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Biomedical subjects

A Vincent

Publications and source records attributed to A Vincent.

At least 289 records · Page 16Linked to original sources
PubMed1991

Two isoforms of the muscle acetylcholine receptor alpha-subunit are translated in the human cell line TE671.

We have previously reported the existence of 2 forms of mRNA for the human muscle acetylcholine receptor (AChR) alpha-subunit, thought to be generated by alternate splicing of a primary transcript and to encode 2 alpha-subunit protein isoforms. The 2 predicted alpha-subunit isoforms, differing by the insertion of 25 amino acids at position 58/59, have been synthesized from cRNA transcripts using rabbit reticulocyte lysates; these protein isoforms could be differentiated by immunoprecipitation using antibodies raised against synthetic peptides. The antibodies were used to demonstrate translation of both AChR alpha-subunit isoforms in the rhabdomyosarcoma (muscle) cell line TE671, in an approximate 1:1 ratio.

Amino Acid Sequence↗
PubMed1991

Critical role for the Val/Gly86 HLA-DR beta dimorphism in autoantigen presentation to human T cells.

Helper T lymphocytes recognize fragments of foreign (or self) antigens in the peptide-binding clefts of major histocompatibility complex class II molecules; their activation is a crucial step in the induction of many immune and autoimmune responses. While studying the latter, we raised a T-cell line from the thymus of a myasthenia gravis patient against recombinant alpha subunit of the human acetylcholine receptor, the target of this autoimmune disease. The line responds to the 144-156 region of the human sequence and not to the same region of the electric fish homolog, which differs by only three residues. These CD4+ T cells recognize this epitope only in the context of HLA-DR4 class II molecules, of which the variants with Gly86 are absolutely required. Thus the naturally occurring alternatives Dw14.2 (Gly86) and Dw14.1 (Val86)--which differ only at this one position in the entire antigen-binding region--show an all-or-nothing difference in presenting activity. This dimorphism at position 86 is widespread, occurring in subtypes of DR1, DR2, DR3, DR5, and DR6 alleles as well as DR4. Since other DR4 subtypes with substitutions at positions 70-74 also fail to present this peptide, and glycine residues can be uniquely flexible, we suggest that this replacement at position 86 acts locally or at a distance by altering the conformation of the peptide-binding cleft. Such profound functional consequences for T-cell recognition as we report here may explain this example of conserved major histocompatibility complex diversity.

Adolescent↗
PubMed1991

Autoimmune aetiology for acquired neuromyotonia (Isaacs' syndrome)

Neuromyotonia is a rare disorder of unknown cause in which hyperexcitability of peripheral motor nerves leads to incapacitating muscle twitching, cramps, and weakness. We investigated an antibody-mediated mechanism for neuromyotonia in a 24-year-old man with a 7-year history of severe disease unresponsive to pharmacological treatment. Two periods of plasma exchange each produced almost complete disappearance of symptoms for 2-3 weeks, and a highly significant decrease in recorded neuromyotonic discharges. Injection of the patient's plasma or purified IgG into mice significantly enhanced in-vitro resistance to d-tubocurarine at the neuromuscular junction of phrenic nerve-diaphragm preparations. This finding suggests that an increase in neurotransmitter release might result from an antibody-mediated reduction in the number of functional potassium channels that normally regulate nerve excitability. The demonstration of pathogenic IgG autoantibodies in acquired neuromyotonia suggests that immunosuppressive treatment may be helpful in severe cases.

Adolescent↗
PubMed1991

A Drosophila nuclear localisation signal included in an 18 amino acid fragment from the serendipity delta zinc finger protein.

Sequence analysis of the nuclear Drosophila serendipity delta Cys-2/His-2 finger protein indicated the presence of a short motif of positively charged amino acids, with homology to the SV40 large T and c-myc nuclear localisation signals. Using P-element mediated transformation we constructed transgenic Drosophila lines expressing beta-galactosidase fusion proteins, containing (or not) an 18 residue segment of sry delta including this basic, PTKKRVK, motif. Histochemical detection of fusion proteins on dissected tissues showed that this segment of sry delta can act autonomously to drive the beta-galactosidase in nuclei.

Amino Acid Sequence↗
PubMed1991

Isolation of sequences that span the fragile X and identification of a fragile X-related CpG island.

Yeast artificial chromosomes (YACs) were obtained from a 550-kilobase region that contains three probes previously mapped as very close to the locus of the fragile X syndrome. These YACs spanned the fragile site in Xq27.3 as shown by fluorescent in situ hybridization. An internal 200-kilobase segment contained four chromosomal breakpoints generated by induction of fragile X expression. A single CpG island was identified in the cloned region between markers DXS463 and DXS465 that appears methylated in mentally retarded fragile X males, but not in nonexpressing male carriers of the mutation nor in normal males. This CpG island may indicate the presence of a gene involved in the clinical phenotype of the syndrome.

Base Sequence↗
PubMed1991

Abnormal pattern detected in fragile-X patients by pulsed-field gel electrophoresis.

The fragile-X syndrome is the most frequent inherited form of mental retardation, with an incidence of 1 in 1,500 males. It is characterized by the presence of a fragile site at Xq27.3 induced in vitro by folate deprivation or by inhibitors of deoxynucleotide synthesis. Its mode of inheritance is unusual for an X-linked trait, with incomplete penetrance in both males and females. Some phenotypically normal males transmit the mutation to all their daughters who rarely express any symptoms, but penetrance is high in sons and daughters of these carrier women. Genetic and physical mapping of the Xq27-q28 region has confirmed that the disease locus is located at or very near the fragile site. Hypotheses proposed to account for the abnormalities in the inheritance of the disease include sequence rearrangements by meiotic recombination or a mutation that affects reactivation of an inactive X chromosome during differentiation of female germ cells. To detect such rearrangements, or methylation changes that may reflect a locally inactive X chromosome, we used pulsed-field gel analysis of DNA from fragile-X patients with probes close to the fragile-X locus. The probe Do33 (DXS465) detected abnormal patterns in fragile-X patients, but not in normal controls or in non-expressing male transmitters.

DNA Probes↗
PubMed1991

Seronegative myasthenia gravis: a plasma factor inhibiting agonist-induced acetylcholine receptor function copurifies with IgM.

Anti-acetylcholine receptor antibodies cannot be detected by standard radioimmunoassay in 10 to 15% of patients with generalized myasthenia gravis (seronegative myasthenia gravis). We investigated the effect of seronegative myasthenia gravis plasma on 22Na+ flux through acetylcholine receptors and voltage-gated sodium channels in the human rhabdomyosarcoma cell line, TE671. Fourteen of 19 seronegative MG plasmas inhibited acetylcholine receptor 22Na+ flux; none inhibited voltage-gated sodium channel flux. The inhibitory activity was found in the IgG-depleted fraction, and copurified with IgM after gel-filtration chromatography. Inhibitory activity was absent from the plasma of 8 healthy control subjects and of 6 patients with the Lambert-Eaton myasthenic syndrome, but was present in the IgG-depleted plasma fraction of 4 of 6 seropositive patients with myasthenia gravis and all 5 patients with demyelinating polyneuropathy. We conclude that a low-affinity serum factor, probably an IgM antibody, found in a high proportion in patients with seronegative and those with seropositive myasthenia gravis may contribute to the muscle weakness in myasthenia gravis, but its role in these and other neuroimmunological disorders requires further investigation.

Autoantibodies↗
PubMed1991

Genomic targets of the serendipity beta and delta zinc finger proteins and their respective DNA recognition sites.

The closely related Drosophila serendipity (sry) beta (beta) and delta (delta) Cys2-His2 zinc finger proteins show partly overlapping in vitro DNA binding specificities and distinct patterns of binding sites on polytene chromosomes. Using a newly developed procedure, we identified genomic DNA targets for these two proteins. Both the sry beta and delta proteins protect an 18-22 base region from DNase I digestion within each analysed genomic binding site, that includes a 13 bp consensus sequence. The consensus recognition sites sry beta 5'-YCAGAGATGCGCA-3' and sry delta 5'-YTAGAGATGGRAA-3' thus differ by nucleotides at four out of 13 positions. They are determinant for specific binding of the sry beta and delta proteins, respectively, produced in Escherichia coli or present in Drosophila embryos. We further show that sry beta is the major (if not exclusive) Drosophila nuclear protein that specifically binds the 5'-CAGAGTGCGC-3' sequence. The identified sry beta genomic targets are all contained within single-copy DNA in euchromatic regions of the genome. Two out of the five characterized in detail map at cytological positions coincident with binding sites of the native sry beta protein on polytene chromosomes.

Animals↗
PubMed1991

Linkage relationship between incontinentia pigmenti (IP2) and nine terminal X long arm markers.

Linkage data for familial incontinentia pigmenti (IP2) and nine X chromosomal markers are reported. Previously found linkage between IP2 and the DXS52 locus is confirmed with the maximum lod score of 6.19 at a recombination fraction of 0.03. Linkage is also established with loci DXS134, DXS15 and DXS33. Multipoint analysis allows us to localize the IP2 locus outside a block of seven linked markers of the Xq28 region.

Chromosome Mapping↗
PubMed1991

Electrodermal differentiation of deception: perceived accuracy and perceived memorial content manipulations.

The demonstration of deception as a psychophysiological phenomenon requires a comparison of physiological responses to two conditions (experimental and control) which differ only with respect to deception. Such electrodermal (skin conductance response) differentiation was recently reported in the Differentiation of Deception paradigm, which controls for two potentially important sources of confounding in polygraph (often referred to as the Detection of Deception): differential question significance and differential frequency of question occurrence. The present study manipulated (between 32 subjects in a 2 x 2 design) two two-level, subjective factors in the paradigm: Perceived Accuracy of polygraphy (written and oral instructions characterising accuracy as high vs low) and Perceived Memorial Content (20 more complex, less personal, and less meaningful questions vs 6 less complex, more personal, and more meaningful questions). Significant differentiation of deception was again obtained, as was evidence for the effectiveness of the manipulations. However, the deception phenomenon was not clearly affected by either of the two subjective factors. In addition, one post-hoc test showed significantly increased differentiation under the low Perceived Accuracy condition, which is contrary to the widespread belief of polygraphers that high perceived accuracy is not only important but even essential for the detection of deception. However, the applied, polygraphic aim of detecting guilt in individuals is quite different from the scientific, psychophysiological aim of differentiating deception as a psychological process, and the phenomena involved probably have different causes.

Deception↗
PubMed1991

Genetic analysis of the cellularization of the Drosophila embryo.

The synchronous cellularization of the Drosophila embryo at the blastoderm stage provides a unique system for studying the molecular mechanisms involved in cytokinesis, using genetical and biochemical approaches. The cellularization process requires the major components of the embryonic cytoskeleton that are deposited into the egg during oogenesis. Genetical analysis indicates that it requires also the products of additional maternally-acting genes, as well as that of a limited set of zygotically-acting genes. The cellularization defective phenotypes associated with small deficiencies uncovering these latter loci reveal specific steps within this complex process. The molecular analysis of these genes will ultimately provide meaningful insights into the normal process of cellularization. Among them, the serendipity alpha gene encodes a membrane-associated protein, which is exclusively accumulated during cellularization, and is required for the reorganization of the microfilaments as the onset of cellularization.

Actins↗
PubMed1991

Physical mapping of two loci (D9S5 and D9S15) tightly linked to Friedreich ataxia locus (FRDA) and identification of nearby CpG islands by pulse-field gel electrophoresis.

The Friedreich's ataxia locus (FRDA) has recently been mapped to 9q13-q21 by tight linkage to D9S15 and D9S5 loci. The present lack of recombination between these loci precludes further genetic mapping and suggests that the distances involved are in the megabase range. We have established a 1-Mb map around loci D9S15 (defined by probe MCT112) and D9S5 (defined by probe DR47) and found that they are at most 260 apart. Six rare cutting site clusters were found in a 450-kb segment containing both loci. Three clusters were completely unmethylated in two cell lines tested and might correspond to CpG islands flanking transcribed sequences. Cosmid mapping of a 52-kb region around D9S5 and pulse-field gel electrophoresis analysis showed the presence of three other CpG clusters that were partially or completely methylated. Two of them were present in the cosmid clones available and were associated with sequences conserved in other vertebrate species. The CpG islands and conserved sequences presented here can be used to search for genes defective in Friedreich's ataxia.

Animals↗
PubMed1991

Antibody-mediated neurological disease.

The number of neurological disorders in which autoantibodies are thought to play a pathogenic role continues to increase although the strength of the evidence varies. Many of the disorders are tumour associated.

Animals↗
PubMed1991

Immunological evidence for the co-existence of the Lambert-Eaton myasthenic syndrome and myasthenia gravis in two patients.

Two patients are described in whom a clinical and electromyographic diagnosis of the Lambert-Eaton myasthenic syndrome (LEMS) was made. Serum antibodies to voltage-gated calcium channels (VGCCs), the antigenic target in LEMS and to acetylcholine receptors (AChRs), the antigen in myasthenia gravis, were detected at raised titres in both cases, using radioimmunoassays based on 125I-omega-Conotoxin labelled VGCCs and 125I-alpha-Bungarotoxin labelled AChRs. These data provide immunological evidence for the coexistence of the two disorders in these patients.

Adult↗
PubMed1991

Four chromosomal breakpoints and four new probes mark out a 10-cM region encompassing the fragile-X locus (FRAXA).

We report the validation and use of a cell hybrid panel which allowed us a rapid physical localization of new DNA probes in the vicinity of the fragile-X locus (FRAXA). Seven regions are defined by this panel, two of which lie between DXS369 and DXS296, until now the closest genetic markers that flank FRAXA. Of those two interesting regions, one is just distal to DXS369 and defined by probe 2-71 (DXS476), which is not polymorphic. The next one contains probes St677 (DXS463) and 2-34 (DXS477), which are within 130 kb and both detect TaqI RFLPs. The combined informativeness of these two probes is 30%. We cloned from an irradiation-reduced hybrid line another new polymorphic probe, Do33 (DXS465; 42% heterozygosity). This probe maps to the DXS296 region, proximal to a chromosomal breakpoint that corresponds to the Hunter syndrome locus (IDS). The physical order is thus Cen-DXS369-DXS476-(DXS463,DXS477)-(DXS296, DXS465)-IDS-DXS304-tel. We performed a linkage analysis for five of these markers in both the Centre d'Etude du Polymorphisme Humain families and in a large set of fragile-X families. This establishes that DXS296 is distal to FRAXA. The relative position of DXS463 and DXS477 with respect to FRAXA remains uncertain, but our results place them genetically halfway between DXS369 and DXS304. Thus the DXS463-DXS477 cluster defines presently either the closest proximal or the closest distal polymorphic marker with respect to FRAXA. The three new polymorphic probes described here have a combined heterozygosity of 60% and represent a major improvement for genetic analysis of fragile-X families, in particular for diagnostic applications.

Blotting, Southern↗
PubMed1991

Osteochondral allografts in arm and forearm surgery.

Osteochondral allografting can restore the skeletal continuity anatomically after a limb salvage procedure. Evaluation of the clinical function indicates that a good result can be anticipated. Fracture was the most frequent complication, and the fixation technique we used initially predisposed the problem. The major advantage of allograft is the possibility of reinsertion of soft tissue to help stabilize the new joint. In addition, any part of the limb can potentially be reconstructed with an allograft.

Adolescent↗