Structure and regulation of the cystic fibrosis transmembrane conductance regulator (CFTR) gene in killifish: A comparative genomics approach

The structure, regulation and evolution of the cystic fibrosis transmembrane conductance regulator (CFTR) gene were characterized in common killifish (Fundulus heteroclitus). Killifish CFTR (kfCFTR) structure was conserved with other CFTR homologues, but was more compact than those of mammals. A motif in intron 1 was conserved across all teleost CFTR homologues except zebrafish, and was similar to a functionally important site in human CFTR. The sequence of the CFTR promoter was highly conserved across nine species within the genus Fundulus, but contained additional glucocorticoid responsive elements in seawater species. The promoters of the seawater species also contained a putative osmotic responsive element that differed by a single base in the freshwater species. The kfCFTR promoter was only active in cell lines that express the endogenous CFTR gene. Transcription from the kfCFTR promoter was unaffected by application of dexamethasone or cortisol in cell culture, but increased by 1.5-fold in response to high osmolarity. Cortisol injection in vivo increased CFTR mRNA but there was no increase in luciferase expression driven by the kfCFTR promoter in transiently transgenic fish. Administration of the cortisol blocker RU486 resulted in a significant reduction in luciferase activity driven by the kfCFTR promoter in vivo.