CFTR and cystic fibrosis: This tissue specific profile of Cftr expression, which is similar between CF/1-CftrTgH(neoim)Hgu and CF/3-CftrTgH(neoim)Hgu could be due to the existence of tissue specific elements which either down-regulate (duodenum, jejunum) or up-regulate (ileum, nasal epithelium) Cftr expression.