Outline of Neurodevelopment

Fertilization

Embryonic morphogenesis

Induction of Neuroectoderm

Neurulation

Differentiation:1. Formation and placement of neuroblasts2. Axonal outgrowth3. Growth cones, selective migration4. Selective fasciculation5. Target selection6. Synaptogenesis7. Etc…(cell shape, neurotransmitter, ionic channels, receptors)

Adult neuronal plasticity(Activity-dependent?)

Seg

men

tati

on

Selective Adhesion Determines Specificity of Tissue and

Cellular Associations.

Selective Aggregation with DissociatedVertebrate and Invertebrate Tissues

suggest (Neuronal) Adhesion Molecules.

(Townes and Holtfretter, 1955)

1. Sponges (Wilson, 1907)

2. Amphibians (Townes and Holtfretter, 1955)

3. Chick (Moscona, 1952)

Epidermis+

Mesoderm

VD

N

T

DV

N

T

(Friche,et al. 2001)

Retinotectal Mapping Visualizedby Dye Injection in Zebrafish

Do Molecular Cues Determine the Retinotectal Spatial-topic Map?

dorsal ventral

temporal nasalA(T)

P(N)

L(V)

M(D)

Retina

T N

D

V

Optic Tectum

M(D)

L(V)

A(T)

P(N)

D

V

T N

Retina

Subjective “up”

Optic Tectum

(T)

(N)

(D) (V)

Subjective “down”

(T)

(N)

(D) (V)

Retinotectal Map is Preserved DespiteExperimental Rotation of the Eye.

“Chemaffinity Hypothesis”(Sperry, 1956)

Rot

ate

Eye

180

o

N

V

D

T

Early Embryonic Insect Neurons form a Repeated Segmental Scaffold.

Identified neuronsCommissural

Tracts

LongitudinalTracts

Grasshopperembryo

Pioneer Neurons Create the Early Scaffold of the Adult Nervous System.

pioneer neuron

guidepost cells

growth cone

selectivefasciculation

Pioneer Neurons and Guidepost CellsGuide the Initial Path of Peripheral Nerve

Tracts in Embryonic Grasshopper Limb Buds.

PioneerNeurons

Guidepost Cells

(Bentley and Caudy, 1983)

Growth Cone

CT1 Photoablated Control

Growth Cones are Dynamic Sensory Organellesthat Guide the Growth of Embryonic Neurons.

Sensing and Transducing:• Diffusible Cues• Contact-dependent Cues• Trophic Factors• Neurotransmitters?

(Play GFP-Actin Growth Cone Movie)Andrew Matus, Friedrich Miescher Institute, Switzerland

(Play Time-Lapse Dendritic Spines Movie)Anna Dunaevsky and Rafael Yuste, Columbia U

Extracellular signal

Intracellular SignalingPathway

Ca+2

GTP

cAMP

CytoskeletalRearrangment

Identification of Molecules Mediating Axonal Guidance using Model Systems.

1. Biochemical approaches: Friedrich Bonhoeffer, retinotectal culture assay.

Temporal Nasal

Functional Assay

Fractionate Native Factors

ObserveNeuronal Specificity

Purify and IdentifyFactor

(Ephrins...)

Temporal Axons Nasal Axons

2. Molecular genetic approach: Corey Goodman, Drosophila screens for neurodevelopmental defects.

Identification of Molecules Mediating Axonal Guidance using Model Systems.

Screen for Mutantsof Neuronal Specificity

Clone Mutant Genes

Observe WTNeuronal Specificity

IdentifyFactors

(Semphorins, Slit,Robo, Commissureless...)

Conserved Structural Classes ofAxonal Guidance Molecules.

1. Laminin, fibronectin and extracellular matrix proteins.2. Cadherins and catenins. (Ca+2 dependent)3. Cell adhesion molecules (CAMs) (containing IgG domains).4. Receptor tyrosine kinases and receptor phosphatases.

IgGrepeats

Functional Classes of Axonal Guidance Molecules.

(Secreted)

(Membrane Associated)

(netrin) (sema, slit)

(fas) (eph)

Molecules may function for both:1. Selective adhesion2. Intracellular signaling

Axonal Guidance Cues.

selectivefasciculation

diffusibleattractant

diffusiblerepellant

Contact-dependentattractant

Contact-dependentrepellant

Axonal Guidance

1. Pioneer neurons construct the earliest scaffold of the nervous system, following chemical cues.

2. Multiple chemical cues guide growth cones, including long-range diffusible cues (secreted molecules) and short-range contact mediated cues (membrane associated).

3. Chemical cues may be attractive or repulsive.

4. Chemical cues mediate both selective adhesion and intercellular signaling.

5. Axonal guidance molecules are ancient conserved molecules, including a large class with structural similarity to immunoglobulins.

6. Final axonal pathways likely specified by unique combinations of molecular cues expressed by growing neurons and targets (Sperry’s Chemoaffinity Hypothesis).

Human ROBO Mutation causes HGPPS(Horizontal Gaze Palsy with

Progressive Scoliosis)

HG

PP

SN

orm

al

(reduced hindbrain volume) (scoliosis)

(horizontal gaze palsy)

(Jen, et al., 2004)

Drosophila robo disruptsembryonic CNS scaffold

The Axon Guidance Receptor Gene ROBO1Is a Candidate Gene for Developmental Dyslexia

Katariina Hannula-Jouppi1, Nina Kaminen-Ahola1, Mikko Taipale1,2, Ranja Eklund1, Jaana Nopola Hemmi1,3,Helena Kaariainen4,5, Juha Kere1,6*

1 Department of Medical Genetics, University of Helsinki, Finland, 2 European Molecular Biology Laboratory, Gene Expression Programme, Heidelberg, Germany,3 Department of Pediatrics, Jorvi Hospital, Espoo, Finland, 4 Department of Medical Genetics, The Family Federation of Finland, Helsinki, Finland, 5 Department of Medical Genetics, University of Turku, Turku, Finland, 6 Department of Biosciences at Novum and Clinical Research Centre, Karolinska Institutet, Stockholm, Sweden

PLOS Genetics (2005) 1: 0467

Development Proceeds by ProgressiveDevelopmental Restrictions.

(pluripotent)

(differentiated)