Strain-specific variants of the mouse Cftr promoter region reveal transcriptional regulatory elements

Regulation of cystic fibrosis transmembrane conductance regulator (CFTR) mRNA levels is not well understood. Mouse Cftr mRNA shows strain-dependent expression differences that cannot be fully explained by variation at non-Cftr loci. Differences in tracheal and colonic expression appear to be due predominantly to elements linked to Cftr. Fifteen single nucleotide sequence variations were found within 1.4 kb 5' to the translation start site between the inbred lines A/J, C57BL/6J and 129/SvJ. In addition, 129/SvJ carries a 100 bp deletion relative to the other two strains. These variants were investigated by sequentially deleting 5' regions and measuring luciferase reporter activity from transfected, mouse epithelial cell lines derived from pancreatic duct, renal collecting duct, salivary gland and trachea. These assays identified a region between -524 and -834 in the C57BL/6J promoter, but not in A/J or 129/SvJ, capable of repressing expression. Sequence analysis and gel mobility shift assays suggest that the transcription factor MZF is involved in the strain-dependent effect. It was also apparent that several reporter constructs displayed expression differences between cell lines, possibly indicating the presence of tissue-specific elements.