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Query: UNIPROT:P06889 (Mol)
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Three different putative splicing mutations in the CFTR gene have been studied by analysing mRNA extracted from nasal epithelial cells harvested from patients with cystic fibrosis. Six patients were analysed, all of whom had classical symptoms of cystic fibrosis (CF). Two patients carried the 621 + 1G-->T mutation, 3 patients carried the 1717 - 1G-->A mutation and 1 patient carried the 1898 + 1G-->A mutation. All patients carried the delta F508 mutation on the other chromosome. Ten non-CF control subjects were also studied. The 621 + 1G-->T mutation resulted in activation of an alternative splice site within exon 4 in one patient and activation of this site or skipping of exon 4 in the other patient. The 1717 - 1G-->A mutation resulted in skipping of exon 11 in all 3 patients studied and the 1898 + 1G-->T mutation resulted in skipping of exon 12. These experiments demonstrate that these mutations do result in aberrant splicing of CFTR mRNA as predicted from the changes in genomic sequence.
Hum Mol Genet 1993 Jun
PMID:Abnormal mRNA splicing resulting from three different mutations in the CFTR gene. 768 9

Highly informative intragenic microsatellite markers within the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene allow the analysis of associations between specific mutations and haplotypes. We have analysed 440 Spanish CF families carrying 22 different CF mutations and have established haplotypes in 1,036 chromosomes for microsatellites IVS8CA, IVS17BTA and IVS17BCA. No new alleles were detected at the three CFTR microsatellites, in more than 3,000 meiosis analysed (estimated mutation rate of less than 3.3 x 10(-4)). The evolution of 16 haplotypes associated with the most common CF mutation, delta F508, and the low mutation rate at these microsatellite loci suggest that delta F508 originated within the 23-31-13 haplotype at least 53,000 years ago, very early in the history of the European population. The number of haplotype changes seen for two other common mutations, G542X (haplotype 23-33-13) and N1303K (23-31-13), suggests that they originated at least 35,000 years ago. Microsatellite allele variability associated with delta F508, G542X and N1303K demonstrates that slippage and mispairing is the main mechanism generating microsatellite alleles. In spite of the haplotype variability detected for these 3 common mutations, the association between haplotype and mutations is very strong. Mutations 1609delCA, 3667del4, delta I507 and G551D are all associated with haplotype 16-7-17, which has a frequency of 14.5% in normal chromosomes. 5 haplotypes bearing specific CF mutations were not found in normal chromosomes. Haplotype 16-46-13 is strongly associated with CF mutations E92K and 3601-111G-->C. About 23% of CF chromosomes with unknown mutations show significant linkage disequilibrium for microsatellite haplotypes.(ABSTRACT TRUNCATED AT 250 WORDS)
Hum Mol Genet 1993 Jul
PMID:Microsatellite haplotypes for cystic fibrosis: mutation frameworks and evolutionary tracers. 768 96

The past decade of research in cystic fibrosis has produced a wealth of information about the underlying defect responsible for the disease. The initial finding that the physiological disturbance in CF is one of abnormal electrolyte transport across epithelial tissues led to the elucidation of a pathway in which epithelial chloride transport is normally elicited in response to beta-adrenergic stimuli and involves the second messenger cAMP to activate protein kinase A. While that pathway was being described, work on the genetic front was concurrently providing information about the genomic location of the gene causing CF, which ultimately led to the identification and cloning of the gene encoding the cystic fibrosis transmembrane conductance regulator. The cloned CFTR gene provided a powerful reagent to use in the next generation of cell physiology experiments, in which it was determined that CFTR is not only the substrate of PKA phosphorylation, a step previously determined to be in the activation pathway of the chloride channel, but is in fact a cAMP-dependent chloride conducting channel itself. Further analysis of the gene has shown that although there is a single mutation that accounts for most of CF, there are well over 200 other lesions within the gene that can cause disease as well. Identification of these mutations has provided information into the normal function of CFTR by studying these variants in heterologous expression systems. As a result, the molecular mechanism of CFTR function is beginning to unfold, as well as the mechanism by which particular mutations impair that function. From a clinical perspective, the research brings optimism from two directions. First, understanding how disease-causing mutations impair function may culminate in pharmacologic approaches that can restore function to some of these mutants. Second, treating the disease at the level of the gene appears to be a realistic goal: Gene transfer experiments in cultured CF cells have shown that the procedure will restore cAMP-dependent chloride conductance to the cells, laying the groundwork for somatic cell gene therapy as a feasible treatment for CF. Currently, work is rapidly progressing in developing delivery systems for this purpose. Finally, animal models that should not only aid in understanding the physiology of electrolyte transport in epithelia but should serve as indicators for tests of therapeutic approaches to treating CF are being developed, either by pharmacological means or by gene delivery protocols.(ABSTRACT TRUNCATED AT 400 WORDS)
Mol Genet Med 1993
PMID:Molecular biology of cystic fibrosis. 769 8

We have identified a novel CFTR missense mutation associated with a protein trafficking defect in mammalian cells but normal chloride channel properties in a Xenopus oocyte assay. The mutation, a cysteine for glycine substitution at residue 480 (G480C), was detected in a pancreatic insufficient, African-American, cystic fibrosis (CF) patient. G480C was found on one additional CF chromosome and on none of 220 normal chromosomes, including 160 chromosomes from normal African-American individuals. Western blot analysis and immunofluorescence studies revealed that, in 293T cells, the encoded mutant protein was not fully glycosylated and failed to reach the plasma membrane, suggesting that the G480C protein was subject to defective intracellular processing. However, in Xenopus oocytes, a system in which mutant CFTR proteins are less likely to experience an intracellular processing/trafficking deficit, expression of G480C CFTR was associated with a chloride conductance that exhibited a sensitivity to activation by forskolin and 3-isobutyl-1-methylxanthine (IBMX) that was similar to that of wild-type CFTR. This appears to be the first identification of a CFTR mutant with a single amino acid substitution in which the sole basis for disease is mislocalization of the protein.
Hum Mol Genet 1995 Feb
PMID:Missense mutation (G480C) in the CFTR gene associated with protein mislocalization but normal chloride channel activity. 775 78

We propose a newborn cystic fibrosis (CF) screening test based on the analysis of dried blood spot DNA by a strategy involving simple or multiplex denaturing gradient gel electrophoresis (DGGE) of PCR products of CFTR gene fragments, in conjunction with the immunoreactive-trypsin (IRT) assay. From May 1988 to May 1992 we have performed a neonatal screening programme of 42,000 newborns in Brittany. We identified 450 infants with an elevated IRT level. From this cohort, to evaluate the feasibility of measuring IRT in conjunction with mutation analysis in Guthrie cards, a pilot study was initially conducted on 200 individuals with normal IRT and 150 with raised IRT levels. Furthermore, a retrospective study was performed on 189 IRT positive cards, involving mutation scanning of exons 10 and 11 of the CFTR gene, which contains a number of frequent mutations including the deletion delta F508. We show that this approach has several implications for neonatal CF screening especially in decreasing the recall rate and detecting CF carriers.
Mol Cell Probes 1993 Dec
PMID:Screening for cystic fibrosis in dried blood spots of newborns. 814 80

The chromosome localizations for 159 gene and DNA segments have been refined to one of five intervals in the 7q21-132 region through hybridization analysis with a panel of somatic cell hybrid lines. Seventy-two of these chromosome 7 markers are also mapped on common or overlapping yeast artificial chromosome (YAC) clones. In addition, the breakpoints of chromosome rearrangement contained in five of the somatic cell hybrid lines have been defined by flanking probes within YAC contigs. To provide a framework for further mapping of the 7q21-q32 region, we have established the physical order of a set of reference markers: cen-(COL1A2-D7S15-CYP3A4-PON)-D7S456-(brea kpoint contained in cell hybrid 1EF2/3/K017)-GUSB-D7S186-ASL-(PGY1-PGY3 -GNB2-EPO-ACHE)-D7S238-(proximal breakpoint in GM1059-Rag5)-D7S240-(CUTL1-PLANH1)-(breakp oints in 1CF2/5/K016 and 2068Rag22-2)-(PRKAR2B-D7S13)-LAMB1-(breakpoint in JSR-17S)-DLD-D7S16-MET-WNT2-CFTR-D7S8-tel.
Hum Mol Genet 1993 Jun
PMID:Refined localization and yeast artificial chromosome (YAC) contig--mapping of genes and DNA segments in the 7q21-q32 region. 835 94

Gene targeting was used to introduce nonselectable genetic changes into chromosomal loci in mouse embryo-derived stem cells. The nonselectable markers were linked to a selectable marker in both insertion- and replacement-type vectors, and the transfer of the two elements to the Hprt locus was assayed. When insertion vectors were used as substrates, the frequency of transfer was highly dependent upon the distance between the nonselectable marker and the double-strand break in the vector. A marker located close to the vector ends was frequently lost, suggesting that a double-strand gap repair activity is involved in vector integration. When replacement vectors were used, cotransfer of a selectable marker and a nonselectable marker 3 kb apart was over 50%, suggesting that recombination between vector and target often occurs near the ends of the vector. To illustrate the use of replacement vectors to transfer specific mutations to the genome, we describe targeting of the delta F508 mutation to the CFTR gene in mouse embryo-derived stem cells.
Mol Cell Biol 1993 Apr
PMID:Location of crossovers during gene targeting with insertion and replacement vectors. 845 2

The presence of two different mutations carried by the same CF allele has been demonstrated in four out of 44 Bulgarian CF patients during a systematic search of the entire coding sequence of the CFTR gene. Two of the double mutant alleles include one nonsense and one missense mutation and although the nonsense mutation can be considered to be the main defect, the amino acid substitutions are good candidates for disease-causing mutations as well. One double mutant carries two missense mutations whose contribution to the CF phenotype is difficult to evaluate. The findings suggest that double mutant alleles may be more common than expected and could account for some of the problems in phenotype-genotype correlations. Such alleles may have important implications for molecular diagnosis and genetic counselling.
Hum Mol Genet 1995 Jul
PMID:Double mutant alleles: are they rare? 852 4

Phase one clinical trials for gene therapy of cystic fibrosis are in progress using either liposomes or adenoviral vectors for CFTR gene transfer to epithelial cells in the airways. In addition to electrophysiological measurements, expression of vector CFTR is usually assessed by RT-PCR. We have developed a CFTR-expression vector, pCFAS, that simplifies the distinction of transgene-derived CFTR mRNA from endogenous mRNA. Two point mutations were introduced into CFTR cDNA which eliminated a SphI restriction site and created a new, unique AgeI restriction site. Neither mutation altered the predicted amino acid sequence of the protein. Restriction digestion of RT-PCR products from cells transfected with pCFAS allowed the differentiation of transgene and endogenous CFTR transcripts. To verify function of the mutated CFTR, the plasmid was transferred into freshly obtained nasal epithelial cells from CF patients ex vivo using cationic liposomes. Fluorescence microscopy using the halide-sensitive fluorophore SPQ demonstrated restoration of cAMP-mediated Cl- secretion. This plasmid will be useful for CFTR gene transfer studies in vitro and in vivo.
Hum Mol Genet 1995 Sep
PMID:The introduction of two silent mutations into a CFTR cDNA construct allows improved detection of exogenous mRNA in gene transfer experiments. 854 45

Using an 125I- efflux assay, we have studied the expression of various types of chloride channels in isolated neonatal rat cardiomyocytes. Three different classes of anion conductances were distinguished: (1) a Ca(2+)-sensitive Cl- conductance, triggered upon stimulation of the cells with endothelin-1 or Ca(2+)-ionophore; (2) a cAMP/protein kinase A-operated Cl- conductance, activated by addition of forskolin. This anion channel could be identified as the Cystic Fibrosis Transmembrane conductance Regulator (CFTR-CI- channel) by Western blotting as well as by its enhanced activity in cultures pretreated with the tyrosine kinase inhibitor genistein; (3) a distinct class of cell volume-regulated Cl- channels, potentiated in the presence of endothelin-1 or the phosphotyrosine phosphatase inhibitor pervanadate. The potential role of each class of Cl- channels in the generation and/or modulation of action potentials as well as in maintaining cell volume is discussed.
Mol Cell Biochem
PMID:Expression and regulation of chloride channels in neonatal rat cardiomyocytes. 873 39


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