Extensive posttranscriptional deletion of the coding sequences for part of nucleotide-binding fold 1 in respiratory epithelial mRNA transcripts of the cystic fibrosis transmembrane conductance regulator gene is not associated with the clinical manifestations of cystic fibrosis.
Cystic fibrosis (CF) is a recessive hereditary disorder, requiring both parental cystic fibrosis conductance transmembrane regulator (CFTR) genes to carry mutations for clinical disease to manifest, i.e., only 50% of normal CFTR gene expression is required to maintain a normal phenotype. To help define the minimum amount of normal CFTR gene expression necessary to maintain normalcy, we have capitalized on our prior observation (Chu, C.-S., B. C. Trapnell, J. J. Murtagh, Jr., J. Moss, W. Dalemans, S. Jallat, A. Mercenier, A. Pavirani, J.-P. Lecocq, G. R. Cutting, et al. 1991. EMBO [Eur. Mol. Biol. Organ] J. 10:1355-1363) that normal individuals can have up to 66% of bronchial CFTR mRNA transcripts that are missing exon 9, a region representing 21% of the sequence coding for the critical nucleotide (ATP)-binding fold 1 (NBF1) of the predicted CFTR protein. The study population included 78 individuals with no prior diagnosis of CF. Evaluation of bronchial epithelial cells (obtained by bronchoscopy) revealed that exon 9 was variably deleted in all individuals. Remarkably, there were four individuals, all greater than or equal to 35 yr, in whom bronchial epithelial cells exhibited 73, 89, 90, and 92% CFTR transcripts with inframe deletion of exon 9, respectively, despite normal sweat Cl- and no clinical manifestation of CF. In the context that only 8% or less of bronchial CFTR transcripts need exon 9 to maintain normal airway function, these observations strongly suggest that either exon 9 is not necessary for CFTR structure and/or function or that only a very small fraction of bronchial epithelial cells need to express normal CFTR mRNA transcripts with exon 9 to perform the function of CFTR sufficient to maintain a normal phenotype in vivo.
Chu
C S
CS
Pulmonary Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.
Trapnell
B C
BC
Curristin
S M
SM
Cutting
G R
GR
Crystal
R G
RG
D000328:Adult; D000483:Alleles; D001483:Base Sequence; D001980:Bronchi / Q000378:metabolism*; D002872:Chromosome Deletion; D003550:Cystic Fibrosis / Q000235:genetics*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005091:Exons; D005260:Female; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000235:genetics*; D008875:Middle Aged; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000378:metabolism*; D014158:Transcription, Genetic
C505032:CFTR protein, human; D008565:Membrane Proteins; D012333:RNA, Messenger; D019005:Cystic Fibrosis Transmembrane Conductance Regulator