Analysis of gut-specific promoters in live X. laevis tadpoles. Green fluorescence is seen where the promoter is active, and yellow is due to autofluorescence of the tadpole gut. Black patches are pigment cells. (a) The Elastase enhancer (rat) driving the expression of GFP in the pancreas of a 7-day-old tadpole; ventral view, anterior to the right. (b) The Transthyretin promoter (mouse) driving expression of GFP in the liver of a 6-day-old tadpole; ventral/left view, anterior to the left. (c) The Intestinal fatty acid binding protein promoter (rat) driving expression of GFP in the small intestine of a 7-day-old tadpole, ventral view, anterior to the left. Abbreviations: gb, gall bladder; li, liver; p, pancreas; si, small intestine; st, stomach. Reproduced with permission from .