During the past 10 yr, the zebrafish has emerged as an important model system for the study of vertebrate development. This is primarily because of the promise of the system for developmental genetic studies. but, in addition to the necessary features of an animal that can be used for genetics, there are a range of experimental approaches that have proven successful in studies of tissue interactions, gene function, and early neural development. Such methods include embryonic cell transplantation, the analysis of gene function by injection of RNA or antibodies into the fertilized egg, and the analysis of identified neurons in the developing central nervous system. The object of this chapter is to outline the main features of early zebrafish development and to provide details of the methods for injecting the fertilized egg with nucleic acid or protein.
It is important to point out that analysis of gene function in the zebrafish, whether by mutational screens or DNA/RNA injection, is carried out against an increasingly extensive knowledge of basic embryology. Thus, the transparency and rapid development of the embryo have been exploited to great effect in establishing fate maps (1-3) produced using cell marking experiments in which fluorescent dyes are injected into single or small groups of cells. This kind of analysis has also led to an understanding of the lineage relationships of cells in the blastula and an assessment of the timing of commitment. It is now clear, despite some data to the contrary (4,5), that there is no clear restriction of cell fate in the zebrafish until gastrulation begins (6-8). Consistent with this is the dem-
From: Methods in Molecular Biology, Vol. 97: Molecular Embryology: Methods and Protocols Edited by: P. T. Sharpe and I. Mason © Humana Press Inc., Totowa, NJ
onstration that the dorsoventral axis, despite being established during blastula stages, is positioned randomly with respect to the initial blastomere divisions (9).
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