Chapter 8: Zebrafish Development

Early embryogenesis is defined by meroblastic cleavage at the animal pole, leading to the mid-blastula transition where the zygotic genome is activated and the yolk syncytial layer (YSL) forms to drive subsequent cell movements. Morphogenesis is explained through the integrated processes of epiboly, involution, and convergent extension, with the embryonic shield serving as the critical organizer for the dorsal axis. Notably, zebrafish neurulation differs from other vertebrates as it involves the formation of a solid neural keel that undergoes secondary cavitation to create the neural tube. The text provides an in-depth look at the sophisticated genetic tools available to researchers, from large-scale forward genetic screens using chemical mutagens like ethyl nitrosourea (ENU) to reverse genetic techniques involving morpholinos, the Gal4 system, and transposon-mediated transgenesis. Molecular signaling pathways are highlighted as the architects of the body plan, specifically the Wnt/beta-catenin pathway for dorsal specification, Nodal signaling through factors like cyclops and squint for mesendoderm induction, and the antagonistic relationship between BMP gradients and inhibitors like chordin. The chapter concludes by discussing how the zebrafish's physiological similarity to humans and its suitability for high-throughput screening have made it an invaluable tool for toxicology, drug discovery, and modeling human diseases.