Lecture Notes: Induction in Cell Differentiation

Overview

• Induction: Process of determining the fate of cells by interaction with neighboring cells.
• Inducers/Organizers: Neighboring cells releasing chemicals (inductors) to influence other cells.
• Differential Gene Expression: Key in cell differentiation where certain genes are turned on/off.

Historical Experiment

• 1920s Experiment by Spemann:
  • Conducted on amphibians, specifically observing the dorsal lip of the blastopore.
  • When the dorsal lip was introduced into another gastrula, it led to the development of a neural plate and eventually a complete embryo.
  • Conclusion: The dorsal lip of the blastopore acts as an organizer, capable of inducing the nervous system formation.

Examples of Induction

1. Mesodermal Induction

• Experiment by Nieuwkoop (1969):

  • Studied on amphibian blastula.
  • Separated and cultured blastomeres from the animal and vegetal poles.
  • Findings:
    • Animal pole cells developed into epidermal cells (ectoderm).
    • Vegetal pole cells developed into endoderm.
    • When cultured together, a new layer (mesoderm) formed between them.
  • Induction: Vegetal cells released inductors prompting animal pole cells to form mesoderm.

• Experiment by Dale and Slack (1987):

  • Identified two types of vegetal cells: dorsal and ventral.
  • Dorsal Vegetal Cells: Induce the formation of dorsal mesoderm (notochord and muscle cells).
  • Ventral Vegetal Cells: Induce the formation of ventral mesoderm (blood cells).

2. Induction of Central Nervous System

• Experiment by Spemann and Mangold:
  • Focused on the interaction between dorsal mesoderm and ectoderm.
  • Early Gastrula Stage:
    • Grafted prospective neural ectoderm into non-neural regions.
    • Resulted in epidermal characteristics showing the fate was not fixed.
  • Late Gastrula Stage:
    • Similar grafting led to the formation of secondary neural plates.
    • Conclusion: Fate of the neural ectoderm is fixed during the late gastrula stage.

Key Concepts

• Primary Induction: Initial interaction between ectoderm and dorsal mesoderm leading to neural induction.
• Terminology Persistence: Despite new findings, some terms like 'primary induction' remain in use.