhesion molecules (CAMs)

Ca+2-dependent cell adhesion (cadherins)Ephrins and eph receptors

4/13/2015

20

Neurotrophin Signaling

Neurotrophin Signaling leads to:

Cell survivalNeurite outgrowthNeuronal differentiationActivity-dependent plasticityCell cycle arrestCell death

Interactions with cell surface receptors.

Arvanitis D , and Davy A Genes Dev. 2008;22:416-429

©2008 by Cold Spring Harbor Laboratory Press

Interactions with cell surface receptors. (A) Eph receptors interact with FGFR, Ryk, and chemokine receptors. Direct interactions are indicated by dashed green lines. Arrows represent agonistic interaction, while blunted lines indicate antagonistic regulation of downstream effectors or biological processes. Tyrosine phosphorylation events are shown in red. (B) Ephrins interact with FGFR and chemokine receptors.

4/13/2015

21

Interactions with synaptic proteins.

Arvanitis D , and Davy A Genes Dev. 2008;22:416-429©2008 by Cold Spring Harbor Laboratory Press

The figure shows a holistic view of Eph/ephrin interactions at sites of synapse formation/regulation.

Eph-A4-induced forward signaling inhibits β1-integrin, which induces spine remodeling.

Eph-B receptors and ephrins-B interact with NMDAR and potentiates its activity.

Recruitment of Tiam1 to the Eph-B/NMDAR complex and activation of small GTPases facilitates spine formation.

Activation of NMDAR induces processing of Eph receptors by MMPs and PS.

Interactions at growth cones.

Arvanitis D , and Davy A Genes Dev. 2008;22:416-429

©2008 by Cold Spring Harbor Laboratory Press

Binding of WRK-1 and Eph/VAB-1 in trans prevents midline crossing. VAB-1 also interacts with SAX-3 in cis. Growth cone retraction requires termination of contact between Eph- and ephrin-expressing cells. This is achieved by cleavage of ephrin ectodomain by ADAM10 in trans and/or endocytosis of Eph/ephrin complexes, followed by processing of the ectodomain in the endosomal/lyzosomal pathway. Subsequent to ectodomainshedding, processed ephrins are targets for PS cleavage that releases the ICD in the cytosol.

4/13/2015

22

Fig. 1   Eph/ephrin signaling and the innervation of LMC spinal motor neurons to the limb.  (A) Binding of Ephs and ephrins in <ce:italic> trans</ce:italic>  can induce bi‐directional signaling in Eph (forward signaling) <ce:cross‐ref refid="bib006...

Tzu‐Jen  Kao , Chris  Law , Artur  Kania

Eph and ephrin signaling: Lessons learned from spinal motor neurons

Seminars in Cell &amp; Developmental Biology Volume 23, Issue 1 2012 83 ‐ 91

http://dx.doi.org/10.1016/j.semcdb.2011.10.016