Improved Tol2-mediated enhancer trap identifies weakly expressed genes during liver and β cell development and regeneration in zebrafish.

The liver and pancreas are two major digestive organs, and among the different cell types in them, hepatocytes and the insulin-producing β cells have roles in both health and diseases. Accordingly, clinicians and researchers are very interested in the mechanisms underlying the development and regeneration of liver and pancreatic β cells. Gene and enhancer traps such as the Tol2 transposon-based system are useful for identifying genes potentially involved in developmental processes in the zebrafish model. Here, we developed a strategy that combines a Tol2-mediated enhancer trap and the Cre/loxP system by using loxP-flanked reporters driven by β cell- or hepatocyte-specific promoters and the upstream activating sequence (UAS)-driving Cre. Two double-transgenic reporter lines, Tg(ins:loxP-CFPNTR-loxP-DsRed; 10×UAS:Cre, cryaa:Venus) and Tg(fabp10:loxP-CFPNTR-loxP-DsRed; 10×UAS:Cre, cryaa:Venus), were established to label pancreatic β cells and hepatocytes, respectively. These two double-transgenic lines were each crossed with the Tol2-enhancer trap founder lines to screen for and identify genes expressed in the β cell and hepatocytes during development. This trap system coupled with application of nitroreductase (NTR)/metronidazole (Mtz)-mediated cell ablation could identify genes expressed during regeneration. Of note, pilot enhancer traps captured transiently and weakly expressed genes such as rab3da and ensab with higher efficiencies than traditional enhancer trap systems. In conclusion, through permanent genetic labeling by Cre/loxP, this improved Tol2-mediated enhancer trap system provides a promising method to identify transiently or weakly expressed, but potentially important, genes during development and regeneration.