The cystic fibrosis transmembrane conductance regulator as a marker of human pancreatic duct development

BACKGROUND & AIMS

The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a small conductance adenosine 3',5'-cyclic monophosphate (cAMP)-activated chloride ion channel found in the apical membranes of epithelia within the pancreas, airway, intestine, bile duct, sweat gland, and male genital ducts. Pancreatic insufficiency is a feature of about 85% of patients with cystic fibrosis and is believed to be caused by pancreatic autolysis after pancreatic duct obstruction. The aim of this study was to investigate the expression of CFTR in the pancreas from early development to postnatal life to establish whether the CFTR plays a key role in development of the pancreatic duct epithelium.

METHODS

Expression of CFTR from the start of the mid-trimester of human development through term to adult life by messenger RNA (mRNA) in situ hybridization was examined.

RESULTS

CFTR mRNA is detected throughout the pancreatic duct epithelium and its pattern of expression follows the differentiation of the duct system.

CONCLUSIONS

CFTR is a valuable marker of human pancreatic duct cell development and differentiation.

An ovine CFTR variant as a putative cystic fibrosis causing mutation

This report describes a DNA variant in the ovine cystic fibrosis transmembrane conductance regulator (CFTR) gene that has been previously reported as a putative cystic fibrosis causing mutation in humans. The variant is a guanine to adenine base change at position 1019 of the ovine CFTR cDNA, corresponding to an arginine (R) to glutamine (Q) amino acid substitution at position 297 in the predicted CFTR polypeptide. The equivalent R297Q mutation in exon 7 of the human CFTR gene has been reported in a CF patient. This is the first putative cystic fibrosis mutation to be detected in another animal species.

Cystic fibrosis resources on the World Wide Web

A great deal of information is currently available on the Internet concerning the complex and life-threatening genetic disorder cystic fibrosis (CF). The disease is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). World Wide Web (WWW) sites offer a range of information from gene structure and function to individual discussion groups. Specifically, they allow access to CFTR nucleic predicted protein sequences, pages for medical doctors and researchers, and support-group sites directed towards CF patients, their families and friends.

Genetic and physical mapping of the ovine cystic fibrosis gene

Two yeast artificial chromosomes (YACs 48B6 and 88F7) that span the ovine cystic fibrosis transmembrane conductance regulator (CFTR) gene locus have been isolated. These YAC clones have been physically assigned to the interval 4q23-->q25 on sheep chromosome 4, using fluorescence in situ hybridization. A sequence polymorphism in exon 7 of the CFTR gene was identified in Merino sheep and present at a low frequency. This polymorphism segregated in several flocks. Linkage analysis confirmed the location of CFTR on sheep chromosome 4. The most likely location is within a 13.7-cM region close to markers MAF70 and TGLA116.

Animal studies of cystic fibrosis

Cystic fibrosis is the most common life-threatening autosomal recessive genetic disorder in Caucasian populations. It is a disease primarily of epithelial tissues, including the airway, pancreatic duct, intestine, genital tract and sweat glands. The affected gene was cloned and characterized in 1989. In the absence of an identified natural animal model of the disease, a major effort has been made to develop transgenic cystic fibrosis mice, by disrupting the gene in these laboratory animals. Such mice show many, but not all, of the symptoms of cystic fibrosis. In this article, the major past and present contributions of other animal systems to our understanding of cystic fibrosis are examined and their potential for future studies of this disease are discussed. It is intended to give the reader a broad overview of the field, exploring the usefulness of animal studies, rather than dealing more fully with specific aspects of cystic fibrosis.

Molecular analysis of the ovine cystic fibrosis transmembrane conductance regulator gene

There is a need for a large-animal model to investigate the etiology and biology of cystic fibrosis (CF) lung disease and to study potential therapies. The development and electrophysiology of the sheep airway have been shown to exhibit close functional parallels with the human airway, particularly with respect to the respiratory epithelium. We have cloned and sequenced the ovine cystic fibrosis transmembrane conductance regulator (CFTR) cDNA. It shows a high degree of conservation at the DNA coding and predicted polypeptide levels with human CFTR: at the nucleic acid level there is a 90% conservation (compared with 80% between human and mouse CFTR cDNA); at the polypeptide level, the degree of similarity is 95% (compared with 88% between human and mouse). Northern blot analysis and reverse transcription-PCR have shown that the patterns of expression of the ovine CFTR gene are very similar to those seen in humans. Further, the developmental expression of CFTR in the sheep is equivalent to that observed in humans. Thus, overall a CF sheep should show lung pathology similar to that of humans with CF.

Characterization of a tobacco gene encoding a pollen-specific polygalacturonase

We report here the isolation and characterization of a gene which is specifically expressed during late pollen development in Nicotiana tabacum L. cv. Havana and which exhibits homology to bacterial, fungal and plant polygalacturonases. This gene is ca. 4.3 kb, from the transcription start-site to the 3' polyadenylation-site sequences. It contains three introns of 620, 706 and 1400 bp and encodes a 1.5 kb message that contains an A-rich 5'-untranslated-leader sequence of 81 bases and a variable-length 3'-untranslated sequence of between 180 and 320 bases. Located within intron 3 is a 414 bp sequence which exhibits 79% homology to a sequence within the endochitinase gene; both sequences share the same internal repeat structure and exhibit features consistent with them being defective transposable elements. The predicted protein sequence coded for by Npg1 shows, in addition to a number of highly conserved cysteines, four conserved domains with the bacterial and fungal polygalacturonase genes. The pollen-specific polygalacturonases as a group can be distinguished from the fruit-ripening polygalacturonases by a number of criteria. It is suggested that these differences reflect the functional differences between plant endo- and exo-polygalacturonases. Npg1 is one of a two-member gene family expressed predominantly in the male gametophyte upon first microspore mitosis. From expression studies of promoter::GUS transgenes it is clear that the -744 bp to +74/+85 bp of Npg1 sequence (with respect to the transcription start site) is sufficient to drive the expression of the GUS reporter gene in a manner that reflects the spatial and temporal expression of Npg1 as determined by dot-blot and northern analysis.

Tumour necrosis factor-mediated release of plasminogen activator inhibitor 1 by human peritoneal mesothelial cells

Human mesothelial cells synthesize plasminogen activator inhibitor (PAI) 1 in inflamed peritoneal tissue. The role of tumour necrosis factor (TNF) in the mediation of this response was studied. Postoperative peritoneal drain fluid contained both TNF and PAI-1. Peak levels of TNF at 4 h (median 271 pg/ml) preceded a rise in PAI-1 concentration, which peaked at 18 h (median 943.1 ng/ml). Thus TNF may mediate increased PAI-1 release in inflamed peritoneum. TNF significantly increased the mean(s.e.m.) release of PAI-1 by human peritoneal mesothelial cells in vitro at 4 h (control 1.84(0.17) ng/micrograms versus TNF 2.37(0.17) ng/micrograms, P < 0.05), 6 h (2.53(0.09) versus 3.88(0.46) ng/micrograms, P < 0.05), 18 h (0.50(0.02) versus 1.04(0.11) ng/micrograms, P < 0.05) and 24 h (0.87(0.05) versus 1.35(0.11) ng/micrograms, P < 0.05). TNF may be an important mediator of PAI-1 production by human mesothelial cells during peritoneal inflammation.

Identification of a defective transposable element in tobacco

A putative defective transposable element has been identified in tobacco. This element has been found and characterised in two separate parts of the tobacco genome, specifically within the 3rd intron of the pollen-specific polygalacturonase gene (Npg1) and upstream of the endochitinase gene (Chn50). The element is ca. 0.4 kb in length and is bounded by conserved inverted repeats and putative target site duplications. It appears to fall into the category of non-autonomous transposable elements.