21 - Neural Induction


  • Labeling Techniques:

    • a. Labeling cells: Techniques used to visualize cellular and tissue structures.

    • b. Tract tracing: A method to observe how neurons or brain regions connect with one another.

  • Immunostaining/Immunolabeling: A broad term for using antibodies and fluorophores to detect protein locations in biological samples.

    • Immunohistochemistry: Immunostaining applied to tissue samples.

    • Immunocytochemistry: Immunostaining applied to cell culture samples.

Neural Induction: biological process where a cell or tissue changes state in response to an inducing stimulus, such as a molecule presented by another tissue.

  • Discussed embryonic developmental stages:

    • Fertilized Egg

    • 2-Cell Stage

    • 4-Cell Stage

    • 8-Cell Stage

    • Morula

    • Blastula

    • Invaginating Gastrula

    • Gastrula

Gastrulation: is the process involving cell movements in the early embryo, resulting in the formation of three distinct germ layers. It is during this process that neural induction occurs.

Germ Layers:

  • Ectoderm: Forms nervous system, skin, and some internal organs.

  • Mesoderm: Forms muscles, bones, blood, and the circulatory and immune systems.

  • Endoderm: Forms gut and associated organs like the liver and pancreas.


  • Any alterations to developmental stages can lead to significant effects on survival, such as spina bifida and other neural tube defects.

Experimental Methods in Understanding Embryonic Development

  • Ablation and Constriction: Utilized to test whether different embryo regions are interchangeable or specified for tissue production.

  • Spemann's Organizer: demonstrating how the organizer (dorsal lip of the blastopore) influences body axis development.

    • Experiment: Hair constriction method led to two complete embryos when applied appropriately across the blastopore.

Insights from the Spemann/Mangold Experimentation

  • Provided fundamental contributions to embryology and revealed body axis determination mechanisms.

  • The dorsal lip of the blastopore plays a crucial role in inducing secondary structures and determining the body axis.

Molecular Mechanisms of Primary Induction

  • Expression Cloning Technique: Captures RNA from organizer tissue converted to cDNAs which are injected into embryos.

  • Key Discoveries:

    • Noggin: A secreted protein capable of inducing dorsal neural tissue.

    • Others: Chordin and Follistatin show similar capabilities.

BMP Signaling Pathway

  • Bone Morphogenic Proteins (BMPs): In the absence of external signals, ectodermal cells tend to acquire neuronal identity.

    • BMPs inhibit this neuronal induction fostering an epidermal fate.

    • Noggin and chordin counteract BMPs, restoring the default neuronal fate.

Summary of Neural Induction Mechanism

  • During gastrulation, mesoderm invagination drives the overlying ectoderm towards a neuronal fate via signals like Noggin and Chordin.

  • These factors block BMP signaling, thus facilitating neural induction.

Loss-of-Function Experiments

  • Noggin Knockout (KO): If Noggin is absent, Chordin can compensate for its function.

  • Observations indicate that loss primarily affects anterior neural structures, with posterior structures remaining unaffected.

  • Peter Nieuwkoop's Work: Advance understanding of anterior-posterior patterning during neural development through placing induced ectoderm at various axes.