Variable deletion of exon 9 coding sequences in cystic fibrosis transmembrane conductance regulator gene mRNA transcripts in normal bronchial epithelium.

Abstract

The predicted protein domains coded by exons 9–12 and 19–23 of the 27 exon cystic fibrosis transmembrane conductance regulator (CFTR) gene contain two putative nucleotide‐binding fold regions. Analysis of CFTR mRNA transcripts in freshly isolated bronchial epithelium from 12 normal adult individuals demonstrated that all had some CFTR mRNA transcripts with exon 9 completely deleted (exon 9‐ mRNA transcripts). In most (9 of 12), the exon 9‐ transcripts represented less than or equal to 25% of the total CFTR transcripts. However, in three individuals, the exon 9‐ transcripts were more abundant, comprising 39, 62 and 66% of all CFTR transcripts. Re‐evaluation of the same individuals 2–4 months later showed the same proportions of exon 9‐ transcripts. Of the 24 CFTR alleles in the 12 individuals, the sequences of the exon‐intron junctions relevant to exon 9 deletion (exon 8‐intron 8, intron 8‐exon 9, exon 9‐intron 9, and intron 9‐exon 10) were identical except for the intron 8‐exon 9 region sequences. Several individuals had varying lengths of a TG repeat in the region between splice branch and splice acceptor consensus sites. Interestingly, one allele in each of the two individuals with 62 and 66% exon 9‐ transcripts had a TT deletion in the splice acceptor site for exon 9. These observations suggest either the unlikely possibility that sequences in exon 9 are not critical for the functioning of the CFTR or that only a minority of the CFTR mRNA transcripts need to contain exon 9 sequences to produce sufficient amounts of a normal CFTR to maintain a normal clinical phenotype.

The Phenotypic Consequences of CFTR Mutations

“…A dinucleotide repeat (TG) m was identified at the intron 8 -exon 9 junction with 10-12 repeats and a thymidine nucleotide tract ((T) n ) varying between 5 to 9 nucleotides. Notably, the two alleles analysed with T 5 correlated with expression of high amounts of exon 9-CFTR mRNA (Chu et al 1991). This was supported by a study of 124 individuals in which it was found that the shorter the poly-T tract the greater the relative amount of exon 9-CFTR mRNA transcripts present in respiratory epithelium .…”

“…Exon 9 of the CFTR gene encodes the first 21% of NBD1 and is critical 1 Class VI may be re-named Class V following the re-classification by Welsh (2001). for CFTR function (Riordan et al 1989). RT-PCR analysis of bronchial epithelial cells from 12 non-CF individuals revealed that all samples contained some CFTR mRNA transcripts that were lacking exon 9 (exon 9-) (Chu et al 1991). The amount of exon 9-transcript varied in non-CF individuals between 0-92% .…”

The CFTR polymorphisms poly-T, TG-repeats and M470V in Chinese males with congenital bilateral absence of the vas deferens

“…Prior studies have demonstrated that a 5T variant, along with the preceding higher repetitive dinucleotide TG sequences such as (TG)13 or (TG)12, produces more mRNA transcripts with inframe deletion of exon 9. 11,15, 28 Groman et al 13 suggested that TG repeat number is a reliable predictor of penetrance for pathogenic 5T alleles. Those individuals carrying TG12-5T or TG13-5T were substantially more likely to exhibit an abnormal phenotype than those carrying TG11-5T.…”

TDP43 depletion rescues aberrant CFTR exon 9 skipping

“…As a control, the effect of TDP43 siRNA was tested on an unrelated hybrid minigene system containing exons 34-38 of the neurofibromin 1 (NF1) gene carrying a mutation that leads to the skipping of one or two exons. healthy individuals [16] (Fig. 2).…”