A SEVERE PHENOTYPE IN MICE WITH A DUPLICATION OF EXON-3 IN THE CYSTIC-FIBROSIS LOCUS

To develop an animal model for cystic fibrosis (CF), targeted gene dis ruption in embryonic stem (ES) cells was used to generate a duplicatio n of exon 3 (cftr(m1Bay) allele) of the mouse CF gene. ES cells contai ning this mutation were used to generate chimeric animals that transmi tted the mutant allele through the germline. Homozygous mutant animals display a severe phenotype, with approximately 40% dying within 1 wee k from intestinal obstruction. RNAase protection analysis of the cftr( m1Bay) allele did not detect any normal mRNA (< 1 - 2% of wild-type) i n mutant animals. Pathologic changes in the intestines from mutant mic e included mucus accumulation in the crypts and intestinal lumen, dila tation of the bases of the crypts, enlargement of goblet cells, and th e presence of concretions in the crypts or between the villi. Changes were also present in the mucosal glands of the pharynx and the minor s ublingual glands, where dilatation of acini and accumulation of eosino philic material were evident. Atrophy of acinar cells that may be seco ndary to nutritional deficiency and mild inflammation in the main panc reatic duct were present in the pancreas of mutant animals. No changes were noted in the lung, trachea, liver, or male reproductive tract of mutant animals, and mutant males were fertile, Homozygous mutant mice showed defects in cAMP-mediated ion transport both in ileum and in cu ltured fetal tracheal explants. Thus, an additional mouse model for CF has been generated that should prove useful for the understanding of the pathogenesis and the development of treatments for CF.