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BIO 334 Principles of Neurobiology

Development of Nervous Systems

Overview

  • This course focuses on the developmental biology of the nervous system, with an emphasis on early embryonic development phases and signaling processes.

Lecture Outline / Study Guide

  1. Early Development

    • Gastrulation

    • Neurulation

    • Spemann-Mangold Organizer

      • Morphogens: Chordin, Noggin, Follistatin, BMP4

      • Cell migration and formation of neural tube and neural crest.

    • Anterior-Posterior Patterning of the Neural Tube

      • Hox genes.

    • Dorsal-Ventral Patterning of the Neural Tube

      • Morphogens: SHH, retinoic acid, BMPs, Dorsalin, others.

  2. Connecting Cells in the Nervous System

    • Cell Proliferation and Differentiation.

    • Cell Migration.

    • Process Outgrowth.

    • Synapse Formation.

    • Note: This outline serves as a guideline; topics may vary in exams.

Central Nervous System (CNS)

  • Development: The CNS begins as a hollow tube, later differentiating into distinct brain regions.

  • Major CNS subdivisions: Prosencephalon (forebrain), Mesencephalon (midbrain), Rhombencephalon (hindbrain).

Developmental Stages

  1. Fertilization: The fusion of sperm and egg forms a zygote.

  2. Cleavage: Quick cell division forms a multicellular embryo.

  3. Blastulation: Formation of the blastula, a hollow ball of cells.

  4. Gastrulation: Creation of three germ layers:

    • Ectoderm (outer layer)

    • Mesoderm

    • Endoderm (inner layer)

  5. Neurulation: Formation of the neural tube, leading to the brain and spinal cord.

Spemann-Mangold Organizer

  • Function: Induces neural tissue development.

  • Discovery (1924): Conducted experiments showing that embryonic cells can alter the fate of surrounding cells through signaling factors.

  • Experimental Insights:

    • Transplantation of upper blastopore lip induced secondary embryos with neural structures.

    • Identified a phenomenon known as induction.

  • Key Contributors: Hans Spemann, Hilde Mangold, and Ethel Browne (previously explored induction in hydra).

Induction and Differentiation

  • Induction Evidence:

    • Experiments utilized colored salamanders demonstrating color differentiation in induced structures.

    • Organizing effects of transplanted tissue confirmed.

  • Morphogens released: Chordin, Noggin, Follistatin inhibit BMP4, allowing differentiation into neural tissue.

Neurulation Process

  • Neural Tube Formation: Ectoderm proliferation creates a neural groove that overlaps the notochord and mesoderm, eventually fusing to form the neural tube.

  • Neural Crest Development: Neural crest cells differentiate into various cell types including sensory neurons, Schwann cells, and others.

Hox Genes and Axial Patterning

  • Hox Genes Overview:

    • Encode transcription factors that determine segment identity.

    • Duplications lead to paralogous genes and specific regional expression.

  • Collinearity Principle: Sequence order on chromosomes corresponds with expression along the embryo.

Morphogens in Development

  • Definition: A morphogen is a signaling molecule crucial for cell differentiation in morphogenesis.

  • Role:

    • Establishes concentration gradients influencing cell type specialization.

    • Examples include Sonic hedgehog (Shh) and retinoic acid.

  • Interaction with Receptors: Activation leads to specific gene expression patterns.

Dorsal-Ventral Patterning

  • Notochord Role: Provides morphogens, crucial for distinguishing dorsal and ventral structures.

  • Sonic Hedgehog (Shh): A primary morphogen involved in neuronal cell differentiation and organization.

  • BMP4 and TGF-β Pathways: Work in parallel with Shh to induce differentiation between dorsal and ventral neural tube structures.

Connecting Cells: Processes Detailing

  1. Cell Proliferation and Differentiation: Generation of neural precursors.

  2. Cell Migration: Movement of neurons/glia to final locations.

  3. Process Outgrowth: Neurites develop dendrites and axons for communication.

  4. Synapse Formation: Establishment of specialized intercellular connections.

Cell Adhesion and Growth Cones

  • Growth Cone Dynamics: Active exploration by neurites guided by chemotropic factors; includes positive (chemoattractants) and negative (chemorepellents) signals.

  • Cell Adhesion Molecules (CAMs): Integral for cell-to-substrate and cell-to-cell interactions essential in process outgrowth.

    • Major families include integrins, cadherins, and immunoglobulin families.

The Neuromuscular Junction Formation

  • α- motor neurons: Establish synapse with muscle cells; growth cones release agrin to facilitate receptor clustering on muscle.

  • Neuronal Apoptosis: Significant during early development; aligns motor neuron inputs per muscle fiber, ensuring precise innervation.

Closing Remarks

  • Cell Communication: Essential throughout development and during the establishment of neural circuits.

  • Importance of Morphogen Gradients: Critical for the correct spatial arrangement of neural structures and function.