Biomedical subjects

Sophie Saunier

Publications and source records attributed to Sophie Saunier.

5 recordsLinked to original sources

PubMed2006

The Meckel-Gruber syndrome gene, MKS3, is mutated in Joubert syndrome.

Joubert syndrome (JS) is an autosomal recessive disorder characterized by cerebellar vermis hypoplasia associated with hypotonia, developmental delay, abnormal respiratory patterns, and abnormal eye movements. The association of retinal dystrophy and renal anomalies defines JS type B. JS is a genetically heterogeneous condition with mutations in two genes, AHI1 and CEP290, identified to date. In addition, NPHP1 deletions identical to those that cause juvenile nephronophthisis have been identified in a subset of patients with a mild form of cerebellar and brainstem anomaly. Occipital encephalocele and/or polydactyly have occasionally been reported in some patients with JS, and these phenotypic features can also be observed in Meckel-Gruber syndrome (MKS). MKS is a rare, autosomal recessive lethal condition characterized by central nervous system malformations (typically, occipital meningoencephalocele), postaxial polydactyly, multicystic kidney dysplasia, and ductal proliferation in the portal area of the liver. Since there is obvious phenotypic overlap between JS and MKS, we hypothesized that mutations in the recently identified MKS genes, MKS1 on chromosome 17q and MKS3 on 8q, may be a cause of JS. After mutation analysis of MKS1 and MKS3 in a series of patients with JS (n=22), we identified MKS3 mutations in four patients with JS, thus defining MKS3 as the sixth JS locus (JBTS6). No MKS1 mutations were identified in this series, suggesting that the allelism is restricted to MKS3.

Abnormalities, Multiple↗

PubMed2005

Solution NMR structure of the SH3 domain of human nephrocystin and analysis of a mutation-causing juvenile nephronophthisis.

Human nephrocystin is a protein associated with juvenile NPH, an autosomal recessive, inherited kidney disease responsible for chronic renal failure in children. It contains an SH3 domain involved in signaling pathways controlling cell adhesion and cytoskeleton organization. The solution structure of this domain was solved by triple resonance NMR spectroscopy. Within the core, the structure is similar to those previously reported for other SH3 domains but exhibits a number of specific noncanonical features within the polyproline ligand binding site. Some of the key conserved residues are missing, and the N-Src loop exhibits an unusual twisted geometry, which results in a narrowing of the binding groove. This is induced by the replacement of a conserved Asp, Asn, or Glu residue by a Pro at one side of the N-Src loop. A systematic survey of other SH3 domains also containing a Pro at this position reveals that most of them belong to proteins involved in cell adhesion or motility. A variant of this domain, which carries a point mutation causing NPH, was also analyzed. This change, L180P, although it corresponds to a nonconserved and solvent-exposed position, causes a complete loss of the tertiary structure. Similar effects are also observed with the L180A variant. This could be a context-dependent effect resulting from an interaction between neighboring charged side-chains.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Characterization of the nephrocystin/nephrocystin-4 complex and subcellular localization of nephrocystin-4 to primary cilia and centrosomes.

Nephrocystin and nephrocystin-4 are newly identified proteins involved in familial juvenile nephronophthisis, an autosomal recessive nephropathy characterized by cyst formation and renal fibrosis. Nephrocystin is an adaptor protein that is able to associate with signaling molecules involved in cell adhesion and actin cytoskeleton organization, such as p130Cas, Pyk2, tensin and filamins. Nephrocystin was recently shown to interact and to co-localize with the microtubule component beta-tubulin to the primary cilia in renal epithelial cells, an organelle known to play a key role in the pathogenesis of cystic kidney diseases. In this study, we demonstrated that nephrocystin-4 also localizes to the primary cilia in polarized epithelial tubular cells, particularly at the basal bodies, and associates with microtubule component alpha-tubulin, suggesting a common role for the nephrocystin proteins in ciliary function. However, the co-localization of nephrocystin-4 with the microtubules is not restricted to the primary cilia, as nephrocystin-4 was also detected at the centrosomes of dividing cells and close to the cortical actin cytoskeleton in polarized cells. We also detected p130Cas and Pyk2 in the nephrocystin-4-containing complex, confirming the role of the nephrocystin proteins in cell-cell and cell-matrix adhesion signaling events. Finally, we refined the structural and functional regions involved in the interaction between nephrocystin and nephrocystin-4. These data suggest that nephrocystin and nephrocystin-4 belong to a multifunctional complex localized in actin- and microtubule-based structures involved in cell-cell and cell-matrix adhesion signaling as well as in cell division.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Nephronophthisis.

There has been tremendous progress in the past few years in understanding the molecular basis of nephronophthisis, and it is now evident that the disease is characterized by both clinical and genetic heterogeneity. Within the three different clinical forms there is a large spectrum of phenotypes, which have been associated, to date, with five gene defects. These genes encode proteins that localize in different cell compartments - in particular, to the primary apical cilia - as is the case for virtually all gene products involved in cystic kidney diseases. Two animal models with mutations in the mouse orthologs of the genes involved in the adolescent and infantile forms also exist. These models have been of considerable help in deciphering disease pathogenesis.

Animals↗

PubMed2002

The gene mutated in juvenile nephronophthisis type 4 encodes a novel protein that interacts with nephrocystin.

Nephronophthisis, the most common genetic cause of chronic renal failure in children, is a progressive tubulo-interstitial kidney disorder that is inherited as an autosomal recessive trait. The disease is characterized by polyuria, growth retardation and deterioration of renal function during childhood or adolescence. The most prominent histological features are modifications of the tubules with thickening of the basement membrane, interstitial fibrosis and, in the advanced stages, medullary cysts. Nephronophthisis can also be associated with conditions affecting extrarenal organs, such as retinitis pigmentosa (Senior-Løken syndrome) and ocular motor apraxia (Cogan syndrome). Three loci are associated with the juvenile, infantile and adolescent forms, on chromosomes 2q13 (NPHP1; refs 5,6), 9q22 (NPHP2; ref. 7) and 3q21 (NPHP3; ref. 8), respectively. NPHP1, the only gene identified so far, encodes nephrocystin, which contains a Src homology 3 (SH3) domain and interacts with intracytoplasmic proteins involved in cell adhesion. Recently, a second locus associated with the juvenile form of the disease, NPHP4, was mapped to chromosome 1p36 (ref. 14). We carried out haplotype analysis of families affected with nephronophthisis that were not linked to the NPHP1, NPHP2 or NPHP3 loci, using markers covering this region. This allowed us to reduce the NPHP4 interval to a one centimorgan interval between D1S2795 and D1S2870, which contains six genes. We identified five different mutations in one of these genes, designated NPHP4, in unrelated individuals with nephronophthisis. The NPHP4 gene encodes a 1,250-amino acid protein of unknown function that we named nephrocystin-4. We demonstrated the interaction of nephrocystin-4 with nephrocystin suggesting that these two proteins participate in a common signaling pathway.

Adaptor Proteins, Signal Transducing↗