Analyses of pancreas development by generation of gfp transgenic zebrafish using an exocrine pancreas-specific elastaseA gene promoter

In contrast to what we know on development of endocrine pancreas, the formation of exocrine pancreas remains poorly understood. To create an animal model that allows observation of exocrine cell differentiation, proliferation, and morphogenesis in living animals, we used the zebrafish elastaseA (elaA) regulatory sequence to develop transgenic zebrafish that display highly specific exocrine pancreas expression of GFP in both larvae and adult. By following GFP expression, we found that the pancreas in early development was a relatively compact organ and later extended posterior along the intestine. By transferring the elaA:gfp transgene into slow muscle omitted mutant that is deficient in receiving Hedgehog signals, we further showed that Hedgehog signaling is required for exocrine morphogenesis but not for cell differentiation. We also applied the morpholino knockdown and toxin-mediated cell ablation approaches to this transgenic line. We showed that the development of exocrine pancreas is Islet-1 dependent. Injection of the diphtheria toxin A (DTA) construct under the elastaseA promoter resulted in selective ablation of exocrine cells while the endocrine cells and other endodermal derivatives (liver and intestine) were not affected. Thus, our works demonstrated the new transgenic line provided a useful experimental tool in analyzing exocrine pancreas development.