Outline of Neurodevelopment 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

Selective Adhesion Determines Specificity of Tissue and Cellular Associations.

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

Retinotectal Mapping Visualized by Dye Injection in Zebrafish (Friche,et al. 2001)

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

Retinotectal Map is Preserved Despite Experimental Rotation of the Eye. “Chemaffinity Hypothesis” (Sperry, 1956) (T) (N) (D) (V) D V T N Retina Subjective “up” Optic Tectum Rotate Eye 180o N V D T (T) (D) (V) Subjective “down” (N)

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. guidepost cells growth cone selective fasciculation

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

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 Intracellular Signaling Pathway Ca+2 GTP cAMP Cytoskeletal Rearrangment (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. Temporal Nasal Functional Assay Fractionate Native Factors Observe Neuronal Specificity 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. Screen for Mutants of Neuronal Specificity Clone Mutant Genes Observe WT Neuronal Specificity 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

Axonal Guidance Molecules. 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

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

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 (reduced hindbrain volume) (scoliosis) (horizontal gaze palsy) (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, 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

Development Proceeds by Progressive Developmental Restrictions. (pluripotent) (differentiated)