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Biomedical subjects

A Vincent

Publications and source records attributed to A Vincent.

At least 433 records · Page 24Linked to original sources
PubMed1981

Acetylcholine receptor antibody synthesis by thymic lymphocytes: correlation with thymic histology.

Antiacetylcholine receptor antibody (anti-AChR) was spontaneously synthesized by cultured thymic tissue from 19 of 35 patients with myasthenia gravis. Two other thymus cultures produced antibody after stimulation by pokeweed mitogen. Antibody production correlated with histologic evidence of thymitis, long duration of symptoms, or high serum anti-AChR values. None of seven thymomas synthesized antibody in culture, but evidence suggested that there had been in vivo synthesis or trapping of anti-AChR. Clinical improvement after thymectomy, during the short period of study, did not correlate with synthesis rates of anti-AChR production by the removed thymus. The rates of anti-AChR production in culture were too low to suggest that the thymus is the major source of this antibody. Although we did not find a clear relationship between anti-AChR antibody and clinical state within 3 months of thymectomy, in a study of 25 nonimmunosuppressed, nonthymoma patients followed for 1 to 4 years, we found a significant correlation (p less than 0.05, Spearman Rank correlation) between fall in anti-AChR antibody and clinical improvement after thymectomy (unpublished observations).

Acetylcholine↗
PubMed1981

Absence of anti-acetylcholine receptor antibodies in Praomys (Mastomys) natalensis.

It has been suggested in the past that Praomys (Mastomys) natalensis might be an animal model for human myasthenia gravis. This suggestion was based on the occurrence of thymomas and autoantibody to striated muscle in this animal species. Myasthenia gravis in man is associated with anti-striated muscle antibody and thymoma as well as antiacetylcholine receptor antibody. This prompted us to search for such autoantibodies in Mastomys. There was no evidence of anti-acetylcholine receptor antibody in any of the serum samples tested. The titres found in Mastomys correspond to those observed in human control sera. No difference was found in the number of alpha-bungarotoxin-binding sites at the motor endplate and in muscle extracts between animals with and without thymoma and with and without anti-striated muscle antibody. These findings lead to the conclusion that it is very unlikely that myasthenia gravis occurs with any frequency in Praomys (Mastomys) natalensis.

Acetylcholine↗
PubMed1980

Ribonucleotide sequences non-adjacent to poly(A) participate in the poly(A)-protein complex in 15S duck globin mRNP particles.

The study of the interaction between mRNA and proteins in the polyribosomal 15 S duck globin messenger ribonucleoprotein complex showed that proteins protect specific mRNA sequences against digestion by the nonspecific micrococcal nuclease (Nucleic Acids Research 6 (8) 2787, 1979). Here we report the isolation of the poly(A)-protein RNP complex from nuclease digested 15 S mRNP by two different methods: sucrose gradient sedimentation and oligo(dT)-cellulose chromatography. We show by fingerprint analysis, that aprt from the periodically fragmented poly(A) segment, mRNA sequences adjacent and non-adjacent to the poly(A) segment are protected by the poly(A) binding proteins against nuclease digestion. The duck globin poly(A)-protein RNP complex, with a sedimentation coefficient between 7 S and 10 S, shows a characteristic protein composition, with a major 73,000 MW polypeptide and some minor components. The results are discussed in view of a dynamic ribonucleoprotein structure.

Animals↗
PubMed1980

Messenger RNA for cataractous lens proteins are also present on normal lens polyribosomes.

We have previously described an experimental model in vivo where cataract is induced by injection of the antimitotic bleomycin in the newborn rat. The first opacity of the lens appears 12--15 days after the injection of the drug concomitantly with a group of precise biochemical modifications among the soluble crystallins. These modifications are mainly the accumulation of two additional low-molecular-weight beta crystallin subunits (beta L subunits) and of several smaller alpha-crystallin polypeptides. Messenger RNA isolated from normal and cataractous lenses was assayed for translation in a cell-free wheat germ extract. Analysis of the translation products by one-dimensional and two-dimensional gel electrophoresis indicated that the messenger RNAs coding for the two beta L subunits are also present on normal lens polyribosomes. Purification and subsequent analysis by peptide mapping of the cataractous Beta L subunits suggest that they are precursor polypeptides of the normal low-molecular-weight beta-crystallins, which are no longer processed after translation and therefore accumulate in the pathological lens cell. On the other hand, in the translation of the cataractous mRNA in vitro, only the normal alpha chains are detected. These cataractous alpha-crystallins are therefore post-translational degradation products of the normal alpha polypeptides. This phenomenon seems similar to the one observed in the senescent lens. The possible involvement of these modifications in the etiology of this experimental cataract is discussed further.

Animals↗
PubMed1980

Identification and characterization of the translationally repressed cytoplasmic globin messenger-ribonucleoprotein particles from duck erythroblasts.

Globin messenger ribonucleoprotein (mRNP) particles which have been isolated from duck erythroblast post-polyribosomal supernatant are translationally inactive in vivo and in vitro but contain translatable mRNA active after deproteinisation. They were characterized following purification by successive sucrose gradient sedimentation in a buffer containing 0.05 M KCl. The complex, which sediments homogeneously at about 20 S, has a density of 1.39 g/cm3 and thus consists of four parts protein to one part RNA; 40% of this RNA is globin mRNA and no other mRNA could be detected. Sedimentation of the purified globin mRNP on sucrose gradients in 0.5 M KCl produced four components while polyacrylamide gel electrophoresis in non-denaturing conditions and in the presence of EDTA resulted in the separation of three components. Hybridization to globin cDNA and translation in vitro of the RNA extracted from these subparticles revealed the existence of two core particles containing globin mRNA with nominal sedimentation coefficients of 13 S and 16 S. Analysis of the protein components of the isolated sub-complexes by dodecyl sulfate and bidimensional gel electrophoresis indicated a very characteristic protein composition for each of these complexes. The 16-S and 13-S globin mRNPs differed essentially by the presence in the 13-S mRNP only of a group of major polypeptides. Of the other two sub-complexes, one consisted of 90% small RNA in the 4-S range; the second sedimented ahead of the globin mRNP core particles at about 19S and consisted of a very characteristic set of about 14 polypeptides. The polyribosomal 73000-Mr poly(A)-binding protein was not detected in the purified free globin mRNP although the mRNA in the untranslatable particle is polyadenylated. The presence in the cytoplasm of duck erythroblasts of two forms of untranslated globin messenger ribonucleoprotein particles, distinct in their protein composition from polyribosomal globin mRNP, suggests that they may have a specific role in the regulation of translation of globin mRNA.

Animals↗
PubMed1980

Anti-acetylcholine receptor antibodies.

Early suggestions that a humoral factor might be implicated in the disorder of neuromuscular transmission in myasthenia gravis have been confirmed by the detection of anti-AChR antibody in 85-90% of the patients with generalised disease and in 75% of cases with restricted ocular myasthenia. Plasma exchange reveals that serum anti-AChR usually has an inverse relationship to muscle strength and present evidence indicates that patients responding to thymectomy and immunosuppressive drug treatment usually show a consistent decline in serum anti-AChR titres. The antibody is heterogeneous and can lead to a loss of muscle AChR by several mechanisms. Anti-AChR is produced in the thymus in relatively small amounts. Anti-AChR antibody synthesis by thymic lymphocytes and pokeweed stimulated peripheral lymphocytes in culture provides a means of studying the effect of different lymphocyte populations in vitro. Analysis of clinical, immunological and HLA antigen characteristics in MG suggest that more than one mechanism may underlie the breakdown in tolerance to AChR, leading to the production of anti-AChR antibodies.

Acetylcholine↗
PubMed1979

A rapid and sensitive method for detection of proteins in polyacrylamide SDS gels: staining with ethidium bromide.

We describe here a fluorometric method of detection of proteins fractionated by electrophoresis in polyacrylamide-SDS gels. This method, using ethidium bromide as fluorescent dye, is performed within 40 minutes after the end of the electrophoretic run. It does not require treatment of proteins prior to electrophoresis, and entails neither fixation of proteins in the gel, nor destaining. It is sufficiently sensitive to detect 0.5 - 1.0 microgram of protein per band. Furthermore, the simultaneous electrophoretic resolution and detection of protein and RNA on a single SDS-polyacrylamide gradient gel is reported.

Electrophoresis, Polyacrylamide Gel↗
PubMed1979

Evidence for the protection of specific RNA sequences in globin messenger ribonucleoprotein particles.

Purified 15 S globin mRNA-protein (mRNP) complexes obtained by EDTA dissociation of duck reticulocytes polyribosomes were digested with the calcium dependant Staphylococcus aureus nuclease (EC 3. 1. 4. 7.). 25% of the globin mRNA sequences were resistant to extensive nuclease digestion as determined by TCA precipitation of the digested 15 S particles labelled in vivo with tritiated uridine. Polyacrylamide gel electrophoresis of the RNA from nuclease digested 15 S particles showed that the protected oligoribonucleotides were distributed into two distinct size classes of 25,000 and 12,000 MW. Comparison between in vitro iodine-labelled 9 S globin mRNA extracted from Staphylococcal nuclease digested 15 S mRNP particles was carried out by fingerprinting. Mapping of T1 ribonuclease digests by high-voltage electrophoresis and homochromatography showed that specific oligoribonucleotides were protected against nuclease attack by proteins of the 15 S mRNP.

Animals↗