Download Lecture VI. Making Connections

Lecture VI. Making
Connections
Bio 3411
Monday
September 20, 2010
September 20, 2010
Lecture VI. Making Connections
1
Reading
NEUROSCIENCE: 4th ed, Chapter 23, pp 577609
†Bentley,
D., & Caudy, M. (1983). Nature, 304(5921), 62-65.
B. J. (2002). Science, 298, 1959-1964.
†Dickson,
†Hannula-Jouppi,
†Foty,
et al. (2005). PLoS Genet 14, e50.
R. A., & Steinberg, M. S. (2004). Int J Dev Biol, 48(5-6), 397-409.
†Hayashi,
T., & Carthew, R. W. (2004). Nature, 431(7009), 647-652.
Jen, J. C., et al. (2004). Science, 304, 1509-1513.
†Moscona, A.,
& Moscona, H. (1952). J Anat, 86(3), 287-301.
†Myers,
P. Z., & Bastiani, M. J. (1993). J Neurosci, 13(1), 115-126.
†Sperry,
R. W. (1963). Proc Natl Acad Sci U S A, 50, 703-710.
†Tessier-Lavigne,
†Townes,
†Walter,
†Wilson,
M., & Goodman, C. S. (1996). Science, 274(5290), 1123-1133.
P. L., & Holtfreter, J. (1955). J Exp Zool, 128, 53–120.
J., Henke-Fahle, S., & Bonhoeffer, F. (1987). Development, 101(4), 909-913.
H. (1907). Science, 25, 912-915.
_________________
†(pdfs
on course websites: [http://artsci.wustl.edu/~bio3411/] & [http://www.nslc.wustl.edu/courses/Bio3411/bio3411.html]
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What the last Lecture was about
•
Programmed cell death (apoptosis) is a physiological mechanism distinct
from necrotic cell death.
•
Apoptosis occurs widely during normal development of the nervous
system.
•
Isolation of specific molecules involved in promoting growth and survival –
“trophism,” e.g., Nerve Growth Factor (NGF).
•
What is the “death mechanism” that NGF (and other neruotrophins)
inhibit?
•
Broader implications: controlled cell death in neuroembryology vs
uncontrolled cell growth of cancer.
•
Gene homologies between organisms - humans and worms (nematodes)
•
Molecular models for apoptosis
•
How do trophic factors connect to this cell death pathway(s)?
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What this Lecture is about
• General mechanisms for assembling neurons and
groups of neurons
• Diffusion vs Contact
• Attraction vs Repulsion
• Examples of impacts of contact
• Examples of impacts of diffusion
• Specification by growth factors
• The chemoaffinity hypothesis
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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?)
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Selective Adhesion Determines Specificity
of Tissue and Cellular Associations
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Selective Aggregation of dissociated embryonic tissues
(vertebrate and invertebrate) suggests ancient (surface)
Adhesion Molecules
Epidermis + Mesoderm
1. Sponges
(Wilson, 1907)
(Townes & Holtfretter, 1955)
2. Amphibians
(Townes and
Holtfretter, 1955)
3. Chick
(Moscona, 1952)
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Experimental recreation of morphogenesis by mixing
cells expressing low and high levels of one surface
adhesion gene (N-cadherin)
+4 hrs
+24 hrs
Green = high N-cadherin
Red = low N-cadherin
(Foty and Steinberg, 2004)
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Growth Cones are Dynamic Sensory Organelles that
Guide the Growth of Embryonic Axons
Sensing and Transducing:
• Diffusible Cues
• Contact-dependent Cues
• Trophic Factors
• Neurotransmitters
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Extracellular Cues
Intracellular Signaling
Pathways
2nd
Messengers
Ca+2
GTP
Cytoskeletal
Rearrangment
cAMP
(Forscher lab)
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(Play GFP-Actin Growth Cone Movie)
Dr. Andrew Matus
Friedrich Miescher Institute, Switzerland
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Effect/Pro Attraction Repulsion
ximity
Distant
Contact
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Functional Classes of
Axonal Guidance Molecules
(Secreted)
(sema,
slit)
(net
rin)
Molecules may function
for both:
1. Selective adhesion
2. Intracellular signaling
(f
as
)
(e
ph
)
(Membrane Associated)
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Conserved Structural Classes of Axonal Guidance
Molecules: Modular Construction and Multifunctionality
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.
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Pioneer Neurons and Guidepost Cells guide the initial
path of peripheral nervetracts in embryonic grasshopper
limbs
Guidepost Cells
Growth Cone
Pioneer
Neurons
CT1 Photoablated
Control
(Bentley and Caudy, 1983)
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Early Embryonic Insect Neurons form a Repeated
Segmental Scaffold
Longitudinal Tracts
MP1
Q1
Grasshopper
embryo
aCC
pCC
MP1
Q1
MP1
Q1
aCC
pCC
Commissural Tracts Identified Neurons
Q1
(Meyers and Bastiani, 1993)
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Molecules Mediating Axonal Guidance
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Robo acts as a receptor for a midline repulsive cue
Drosophila robo
disrupts longitudinal
tract formation
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Human ROBO Mutation causes HGPPS
(Horizontal Gaze Palsy with Progressive Scoliosis)
Jen, et al., 2004
(horizontal gaze palsy)
(reduced hindbrain volume)
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(scoliosis)
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Retinotectal Mapping Visualized by Dye Injection in
Zebrafish
(Friche,et al. 2001)
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Zebrafish ROBO Mutant (astray)
Disrupts Midline Retinotectal Axonal Projections
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Do Molecular Cues Determine the Retinotectal
Spatial-topic Map?
A anterior
D dorsal
L (V)
M (D)
A (T)
P (N)
L lateral
M medial
N nasal
P posterior
Optic tectum
T temporal
V ventral
A (T)
D
T
N
V
Retina
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M
L
(D)
(V)
P (N)
Optic Tectum
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Molecules Mediating Axonal Guidance
1. Biochemical approach: Friedrich Bonhoeffer, retinotectal culture assay.
Observe
Neuronal Specificity
Functional Assay
Temporal
Nasal
Fractionate
Native Factors
Purify and Identify
Factor
(Ephrins...)
Temporal AxonsNasal Axons
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Pioneer Neurons Create the Early Scaffold of the Adult
Nervous System
growth cone
pioneer neuron
guidepost cells
Pioneer neuron and guidepost cells
may die after pathway is pioneered,
by apoptosis
selective
fasciculation
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Axonal Guidance Cues
diffusible
repellant
diffusible
attractant
Contact-dependent
attractant
Contact-dependent
repellant
selective
fasciculation
(Timing is critical)
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What this Lecture was about
• Grouping neurons and processes
• Partner selection
• Some genetic foundations/correlates
• Systematic organization of connections
• Roles of contact and diffusion
• Deja vu
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Sequential Restrictions (Refinements) are the Bases for
Development
pluripotent, stem cell
genetic
environmental
differentiated
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Finis
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