Lecture VI. Making Connections Bio 3411 Monday September 20, Lecture VI. Making Connections

† Bentley, D., & Caudy, M. (1983). Nature, 304(5921), † Dickson, B. J. (2002). Science, 298, † Hannula-Jouppi, et al. (2005). PLoS Genet 14, e50. † Foty, R. A., & Steinberg, M. S. (2004). Int J Dev Biol, 48(5-6), † Hayashi, T., & Carthew, R. W. (2004). Nature, 431(7009), Jen, J. C., et al. (2004). Science, 304, † Moscona, A., & Moscona, H. (1952). J Anat, 86(3), † Myers, P. Z., & Bastiani, M. J. (1993). J Neurosci, 13(1), † Sperry, R. W. (1963). Proc Natl Acad Sci U S A, 50, † Tessier-Lavigne, M., & Goodman, C. S. (1996). Science, 274(5290), † Townes, P. L., & Holtfreter, J. (1955). J Exp Zool, 128, 53–120. † Walter, J., Henke-Fahle, S., & Bonhoeffer, F. (1987). Development, 101(4), † Wilson, H. (1907). Science, 25, _________________ Reading NEUROSCIENCE: 4 th ed, Chapter 23, pp Lecture VI. Making Connections September 20, 2010 † (pdfs on course websites: [ & [

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)? September 20, 2010Lecture VI. Making Connections3

September 20, 2010Lecture VI. Making Connections4

September 20, 2010Lecture VI. Making Connections5

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 September 20, 2010Lecture VI. Making Connections6

September 20, 20107Lecture VI. Making Connections 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 Outline of Neurodevelopment

Selective Adhesion Determines Specificity of Tissue and Cellular Associations September 20, 20108Lecture VI. Making Connections

Selective Aggregation of dissociated embryonic tissues (vertebrate and invertebrate) suggests ancient (surface) Adhesion Molecules September 20, 20109Lecture VI. Making Connections (Townes & Holtfretter, 1955) 1. Sponges (Wilson, 1907) 2. Amphibians (Townes and Holtfretter, 1955) 3. Chick (Moscona, 1952) Epidermis + Mesoderm

September 20, Lecture VI. Making Connections 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 20, Lecture VI. Making Connections (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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September 20, 2010Lecture VI. Making Connections13 (Play GFP-Actin Growth Cone Movie) Dr. Andrew Matus Friedrich Miescher Institute, Switzerland

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September 20, 2010Lecture VI. Making Connections17 Effect/Pro ximity AttractionRepulsion Distant Contact

Functional Classes of Axonal Guidance Molecules (Secreted) (Membrane Associated) (net rin) (sema, slit) (f as ) (e ph ) Molecules may function for both: 1. Selective adhesion 2. Intracellular signaling September 20, Lecture VI. Making Connections

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September 20, 2010Lecture VI. Making Connections20

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. September 20, Lecture VI. Making Connections

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September 20, 2010Lecture VI. Making Connections23

Pioneer Neurons and Guidepost Cells guide the initial path of peripheral nervetracts in embryonic grasshopper limbs (Bentley and Caudy, 1983) September 20, Lecture VI. Making Connections Pioneer Neurons Guidepost Cells Growth Cone CT1 PhotoablatedControl

Early Embryonic Insect Neurons form a Repeated Segmental Scaffold September 20, Lecture VI. Making Connections Grasshopper embryo Commissural Tracts Longitudinal Tracts Identified Neurons Q1 pCC aCC MP1 Q1 MP1 pCC aCC Q1 (Meyers and Bastiani, 1993)

Molecules Mediating Axonal Guidance September 20, Lecture VI. Making Connections

September 20, 2010Lecture VI. Making Connections27 Drosophila robo disrupts longitudinal tract formation Robo acts as a receptor for a midline repulsive cue

September 20, 2010Lecture VI. Making Connections28 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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September 20, 2010Lecture VI. Making Connections30

September 20, 2010Lecture VI. Making Connections31

Retinotectal Mapping Visualized by Dye Injection in Zebrafish September 20, Lecture VI. Making Connections (Friche,et al. 2001)

Zebrafish ROBO Mutant (astray) Disrupts Midline Retinotectal Axonal Projections September 20, Lecture VI. Making Connections

September 20, 2010 Do Molecular Cues Determine the Retinotectal Spatial-topic Map? 34Lecture VI. Making Connections A (T) D V TN 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. 35 TemporalNasal Functional Assay Fractionate Native Factors Observe Neuronal Specificity Purify and Identify Factor (Ephrins...) Temporal Axons Nasal Axons September 20, 2010Lecture VI. Making Connections

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Pioneer Neurons Create the Early Scaffold of the Adult Nervous System September 20, Lecture VI. Making Connections pioneer neuron guidepost cells growth cone selective fasciculation Pioneer neuron and guidepost cells may die after pathway is pioneered, by apoptosis

Axonal Guidance Cues September 20, Lecture VI. Making Connections 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 20, 2010Lecture VI. Making Connections39

Sequential Restrictions (Refinements) are the Bases for Development September 20, Lecture VI. Making Connections pluripotent, stem cell differentiated genetic environmental

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September 20, 2010Lecture VI. Making Connections42 Finis