A MOUSE MODEL FOR THE CYSTIC-FIBROSIS DELTA-F508 MUTATION

Most cystic fibrosis (CF) patients produce a mutant form (Delta F508) of the cystic fibrosis transmembrane conductance regulator (CFTR), whi ch is not properly processed in normal cells but is active as a chlori de channel in several experimental systems. We used a double homologou s recombination ('Hit and Run') procedure to generate a mouse model fo r the Delta F508 mutation. Targeted embryonic stem (ES) cells (Hit clo nes) were found; of these either 80 or 20% of the clones had lost the Delta F508 mutation, depending on the distance between the linearizati on site in the targeting construct and the Delta F508 mutation. Correc tly targeted clones underwent a second selection step resulting in ES cell clones (Run clones) heterozygous for the Delta F508 mutation with an efficiency of 2-7%. Chimeric mice were generated and offspring hom ozygous for the Delta F508 mutation showed electrophysiological abnorm alities in nasal epithelium, gallbladder and in the intestine, and his tological abnormalities in the intestine, typical of CF. Our data sugg est that the Delta F508 mice have residual Delta F508 CFTR activity wh ich would explain the mild pathology of the Delta F508 mice. The Delta F508 mouse may provide a useful model for the study of the processing defect of Delta F508 CFTR and for the development of novel therapeuti c approaches based on circumvention of the processing block.