lacZ expression in germline transgenic zebrafish can be detected in living embryos.

Use of transgenic technology in zebrafish has been limited by the inability to efficiently express transgenes in early embryos of F1 and subsequent generations and to rapidly detect transgenic fish. We generated transgenic fish by injecting fertilized eggs with the Escherichia coli lacZ gene under the control of the Xenopus elongation factor 1 alpha transcriptional regulatory element. Four of five lines of transgenic fish we obtained express the lacZ gene in early embryos. The pattern of expression was distinct for each line, with two lines showing extensive expression beginning at approximately the midblastula transition, one showing patchy expression and one showing expression almost exclusively in motor neurons. Expression patterns were stable through the F2 generation in the three lines studied to date. The availability of these lines facilitated the development of a reliable and rapid method for live-staining lacZ-expressing embryos using the substrate fluorescein-di-beta-D-galactopyranoside (FDG). Positive embryos of the two most highly lacZ-expressing lines could be identified after 2-3 min of staining in FDG and then picked out and raised. These observations should prove useful for a variety of studies in zebrafish.