The IFABP-TRDN-GFP transgene specifically inhibits TH direct-response genes in the epithelium, but not in the mesenchyme. Cross sections of duodenums from A,B) wild-type NF54 tadpoles treated with either 0 nM T3; C,D) 5nM T3 for 48 hrs. Cross-sections of duodenums from E,F) sibling tadpoles transgenic for IFABP-TRDN-GFP treated with 5nM T3 for 48 hrs. A,C,E) Expression of the TH direct-response gene, bZip, mRNA in the epithelium. B,D,F) Expression of the TH direct-response gene, stromelysin-3 (ST3), mRNA in the mesenchyme. mRNA localized by in situ hybridization (purple stain). Scale bar in F denotes 0.2 mm length.