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author:("amsler, Serge")
1.  Clinical and molecular findings in a Moroccan patient with popliteal pterygium syndrome: a case report 
Introduction
Popliteal pterygium syndrome is a congenital malformation that includes orofacial, musculoskeletal and genitourinary anomalies. It is a rare autosomal dominant disorder due to a mutation of the IRF6 gene on 1q32.2.
Case presentation
A one-month-old Moroccan baby boy was diagnosed with typical features of popliteal pterygium syndrome and carried the c.250C>T; p.Arg84Cys mutation of the IRF6 gene.
Conclusions
We report on the first description of a Moroccan popliteal pterygium syndrome patient. This diagnosis allowed us to provide an appropriate course of management to the patient and offer genetic counseling to his family.
doi:10.1186/1752-1947-8-471
PMCID: PMC4320515  PMID: 25547932
Popliteal pterygium syndrome; Autosomal dominant; IRF6 gene
2.  Proteomic Analysis of Nasal Epithelial Cells from Cystic Fibrosis Patients 
PLoS ONE  2014;9(9):e108671.
The pathophysiology of cystic fibrosis (CF) lung disease remains incompletely understood. New explanations for the pathogenesis of CF lung disease may be discovered by studying the patterns of protein expression in cultured human nasal epithelial cells (HNEC). To that aim, we compared the level of protein expressions in primary cultures of HNEC from nasal polyps secondary to CF (CFNP, n = 4), primary nasal polyps (NP, n = 8) and control mucosa (CTRL, n = 4) using isobaric tag for relative and absolute quantification (iTRAQ) labeling coupled with liquid chromatography (LC)-MS-MS. The analysis of the data revealed 42 deregulated protein expressions in CFNP compared to NP and CTRL, suggesting that these alterations are related to CF. Overall, AmiGo analysis highlighted six major pathways important for cell functions that seem to be impaired: metabolism, G protein process, inflammation and oxidative stress response, protein folding, proteolysis and structural proteins. Among them, glucose and fatty acid metabolic pathways could be impaired in CF with nine deregulated proteins. Our proteomic study provides a reproducible set of differentially expressed proteins in airway epithelial cells from CF patients and reveals many novel deregulated proteins that could lead to further studies aiming to clarify the involvement of such proteins in CF pathophysiology.
doi:10.1371/journal.pone.0108671
PMCID: PMC4182543  PMID: 25268127
3.  The role of GHR and IGF1 genes in the genetic determination of African pygmies' short stature 
African pygmies are at the lower extreme of human variation in adult stature and many evolutionary hypotheses have been proposed to explain this phenotype. We showed in a recent study that the difference in average stature of about 10 cm observed between contemporary pygmies and neighboring non-pygmies has a genetic component. Nevertheless, the genetic basis of African pygmies' short stature remains unknown. Using a candidate-gene approach, we show that intronic polymorphisms in GH receptor (GHR) and insulin-like growth factor 1 (IGF1) genes present outlying values of the genetic distance between Baka pygmies and their non-pygmy Nzimé neighbors. We further show that GHR and IGF1 genes have experienced divergent natural selection pressures between pygmies and non-pygmies throughout evolution. In addition, these SNPs are associated with stature in a sample composed of 60 pygmies and 30 non-pygmies and this association remains significant when correcting for population structure for the GHR locus. We conclude that the GHR and IGF1 genes may have a role in African pygmies' short stature. The use of phenotypically contrasted populations is a promising strategy to identify new variants associated with complex traits in humans.
doi:10.1038/ejhg.2012.223
PMCID: PMC3658195  PMID: 23047741
pygmies; height; human evolution
4.  Involvement of the Same TNFR1 Residue in Mendelian and Multifactorial Inflammatory Disorders 
PLoS ONE  2013;8(7):e69757.
Objectives
TNFRSF1A is involved in an autosomal dominant autoinflammatory disorder called TNFR-associated periodic syndrome (TRAPS). Most TNFRSF1A mutations are missense changes and, apart from those affecting conserved cysteines, their deleterious effect remains often questionable. This is especially true for the frequent R92Q mutation, which might not be responsible for TRAPS per se but represents a susceptibility factor to multifactorial inflammatory disorders. This study investigates TRAPS pathophysiology in a family exceptional by its size (13 members) and compares the consequences of several mutations affecting arginine 92.
Methods
TNFRSF1A screening was performed by PCR-sequencing. Comparison of the 3-dimensional structure and electrostatic properties of wild-type and mutated TNFR1 proteins was performed by in silico homology modeling. TNFR1 expression was assessed by FACS analysis, western blotting and ELISA in lysates and supernatants of HEK293T cells transiently expressing wild-type and mutated TNFR1.
Results
A TNFRSF1A heterozygous missense mutation, R92W (c.361C>T), was shown to perfectly segregate with typical TRAPS manifestations within the family investigated (p<5.10−4). It was associated with very high disease penetrance (0.9). Prediction of its impact on the protein structure revealed local conformational changes and alterations of the receptor electrostatic properties. R92W also impairs the TNFR1 expression at the cell surface and the levels of soluble receptor. Similar results were obtained with R92P, another mutation previously identified in a very small familial form with incomplete penetrance and variable expressivity. In contrast, TNFR1-R92Q behaves like the wild-type receptor.
Conclusions
These data demonstrate the pathogenicity of a mutation affecting arginine 92, a residue whose involvement in inflammatory disorders is deeply debated. Combined with previous reports on arginine 92 mutations, this study discloses an unusual situation in which different amino acid substitutions at the same position in the protein are associated with a clinical spectrum bridging Mendelian to multifactorial conditions.
doi:10.1371/journal.pone.0069757
PMCID: PMC3722142  PMID: 23894535
5.  The Risk of Familial Mediterranean Fever in MEFV Heterozygotes: A Statistical Approach 
PLoS ONE  2013;8(7):e68431.
Background
Familial Mediterranean fever (FMF) is an autosomal recessive autoinflammatory disorder due to MEFV mutations and one of the most frequent Mediterranean genetic diseases. The observation of many heterozygous patients in whom a second mutated allele was excluded led to the proposal that heterozygosity could be causal. However, heterozygosity might be coincidental in many patients due to the very high rate of mutations in Mediterranean populations.
Objective
To better delineate the pathogenicity of heterozygosity in order to improve genetic counselling and disease management.
Methods
Complementary statistical approaches were used: estimation of FMF prevalence at population levels, genotype comparison in siblings from 63 familial forms, and genotype study in 557 patients from four Mediterranean populations.
Results
At the population level, we did not observe any contribution of heterozygosity to disease prevalence. In affected siblings of patients carrying two MEFV mutations, 92% carry two mutated alleles, whereas 4% are heterozygous with typical FMF diagnosis. We demonstrated statistically that patients are more likely to be heterozygous than healthy individuals, as shown by the higher ratio heterozygous carriers/non carriers in patients (p<10−7–p<0.003). The risk for heterozygotes to develop FMF was estimated between 2.1×10−3 and 5.8×10−3 and the relative risk, as compared to non carriers, between 6.3 and 8.1.
Conclusions
This is the first statistical demonstration that heterozygosity is not responsible for classical Mendelian FMF per se, but constitutes a susceptibility factor for clinically-similar multifactorial forms of the disease. We also provide a first estimate of the risk for heterozygotes to develop FMF.
doi:10.1371/journal.pone.0068431
PMCID: PMC3700951  PMID: 23844200
6.  Genomic imbalances detected by array-CGH in patients with syndromal ocular developmental anomalies 
In 65 patients, who had unexplained ocular developmental anomalies (ODAs) with at least one other birth defect and/or intellectual disability, we performed oligonucleotide comparative genome hybridisation-based microarray analysis (array-CGH; 105A or 180K, Agilent Technologies). In four patients, array-CGH identified clinically relevant deletions encompassing a gene known to be involved in ocular development (FOXC1 or OTX2). In four other patients, we found three pathogenic deletions not classically associated with abnormal ocular morphogenesis, namely, del(17)(p13.3p13.3), del(10)(p14p15.3), and del(16)(p11.2p11.2). We also detected copy number variations of uncertain pathogenicity in two other patients. Rearranged segments ranged in size from 0.04 to 5.68 Mb. These results show that array-CGH provides a high diagnostic yield (15%) in patients with syndromal ODAs and can identify previously unknown chromosomal regions associated with these conditions. In addition to their importance for diagnosis and genetic counselling, these data may help identify genes involved in ocular development.
doi:10.1038/ejhg.2011.233
PMCID: PMC3330214  PMID: 22234157
ocular developmental anomaly; array-CGH; OTX2; FOXC1; 16p11.2 deletion; YWHAE
7.  Molecular and cellular characteristics of ABCA3 mutations associated with diffuse parenchymal lung diseases in children 
Human Molecular Genetics  2011;21(4):765-775.
ABCA3 (ATP-binding cassette subfamily A, member 3) is expressed in the lamellar bodies of alveolar type II cells and is crucial to pulmonary surfactant storage and homeostasis. ABCA3 gene mutations have been associated with neonatal respiratory distress (NRD) and pediatric interstitial lung disease (ILD). The objective of this study was to look for ABCA3 gene mutations in patients with severe NRD and/or ILD. The 30 ABCA3 coding exons were screened in 47 patients with severe NRD and/or ILD. ABCA3 mutations were identified in 10 out of 47 patients, including 2 homozygous, 5 compound heterozygous and 3 heterozygous patients. SP-B and SP-C expression patterns varied across patients. Among patients with ABCA3 mutations, five died shortly after birth and five developed ILD (including one without NRD). Functional studies of p.D253H and p.T1173R mutations revealed that p.D253H and p.T1173R induced abnormal lamellar bodies. Additionally, p.T1173R increased IL-8 secretion in vitro. In conclusion, we identified new ABCA3 mutations in patients with life-threatening NRD and/or ILD. Two mutations associated with ILD acted via different pathophysiological mechanisms despite similar clinical phenotypes.
doi:10.1093/hmg/ddr508
PMCID: PMC3263986  PMID: 22068586
8.  CCDC39 is required for assembly of inner dynein arms and the dynein regulatory complex and for normal ciliary motility in humans and dogs 
Nature genetics  2010;43(1):72-78.
Primary ciliary dyskinesia (PCD) is an inherited disorder characterized by recurrent infections of the upper and lower respiratory tract, reduced fertility in males and situs inversus in about 50% of affected individuals (Kartagener syndrome). It is caused by motility defects in the respiratory cilia that are responsible for airway clearance, the flagella that propel sperm cells and the nodal monocilia that determine left-right asymmetry1. Recessive mutations that cause PCD have been identified in genes encoding components of the outer dynein arms, radial spokes and cytoplasmic pre-assembly factors of axonemal dyneins, but these mutations account for only about 50% of cases of PCD. We exploited the unique properties of dog populations to positionally clone a new PCD gene, CCDC39. We found that loss-of-function mutations in the human ortholog underlie a substantial fraction of PCD cases with axonemal disorganization and abnormal ciliary beating. Functional analyses indicated that CCDC39 localizes to ciliary axonemes and is essential for assembly of inner dynein arms and the dynein regulatory complex.
doi:10.1038/ng.726
PMCID: PMC3509786  PMID: 21131972
9.  Quantitative analysis of ciliary beating in primary ciliary dyskinesia: a pilot study 
Background
Primary ciliary dyskinesia (PCD) is a rare congenital respiratory disorder characterized by abnormal ciliary motility leading to chronic airway infections. Qualitative evaluation of ciliary beat pattern based on digital high-speed videomicroscopy analysis has been proposed in the diagnosis process of PCD. Although this evaluation is easy in typical cases, it becomes difficult when ciliary beating is partially maintained. We postulated that a quantitative analysis of beat pattern would improve PCD diagnosis. We compared quantitative parameters with the qualitative evaluation of ciliary beat pattern in patients in whom the diagnosis of PCD was confirmed or excluded.
Methods
Nasal nitric oxide measurement, nasal brushings and biopsies were performed prospectively in 34 patients with suspected PCD. In combination with qualitative analysis, 12 quantitative parameters of ciliary beat pattern were determined on high-speed videomicroscopy recordings of beating ciliated edges. The combination of ciliary ultrastructural abnormalities on transmission electron microscopy analysis with low nasal nitric oxide levels was the “gold standard” used to establish the diagnosis of PCD.
Results
This “gold standard” excluded PCD in 15 patients (non-PCD patients), confirmed PCD in 10 patients (PCD patients) and was inconclusive in 9 patients. Among the 12 parameters, the distance traveled by the cilium tip weighted by the percentage of beating ciliated edges presented 96% sensitivity and 95% specificity. Qualitative evaluation and quantitative analysis were concordant in non-PCD patients. In 9/10 PCD patients, quantitative analysis was concordant with the “gold standard”, while the qualitative evaluation was discordant with the “gold standard” in 3/10 cases. Among the patients with an inconclusive “gold standard”, the use of quantitative parameters supported PCD diagnosis in 4/9 patients (confirmed by the identification of disease-causing mutations in one patient) and PCD exclusion in 2/9 patients.
Conclusions
When the beat pattern is normal or virtually immotile, the qualitative evaluation is adequate to study ciliary beating in patients suspected for PCD. However, when cilia are still beating but with moderate alterations (more than 40% of patients suspected for PCD), quantitative analysis is required to precise the diagnosis and can be proposed to select patients eligible for TEM.
doi:10.1186/1750-1172-7-78
PMCID: PMC3562218  PMID: 23057704
Cilia; Electron microscopy; High-speed videomicroscopy; Kartagener syndrome; Nitric oxide
12.  Two Siblings with Isolated GH Deficiency Due to Loss−of−Function Mutation in the GHRHR Gene: Successful Treatment with Growth Hormone Despite Late Admission and Severe Growth Retardation 
Patients with growth hormone releasing hormone receptor (GHRHR) mutations exhibit pronounced dwarfism and are phenotypically and biochemically indistinguishable from other forms of isolated growth hormone deficiency (IGHD). We presented here two siblings with clinical findings of IGHD due to a nonsense mutation in the GHRHR gene who reached their target height in spite of late GH treatment. Two female siblings were admitted to our clinic with severe short stature at the age of 13.8 (patient 1) and 14.8 years (patient 2). On admission, height in patient 1 was 107 cm (−8.6 SD) and 117 cm (−6.7 SD) in patient 2. Bone age was delayed in both patients (6 years and 9 years). Clinical and biochemical analyses revealed a diagnosis of complete IGHD (peak GH levels on stimulation test was 0.06 ng/mL in patient 1 and 0.16 ng/mL in patient 2). Patients were given recombinant human GH treatment. Genetic analysis of the GH and GHRHR genes revealed that both patientscarried the GHRHR gene mutation p.Glu72X (c.214 G>T) in exon 3 in homozygous (or hemizygous) state. After seven years of GH treatment, the patients reached a final height appropriate for their target height. Final height was 151 cm (−1.5 SD) in patient 1 and 153 cm (−1.2 SD) in patient 2. In conclusion, genetic analysis is indicated in IGHD patients with severe growth failure and a positive family history. In spite of the very late diagnosis in these two patients who presented with severe growth deficit due to homozygous loss−of−function mutations in GHRHR, their final heights reached the target height.
Conflict of interest:None declared.
doi:10.4274/jcrpe.v2i4.164
PMCID: PMC3005690  PMID: 21274317
GHRHR mutation; final height; transition; GH deficiency
13.  Muco-ciliary differentiation of nasal epithelial cells is decreased after wound healing in vitro 
Allergy  2009;64(8):1136-1143.
Epithelial damage and modifications of cell differentiation are frequent in airway diseases with chronic inflammation, in which Transforming Growth Factor-β1 (TGF-β1) plays an important role. The aim of this study was to evaluate the differentiation of human nasal epithelial cells (HNEC) after wound healing and the potential effects of TGF-β1.
Basal, mucous and ciliated cells were characterized by cytokeratin-14, MUC5AC and βIVtubulin immunodetection, respectively. Their expression was evaluated in situ in nasal polyps and in an in vitro model of wound healing in primary cultures of HNEC after wound closure, under basal conditions and after TGF-β1 supplementation. Using RT-PCR, the effects of TGF-β1 on MUC5AC and DNAI1 genes, specifically transcribed in mucous and ciliated cells, were evaluated.
In situ, high TGF-β1 expression was associated with low MUC5AC and βIVtubulin expression. In vitro, under basal conditions, MUC5AC expression remained stable, cytokeratin-14 expression was strong and decreased with time, while βIV tubulin expression increased. TGF-β1 supplementation down-regulated MUC5AC and βIV tubulin expression as well as MUC5AC and DNAI1 transcripts.
After a wound, differentiation into mucous and ciliated cells was possible and partially inhibited in vitro by TGF-β1, a cytokine that may be involved in epithelial remodeling observed in chronic airway diseases.
doi:10.1111/j.1398-9995.2009.02003.x
PMCID: PMC2846321  PMID: 19245428
Axonemal Dyneins; Cell Differentiation; drug effects; Cells, Cultured; Cilia; metabolism; Down-Regulation; Dyneins; metabolism; Epithelial Cells; cytology; metabolism; Humans; Keratin-14; metabolism; Mucin 5AC; genetics; metabolism; Mucins; metabolism; Nasal Mucosa; cytology; metabolism; Nasal Polyps; metabolism; pathology; Transforming Growth Factor beta1; metabolism; pharmacology; Tubulin; metabolism; Wound Healing; ciliated cells; human nasal epithelial differentiation; mucous cells; TGF-beta 1; wound healing
14.  Involvement of the Modifier Gene of a Human Mendelian Disorder in a Negative Selection Process 
PLoS ONE  2009;4(10):e7676.
Background
Identification of modifier genes and characterization of their effects represent major challenges in human genetics. SAA1 is one of the few modifiers identified in humans: this gene influences the risk of renal amyloidosis (RA) in patients with familial Mediterranean fever (FMF), a Mendelian autoinflammatory disorder associated with mutations in MEFV. Indeed, the SAA1 α homozygous genotype and the p.Met694Val homozygous genotype at the MEFV locus are two main risk factors for RA.
Methodology/Principal Findings
Here, we investigated Armenian FMF patients and controls from two neighboring countries: Armenia, where RA is frequent (24%), and Karabakh, where RA is rare (2.5%). Sequencing of MEFV revealed similar frequencies of p.Met694Val homozygotes in the two groups of patients. However, a major deficit of SAA1 α homozygotes was found among Karabakhian patients (4%) as compared to Armenian patients (24%) (p = 5.10−5). Most importantly, we observed deviations from Hardy-Weinberg equilibrium (HWE) in the two groups of patients, and unexpectedly, in opposite directions, whereas, in the two control populations, genotype distributions at this locus were similar and complied with (HWE).
Conclusions/Significance
The excess of SAA1α homozygotes among Armenian patients could be explained by the recruitment of patients with severe phenotypes. In contrast, a population-based study revealed that the deficit of α/α among Karabakhian patients would result from a negative selection against carriers of this genotype. This study, which provides new insights into the role of SAA1 in the pathophysiology of FMF, represents the first example of deviations from HWE and selection involving the modifier gene of a Mendelian disorder.
doi:10.1371/journal.pone.0007676
PMCID: PMC2765618  PMID: 19888326
15.  Matrix Metalloproteinase Gene Polymorphisms and Bronchopulmonary Dysplasia: Identification of MMP16 as a New Player in Lung Development 
PLoS ONE  2008;3(9):e3188.
Backgound
Alveolarization requires coordinated extracellular matrix remodeling, a process in which matrix metalloproteinases (MMPs) play an important role. We postulated that polymorphisms in MMP genes might affect MMP function in preterm lungs and thus influence the risk of bronchopulmonary dysplasia (BPD).
Methods and Findings
Two hundred and eighty-four consecutive neonates with a gestational age of <28 weeks were included in this prospective study. Forty-five neonates developed BPD. Nine single-nucleotide polymorphisms (SNPs) were sought in the MMP2, MMP14 and MMP16 genes. After adjustment for birth weight and ethnic origin, the TT genotype of MMP16 C/T (rs2664352) and the GG genotype of MMP16 A/G (rs2664349) were found to protect from BPD. These genotypes were also associated with a smaller active fraction of MMP2 and with a 3-fold-lower MMP16 protein level in tracheal aspirates collected within 3 days after birth. Further evaluation of MMP16 expression during the course of normal human and rat lung development showed relatively low expression during the canalicular and saccular stages and a clear increase in both mRNA and protein levels during the alveolar stage. In two newborn rat models of arrested alveolarization the lung MMP16 mRNA level was less than 50% of normal.
Conclusions
MMP16 may be involved in the development of lung alveoli. MMP16 polymorphisms appear to influence not only the pulmonary expression and function of MMP16 but also the risk of BPD in premature infants.
doi:10.1371/journal.pone.0003188
PMCID: PMC2527515  PMID: 18784838
16.  Unusual Phenotypic Features in a Patient with a Novel Splice Mutation in the GHRHR Gene 
Molecular Medicine  2008;14(5-6):286-292.
Isolated growth hormone deficiency (IGHD) may be of genetic origin. One of the few genes involved in that condition encodes the growth hormone releasing hormone receptor (GHRHR) that, through its ligand (GHRH), plays a pivotal role in the GH synthesis and secretion by the pituitary. Our objective is to describe the phenotype of two siblings born to a consanguineous union presenting with short stature (IGHD) and Magnetic Resonance Imaging (MRI) abnormalities, and to identify the molecular basis of this condition. Our main outcome measures were clinical and endocrinological investigations, MRI of the pituitary region, study of the GHRHR gene sequence and transcripts. In both patients, the severe growth retardation (−5SD) was combined with anterior pituitary hypoplasia. In addition to these classical phenotypic features for IGHD, one of the patients had a Chiari I malformation, an arachnoid cyst, and a dysmorphic anterior pituitary. A homozygous sequence variation in the consensus donor splice site of intron 1 (IVS1 + 2T > G) of the GHRHR gene was identified in both patients. Using in vitro transcription assay, we showed that this mutation results in abnormal splicing of GHRHR transcripts. In this report, which broadens the phenotype associated with GHRHR defects, we discuss the possible role of the GHRHR in the proper development of extrapituitary structures, through a mechanism that could be direct or secondary to severe GH deficiency.
doi:10.2119/2007-00128.Hilal
PMCID: PMC2249753  PMID: 18297129
17.  Mutations of DNAI1 in Primary Ciliary Dyskinesia 
Rationale: Primary ciliary dyskinesia (PCD) is a rare, usually autosomal recessive, genetic disorder characterized by ciliary dysfunction, sino-pulmonary disease, and situs inversus. Disease-causing mutations have been reported in DNAI1 and DNAH5 encoding outer dynein arm (ODA) proteins of cilia.
Objectives: We analyzed DNAI1 to identify disease-causing mutations in PCD and to determine if the previously reported IVS1+2_3insT (219+3insT) mutation represents a “founder” or “hot spot” mutation.
Methods: Patients with PCD from 179 unrelated families were studied. Exclusion mapping showed no linkage to DNAI1 for 13 families; the entire coding region was sequenced in a patient from the remaining 166 families. Reverse transcriptase–polymerase chain reaction (RT-PCR) was performed on nasal epithelial RNA in 14 families.
Results: Mutations in DNAI1 including 12 novel mutations were identified in 16 of 179 (9%) families; 14 harbored biallelic mutations. Deep intronic splice mutations were not identified by reverse transcriptase–polymerase chain reaction. The prevalence of mutations in families with defined ODA defect was 13%; no mutations were found in patients without a defined ODA defect. The previously reported IVS1+2_3insT mutation accounted for 57% (17/30) of mutant alleles, and marker analysis indicates a common founder for this mutation. Seven mutations occurred in three exons (13, 16, and 17); taken together with previous reports, these three exons are emerging as mutation clusters harboring 29% (12/42) of mutant alleles.
Conclusions: A total of 10% of patients with PCD are estimated to harbor mutations in DNAI1; most occur as a common founder IVS1+2_3insT or in exons 13, 16, and 17. This information is useful for establishing a clinical molecular genetic test for PCD.
doi:10.1164/rccm.200603-370OC
PMCID: PMC2648054  PMID: 16858015
cilia; dynein; dextrocardia; Kartagener syndrome; mutation
18.  Oriented Scanning Is the Leading Mechanism Underlying 5′ Splice Site Selection in Mammals 
PLoS Genetics  2006;2(9):e138.
Splice site selection is a key element of pre-mRNA splicing. Although it is known to involve specific recognition of short consensus sequences by the splicing machinery, the mechanisms by which 5′ splice sites are accurately identified remain controversial and incompletely resolved. The human F7 gene contains in its seventh intron (IVS7) a 37-bp VNTR minisatellite whose first element spans the exon7–IVS7 boundary. As a consequence, the IVS7 authentic donor splice site is followed by several cryptic splice sites identical in sequence, referred to as 5′ pseudo-sites, which normally remain silent. This region, therefore, provides a remarkable model to decipher the mechanism underlying 5′ splice site selection in mammals. We previously suggested a model for splice site selection that, in the presence of consecutive splice consensus sequences, would stimulate exclusively the selection of the most upstream 5′ splice site, rather than repressing the 3′ following pseudo-sites. In the present study, we provide experimental support to this hypothesis by using a mutational approach involving a panel of 50 mutant and wild-type F7 constructs expressed in various cell types. We demonstrate that the F7 IVS7 5′ pseudo-sites are functional, but do not compete with the authentic donor splice site. Moreover, we show that the selection of the 5′ splice site follows a scanning-type mechanism, precluding competition with other functional 5′ pseudo-sites available on immediate sequence context downstream of the activated one. In addition, 5′ pseudo-sites with an increased complementarity to U1snRNA up to 91% do not compete with the identified scanning mechanism. Altogether, these findings, which unveil a cell type–independent 5′−3′-oriented scanning process for accurate recognition of the authentic 5′ splice site, reconciliate apparently contradictory observations by establishing a hierarchy of competitiveness among the determinants involved in 5′ splice site selection.
Synopsis
Typically, mammalian genes contain coding sequences (exons) separated by non-coding sequences (introns). Introns are removed during pre-mRNA splicing. The accurate recognition of introns during splicing is essential, as any abnormality in that process will generate abnormal mRNAs that can cause diseases. Understanding the mechanisms of accurate splice site selection is of prime interest to life scientists. Exon–intron borders (splice sites) are defined by short sequences that are poorly conserved. The strength of any splice sequence can be assessed by its degree of homology with a splice site consensus sequence. Within exons and introns, several sequences can match with this consensus as well as or better than the splice sites. Using a system in which a splice site sequence is repeated several times in the intron, the authors showed that linear 5′−3′ search is a leading mechanism underlying splice site selection. This scanning mechanism is cell type–independent, and only the most upstream splice site of all the series is selected, even if splice sites with a better match to the consensus are in the vicinity. These findings reconciliate contradictory observations and establish a hierarchy among the determinants involved in splice site selection.
doi:10.1371/journal.pgen.0020138
PMCID: PMC1557585  PMID: 16948532
19.  Loss of constitutive activity of the growth hormone secretagogue receptor in familial short stature 
Journal of Clinical Investigation  2006;116(3):760-768.
The growth hormone (GH) secretagogue receptor (GHSR) was cloned as the target of a family of synthetic molecules endowed with GH release properties. As shown recently through in vitro means, this receptor displays a constitutive activity whose clinical relevance is unknown. Although pharmacological studies have demonstrated that its endogenous ligand — ghrelin — stimulates, through the GHSR, GH secretion and appetite, the physiological importance of the GHSR-dependent pathways remains an open question that gives rise to much controversy. We report the identification of a GHSR missense mutation that segregates with short stature within 2 unrelated families. This mutation, which results in decreased cell-surface expression of the receptor, selectively impairs the constitutive activity of the GHSR, while preserving its ability to respond to ghrelin. This first description, to our knowledge, of a functionally significant GHSR mutation, which unveils the critical importance of the GHSR-associated constitutive activity, discloses an unusual pathogenic mechanism of growth failure in humans.
doi:10.1172/JCI25303
PMCID: PMC1386106  PMID: 16511605

Results 1-19 (19)