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Bio 3411 Lecture VI. Making Connections
9/19/11
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Lecture VI. Making Connections
Bio 3411 Monday
September 19, 2011
September 19, 2011 1 Lecture VI. Making Connec<ons
†Bentley, D., & Caudy, M. (1983). Nature, 304(5921), 62-65. †Dickson, B. J. (2002). Science, 298, 1959-1964. †Hannula-Jouppi, et al. (2005). PLoS Genet 14, e50. †Foty, 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, M., & Goodman, C. S. (1996). Science, 274(5290), 1123-1133. †Townes, P. L., & Holtfreter, J. (1955). J Exp Zool, 128, 53–120. †Walter, J., Henke-Fahle, S., & Bonhoeffer, F. (1987). Development, 101(4), 909-913. †Wilson, H. (1907). Science, 25, 912-915. _________________
Reading NEUROSCIENCE: 4th ed, Chapter 23, pp
577-609
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†(pdfs on course website: [http://www.nslc.wustl.edu/courses/Bio3411/bio3411.html]
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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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?)
Segm
enta
tion
Outline of Neurodevelopment 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
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1. Sponges (Wilson, 1907) 2. Amphibians (Townes and Holtfretter, 1955) 3. Chick (Moscona, 1952)
Epidermis + Mesoderm
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Experimental recreation of morphogenesis by mixing cells expressing low and high levels of one surface
adhesion gene (N-cadherin)
Green = high N-cadherin Red = low N-cadherin
+4 hrs +24 hrs
(Foty and Steinberg, 2004)
Growth Cones are Dynamic Sensory Organelles that Guide the Growth of Embryonic Axons
September 19, 2011 11 Lecture VI. Making Connec<ons
(Forscher lab)
Sensing and Transducing: • Diffusible Cues • Contact-dependent Cues • Trophic Factors • Neurotransmitters
Extracellular Cues
Intracellular Signaling Pathways
Cytoskeletal Rearrangment
Ca+2
GTP cAMP
2nd
Messengers
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(Play GFP-Actin Growth Cone Movie) Dr. Andrew Matus
Friedrich Miescher Institute, Switzerland
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Effect/Proximity
A0rac2on Repulsion
Distant Contact
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
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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
(Bentley and Caudy, 1983)
September 19, 2011 24 Lecture VI. Making Connec<ons
Pioneer Neurons
Guidepost Cells Growth Cone
CT1 Photoablated Control
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Early Embryonic Insect Neurons form a Repeated Segmental Scaffold
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Grasshopper embryo
Commissural Tracts
Longitudinal Tracts
Identified Neurons
Q1 pCC aCC
MP1
Q1
Q1
MP1
MP1
pCC aCC
Q1 (Meyers and Bastiani, 1993)
Molecules Mediating Axonal Guidance
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Drosophila robo disrupts longitudinal
tract formation
Robo acts as a receptor for a midline repulsive cue
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Human ROBO Mutation causes HGPPS (Horizontal Gaze Palsy with Progressive Scoliosis)
(reduced hindbrain volume) (scoliosis)
(horizontal gaze palsy)
Jen, et al., 2004
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Retinotectal Mapping Visualized by Dye Injection in Zebrafish
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(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?
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A (T) D
V
T N
Retina
P (N)
M (D)
L (V)
Optic Tectum
Optic tectum
A
P
dorsal
ventral
temporal
nasal
D
T
N
V
M
L
anterior
medial
posterior
lateral
A (T) P (N)
M (D) L (V)
Molecules Mediating Axonal Guidance
1. Biochemical approach: Friedrich Bonhoeffer, retinotectal culture assay.
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Temporal Nasal Functional Assay
Fractionate Native Factors
Observe Neuronal Specificity
Purify and Identify Factor
(Ephrins...) Temporal Axons Nasal Axons
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Pioneer Neurons Create the Early Scaffold of the Adult Nervous System
September 19, 2011 37 Lecture VI. Making Connec<ons
pioneer neuron
guidepost cells
growth cone
selective fasciculation
Pioneer neuron and guidepost cells may die after pathway is pioneered,
by apoptosis
Axonal Guidance Cues
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selective fasciculation
diffusible attractant
diffusible repellant
Contact-dependent attractant
Contact-dependent repellant
(Timing is critical)
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
September 19, 2011 Lecture VI. Making Connec<ons 39
Sequential Restrictions (Refinements) are the Bases for Development
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pluripotent, stem cell
differentiated
genetic
environmental