Deficiency of a glycoprotein component of the dystrophin complex in dystrophic muscle

Dystrophin, the protein encoded by the Duchenne muscular dystrophy (DMD) gene, exists in a large oligomeric complex. We show here that four glycoproteins are integral components of the dystrophin complex and that the concentration of one of these is greatly reduced in DMD patients. Thus, the absence of dystrophin may lead to the loss of a dystrophin-associated glycoprotein, and the reduction in this glycoprotein may be one of the first stages of the molecular pathogenesis of muscular dystrophy.     

运动与骨骼肌中的基因表达

通过献资料法阐述了运动对骨骼肌基因表达的影响,以便深入理解骨骼肌的工作原理,为客观指导运动训练提供依据．     

肌肉组织疲劳过程的超声衰减特征

基于超声波在生物软组织中的传播机理以及肌肉疲劳过程中组织厚度、弹性等特征的变化,研究了超声衰减特性与肌肉疲劳过程的相关性,理论分析了超声波幅度随肌肉疲劳的变化规律。设计针对右肱二头肌的实验,探讨了激励声波在逐渐疲劳的组织中传输的响应规律。同步采集表面肌电信号,研究肌肉疲劳过程中肌电信号与超声衰减特征的相关性。理论分析及实验结果表明,在肌肉疲劳过程中,随着疲劳程度的增强,超声波传输后平均能量幅度逐渐减小,其减小趋势满足指数衰减规律,同时同步采集的表面肌电信号均方根值呈线性增加趋势。     

人颞肌亚部化及其肌内神经分布研究

目的:查明人颞肌肌内神经、肌梭的配布特征以及相互关系,为临床成功进行肌移植提供解剖学依据.方法:20侧成人尸体颢肌标本,每具尸体选1侧,共10侧采用改良Sihler氏神经染色观察颞肌肌内神经分布.另10侧标本,依据颞肌肌纤维排列方向分前、中、后3部份,分别制作组织块,HE染色后应用图像分析仪对颞肌肌梭的形态结构、空间构象以及分布密度进行体视学分析.结果:改良Sihler氏神经染色显示颞肌有3条独立的神经分支呈放射状由颢肌下缘向肌远端分布.颞肌肌梭分布呈不均质性.在颞肌前部近喙突处神经分支密集区,肌梭分布密度高,空间构象多样;而在颞肌后部以及颞肌的远端缺乏肌梭的分布.结论:颞肌可划分为3个功能完整和独立的肌亚部.     

The Duchenne muscular dystrophy gene product is localized in sarcolemma of human skeletal muscle

Duchenne muscular dystrophy (DMD) and its milder form, Becker muscular dystrophy (BMD), are allelic X-linked muscle disorders in man. The gene responsible for the disease has been cloned from knowledge of its map location at band Xp21 on the short arm of the X chromosome. The product of the DMD gene, a protein of relative molecular mass 400,000 (Mr 400K) recently named dystrophin, has been reported to co-purify with triads of mouse and rabbit skeletal muscle when assayed using polyclonal antibodies raised against fusion proteins encoded by regions of mouse DMD complementary DNA. Here we show that antibodies directed against synthetic peptides and fusion proteins derived from the N-terminal region of human DMD cDNA strongly react with an antigen present in skeletal muscle sarcolemma on cryostat sections of normal human muscle biopsies. This immunoreactivity is reduced or absent in muscle fibres from DMD patients but appears normal in muscle fibres from patients with other myopathic diseases. The same antibodies specifically react with a 400K protein in sodium dodecyl sulphate (SDS) extracts of normal human muscle subjected to Western blot analysis. We conclude that the product of the DMD gene is associated with the sarcolemma rather than with the triads and speculate that it strengthens the sarcolemma by anchoring elements of the internal cytoskeleton to the surface membrane.     

Immunoelectron microscopic localization of dystrophin in myofibres

Duchenne muscular dystrophy, a common X-linked recessive human disease, has recently been shown to be caused by the deficiency of a large, low abundance protein called 'dystrophin'. Biochemical techniques have shown dystrophin to be membrane-associated in skeletal muscle, with enrichment of dystrophin in the t-tubules of 'triads'. Other studies using immunohistochemistry on thick (10 micron) sections have shown dystrophin to be located at the periphery of muscle fibres, possibly at the plasma membrane. These results have been interpreted as being either consistent and complementary, or contradictory. To localize dystrophin more precisely relative to these membrane systems we have employed highly sensitive and spatially accurate immuno-gold electron microscopy of ultra-thin (70-100 nm) cryosections. The major distribution of dystrophin was on the cytoplasmic face of the plasma membrane of muscle fibres, and possibly on the contiguous t-tubule membranes. The presented data, taken together with recently accumulated information regarding the primary structure of dystrophin, suggests that dystrophin is a component of the membrane cytoskeleton in myogenic cells. Thus, myofibre necrosis in patients affected with Duchenne muscular dystrophy is likely the result of plasma membrane instability.     

Single postsynaptic channel currents in tissue cultured muscle

Some of the most compelling evidence for the existence of ionic channels in cell membranes comes from direct recording of quantised current jumps generated by the opening and closing of individual channels. Single-channel jumps have been extensively studied for lipid bilayer membranes doped with various channel-forming additives. Recently agonist-induced single-channel currents were detected in denervated frog muscle by use of extracellular electrodes, which can isolate the current from a small area of membrane. The current jumps provide a means for the direct test of many of the inferences about ionic channels which have come from electrical noise analysis. In this report we present measurements of single-channel currents induced by the agonist carbamylcholine in tissue-cultured mammalian muscle. These measurements confirm the earlier noise studies on tissue culture preparations. Recordings of single-channel currents induced by the agonist, suberyldicholine, in avian muscle are presented by Nelson and Sachs.     

广东地区宫颈癌组织HPV18L1基因的克隆及序列分析

目的:了解广东地区地方株HFV18L1基因结构特点,为HPV感染的检测和基因工程疫苗的研制提供实验基础.方法:采用PCR技术从广东地区宫颈癌组织中扩增HPV18L1基因,克隆人毕赤酵母表达载体pPICZaB,测序并对HPV18L1基因进行序列分析.结果:广东地区分离株与德国标准株在核苷酸序列上有4处不同,其中3处由于核苷酸的改变,其编码的氨基酸也发生相应变化,与标准株的同源性为99.8%.与中国西安地区分离株比较有两处突变点相同.结论:广东地区HPV18L1分离株与德国标准株、中国其他地区分离株之间均存在差异.     

Localization of muscle gene products in nuclear domains

The localization of gene products is central to the development of cell polarity and pattern specification during embryogenesis. To monitor the distribution of gene products encoded by different nuclei in the same cell in tissue culture, we fused cells of different species to form multinucleated non-dividing heterokaryons. In previous fusion studies, cell-surface antigens and organelles contributed by disparate cell types intermixed within minutes. Using heterokaryons produced with differentiated muscle cells, we demonstrate here that a muscle membrane component, the Golgi apparatus mediating its transport, and a sarcomeric myosin heavy chain are localized in the vicinity of the nuclei responsible for their synthesis. These results provide direct evidence that products (organelle, membrane and structural proteins) derived from individual nuclei can remain localized in myotubes, a finding with implications both for neuromuscular synapse formation and for the carrier state of Duchenne muscular dystrophy.     

Nucleotide sequence of the rat skeletal muscle actin gene

The actins constitute a family of highly conserved proteins found in all eukaryotic cells. Their conservation through a very wide range of taxonomic groups and the existence of tissue-specific isoforms make the actin genes very interesting for the study of the evolution of genes and their controlling elements. On the basis of amino acid sequence data, at least six different mammalian actins have been identified (skeletal muscle, cardiac muscle, two smooth muscle actins and the cytoplasmic beta- and gamma-actins). Rat spleen DNA digested by the EcoRI restriction enzyme contains at least 12 different fragments with actin-like sequences but only one which hybridized, in very stringent conditions, with the skeletal muscle cloned cDNA probe. Here we describe the sequence of the actin gene in that fragment. The nucleotide sequence codes for two amino acids, Met-Cys, preceding the known N-terminal Asp of the mature protein. There are five small introns in the coding region and a large intron in the 5'-untranslated region. Comparison of the structure of the rat skeletal muscle actin gene with available data on actin genes from other organisms shows that while the sequenced actin genes from Drosophila and yeast have introns at different locations, introns located at codons specifying amino acids 41, 121, 204 and 267 have been preserved at least from the echinoderm to the vertebrates. A similar analysis has been done by Davidson. An intron at codon 150 is common to a plant actin gene and the skeletal muscle acting gene.     

Association of dystrophin and an integral membrane glycoprotein

Duchenne muscular dystrophy (DMD) is caused by a defective gene found on the X-chromosome. Dystrophin is encoded by the DMD gene and represents about 0.002% of total muscle protein. Immunochemical studies have shown that dystrophin is localized to the sarcolemma in normal muscle but is absent in muscle from DMD patients. Many features of the predicted primary structure of dystrophin are shared with membrane cytoskeletal proteins, but the precise function of dystrophin in muscle is unknown. Here we report the first isolation of dystrophin from digitonin-solubilized skeletal muscle membranes using wheat germ agglutinin (WGA)-Sepharose. We find that dystrophin is not a glycoprotein but binds to WGA-Sepharose because of its tight association with a WGA-binding glycoprotein. The association of dystrophin with this glycoprotein is disrupted by agents that dissociate cytoskeletal proteins from membranes. We conclude that dystrophin is linked to an integral membrane glycoprotein in the sarcolemma. Our results indicate that the function of dystrophin could be to link this glycoprotein to the underlying cytoskeleton and thus help either to preserve membrane stability or to keep the glycoprotein non-uniformly distributed in the sarcolemma.     

Mutations of the BRAF gene in human cancer

Cancers arise owing to the accumulation of mutations in critical genes that alter normal programmes of cell proliferation, differentiation and death. As the first stage of a systematic genome-wide screen for these genes, we have prioritized for analysis signalling pathways in which at least one gene is mutated in human cancer. The RAS RAF MEK ERK MAP kinase pathway mediates cellular responses to growth signals. RAS is mutated to an oncogenic form in about 15% of human cancer. The three RAF genes code for cytoplasmic serine/threonine kinases that are regulated by binding RAS. Here we report BRAF somatic missense mutations in 66% of malignant melanomas and at lower frequency in a wide range of human cancers. All mutations are within the kinase domain, with a single substitution (V599E) accounting for 80%. Mutated BRAF proteins have elevated kinase activity and are transforming in NIH3T3 cells. Furthermore, RAS function is not required for the growth of cancer cell lines with the V599E mutation. As BRAF is a serine/threonine kinase that is commonly activated by somatic point mutation in human cancer, it may provide new therapeutic opportunities in malignant melanoma.