Delayed and Restricted Expression of UAS-Regulated GFP Gene in Early Transgenic Zebrafish Embryos by Using the GAL4/UAS System

A stable Tg(UAS:GFP) zebrafish line was generated and crossed with Tg(hsp70:GAL4) line, in which the GAL4 gene is under the control of an inducible zebrafish promoter derived from the heat shock 70 protein gene (hsp70). The dynamic green fluorescent protein (GFP) expression in early zebrafish embryos in the GAL4/UAS binary system was then investigated. We found that, at early developmental stages, expression of GFP effector gene was restricted and required a long recovery time to reach a detectable level. At later developmental stage (after 2 days postfertilization), GFP could be activated in multiple tissues in a shorter time, apparently due to a higher level of GAL4 messenger RNA induction. It appears that the type of tissues expressing GFP was dependent on whether they had been developed at the time of heat shock. Therefore, the delayed and restricted transgene expression should be taken into consideration when GAL4/UAS system is used to study transgene expression in early developmental stages.