Proteomic investigation of the molecular pathophysiology of dysferlinopathy

Mutations in dysferlin gene cause several types of muscular dystrophy in humans, including the limb-girdle muscular dystrophy type 2B and the distal muscular dystrophy of Miyoshi. The dysferlin gene product is a membrane-associated protein belonging to the ferlins family of proteins. The function of the dysferlin protein and the cause of deterioration and regression of muscle fibres in its absence, are incompletely known. A functional clue may be the presence of six hydrophilic domains, C2, that bind calcium and mediate the interaction of proteins with cellular membranes. Dysferlin seems to be involved in the membrane fusion or repair. Molecular diagnosis of dysferlinopathies is now possible and the types of gene alterations that have been characterized so far include missense mutations, deletions and insertions.     

Aberrant Mitochondria in a Bethlem Myopathy Patient with a Homozygous Amino Acid Substitution That Destabilizes the Collagen VI α2(VI) Chain

Bethlem myopathy and Ullrich congenital muscular dystrophy (UCMD) sit at opposite ends of a clinical spectrum caused by mutations in the extracellular matrix protein collagen VI. Bethlem myopathy is relatively mild, and patients remain ambulant in adulthood while many UCMD patients lose ambulation by their teenage years and require respiratory interventions. Dominant and recessive mutations are found across the entire clinical spectrum; however, recessive Bethlem myopathy is rare, and our understanding of the molecular pathology is limited. We studied a patient with Bethlem myopathy. Electron microscopy of his muscle biopsy revealed abnormal mitochondria. We identified a homozygous COL6A2 p.D871N amino acid substitution in the C-terminal C2 A-domain. Mutant α2(VI) chains are unable to associate with α1(VI) and α3(VI) and are degraded by the proteasomal pathway. Some collagen VI is assembled, albeit more slowly than normal, and is secreted. These molecules contain the minor α2(VI) C2a splice form that has an alternative C terminus that does include the mutation. Collagen VI tetramers containing the α2(VI) C2a chain do not assemble efficiently into microfibrils and there is a severe collagen VI deficiency in the extracellular matrix. We expressed wild-type and mutant α2(VI) C2 domains in mammalian cells and showed that while wild-type C2 domains are efficiently secreted, the mutant p.D871N domain is retained in the cell. These studies shed new light on the protein domains important for intracellular and extracellular collagen VI assembly and emphasize the importance of molecular investigations for families with collagen VI disorders to ensure accurate diagnosis and genetic counseling.     

基因突变的分子检测技术

基因突变的分子检测是确定生物性状与某种遗传变异的关系、探讨生物物种内基因的差异、了解生物种间亲缘和进化的关键技术,对群体遗传学和生物分类学研究、遗传病诊断等都有着重要的理论意义和实用价值。因此,对于基因突变的检测方法的研究目前受到广泛关注。对基因突变的形式及其分子检测技术作了全面综述。     

构建遗传图的新方法:单精子PCR分型技术

构建遗传图的新方法———单精子ＰＣＲ分型技术①赵书红李奎彭中镇（华中农业大学动物分子生物学与育种研究室,武汉４３００７０）盛志廉（东北农业大学动物科学研究所,哈尔滨１５００３０）ＲｅｖｉｅｗｏｆＳｉｎｇｌｅＳｐｅｒｍＴｙｐｉｎｇｂｙＰＣＲＭｅｔｈｏｄ...     

Reduced Plasma Membrane Expression of Dysferlin Mutants Is Attributed to Accelerated Endocytosis via a Syntaxin-4-associated Pathway

Ferlins are an ancient family of C2 domain-containing proteins, with emerging roles in vesicular trafficking and human disease. Dysferlin mutations cause inherited muscular dystrophy, and dysferlin also shows abnormal plasma membrane expression in other forms of muscular dystrophy. We establish dysferlin as a short-lived (protein half-life ∼4–6 h) and transitory transmembrane protein (plasma membrane half-life ∼3 h), with a propensity for rapid endocytosis when mutated, and an association with a syntaxin-4 endocytic route. Dysferlin plasma membrane expression and endocytic rate is regulated by the C2B-FerI-C2C motif, with a critical role identified for C2C. Disruption of C2C dramatically reduces plasma membrane dysferlin (by 2.5-fold), due largely to accelerated endocytosis (by 2.5-fold). These properties of reduced efficiency of plasma membrane expression due to accelerated endocytosis are also a feature of patient missense mutant L344P (within FerI, adjacent to C2C). Importantly, dysferlin mutants that demonstrate accelerated endocytosis also display increased protein lability via endosomal proteolysis, implicating endosomal-mediated proteolytic degradation as a novel basis for dysferlin-deficiency in patients with single missense mutations. Vesicular labeling studies establish that dysferlin mutants rapidly transit from EEA1-positive early endosomes through to dextran-positive lysosomes, co-labeled by syntaxin-4 at multiple stages of endosomal transit. In summary, our studies define a transient biology for dysferlin, relevant to emerging patient therapeutics targeting dysferlin replacement. We introduce accelerated endosomal-directed degradation as a basis for lability of dysferlin missense mutants in dysferlinopathy, and show that dysferlin and syntaxin-4 similarly transit a common endosomal pathway in skeletal muscle cells.     

AhR deficiency impairs expression of LPS-induced inflammatory genes in mice

Mutations in the gene encoding dysferlin cause two distinct muscular dystrophy phenotypes: limb-girdle muscular dystrophy type 2B (LGMD-2B) and Miyoshi myopathy (MM). Dysferlin is a large transmembrane protein involved in myoblast fusion and membrane resealing. Zebrafish represent an ideal animal model to use for studying muscle disease including abnormalities of dysferlin. cDNAs of zebrafish dysferlin were cloned (6.3 kb) and the predicted amino acid sequences, showed 68% similarity to predicted amino acid sequences of mammalian dysferlin. The expression of dysferlin was mainly in skeletal muscle, heart and eye, and the expression could be detected as early as 11 h post fertilization (hpf). Three different antisense oligonucleotide morpholinos were targeted to inhibit translation of this dysferlin mRNA and the morpholino-injected fish showed marked muscle disorganization which could be detected by birefringence assay. Western blot analysis using dysferlin antibodies showed that the expression of dysferlin was reduced in each of the three morphants. Dysferlin expression was shown to be reduced at the myosepta of zebrafish muscle using immunohistochemistry, although the expression of other muscle membrane components, dystrophin, laminin, β-dystroglycan were detected normally. Our data suggest that zebrafish dysferlin expression is involved in stabilizing muscle structures and its downregulation causes muscle disorganization.     

Proteasomal inhibition restores biological function of mis-sense mutated dysferlin in patient-derived muscle cells

Dysferlin is a transmembrane protein implicated in surface membrane repair of muscle cells. Mutations in dysferlin cause the progressive muscular dystrophies Miyoshi myopathy, limb girdle muscular dystrophy 2B, and distal anterior compartment myopathy. Dysferlinopathies are inherited in an autosomal recessive manner, and many patients with this disease harbor mis-sense mutations in at least one of their two pathogenic DYSF alleles. These patients have significantly reduced or absent dysferlin levels in skeletal muscle, suggesting that dysferlin encoded by mis-sense alleles is rapidly degraded by the cellular quality control system. We reasoned that mis-sense mutated dysferlin, if salvaged from degradation, might be biologically functional. We used a dysferlin-deficient human myoblast culture harboring the common R555W mis-sense allele and a DYSF-null allele, as well as control human myoblast cultures harboring either two wild-type or two null alleles. We measured dysferlin protein and mRNA levels, resealing kinetics of laser-induced plasmalemmal wounds, myotube formation, and cellular viability after treatment of the human myoblast cultures with the proteasome inhibitors lactacystin or bortezomib (Velcade). We show that endogenous R555W mis-sense mutated dysferlin is degraded by the proteasomal system. Inhibition of the proteasome by lactacystin or Velcade increases the levels of R555W mis-sense mutated dysferlin. This salvaged protein is functional as it restores plasma membrane resealing in patient-derived myoblasts and reverses their deficit in myotube formation. Bortezomib and lactacystin did not cause cellular toxicity at the regimen used. Our results raise the possibility that inhibition of the degradation pathway of mis-sense mutated dysferlin could be used as a therapeutic strategy for patients harboring certain dysferlin mis-sense mutations.     

绿色荧光蛋白——现代细胞生物学与分子生物学研究领域的新标记物

从多管水母属A equoren v ictu ria 分离出的绿色荧光蛋白(GFP) , 因其特有的生物化学性质及该基因在异源细胞内的表达产物亦能产生强烈的绿色荧光, 使其在现代细胞生物学和分子生物学研究领域的应用具有广阔前景。本文就其研究进展及其应用进行简要综述。     

Human male infertility may be due to a decrease of the protamine P2 content in sperm chromatin

Basic chromosomal proteins were extracted from the sperm of fertile and infertile human males. The relative proportions of protamine 1, 2, and 3 were determined by scanning microdensitometry following electrophoresis of total protamine in polyacrilamide gels. The findings were as follows: (1) The proportion of protamine P(2 + 3) in sperm obtained from infertile males was lower than that in fertile males. (2) Protamine P(2 + 3) in infertile human males showed reduced affinity to DNA. The possibility that some cases of human male infertility may be due to mutation within the protamine P2 gene is discussed. © 1993 Wiley-Liss, Inc.     

大豆短叶柄性状的遗传分析

２个短叶柄遗传材料ＮＪ９０Ｌ１ＳＰ及Ｄ７６１６０９与长叶柄品种（系）杂交的９个组合的后代分离结果表明：（１）新发现的突变体ＮＪ９０Ｌ１ＳＰ的短叶柄与不正常叶枕两性状之间为一因多效,受２对隐性重叠基因控制;（２）由美国引进的Ｄ７６１６０９的短叶柄性状受２对隐性重叠基因控制;（３）ＮＪ９０Ｌ１ＳＰ与Ｄ７６１６０９短叶柄性状的遗传控制不同,叶柄长度至少受两两重叠的４对基因控制。     

一种改进的快速PCR定点突变技术

在基因工程与蛋白质工程研究中常常用到基因突变技术制备突变体,用于研究基因调控、蛋白质的结构与功能。本项研究在快速PCR定点突变技术的基础上,改进实验方法,简化实验步骤,以适用蛋白质结构改造研究的需要。建立的突变技术仅需一次PCR反应即可完成基因的定点突变,突变效率为79.6%左右。该法对1～3个连续碱基的突变和对间隔4个甚至多达15个碱基的数个密码子突变效果都很好。     

Endocytic recycling proteins EHD1 and EHD2 interact with fer-1-like-5 (Fer1L5) and mediate myoblast fusion

The mammalian ferlins are calcium-sensing, C2 domain-containing proteins involved in vesicle trafficking. Myoferlin and dysferlin regulate myoblast fusion and muscle membrane resealing, respectively. Correspondingly, myoferlin is most highly expressed in singly nucleated myoblasts, whereas dysferlin expression is increased in mature, multinucleated myotubes. Myoferlin also mediates endocytic recycling and participates in trafficking the insulin-like growth factor receptor. We have now characterized a novel member of the ferlin family, Fer1L5, because of its high homology to dysferlin and myoferlin. We found that Fer1L5 protein is expressed in small myotubes that contain only two to four nuclei. We also found that Fer1L5 protein binds directly to the endocytic recycling proteins EHD1 and EHD2 and that the second C2 domain in Fer1L5 mediates this interaction. Reduction of EHD1 and/or EHD2 inhibits myoblast fusion, and EHD2 is required for normal translocation of Fer1L5 to the plasma membrane. The characterization of Fer1L5 and its interaction with EHD1 and EHD2 underscores the complex requirement of ferlin proteins and mediators of endocytic recycling for membrane trafficking events during myotube formation.     

基因枪介导的籼稻遗传转化及外源基因在受体中的遗传研究

由来自水稻成熟胚的愈伤组织或由此而建立的悬浮细胞系作基因枪转化的靶材料 ,将质粒 p ILTAB2 2 7(含 hph基因和 gus基因 )导入籼稻 ,在 Basmati- 1、青油粘、新山粘 2 9、胜优 2号 ,明恢 63等品种获得了转基因植株。 T0 转化体 gus基因组织化学染色和 DNA分子杂交 ( Southern blot)证实 ,gus和 hph基因已整合到上述品种的基因组中。本实验仔细研究了hph基因在 Basmati- 1的 T1、T2 和 T3等各个世代的遗传及表达。对 T1家系中各个体核 DNA的分子检测表明 ,hph基因普遍呈 3∶ 1的分离 (转基因阳性∶阴性 ) ,表明 hph基因为单一位点的整合 ,其遗传符合单 (显性 )基因控制的孟德尔遗传规律。还发现一些株系表现 1∶ 1的不正常的分离 (阳性个体较预期的少 ) ,推测这是由于雌或雄配子之一方的 hph基因受到抑制而产生基因沉默的结果。在 T2 、T3世代获得了具 hph基因的纯合体。笔者还探讨了外源基因在核基因组中的遗传稳定性及基因的沉默与活化问题     

基因枪介导的籼稻遗传转化及外源基因在受体中的遗传研究

由来自水稻成熟胚的愈伤组织或由此而建立的悬浮细胞系作基因枪转化的靶材料,将质粒ｐＩＬＴＡＢ２２７（含ｈｐｈ基因和ｇｕｓ基因）导入籼稻,在Ｂａｓｍａｔｉ－１、青油粘、新山粘２９、胜优２号,明恢６３等品种获得了转基因植株。Ｔ０转化体ｇｕｓ基因组织化学染色和ＤＮＡ分子杂交（Ｓｏｕｔｈｅｒｎ ｂｌｏｔ）证实,ｇｕｓ和ｈｐｈ基因已整合到上述品种的基因组中。本实验仔细研究了ｈｐｈ基因在Ｂａｓｍａｔｉ－１的Ｔ１     

Nickel enhances telomeric silencing in Saccharomyces cerevisiae

Certain nickel compounds including crystalline nickel sulfide (NiS) and subsulfide (Ni₃S₂) are potent human and animal carcinogens. In Chinese hamster embryo cells, an X-linked senescence gene was inactivated following nickel-induced DNA methylation. Nickel also induced the inactivation of the gpt reporter gene by chromatin condensation and a DNA methylation process in a transgenic gpt+ Chinese hamster cell line (G12), which is located near a heterochromatic region. To determine if nickel can cause gene silencing independently of DNA methylation, based only on the induction of changes in chromatin structure, we measured its effect on gene silencing in Saccharomyces cerevisiae. Growth of yeast in the presence of nickel chloride repressed a telomeric marker gene (URA3) and resulted in a stable epigenetic switch. This phenomenon was dependent on the number of cell doubling prior to selection and also on the distance of the marker gene from the end of the chromosome. The level of TPE (telomeric position effect) increased linearly with elevations of nickel concentration. Addition of magnesium inhibited this effect, but magnesium did not silence the reporter gene by itself. The level of silencing was also assessed following treatment with other transition metals: cobalt, copper and cadmium. In the sublethal range, cobalt induced similar effects as nickel, while copper and cadmium did not change the basal level of gene expression. Silencing by copper and cadmium were evident only at concentrations of those metals where the viability was very low.     

Gene conversion as a focusing mechanism for correlated mutations: a hypothesis

Ways of producing complex mutational events without substantially raising the primary mutation rate are explored. If the small amount of DNA that is resynthesised through the action of the mismatch DNA repair system is not subject to further repair, the incidence of double mutations can increase by a factor of 100, while single mutations would increase by only 30%. Such a boost in the incidence of double mutations seems insufficient to meet the needs of higher organisms. For them, an alternative strategy would be to produce complex events by a succession of single mutations occurring in a correlated manner over several sexual generations. It is proposed that gene conversion may fulfill this role. Assuming that the resynthesis of DNA that occurs during gene conversion produces mutations in the conversion tract, one predicts a tendency for close mutations in corresponding sequences in the two homologous chromosomes, to promote, during conversion, further mutations in their vicinity. Semiquantitative calculations suggest that such a mechanism can be quite effective, provided the divergence between two paired chromosomes is around 10^–4 or less. Such a mechanism might constitute an adaptive mutation strategy acting at the population level.     

Modular Dispensability of Dysferlin C2 Domains Reveals Rational Design for Mini-dysferlin Molecules

Dysferlin is a large transmembrane protein composed of a C-terminal transmembrane domain, two DysF domains, and seven C2 domains that mediate lipid- and protein-binding interactions. Recessive loss-of-function mutations in dysferlin lead to muscular dystrophies, for which no treatment is currently available. The large size of dysferlin precludes its encapsulation into an adeno-associated virus (AAV), the vector of choice for gene delivery to muscle. To design mini-dysferlin molecules suitable for AAV-mediated gene transfer, we tested internally truncated dysferlin constructs, each lacking one of the seven C2 domains, for their ability to localize to the plasma membrane and to repair laser-induced plasmalemmal wounds in dysferlin-deficient human myoblasts. We demonstrate that the dysferlin C2B, C2C, C2D, and C2E domains are dispensable for correct plasmalemmal localization. Furthermore, we show that the C2B, C2C, and C2E domains and, to a lesser extent, the C2D domain are dispensable for dysferlin membrane repair function. On the basis of these results, we designed small dysferlin molecules that can localize to the plasma membrane and reseal laser-induced plasmalemmal injuries and that are small enough to be incorporated into AAV. These results lay the groundwork for AAV-mediated gene therapy experiments in dysferlin-deficient mouse models.     

膀胱癌H-ras基因点突变和ras癌基因产物P21的表达

应用聚合酶链反应(PCR)技术结合地高辛化寡核甘酸探针杂交以及免疫组织化学方法,检测人膀眈癌组织中H-ras癌基因第12位密码子点突变和基因产物P21蛋白的表达.58例膀胱癌组织中有23例出现H-ras基因的点突变,36例P21蛋白表达阳性,5例正常膀胱组织未见点突变和P21蛋白阳性表达.本组膀胱癌第12位密码子点突变和P21阳性表达水平呈正相关,多发生在肿瘤临床T2-T4期和分化差的肿瘤,并且与膀胱癌的预后有关、提示H-ras癌基因点突变和P21蛋白阳性表达是膀胱癌的晚期表现,并在膀胱癌的发生,发展及预后中起着重要作用.