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Biomedical subjects

K White

Publications and source records attributed to K White.

At least 91 records · Page 5Linked to original sources
PubMed1998

Formation and specification of ventral neuroblasts is controlled by vnd in Drosophila neurogenesis.

During Drosophila neural development, neuroblasts delaminate from the neuroectoderm of each hemisegment in a stereotypic orthogonal array of five rows and three columns (ventral, intermediate, and dorsal). Prevailing evidence indicates that the individual neuroblast fate is determined by the domain-specific expression of genes along the dorsoventral and anteroposterior axis. Here, we analyze the role of Vnd, a NK-2 homeodomain protein, expressed initially in the ventral neuroectoderm adjacent to the ventral midline, in the dorsoventral patterning of the neuroectoderm and the neuroblasts. We show that in vnd null mutants most ventral neuroblasts do not form and the few that form do not develop ventral fates, but instead develop intermediate-like fates. Furthermore, we demonstrate that Vnd influences the gene expression patterns in the ventral proneural clusters and neuroectoderm, and that its action in neuroblast formation includes, but is not exclusive to the activation of proneural AS-C genes. Through the use of GAL4/UAS gene-expression system we show that ectopic Vnd expression can promote ventral-like fates in intermediate and dorsal neuroblasts and can suppress certain normal characteristics of the intermediate and dorsal neuroectoderm. Our results are discussed in the context of the current evidence in dorsoventral patterning in the Drosophila neuroectoderm.

Animals↗
PubMed1998

Ras promotes cell survival in Drosophila by downregulating hid expression.

Activation of Ras inhibits apoptosis during Drosophila development. Genetic evidence indicates that Ras antiapoptotic activity in the developing eye is regulated by the Drosophila EGF receptor and operates through the Raf/MAPK pathway. Decreased activity of this pathway enhances, and increased activity suppresses, apoptosis induced by ectopic expression of the cell death regulators reaper (rpr) and head involution defective (hid). In addition, ectopic activation of the Ras/MAPK pathway in the developing embryo and in the developing eye suppresses naturally occurring apoptosis and regulates the transcription of the proapoptotic gene hid. Null alleles of hid recapitulate the antiapoptotic activities of Ras/MAPK, providing genetic evidence that downregulation of hid is an important mechanism by which Ras promotes survival.

Alleles↗
PubMed1998

Regulation of endothelin-1 in human non-pigmented ciliary epithelial cells by tumor necrosis factor-alpha.

Endothelins (ET) are potent vasoactive peptides present in many ocular structures and are formed from precursor Big endothelins (Big ET-1) by the action of an endothelin-converting enzyme (ECE). ET-1 is thought to decrease intraocular pressure by contracting the ciliary muscle thus enhancing the outflow of aqueous humor through the Canal of Schlemm and trabecular meshwork. However, the mechanisms involved in the regulation of endothelin-1 (ET-1) synthesis and release in ocular tissues have not been fully characterized. In this study we examined the effect of tumor necrosis factor-alpha(TNF-alpha; 10 nm), a proinflammatory cytokine, on the cellular mechanisms leading to ET-1 synthesis and release in SV-40 transformed human ciliary non-pigmented epithelial cells (HNPE). ET-1 and Big endothelin-1 (Big ET-1) immunoreactivity was time-dependently increased following TNF-alphatreatment. Phorbol esters (PMA), activators of PKC, also raised the immunoreactive levels of ET-1 and Big ET-1 while, staurosporine, a PKC inhibitor (20 nm), decreased ET-1 levels in TNF-alpha-stimulated cells. Pre-treatment with phosphoramidon (1 micron) an ECE-inhibitor, followed by TNF-alpha stimulation, decreased ir-ET-1 levels. Cycloheximide (9 micron), a protein synthesis inhibitor, decreased TNF-alpha-stimulated levels for ir-ET-1 and ir-Big ET-1, suggesting that TNF-alpha may be directly regulating ET-1 expression at the ET-1 gene. Our data indicates that TNF-alpha regulates ET-1 levels in HNPE cells possibly by activating PKC either to stimulate protein synthesis and/or to enhance ET-1 secretion. These results suggest that ET-1 released from the ciliary body may play an important role in aqueous humor dynamics following cytokine activation.

Cells, Cultured↗
PubMed1998

Apoptosis and morphologic changes in drug-treated trabecular meshwork cells in vitro.

Using an in vitro culture system, we investigated whether bovine trabecular meshwork cells undergo apoptosis (programmed cell death) following exposure to anti-glaucoma medications (timolol, pilocarpine and epinephrine) and known inducers of apoptosis (5-fluorouracil, mitomycin-C and dexamethasone). Third to fifth passage bovine trabecular meshwork cells were grown to confluence and incubated for 1-12 days in growth media with timolol (1-1000 microM), pilocarpine (15-15,000 microM), epinephrine (5-5000 microM), 5-fluorouracil (10-100 micrograms ml-1), mitomycin-C (0.01-100 micrograms ml-1) and dexamethasone (0.01-100 microM). The cultures were evaluated for apoptosis by phase-contrast microscopy, transmission electron microscopy and in situ apoptosis labeling. 5-Fluorouracil (10-100 micrograms ml-1), mitomycin-C (0.1-100 micrograms ml-1) and epinephrine (500-5000 microM) induced apoptosis in a dose and time-dependent manner. Timolol, pilocarpine, and dexamethasone-treated specimens did not show evidence of apoptosis at any of the concentrations tested. Trabecular meshwork cells incubated in timolol (100-1000 microM) developed cytoplasmic granules, and specimens treated with pilocarpine (15,000 microM) developed cytoplasmic vacuoles. These granules and vacuoles have the appearance of secondary lysosomes. Dexamethasone-treated cells developed an increased number of mitochondria. This study suggests that the trabecular meshwork may undergo apoptosis following exposure to 5-fluorouracil, mitomycin-C and epinephrine. Timolol, pilocarpine and dexamethasone did not induce apoptosis. However, these drugs can incite characteristic morphologic changes in cultured trabecular meshwork cells.

Animals↗
PubMed1998

Preclinical antitumor efficacy of analogs of XK469: sodium-(2-[4-(7-chloro-2-quinoxalinyloxy)phenoxy]propionate.

A series of quinoxaline analogs of the herbicide Assure was found to have selective cytotoxicity for solid tumors of mice in a disk-diffusion-soft-agar-colony-formation-assay compared to L1210 leukemia. Four agents without selective cytotoxicity and 14 agents with selective cytotoxicity were evaluated in vivo for activity against a solid tumor. The four agents without selective cytotoxicity in the disk-assay were inactive in vivo (T/C > 42%). Thirteen of the fourteen agents with selectivity in the disk-assay were active in vivo (T/C < 42%). Five of the agents had curative activity. These five agents had a halogen (F, Cl, Br) in the 7-position (whereas Assure had a CI in the 6 position). All agents with curative activity were either a carboxylic acid, or a derivative thereof, whereas Assure is the ethyl ester of the carboxylic acid. All other structural features were identical between Assure and the curative agents. Assure had no selective cytotoxicity for solid tumors in the disk-assay, and was devoid of antitumor activity. The analog XK469 is in clinical development.

Animals↗
PubMed1998

Long-term efficacy and immune responses following immunization with the RTS,S malaria vaccine.

The malaria sporozoite vaccine candidate RTS,S, formulated with an oil-in-water emulsion plus the immunostimulants monophosphoryl lipid A and the saponin derivative QS21 (vaccine 3), recently showed superior efficacy over two other experimental formulations. Immunized volunteers were followed to determine the duration of protective immune responses. Antibody levels decreased to between one-third and one-half of peak values 6 months after the last dose of vaccine. T cell proliferation and interferon-gamma production in vitro were observed in response to RTS,S or hepatitis B surface antigen. Seven previously protected volunteers received sporozoite challenge, and 2 remained protected (1/1 for vaccine 1, 0/1 for vaccine 2, and 1/5 for vaccine 3). The prepatent period was 10.8 days for the control group and 13.2 days for the vaccinees (P < .01). Immune responses did not correlate with protection. Further optimization in vaccine composition and/or immunization schedule will be required to induce longer-lasting protective immunity.

Adolescent↗
PubMed1998

Health care markets in Australia: ownership of the private hospital sector.

Over the past decade, the Australian hospital sector has undergone a massive economic and administrative reorganization with ramifications for both the private and the public sectors. Changes such as privatization, deregulation, and the entry of foreign capital into the hospital sector are occurring in the hospital systems of many countries, including Australia, the United States, and the United Kingdom. These developments are radically transforming the hospital sector, altering established relationships between the state, the medical profession, the consumer, and the corporate investor, and raising important questions about the future of hospital services in regard to equity, accessibility, and quality.

Australia↗
PubMed1997

Association of the neuron-specific RNA binding domain-containing protein ELAV with the coiled body in Drosophila neurons.

The subcellular distribution of the Drosophila nervous system-specific RNA binding domain-containing protein ELAV was investigated using ELAV-specific antibodies and scanning confocal laser microscopy. ELAV is predominantly localized within the nucleus where it concentrates within discrete domains we describe as dots and webs. To characterize these discrete domains an analysis of Drosophila coiled bodies was initiated. The polyclonal antibody R288 raised against human coilin was used to identify coiled bodies in cells of the Drosophila larval central nervous system. Double-labeling immunohistochemistry showed that, similar to vertebrate and plant systems, small nuclear ribonucleoproteins are enriched within these structures. Further analysis of ELAV revealed that subnuclear domains enriched with this molecule localize within and close to coiled bodies and close to subnuclear domains enriched with splicing factors. A preliminary analysis aimed at defining a region within ELAV that may mediate a molecular or functional interaction important for its subnuclear localization revealed that deletion of the ELAV alanine/glutamine-rich amino-terminal auxiliary domain has no discernible effect on localization and that proteins produced from elav lethal alleles distribute normally.

Animals↗
PubMed1997

Identification of a novel keratin epitope: evidence for association between non-helical sub-domains L12 during filament assembly.

Keratin filaments in simple epithelial cells are heteropolymers of keratin 8 (K8) and keratin 18 (K18) polypeptides. The assembly of these polypeptides into intermediate filaments is a complex multi-stage phenomenon that involves several levels of associations. These molecular associations are not very well characterized. Monoclonal antibodies (MAbs) with defined specificities can be used to probe these associations and to isolate various intermediates in the assembly pathway. Here we describe the specificity of a MAb LE65 that has been widely used in keratin expression studies. We report that the MAb LE65 does not recognize individual keratin polypeptides but it instead reacts with a complex of K8 with K18. The MAb also did not react with complexes of K8 or K18 with other keratins. By allowing the antibody to react with complexes reconstituted from keratin fragments plus the complementary keratin, we have mapped the MAb LE65 epitope on the L12 sub-domains of K18, residues 214-231, and K8, residues 234-265, which must associate together to achieve antibody binding. These results suggest that the non-helical linkers, L12, of complementary keratins associate directly during filament assembly. This would explain why microinjection of MAb LE65 has been shown to disrupt keratin filaments. Furthermore, it may also help to explain the mechanism of filament disruption in some skin blistering syndromes induced by spontaneous mutations in the L12 region.

Amino Acid Sequence↗
PubMed1997

Treatment of human prostate tumors PC-3 and TSU-PR1 with standard and investigational agents in SCID mice.

Both the PC-3 and the TSU-PR1 prostate tumor models were found to be satisfactory for chemotherapeutic investigations in ICR-SCID mice. The 30 to 60 mg fragments implanted took in all mice (as judged by 100% takes in the controls of all experiments as well as the passage mice). The tumor volume doubling time was 4.0 days for PC-3 and 2.5 days for TSU-PR1. Nine agents were evaluated IV against early stage subcutaneous PC-3 tumors, with Nano-piposulfan being the only agent highly active (4.9 log kill). Three other agents were moderately active: Taxol (1.5 log kill), Cryptophycin-8 (1.6 log kill), Vinblastine (1.0 log kill). Five agents were inactive: VP-16, Adriamycin, CisDDPt, 5-FUra, and Cyclophosphamide. Ten agents were evaluated IV against early stage subcutaneous TSU-PR1 tumors. Three agents were highly active, producing > 6 log kill and cures: Taxol (5/5 cures), Cryptophycin-8 (5/5 cures), Vinblastine (2/4 cures). Two other agents were moderately active: Nano-piposulfan (1.2 log kill), and Cyclophosphamide (1.1 log kill). Five agents were inactive: VP-16, Adriamycin, CisDDPt, 5-FUra, and BCNU. In part, activity was determined by the ability of the SCID mice to tolerate meaningful dosages of the agents. Agents producing granulocyte toxicity (e.g., Adriamycin) were poorly tolerated and appeared less active than expected. Vinblastine, producing little or no granulocyte toxicity was very well tolerated and appeared to be more active than expected.

Aged↗
PubMed1997

Discovery of cryptophycin-1 and BCN-183577: examples of strategies and problems in the detection of antitumor activity in mice.

Historically, many new anticancer agents were first detected in a prescreen; usually consisting of a molecular/biochemical target or a cellular cytotoxicity assay. The agent then progressed to in vivo evaluation against transplanted human or mouse tumors. If the investigator had a large drug supply and ample resources, multiple tests were possible, with variations in tumor models, tumor and drug routes, dose-decrements, dose-schedules, number of groups, etc. However, in most large programs involving several hundred in vivo tests yearly, resource limitations and drug supply limitations have usually dictated a single trial. Under such restrictive conditions, we have implemented a flexible in vivo testing protocol. With this strategy, the tumor model is dictated by in vitro cellular sensitivity; drug route by water solubility (with water soluble agents injected intravenously); dosage decrement by drug supply, dose-schedule by toxicities encountered, etc. In this flexible design, many treatment parameters can be changed during the course of treatment (e.g., dose and schedule). The discovery of two active agents are presented (Cryptophycin-1, and Thioxanthone BCN 183577). Both were discovered by the intravenous route of administration. Both would have been missed if they were tested intraperitoneally, the usual drug route used in discovery protocols. It is also likely that they would have been missed with an easy to execute fixed protocol design, even if injected i.v.

Animals↗
PubMed1997

To market, to market: corporatisation, privatisation and hospital costs.

The Australian political arena echoes with calls for the privatisation of health care institutions, the contracting-out of health care services and the introduction of various marketing strategies into hospital management. These calls are justified by asserting that the market, rather than the public sector, can provide better services, greater productivity and increased efficiency. The National Health Strategy (1991, p 17) provides a good example. Noting that Australia is copying American investment trends for hospital 'chains' rather than for independent small establishments, the strategy dismisses any concern over changes in ownership, pointing instead to a 'process of rationalisation' that is to be 'welcomed'. Using evidence from the United States, United Kingdom and Australian hospital sectors, this paper examines claims for the greater efficiency of market processes.

Australia↗
PubMed1997

Fatal pulmonary embolism in hospitalised medical patients.

This study aimed to determine the frequency of fatal pulmonary emboli in hospitalised medical patients by a retrospective necropsy review and prospective non-interventional patient follow up study. The main outcome measure, necropsy proven fatal pulmonary embolism, was determined from 400 consecutive necropsy records and 200 consecutive medical inpatient episodes. Fatal pulmonary embolism was recorded in 29 of 400 necropsies; 17 were medical patients. Thirty one of 200 consecutive medical patients died. Fourteen necropsies were performed and revealed pulmonary embolism as the cause of death in five patients. The incidence of necropsy proven fatal pulmonary embolism was therefore 2.5% (95% confidence intervals 0.8% to 5.7%). Therefore, one in 40 medical patients had pulmonary embolism recorded as the cause of death at necropsy. As the necropsy rate was only 45% the incidence of fatal pulmonary embolism may be greater. There is, therefore, a need to perform more large prospective studies to confirm the incidence of fatal pulmonary embolism in medical patients and to identify risk factors and effective antithrombotic prophylaxis.

Aged↗
PubMed1996

ELAV, a Drosophila neuron-specific protein, mediates the generation of an alternatively spliced neural protein isoform.

BACKGROUND: Tissue-specific alternative pre-mRNA splicing is a widely used mechanism for gene regulation and the generation of different protein isoforms, but relatively little is known about the factors and mechanisms that mediate this process. Tissue-specific RNA-binding proteins could mediate alternative pre-mRNA splicing. In Drosophila melanogaster, the RNA-binding protein encoded by the elav (embryonic lethal abnormal visual system) gene is a candidate for such a role. The ELAV protein is expressed exclusively in neurons, and is important for the formation and maintenance of the nervous system. RESULTS: In this study, photoreceptor neurons genetically depleted of ELAV, and elav-null central nervous system neurons, were analyzed immunocytochemically for the expression of neural proteins. In both situations, the lack of ELAV corresponded with a decrease in the immunohistochemical signal of the neural-specific isoform of Neuroglian, which is generated by alternative splicing. Furthermore, when ELAV was expressed ectopically in cells that normally express only the non-neural isoform of Neuroglian, we observed the generation of the neural isoform of Neuroglian. CONCLUSIONS: Drosophila ELAV promotes the generation of the neuron-specific isoform of Neuroglian by the regulation of pre-mRNA splicing. The findings reported in this paper demonstrate that ELAV is necessary, and the ectopic expression of ELAV in imaginal disc cells is sufficient, to mediate neuron-specific alternative splicing.

Alternative Splicing↗