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T-tubule biogenesis and triad formation in skeletal muscle and implication in human diseases
Lama Al-Qusairi, Jocelyn Laporte
Skeletal Muscle , 2011, DOI: 10.1186/2044-5040-1-26
Abstract: To trigger skeletal muscle contraction, the action potential generated by motor neurons is transmitted through motor nerves to muscle cells. The excitation-contraction (EC) coupling, i.e. signal transmission from the sarcolemma to the actin/myosin apparatus, is mediated by a second messenger, calcium ions. Indeed, muscle fibers contain large internal calcium stores with the ability to quickly release and retrieve calcium (Figure 1, right panel). For a fast and fine-tuning of muscle contraction, these stores are maintained under the control of the action potential, which ensures calcium release simultaneously within the whole interior of the muscle fiber. As myofibers are 50-100 μm in diameter and several millimeters to centimeters long, a highly specialized structure named the triad is necessary to overcome spatial limits in using calcium as secondary messenger, and connect the sarcolemma with the calcium stores. The sarcolemma forms regular invaginations which insert between myofibrils, termed transverse tubules (T-tubules). In skeletal muscle, T-tubules tightly associate with the sarcoplasmic reticulum (SR), in a region called terminal cisternae/junctional SR. The close association of one T-tubule with two terminal cisternae on both sides of the tubule forms the triad (Figure 1).A large set of specialized proteins takes part in EC coupling and includes: i) the Dihydhropyridine Receptor (DHPR), a voltage gated calcium channel located on T-tubule membranes [1,2], ii) the Ryanodine Receptor (RyR1), a calcium release channel that is localized on the junctional face of SR and appears as "feet" when observed by electron microscopy (Figure 1, left panel) [3], iii) calcium buffering proteins such as calsequestrin in the lumen of the SR [4], iv) calcium channel regulators such as calmodulin, FKBP12 and many others [5,6], v) Sarco-Endoplasmic Reticulum Calcium ATPase pumps (SERCA), which is indirectly involved in EC coupling via its action in the rapid removal of the cytoso
Centronuclear (myotubular) myopathy
Heinz Jungbluth, Carina Wallgren-Pettersson, Jocelyn Laporte
Orphanet Journal of Rare Diseases , 2008, DOI: 10.1186/1750-1172-3-26
Abstract: The incidence of X-linked myotubular myopathy is estimated at 2/100000 male births but epidemiological data for other forms are not currently available.The clinical picture is highly variable. The X-linked form usually gives rise to a severe phenotype in males presenting at birth with marked weakness and hypotonia, external ophthalmoplegia and respiratory failure. Signs of antenatal onset comprise reduced foetal movements, polyhydramnios and thinning of the ribs on chest radiographs; birth asphyxia may be the present. Affected infants are often macrosomic, with length above the 90th centile and large head circumference. Testes are frequently undescended. Both autosomal-recessive (AR) and autosomal-dominant (AD) forms differ from the X-linked form regarding age at onset, severity, clinical characteristics and prognosis. In general, AD forms have a later onset and milder course than the X-linked form, and the AR form is intermediate in both respects.Mutations in the myotubularin (MTM1) gene on chromosome Xq28 have been identified in the majority of patients with the X-linked recessive form, whilst AD and AR forms have been associated with mutations in the dynamin 2 (DNM2) gene on chromosome 19p13.2 and the amphiphysin 2 (BIN1) gene on chromosome 2q14, respectively. Single cases with features of CNM have been associated with mutations in the skeletal muscle ryanodine receptor (RYR1) and the hJUMPY (MTMR14) genes.Diagnosis is based on typical histopathological findings on muscle biopsy in combination with suggestive clinical features; muscle magnetic resonance imaging may complement clinical assessment and inform genetic testing in cases with equivocal features. Genetic counselling should be offered to all patients and families in whom a diagnosis of CNM has been made.The main differential diagnoses include congenital myotonic dystrophy and other conditions with severe neonatal hypotonia.Management of CNM is mainly supportive, based on a multidisciplinary approach. Wher
Defective Membrane Remodeling in Neuromuscular Diseases: Insights from Animal Models
Belinda S. Cowling equal contributor,Anne Toussaint equal contributor,Jean Muller,Jocelyn Laporte
PLOS Genetics , 2012, DOI: 10.1371/journal.pgen.1002595
Abstract: Proteins involved in membrane remodeling play an essential role in a plethora of cell functions including endocytosis and intracellular transport. Defects in several of them lead to human diseases. Myotubularins, amphiphysins, and dynamins are all proteins implicated in membrane trafficking and/or remodeling. Mutations in myotubularin, amphiphysin 2 (BIN1), and dynamin 2 lead to different forms of centronuclear myopathy, while mutations in myotubularin-related proteins cause Charcot-Marie-Tooth neuropathies. In addition to centronuclear myopathy, dynamin 2 is also mutated in a dominant form of Charcot-Marie-Tooth neuropathy. While several proteins from these different families are implicated in similar diseases, mutations in close homologues or in the same protein in the case of dynamin 2 lead to diseases affecting different tissues. This suggests (1) a common molecular pathway underlying these different neuromuscular diseases, and (2) tissue-specific regulation of these proteins. This review discusses the pathophysiology of the related neuromuscular diseases on the basis of animal models developed for proteins of the myotubularin, amphiphysin, and dynamin families. A better understanding of the common mechanisms between these neuromuscular disorders will lead to more specific health care and therapeutic approaches.
From Dynamic Live Cell Imaging to 3D Ultrastructure: Novel Integrated Methods for High Pressure Freezing and Correlative Light-Electron Microscopy
Coralie Spiegelhalter,Valérie Tosch,Didier Hentsch,Marc Koch,Pascal Kessler,Yannick Schwab,Jocelyn Laporte
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0009014
Abstract: In cell biology, the study of proteins and organelles requires the combination of different imaging approaches, from live recordings with light microscopy (LM) to electron microscopy (EM).
Mild Functional Differences of Dynamin 2 Mutations Associated to Centronuclear Myopathy and Charcot-Marie-Tooth Peripheral Neuropathy
Olga S. Koutsopoulos, Catherine Koch, Valerie Tosch, Johann B?hm, Kathryn N. North, Jocelyn Laporte
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0027498
Abstract: The large GTPase dynamin 2 is a key player in membrane and cytoskeletal dynamics mutated in centronuclear myopathy (CNM) and Charcot-Marie Tooth (CMT) neuropathy, two discrete dominant neuromuscular disorders affecting skeletal muscle and peripheral nerves respectively. The molecular basis for the tissue-specific phenotypes observed and the physiopathological mechanisms linked to dynamin 2 mutations are not well established. In this study, we have analyzed the impact of CNM and CMT implicated dynamin 2 mutants using ectopic expression of four CNM and two CMT mutations, and patient fibroblasts harboring two dynamin 2 CNM mutations in established cellular processes of dynamin 2 action. Wild type and CMT mutants were seen in association with microtubules whereas CNM mutants lacked microtubules association and did not disrupt interphase microtubules dynamics. Most dynamin 2 mutants partially decreased clathrin-mediated endocytosis when ectopically expressed in cultured cells; however, experiments in patient fibroblasts suggested that endocytosis is overall not defective. Furthermore, CNM mutants were seen in association with enlarged clathrin stained structures whereas the CMT mutant constructs were associated with clathrin structures that appeared clustered, similar to the structures observed in Dnm1 and Dnm2 double knock-out cells. Other roles of dynamin 2 including its interaction with BIN1 (amphiphysin 2), and its function in Golgi maintenance and centrosome cohesion were not significantly altered. Taken together, these mild functional defects are suggestive of differences between CMT and CNM disease-causing dynamin 2 mutants and suggest that a slight impairment in clathrin-mediated pathways may accumulate over time to foster the respective human diseases.
Case report of intrafamilial variability in autosomal recessive centronuclear myopathy associated to a novel BIN1 stop mutation
Johann B?hm, Ulu? Yi?, Rag?p Orta?, Handan ?akmak??, Semra Kurul, Eray Dirik, Jocelyn Laporte
Orphanet Journal of Rare Diseases , 2010, DOI: 10.1186/1750-1172-5-35
Abstract: Centronuclear myopathies (CNM) are a group of congenital disorders characterized by hypotonia and skeletal muscle biopsies typically showing small rounded fibers with central nuclei [1-4]. Abnormal nuclear positioning is seen in several myopathies, but clinical, genetic and pathological factors clearly distinguish these myopathies from CNM. Three CNM classes have been described: the severe neonatal X-linked form, also called myotubular myopathy (XLCNM, OMIM 310400), the autosomal recessive form with childhood onset (ARCNM, OMIM 255200), and the autosomal dominant form with adult onset (ADCNM, OMIM 160150). Myotubularin (MTM1) is mutated in XLCNM [5] and belongs to a large family of ubiquitously expressed phosphoinositide phosphatases implicated in intracellular vesicle trafficking [6-8]. The large GTPase dynamin 2 (DNM2), mutated in ADCNM, is a mechanochemical enzyme and a key factor in membrane trafficking and endocytosis [9-11]. Amphiphysin 2 (BIN1) is mutated in ARCNM and possesses an N-terminal BAR domain able to sense and bend membranes and a SH3 domain mediating protein-protein interactions [12,13]. A muscle-specific isoform is implicated in T-tubule biogenesis and contains a polybasic residue sequence binding to phosphoinositides [14]. Only 4 unrelated individuals with BIN1 mutations have been molecularly and clinically characterized to date [12,15] and this report is the first description of intrafamilal variability in two patients from a consanguineous family. Clinical analysis of respiratory and cardiac involvement diagnosed for the more severely affected male patient expand the phenotypic spectrum in autosomal recessive centronuclear myopathy. It is furthermore the first time that patients with a BIN1 mutation are analyzed by whole-body MRI and the results contrast previous findings on DNM2-related CNM.Patient 1 is a 13 year old girl belonging to a consanguineous family from Turkey without ancestral history of neuromuscular disorders (Figure 1A-B). There
Choosing an Ideal Graduate Education: The Nueva Ecija University of Science and Technology Experience  [PDF]
Jocelyn B. Cruz
Open Journal of Social Sciences (JSS) , 2018, DOI: 10.4236/jss.2018.69018
Abstract: With the use of descriptive research, the researcher investigated the reasons of 152 freshman graduate school students in choosing NEUST for their graduate education. The respondents agreed that enrolling in NEUST Graduate Programs will make them good critical thinkers, collaborators, proficient speakers, responsible and productive citizens. Likewise, they have chosen the university because of its quality education, highly qualified teachers, affordable fees and high accreditation status. Efficiency of the services of the different offices was experienced by the respondents. However, they want to improve on the classroom condition, students’ lounge, graduate school library schedule and library holdings. Likewise, they wished for accessible clean restroom per level of graduate school building.
Appropriate Nouns with Obligatory Modifiers
E. Laporte
Computer Science , 2012,
Abstract: The notion of appropriate sequence as introduced by Z. Harris provides a powerful syntactic way of analysing the detailed meaning of various sentences, including ambiguous ones. In an adjectival sentence like 'The leather was yellow', the introduction of an appropriate noun, here 'colour', specifies which quality the adjective describes. In some other adjectival sentences with an appropriate noun, that noun plays the same part as 'colour' and seems to be relevant to the description of the adjective. These appropriate nouns can usually be used in elementary sentences like 'The leather had some colour', but in many cases they have a more or less obligatory modifier. For example, you can hardly mention that an object has a colour without qualifying that colour at all. About 300 French nouns are appropriate in at least one adjectival sentence and have an obligatory modifier. They enter in a number of sentence structures related by several syntactic transformations. The appropriateness of the noun and the fact that the modifier is obligatory are reflected in these transformations. The description of these syntactic phenomena provides a basis for a classification of these nouns. It also concerns the lexical properties of thousands of predicative adjectives, and in particular the relations between the sentence without the noun : 'The leather was yellow' and the adjectival sentence with the noun : 'The colour of the leather was yellow'.
Lexicon management and standard formats
Eric Laporte
Computer Science , 2007,
Abstract: International standards for lexicon formats are in preparation. To a certain extent, the proposed formats converge with prior results of standardization projects. However, their adequacy for (i) lexicon management and (ii) lexicon-driven applications have been little debated in the past, nor are they as a part of the present standardization effort. We examine these issues. IGM has developed XML formats compatible with the emerging international standards, and we report experimental results on large-coverage lexica.
Evaluation of a Grammar of French Determiners
Eric Laporte
Computer Science , 2007,
Abstract: Existing syntactic grammars of natural languages, even with a far from complete coverage, are complex objects. Assessments of the quality of parts of such grammars are useful for the validation of their construction. We evaluated the quality of a grammar of French determiners that takes the form of a recursive transition network. The result of the application of this local grammar gives deeper syntactic information than chunking or information available in treebanks. We performed the evaluation by comparison with a corpus independently annotated with information on determiners. We obtained 86% precision and 92% recall on text not tagged for parts of speech.
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