Formation and Functions of the Gastrula Organizer in Zebrafish

Abstract

The use of amphibian embryos in experimental embryology has a rich history dating back to the late nineteenth century. Manipulations that are possible in certain salamander and frog embryos due to their large size led to the discovery of the dorsal lip as Spemann’s organizer, also known as the gastrula organizer (Spemann and Mangold 1924). Transplantation of the dorsal lip to the ventral side of the amphibian embryo yields a duplicated body axis. While not as famous as the amphibian history in experimental embryology, work using fish does have a proud track record. Early experimental work predominantly used Fundulus heteroclitus, commonly known as the killifish or mummichog, because of the large size of its embryos (~1.8 mm) that lends itself to experimental manipulations. Recent experimental and genetic work has turned to zebrafish (Danio rerio). Experimental manipulations combined with modern genetic techniques have complemented and expanded our understanding of organizer development derived from amphibian work. In this chapter, we will provide a brief history of observations and classical experimental manipulations concerning the teleost gastrula organizer. We shall then move onto more recent experiments that define the nature of the teleost organizer and how it is formed. Finally, we will describe molecules, many of which were identified through the characterization of zebrafish mutants, which are involved in organizer formation and function.