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Outline of Neurodevelopment
Fertilization
Induction of Neuroectoderm
Neurulation
Segmentation
Embryonic morphogenesis
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?)
Selective Adhesion Determines
Specificity of Tissue and
Cellular Associations.
Selective Aggregation with Dissociated
Vertebrate and Invertebrate Tissues
suggest (Neuronal) Adhesion Molecules.
Epidermis
+
Mesoderm
1. Sponges
(Wilson, 1907)
2. Amphibians
(Townes and
Holtfretter, 1955)
3. Chick
(Moscona, 1952)
(Townes and Holtfretter, 1955)
Retinotectal Mapping Visualized
by Dye Injection in Zebrafish
N
T
D
V
T
D
V
N
(Friche,et al. 2001)
Do Molecular Cues Determine
the Retinotectal Spatial-topic Map?
L(V)
M(D)
dorsal
temporal
ventral
A
P
(T)
(N)
nasal
A
(T)
D
T
N
M
L
(D)
(V)
V
P
Retina
(N)
Optic Tectum
Retinotectal Map is Preserved Despite
Experimental Rotation of the Eye.
“Chemaffinity Hypothesis”
(Sperry, 1956)
(T)
D
T
N
Subjective “up”
V
Rotate Eye 180o
(V)
(D)
(N)
Retina
Optic Tectum
(T)
V
N
T
D
(V)
(D)
(N)
Subjective “down”
Early Embryonic Insect Neurons
form a Repeated Segmental Scaffold.
Grasshopper
embryo
Longitudinal
Tracts
Identified neurons
Commissural
Tracts
Pioneer Neurons Create the Early
Scaffold of the Adult Nervous System.
growth cone
pioneer neuron
guidepost cells
selective
fasciculation
Pioneer Neurons and Guidepost Cells
Guide the Initial Path of Peripheral Nerve
Tracts in Embryonic Grasshopper Limb Buds.
Guidepost Cells
CT1 Photoablated
Growth Cone
Pioneer
Neurons
Control
(Bentley and Caudy, 1983)
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
Ca+2
Intracellular Signaling
Pathway
GTP
Cytoskeletal
Rearrangment
cAMP
(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
Identification of Molecules Mediating
Axonal Guidance using Model Systems.
1. Biochemical approaches:
Friedrich Bonhoeffer, retinotectal culture assay.
Observe
Neuronal Specificity
Functional Assay
Fractionate
Native Factors
Temporal
Nasal
Purify and Identify
Factor
(Ephrins...)
Temporal Axons
Nasal Axons
Identification of Molecules Mediating
Axonal Guidance using Model Systems.
2. Molecular genetic approach:
Corey Goodman, Drosophila screens for
neurodevelopmental defects.
Observe WT
Neuronal Specificity
Screen for Mutants
of Neuronal Specificity
Clone Mutant Genes
Identify
Factors
(Semphorins, Slit,
Robo, Commissureless...)
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
Functional Classes of
Axonal Guidance Molecules.
(Secreted)
(sema, slit)
(netrin)
(fas)
(eph)
(Membrane Associated)
Molecules may function for both:
1. Selective adhesion
2. Intracellular signaling
Axonal Guidance Cues.
diffusible
repellant
diffusible
attractant
Contact-dependent
attractant
Contact-dependent
repellant
selective
fasciculation
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)
HGPPS
Normal
(horizontal gaze palsy)
(reduced hindbrain volume)
(scoliosis)
(Jen, et al., 2004)
Drosophila robo disrupts
embryonic CNS scaffold
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,
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
2 European
PLOS Genetics (2005) 1: 0467
Development Proceeds by Progressive
Developmental Restrictions.
(pluripotent)
(differentiated)