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Biomedical subjects

M Dawson

Publications and source records attributed to M Dawson.

At least 109 records · Page 6Linked to original sources
PubMed1990

Bovine spongiform encephalopathy: detection and quantitation of fibrils, fibril protein (PrP) and vacuolation in brain.

Bovine spongiform encephalopathy (BSE) is a new disease of cattle which has considerable homology with scrapie, the archetype of the transmissible spongiform encephalopathies. Abnormal brain fibrils, called scrapie associated fibrils (SAF), are specific ultrastructural markers for these diseases. Fibril detection was compared with histopathological diagnosis in the brains of 167 cattle; 157 clinically suspect BSE and 10 clinically normal. Fibrils were detected in samples of pooled brain regions of 67/144 in which vacuolar changes of BSE were confirmed, but absent in the remaining 23 brains, in which no vacuolation was found, including those from the clinically normal cattle and 13 with alternative neuropathological diagnoses. When eight defined anatomic regions from the brains of another 22 affected cows were examined, the sensitivity of fibril detection was greater than 90% for the brain stem areas. Fibril prevalence in these areas approximated to severity of vacuolar changes. When the same defined regions from four of the affected cows were assayed for fibril protein (PrP) by western blotting, the density of immuno-labelling generally correlated with the fibril prevalence. This study confirms the specificity of fibril detection for BSE, shows that the ease of fibril detection depends on anatomic region sampled and suggests an association between PrP accumulation and vacuolar changes in certain neuroanatomic areas.

Animals↗
PubMed1990

Improved expression of human interleukin-2 in high-cell-density fermentor cultures of Escherichia coli K-12 by a phosphotransacetylase mutant.

A fluoroacetate-resistant mutant of Escherichia coli K-12 (MM-294) accumulated less acetate in the medium during growth to high cell density in fermentor cultures and was shown to be defective in its phosphotransacetylase activity. The mutant had an improved ability to continue growing during induction of interleukin-2 (IL-2) synthesis, and in fermentor cultures it gave a higher level of specific IL-2 accumulation than its parent during expression under control of the temperature-sensitive pL promoter. In flask cultures at lower cell density, the mutant again produced less acetate than the parent, although both showed a much lower level of acetate accumulation than that seen in fermentors at high cell density. Both showed a higher specific expression level of IL-2 in flask cultures, and there was a greater difference between the mutant and its parent in the final extent of specific IL-2 accumulation in fermentor cultures compared with flask cultures. Thus, the concentration of acetate in the medium, which was much higher in fermentor cultures (greater than or equal to 300 mM after 5 h of induction) than in flask cultures (less than or equal to mM) of the parent organism, was a significant factor in limiting expression of the heterologous protein product, IL-2. The acetate kinase-phosphotransacetylase pathway was therefore a major source of acetate formation in these cultures. Blocking this pathway improved accumulation of IL-2 and did not slow growth.

Acetates↗
PubMed1989

Recurrent hypertonic dehydration due to selective defect in the osmoregulation of thirst.

A 6-year-old girl with recurrent episodes of hypertonic dehydration was studied. She denied thirst even with a plasma osmolality as high as 421 mosmol/kg. The hypernatremia was associated with an ability to concentrate urine (854 mosmol/kg). Volume expansion with water corrected hypernatremia (162 to 148 mEq/l) and resulted in an increased urine flow and urinary dilution (137 mosmol/kg) because of suppression of endogenous vasopressin (AVP) release (5.1 pg/ml). Hypertonic saline infusion raised the plasma AVP level (25.6 pg/ml) in response to changes in plasma osmolality (305 to 330 mosmol/kg) and led to a maximal urine osmolality of 818 mosmol/kg. With chronic forced fluid intake, the patient maintained a normal serum sodium concentration (range, 135-145 mEq/l) with a urine osmolality as low as 65 mosmol/kg. These findings are consistent with an isolated defect in the osmoregulation of thirst as the cause of the chronic hypertonic dehydration without deficiency in AVP secretion.

Arginine Vasopressin↗
PubMed1988

Fibrils from brains of cows with new cattle disease contain scrapie-associated protein.

During the past two years, more than 1,000 cases of a neurological disorder of cattle, bovine spongiform encephalopathy (BSE), have been confirmed from farms throughout Great Britain. The neurological signs and brain pathology of BSE resemble those produced in other species by the pathogens of scrapie and related disorders. The discovery of fibrils similar to scrapie-associated fibrils in detergent extracts o BSE-affected brain supported the clinical and pathological diagnosis of the disease, but has been controversial. Scrapie-associated fibrils are found in brain extracts of all species affected by scrapie and diseases caused by related pathogens. They are pathological aggregates of a neuronal membrane protein termed PrP and a protease-resistant form of PrP is a molecular marker of scrapie-associated fibrils. In this report, we show the major protein of BSE fibrils is the bovine homologue of PrP as judged by its size, protease resistance, immunoreactivity, lectin binding and partial N-terminal protein sequence. This confirms that BSE is a scrapie-like disease.

Amino Acid Sequence↗
PubMed1988

Quantification of leukotriene B4 in synovial fluid by gas chromatography/tandem mass spectrometry.

A procedure for the quantification of leukotriene B4 (LTB4) in synovial fluid has been developed using gas chromatography/tandem mass spectrometry based on selected reaction monitoring of the elimination of t-butyldimethylsilanol from the ions of m/z 431 and 438 in the negative ion chemical ionization mass spectra of the di-t-butyldimethylsilyl/pentafluorobenzyl derivatives of leukotriene B4 and the internal standard (2H8)leukotriene B4. The detection limit (approximately 10 pg ml-1) is sufficiently low to permit determination of LTB4 concentration in the synovial fluid of patients with various arthropathies. Single-stage mass spectrometry was found not to be selective enough to permit quantification of LTB4 in synovial fluid.

Arthritis, Rheumatoid↗
PubMed1988

The disposition of biphenylacetic acid following topical application.

Plasma and synovial fluid concentrations of biphenylacetic acid were determined following application of 3 g of 3% biphenylacetic acid gel to one knee of patients suffering from rheumatoid arthritis. The mean peak plasma concentration was 34 ng/ml. Synovial fluid concentrations tended to follow plasma concentrations but at a somewhat lower level, the mean peak synovial fluid concentration was 21 ng/ml. The average ratio of synovial fluid AUC (0-24 h) to plasma AUC (0-24 h) was 0.58, r = 0.97. Where patients had bilateral effusions, the concentration in the ipsilateral knee at each time point examined was not significantly different to that in the contralateral knee, suggesting that absorption was initially into the plasma and subsequently into the synovium.

Administration, Topical↗
PubMed1988

Routine application of enzyme-linked immunosorbent assay in comparison with complement fixation for the diagnosis of foot-and-mouth and swine vesicular diseases.

An indirect, sandwich enzyme-linked immunosorbent assay (ELISA) has been compared in parallel with the standard complement-fixation typing test (CFT) for the diagnosis of foot-and-mouth and swine vesicular diseases. The superior sensitivity, reproducibility, economical use of reagents and ease of performance of the ELISA confirm the hypothesis that it should replace the CFT as the routine test of choice.

Animals↗
PubMed1988

Autogenous regulation of the regA gene of bacteriophage T4: derepression of translation.

The regA gene of phage T4 encodes a translational repressor that inhibits utilization of its own mRNA as well as the translation of a number of other phage-induced mRNAs. In recombinant plasmids, autogenous translational repression limits production of the RegA protein when the cloned structural gene is expressed under control of a strong, plasmid-borne promoter (lambda PL). We have found that a genetic fusion which places the regA ribosome binding domain in proximity to active translation leads to partial derepression of wild-type RegA protein synthesis. The derepression is not due to increased synthesis of regA RNA, suggesting that it occurs at the translational level. Derepressed clones of the wild-type regA gene were used to overproduce and purify the repressor. In an in vitro assay the wild-type target was sensitive and a mutant target was resistant to inhibition by the added protein. The results suggest that the sensitivity of a regA-regulated cistron to translational repression may depend on the competition between ribosomes and RegA protein for overlapping recognition sequences in the translation initiation domain of the mRNA.

Cloning, Molecular↗
PubMed1987

Pathogenesis of maedi-visna.

In most cases, maedi-visna virus infection is characterised by a subclinical, persistent virus-carrier state. However, in heavily infected flocks, economically significant disease does occur, mainly apparent as ill-thrift and chronic respiratory disease (maedi) in older ewes and as an indurative mastitis, which can result in delayed weight gain of suckled lambs. Meningoencephalitis (visna) and arthritis may also occur. Maedi-visna virus, a lentivirus, replicates via proviral intermediary DNA copies of its RNA genome in circulating monocytes, in which replication is highly restricted, and in tissue macrophages, where viral genome expression is more evident. The presence of macrophages expressing viral antigens on their surface in lungs, udder, joints or central nervous system tissues provides a focus for a local mononuclear cell inflammatory response. Factors which may contribute to macrophage activation and the development of the inflammatory response are discussed in the context of virus replication, transmission of infection and disease susceptibility.

Animals↗
PubMed1987

Translational repression: biological activity of plasmid-encoded bacteriophage T4 RegA protein.

The RegA protein of bacteriophage T4 is a translational repressor that regulates expression of several phage early mRNAs. We have cloned wild-type and mutant alleles of the T4 regA gene under control of the heat-inducible, plasmid-borne leftward promoter (PL) of phage lambda. Expression of the cloned regA+ gene resulted in the synthesis of a protein that closely resembled phage-encoded RegA protein in biological properties. It repressed its own synthesis (autogenous translational control) as well as the synthesis of specific T4-encoded proteins that are known from other studies to be under RegA-mediated translational control. Cloned mutant alleles of regA exhibited derepressed synthesis of the mutant regA gene products and were ineffective in trans against RegA-sensitive mRNA targets. The effects of plasmid-encoded RegA proteins were also demonstrated in experiments using two compatible plasmids in uninfected Escherichia coli. The two-plasmid assays confirm the sensitivities of several cloned T4 genes to RegA-mediated translational repression and are well-suited for genetic analysis of RegA target sites. Repression specificity in this system was demonstrated by using wild-type and operator-constitutive translational initiation sites of T4 rIIB fused to lacZ. The results show that no additional T4 products are required for RegA-mediated translational repression. Additional evidence is provided for the proposal that uridine-rich mRNA sequences are preferred targets for the repressor. Surprisingly, plasmid-generated RegA protein represses the synthesis of some E. coli proteins and appears to enhance selectively the synthesis of others. The RegA protein may have multiple functions, and its binding sites are not restricted to phage mRNAs.

Base Sequence↗