Key Stages in Embryonic Development,

Elaboration of the Vertebrate Body Plan

Overview

  • Topics Covered:

    • Mesoderm Induction and Morphogen Gradients

    • Neural Induction and Morphogen Gradients

    • Somitogenesis and Vertebral Development

    • Vertebrate Trunk Elongation

1. Mesoderm Induction and Morphogen Gradients

  • Germ Layers and Regions of the Mesoderm:

    • The embryonic development results in three primary germ layers: ectoderm, mesoderm, and endoderm.

    • Each layer differentiates into various cell types and structures.

  • Axis Formation in Xenopus:

    • Critical knowledge regarding the orientation of the body structure.

  • Spemann’s Organizer and Mesoderm Induction:

    • Significance of Spemann's Organizer in embryonic development.

    • Historical Context: Spemann and Mangold (1924) conducted experiments showing that dorsal lip of the blastopore, when transplanted, initiated a secondary body axis.

  • The Nieuwkoop Center and β-catenin:

    • Vegetal blastomeres on the dorsal side constitute the Nieuwkoop center which induces organizer formation.

    • Function: Establishes the dorsal side of the embryo.

    • Injection of β-catenin mRNA can mimic Nieuwkoop center activity.

    • Association with Wnt Signaling: β-catenin is a key component in the Wnt signaling pathway.

  • Nodal Signaling - A Morphogen (Zebrafish):

    • Nodal ligands are TGF-β family members that play a role in mesoderm induction and patterning.

    • Nodal signals through the activin receptor with the help of oep (one-eyed pinhead).

2. Induction and Patterning of the Germ Layers

  • **Embryo Stages:

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