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Biomedical subjects

H G Davies

Publications and source records attributed to H G Davies.

At least 19 recordsLinked to original sources
PubMed1992

Oestrogen receptor protein and mRNA in adenocarcinoma of the uterine cervix.

We have investigated the oestrogen receptor (ER) status of 20 cervical adenocarcinomas by immunocytochemistry for ER protein and non-isotopic in situ hybridisation for ER mRNA. Both methods, which are applicable to paraffin sections, were developed and validated in breast carcinomas with known ER content. Six cervical adenocarcinomas contained immunocytochemically demonstrable ER protein; all contained ER mRNA, but staining was less intense in poorly differentiated areas of four tumours. This disparity between protein and mRNA detection needs further investigation as does the possibility that oestrogens may play a role in the pathogenesis of cervical adenocarcinoma.

Adenocarcinoma↗
PubMed1992

Antibiotic susceptibilities, serotypes and auxotypes of Neisseria gonorrhoeae isolated in New Zealand.

OBJECTIVE: The aim of the study was to determine the distribution of auxotypes and serotypes and the prevalence of antibiotic resistance among New Zealand isolates of Neisseria gonorrhoeae. MATERIALS AND METHODS: A total of 486 gonococci isolated in 1988 were auxotyped, serotyped, and tested for susceptibilities to ten antibiotics. RESULTS: The gonococci were susceptible to all the antibiotics tested except penicillin and tetracycline. Eleven (2.2%) produced beta-lactamase, one (0.2%) showed chromosomal penicillin resistance, and 18 (3.7%) were resistant to a low-level of tetracycline. Most of the gonococci belonged to six auxotypes. The three predominant auxotypes were arginine-requiring (Arg-), non-requiring (NR), and arginine, hypoxanthine, uracil-requiring (AHU-). The majority of the isolates belonged to serogroup IB and to six serovars. The most prevalent serovars were IB-3 and IB-1. There was an association between penicillin susceptibility and auxotype or serovar among non-penicillinase producing N. gonorrhoeae (PPNG) isolates. CONCLUSIONS: Antibiotic resistance, including penicillin resistance, remains uncommon among gonococci in New Zealand. Baselines have been established for future epidemiological studies using both auxotyping and serotyping.

Animals↗
PubMed1990

Recent advances in the generation of chiral intermediates using enzymes.

Different types of enzyme-catalyzed processes are reviewed, with particular regard to those procedures leading to the generation of chiral compounds of high optical purity. The main body of the review deals with hydrolyses and esterification as well as the reduction and oxidation of organic substrates. Other biotransformations of current and/or future importance in the synthesis of homochiral fine chemicals (such as the formation of carbon-carbon bonds using aldolases) are also discussed in some detail. Attention is drawn to current trends in the area and, to this end, a majority of the references are taken from journals published during the period April 1987 to September 1988.

Alcohols↗
PubMed1989

Methicillin-resistant Staphylococcus aureus: an increasing threat in New Zealand hospitals.

During the three years 1985 to 1987 an increasing number of methicillin-resistant Staphylococcus aureus (MRSA) strains were identified in New Zealand each year. A total of 66 strains of MRSA were identified among isolates received from 418 patients and health personnel. The majority (337/418, 80.6%) of the isolates were from two independent large outbreaks of MRSA. All strains of MRSA were sensitive to vancomycin, rifampicin and fusidic acid. An overseas origin, usually Australia, was identified for 48.4% of strains. The majority of isolates were from patients whose host defences had been breached. Postoperative and cutaneous wounds were the commonest sites of acquisition.

Anti-Bacterial Agents↗
PubMed1988

Association study between Alzheimer's disease and restriction fragment length polymorphisms at the human amyloid beta protein gene locus.

Alzheimer's disease, an autosomal dominant disorder, is characterized by the presence of neurofibrillary tangles and senile extracellular plaques in the brain of affected individuals. An amyloid beta protein has been isolated from the core of these plaques, and the gene encoding this protein has been mapped to region q11.2 to q22.2 of chromosome 21. Independent linkage studies have shown that the locus responsible for familial Alzheimer's disease also maps to the long arm of chromosome 21. It is thus very tempting to speculate that a defect (or defects) of the amyloid beta protein gene is the cause of Alzheimer's disease. For this reason, we have done association studies between Alzheimer's disease and restriction fragment length polymorphisms of the amyloid beta protein gene locus. We report a study of six restriction fragment length polymorphisms at the human amyloid beta protein gene locus. Several haplotypes constitute very informative marker systems for this region of chromosome 21. One of the six polymorphisms, a 6.6/7.3 kb (kb = 10(3) base-pairs) EcoRI restriction fragment length polymorphism, is loosely associated with the presence of Alzheimer's disease in a population of 34 subjects.

Alleles↗
PubMed1987

Heat shocking as a useful adjunct to routine phage typing of Staphylococcus aureus.

The heat shock technique (heating a culture at 55 degrees C for 3 min immediately before phage typing) has been used in our laboratory as an adjunct to routine phage typing for 2 years. This has enabled phage typing patterns to be determined on isolates otherwise recorded as untypable. The method is easily performed and standardized. Phage patterns were found to be reproducible and adequate discrimination was achieved. We found the technique provided significant information which was not available by conventional typing.

Bacteriological Techniques↗
PubMed1984

Observations on the kinetics of uranyl acetate and phosphotungstic acid staining of chromatin in thin sections for electron microscopy.

When thin sections of spermatogenic chromatin are fixed with either glutaraldehyde alone or postfixed with osmium tetroxide (OsO4) and stained with uranyl acetate (UAc) for increasing times, even after as little as 1 min, stain uptake is proportional to section thickness. Greater UAc uptake is observed in chromatin fixed with glutaraldehyde only, but seen with postfixed chromatin. Lead citrate poststaining of chromatin fixed with either glutaraldehyde or postfixed with OsO4 increases UAc uptake by a factor of about 3. The staining of thin sections of spermatogenic chromatin with ethanolic phosphotungstic acid (PTA) shows a region where stain uptake is proportional to section thickness followed by a plateau. This staining pattern is seen in chromatin fixed with glutaraldehyde alone or postfixed with OsO4; similar levels for final PTA uptake are also observed. An increase in the resin content of embedded chromatin postfixed with OsO4 is proposed to explain the decrease and increase in the rate of migration of UAc and ethanolic PTA staining solutions, respectively.

Animals↗
PubMed1983

Kinetics of lead citrate staining of thin sections for electron microscopy.

The staining of thin sections with lead citrate shows an initial increase followed by a decrease much later; the rate of the initial increase and subsequent loss varies for different cellular components. The decrease eventually reaches a stable minimum. At this level electron scattering is less than that of unstained sections, demonstrating a loss of biological material. Lead citrate used as a poststain following uranyl acetate causes an increase in electron density that is independent of staining time over 1-30 min; this increase appears to depend only on the quantity of uranyl acetate already bound, implying that the lead binds predominantly to the uranyl acetate.

Animals↗
PubMed1982

A critical evaluation of Bernhard's EDTA regressive staining technique for RNA.

The EDTA regressive staining procedure to detect RNA (Bernhard's technique) is based on the proposition that after staining ultrathin sections with uranyl the stain is preferentially removed from DNA rather than RNA by the action of the chelating agent EDTA. Whilst attempting to use the EDTA regressive staining procedure to detect the presence of RNA in the large granule complexes of chicken erythrocyte nuclei, certain anomalous staining patterns were observed in the chromatin of these nuclei. Essentially, these were that the edges of condensed chromatin bodies stained positively for RNA even though this molecule is known not to be present there in significant quantities. The staining patterns suggested that chromatin was retaining its stain in a manner expected of RNA but not DNA as a consequence of EDTA-containing species failing to pass freely through the section. This hypothesis was tested by carrying out the EDTA procedure on embedded specimens of a DNA-containing virus, simian virus 40 (SV40), small enough not to be exposed at the surface of the section. In this way it has been shown that virus particles completely surrounded by resin destain so much more slowly than chromatin, which is accessible at the surface of the section, that without any other information it would be concluded that the viruses contained RNA, not DNA. This apparently anomalous result arises because the difficulties encountered by stain or EDTA molecules in passing through a plastic section were not appreciated at the time of the initial publication of the technique. The observations are discussed in the light of recent knowledge that has been gained on the kinetics of staining by measuring the electron-scattering densities of stained sections, similar measurements having been made on sections stained by Bernhard's technique. A model for the mechanism of the EDTA regressive staining technique consistent with the experimental observations is proposed and the conditions under which Bernhard's staining procedure retains its specificity are defined. Briefly, these conditions are that: (a) the sections be stained for only a short period with uranyl before treating them with EDTA even though such brief staining is undesirable for quantitative measurements of stain uptake into biological material; and (b) that sections stained in lead only be compared as controls with sections stained by Bernhard's technique so that any specificity of lead for sub-cellular components is not confused with a positive indication of the presence of RNA. Unless these conditions are fulfilled, results obtained by the use of the regressive staining technique may be highly misleading.

Animals↗
PubMed1982

Electron microscopic observations on the development and cytochemistry of the large granule complexes in chicken erythrocyte nuclei.

Large granule complexes are structures found in a small percentage of chicken erythrocyte nuclei when observed in ultra-thin sections in the electron microscope. They consist of an amorphous region associated with a number of large (approximately 30 min) granules. We have shown, by a novel use of phenylhydrazine to synchronize populations of chicken erythrocytes in vivo, that large granule complexes do not occur in the nuclei until the cells have reached one-third to one-half of their normal intravascular lifespan. The mature large granule complexes are formed by aggregation of pre-existing fibrillar, granular and amorphous material, and their presence is correlated with the presence of another ultrastructural feature of the nucleus, the so-called "filled cavities' in the chromatin. Digestion of ultra-thin sections of erythrocytes embedded in the hydrophilic resin glycol methacrylate (GMA) has shown that the major component of the amorphous region is a rather acidic protein that is not haemoglobin, the most abundant protein in the erythrocyte. The large granules also contain protein and, almost certainly, RNA. The problems encountered in reaching this conclusion have emphasized the lack of unambiguous cytochemical tests for use on ultra-thin sections. We have shown that the large granule complex differs in many respects from the nucleolus in the erythrocyte series, even though the two organelles have certain superficial similarities such as their overall dimensions and the presence of granular and fibrillar regions. The most likely function of the large granule complex is as a repository for material, including RNA, the processing of which has ceased in the inactivated erythrocyte nucleus.

Animals↗
PubMed1979

Three-dimensional reconstruction of the chromatin bodies in the nuclei of mature erythrocytes from the newt Triturus cristatus: the number of nuclear envelope-attachment sites.

The arrangement of the chromatin bodies in the interphase nuclei of 6 erythrocytes has been investigated by means of 3-dimensional reconstruction from electron micrographs of serial sections. When the borders of chromatin bodies are marked on the surface of each model, discrete areas of chromatin in contact with the nuclear envelope are revealed. The number of these areas in approximately equal to the number of chromosomes in the diploid set. The data suggest that each chromatin body corresponds to a condensed interphase chromosome and that each chromosome is attached to one discrete site on the nuclear envelope. The data are insufficient to show whether or not the condensed chromosomes are arranged in any orderly pattern in these nuclei.

Animals↗
PubMed1976

Electron microscopy of interphase chromosomes in situ; binding of permanganate to chicken erythrocytes.

From quantitative electron-microscope observations on the binding of permanganate to regions of erythrocytes and reticulocytes of known chemical composition, it is concluded that KMnO4, like phosphotungstic acid (PTA), binds preferentially to sites on proteins. Compared with PTA, KMnO4 binding exhibits less anomalous behaviour. The data support the hypothesis previously put forward that the 2 regions, or phases, in condensed chromatin differ in both molecular composition and concentration. The increase in binding to protein which occurs during nuclear haemolysis is interpreted in terms of protein-protein interaction in the chromatin of the intact cell.

Animals↗
PubMed1976

Electron-microscope observations on cell nuclei in various tissues of a teleost fish: the nucleolus-associated monolayer of chromatin structural units.

Observations on stain uptake by thin sections through condensed interphase chromosomes in cells from epithelial and muscle tissue in kidney and intestine, and also in fibroblasts, show a distribution into DNA-rich and DNA-poor phases similar to that already described in cells from the connective tissue blood. In all the nuclei the nucleolus, when adjacent to the nuclear envelope, is separated from the inner membrane by a monolayer of chromatin structural units, similar to the monolayer enclosed on both sides by nuclear envelope, previously described in a wide variety of organisms. The data provide further support for the hypothesis that the condensed interphase chromosomes in eukaryotes are characterized by essentially similar structural units folded to form similar patterns. This hypothesis, regarding the higher order units, is consistent with data of others which show that histones and DNA fold to form similar repeating subunits in chromatin, irrespective of the base sequence in the DNA and the origin of the histones.

Animals↗
PubMed1975

Ultrastructural and biochemical observations on interphase nuclei isolated from chicken erythrocytes.

Adult hen erythrocyte nuclei are isolated from cells or haemolysed in situ by acting on the plasma membrane with rotating knives or with non-ionic detergents. When the isolation medium contains magnesium ions (1 mM), sucrose (0-4 M) and Tris buffer (0.01 M, pH 7-5) called SMTOG (see text), the ultrastructure in thin sections through the condensed chromatin bodies, after staining with either uranyl-lead or phosphotungstic acid (PTA), is similar to that found in the intact cell. Hence it can be concluded that the 2 phases which comprise chromatin, the o- and e-phase, survive nuclear isolation. These are so called because the structural units in chromatin are arranged at the surface of the nucleus into one or more layers and give rise to oddly (o) and evenly (e) numbered bands. The 0-phase is also largely retained after extensive washing in 0-07 M NaC1 as shown by electron microscopy and biochemical measurements; only 6% of the total nuclear protein is removed, a value small compared with the fractional amount of the chromatin protein calculated to lie in the o-phase, about 70%. After extensive washing in saline-EDTA there are structural changes in chromatin, but biochemical data show that the molecules in the o-phase are also largely retained; loss of protein amounts to between 5 and 11%. These data suggest that the o-phase is a structural component of the chromatin bodies. They support the hypothesis that condensed chromatin is formed by folding superunit threads. These units consist of a central thread-like element about 17 nm diameter which stains preferentially with uranyl-lead and forms the e-phase, with an outer cylindrical shell forming the o-phase of total diameter about 28nm. The 5-10% proteins removed by salt washes are located exclusively in a particulate component, quite likely the chromatin. They have been examined by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis. There are about 10 or more protein species, ranging in molecular weight from 21000 upwards. The groups of large granules previously found in the nuclear sap of intact erythrocytes are shown to be associated with an amorphous or finely fibrillar body.

Animals↗
PubMed1975

Light- and electron-microscope observations on certain leukocytes in a teleost fish and a comparison of the envelope-limited monolayers of chromatin structural units in different species.

Previously it was shown that the nuclear envelope-limited sheets of chromatin, monolayers of nucleoprotein structural units, are present in blood cells from 4 classes of vertebrates. Now we show that sheets of similar width are present in certain leukocytes of a fifth class, a teleost fish. We describe the fine structure of leukocytes in peripheral blood and in the main haematopoietic organ, kidney. We also examined the granulocytes of connective tissue in intestine. By May-Grunwald-Giemsa staining and electron microscopy heterophilic granulocytes, cosinophils but no basophils could be recognized in peripheral blood and kidney. Problems in classification of the cells are discussed. In one group (A) of 5 fish, sheets occurred at a frequency of roughly 1% in heterophilic (type 1) granulocytes and lymphocytes from peripheral blood. No sheets were found in a second group (B) of 5 fish. Kidney and intestine were examined in some fish from both groups and no sheets were present. In an atypical group (C) sheets were found in the eosinophilic (type 2) granulocytes from peripheral blood of one fish and in lymphocytes from connective tissue of intestine in another. Sheets were usually associated with nuclei of irregular shape and their width averaged 36 nm. We tabulate data from other workers on occurence and width of sheets. They are found in all the main classes of tissue in mammals, namely blood and other connective tissues, in epithelial, nervous, germinal tissue and muscle, as well as in invertebrate and certain plants. Their nearly constant width, average value 35 nm, provides very convincing evidence for the hypothesis that the molecules of DNA and protein are organized into the same fundamental structural units, irrespective of species. We discuss the variable incidence of sheets among different cell types and the factors which might determine this.

Animals↗