Outline of Neurodevelopment

1. Outline of Neurodevelopment Fertilization Embryonic morphogenesis Induction of Neuroectoderm Segmentation 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?)

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

3. Epidermis + Mesoderm 1. Sponges (Wilson, 1907) 2. Amphibians (Townes and Holtfretter, 1955) 3. Chick (Moscona, 1952) (Townes and Holtfretter, 1955) Selective Aggregation with Dissociated Vertebrate and Invertebrate Tissues suggest (Neuronal) Adhesion Molecules.

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

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

6. (T) D T N (V) (D) Rotate Eye 180o V (N) Retina V N T D Retinotectal Map is Preserved Despite Experimental Rotation of the Eye. “Chemaffinity Hypothesis” (Sperry, 1956) Subjective “up” Optic Tectum (T) (V) (D) 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. growth cone pioneer neuron guidepost cells selective fasciculation

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

10. Extracellular signal Ca+2 Cytoskeletal Rearrangment Intracellular Signaling Pathway GTP cAMP Growth Cones are Dynamic Sensory Organelles that Guide the Growth of Embryonic Neurons. • Sensing and Transducing: • Diffusible Cues • Contact-dependent Cues • Trophic Factors • Neurotransmitters? (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. Observe Neuronal Specificity Functional Assay Fractionate Native Factors Temporal Nasal Purify and Identify Factor (Ephrins...) Nasal Axons Temporal Axons

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

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

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

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

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)