A combined analysis of the cystic fibrosis transmembrane conductance regulator: implications for structure and disease models

Fish response to hypoxia stress: growth, physiological, and immunological biomarkers

Water quality encompasses the water physical, biological, and chemical parameters. It generally affects the fish growth and welfare. Thus, the success of a commercial aquaculture project depends on supplying the optimum water quality for prompt fish growth at the minimum cost of resources. Although the aquaculture environment is a complicated system, depending on various water quality variables, only less of them have a critical role. One of these vital parameters is dissolved oxygen (DO) level, which requires continuous oversight in aquaculture systems. In addition, the processes of natural stream refinement require suitable DO levels in order to extend for aerobic life forms. The depletion of DO concentration (called hypoxia) in pond water causes great stress on fish where DO levels that remain below 1-2 mg/L for a few hours can adversely affect fish growth resulting in fish death. Furthermore, hypoxia has substantial effects on fish physiological and immune responses, making them more susceptible to diseases. Therefore, to avoid disease outbreak in modern aquaculture production systems where fish are intensified and more crowded, increasing attention should be taken into account on DO levels.

Residual function of cystic fibrosis mutants predicts response to small molecule CFTR modulators

Treatment of individuals with cystic fibrosis (CF) has been transformed by small molecule therapies that target select pathogenic variants in the CF transmembrane conductance regulator (CFTR). To expand treatment eligibility, we stably expressed 43 rare missense CFTR variants associated with moderate CF from a single site in the genome of human CF bronchial epithelial (CFBE41o-) cells. The magnitude of drug response was highly correlated with residual CFTR function for the potentiator ivacaftor, the corrector lumacaftor, and ivacaftor-lumacaftor combination therapy. Response of a second set of 16 variants expressed stably in Fischer rat thyroid (FRT) cells showed nearly identical correlations. Subsets of variants were identified that demonstrated statistically significantly higher responses to specific treatments. Furthermore, nearly all variants studied in CFBE cells (40 of 43) and FRT cells (13 of 16) demonstrated greater response to ivacaftor-lumacaftor combination therapy than either modulator alone. Together, these variants represent 87% of individuals in the CFTR2 database with at least 1 missense variant. Thus, our results indicate that most individuals with CF carrying missense variants are (a) likely to respond modestly to currently available modulator therapy, while a small fraction will have pronounced responses, and (b) likely to derive the greatest benefit from combination therapy.

Combination of Correctors Rescues CFTR Transmembrane-Domain Mutants by Mitigating their Interactions with Proteostasis

Background/Aims:

Premature degradation of mutated cystic fibrosis transmembrane conductance regulator (CFTR) protein causes cystic fibrosis (CF), the commonest Mendelian disease in Caucasians. Despite recent advances in precision medicines for CF patients, many CFTR mutants have not been characterized and the effects of these new therapeutic approaches are still unclear for those mutants.

Methods:

Cells transfected or stably expressing four CFTR transmembrane-domain mutants (G85E, E92K, L1077P, and M1101K) were used to: 1) characterize the mutants according to their protein expression, thermal sensitivity, and degradation pathways; 2) evaluate the effects of correctors in rescuing them; and 3) explore the effects of correctors on CFTR interactions with proteostasis components.

Results:

All four mutants exhibited lower protein expression than did wild type-CFTR, and they were degraded by proteasomes and aggresomes. At low temperature, only cells expressing the mutants L1077P and M1101K exhibited increased CFTR maturation. Co-administration of C4 and C18 showed the greatest effect, restoring functional expression and partial stability of CFTR bearing E92K, L1077P, or M1101K at the cell surface. However, this treatment was inefficient in rectifying the defect of CFTR bearing G85E. Correctors rescued CFTR mutants by reducing their interactions with proteostasis components associated with protein retention in the endoplasmic reticulum and ubiquitination.

Conclusion:

Co-administration of C4 and C18 rescued CFTR transmembrane-domain mutants by remodeling the CFTR interactome.

Exploiting species differences to understand the CFTR Cl- channel

The anion channel cystic fibrosis transmembrane conductance regulator (CFTR) is a unique ATP-binding cassette (ABC) transporter. CFTR plays a pivotal role in transepithelial ion transport as its dysfunction in the genetic disease cystic fibrosis (CF) dramatically demonstrates. Phylogenetic analysis suggests that CFTR first appeared in aquatic vertebrates fulfilling important roles in osmosensing and organ development. Here, we review selectively, knowledge of CFTR structure, function and pharmacology, gleaned from cross-species comparative studies of recombinant CFTR proteins, including CFTR chimeras. The data argue that subtle changes in CFTR structure can affect strongly channel function and the action of CF mutations.

Characterizing diverse orthologues of the cystic fibrosis transmembrane conductance regulator protein for structural studies

As an ion channel, the cystic fibrosis transmembrane conductance regulator (CFTR) protein occupies a unique niche within the ABC family. Orthologues of CFTR are extant throughout the animal kingdom from sharks to platypods to sheep, where the osmoregulatory function of the protein has been applied to differing lifestyles and diverse organ systems. In humans, loss-of-function mutations to CFTR cause the disease cystic fibrosis, which is a significant health burden in populations of white European descent. Orthologue screening has proved fruitful in the pursuit of high-resolution structural data for several membrane proteins, and we have applied some of the princples developed in previous studies to the expression and purification of CFTR. We have overexpressed this protein, along with evolutionarily diverse orthologues, in Saccharomyces cerevisiae and developed a purification to isolate it in quantities sufficient for structural and functional studies.

Optimizing de novo transcriptome assembly and extending genomic resources for striped catfish (Pangasianodon hypophthalmus)

Striped catfish (Pangasianodon hypophthalmus) is a commercially important freshwater fish used in inland aquaculture in the Mekong Delta, Vietnam. The culture industry is facing a significant challenge however from saltwater intrusion into many low topographical coastal provinces across the Mekong Delta as a result of predicted climate change impacts. Developing genomic resources for this species can facilitate the production of improved culture lines that can withstand raised salinity conditions, and so we have applied high-throughput Ion Torrent sequencing of transcriptome libraries from six target osmoregulatory organs from striped catfish as a genomic resource for use in future selection strategies. We obtained 12,177,770 reads after trimming and processing with an average length of 97bp. De novo assemblies were generated using CLC Genomic Workbench, Trinity and Velvet/Oases with the best overall contig performance resulting from the CLC assembly. De novo assembly using CLC yielded 66,451 contigs with an average length of 478bp and N50 length of 506bp. A total of 37,969 contigs (57%) possessed significant similarity with proteins in the non-redundant database. Comparative analyses revealed that a significant number of contigs matched sequences reported in other teleost fishes, ranging in similarity from 45.2% with Atlantic cod to 52% with zebrafish. In addition, 28,879 simple sequence repeats (SSRs) and 55,721 single nucleotide polymorphisms (SNPs) were detected in the striped catfish transcriptome. The sequence collection generated in the current study represents the most comprehensive genomic resource for P. hypophthalmus available to date. Our results illustrate the utility of next-generation sequencing as an efficient tool for constructing a large genomic database for marker development in non-model species.

An integrated transcriptomic and comparative genomic analysis of differential gene expression in Arctic charr (Salvelinus alpinus) following seawater exposure

High-throughput RNA sequencing was employed to compare expression profiles in two Arctic charr (Salvelinus alpinus) families post seawater exposure to identify genes and biological processes involved in hypo-osmoregulation and regulation of salinity tolerance. To further understand the genetic architecture of hypo-osmoregulation, the genomic organization of differentially expressed (DE) genes was also analysed. Using a de novo gill transcriptome assembly we found over 2300 contigs to be DE. Major transporters from the seawater mitochondrion-rich cell (MRC) complex were up-regulated in seawater. Expression ratios for 257 differentially expressed contigs were highly correlated between families, suggesting they are strictly regulated. Based on expression profiles and known molecular pathways we inferred that seawater exposure induced changes in methylation states and elevated peroxynitrite formation in gill. We hypothesized that concomitance between DE immune genes and the transition to a hypo-osmoregulatory state could be related to Cl- sequestration by antimicrobial defence mechanisms. Gene Ontology analysis revealed that cell division genes were up-regulated, which could reflect the proliferation of ATP1α1b-type seawater MRCs. Comparative genomics analyses suggest that hypo-osmoregulation is influenced by the relative proximities among a contingent of genes on Arctic charr linkage groups AC-4 and AC-12 that exhibit homologous affinities with a region on stickleback chromosome Ga-I. This supports the hypothesis that relative gene location along a chromosome is a property of the genetic architecture of hypo-osmoregulation. Evidence of non-random structure between hypo-osmoregulation candidate genes was found on AC-1/11 and AC-28, suggesting that interchromosomal rearrangements played a role in the evolution of hypo-osmoregulation in Arctic charr.

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

Congenital bilateral absence of the vas deferens (CBAVD) is a frequent cause of obstructive azoospermia, and mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene have also been frequently identified in patients with CBAVD. However, the distribution of the CFTR polymorphisms M470V, poly-T, TG-repeats and F508del mutation in the Chinese CBAVD population with presumed low cystic fibrosis (CF) frequency remains to be evaluated. Samples obtained from 109 Chinese infertile males with CBAVD and 104 normal controls were analyzed for the presence of CFTR (TG)m(T)n, M470V and F508del by PCR amplification followed by direct sequencing. Our study showed that the F508del mutation was not found in our patients. The 5T mutation was present with high frequency in Chinese CBAVD patients and IVS8-5T linked to either 12 or 13 TG repeats was highly prevalent among CBAVD patients (97.22% of 72 cases and 96.91% of 97 alleles with IVS8-5T). Moreover, a statistically significant relationship between TG12-5T-V470 haplotype and CBAVD was detected. This study indicated that the CFTR polymorphisms poly-T, TG-repeats and M470V might affect the process of CBAVD in the Chinese population.

Cystic fibrosis transmembrane conductance regulator in the gills of the climbing perch, Anabas testudineus, is involved in both hypoosmotic regulation during seawater acclimation and active ammonia excretion during ammonia exposure

This study aimed to clone and sequence the cystic fibrosis transmembrane conductance regulator (cftr) from, and to determine the effects of seawater acclimation or exposure to 100 mmol l⁻¹ NH₄Cl in freshwater on its mRNA and protein expressions in, the gills of Anabas testudineus. There were 4,530 bp coding for 1,510 amino acids in the cftr cDNA sequence from A. testudineus. The branchial mRNA expression of cftr in fish kept in freshwater was low (<50 copies of transcript per ng cDNA), but significant increases were observed in fish acclimated to seawater for 1 day (92-fold) or 6 days (219-fold). Branchial Cftr expression was detected in fish acclimated to seawater but not in the freshwater control, indicating that Cl⁻ excretion through the apical Cftr of the branchial epithelium was essential to seawater acclimation. More importantly, fish exposed to ammonia also exhibited a significant increase (12-fold) in branchial mRNA expression of cftr, with Cftr being expressed in a type of Na⁺/K⁺-ATPase-immunoreactive cells that was apparently different from the type involved in seawater acclimation. It is probable that Cl⁻ excretion through Cftr generated a favorable electrical potential across the apical membrane to drive the excretion of NH₄⁺ against a concentration gradient through a yet to be determined transporter, but it led to a slight loss of endogenous Cl⁻. Since ammonia exposure also resulted in significant decreases in blood pH, [HCO₃⁻] and [total CO₂] in A. testudineus, it can be deduced that active NH₄⁺ excretion could also be driven by the exit of HCO₃⁻ through the apical Cftr. Furthermore, A. testudineus uniquely responded to ammonia exposure by increasing the ambient pH and decreasing the branchial bafilomycin-sensitive V-type H⁺-ATPase activity, which suggests that its gills might have low NH₃ permeability.

Generation of SV40-transformed rabbit tracheal-epithelial-cell-derived blastocyst by somatic cell nuclear transfer

The prospect of developing large animal models for the study of inherited diseases, such as cystic fibrosis (CF), through somatic cell nuclear transfer (SCNT) has opened up new opportunities for enhancing our understanding of disease pathology and for identifying new therapies. Thus, the development of species-specific in vitro cell systems that will provide broader insight into organ- and cell-type-specific functions relevant to the pathology of the disease is crucial. Studies have been undertaken to establish transformed rabbit airway epithelial cell lines that display differentiated features characteristic of the primary airway epithelium. This study describes the successful establishment and characterization of two SV40-transformed rabbit tracheal epithelial cell lines. These cell lines, 5RTEo- and 9RTEo-, express the CF transmembrane conductance regulator (CFTR) gene, retain epithelial-specific differentiated morphology and show CFTR-based cAMP-dependent Cl(-) ion transport across the apical membrane of a confluent monolayer. Immunocytochemical analysis indicates the presence of airway cytokeratins and tight-junction proteins in the 9RTEo- cell line after multiple generations. However, the tight junctions appear to diminish in their efficacy in both cell lines after at  least 100 generations. Initial SCNT studies with the 9RTEo- cells have revealed that SV40-transformed rabbit airway epithelial donor cells can be used to generate blastocysts. These cell systems provide valuable models for studying the developmental and metabolic modulation of CFTR gene expression and rabbit airway epithelial cell biology.

The genetic basis of salinity tolerance traits in Arctic charr (Salvelinus alpinus)

BACKGROUND

The capacity to maintain internal ion homeostasis amidst changing conditions is particularly important for teleost fishes whose reproductive cycle is dependent upon movement from freshwater to seawater. Although the physiology of seawater osmoregulation in mitochondria-rich cells of fish gill epithelium is well understood, less is known about the underlying causes of inter- and intraspecific variation in salinity tolerance. We used a genome-scan approach in Arctic charr (Salvelinus alpinus) to map quantitative trait loci (QTL) correlated with variation in four salinity tolerance performance traits and six body size traits. Comparative genomics approaches allowed us to infer whether allelic variation at candidate gene loci (e.g., ATP1α1b, NKCC1, CFTR, and cldn10e) could have underlain observed variation.

RESULTS

Combined parental analyses yielded genome-wide significant QTL on linkage groups 8, 14 and 20 for salinity tolerance performance traits, and on 1, 19, 20 and 28 for body size traits. Several QTL exhibited chromosome-wide significance. Among the salinity tolerance performance QTL, trait co-localizations occurred on chromosomes 1, 4, 7, 18 and 20, while the greatest experimental variation was explained by QTL on chromosomes 20 (19.9%), 19 (14.2%), 4 (14.1%) and 12 (13.1%). Several QTL localized to linkage groups exhibiting homeologous affinities, and multiple QTL mapped to regions homologous with the positions of candidate gene loci in other teleosts. There was no gene × environment interaction among body size QTL and ambient salinity.

CONCLUSIONS

Variation in salinity tolerance capacity can be mapped to a subset of Arctic charr genomic regions that significantly influence performance in a seawater environment. The detection of QTL on linkage group 12 was consistent with the hypothesis that variation in salinity tolerance may be affected by allelic variation at the ATP1α1b locus. IGF2 may also affect salinity tolerance capacity as suggested by a genome-wide QTL on linkage group 19. The detection of salinity tolerance QTL in homeologous regions suggests that candidate loci duplicated from the salmonid-specific whole-genome duplication may have retained their function on both sets of homeologous chromosomes. Homologous affinities suggest that loci affecting salinity tolerance in Arctic charr may coincide with QTL for smoltification and salinity tolerance traits in rainbow trout. The effects of body size QTL appear to be independent of changes in ambient salinity.

Thermal unfolding studies show the disease causing F508del mutation in CFTR thermodynamically destabilizes nucleotide-binding domain 1

Misfolding and degradation of CFTR is the cause of disease in patients with the most prevalent CFTR mutation, an in-frame deletion of phenylalanine (F508del), located in the first nucleotide-binding domain of human CFTR (hNBD1). Studies of (F508del)CFTR cellular folding suggest that both intra- and inter-domain folding is impaired. (F508del)CFTR is a temperature-sensitive mutant, that is, lowering growth temperature, improves both export, and plasma membrane residence times. Yet, paradoxically, F508del does not alter the fold of isolated hNBD1 nor did it seem to perturb its unfolding transition in previous isothermal chemical denaturation studies. We therefore studied the in vitro thermal unfolding of matched hNBD1 constructs ±F508del to shed light on the defective folding mechanism and the basis for the thermal instability of (F508del)CFTR. Using primarily differential scanning calorimetry (DSC) and circular dichroism, we show for all hNBD1 pairs studied, that F508del lowers the unfolding transition temperature (T(m)) by 6-7°C and that unfolding occurs via a kinetically-controlled, irreversible transition in isolated monomers. A thermal unfolding mechanism is derived from nonlinear least squares fitting of comprehensive DSC data sets. All data are consistent with a simple three-state thermal unfolding mechanism for hNBD1 ± F508del: N(±MgATP) <==> I(T)(±MgATP) → A(T) → (A(T))(n). The equilibrium unfolding to intermediate, I(T), is followed by the rate-determining, irreversible formation of a partially folded, aggregation-prone, monomeric state, A(T), for which aggregation to (A(T))(n) and further unfolding occur with no detectable heat change. Fitted parameters indicate that F508del thermodynamically destabilizes the native state, N, and accelerates the formation of A(T).

Folding and rescue of a cystic fibrosis transmembrane conductance regulator trafficking mutant identified using human-murine chimeric proteins

Impairment of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel causes cystic fibrosis, a fatal genetic disease. Here, to gain insight into CFTR structure and function, we exploited interspecies differences between CFTR homologues using human (h)-murine (m) CFTR chimeras containing murine nucleotide-binding domains (NBDs) or regulatory domain on an hCFTR backbone. Among 15 hmCFTR chimeras analyzed, all but two were correctly processed, one containing part of mNBD1 and another containing part of mNBD2. Based on physicochemical distance analysis of divergent residues between human and murine CFTR in the two misprocessed hmCFTR chimeras, we generated point mutations for analysis of respective CFTR processing and functional properties. We identified one amino acid substitution (K584E-CFTR) that disrupts CFTR processing in NBD1. No single mutation was identified in NBD2 that disrupts protein processing. However, a number of NBD2 mutants altered channel function. Analysis of structural models of CFTR identified that although Lys(584) interacts with residue Leu(581) in human CFTR Glu(584) interacts with Phe(581) in mouse CFTR. Introduction of the murine residue (Phe(581)) in cis with K584E in human CFTR rescued the processing and trafficking defects of K584E-CFTR. Our data demonstrate that human-murine CFTR chimeras may be used to validate structural models of full-length CFTR. We also conclude that hmCFTR chimeras are a valuable tool to elucidate interactions between different domains of CFTR.

Specific resistance to Pseudomonas aeruginosa infection in zebrafish is mediated by the cystic fibrosis transmembrane conductance regulator

Cystic fibrosis (CF) is a genetic disease caused by recessive mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene and is associated with prevalent and chronic Pseudomonas aeruginosa lung infections. Despite numerous studies that have sought to elucidate the role of CFTR in the innate immune response, the links between CFTR, innate immunity, and P. aeruginosa infection remain unclear. The present work highlights the zebrafish as a powerful model organism for human infectious disease, particularly infection by P. aeruginosa. Zebrafish embryos with reduced expression of the cftr gene (Cftr morphants) exhibited reduced respiratory burst response and directed neutrophil migration, supporting a connection between cftr and the innate immune response. Cftr morphants were infected with P. aeruginosa or other bacterial species that are commonly associated with infections in CF patients, including Burkholderia cenocepacia, Haemophilus influenzae, and Staphylococcus aureus. Intriguingly, the bacterial burden of P. aeruginosa was found to be significantly higher in zebrafish Cftr morphants than in controls, but this phenomenon was not observed with the other bacterial species. Bacterial burden in Cftr morphants infected with a P. aeruginosa ΔLasR mutant, a quorum sensing-deficient strain, was comparable to that in control fish, indicating that the regulation of virulence factors through LasR is required for enhancement of infection in the absence of Cftr. The zebrafish system provides a multitude of advantages for studying the pathogenesis of P. aeruginosa and for understanding the role that innate immune cells, such as neutrophils, play in the host response to acute bacterial infections commonly associated with cystic fibrosis.

Molecular dynamics simulation of the transmembrane subunit of BtuCD in the lipid bilayer

Based on the crystal structure of the vitamin B(12) transporter protein of Escherichia coli (BtuCD) a system consisting of the BtuCD transmembrane domain (BtuC) and the palmitoyloleoyl phosphatidylcholine (POPC) lipid bilayer was constructed in silica, and a more-than-57-nanosecond molecular dynamics (MD) simulation was performed on it to reveal the intrinsic functional motions of BtuC. The results showed that a stable protein-lipid bilayer was obtained and the POPC lipid bilayer was able to adjust its thickness to match the embedded BtuC which underwent relatively complicated motions. These results may help to understand the mechanism of transmembrane substrate transport at the atomic level.

Influence of salinity on the localization and expression of the CFTR chloride channel in the ionocytes of Dicentrarchus labrax during ontogeny

The expression and localization of the cystic fibrosis transmembrane conductance regulator (CFTR) were determined in four osmoregulatory tissues during the ontogeny of the sea-bass Dicentrarchus labrax acclimated to fresh water and sea water. At hatch in sea water, immunolocalization showed an apical CFTR in the digestive tract and integumental ionocytes. During the ontogeny, although CFTR was consistently detected in the digestive tract, it shifted from the integument to the gills. In fresh water, CFTR was not present in the integument and the gills, suggesting the absence of chloride secretion. In the kidney, the CFTR expression was brief from D4 to D35, prior to the larva-juvenile transition. CFTR was apical in the renal tubules, suggesting a chloride secretion at both salinities, and it was basolateral only in sea water in the collecting ducts, suggesting chloride absorption. In the posterior intestine, CFTR was located differently from D4 depending on salinity. In sea water, the basolateral CFTR may facilitate ionic absorption, perhaps in relation to water uptake. In fresh water, CFTR was apical in the gut, suggesting chloride secretion. Increased osmoregulatory ability was acquired just before metamorphosis, which is followed by the sea-lagoon migration.

Molecular and functional characterization of the cystic fibrosis transmembrane conductance regulator from the Australian common brushtail possum, Trichosurus vulpecula

Unlike eutherian mammals, the colon of the Australian common brushtail possum, Trichosurus vulpecula, a metatherian mammal, is incapable of electrogenic Cl(-) secretion and has elevated levels of electrogenic Na(+) absorption, while the ileum secretes HCO (3) (-) rather than Cl(-). In eutherian mammals, the cystic fibrosis transmembrane conductance regulator (CFTR) is essential for both Cl(-) and HCO (3) (-) secretion and the regulation of Na(+) absorption. Therefore, we have sequenced possum (p)CFTR, described its distribution and characterized the properties of cloned pCFTR expressed in Fischer rat thyroid (FRT) cells. pCFTR (GenBank accession No. AY916796) has a 1,478 amino acid open reading frame, which has >90% identity with CFTR from other marsupials and >80% identity with non-rodent eutherian mammals. In pCFTR, there is a high level of conservation of the transmembrane and nucleotide binding domains although, with the exception of other marsupials, there is considerable divergence from other species in the R domain. FRT cells transfected with pCFTR express mature CFTR protein which functions as a small Cl(-) channel activated by cAMP-dependent phosphorylation. In whole-cell recordings it has a linear, time and voltage-independent conductance, with a selectivity sequence P(Br) > P(Cl) > P(I) > P(HCO)(3) >> P(Gluconate). pCFTR transcript is present in a range of epithelia, including the ileum and the colon. The presence of pCFTR in the ileum and its measured HCO (3) (-) permeability suggest that it may be involved in ileal HCO (3) (-) secretion. Why the possum colon does not secrete Cl(-) and has elevated electrogenic Na(+) absorption, despite the apparent expression of CFTR, remains to be determined.

Deletion of CFTR translation start site reveals functional isoforms of the protein in CF patients

BACKGROUND/AIMS

Mutations in the CFTR gene cause Cystic Fibrosis (CF) the most common life-threatening autosomal recessive disease affecting Caucasians. We identified a CFTR mutation (c.120del23) abolishing the normal translation initiation codon, which occurs in two Portuguese CF patients. This study aims at functionally characterizing the effect of this novel mutation.

METHODS

RNA and protein techniques were applied to both native tissues from CF patients and recombinant cells expressing CFTR constructs to determine whether c.120del23 allows CFTR protein production through usage of alternative internal codons, and to characterize the putative truncated CFTR form(s).

RESULTS

Our data show that two shorter forms of CFTR protein are produced when the initiation translation codon is deleted indicating usage of internal initiation codons. The N-truncated CFTR generated by this mutation has decreased stability, very low processing efficiency, and drastically reduced function. Analysis of mutants of four methionine codons downstream to M1 (M82, M150, M152, M156) revealed that each of the codons M150/M152/M156 (exon 4) can mediate CFTR alternative translation.

CONCLUSIONS

The CFTR N-terminus has an important role in avoiding CFTR turnover and in rendering effective its plasma membrane traffic. These data correlate well with the severe clinical phenotype of CF patients bearing the c.120del23 mutation.

Mild processing defect of porcine DeltaF508-CFTR suggests that DeltaF508 pigs may not develop cystic fibrosis disease

Recent efforts have made significant progress in generating transgenic pigs with the DeltaF508-CFTR mutation to model the lung and pancreatic disease of human cystic fibrosis. However, species differences in the processing and function of human, pig and mouse DeltaF508-CFTR reported recently raise concerns about the phenotypic consequence of the gene-targeted pig model. The purpose of the present study was to characterize the DeltaF508 mutant of porcine CFTR to evaluate the severity of its processing defect. Biochemical and immunofluorescence analysis in transfected COS7 and FRT cells indicated that pig DeltaF508-CFTR efficiently targets to the plasma membrane and is present mainly as the mature glycosylated protein. Functional characterization in stably transfected FRT cells by fluorometric and electrophysiological assays supported efficient plasma membrane targeting of pig DeltaF508-CFTR. The mild cellular processing defect of pig DeltaF508-CFTR suggests that its gene-targeted pig model may not develop the lung and pancreatic phenotypes seen in CF patients.

Mutations at arginine 352 alter the pore architecture of CFTR

Arginine 352 (R352) in the sixth transmembrane domain of the cystic fibrosis transmembrane conductance regulator (CFTR) previously was reported to form an anion/cation selectivity filter and to provide positive charge in the intracellular vestibule. However, mutations at this site have nonspecific effects, such as inducing susceptibility of endogenous cysteines to chemical modification. We hypothesized that R352 stabilizes channel structure and that charge-destroying mutations at this site disrupt pore architecture, with multiple consequences. We tested the effects of mutations at R352 on conductance, anion selectivity and block by the sulfonylurea drug glipizide, using recordings of wild-type and mutant channels. Charge-altering mutations at R352 destabilized the open state and altered both selectivity and block. In contrast, R352K-CFTR was similar to wild-type. Full conductance state amplitude was similar to that of wild-type CFTR in all mutants except R352E, suggesting that R352 does not itself form an anion coordination site. In an attempt to identify an acidic residue that may interact with R352, we found that permeation properties were similarly affected by charge-reversing mutations at D993. Wild-type-like properties were rescued in R352E/D993R-CFTR, suggesting that R352 and D993 in the wild-type channel may interact to stabilize pore architecture. Finally, R352A-CFTR was sensitive to modification by externally applied MTSEA+, while wild-type and R352E/D993R-CFTR were not. These data suggest that R352 plays an important structural role in CFTR, perhaps reflecting its involvement in forming a salt bridge with residue D993.

Molecular and clinical features associated with CFTR gene rearrangements in Italian population: identification of a new duplication and recurrent deletions

Cystic fibrosis (CF) is mainly caused by small deletions or missense mutations in the CFTR gene. The CF mutation database lists more than 35 large rearrangements that may escape detection using polymerase chain reaction-base techniques. The Innogenetics assay, the denaturing high-performance liquid chromatography and sequencing screening showed a mutation detection rate of 92.6% in our population. We report here the results of multiplex ligation-dependent probe amplification (MLPA) screening for CFTR gene rearrangements, performed on the unidentified alleles of our CF patients. Our sample population consists of 692 non-related Italian CF patients (for a total of 1384 alleles), followed at CF Centres in the Lombardia Region. MLPA analysis was performed in 49 patients who still had one or two unidentified alleles (for a total of 52 unidentified alleles) after extensive analysis of CFTR gene. All patients who were studied had the classical form of CF. We characterized nine different deletions and a new duplication. The deletion of exons 22-23 (7/82) was the most frequent in our cohort. The search for deletion/duplications of the CFTR gene has made it possible to reach a 94.1% detection rate, with an improvement (1.6%) of the carrier detection rate in the Italian population.

Differential expression of gill Na+,K+-ATPase alpha- and beta-subunits, Na+,K+,2Cl- cotransporter and CFTR anion channel in juvenile anadromous and landlocked Atlantic salmon Salmo salar

This study examines changes in gill Na(+),K(+)-ATPase (NKA) alpha- and beta-subunit isoforms, Na(+),K(+),2Cl(-) cotransporter (NKCC) and cystic fibrosis transmembrane conductance regulator (CFTR I and II) in anadromous and landlocked strains of Atlantic salmon during parr-smolt transformation, and after seawater (SW) transfer in May/June. Gill NKA activity increased from February through April, May and June among both strains in freshwater (FW), with peak enzyme activity in the landlocked salmon being 50% below that of the anadromous fish in May and June. Gill NKA-alpha1b, -alpha3, -beta(1) and NKCC mRNA levels in anadromous salmon increased transiently, reaching peak levels in smolts in April/May, whereas no similar smolt-related upregulation of these transcripts occurred in juvenile landlocked salmon. Gill NKA-alpha1a mRNA decreased significantly in anadromous salmon from February through June, whereas alpha1a levels in landlocked salmon, after an initial decrease in April, remained significantly higher than those of the anadromous smolts in May and June. Following SW transfer, gill NKA-alpha1b and NKCC mRNA increased in both strains, whereas NKA-alpha1a decreased. Both strains exhibited a transient increase in gill NKA alpha-protein abundance, with peak levels in May. Gill alpha-protein abundance was lower in SW than corresponding FW values in June. Gill NKCC protein abundance increased transiently in anadromous fish, with peak levels in May, whereas a slight increase was observed in landlocked salmon in May, increasing to peak levels in June. Gill CFTR I mRNA levels increased significantly from February to April in both strains, followed by a slight, though not significant increase in May and June. CFTR I mRNA levels were significantly lower in landlocked than anadromous salmon in April/June. Gill CFTR II mRNA levels did not change significantly in either strain. Our findings demonstrates that differential expression of gill NKA-alpha1a, -alpha1b and -alpha3 isoforms may be important for potential functional differences in NKA, both during preparatory development and during salinity adjustments in salmon. Furthermore, landlocked salmon have lost some of the unique preparatory upregulation of gill NKA, NKCC and, to some extent, CFTR anion channel associated with the development of hypo-osmoregulatory ability in anadromous salmon.

Co-inheritance of a novel deletion of the entire SPINK1 gene with a CFTR missense mutation (L997F) in a family with chronic pancreatitis

Quantitative fluorescent multiplex PCR (QFM-PCR) was established in order to make possible the rapid and efficient mutational analysis of the pancreatic secretory trypsin inhibitor (SPINK1) gene. Using QFM-PCR, a novel heterozygous deletion encompassing the entire SPINK1 gene was identified in one of nine newly recruited French Caucasian families with chronic pancreatitis. The breakpoints were fully characterized and the approximately 30 kb deletion was termed c.1-15969_c.240+7702del30588bp. Whilst sequences with the potential to form non-B DNA structures were found to span both the 5' and 3' deletion breakpoints, the generation of this gross deletion is potentially explicable in terms of non-homologous end-joining facilitated by the presence of a 1-bp microhomology at the two ends. The SPINK1 gene deletion identified in the index patient was also detected in her affected father and paternal uncle but not in 50 healthy French Caucasians. Remarkably, in all three affected individuals, the SPINK1 deletion was found to be co-inherited with a heterozygous p.L997F missense mutation in the unlinked CFTR gene, a lesion previously reported to be associated with a variety of cystic fibrosis-related diseases including idiopathic pancreatitis. Given that the SPINK1 deletion constitutes a clear-cut disease-causing factor, it may be that the CFTR missense mutation acts as a disease modifier in the context of this particular family.

Functional analysis of pancreatitis-associated missense mutations in the pancreatic secretory trypsin inhibitor (SPINK1) gene

Variations in the SPINK1 gene (encoding pancreatic secretory trypsin inhibitor (PSTI)) are associated with chronic pancreatitis. We have recently determined the functional consequences of three missense mutations that occurred within the signal peptide sequence of PSTI by Western blotting analysis of wild-type and mutant PSTI expressed in Chinese hamster ovary cells. Here, this approach was extended to analyze seven missense mutations (p.N34S, p.G48E, p.D50E, p.Y54H, p.P55S, p.R65Q and p.R67C) occurring within the mature peptide of PSTI. This analysis enabled us to classify these missense mutations into three categories. The first category comprises the p.N34S and p.P55S polymorphisms, both of which occur in evolutionarily non-conserved residues, involve amino-acid substitutions with similar physicochemical properties, and do not cause any significant reduction in terms of PSTI mature peptide expression. The second category contains only the p.R65Q missense mutation, which occurs in a well-conserved residue, involves the substitution of a positively charged amino acid by a non-charged one, and causes a approximately 60% reduction of protein expression. The third category comprises p.G48E, p.D50E, p.Y54H, and p.R67C, all of which occur in strictly conserved residues, involve charged amino acids, and cause complete or nearly complete loss of PSTI expression. Having excluded the possibility that the reduced protein expression may have resulted from reduced transcription or unstable mRNA, we surmise that these missense mutations probably cause intracellular retention of their respective mutant proteins. This is suggestive of a potential unifying pathological mechanism underlying both the signal peptide and mature peptide mutations.

Variation in salinity tolerance, gill Na+/K+-ATPase,Na+/K+/2Cl– cotransporter and mitochondria-rich cell distribution in three salmonids Salvelinus namaycush, Salvelinus fontinalis and Salmo salar

We compared seawater tolerance, gill Na+/K+-ATPase and Na+/K+/2Cl– cotransporter (NKCC)abundance, and mitochondria-rich cell (MRC) morphology of three salmonids,lake trout Salvelinus namaycush, brook trout Salvelinus fontinalis and Atlantic salmon Salmo salar. They were transferred directly from 0 p.p.t. (parts per thousand; freshwater) to 30 p.p.t. seawater, or transferred gradually from 0 to 10, 20 and 30 p.p.t. at 1-week intervals and kept in 30 p.p.t. for 3 weeks. The survival rates of lake trout, brook trout and Atlantic salmon were 80%, 50% and 100% following direct transfer, and 80%, 100% and 100% during gradual transfer, respectively. Plasma Na+, K+ and Cl– concentrations in surviving lake trout increased rapidly and remained at high levels in 30 p.p.t. of both direct and gradual transfer, whereas those in brook trout showed a transient increase following direct transfer but did not change significantly during gradual transfer. Only minor changes in plasma ions were observed in Atlantic salmon smolts in both direct and gradual transfer. These results suggest that lake trout retains some degree of euryhalinity and that brook trout possesses intermediate euryhalinity between lake trout and Atlantic salmon smolts. Gill Na+/K+-ATPase activity of lake trout and brook trout increased in seawater, whereas that of Atlantic salmon smolts was already upregulated in freshwater and remained high after seawater exposure. NKCC abundance was upregulated in parallel with gill Na+/K+-ATPase activity in each species. Immunocytochemistry with anti-Na+/K+-ATPaseα-subunit and anti-NKCC revealed that the two ion transporters were colocalized on the basolateral membrane of gill MRCs. Immunopositive MRCs were distributed on both primary filaments and secondary lamellae in all three species kept in freshwater; following transfer to seawater this pattern did not change in lake trout and brook trout but lamellar MRCs disappeared in Atlantic salmon. Previous studies on several teleost species have suggested that filament and lamellar MRCs would be involved in seawater and freshwater acclimation, respectively. However, our results in lake trout and brook trout suggest that lamellar MRCs could be also functional during seawater acclimation.

Molecular characterization of the cystic fibrosis transmembrane conductance regulator gene in congenital absence of the vas deferens

PURPOSE

Approximately 20% of patients with congenital absence of the vas deferens remain without two mutations identified. We applied a strategy of serial screening steps to 45 patients with congenital absence of the vas deferens and characterized cystic fibrosis transmembrane conductance regulator gene mutations in all cases.

METHODS

DNA samples of 45 patients with congenital absence of the vas deferens were screened by successive different molecular genetics approaches.

RESULTS

Initial screening for the 31 most frequent cystic fibrosis mutations, IVS8 poly(TG)m, poly(T)n, and M470V polymorphisms, identified 8 different mutations in 40 patients (88.9%). Extensive cystic fibrosis transmembrane conductance regulator gene analysis by denaturing gradient gel electrophoresis, denaturing high-performance liquid chromatography, and DNA sequencing detected 17 further mutations, of which three were novel. Cystic fibrosis transmembrane conductance regulator gene rearrangements were searched by semiquantitative fluorescent multiplex polymerase chain reaction, which detected a CFTRdele2,3 (21 kb) large deletion and confirmed two homozygous mutations. Overall, 42 patients (93.3%) had two mutations and 3 patients (6.7%) had one mutation detected.

CONCLUSIONS

The present screening strategy allowed a higher mutation detection rate than previous studies, with at least one cystic fibrosis transmembrane conductance regulator gene mutation found in all patients with congenital absence of the vas deferens.

The ichthyotoxic alga Chattonella marina induces Na+, K+ -ATPase, and CFTR proteins expression in fish gill chloride cells in vivo

Our previous studies demonstrated that the ichthyotoxic Chattonella marina stimulated proliferation of branchial chloride cell (CC) and induced osmotic distress akin to hyperactive elimination of ions in fish (Rhabdosargus sarba). To ascertain the in vivo effects of C. marina on key CC ion transporters, the localization and expression of Na(+), K(+)-ATPase (NKA) and cystic fibrosis transmembrane conductance regulator (CFTR) proteins in response to C. marina exposure were investigated, using a quantitative immunocytochemical approach. The polarized distributions of NKA (alpha subunit) and CFTR proteins in branchial CCs of R. sarba remained unchanged under C. marina exposure. However, significant inductions of these two ion-transporters were detected in CCs of fish after 6h exposure. By real-time PCR, no significant changes in gill NKA and CFTR mRNA expressions were detected, suggesting a post-transcriptional pathway is likely involved in regulating the ion transporters abundance. This study is the first to demonstrate the in vivo effects of harmful algal toxin on NKA and CFTR protein expressions in gill transepithelial cells. Taken together, an augmentation of branchial CCs together with hyper-stimulation of NKA and CFTR in CCs attribute to the rapid development of osmotic distress in C. marina susceptible fish.

Generation and characterization of rabbit embryonic stem cells

We described the derivation of four stable pluripotent rabbit embryonic stem cell (ESC) lines, one (RF) from blastocysts fertilized in vivo and cultured in vitro and three (RP01, RP02, and RP03) from parthenogenetic blastocysts. These ESC lines have been cultivated for extended periods (RF >1 year, RP01 >8 months, RP02 >8 months, and RP03 >6 months) in vitro while maintaining expression of pluripotent ESC markers and a normal XY or XX karyotype. The ESCs from all lines expressed alkaline phosphatase, transcription factor Oct-4, stage-specific embryonic antigens (SSEA-1, SSEA-3, and SSEA-4), and the tumor-related antigens (TRA-1-60 and TRA-1-81). Similar to human and mouse ESCs, rabbit ESCs expressed pluripotency (Oct-4, Nanog, SOX2, and UTF-1) and signaling pathway genes (fibroblast growth factor, WNT, and transforming growth factor pathway). Morphologically, rabbit ESCs resembled primate ESCs, whereas their proliferation characteristics were more like those seen in mouse ESCs. Rabbit ESCs were induced to differentiate into many cell types in vitro and formed teratomas with derivatives of the three major germ layers in vivo when injected into severe combined immunodeficient mice. Our results showed that pluripotent, stable ESC lines could be derived from fertilized and parthenote-derived rabbit embryos.

The role of aquaporin 3 in teleost fish

The aquaporin isoform, AQP3 has now been identified in a number of different teleost fish species, with additional DNA sequence information on AQP3 genes in further fish species available in genome databases. In zebrafish (Danio rerio), the AQP3 gene is present as two duplicate isoforms resulting from a teleostean fish genome-wide duplication. A further splicoform/isoform has also been identified in rainbow trout (Oncorhynchus mykiss). The identification of these AQP3 isoforms in other fish species is consequently explored. The role of AQP3 in physiological/osmoregulatory processes, in various teleost organs is then described. In teleost gill, AQP3 is expressed in 'chloride' cells, and in some species, in other epithelial cell types, where it may have a number of different functions including the prevention of dehydration. In eel esophagus, immunohistochemistry shows that AQP3 is expressed in surface epithelial cells in the anterior esophagus, but in mucus cells within the epithelium of the posterior esophagus. In eel intestine, AQP3 is found in macrophage-like cells and probably plays no part in osmoregulatory processes. In the rectum, as in the posterior esophagus AQP3 is expressed in mucus cells. In eel kidney, AQP3 is expressed in a subset of renal tubules, and localizes to the apical pole of tubule cells. There is no apparent change in the location or protein abundance of renal AQP3 following the acclimation of eels from freshwater to seawater.

Extensive Sequencing of the CFTR gene: lessons learned from the first 157 patient samples

Cystic fibrosis (CF) is one of the most common monogenic diseases affecting Caucasians and has an incidence of approximately 1:3,300 births. Currently recommended screening panels for mutations in the responsible gene (CF transmembrane regulator gene, CFTR) do not detect all disease-associated mutations. Our laboratory offers extensive sequencing of the CFTR (ABCC7) gene (including the promoter, all exons and splice junction sites, and regions of selected introns) as a clinical test to detect mutations which are not found with conventional screening. The objective of this report is to summarize the findings of extensive CFTR sequencing from our first 157 consecutive patient samples. In most patients with classic CF symptoms (18/24, 75%), extensive CFTR sequencing confirmed the diagnosis by finding two disease-associated mutations. In contrast, only 5 of 75 (7%) patients with atypical CF had been identified with two CFTR mutations. A diagnosis of CF was confirmed in 10 of 17 (58%) newborns with either positive sweat chloride readings or positive immunoreactive trypsinogen (IRT) screen results. We ascertained ten novel sequence variants that are potentially disease-associated: two deletions (c.1641AG>T, c.2949_2853delTACTC), seven missense mutations (p.S158T, p.G451V, p.K481E, p.C491S, p.H949L, p.T1036N, p.F1099L), and one complex allele ([p.356_A357del; p.358I]). We ascertained three other apparently novel complex alleles. Finally, several patients were found to carry partial CFTR gene deletions. In summary, extensive CFTR gene sequencing can detect rare mutations which are not found with other screening and diagnostic tests, and can thus establish a definitive diagnosis in symptomatic patients with previously negative results. This enables carrier detection and prenatal diagnosis in additional family members.

A novel missense mutation P1290S at exon-20 of the CFTR gene in a Portuguese patient with congenital bilateral absence of the vas deferens

OBJECTIVE

To report a novel cystic fibrosis transmembrane conductance regulator (CFTR) gene missense mutation in a compound heterozygote with congenital bilateral absence of the vas deferens (CBAVD).

DESIGN

Descriptive, controlled study.

SETTING

Tertiary academic hospital genetics laboratory and private in vitro fertilization (IVF) clinic.

PATIENT(S)

One 46-year-old man with CBAVD and no clinical cystic fibrosis (CF) phenotype as indicated by the advanced age at diagnosis, absence of chronic airways and gastrointestinal disease, and normal pancreatic function and sweat chloride concentration. Genomic blood DNA from the patient's parents was analyzed to perform family studies, and 109 fertile men, 32 patients with CBAVD, 15 children carriers of one CFTR mutation, and 5 patients with CF were used to rule out polymorphism.

INTERVENTION(S)

Clinical evaluation and treatment, genetical screenings.

MAIN OUTCOME MEASURE(S)

Clinical data, biochemical assays, spermiogram analysis, testicle biopsy, intracytoplasmic sperm injection (ICSI) outcome, and CFTR whole gene mutation screening and IVS8T polymorphism.

RESULT(S)

The DNA analysis revealed a 7T/7T homozygote at IVS8-T, with a 4000C-->T change (P1290S) in exon 20 of the CFTR gene, which was inherited from the patient's father. It was associated with a 3272-26A-->G mutation in the other allele that was inherited from his mother.

CONCLUSION(S)

The novel P1290S missense CFTR mutation causes an amino acid change in a highly conserved region of the CFTR protein that controls channel opening. Pathogenicity is suggested by development of CBAVD in association with a mild CFTR mutation.

A neutral variant involved in a complex CFTR allele contributes to a severe cystic fibrosis phenotype

In order to further elucidate the contribution of complex alleles to the wide phenotypic variability of cystic fibrosis (CF), we investigated the structure-function relationships of a severe CF-associated complex allele [p.S912L;p.G1244V]. To evaluate the contribution of each mutation to the phenotype, cystic fibrosis transmembrane conductance regulator (CFTR) mutants were expressed in HeLa cells and analysed for protein processing and Cl- channel activity. Both p.G1244V and [p.S912L;p.G1244V] mutants had normal protein processing but markedly decreased Cl- channel activity compared with wild-type. Notably, the double mutant displayed a dramatic decrease in Cl- channel activity compared with p.G1244V (P<0.001). p.S912L had normal protein processing and no detectable impact on CFTR function. In other respects, the p.S912L variation was identified in compound heterozygosity with p.R709X in a healthy fertile man. Together, these data strongly support the view that p.S912L in isolation should be considered as a neutral variant but one that might significantly impair CFTR function when inherited in cis with another CFTR mutation. Our data also further document the contribution of complex alleles to the wide phenotypic variability of CF. The results of functional studies of such complex alleles in other genetic diseases are discussed.

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.

Molecular biology of ion motive proteins in comparative models

This article will review the utility of comparative animal models in understanding the molecular biology of ion transport. Due to the breadth of this field some 'disclaimers' need to be established up front. 'Comparative' will be defined as non-mammalian. 'Genetic species' will be defined as organisms that have been selected as models for genetic studies and for which the genome has been largely sequenced. 'Non-genetic species' will include other non-mammalian organisms. The review will be limited to ions that play a major role in extracellular (EC) ionoregulation (Na/K/Ca/Cl) and not to micronutrients (Fe) or heavy metals (Cd, Zn). The review will focus only on ion motive proteins that have been associated with vectorial transfer at epithelial tissues. The review is therefore intended as a guidepost to researchers new to the field as well as to inform biologists of the power of comparative genomics.

Destabilization of the transmembrane domain induces misfolding in a phenotypic mutant of cystic fibrosis transmembrane conductance regulator

Two phenotypic missense mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) channel pore (L346P and R347P in transmembrane (TM) segment 6) involve gain of a proline residue, but only L346P represents a significant loss of segment hydropathy. We show here that, for synthetic peptides corresponding to sequences of CFTR TM6 segments, circular dichroism spectra of wild type and R347P TM6 in membrane mimetic environments are virtually identical, but L346P loses approximately 50% helicity, implying a membrane insertion defect in the latter mutant. A similar defect was observed in the corresponding double-spanning ("hairpin") TM5/6-L346P synthetic peptide. Examination of the biogenesis of CFTR revealed that the full-length protein harboring the L346P mutation is rapidly degraded at the endoplasmic reticulum (ER), whereas the wild type and the R347P protein process normally. Furthermore, a second site mutation (R347I) that restores in vitro membrane insertion and folding of the TM5/6-L346P peptide also rescues the folding and cell surface chloride channel function of full-length L346P CFTR. The correlated in vitro/in vivo results demonstrate that destabilizing local hydrophobic character represents a sufficient signal for marking CFTR as a non-native protein by the ER quality control, with accompanying deleterious consequences to global protein folding events.

Genomic rearrangements in the CFTR gene: extensive allelic heterogeneity and diverse mutational mechanisms

Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR/ABCC7). Despite the extensive and enduring efforts of many CF researchers over the past 14 years, up to 30% of disease alleles still remain to be identified in some populations. It has long been suggested that gross genomic rearrangements could account for these unidentified alleles. To date, however, only a few large deletions have been found in the CFTR gene and only three have been fully characterized. Here, we report the first systematic screening of the 27 exons of the CFTR gene for large genomic rearrangements, by means of the quantitative multiplex PCR of short fluorescent fragments (QMPSF). A well-characterized cohort of 39 classical CF patients carrying at least one unidentified allele (after extensive and complete screening of the CFTR gene by both denaturing gradient gel electrophoresis and denaturing high-performance liquid chromatography) participated in this study. Using QMPSF, some 16% of the previously unidentified CF mutant alleles were identified and characterized, including five novel mutations (one large deletion and four indels). The breakpoints of these five mutations were precisely determined, enabling us to explore the underlying mechanisms of mutagenesis. Although non-homologous recombination may be invoked to explain all five complex lesions, each mutation appears to have arisen through a different mechanism. One of the indels was highly unusual in that it involved the insertion of a short 41 bp sequence with partial homology to a retrotranspositionally-competent LINE-1 element. The insertion of this ultra-short LINE-1 element (dubbed a "hyphen element") may constitute a novel type of mutation associated with human genetic disease.

Mitochondria-rich cells as experimental model in studies of epithelial chloride channels

The mitochondria-rich (mr) cell of amphibian skin epithelium is differentiated as a highly specialised pathway for passive transepithelial transport of chloride. The apical membrane of mr cells expresses several types of Cl(-) channels, of which the function of only two types has been studied in detail. (i) One type of channel is gated by voltage and external chloride concentration. This intriguing type of regulation leads to opening of channels only if [Cl(-)](o) is in the millimolar range and if the electrical potential is of a polarity that secures an inwardly directed net flux of this ion. Reversible voltage activations of the conductance proceed with long time constants, which depend on V in such a way that the rate of conductance activation increases when V is clamped at more negative values (serosal bath grounded). The gating seems to involve processes that are dependent on F-actin localised in the submembrane domain in the neck region of the flask-shaped mr cell. (ii) The other identified Cl(-) pathway of mr cells is mediated by small-conductance apical CFTR chloride channels as concluded from its activation via beta-adrenergic receptors, ion selectivity, genistein stimulation and inhibition by glibenclamide. bbCFTR has been cloned, and immunostaining has shown that the gene product is selectively expressed in mr cells. There is cross-talk between the two pathways in the sense that activation of the conductance of the mr cell by voltage clamping excludes activation via receptor occupation, and vice versa. The mechanism of this cross-talk is unknown.

Cystic fibrosis transmembrane conductance regulator in teleost fish

The gills and intestinal epithelia of teleost fish express cystic fibrosis transmembrane conductance regulator (CFTR), and utilize this low conductance anion channel in the apical membrane for ion secretion in seawater gill and in the basolateral membrane for ion absorption in freshwater gill. Similarly, in the intestine CFTR is present in the basolateral membrane for intestinal absorption and also in the apical membrane of secreting intestine. The expression of CFTR and the directed trafficking of the protein to the apical or basolateral membrane is salinity-dependent. The CFTR gene has been cloned and sequenced from several teleost species and although all the major elements in the human gene are present, including two nucleotide binding domains that are common to all ATP binding cassette (ABC) transporters, the sequences are divergent compared to shark or human. In euryhaline fish adapting to seawater, CFTR, localized immunocytochemically, redistributes slowly from a basolateral location to the apical membrane while ion secretory capacity increases. The facility with which teleosts regulate CFTR expression and activation during salinity adaptation make this system an appealing model for the expression and trafficking operation of this labile gene product.

The I148T CFTR allele occurs on multiple haplotypes: a complex allele is associated with cystic fibrosis

PURPOSE

To determine whether intragenic changes modulate the cystic fibrosis (CF) phenotype in individuals who are positive for the I148T allele.

METHODS

The genes from individuals who carried at least one copy of the I148T allele were analyzed for additional changes that may be acting as genetic modifiers.

RESULTS

Seven of eight individuals with a known or suspected diagnosis of CF who carried I148T in combination with a severe CF mutation also carried 3199del6. Eight apparently healthy adult individuals who were compound heterozygous for I148T and a severe CF mutation or homozygous for I148T did not carry the deletion ( = 0.0014). The I148T allele occurs on at least three haplotypes: an IVS-8 9T background, a 7T background, or a 9T + 3199del6 background. The 3199del6 allele was not identified in 386 non-CF chromosomes.

CONCLUSIONS

It is concluded that I148T occurs on at least three haplotypes and the complex allele I148T + 9T + 3199del6 is associated with a classic CF phenotype.

Na(+), Cl(-), Ca(2+) and Zn(2+) transport by fish gills: retrospective review and prospective synthesis

The secondary active Cl(-) secretion in seawater (SW) teleost fish gills and elasmobranch rectal gland involves basolateral Na(+),K(+)-ATPase and NKCC, apical membrane CFTR anion channels, and a paracellular Na(+)-selective conductance. In freshwater (FW) teleost gill, the mechanism of NaCl uptake is more controversial and involves apical V-type H(+)-ATPase linked to an apical Na(+) channel, apical Cl(-)-HCO-3 exchange and basolateral Na(+),K(+)-ATPase. Ca(2+) uptake (in FW and SW) is via Ca(2+) channels in the apical membrane and Ca(2+)-ATPase in the basolateral membrane. Mainly this transport occurs in mitochondria rich (MR) chloride cells, but there is a role for the pavement cells also. Future research will likely expand in two major directions, molded by methodology: first in physiological genomics of all the transporters, including their expression, trafficking, operation, and regulation at the molecular level, and second in biotelemetry to examine multivariable components in behavioral physiological ecology, thus widening the integration of physiology from the molecular to the environmental levels while deepening understanding at all levels.

Biochemical implications of sequence comparisons of the cystic fibrosis transmembrane conductance regulator

The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel that is both of medical significance in humans and of interest with regard to osmoregulation in aquatic organisms. CFTR is composed of five domains: two membrane-spanning domains, two nucleotide-binding domains, and a regulatory domain. Notwithstanding the plethora of information concerning the structure and function of CFTR, the biochemistry of many facets of CFTR are not completely understood. In this regard, we have performed a sequence alignment of representative vertebrate CFTR with the aim of generating hypotheses on the functional significance of conserved and variable residues. Postulates on function common to all organisms are: (i) Thr338 in the sixth transmembrane segment could have a function related to that of the pore-lining residue Lys335, and it is possible that Thr338 hydrogen bonds to Lys335, thus indirectly affecting anion permeability; (ii) the fragment (111)PDNKE could be an ion sensor; (iii) motifs in the two nucleotide-binding domains reflect differential ATP binding and hydrolysis; and (iv) an interaction in the R domain involving (765)RRQSVL and the C terminal end of the domain results in an inhibitory conformation. Major adaptations in fishes include variations in the postulated ion sensor (111)PDNKE, and the absence of a proline residue in the R domain with consequent higher chloride efflux.

Cloned rabbits produced by nuclear transfer from adult somatic cells

We have developed a method to produce live somatic clones in the rabbit, one of the mammalian species considered up to now as difficult to clone. To do so, we have modified current cloning protocols proven successful in other species by taking into account both the rapid kinetics of the cell cycle of rabbit embryos and the narrow window of time for their implantation after transfer into foster recipients. Although our method still has a low level of efficiency, it has produced several clones now proven to be fertile. Our work indicates that cloning can probably be carried out successfully in any mammalian species by taking into account physiological features of their oocytes and embryos. Our results will contribute to extending the use of rabbit models for biomedical research.

Determination of the relative contribution of three genes-the cystic fibrosis transmembrane conductance regulator gene, the cationic trypsinogen gene, and the pancreatic secretory trypsin inhibitor gene-to the etiology of idiopathic chronic pancreatitis

In the last 5 years, mutations in three genes, the cystic fibrosis transmembrane conductance regulator (CFTR) gene, the cationic trypsinogen (PRSS1) gene, and the pancreatic secretory trypsin inhibitor (PSTI) gene, have been found to be associated with chronic pancreatitis (CP). In this study, using established mutation screening methods, we systematically analysed the entire coding sequences and all exon/intron junctions of the three genes in 39 patients with idiopathic CP (ICP), with a view to evaluating the relative contribution of each gene to the aetiology of the disease. Our results demonstrate that, firstly, 'gain-of-function' mutations in the PRSS1 gene may occasionally be found in an obvious ICP subject. Secondly, presumably 'loss-of-function' mutations in the PSTI gene appear to be frequent, with a detection rate of at least 10% in ICP and, finally, abnormal CFTR alleles are common: at least 20% of patients carried one of the most common CFTR mutations, and about 10% of patients were compound heterozygotes, having at least one 'mild' allele. Thus, in total, about 30% of ICP patients carried at least one abnormal allele in one of the three genes, and this is the most conservative estimate. Moreover, a trans-heterozygous state with sequence variations in the PSTI/CFTR genes was found in three patients. However, an association between the 5T allele in intron 8 of the CFTR gene and ICP remains unproven.

How should salinity influence fish growth?

Development and growth (continuous in fish) are controlled by 'internal factors' including CNS, endocrinological and neuroendocrinological systems. Among vertebrates, they also are highly dependent on environmental conditions. Among other factors, many studies have reported an influence of water salinity on fish development and growth. In most species, egg fertilization and incubation, yolk sac resorption, early embryogenesis, swimbladder inflation, larval growth are dependent on salinity. In larger fish, salinity is also a key factor in controlling growth. Do the changes in growth rate, that depend on salinity, result from an action on: (1) standard metabolic rate; (2) food intake; (3) food conversion; and/or (4) hormonal stimulation? Better growth at intermediate salinities (8-20 psu) is very often, but not systematically, correlated to a lower standard metabolic rate. Numerous studies have shown that 20 to >50% of the total fish energy budget are dedicated to osmoregulation. However, recent ones indicate that the osmotic cost is not as high (roughly 10%) as this. Data are also available in terms of food intake and stimulation of food conversion, which are both dependent on the environmental salinity. Temperature and salinity have complex interactions. Many hormones are known to be active in both osmoregulation and growth regulation, e.g. in the control of food intake. All of these factors are reviewed. As often, multiple causality is likely to be at work and the interactive effects of salinity on physiology and behaviour must also be taken into account.