Chapter 12 Outline

Fertilization and Cleavage in Amphibians

• Fertilization and cortical rotation
• Cleavage
• The mid-blastula transition: Preparing for gastrulation

Amphibian Gastrulation

• Epiboly of the prospective ectoderm
• Vegetal rotation and invagination of the bottle cells
• Involution at the blastopore lip
• Convergent extension of the dorsal mesoderm
• Specification of the germ layers
• The dorsal-ventral and anterior-posterior axes

Axis Formation and the Amphibian Organizer: Molecular Mechanisms

• Discovery of the organizer
• How does the organizer form?
• The dorsal signal, part 1: the nieuwkoop center
• The dorsal signal, part 2: β-catenin
• The dorsal signal, part 3: synergy with vegetal signals
• Formation of the organizer: a summary

Functions of the organizer

• Induction of neural ectoderm and dorsal mesoderm: BMP inhibitors
• Ectodermal bias
• Conservation of BMP signaling during dorsal-ventral patterning

Neural Induction along the Anterior-Posterior Axis

• Anterior-posterior and dorsal-ventral axis formation: A Summary

The Amphibian Left-Right Axis

Early Zebrafish Development

• Zebrafish Cleavages: Yolking Up the Process
• Mid-blastula transition and the YSL
• Gastrulation and Formation of the Germ Layers
• Progression of epiboly
• Internalization of the hypoblast
• The embryonic shield and the neural keel

Axis Formation in Zebrafish

• The embryonic shield establishes the dorsal-ventral axis
• The fish blastopore lip

• Left-right axis formation