1. Outline of Neurodevelopment
Fertilization
Embryonic morphogenesis
Induction of Neuroectoderm
Neurulation
Differentiation:
1. Formation and placement of neuroblasts
2. Axonal outgrowth
3. Growth cones, selective migration
4. Selective fasciculation
5. Target selection
6. Synaptogenesis
7. Etc…(cell shape, neurotransmitter,
ionic channels, receptors)
Adult neuronal plasticity
(Activity-dependent?)
Segmentation

2. Selective Adhesion Determines Specificity of Tissue and
Cellular Associations.

3. Selective Aggregation with Dissociated
Vertebrate 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

4. Retinotectal Mapping Visualized by Dye Injection in Zebrafish
(Friche,et al. 2001)

5. Do Molecular Cues Determine
the Retinotectal Spatial-topic Map?
dorsal
ventral
temporal
nasal A
(T) P
(N)
L(V)
M(D) A
(T) D T N M
(D) L
(V) V P
(N)
Retina
Optic Tectum

6. Retinotectal Map is Preserved Despite
Experimental Rotation of the Eye.
“Chemaffinity Hypothesis”
(Sperry, 1956)
(T)
(N)
(D)
(V) D V T N
Retina
Subjective “up”
Optic Tectum
Rotate Eye 180o N V D T
(T)
(D)
(V)
Subjective “down”
(N)

7. Early Embryonic Insect Neurons
form a Repeated Segmental Scaffold.
Grasshopper
embryo
Longitudinal
Tracts
Identified neurons
Commissural
Tracts

8. Pioneer Neurons Create the Early Scaffold of the Adult Nervous System.
guidepost cells
growth cone
selective
fasciculation

9. Pioneer Neurons and Guidepost Cells
Guide the Initial Path of Peripheral Nerve
Tracts in Embryonic Grasshopper Limb Buds.
Pioneer
Neurons
Guidepost Cells
(Bentley and Caudy, 1983)
Growth Cone
CT1 Photoablated
Control

10. Growth Cones are Dynamic Sensory Organelles
that Guide the Growth of Embryonic Neurons.
Sensing and Transducing:
Diffusible Cues
Contact-dependent Cues
Trophic Factors
Neurotransmitters?
Extracellular signal
Intracellular Signaling
Pathway
Ca+2
GTP
cAMP
Cytoskeletal
Rearrangment
(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

11. Identification of Molecules Mediating
Axonal Guidance using Model Systems.
1. Biochemical approaches:
Friedrich Bonhoeffer, retinotectal culture assay.
Temporal
Nasal
Functional Assay
Fractionate
Native Factors
Observe
Neuronal Specificity
Purify and Identify
Factor
(Ephrins...)
Temporal Axons
Nasal Axons

12. Identification of Molecules Mediating
Axonal Guidance using Model Systems.
2. Molecular genetic approach:
Corey Goodman, Drosophila screens for
neurodevelopmental defects.
Screen for Mutants
of Neuronal Specificity
Clone Mutant Genes
Observe WT
Neuronal Specificity
Identify
Factors
(Semphorins, Slit,
Robo, Commissureless...)

13. Conserved Structural Classes of Axonal 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.
IgG
repeats

14. Axonal Guidance Molecules.
Functional Classes of
Axonal Guidance Molecules.
(Secreted)
(Membrane Associated)
(netrin)
(sema, slit)
(fas)
(eph)
Molecules may function for both:
1. Selective adhesion
2. Intracellular signaling

15. Axonal Guidance Cues. repellant diffusible attractant
selective
fasciculation
diffusible
attractant
repellant
Contact-dependent

16. 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).

17. Human ROBO Mutation causes HGPPS (Horizontal Gaze Palsy with
Progressive Scoliosis)
HGPPS
Normal
(reduced hindbrain volume)
(scoliosis)
(horizontal gaze palsy)
(Jen, et al., 2004)
Drosophila robo disrupts
embryonic CNS scaffold

18. The Axon Guidance Receptor Gene ROBO1
Is 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

19. Development Proceeds by Progressive Developmental Restrictions.
(pluripotent)
(differentiated)