From Paul Collodi

The zebrafish possesses several favorable characteristics including a short generation time, external fertilization and optically clear embryos that make it an excellent model for studies involving the early stages of embryogenesis. Despite these advantages, one deficiency of the zebrafish model is the lack of methods for targeted gene inactivation and the production of knockouts. We have been working to address this problem by developing gene-targeting methods using pluripotent embryonic stem (ES) cell and primordial germ cell (PGC) lines derived from zebrafish embryos. Methods have been established for the culture of zebrafish ES cells that possess the capacity to contribute to the germ cell lineage of a host embryo. The ES cell cultures have been used to generate transgenic lines of fish and we are currently working to use the cultures to introduce targeted mutations by homologous recombination and produce zebrafish knockouts. The ES cell cultures will enhance the value of the zebrafish model for studies of gene function.

http://zebrafish.org/zirc/home/guide.php