Showing papers by "Kay E. Davies published in 1997"
TL;DR: It is suggested that utrophin and dystrophin have complementing roles in normal functional or developmental pathways in muscle and that these mice should provide novel insights into the pathogenesis of DMD and provide an improved model for rapid evaluation of gene therapy strategies.
733 citations
TL;DR: The crystal structures of PDZ domains, with and without ligand, have been determined and demonstrate the mode of ligand‐binding and the structural bases for sequence conservation among diversePDZ domains.
Abstract: PDZ (also called DHR or GLGF) domains are found in diverse membrane associated proteins including members of the MAGUK family of guanylate kinase homologues, several protein phosphatases and kinases, neuronal nitric oxide synthase, and several dystrophin-associated proteins, collectively known as syntrophins. Many PDZ domain-containing proteins appear to be localised to highly specialised submembranous sites, suggesting their participation in cellular junction formation, receptor or channel clustering, and intracellular signalling events. PDZ domains of several MAGUKs interact with the C-terminal polypeptides of a subset of NMDA receptor subunits and/or with Shaker-type K+ channels. Other PDZ domains have been shown to bind similar ligands of other transmembrane receptors. Recently, the crystal structures of PDZ domains, with and without ligand, have been determined. These demonstrate the mode of ligand-binding and the structural bases for sequence conservation among diverse PDZ domains.
432 citations
TL;DR: Surprisingly, data show that mutations in SMA types II and III, previously classed as deletions, are in fact due to gene-conversion events in which SMNtel is replaced by its centromeric counterpart, SMNcen, which enables a genotype/phenotype correlation to be made.
Abstract: Autosomal recessive spinal muscular atrophy (SMA) is classified, on the basis of age at onset and severity, into three types: type I, severe; type II, intermediate; and type III, mild. The critical region in 5q13 contains an inverted repeat harboring several genes, including the survival motor neuron (SMN) gene, the neuronal apoptosis inhibitory protein (NAIP) gene, and the p44 gene, which encodes a transcription-factor subunit. Deletion of NAIP and p44 is observed more often in severe SMA, but there is no evidence that these genes play a role in the pathology of the disease. In > 90% of all SMA patients, exons 7 and 8 of the telomeric SMN gene (SMNtel) are not detectable, and this is also observed in some normal siblings and parents. Point mutations and gene conversions in SMNtel suggest that it plays a major role in the disease. To define a correlation between genotype and phenotype, we mapped deletions, using pulsed-field gel electrophoresis. Surprisingly, our data show that mutations in SMA types II and III, previously classed as deletions, are in fact due to gene-conversion events in which SMNtel is replaced by its centromeric counterpart, SMNcen. This results in a greater number of SMNcen copies in type II and type III patients compared with type I patients and enables a genotype/phenotype correlation to be made. We also demonstrate individual DNA-content variations of several hundred kilobases, even in a relatively isolated population from Finland. This explains why no consensus map of this region has been produced. This DNA variation may be due to a midisatellite repeat array, which would promote the observed high deletion and gene-conversion rate.
320 citations
TL;DR: It is demonstrated that trc-utrophin expression leads to major improvements of the mechanical performance of muscle (that is, force development, mechanical resistance to forced lengthenings and maximal spontaneous activity) and of the maintenance of the intracellular calcium homeostasis.
Abstract: Dystrophin-deficient mice (mdx) expressing a truncated (trc) utrophin transgene show amelioration of the dystrophic phenotype. Here we report a multifunctional study demonstrating that trcutrophin expression leads to major improvements of the mechanical performance of muscle (that is, force development, mechanical resistance to forced lengthenings and maximal spontaneous activity) and of the maintenance of the intracellular calcium homeostasis. These are two essential functions of muscle fibers, known to be impaired in mdx mouse muscles and Duchenne muscular dystrophy (DMD) patients. Our results bring strong support to the hypothesis that muscle wasting in dystrophin-deficient DMD patients could be prevented by upregulation of utrophin.
245 citations
TL;DR: Utrophin is thus not essential for AChR clustering at the NMJ but may act as a component of the postsynaptic cytoskeleton, contributing to the development or maintenance of thePostsynaptic folds.
Abstract: Utrophin is a dystrophin-related cytoskeletal protein expressed in many tissues. It is thought to link F-actin in the internal cytoskeleton to a transmembrane protein complex similar to the dystrophin protein complex (DPC). At the adult neuromuscular junction (NMJ), utrophin is precisely colocalized with acetylcholine receptors (AChRs) and recent studies have suggested a role for utrophin in AChR cluster formation or maintenance during NMJ differentiation. We have disrupted utrophin expression by gene targeting in the mouse. Such mice have no utrophin detectable by Western blotting or immunocytochemistry. Utrophindeficient mice are healthy and show no signs of weakness. However, their NMJs have reduced numbers of AChRs (α-bungarotoxin [α-BgTx] binding reduced to ∼60% normal) and decreased postsynaptic folding, though only minimal electrophysiological changes. Utrophin is thus not essential for AChR clustering at the NMJ but may act as a component of the postsynaptic cytoskeleton, contributing to the development or maintenance of the postsynaptic folds. Defects of utrophin could underlie some forms of congenital myasthenic syndrome in which a reduction of postsynaptic folds is observed.
222 citations
TL;DR: A novel missense mutation is described and the subsequent identification of a triplicated tyrosine-glycine (Y-G) peptide sequence at the C-terminal of SMN which encompasses each of the three predicted amino acid sequence substitutions.
Abstract: The Survival Motor Neuron (SMN) gene shows deletions in the majority of patients with Spinal Muscular Atrophy (SMA), a disease of motor neuron degeneration. To date only two missense mutations have been reported in SMN in patients with SMA. The fact that no SMN-homologues have been forthcoming from database searching has resulted in a lack of hypotheses concerning the structural and functional consequences of these mutations. Recently SMN has been shown to interact with heterogeneous nuclear ribonu-cleoproteins (hnRNPs) suggesting a role in mRNA metabolism. We describe a novel missense mutation and the subsequent identification of a triplicated tyrosine-glycine (Y-G) peptide sequence at the C-terminal of SMN which encompasses each of the three predicted amino acid sequence substitutions. We have identified apparent orthologues of SMN in Caenorhabditis elegans and Schizosaccharomyces pombe. These sequences retain the highly conserved Y-G motif and provide additional support for a role of SMN in mRNA metabolism.
158 citations
TL;DR: Results indicate that nerve-derived factors regulate locally the transcriptional activation of the utrophin gene in skeletal muscle fibers and that myonuclei located in extrasynaptic regions are capable of expressing utphin upon receiving appropriate neuronal cues.
83 citations
TL;DR: The results show that dystrobrevin-deficiency is a generic feature of dystrophies linked to Dystrophin and the dystrophicin-associated proteins, the first indication that a cytoplasmic component of the dyStrophin- associated protein complex may be involved in the pathogenesis of limb-girdle muscular dystrophy.
Abstract: Mutations in the genes encoding dystrophin or dystrophin-associated proteins are responsible for Duchenne muscular dystrophy or various forms of limb-girdle muscular dystrophies respectively. We have recently cloned the gene for the murine 87 kDa postsynaptic protein dystrobrevin, a dystrophin-associated protein. Anti-dystrobrevin antibodies stain the sarcolemma in normal skeletal muscle indicating that dystrobrevin co-localises with dystrophin and the dystrophin-associated protein complex. By contrast, dystrobrevin membrane staining is severely reduced in muscles of Duchenne muscular dystrophy patients, consistent with dystrobrevin being a dystrophin-associated protein. Interestingly, dystrobrevin staining at the sarcolemma is dramatically reduced in patients with limb-girdle muscular dystrophy arising from the loss of one or all of the sarcoglycan components. Normal dystrobrevin staining is observed in patients with other forms of limb-girdle muscular dystrophy where dystrophin and the rest of the dystrophin-associated protein complex are normally expressed and in other neuromuscular disorders. Our results show that dystrobrevin-deficiency is a generic feature of dystrophies linked to dystrophin and the dystrophin-associated proteins. This is the first indication that a cytoplasmic component of the dystrophin-associated protein complex may be involved in the pathogenesis of limb-girdle muscular dystrophy.
71 citations
TL;DR: It is determined that the mouse dystrobrevin gene is organized into 24 coding exons that span between 130 and 170 kb at the genomic level and encodes at least three distinct protein isoforms that are expressed in a tissue-specific manner.
43 citations
TL;DR: Comparisons support the idea that FRAXE is associated with nonspecific developmental delay and possibly high-functioning autism.
Abstract: Standardized cognitive, behavioral, and neuroanatomical data are presented on 2 unrelated boys with the FRAXE (FMR2) GCC expansion mutation. In the context of normal IQ, both boys had a history of developmental delay, including significant problems with communication, attention, and overactivity. Additionally, one child was diagnosed with autistic disorder. Data from these 2 cases are compared to analogous information from previous reports about individuals with the FRAXE or FRAXA (FMR1) mutation. These comparisons support the idea that FRAXE is associated with nonspecific developmental delay and possibly high-functioning autism.
43 citations
TL;DR: The last seven years has witnessed an explosion in our understanding of the muscular dystrophies as mentioned in this paper, which has had an impact in the clinical management of pateints and the promise the progress holds for the future.
TL;DR: In all patients where there was absence of PCR amplification of exon 7 but not exon 8 of SMNtel this was found to be due to replacement with the homologous copy ofSMNcen by a possible gene conversion event, which occurred in all grades of severity of SMA.
TL;DR: The probe StB12.3 has been used to screen the FMR-1 gene in 42 pedigrees with a distal Xq fragile site for expansion of the CCG repeat and aberrant methylation of the FRAXA locus and illustrates the need for the F RAXE phenotype to be defined further.
Abstract: The probe StB12.3 has been used to screen the FMR-1 gene in 42 pedigrees with a distal Xq fragile site for expansion of the CCG repeat and aberrant methylation of the FRAXA locus. Four families did not have a FRAXA mutation and were investigated further. Fluorescent in situ hybridisation (FISH) and molecular analyses showed that three of these families had an expansion at FRAXE and one at FRAXE. Detailed psychiatric, psychological, and behavioural features of three families with FRAXE identified in the study are presented. All the males who expressed FRAXE had a large methylated CCG repeat at FRAXF. All males with the mutation had some degree of mental handicap. This study illustrates the need for the FRAXE phenotype to be defined further.
TL;DR: The localization of the human orthologue of this gene, HB5, to within 150 kb of H19 on human chromosome 11p15.5 is reported, suggesting an evolutionary split between MKPs displaying specificity toward different MAP kinases.
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TL;DR: An expansion of a CGG repeat in the 5' end of the FMR1 gene results in the absence of the encoded fragile X mental retardation protein, known to play an important role in RNA processing and probably the developmental maturation of brain neurons.
Abstract: The fragile X syndrome is characterized by mental handicap, facial dysmorphism and expression of a fragile site at Xq27.3. An expansion of a CGG repeat in the 5' end of the fragile X mental retardation 1 (FMR1) gene results in the absence of the encoded fragile X mental retardation protein, known to play an important role in RNA processing and probably the developmental maturation of brain neurons.
TL;DR: An analysis of repeats at two fragile site loci, FRAXE and FRAxF, and a novel CGG repeat in Xq28, in five different human populations, which suggests that these loci may also be subject to the same mutation process.
Abstract: Most of the rare folate sensitive fragile sites cloned to date arise from expansion of a CGG:CCG trinucleotide repeat array. Analysis of the CAG repeat at the Huntington Disease (HD) locus showed a positively skewed repeat distribution leading to the proposal that microsatellites are subject to a mutational bias toward expansion. Such a mutational bias predicts an increase in mean repeat size at all microsatellite loci. We present an analysis of repeats at two fragile site loci, FRAXE and FRAXF, and a novel CGG repeat in Xq28, in five different human populations, which suggests that these loci may also be subject to the same mutation process. The novel repeat array may represent the first evidence for the existence of a fourth fragile site in Xq27.3-28.
Patent•
01 Dec 1997TL;DR: In this article, the cloning of a murine guanine nucleotide exchange factor (MNGEF) and a human homologue thereof is described, and polynucleotide probes derived from the nucleotide sequence of MNGEF are also provided.
Abstract: The present invention concerns the cloning of a murine guanine nucleotide exchange factor designated MNGEF and a human homologue thereof. Polynucleotide probes derived from the nucleotide sequence of MNGEF and antibodies that recognise MNGEF are also provided.
TL;DR: Although the use of genetic tests raises many social, ethical, legal and economic issues, this potential is already with us and the enormous benefits to human health can be gained without too many suffering from misuse of the technology.