Green fluorescent fusion proteins: powerful tools for monitoring protein expression in live zebrafish embryos.

The recent development of transgenic technology in zebrafish has opened an exciting new avenue in which to explore vertebrate development. However, as in other species, the inability to easily identify live transgenic fish severely limits the potential of this promising technology. To determine whether the recently described green fluorescent protein (GFP) might provide a convenient live staining method in zebrafish, we constructed a glutathione S-transferase/GFP fusion protein (GST-GFP). GST-GFP cRNA, when injected into individual blastomeres of early zebrafish embryos, resulted in the rapid development (3 hr) of easily detectable green fluorescence which persisted for up to 4 days. GFP fluorescence was restricted to progeny of the injected cell and appeared to have no adverse effects on embryonic development despite widespread expression. Our findings demonstrate that GFP fusion proteins will provide a simple yet powerful means of monitoring production of heterologous proteins in live zebrafish.