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Biomedical subjects

C E Fisher

Publications and source records attributed to C E Fisher.

12 recordsLinked to original sources
PubMed2001

Glycosaminoglycans in the study of mammalian organ development.

Glycosaminoglycans (GAGs) are linear polymers of amino sugar uronic acid disaccharides, and are generally attached to protein cores to form proteoglycans. GAGs interact with a large number of proteins and can participate in matrix organization, cell adhesion, differentiation, growth and apoptosis. Proteoglycans are expressed in tightly regulated spatio-temporal patterns during organ development, and changes in expression frequently correlate with developmental events. Here we review the evidence that GAGs play important roles in the development of mouse kidneys, which are organs that will undergo organotypic development in simple culture conditions and that are therefore highly accessible to experimentation. Depleting kidneys of GAGs, either biochemically or genetically, blocks the development of the urinary collecting-duct system, probably because critical signalling molecules require GAGs to form stable associations with their receptors. The insensitivity of GAG-deprived organ rudiments to physiological concentrations of growth factors can be used to screen candidate signalling molecules for morphoregulatory activity; candidate growth factors are applied at supraphysiological levels to GAG-deprived kidneys and assessed for their ability to rescue normal development. This approach has assisted the identification of four collecting-duct morphogens: hepatocyte growth factor, glial cell line-derived neurotrophic factor, nerturin and persephin.

Animals↗
PubMed2001

Erk MAP kinase regulates branching morphogenesis in the developing mouse kidney.

Branching morphogenesis of epithelium is a common and important feature of organogenesis; it is, for example, responsible for development of renal collecting ducts, lung airways, milk ducts of mammary glands and seminal ducts of the prostate. In each case, epithelial development is controlled by a variety of mesenchyme-derived molecules, both soluble (e.g. growth factors) and insoluble (e.g. extracellular matrix). Little is known about how these varied influences are integrated to produce a coherent morphogenetic response, but integration is likely to be achieved at least partly by cytoplasmic signal transduction networks. Work in other systems (Drosophila tracheae, MDCK models) suggests that the mitogen-activated protein (MAP) kinase pathway might be important to epithelial branching. We have investigated the role of the MAP kinase pathway in one of the best characterised mammalian examples of branching morphogenesis, the ureteric bud of the metanephric kidney. We find that Erk MAP kinase is normally active in ureteric bud, and that inhibiting Erk activation with the MAP kinase kinase inhibitor, PD98059, reversibly inhibits branching in a dose-dependent manner, while allowing tubule elongation to continue. When Erk activation is inhibited, ureteric bud tips show less cell proliferation than controls and they also produce fewer laminin-rich processes penetrating the mesenchyme and fail to show the strong concentration of apical actin filaments typical of controls; apoptosis and expression of Ret and Ros, are, however, normal. The activity of the Erk MAP kinase pathway is dependent on at least two known regulators of ureteric bud branching; the GDNF-Ret signalling system and sulphated glycosaminoglycans. MAP kinase is therefore essential for normal branching morphogenesis of the ureteric bud, and lies downstream of significant extracellular regulators of ureteric bud development.

Animals↗
PubMed2000

Release of TNFalpha in response to SiC fibres: differential effects in rodent and human primary macrophages, and in macrophage-like cell lines.

Asbestos has been implicated in the pathogenesis of several lung diseases, but its mechanism of action is not fully understood. However, asbestos-induced oxidative stress and production of inflammatory cytokines may play a significant role. TNFalpha is an inflammatory cytokine which has a central role in inflammation and fibrosis due to its ability to stimulate fibroblasts and collagen deposition. In this study, a panel of fibres designated either pathogenic or non-pathogenic in recent animal studies, were utilized. The amount of TNFalpha released after a 16-hour exposure to the panel of fibres was compared in four different cell types; two primary macrophage cell types and two cell lines. TNFalpha release by cells exposed to the panel did not equate to pathogenicity, although the most pathogenic fibre caused three out of the four cell types tested, to produce the greatest amount of TNFalpha. Primary rat cells and primary human cells behaved in a similar manner as regards to TNFalpha production; the cell lines behaved quite differently to their primary counterparts with regards to TNFalpha production in this study.

Animals↗
PubMed1998

Respirable fibres: surfactant coated fibres release more Fe3+ than native fibres at both pH 4.5 and 7.2.

Exposure to asbestos is associated with several lung diseases. The carcinogenic action of asbestos is not fully understood but oxidative stress is considered to play a role. Iron on the surface can lead to Fenton chemistry and the Haber Weiss reaction producing free radicals such as the hydroxyl radical, which is likely to be important. Little is known of the pathogenic action of man-made fibres. This study involved the use of a panel of man-made fibres, some of which were shown to be pathogenic and others shown to be non-pathogenic in recent animal studies. A short term assay measuring Fe3+ release from the fibres over a 20 hour time period, and also a longer study of 12 week, found that pathogenic and non-pathogenic fibres could not be differentiated according to Fe3+ release only. Iron release from native fibres was compared with that from surfactant-coated fibres, and in all cases surfactant coated fibres released more Fe3+ inferring that in vivo lung lining fluid coats native fibres and therefore affects the fibre surface chemistry and hence reactivity.

Animals↗
PubMed1997

Complementary deoxyribonucleic acid cloning and characterization of a putative human axonemal dynein light chain gene.

Immotile Cilia Syndrome (ICS) is characterized by recurrent sinus and lung infections, bronchiectasis, and sperm immotility. Nasal cilia and sperm tails in patients with ICS exhibit a variety of ultrastructural defects, often including shortening or absence of the inner dynein arms. Immotile mutant strains of Chlamydomonas, a biflagellated algae, have ultrastructural defects similar to those seen in patients with this clinical disorder. Furthermore, splice-site mutations in the Chlamydomonas inner dynein arm gene (p28) are associated with impaired flagellar motility. We therefore hypothesized that the human homologue of the Clamydomonas dynein p28 gene would be an attractive candidate gene for patients with ICS. Accordingly, we cloned the full length complementary DNA (cDNA) and genomic clone by screening of appropriate libraries and databases, using the protein sequence of the Chlamydomonas p28 gene. The human homologue is encoded by a 921 bp transcript (accession no. AF006386) with an open reading frame of 257 amino acids. Using somatic cell and radiation hybrid panels, the hp28 gene was mapped to human chromosome 1p35.1. The hp28 cDNA probe hybridizes to sequences in all species on a zoo blot containing genomic DNA from yeast to human. Northern blot analysis reveals two hp28 gene transcripts, 0.9 and 2.5 kb, in many tissues. The 0.9 kb transcript is expressed at a 20-fold higher level than the 2.5-kb transcript in the testis. The entire gene is included in a 20-kb EcoRI genomic fragment and has 7 exons and 6 introns. Cloning of the hp28 cDNA and mapping of the intron-exon junctions should now make it possible to test whether a subset of ICS is a consequence of mutations in the human axonemal dynein light chain gene hp28.

Base Sequence↗
PubMed1996

Genetic construction and properties of a diphtheria toxin-related substance P fusion protein: in vitro destruction of cells bearing substance P receptors.

We have genetically replaced the native receptor binding domain of diphtheria toxin with an extended form of substance P (SP): SP-glycine (SP-Gly). The resulting fusion protein, DAB389SP-Gly, is composed of the catalytic and transmembrane domains of diphtheria toxin genetically coupled to SP-Gly. Because native SP requires a C-terminal amide moiety to bind with high affinity to the SP receptor, the precursor form of the fusion toxin, DAB389SP-Gly, was converted to DAB389SP by treatment with peptidylglycine-alpha-amidating monooxygenase. We demonstrate that following conversion, DAB389SP is selectively cytotoxic for cell lines that express either the rat or the human SP receptor. We also demonstrate that the cytotoxic action of DAB389SP is mediated via the SP receptor and dependent upon passage through an acidic compartment. To our knowledge, this is the first reported use of a neuropeptide as the targeting ligand for a fusion toxin; and the first instance in which an inactive precursor form of a fusion toxin is converted to the active form by a posttranslational modification.

Amino Acid Sequence↗
PubMed1996

Effects of diazepam and cyclohexyladenosine on open-field behavior in rats perinatally exposed to caffeine.

Adult rat offspring earlier exposed to maternally ingested caffeine during both gestation and lactation were observed in an open field following acute administration of diazepam or cyclohexyladenosine. While both drugs reduced measures of locomotion and emotional reactivity, caffeine-exposed rats showed evidence of greater sensitivity to cyclohexyladenosine (but not diazepam) as determined by its effects on grooming behavior and tendencies to occupy the center squares of the apparatus. This suggested that adenosine (A1) rather than benzodiazepine receptor activity had been affected by the perinatal caffeine experience which also reduced locomotor activity while increasing center occupancy. The acute effects of diazepam and cyclohexyladenosine also depended largely on the sex of the subjects. Diazepam affected locomotor activity more and both drugs affected defecation less in females than in males. No other interaction involving sex was significant.

Adenosine↗
PubMed1996

Carcinogens in food: priorities for regulatory action.

A pragmatic possible approach to the prioritization of chemical carcinogens occurring as food contaminants is described, based on the carcinogenic risk to the population. This should be of value in ensuring that resources for assessment and management of carcinogens in food are directed to the most important areas with regard to carcinogenic risk to the population. Key components of this approach are an assessment of the carcinogenic hazard to humans combined with estimations of intakes per person and of the proportion of the population exposed. These are used to derive an index referred to as the Population Carcinogenic Index. Concerning the hazard assessment expert judgement is used to place the chemical in one of five categories. The highest category is for chemical carcinogens that are believed to act by a genotoxic mechanism. It is recognised that such compounds may vary enormously with respect to their potency and various approaches to ranking carcinogens on the basis of potency are reviewed. The approach adopted is to subdivide the genotoxic carcinogens category into high, medium and low potency based on the TD50 value. Methods of estimating intakes and exposed populations are considered and an approach which groups these into broad categories is developed. The hazard and exposure assessments are then combined to derive the Population Carcinogenicity Index.

Carcinogens↗
PubMed1976

Neisseria lactamica meningitis.

Neisseria lactamica was recovered from the blood and cerebrospinal fluid of a 7-month-old girl with acute purulent meningitis. The isolate was identified initially as N meningitidis. However, additional biochemical testing at the Center for Disease Control showed that the organism fermented lactose and produced beta-D-galactosidase, thereby confirming its identity as N lactamica.

Bacterial Infections↗
PubMed1974

Affinity labelling of the binding site of rabbit antibody. Evidence for the involvement of the hypervariable regions of the heavy chain.

The binding sites of rabbit antibodies with affinity for the haptenic group 4-azido-2-nitrophenyl-lysine have been specifically labelled by photolysis of the hapten-antibody complex. The extent of covalent labelling was 0.5-0.9mol of hapten bound/mol of antibody and, by using an immunoadsorbent, antibody with 1.3mol of hapten/mol was obtained. The antibody was specifically labelled in the binding site and the ratio of labelling of heavy and light chains was in the range 3.3-5.0. The labelled heavy chains were cleaved by CNBr treatment and after reduction and alkylation of the intrachain bonds, were digested with trypsin. Evidence is presented that two regions of the heavy chain, positions 29-34 and 95-114, together contain about 80% of the label on the heavy chain; these two regions respectively include two of the hypervariable regions of rabbit heavy chain.

Affinity Labels↗