Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
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Duchenne and Becker muscular dystrophy patients have mutations in the dystrophin gene. Most show reduced b-wave amplitudes in the dark-adapted electroretinogram (ERG). We studied normal C57BL/6J mice and five X-linked muscular dystrophy strains with different dystrophin mutations to determine whether the location of the mutation within the gene affects the mouse ERG and to correlate such effects with dystrophin isoform expression. Amplitudes and implicit times were measured for a-waves, b-waves, and digitally filtered oscillatory potentials. mdx and mdxCv5 mice, with mutations near the amino terminus and lacking expression of Dp427, had ERGs similar to those of C57BL/6J mice. mdxCv2 and mdxCv4 mice, with mutations in the center of dystrophin and who do not express isoforms Dp427, Dp260, or Dp140 (mdxCv4), had increased b-wave and oscillatory potential implicit times. mdxCv3 mice, with a mutation near the carboxy terminus resulting in deficiency of all dystrophin isoforms, had increased b-wave and oscillatory potential implicit times and reduced scotopic b-wave amplitudes. Fitting the a-wave data to a transduction activation phase mathematical model showed normal responses for all phenotypes, suggesting that the b-wave delays are due to defects beyond the rod outer segment, most likely at the rod to on-bipolar cell synapse. The variation in the ERG phenotype with the position of the dystrophin gene mutation suggests that there are different contributions by each isoform to retinal electrophysiology. Although Dp427 and Dp140 isoforms do not appear to be important contributors to the ERG, lack of Dp260 and possibly Dp71 isoforms is associated with an abnormal ERG.
Mol Genet Metab 1999 Feb
PMID:Effects of dystrophin isoforms on signal transduction through neural retina: genotype-phenotype analysis of duchenne muscular dystrophy mouse mutants. 1006 12

Utrophin is a 400 kDa autosomal homolog of dystrophin and a component of the submembranous cytoskeleton. While multiple dystrophin isoforms have been identified along with alternatively spliced products, to date only two different mRNA species of utrophin have been identified. To determine the degree of evolutionary conservation between dystrophin and utrophin isoforms, we have compared their expression patterns in adult mice. Northern blot analysis of multiple adult tissues confirmed that only two major sizes of transcripts are produced from each gene: 13 and 5.5 kb from utrophin and 14 and 4.8 kb from dystrophin. However, western blot analysis detected several putative short utrophin isoforms that may be homologs of the dystrophin isoforms Dp140, Dp116 and Dp71. We also identified an alternatively spliced utrophin transcript that lacks the equivalent of the alternatively spliced dystrophin exon 71. Finally, we demonstrated that the C-terminal domain of utrophin targeted to neuromuscular junctions in normal mice, but localized to the sarcolemma efficiently only in the absence of dystrophin. Our results provide further evidence for a common evolutionary origin of the utrophin and dystrophin genes.
Hum Mol Genet 1999 Apr
PMID:Characterization of dystrophin and utrophin diversity in the mouse. 1007 26

In 1958 Professor Setsuro Ebashi found that serum creatine kinase activity is increased in patients suffering from various muscular dystrophies, especially Duchenne muscular dystrophy (DMD). He and others proposed that creatine kinase passes through the cell membrane as it is released from DMD muscle fibers. Since then, it has been found that dystrophin and dystrophin-associated proteins are connected to several other components, including the basal lamina and subsarcolemmal cytoskeletal networks on the cell membrane, while dystrophin anchors these dystrophin-associated proteins to the actin filaments inside the muscle cell. In DMD muscle, dystrophin has been found to be absent and dystroglycans and sarcoglycans decreased. However, how creatine kinase molecules can pass through the DMD muscle cell membrane still remains unanswered. On the basis of recent findings on the structure of the protein layers which sandwich the lipid bilayer of muscle cell membranes, this essay stresses the importance of these lipid bilayers in protecting creatine kinase release from protoplasma in normal muscle. It further indicates the possibility that the absence of dystrophin in DMD muscle during muscle contraction may result in temporal damage to the lipid bilayer.
Mol Cell Biochem 1999 Jan
PMID:Creatine kinase, cell membrane and Duchenne muscular dystrophy. 1009 81

Recently, a single gene, DYSF, has been identified which is mutated in patients with limb-girdle muscular dystrophy type 2B (LGMD2B) and with Miyoshi myopathy (MM). This is of interest because these diseases have been considered as two distinct clinical conditions since different muscle groups are the initial targets. Dysferlin, the protein product of the gene, is a novel molecule without homology to any known mammalian protein. We have now raised a monoclonal antibody to dysferlin and report on the expression of this new protein: immunolabelling with the antibody (designated NCL-hamlet) demonstrated a polypeptide of approximately 230 kDa on western blots of skeletal muscle, with localization to the muscle fibre membrane by microscopy at both the light and electron microscopic level. A specific loss of dysferlin labelling was observed in patients with mutations in the LGMD2B/MM gene. Furthermore, patients with two different frameshifting mutations demonstrated very low levels of immunoreactive protein in a manner reminiscent of the dystrophin expressed in many Duchenne patients. Analysis of human fetal tissue showed that dysferlin was expressed at the earliest stages of development examined, at Carnegie stage 15 or 16 (embryonic age 5-6 weeks). Dysferlin is present, therefore, at a time when the limbs start to show regional differentiation. Lack of dysferlin at this critical time may contribute to the pattern of muscle involvement that develops later, with the onset of a muscular dystrophy primarily affecting proximal or distal muscles.
Hum Mol Genet 1999 May
PMID:Dysferlin is a plasma membrane protein and is expressed early in human development. 1019 75

Utrophin/dystrophin-related protein is the autosomal homologue of the chromosome X-encoded dystrophin protein. In adult skeletal muscle, utrophin is highly enriched at the neuromuscular junction. However, the molecular mechanisms underlying regulation of utrophin gene expression are yet to be defined. Here we demonstrate that the growth factor heregulin increases de novo utrophin transcription in muscle cell cultures. Using mutant reporter constructs of the utrophin promoter, we define the N-box region of the promoter as critical for heregulin-mediated activation. Using this region of the utrophin promoter for DNA affinity purification, immunoblots, in vitro kinase assays, electrophoretic mobility shift assays, and in vitro expression in cultured muscle cells, we demonstrate that ets-related GA-binding protein alpha/beta transcription factors are activators of the utrophin promoter. Taken together, these results suggest that the GA-binding protein alpha/beta complex of transcription factors binds and activates the utrophin promoter in response to heregulin-activated extracellular signal-regulated kinase in muscle cell cultures. These findings suggest methods for achieving utrophin up-regulation in Duchenne's muscular dystrophy as well as mechanisms by which neurite-derived growth factors such as heregulin may influence the regulation of utrophin gene expression and subsequent enrichment at the neuromuscular junction of skeletal muscle.
Mol Biol Cell 1999 Jun
PMID:Activation of utrophin promoter by heregulin via the ets-related transcription factor complex GA-binding protein alpha/beta. 1035 16

Utrophin is a large protein which accumulates at the neuromuscular synapse and myotendinous junctions in adult skeletal muscle, and is widely expressed in several non-skeletal muscle tissues. Evidence from a variety of sources suggests that a successful strategy for treatment of Duchenne muscular dystrophy patients will be to increase expression of utrophin in muscle. There is still much to be learnt about utrophin gene regulation, in particular regarding alternative isoforms, their promoters and role in muscle and non-muscle tissues. Using 5"-RACE we have identified two novel transcripts of utrophin, Up71 and Up140, with unique first exons and promoters located in intron 62 and intron 44, respectively. These transcripts appear to be structural homologues of the short dystrophin transcripts, Dp140 and Dp71, emphasizing the high degree of structural conservation between the utrophin and dystrophin genes. RT-PCR shows that Up71 and Up140 are widely expressed in both human and mouse tissues, including skeletal muscle. We present evidence for transcript-specific differential mRNA splicing of exon 71, in both Up71 and Up140, similar to that described for dystrophin. No evidence for splicing of exon 78 of utrophin was found. This is in contrast to dystrophin and may reflect a subtle functional difference in patterns of phosphorylation between the two proteins.
Hum Mol Genet 1999 Jul
PMID:Up71 and up140, two novel transcripts of utrophin that are homologues of short forms of dystrophin. 1036 73

A mechanistic definition of the dystrophic process is proposed, and the effects of growth factors vs. down-regulation of growth are critically analyzed. A conceptual scheme is presented to illustrate the steps leading to pathology, and various compensatory systems which ameliorate the pathology are examined, particularly in regards to the mdv mouse which is resistant to the deficiency of dystrophin, the main protein product of the Duchenne and Becker muscular dystrophy (DMD/BMD) gene. These compensatory systems are analyzed in terms of the differential resistance of fiber types to pathogenesis. The generation of a stable population of maturationally arrested centronucleated fibers which express the mature adult myosin isoforms is proposed to be the main strategy of mdx muscle to minimize apoptosis. Physiological properties of these fibers, such as utrophin expression, and high mitochondrial and endoplasmic reticulum content, together with probable increased glycerophosphorylcholine concentrations and facile access to the vascular system, are hypothesized to be instrumental in their resistance to pathogenesis. It is proposed that the major element that determines the susceptibility of most human muscles to the dystrophic process is their inability to arrest the maturation of regenerated fibers at the centronucleated stage with a concomitant expression of the adult myosins.
Mol Cell Biochem 1999 May
PMID:Mechanisms of resistance to pathogenesis in muscular dystrophies. 1039 79

The spontaneous up-regulation of utrophin, observed in dystrophin-deficient skeletal muscle fibers, may decrease the susceptibility of such fibers to necrosis. It has been reported that the utrophin-rescued double-mutant mdx mouse always develops a lethal cardiomyopathy. We report two patients with severe dilated cardiomyopathy due to dystrophin gene mutations: the first was a manifesting Duchenne muscular dystrophy carrier and the second a patient affected with moderate Becker muscular dystrophy. We studied their explanted heart specimen and/or endoImyocardial biopsies by immunohistochemistry and Western blot for both dystrophin and utrophin. Utrophin was found to be over-expressed in these specimens. Our results suggest that in these patients the up-regulation of utrophin in dystrophin-deficient cardiomyocytes was unable to prevent the development of life-threatening myocardial dysfunction. These findings seem to dampen the enthusiasm raised by the prospect of DMD treatment by utrophin rescue in skeletal muscle fibers, as the myocardium would still remain severely affected.
J Mol Cell Cardiol 1999 Aug
PMID:Could utrophin rescue the myocardium of patients with dystrophin gene mutations? 1042 48

beta-Sarcoglycan, one of the subunits of the sarcoglycan complex, is a transmembranous glycoprotein which associates with dystrophin and is the molecule responsible for beta-sarcoglycanopathy, a Duchenne-like autosomal recessive muscular dystrophy. To develop an animal model of beta-sarcoglycanopathy and to clarify the role of beta-sarcoglycan in the pathogenesis of the muscle degeneration in vivo, we developed beta-sarcoglycan-deficient mice using a gene targeting technique. beta-Sarcoglycan-deficient mice (BSG(-)(/-)mice) exhibited progressive muscular dystrophy with extensive degeneration and regeneration. The BSG(-)(/-)mice also exhibited muscular hypertrophy characteristic of beta-sarcoglycanopathy. Immunohistochemical and immunoblot analyses of BSG(-)(/-)mice demonstrated that deficiency of beta-sarcoglycan also caused loss of all of the other sarcoglycans as well as of sarcospan in the sarcolemma. On the other hand, laminin-alpha2, alpha- and beta-dystroglycan and dystrophin were still present in the sarcolemma. However, the dystrophin-dystroglycan complex in BSG(-)(/-)mice was unstable compared with that in the wild-type mice. Our data suggest that loss of the sarcoglycan complex and sarcospan alone is sufficient to cause muscular dystrophy, that beta-sarcoglycan is an important protein for formation of the sarcoglycan complex associated with sarcospan and that the role of the sarcoglycan complex and sarcospan may be to strengthen the dystrophin axis connecting the basement membrane with the cytoskeleton.
Hum Mol Genet 1999 Sep
PMID:Loss of the sarcoglycan complex and sarcospan leads to muscular dystrophy in beta-sarcoglycan-deficient mice. 1044 21

In the field of muscular dystrophy, advances in understanding the molecular basis of the various disorders in this group have been rapidly translated into readily applicable diagnostic tests, allowing the provision of more accurate prognostic and genetic counselling. The limb-girdle muscular dystrophies (LGMD) have recently undergone a major reclassification according to their genetic basis. Currently 13 different types can be recognized. Amongst this group, increasing diversity of the mechanisms involved in producing a muscular dystrophy phenotype is emerging. Recent insights into the involvement of the dystrophin glycoprotein complex in muscular dystrophy suggests that its members may play distinct or even multiple roles in the maintenance of muscle fibre integrity. In other forms of LGMD, proteins have been implicated which may be important in intracellular signalling, vesicle trafficking or the control of transcription. As these various mechanisms are more fully elucidated, further insights will be gained into the pathophysiology of muscular dystrophy. At a practical level, despite the marked heterogeneity of this group real progress can at last be made in determining a precise diagnosis.
Hum Mol Genet 1999
PMID:The limb-girdle muscular dystrophies-multiple genes, multiple mechanisms. 1046 40


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