Modulation of disease severity in cystic fibrosis transmembrane conductance regulator deficient mice by a secondary genetic factor

Screening practices for mutations in the CFTR gene ABCC7

Cystic fibrosis transmembrane conductance regulator (CFTR) gene studies are now one of the most frequent activities in clinical molecular genetics laboratories. The number of requests is growing, owing to the increasingly wide range of recognized CFTR gene diseases (cystic fibrosis, congenital bilateral absence of the vas deferens, disseminated bronchiectasis, allergic bronchopulmonary aspergillosis and chronic pancreatitis), and the availability of efficient molecular tools for detecting mutations. A growing number of tests capable of simultaneously detecting several frequent CF mutations are being developed, and commercial kits are now available. The most recent kits detect nearly 90% of defective alleles in Caucasians, a rate high enough for carrier screening and for the majority of diagnostic requests. However, because of the wide variety of molecular defects documented in the CFTR gene, only a limited number of laboratories have mastered the entire panoply of necessary techniques, while other laboratories have to refer certain cases to specialized centers with complementary and/or scanning tools at their disposal. A good knowledge of CFTR diseases and their molecular mechanisms, together with expertise in the various techniques, is crucial for interpreting the results. Diagnostic strategies must take into account the indication, the patient's ethnic origin, and the time available in the framework of genetic counseling. This review presents the methods most frequently used for detecting CFTR gene mutations, and discusses the strategies most suited to the different clinical settings.

Morphological changes in the vas deferens and expression of the cystic fibrosis transmembrane conductance regulator (CFTR) in control, deltaF508 and knock-out CFTR mice during postnatal life

The morphology of the mouse vas deferens still undergoes major changes from birth to 40 days of age, such as differentiation of the mesenchymal cells into fibroblasts and muscle cells, differentiation of the epithelium into basal and columnar epithelial cells, development of stereocilia, and the appearance of smooth endoplasmic reticulum organised in fingerprint-like structures or parallel, flattened saccules. In mutant homozygous DeltaF508 (DeltaF/DeltaF) and knock-out (cf/cf) CFTR mice, strain 129/FvB and 129/C57BL-6, respectively, a similar development occurred until the age of 20 days. At 40 days, however, the lumen was filled with eosinophilic secretions, and sperm cells were absent in the majority of the animals examined, although sperm production in testis and epididymis appeared to be normal. CFTR was localised in the apical membrane and cytoplasm of the vas deferens epithelium from 40 days on but could not be detected in the vas deferens before 20 days or in mutant adult CFTR mice as expected. Western blots of membrane preparations showed that the mature form of CFTR was present in vas deferens and testis but absent in seminal vesicles. Our results suggest that the function of CFTR is probably essential after 20 days in the vas deferens and that its absence or dysfunction may result in a vas deferens with a differentiated epithelium but a collapsed lumen, which could at least temporarily delay the transport of spermatozoa. These observations contrast with those made in the overall majority of CF patients. Mol. Reprod. Dev. 55:125-135, 2000.

Differential role of cyclic GMP-dependent protein kinase II in ion transport in murine small intestine and colon

BACKGROUND & AIMS

The aim of this study was to determine the role of guanosine 3',5'-cyclic monophosphate (cGMP)-dependent protein kinase (cGK) type II in intestinal fluid homeostasis under basal conditions and following exposure to cGMP-linked secretagogues, e.g., Escherichia coli heat-stable enterotoxin (STa) and guanylin.

METHODS

Fluid and ion transport was determined in different segments of the intestine of wild-type and cGK II-deficient mice by ligated loop assays in vivo, and by short-circuit current and isotope flux measurements in vitro.

RESULTS

Small intestinal fluid absorption in vivo was enhanced in cGK II-deficient mice under basal conditions and in the presence of STa. Furthermore, STa, guanylin, and 8-pCPT-cGMP stimulation of electrogenic anion secretion and inhibition of Na(+) absorption in vitro were markedly reduced in the small intestine from cGK II -/- mice but not in proximal colon. The type III phosphodiesterase inhibitor amrinone mimicked STa action in cGK II -/- mice, and also stimulated ion secretion in humans.

CONCLUSIONS

This study shows that the cGMP/cGK II pathway regulates fluid homeostasis in the small intestine under basal conditions and mediates STa effects by both increasing anion secretion and inhibiting Na(+) absorption. It also demonstrates the presence of a cGK II-independent pathway for STa/cGMP-provoked secretion predominantly in the colon, which possibly involves a cGMP-inhibitable phosphodiesterase and/or activation of the cAMP-dependent protein kinase pathway.

Alkaline phosphatase knock-out mice recapitulate the metabolic and skeletal defects of infantile hypophosphatasia

Hypophosphatasia is an inborn error of metabolism characterized by deficient activity of the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP) and skeletal disease due to impaired mineralization of cartilage and bone matrix. We investigated two independently generated TNSALP gene knock-out mouse strains as potential models for hypophosphatasia. Homozygous mice (-/-) had < 1% of wild-type plasma TNSALP activity; heterozygotes had the predicted mean of approximately 50%. Phosphoethanolamine, inorganic pyrophosphate, and pyridoxal 5'-phosphate are putative natural substrates for TNSALP and all were increased endogenously in the knock-out mice. Skeletal disease first appeared radiographically at approximately 10 days of age and featured worsening rachitic changes, osteopenia, and fracture. Histologic studies revealed developmental arrest of chondrocyte differentiation in epiphyses and in growth plates with diminished or absent hypertrophic zones. Progressive osteoidosis from defective skeletal matrix mineralization was noted but not associated with features of secondary hyperparathyroidism. Plasma and urine calcium and phosphate levels were unremarkable. Our findings demonstrate that TNSALP knock-out mice are a good model for the infantile form of hypophosphatasia and provide compelling evidence for an important role for TNSALP in postnatal development and mineralization of the murine skeleton.

Cystic fibrosis mutations R1162X and 2183AA®G in two southern Brasilian states

We screened 79 southern Brazilian patients with cystic fibrosis for the rare cystic fibrosis mutations R1162X and 2183AA<FONT FACE="Symbol">®</FONT>G. Forty-nine patients were born in the State of Paraná (PR) and 30 in the State of Santa Catarina (SC). Two 2183AA<FONT FACE="Symbol">®</FONT>G alleles were found among the SC patients and one among the PR patients. Six R1162X alleles were found among the SC patients and one among the PR patients. Fourteen percent of the alleles found among patients of Italian origin were R1162X, and 7% were 2183AA<FONT FACE="Symbol">®</FONT>G mutations. These mutations, together with <FONT FACE="Symbol">D</FONT>F508, were also studied in a sample of 270 normal non-related subjects of Italian origin who have been born in PR. In this sample we found two <FONT FACE="Symbol">D</FONT>F508 alleles and one 2183AA<FONT FACE="Symbol">®</FONT>G allele. <FONT FACE="Symbol">D</FONT>F508, R1162X and 2183AA<FONT FACE="Symbol">®</FONT>G frequencies were not statistically different from those observed in Italy. Our results demonstrate that it is important to include these mutations in southern Brazilian surveys of cystic fibrosis patients, especially when they are of Italian descent.

Pseudomonas aeruginosa exoenzyme S stimulates murine lymphocyte proliferation in vitro

The exuberant immunoinflammatory response that is associated with Pseudomonas aeruginosa infection is the major source of the morbidity and mortality in cystic fibrosis (CF) patients. Previous studies have established that an exoproduct of P. aeruginosa (exoenzyme S) is a mitogen for human T lymphocytes and activates a larger percentage of T cells than most superantigens, which may contribute to the immunoinflammatory response. An animal model would facilitate studies of the pathophysiologic consequences of this activation. As a first step toward developing an animal model, the murine lymphocyte response to exoenzyme S was examined. When stimulated with exoenzyme S, splenocytes isolated from naive mice entered S phase and proliferated. The optimum response occurred after 2 to 3 days in culture, at 4 x 10(5) cells per well and 5.0 micrograms of exoenzyme S per ml. The response was not due to lipopolysaccharide, since Rhodobacter sphaeroides lipid A antagonist did not block the response. Other preparations of exoenzyme S stimulated lymphocyte proliferation, since the response to recombinant exoenzyme S (rHisExo S) cloned from strain 388 was similar to the response to exoenzyme S from strain DG1. There was evidence that genetic variability influenced the response, since A/J, CBA/J, and C57BL/6 mice were high responders and BALB/cJ mice were low responders following stimulation with exoenzyme S. Both splenic T and B lymphocytes entered the cell cycle in response to exoenzyme S. Thus, murine lymphocytes, like human lymphocytes, respond to P. aeruginosa exoenzyme S, which supports the development of a murine model that may facilitate our understanding of the role that exoenzyme S plays in the pathogenesis of P. aeruginosa infections in CF patients.

Cystic fibrosis and the pancreas: recent scientific advances

Cystic fibrosis (CF) is inherited as an autosomal recessive trait due to a mutated gene carried on the long arm of chromosome 7. The protein coded by the CF gene (CFTR) is an apical chloride channel that regulates active chloride transport across epithelial cell membranes. The role of CFTR in pancreatic exocrine secretion is based on the concept that CFTR is localized to the apical membrane of the proximal duct epithelial cells. The primary ductal cell chloride channel abnormality results in dehydrated protein-rich secretions that obstruct the proximal ducts, leading to secondary acinar cell destruction, fibrosis, and exocrine pancreatic insufficiency in 85% of the CF population. A strong correlation between genotype and pancreatic phenotype is recognized. Advances in molecular biology such as cloning of lipase genes and gene therapy are challenging the field of pancreatic enzyme supplementation therapy.

Is the hemochromatosis gene a modifier locus for cystic fibrosis?

The variable clinical manifestations of cystic fibrosis (CF) suggest the influence of modifier genes. For example, meconium ileus is present in approximately 10-15% of neonates with cystic fibrosis; however, the genetic and, or environmental factors that determine whether an individual will develop this complication have not been determined. We propose the HFE gene as a candidate modifier locus for CF based on (1) the suggestion of an association between the HLA loci and CF phenotypes; (2) the location of the HFE gene near the HLA loci and; (3) the similarity between the gastrointestinal manifestations of hereditary hemochromatosis and CF. We have determined the frequency of the C282Y and H63D mutations in a group of 89 CF patients who were homozygous for delta F508 and for whom meconium ileus status was known. The carrier frequency of C282Y among the CF patients with meconium ileus was significantly different from that of our unaffected control group (19.4% versus 7.7%). However, the difference between the meconium ileus and the nonmeconium ileus groups was not significant (19.4% versus 10.3%). There was no difference in the frequency of the H63D among the three groups that were studied. These data are suggestive of a relationship between the development of meconium ileus or other gastrointestinal diseases in CF and the HFE gene. Further study of a larger group of patients is warranted.

Efficient killing of inhaled bacteria in DeltaF508 mice: role of airway surface liquid composition

Cystic fibrosis mice have been generated by gene targeting but show little lung disease without repeated exposure to bacteria. We asked if murine mucosal defenses and airway surface liquid (ASL) Cl(-) were altered by the DeltaF508 cystic fibrosis transmembrane conductance regulator mutation. Naive DeltaF508 -/- and +/- mice showed no pulmonary inflammation and after inhaled Pseudomonas aeruginosa had similar inflammatory responses and bacterial clearance rates. We therefore investigated components of the innate immune system. Bronchoalveolar lavage fluid from mice killed Escherichia coli, and the microbicidal activity was inhibited by NaCl. Because beta-defensins are salt-sensitive epithelial products, we looked for pulmonary beta-defensin expression. A mouse homolog of human beta-defensin-1 (termed "MBD-1") was identified; the mRNA was expressed in the lung. Using a radiotracer technique, ASL volume and Cl(-) concentration ([Cl(-)]) were measured in cultured tracheal epithelia from normal and DeltaF508 -/- mice. The estimated ASL volume was similar for both groups. There were no differences in ASL [Cl(-)] in DeltaF508 -/- and normal mice (13.8 +/- 2.6 vs. 17.8 +/- 5.6 meq/l). Because ASL [Cl(-)] is low in normal and mutant mice, salt-sensitive antimicrobial factors, including MBD-1, may be normally active.

Ion transport across the normal and CF neonatal murine intestine

Neonatal mice with cystic fibrosis (CF) exhibit a very high mortality due to intestinal obstruction localized primarily to the ileum and colon. It has been hypothesized that lack of Cl(-) secretion and possibly elevated Na(+) absorption contribute to the gut problems in CF neonates. Therefore, intestines (ileum, proximal colon, and distal colon) from normal and CF day-old mouse pups were studied on ultra-small-aperture (0.0135 cm(2)) Ussing chambers. All three regions of the normal neonatal intestine responded to forskolin with an increase in short-circuit current, which was completely absent in the CF intestine. The neonatal distal colon exhibited a high rate of amiloride-sensitive electrogenic Na(+) absorption, which did not differ between the normal and CF preparations. The ileum and proximal colon of both genotypes exhibited a small but significant electrogenic Na(+) absorption. The neonatal proximal colon and ileum also exhibited electrogenic Na(+)-glucose cotransport, which was significantly greater in the normal compared with the CF ileum. In addition, all three intestinal regions exhibited electrogenic Na(+)-alanine cotransport, which was significantly reduced in two of the regions of the CF neonatal intestine. It is speculated that: 1) the reduced rate of Na(+)-nutrient cotransport in the CF intestine contributes to the lower rate of growth in CF pups, whereas 2) the elevated electrogenic Na(+) absorption in the neonatal intestine, coupled with an inability to secrete Cl(-), contributes to the intestinal obstruction in the CF pups.

Linkage disequilibrium analysis in Australian haemochromatosis patients indicates bipartite association with clinical expression

BACKGROUND/AIMS

Hereditary haemochromatosis shows a wide variation in phenotypic expression, which is thought to be due, in part, to genetic factors. A single missense mutation in HFE, leading to an amino acid substitution (C282Y) has been shown to be the causative mutation, clearly responsible for clinical expression of the disorder. Since homozygosity for the C282Y mutation can give rise to a disorder which shows wide variation in clinical expression, we investigated the possibility that genetic modifiers of HFE may exist.

METHODS

Linkage disequilibrium analysis was performed on chromosome 6p21.3 in 74 patients homozygous for the C282Y mutation using microsatellite markers spanning the haemochromatosis gene region. Phenotypic expression was evaluated based on transferrin saturation, serum ferritin, hepatic iron concentration and index, and iron grade.

RESULTS

Linkage disequilibrium (LD) analysis showed a predominant ancestral haplotype from D6S265 to D6S2236 covering a region of approximately 5 Mb. The overall LD distribution in this region showed two peaks of highly significant association at D6S105 (2 Mb proximal to HFE) and at D6S2239 approximately 50 kb distal to HFE. Male patients homozygous for D6S105 allele 8, had significantly higher hepatic iron indices than patients heterozygous or nullizygous for D6S105-8 (p<0.038).

CONCLUSION

This analysis indicates that modifying gene(s) or another mutation affecting HHC clinical expression may be located in the region of D6S105.

Effect of genetic background on establishment of mouse embryonic stem cells

We established 13 embryonic stem (ES) cell lines from 542 embryos crossed between various strains of mice: 10 lines from 129/Sv-ter embryos (10/48, 20.8%) and 3 lines out of other 9 combinations of intra- or inter-strain matings (1 from intracross of C57BL/6CrSlc, 1 from B6D2F1 x C57BL/6CrSlc, 1 from Yok:ddY x Slc:ICR). No ES cell line from 129/Sv-ter x Slc:ICR embryos suggests that ICR strain might have inhibitory genetic factor(s) for the ES cell formation. Some ES cell lines could be obtained from hybrids even if none or few lines from their parental strains, suggesting a heterosis effect can be expected for establishing ES cell lines in mice.

Molecular cloning and transmembrane structure of hCLCA2 from human lung, trachea, and mammary gland

The CLCA family of Ca2+-activated Cl- channels has recently been discovered, with an increasing number of closely related members isolated from different species. Here we report the cloning of the second human homolog, hCLCA2, from a human lung cDNA library. Northern blot and RT-PCR analyses revealed additional expression in trachea and mammary gland. A primary translation product of 120 kDa was cleaved into two cell surface-associated glycoproteins of 86 and 34 kDa in transfected HEK-293 cells. hCLCA2 is the first CLCA homolog for which the transmembrane structure has been systematically studied. Glycosylation site scanning and protease protection assays revealed five transmembrane domains with a large, cysteine-rich, amino-terminal extracellular domain. Whole cell patch-clamp recordings of hCLCA2-transfected HEK-293 cells detected a slightly outwardly rectifying anion conductance that was increased in the presence of the Ca2+ ionophore ionomycin and inhibited by DIDS, dithiothreitol, niflumic acid, and tamoxifen. Expression in human trachea and lung suggests that hCLCA2 may play a role in the complex pathogenesis of cystic fibrosis.

HLA class II polymorphism in cystic fibrosis. A possible modifier of pulmonary phenotype

Evolution of lung damage is highly variable in cystic fibrosis (CF) even in patients with the same cystic fibrosis transmembrane conductance regulator (CFTR) mutations. The analysis of genetic factors other than CFTR may help our understanding of genotype-phenotype relationships in CF. As human leukocyte antigen (HLA) class II polymorphism has been associated with a number of diseases including autoimmune and inflammatory diseases, asthma, and allergy, we investigated the possibility that HLA polymorphism contributes to CF-associated pulmonary inflammation. Among the 98 adult CF patients tested, the genotypic frequencies of DR4 and DR7 alleles (serologic group DR53) and DR7/ DQA*0201 haplotype were higher than in 39 selected control subjects without atopy (p </= 10(-)6, relative risk [RR] = 22, and p </= 5.10(-)4, RR = 27, respectively) and in a random population. No significant difference of these allelic distributions was found according to the CFTR genotype. In the CF patients, the DR7 allele was significantly associated with an increase in total IgE and with chronic Pseudomonas aeruginosa colonization (100% of DR7 versus 83% of non-DR7 patients being colonized, p < 0.05). Our results suggest that genetic factors known to modulate the immune response might contribute to chronic infection with Pseudomonas, increased total IgE, and pulmonary outcome in CF.

The cystic fibrosis transmembrane conductance regulator and its function in epithelial transport

CF is a well characterized disease affecting a variety of epithelial tissues. Impaired function of the cAMP activated CFTR Cl- channel appears to be the basic defect detectable in epithelial and non-epithelial cells derived from CF patients. Apart from cAMP-dependent Cl- channels also Ca2+ and volume activated Cl- currents may be changed in the presence of CFTR mutations. This is supported by recent additional findings showing that different intracellular messengers converge on the CFTR Cl- channel. Analysis of the ion transport in CF airways and intestinal epithelium identified additional defects in Na+ transport. It became clear recently that mutations of CFTR may also affect the activity of other membrane conductances including epithelial Na+ channels, KvLQT-1 K+ channels and aquaporins (Fig. 7). Several additional, initially unexpected effects of CFTR on cellular functions, such as exocytosis, mucin secretion and regulation of the intracellular pH were reported during the past. Taken together, these results clearly indicate that CFTR not only acts as a cAMP regulated Cl- channel, but may fulfill several other cellular functions, particularly by regulating other membrane conductances. Failure in CFTR dependent regulation of these membrane conductances is likely to contribute to the defects observed in CF. Currently, no general concept is available that can explain how CFTR controls this variety of cellular functions. Further studies will have to verify whether direct protein interaction, specific effects on membrane turnover, changes of the intracellular ion concentration or additional proteins are involved in these regulatory loops. At the end of this review one cannot share the provocative and reassuring title "CFTR!" of a review written a few years ago [114]. Today one might rather finish with the statement "CFTR?".

Lack of correlation between CFTR expression, CFTR Cl- currents, amiloride-sensitive Na+ conductance, and cystic fibrosis phenotype

Cystic fibrosis (CF) is characterized by defective Cl- and enhanced Na+ conductance, both due to malfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) protein in airway epithelial cells. In the present study we examined whether expression of CFTR mRNA (CFTR messenger ribonucleic acid) is different in airway epithelia derived from either CF patients or healthy volunteers. Moreover, we tried to correlate differences in epithelial Cl- and Na+ conductance with the level of CFTR mRNA expression and studied whether these properties correlate to the clinical phenotype of CF patients. To that end, CFTR mRNA was determined by means of quantitative reverse transcriptase polymerase chain reaction (RT-PCR) and cyclic adenosine monophosphate (cAMP)-activated Cl- and epithelial Na+ conductances were examined in airway epithelial cells using microelectrode techniques. Complementary in vitro data were obtained from cultured CF and non-CF airway epithelial cell lines. Genotype and Shwachman score were assessed for each patient. We found variable levels of CFTR mRNA expression in airway cells of both CF patients and healthy volunteers. As expected, epithelial Na+ conductance was enhanced and CFTR Cl- conductance was absent in airway cells from CF patients. However, CFTR mRNA expression did not correlate with either electrophysiological properties or Shwachman scores obtained from CF patients. In addition, CFTR mRNA expression did not correlate to Cl- conductance in cultured CF and non-CF airway epithelial cells. These results indicate a lack of correlation between levels of CFTR mRNA and CFTR function, and that only small amounts of CFTR are required for expression of the CFTR Cl- conductance.

Ten years of gene targeting: targeted mouse mutants, from vector design to phenotype analysis

Gene targeting, defined as the introduction of site-specific modifications into the genome by homologous recombination, has revolutionarized the field of mouse genetics and allowed the analysis of diverse aspects of gene function in vivo. It is now possible to engineer specific genetic alterations ranging from subtle mutations to chromosomal rearrangements and more recently, even tissue-specific inducible gene targeting with temporo-spatial control has become feasible. This review tries to recapitulate what we have learned in this extremely rapidly expanding field during the past decade. Diverse aspects of the technique will be discussed starting from basic construct design to the analysis of complex phenotypes, including recent advances on inducible expression system. Many examples from different areas of biomedical research are given to illustrate the purpose and limitations of the employed experimental approaches.

Pitfall in the use of genotype analysis as the sole diagnostic criterion for cystic fibrosis

In this report, we present an asymptomatic infant, seen for a second opinion, who was given the diagnosis of cystic fibrosis (CF) as a neonate based on the presence of two mutant alleles, DeltaF508 and R117H. The diagnosis of CF adversely affected the family's emotional, employment, and financial statuses. Our evaluation included sweat chloride, nasal transepithelial potential difference, and bronchoscopy with bronchoalveolar lavage measurements, all which were consistent with findings expected from an individual without CF. Genotype analysis for the sequence polymorphism in intron 8 of the cystic fibrosis transmembrane conductance regulator (CFTR) gene revealed the 7 thymidines and 9 thymidines alleles. We conclude that this patient probably expresses enough epithelial cell surface CFTR function such that she has a normal phenotype. Based on our evaluation, she does not meet the current diagnostic criteria for CF. Although genotype analysis can be an useful adjunct, it should not be the sole diagnostic criterion for CF.

Characterization of a murine gene homologous to the bovine CaCC chloride channel

The bovine CaCC protein is a putative Ca2+-dependent Cl- channel of airway epithelial cells. Therefore, CaCC proteins could contribute to transepithelial Cl- transport and accordingly modify the phenotype of cystic fibrosis (CF) patients. We have identified a murine EST containing a full-length cDNA coding for a 902-amino-acid protein highly homologous to bovine CaCC. The murine gene (mCaCC) maps to chromosome 3 at the H2-H3 band and is expressed, as indicated by Northern blot analysis, in mouse skin and kidney but not in brain, heart, lung or testis. RT-PCR indicates a low expression in tracheal epithelial cells. Heterologous expression of mCaCC in Xenopus oocytes elicits membrane currents that are anion-selective and inhibited by DIDS and by niflumic acid, a blocker of the endogenous chloride current in oocytes. The identification of genes belonging to the CaCC family will help to evaluate their role as ion channels or channel regulators and their actual contribution to epithelial chloride transport.

Recurrent familial intrahepatic cholestasis in the Faeroe Islands. Phenotypic heterogeneity but genetic homogeneity

Recurrent familial intrahepatic cholestasis is an autosomal recessive disorder characterized by episodes of severe pruritus and jaundice lasting for weeks to months without extrahepatic bile duct obstruction. Symptom-free intervals may last for months to years, and chronic liver damage does not develop. We recently studied four of the five patients from the Faeroe Islands described by us 30 years ago (one had recently died) and an additional five patients that were identified after the initial report. The episodes of cholestasis were more frequent and severe in patients with early onset, but tended to reduce in frequency with age. The youngest patient, aged 25 years, who had had 16 episodes each lasting about 6 months, had a liver transplant after which no further episodes were recorded (1 year after surgery). Signs of chronic liver disease were absent in all patients. The FIC1 gene was investigated for mutations in the surviving patients. A single mutation (I661T) was found on both chromosomes in all nine patients, indicating that they are genetically identical for the disease-causing defect. Nevertheless, considerable differences among patients were observed clinically.

Quantitative and qualitative differences in bronchoalveolar inflammatory cells in Pseudomonas aeruginosa-resistant and -susceptible mice

The difference in severity of Pseudomonas aeruginosa-induced chronic lung infection may be determined by differences in host inflammatory responses. In the present study we investigate this possibility using BALB/c and C57Bl/6 mice, resistant and susceptible, respectively, to chronic lung infection with P. aeruginosa. Following intratracheal inoculation of P. aeruginosa-impregnated agar beads, C57Bl/6 mice mounted a stronger inflammatory response with significantly higher total cell numbers in the bronchoalveolar lavage fluid compared with BALB/c mice. While polymorphonuclear leucocytes were the predominant cell in C57Bl/6 mice, macrophages constituted the majority in BALB/c mice at day 7 post-infection. Alveolar macrophages from C57Bl/6 mice showed significantly higher spontaneous production of nitric oxide (NO) at day 7 post-infection compared with BALB/c mice. Following in vitro stimulation with heat-killed Pseudomonas antigen, these cells produced significantly higher NO compared with cells from BALB/c mice at day 21 post-infection. Production of tumour necrosis factor-alpha (TNF-alpha) by alveolar macrophages was significantly higher at day 7 in BALB/c mice compared with C57Bl/6 mice, which showed significantly higher levels at day 28 post-infection. Taken together, these results suggest that defects in the host inflammatory process contribute to the variable outcome of chronic lung infection with P. aeruginosa. An exaggerated inflammatory response dominated by polymorphonuclear cells correlates with susceptibility to infection, whilst a modest inflammatory response dominated by macrophages correlates with resistance. Moreover, the quantity and timing of production of NO and TNF-alpha by alveolar macrophages may modulate the course and outcome of infection.

Genetic factors influence cataract formation in alpha 3 connexin knockout mice

Connexin alpha 3 (Cx46 or Gja3) gene targeted null mice developed lens nuclear cataracts shortly after birth. A large variance in the cataracts was observed in alpha 3 null sibs on a mixed 129SvJae X C57BL/6J F3 background. This suggested that the genetic background might influence the cataract phenotype. Therefore, we placed the alpha 3 null mutation into a 129SvJae background, and also backcrossed the mutation for six generations into 129SvJ and C57BL/6J backgrounds. While alpha 3 nulls on the two 129 backgrounds contained severe cataracts associated with gamma crystallin cleavage, alpha 3 nulls on the C57B16 background had far milder cataracts with no detectable gamma crystallin cleavage. These findings suggest that a genetic modifier exists that influences gamma crystallin stability, and that gamma crystallin breakdown is associated with severe nuclear cataracts.

Clinical and genetic risk factors for cystic fibrosis-related liver disease

OBJECTIVE

The aim of this study was to define the role of possible risk factors for the development of cystic fibrosis (CF)-related liver disease and to analyze the association between liver disease and the different genotypes present in the Israeli CF patient population.

PATIENTS AND METHODS

All patients followed at the seven CF centers in Israel were included in this study. Liver disease was determined by persistently elevated serum liver enzymes and/or bilirubin, and/or significant ultrasonographic changes suggestive of chronic liver disease. The following clinical parameters were evaluated: ethnic origin, age at assessment of liver function, sex, history of meconium ileus, pancreatic function, history of distal intestinal obstruction syndrome, pulmonary function, and cystic fibrosis transmembrane conductance regulator mutation analysis.

RESULTS

Of the 288 patients screened, 80 (28%) had liver disease. Of the 256 patients with pancreatic insufficiency, 80 (31%) had liver disease compared with none of the 32 patients with pancreatic sufficiency. Genotype-phenotype correlation was performed on 207 patients carrying identified mutations that were previously classified according to phenotype severity. Liver disease was found in 56 (32%) of 173 patients carrying mutations associated with a severe phenotype and in 6 (38%) of 16 patients carrying at least one mutation associated with a variable genotype (G85E and/or 5T allele). None of the 18 patients carrying the 3849+10kb C->T mutation had liver disease. Prevalence of liver disease increased with age. No correlation was found between liver disease and severity of lung disease, nutritional status, history of meconium ileus, or distal intestinal obstruction syndrome.

CONCLUSION

CF patients who have pancreatic insufficiency and carry mutations associated with a severe or a variable genotype are at increased risk to develop liver disease.

CFTR is a conductance regulator as well as a chloride channel

CFTR Is a Conductance Regulator as well as a Chloride Channel. Physiol. Rev. 79, Suppl.: S145-S166, 1999. - Cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette (ABC) transporter gene family. Although CFTR has the structure of a transporter that transports substrates across the membrane in a nonconductive manner, CFTR also has the intrinsic ability to conduct Cl- at much higher rates, a function unique to CFTR among this family of ABC transporters. Because Cl- transport was shown to be lost in cystic fibrosis (CF) epithelia long before the cloning of the CF gene and CFTR, CFTR Cl- channel function was considered to be paramount. Another equally valid perspective of CFTR, however, derives from its membership in a family of transporters that transports a multitude of different substances from chemotherapeutic drugs, to amino acids, to glutathione conjugates, to small peptides in a nonconductive manner. Moreover, at least two members of this ABC transporter family (mdr-1, SUR) can regulate other ion channels in the membrane. More simply, ABC transporters can regulate somehow the function of other cellular proteins or cellular functions. This review focuses on a plethora of studies showing that CFTR also regulates other ion channel proteins. It is the hope of the authors that the reader will take with him or her the message that CFTR is a conductance regulator as well as a Cl- channel.

Pathophysiology of gene-targeted mouse models for cystic fibrosis

Pathophysiology of Gene-Targeted Mouse Models for Cystic Fibrosis. Physiol. Rev. 79, Suppl.: S193-S214, 1999. - Mutations in the gene causing the fatal disease cystic fibrosis (CF) result in abnormal transport of several ions across a number of epithelial tissues. In just 3 years after this gene was cloned, the first CF mouse models were generated. The CF mouse models generated to date have provided a wealth of information on the pathophysiology of the disease in a variety of organs. Heterogeneity of disease in the mouse models is due to the variety of gene-targeting strategies used in the generation of the CF mouse models as well as the diversity of the murine genetic background. This paper reviews the pathophysiology in the tissues and organs (gastrointestinal, airway, hepatobiliary, pancreas, reproductive, and salivary tissue) involved in the disease in the various CF mouse models. Marked similarities to and differences from the human disease have been observed in the various murine models. Some of the CF mouse models accurately reflect the ion-transport abnormalities and disease phenotype seen in human CF patients, especially in gastrointestinal tissue. However, alterations in airway ion transport, which lead to the devastating lung disease in CF patients, appear to be largely absent in the CF mouse models. Reasons for these unexpected findings are discussed. This paper also reviews pharmacotherapeutic and gene therapeutic studies in the various mouse models.

Contribution of genetic factors other than CFTR to disease severity in cystic fibrosis

BACKGROUND

Disease severity in patients with cystic fibrosis shows marked variability. Attempts to explain this phenotypic heterogeneity on the basis of CFTR genotype have had limited success. A study was undertaken to test the hypothesis that naturally occurring variants of the pro-inflammatory cytokine tumour necrosis factor alpha (TNF-alpha) and the detoxifying enzyme glutathione S-transferase M1 (GSTM1) could influence disease severity in cystic fibrosis.

METHODS

Fifty-three children with cystic fibrosis were studied. To allow for the effect of age, all clinical details were collected during the eighth year of age. The subjects were divided into groups, both according to the presence or absence of the TNF2 TNF-alpha -308 promoter polymorphism (n = 20), and by homozygosity for the null allele of GSTM1 (n = 26).

RESULTS

Percentage predicted forced expiratory volume in one second (FEV1) and weight z scores were significantly lower in the TNF2 group (mean difference (95% confidence intervals) for FEV1 11.6% (1.7 to 21.5) and 0.59 (0.06 to 1.12) for weight z score). The Chrispin-Norman chest radiographic score was significantly higher and the Shwachman score was significantly lower in patients homozygous for the GSTM1 null allele.

CONCLUSIONS

Two independent genetic factors have been identified which appear to influence disease severity in cystic fibrosis. These results support the contention that inflammation in cystic fibrosis contributes to tissue damage. Isolation of further such factors may lead to identification of patients at risk of more severe disease and allow targeted aggressive therapy in this group.

Strain-dependent myeloid hyperplasia, growth deficiency, and accelerated cell cycle in mice lacking the Rb-related p107 gene

To investigate the function of the Rb-related p107 gene, a null mutation in p107 was introduced into the germ line of mice and bred into a BALB/cJ genetic background. Mice lacking p107 were viable and fertile but displayed impaired growth, reaching about 50% of normal weight by 21 days of age. Mutant mice exhibited a diathetic myeloproliferative disorder characterized by ectopic myeloid hyperplasia in the spleen and liver. Embryonic p107(-/-) fibroblasts and primary myoblasts isolated from adult p107(-/-) mice displayed a striking twofold acceleration in doubling time. However, cell sort analysis indicated that the fraction of cells in G1, S, and G2 was unaltered, suggesting that the different phases of the cell cycle in p107(-/-) cells was uniformly reduced by a factor of 2. Western analysis of cyclin expression in synchronized p107(-/-) fibroblasts revealed that expression of cyclins E and A preceded that of D1. Mutant embryos expressed approximately twice the normal level of Rb, whereas p130 levels were unaltered. Lastly, mutant mice reverted to a wild-type phenotype following a single backcross with C57BL/6J mice, suggesting the existence of modifier genes that have potentially epistatic relationships with p107. Therefore, we conclude that p107 is an important player in negatively regulating the rate of progression of the cell cycle, but in a strain-dependent manner.

Strain-dependent embryonic lethality in mice lacking the retinoblastoma-related p130 gene

The retinoblastoma-related p130 protein is a member of a conserved family, consisting of Rb, p107 and p130, which are believed to play important roles in cell-cycle control and cellular differentiation. We have generated a null mutation in p130 by gene targeting and crossed the null allele into Balb/cJ and C57BL/6J strains of mice. In an enriched Balb/cJ genetic background, p130(−/−) embryos displayed arrested growth and died between embryonic days 11 and 13. Histological analysis revealed varying degrees of disorganization in neural and dermamyotomal structures. Immunohistochemistry with antibody reactive with Islet-1 indicated markedly reduced numbers of neurons in the spinal cord and dorsal root ganglia. Immunohistochemistry with antibody reactive with desmin indicated a similar reduction in the number of differentiated myocytes in the myotome. The myocardium of mutant embryos was abnormally thin and resembled an earlier staged two-chambered heart consisting of the bulbus cordis and the ventricular chamber. TUNEL analysis indicated the presence of extensive apoptosis in various tissues including the neural tube, the brain, the dermomyotome, but not the heart. Immunohistochemistry with antibody reactive with PCNA revealed increased cellular proliferation in the neural tube and the brain, and decreased proliferation in the heart. The placentas of p130(−/−) embryos did not display elevated apoptosis and were indistinguishable from wild type suggesting that the phenotype was not due to placental failure. Following a single cross with the C57BL/6 mice, p130(−/−) animals were derived that were viable and fertile. These results indicate that p130 in a Balb/cJ genetic background plays an essential role that is required for normal development. Moreover, our experiments establish that second-site modifier genes exist that have an epistatic relationship with p130.

Genomic cloning, molecular characterization, and functional analysis of human CLCA1, the first human member of the family of Ca2+-activated Cl- channel proteins

We have cloned and molecularly and functionally characterized the first human member of the family of Ca2+-activated Cl- channels, human (h) CLCA1. The 31,902-bp gene is located on chromosome 1p22-31 and is preceded by a canonic promoter region that contains an L1 transposable element. In contrast to all previously known homologs in other species, hCLCA1 is exclusively expressed in intestinal basal crypt epithelia and goblet cells, suggesting that it does not represent the human counterpart of any of them. Expression of the 914-amino-acid hCLCA1 protein in HEK 293 cells yielded a 125-kDa precursor that was processed to yield two cell-surface-associated subunits, a 90-kDa protein and a group of 37- to 41-kDa proteins. Four transmembrane domains were established within the 90-kDa subunit. HEK 293 cells transfected with CLCA1 exhibited an increase in whole-cell Ca2+-sensitive Cl- currents that were outwardly rectified and inhibited by 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid, dithiothreitol, and niflumic acid. Cell-attached patch recordings of transfected cells revealed single channels with a slope conductance of 13.4 pS. These findings suggest that human CLCA1 mediates a Ca2+-activated Cl- conductance in the human intestine and make it an interesting candidate as a modulating factor in the pathogenesis of cystic fibrosis.

A conserved region of the R domain of cystic fibrosis transmembrane conductance regulator is important in processing and function

The R domain of cystic fibrosis transmembrane conductance regulator (CFTR) connects the two halves of the protein, each of which possess a transmembrane-spanning domain and a nucleotide binding domain. Phosphorylation of serine residues, which reside mostly within the C-terminal two-thirds of the R domain, is required for nucleotide-dependent activation of CFTR chloride channel activity. The N terminus of the R domain is also likely to be important in CFTR function, since this region is highly conserved among CFTRs of different species and exhibits sequence similarity with the "linker region" of the related protein, P-glycoprotein. To date, however, the role of this region in CFTR channel function remains unknown. In this paper, we report the effects of five disease-causing mutations within the N terminus of the CFTR-R domain. All five mutants exhibit defective protein processing in mammalian HEK-293 cells, suggesting that they are mislocalized and fail to reach the cell surface. However, in the Xenopus oocyte, three mutants reached the plasma membrane. One of these mutants, L619S, exhibits no detectable function, whereas the other two, D614G and I618T, exhibit partial activity as chloride channels. Single channel analysis of these latter two mutants revealed that they possess defective rates of channel opening, consistent with the hypothesis that the N terminus of the R domain participates in ATP-dependent channel gating. These findings support recent structural models that include this region within extended boundaries of the first nucleotide binding domain.

Molecular and functional characterization of a calcium-sensitive chloride channel from mouse lung

A protein (mCLCA1) has been cloned from a mouse lung cDNA library that bears strong sequence homology with the recently described bovine tracheal, Ca2+-sensitive chloride channel protein (bCLCA1), bovine lung endothelial cell adhesion molecule-1 (Lu-ECAM-1), and the human intestinal Ca2+-sensitive chloride channel protein (hCLCA1). In vitro, its 3.1-kilobase message translates into a 100-kDa protein that can be glycosylated to an approximately 125-kDa product. SDS-polyacrylamide gel electrophoresis from lysates of mCLCA1 cDNA-transfected transformed human embryonic kidney cells (HEK293) reveals proteins of 130, 125, and 90 kDa as well as a protein triplet in the 32-38 kDa size range. Western analyses with antisera raised against Lu-ECAM-1 peptides show that the N-terminal region of the predicted open reading frame is present only in the larger size proteins (i.e. 130, 125, and 90 kDa), whereas the C-terminal region of the open reading frame is observed in the 32-38 kDa size proteins, suggesting a posttranslational, proteolytic processing of a precursor protein (125/130 kDa) into 90 kDa and 32-38 kDa components similar to that reported for Lu-ECAM-1. Hydrophobicity analyses predict four transmembrane domains for the 90-kDa protein. The mCLCA1 mRNA is readily detected by Northern analysis and by in situ hybridization in the respiratory epithelia of trachea and bronchi. Transient expression of mCLCA1 in HEK293 cells was associated with an increase in whole cell Cl- current that could be activated by Ca2+ and ionomycin and inhibited by 4, 4'-diisothiocyanatostilbene-2,2'-disulfonic acid, dithiothreitol, and niflumic acid. The discovery of mCLCA1 opens the door for further investigating the possible contribution of a Ca2+-sensitive chloride conductance to the pathogenesis of cystic fibrosis.

The molecular basis of disease variability among cystic fibrosis patients carrying the 3849+10 kb C-->T mutation

Disease severity varies among cystic fibrosis (CF) patients carrying the same CFTR genotype. Here we studied the mechanism underlying disease variability in individuals carrying a splicing CFTR mutation, 3849+10 kb C-->T. This mutation was shown to produce both correctly and aberrantly spliced CFTR transcripts containing an additional cryptic exon. Semiquantitative nondifferential RT-PCR showed considerable variability in the level (0-28%) of aberrantly spliced RNA transcribed from the 3849+10 kb C-->T mutation in nasal epithelium from 10 patients. A significant inverse correlation was found between the level of the aberrantly spliced CFTR transcripts and pulmonary function, expressed as FEV1 (r = 0.92, P < 0.0001). Patients with normal pulmonary function (FEV1 > 80% predicted) had lower levels of aberrantly spliced CFTR RNA (0 to 3%) than those with FEV1 < 80%, (9 to 28% aberrantly spliced RNA). Only aberrantly spliced CFTR RNA was detected in the lung of a patient with severe lung disease who underwent lung transplantation. Our results show that the severity of CF lung disease correlates with insufficiency of normal CFTR RNA. Thus, the regulation of alternative splice site selection may be an important mechanism underlying partial penetrance in CF. Further understanding of this regulation will contribute to potential therapy for patients carrying splicing mutations in human disease genes.

Genetic diseases of the seminal ducts

Azoospermia due to an obstruction of the genital tract is one of numerous possible pathophysiologic mechanisms underlying male infertility. The blockage of the seminal ducts may be acquired or congenital. Only recently has the strong association between mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene and various subtypes of obstructive azoospermia been elucidated. Most patients with congenital bilateral absence of the vas deferens or bilateral ejaculatory duct obstruction are carriers of such mutations. The relationship between abnormal CFTR alleles and unilateral absence of the vas deferens, isolated seminal vesicle anomalies, and Young syndrome is less well characterized and awaits further investigation.

Clinical implications of cystic fibrosis transmembrane conductance regulator mutations

Cystic fibrosis (CF) phenotypes are determined by mutations in the CF gene, genetic background, and environment. The nature of the cystic fibrosis transmembrane conductance regulator (CFTR) mutation determines the extent of protein function. CFTR mutations that abolish protein function are associated with severe CF phenotypes. Mutants that retain partial function of CFTR are associated with mild phenotypes. The effect of CFTR dysfunction is variable in different tissues. Atypical phenotypes caused by mutations in the CF gene may be revealed by CFTR mutation analysis and family studies. These phenotypes help to define the spectrum of clinical manifestations caused by CFTR mutations.

Exhaustive screening of the acid beta-glucosidase gene, by fluorescence-assisted mismatch analysis using universal primers: mutation profile and genotype/phenotype correlations in Gaucher disease

Gaucher disease (GD) is one of the most prevalent lysosomal storage disorders and one of the rare genetic diseases now accessible to therapy. Outside the Ashkenazi Jewish community, a high molecular diversity is observed, leaving approximately 30% of alleles undetected. Nevertheless, very few exhaustive methods have been developed for extensive gene screening of a large series of patients. Our approach for a complete search of mutations was the association of fluorescent chemical cleavage of mismatches with a universal strand-specific labeling system. The glucocerebrosidase (GBA) gene was scanned by use of a set of six amplicons, comprising 11 exons, all exon/intron boundaries, and the promoter region. By use of this screening strategy, the difficulties due to the existence of a highly homologous pseudogene were easily overcome, and both GD mutant alleles were identified in all 25 patients studied, thus attesting to a sensitivity that approaches 100%. A total of 18 different mutations and a new glucocerebrosidase haplotype were detected. The mutational spectrum included eight novel acid beta-glucosidase mutations: IVS2 G(+1)-->T, I119T, R170P, N188K, S237P, K303I, L324P, and A446P. These data further indicate the genetic heterogeneity of the lesions causing GD. Established genotype/phenotype correlations generally were confirmed, but notable disparities were disclosed in several cases, thus underlining the limitation in the prognostic value of genotyping. The observed influence of multifactorial control on this monogenic disease is discussed.

Developmental expression of a mucinlike glycoprotein (MUCLIN) in pancreas and small intestine of CF mice

The mucinlike glycoprotein MUCLIN, one of two protein products of the CRP-ductin gene, was used to study changes in the expression of sulfated glycoconjugates during the pathogenesis of cystic fibrosis, using the cystic fibrosis transmembrane conductance regulator (CFTR) knockout mouse (CF mouse). We assessed the appearance of dilated lumina containing protein or mucus plugs in pancreatic acini and crypts of the small intestine and quantified MUCLIN protein and CRP-ductin mRNA during postnatal development. In CF mice, the pancreatic acinar lumen was dilated by postnatal day 16 (P16), but MUCLIN protein was first significantly increased by P23 and remained elevated through adulthood compared with normal mice. Similarly, intestinal crypts had CF-like mucus plugs by P16, but MUCLIN protein was first elevated by P23 and remained elevated through adulthood compared with normal mice. In both organs, MUCLIN labeling of the luminal surface was increased concomitantly with dilation and protein or mucus plugging but before upregulation of expression. The morphological changes were then followed by upregulation of MUCLIN protein and CRP-ductin mRNA expression. This is the first direct study of CF pathogenesis and the resultant increase in glycoconjugate gene expression. The data are consistent with CF pathogenesis progressing from an initial alteration in protein secretory dynamics (increased luminal MUCLIN and protein/mucus plugs) to an upregulation of glycoprotein/mucin gene expression, which is expected to exacerbate obstruction of the luminal spaces.

Genomic strategies for defining and dissecting developmental and physiological pathways

A major challenge in genetics research is defining and dissecting the diversity of developmental and physiological pathways that lie between genes and traits. New functional genomics methods are transforming these studies by providing comprehensive and systematic approaches that complement traditional methods of formal genetics, biochemistry, and cell biology. Together, these complementary approaches will test whether reductionism can account for the complex web of interactions that lead from genetic variation to morphological, physiological, and behavioral traits in health and disease.

Comparison of the gating behaviour of human and murine cystic fibrosis transmembrane conductance regulator Cl- channels expressed in mammalian cells

1. To investigate the function of the murine cystic fibrosis transmembrane conductance regulator (CFTR), a full-length cDNA encoding wild-type murine CFTR was assembled and stably expressed in Chinese hamster ovary (CHO) cells. 2. Like human CFTR, murine CFTR formed Cl- channels that were regulated by cAMP-dependent phosphorylation and intracellular ATP. However, murine CFTR Cl- channels had a reduced single-channel conductance and decreased open probability (Po) compared with those of human CFTR. 3. Analysis of the dwell time distributions of single channels suggested that the reduced Po of murine CFTR was caused by both decreased residence in the open state and transitions to a new closed state, described by an intermediate closed time constant. 4. For both human and murine CFTR, ATP and ADP regulated the rate of exit from the long-lived closed state. 5. 5'-Adenylylimidodiphosphate (AMP-PNP) and pyrophosphate, two compounds that disrupt cycles of ATP hydrolysis, stabilized the open state of human CFTR. However, neither agent locked murine CFTR Cl- channels open, although AMP-PNP increased the Po of murine CFTR. 6. The data indicate that although human and murine CFTR have many properties in common, some important differences in function are observed. These differences could be exploited in future studies to provide new understanding about CFTR.

Bone Marrow Failure in the Fanconi Anemia Group C Mouse Model After DNA Damage

Fanconi anemia (FA) is a pleiotropic inherited disease that causes bone marrow failure in children. However, the specific involvement of FA genes in hematopoiesis and their relation to bone marrow (BM) failure is still unclear. The increased sensitivity of FA cells to DNA cross-linking agents such as mitomycin C (MMC) and diepoxybutane (DEB), including the induction of chromosomal aberrations and delay in the G2 phase of the cell cycle, have suggested a role for the FA genes in DNA repair, cell cycle regulation, and apoptosis. We previously reported the cloning of the FA group C gene (FAC) and the generation of a Fac mouse model. Surprisingly, the Fac −/− mice did not show any of the hematologic defects found in FA patients. To better understand the relationship of FA gene functions to BM failure, we have analyzed the in vivo effect of an FA-specific DNA damaging agent in Fac −/− mice. The mice were found to be highly sensitive to DNA cross-linking agents; acute exposure to MMC produced a marked BM hypoplasia and degeneration of proliferative tissues and caused death within a few days of treatment. However, sequential, nonlethal doses of MMC caused a progressive decrease in all peripheral blood parameters of Fac −/− mice. This treatment targeted specifically the BM compartment, with no effect on other proliferative tissues. The progressive pancytopenia resulted from a reduction in the number of early and committed hematopoietic progenitors. These results indicate that the FA genes are involved in the physiologic response of hematopoietic progenitor cells to DNA damage.

Genomic DNA sequence of Rhesus (M. mulatta) cystic fibrosis (CFTR) gene

Cystic fibrosis is a common human genetic disease caused by mutations in CFTR, a gene that codes for a chloride channel that is regulated by phosphorylation and cytosolic nucleotides. As part of a program to discover natural animal models for human genetic diseases, we have determined the genomic sequence of CFTR in the Rhesus monkey, Macaca mulatta. The coding region of rhesus CFTR is 98.3% identical to human CFTR at the nucleotide level and 98.2% identical and 99.7% similar at the amino acid level. Partial sequences of flanking introns (5582 base pair positions analyzed) revealed 91.1% identity with human introns. Relative to rhesus intronic sequence, the human sequences had 27 insertions and 22 deletions. Primer sequences for amplification of rhesus genomic CFTR sequences are provided. The accession number is AF013753 (all 27 exons and some flanking intronic sequence).

Gene disruption in mice: models of development and disease

Gene targeting technology in mice by homologous recombination has become an important method to generate loss-of-function of genes in a predetermined locus. Although the inactivation is limited to irreversible alteration of chromosomal DNA and a surprising variety of genes have given unexpected and disappointing results, modification of the basic technology now provides additional choices for a more specific and variety of manipulations of the mouse genome. This includes conditional cell-type specific gene targeting, knockin technique and the induction of the specific balanced chromosomal translocations. In the past decade this technique not only generated a wealth of knowledge concerning the roles of growth factors, oncogenes, hormone receptors and Hox genes but also helped to produce animal models for several human genetic disorders. In the future it may provide more powerful and necessary tools to dissect the psychiatric disorders, understanding the complex central nervous system and to correct the inherited disorders.