2025-0310 - amphibian axis - part 2

NEURULATION

General Overview

Neurulation is the process of forming the neural tube which develops into the central nervous system, including the brain and spinal cord. It is influenced by the organization of the ectoderm into neural versus epidermal tissues.

Key Concepts

• Epidermal vs. Neural EctodermDistinguishes between ectoderm that will form skin (epidermal) and that which will develop into neural tissue.

• Anterio-posterior AxisDevelopment along the anterior (front) to posterior (back) axis is crucial for correct formation of the nervous system.

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Posterior NeurulaThe orientation of formations in the neurula stage.Orientation: Anterio-posterior axis affects neural formation.

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Axis Formation in Amphibians

• Gray CrescentSpecial area that initiates gastrulation and influences cell potency.Functionality begins at the dorsal blastoporal lip, known as Spemann’s organizer.

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Molecular Factors in Neurulation

• Stage 8, 9, 10 DevelopmentDifference between epidermal and neural ectoderm.

• Key Molecules

  • Organizer factors:

    • VegT

    • Vg1

    • β-catenin

    • XnrGradients of BMP4 and Xwnt8 influence mesoderm development (ventral and lateral).

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Influence of LiCl

• DorsalizationImpact of Lithium Chloride in dorsal ectoderm formation and differentiation into neural tissue.

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Influence of UV Light

• VentralizationUV exposure leads to a ventral phenotype by inhibiting dorsal structures in neurulation.

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Techniques in Neurulation Studies

• Use of mRNA isolation and cloning techniques for experimenting with dorsalization and ventralization processes.

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Historical Insights

• 1990s studies on mRNA injections led to discoveries about normal versus dorsalized conditions in amphibians.Focus on belly structures during neurula stage.

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Recap of Molecular Interactions

• Stage Annotations (8, 9, 10)More details regarding the role of molecules like Chordin, Noggin, Follistatin.

• Gradient InfluenceMorphogens spread exert influence to develop specific tissues based on their concentration.

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Expression Patterns of Neural Inducers Chordin mRNA similarly expressed as Noggin and Follistatin through early to late gastrulation stages.

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Induction of Neural Tissue Factors from the dorsal blastoporal induce formation of neural tissues, including eyes.Comparison of CM and NE tissue explants highlights differences in potency.

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BMP Inhibition Mechanism Role of Noggin, Chordin, and Follistatin in binding BMPs to inhibit neural tissue formation.BMPs lead ectoderm to epidermal directives.

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Deletion Studies Deleting Noggin, Chordin, Follistatin, and BMPs such as 2, 4, and 7 to study their role in developing neural tissues with Sox2 as a neural marker.

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Molecular Gradients in Amphibians Recap of stages highlighting crucial molecules like VegT, Vg1, and others.

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Organizer Molecules in Dorsalization Core organizer molecules such as Chordin, Noggin, and Follistatin regulate formation of dorsal endoderm and neurectoderm.

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Axis Development Perspective Emphasizes importance of anterior and posterior structure in spinal cord and brain development.

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Neural Plate Formation Neural plate emerges as a result of chordomesoderm and presumptive neurectoderm interactions during neurulation.

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Regional Specification in Neurulation Transplantation experiments demonstrate how different tissues specify anterior-dorsal versus posterior-dorsal structures.

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Advanced Gastrula Specifications Dorsal lip transplants yield insights into temporality of development.

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Temporal & Regional Specification Various endoderm regions (pharyngeal, vegetal) influence ectoderm development throughout gastrulation.

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Organizer Protein List Comprehensive list of proteins associated with organizer activity including Chordin, Dickkopf, and others.

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Wnt Pathway Interaction Cerberus, Dickkopf, and FrzB disrupt Wnt signaling which is vital for neural patterning processes.

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Anterio-Posterior Patterning Pharyngeal and prechordal plate mesoderm contributions to head and neural axis specification.

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Summary of Gradients and Functions BMP, Wnt, and their inhibitors create dynamic gradients directing neural plate developments from anterior to posterior.

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Comparative Ectoderm Analysis Contrasting structures of ectoderm: epidermal regions versus neural development zones, describing tissue types and their functions.

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BMP Inhibitors and Gradients Summary Highlights roles of inhibitors in establishing dorsal structures and neural fates.

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Key Points for Review Gradients and molecular interactions of Xnr proteins lead to organizer expressions.BMP4 and Wnt8's oppositional gradients crucial for neural ectoderm specification.Cerberus, Dickkopf, and Frizzled gradient assist in neural plate patterning along the anterio-posterior axis.

Points to Remember

1. Inducers of Neurectoderm

   • Chordin, Follistatin, and Noggin induce the neurectoderm into the neural pathway.

   • They are classified as inducers and work by inhibiting BMP4 directly.

   • These molecules are considered permissive inducers, and neural induction is a form of permissive induction.

2. Patterning of the Neural Plate

   • Cerberus, Dickkopf, and Frizzled pattern the neural plate along the anterior to posterior axis.

   • They inhibit Wnt8 or its receptors.

   • While Chordin, Follistatin, and Noggin are distributed continuously under the neurectoderm, Cerberus, Dickkopf, and Frizzled are not.

   • These molecules are arranged in a gradient:

     • Higher to Lower Levels:

       • High levels correspond to low Wnt8 function in the neural plate, leading to brain development.

       • Low levels correspond to high Wnt8 function in the neural plate, leading to spinal cord development.

3. Antero-posterior Patterning

   • Involves regional and temporal specification in the neural plate.