Microinjection remains the most popular and effective of the methods to introduce DNA, RNA, and proteins into fertilized zebrafish eggs. The method is simple and reliable. A microinjection pipet is filled with the DNA or RNA solution and attached to an apparatus that forces the solution out of the pipet with air pressure. A small amount of solution is then expelled into the cytoplasm of the embryo before withdrawing the pipet, and the injected embryos are incubated to develop further. Once inside the cells, the foreign DNA or RNA is transcribed and/or translated within the developing embryos and the functional roles of their protein products can be evaluated by morphological, physiological or molecular changes. Thus, microinjection has been widely used for generating transgenic fish (1 –3 ), analyzing gene function by overexpression of DNA or RNA (4 –6 ) and mapping cell fate in early blastula embryos (7 ,8 ).
