PubMed Health⌕ Search

Biomedical subjects

C Webster

Publications and source records attributed to C Webster.

At least 91 records · Page 5Linked to original sources
PubMed1986

[Not Available].

Explore the source record for details and available documents.

History, Early Modern 1451-1600↗
PubMed1985

Plasticity of the differentiated state.

Heterokaryons provide a model system in which to examine how tissue-specific phenotypes arise and are maintained. When muscle cells are fused with nonmuscle cells, muscle gene expression is activated in the nonmuscle cell type. Gene expression was studied either at a single cell level with monoclonal antibodies or in mass cultures at a biochemical and molecular level. In all of the nonmuscle cell types tested, including representatives of different embryonic lineages, phenotypes, and developmental stages, muscle gene expression was induced. Differences among cell types in the kinetics, frequency, and gene dosage requirements for gene expression provide clues to the underlying regulatory mechanisms. These results show that the expression of genes in the nuclei of differentiated cells is remarkably plastic and susceptible to modulation by the cytoplasm. The isolation of the genes encoding the tissue-specific trans-acting regulators responsible for muscle gene activation should now be possible.

Aged↗
PubMed1985

Outbreak of systemic Candida albicans in intensive care unit caused by cross infection.

The first documented outbreak of systemic candidosis shown to be due to cross infection with a particular strain of Candida albicans is reported. Over nine months in an intensive care unit 13 patients developed definite and one probable systemic candidosis. Twenty five further patients had superficial candidal infections. The strain that caused the outbreak (serotype A, morphotype A1, biotype 0/(1)5 5/7) was responsible for all the cases of systemic candidosis acquired in the intensive care unit, 11 (44%) of the superficial candidal infections in the unit, and 17% of candidal infections outside the unit but in the same hospital. The strain was also isolated from oral swabs taken from four nurses working in the unit and the hands of one of these nurses. Two out of 17 nurses were shown to have acquired the strain on their hands when examined immediately after nursing systemically infected patients. No environmental source could be identified. The strain also showed enhanced survival in handwashing experiments and was relatively resistant to Hibiscrub. Management of patients with systemic candidosis might include measures to prevent cross infection and handwashing with disinfectants that are active against candida.

Adult↗
PubMed1984

Chemically defined media for cultivation of Naegleria gruberi.

Cultivation of amebae of the axenic strain of Naegleria gruberi, NEG-M, was achieved in media consisting entirely of chemically defined components. A complete medium that contains 31 components allows growth with yields up to 5 x 10(6) amebae per ml. A minimal medium gives lower yields but defines 22 components that are essential for continuous cultivation: 11 amino acids, 6 vitamins, hematin, guanosine, D-glucose, Mg(2+), and inorganic phosphate. These media allow precise studies of the metabolism and differentiation of this unusual eukaryote.

Journal Article↗
PubMed1983

Differentiation properties of pure populations of human dystrophic muscle cells.

The interpretation of the majority of studies of Duchenne muscular dystrophy (DMD) has been complicated by the heterogeneous composition of the cultures used. In addition to muscle cells, muscle tissue contains adipocytes and fibroblasts and the proportion of these cell types varies, especially in disease states. To overcome this problem we developed culture conditions which permitted isolation and characterization of pure populations of clonally derived human muscle cells [1, 2]. Here we report the successful application of these methods to muscle cells from biopsies of individuals with diagnosed DMD. The normal and mutant human muscle cells were used in experiments of muscle differentiation in the same manner as cell lines. Frozen-stored cells were thawed, plated in a series of replicate plates, and allowed to differentiate under similar culture conditions. Yet, in contrast with cell lines, the cells were karyotypically normal, not altered by adaptation to long-term culture, and had a finite lifespan. We have systematically analysed specific properties of the normal and DMD muscle cells which differentiated in culture. The kinetics and extent of myoblast fusion, myotube morphology, and the accumulation and distribution of membrane acetylcholine receptors were monitored. In addition, the isozyme composition of creatine kinase and its intracellular and extracellular distribution were determined. Our results indicate that DMD muscle cells are fully capable of initiating myogenesis in culture and do not differ from normal muscle in several important parameters of differentiation.

Cell Differentiation↗
PubMed1983

Cytoplasmic activation of human nuclear genes in stable heterocaryons.

We have induced the stable expression of muscle-specific genes in human nonmuscle cells. Normal diploid human amniocytes were fused with differentiated mouse muscle cells by using polyethylene glycol. The fusion product, a stable heterocaryon in which the parental cell nuclei remained distinct, did not undergo division and retained a full complement of chromosomes. This is in contrast with typical interspecific hybrids (syncaryons), in which the parental nuclei are combined and chromosomes are progressively lost during cell division. The human muscle proteins, myosin light chains 1 and 2, MB and MM creatine kinase and a functional mouse-human hybrid MM enzyme molecule were detected in the heterocaryons. Synthesis of these proteins was evident 24 hr after fusion and increased in a time-dependent manner thereafter. Our results indicate that differentiated mouse muscle nuclei can activate human muscle genes in the nuclei of a cell type in which they are not normally expressed, and that this activation occurs via the cytoplasm. The activators are still present in cells which have already initiated differentiation, are recognized by nuclei of another species, and do not diffuse between unfused cells. The reprogrammed amniocyte nuclei of stable heterocaryons provide a unique system in which to study the mechanisms regulating gene expression during cell specialization.

Amniotic Fluid↗
PubMed1983

Defective myoblasts identified in Duchenne muscular dystrophy.

A defect in the proliferative capacity of satellite cells, mononucleated precursors of mature muscle fibers, was found in clonal analyses of cells cultured from Duchenne muscular dystrophy (DMD) patients. The total yield of myoblasts per gram of muscle biopsy was decreased to 5% of normal. Of the DMD myoblast clones obtained, a large proportion contained a morphological class of flat distended cells that had an increased generation time and ceased to proliferate beyond 100-1,000 cells but could be induced to fuse and form myotubes. The altered muscle phenotype was detected in all cultures from DMD patients but was rarely found among myoblasts of controls. By age 14 yr, it comprised as man as 90% of DMD myoblasts. The remaining DMD myoblast clones, which initially grew well, had severely impaired proliferative capacity upon passage and further cultivation. Eventually all myoblasts from DMD muscle tissue exhibited defective growth potential. In contrast, the fibroblast yield and proliferative capacity from DMD samples did not differ from normal. Based on these findings, we propose a hypothesis for the etiology of DMD: Dividing myoblasts are required for muscle growth and maintenance, and the limited capacity of DMD myoblasts to grow is directly related to the progressive muscle degeneration characteristic of the disease.

Adolescent↗
PubMed1981

Isolation and characterization of human muscle cells.

We have developed an in vitro system for the study of postnatal human muscle under standardized conditions. The technique utilizes cloning to isolate pure populations of muscle cells. By manipulating culture conditions we can maximize either proliferation or differentiation of individual clones or of clones pooled to yield mass cultures of muscle cells. The muscle phenotype is stable; cells can be stored in liquid nitrogen for long-term use without loss of proliferative or differentiative potential. We have determined proliferative capacity of muscle cells from an analysis of clonal growth kinetics; we determined differentiative capacity from morphological evidence (cell fusion, striations, contractions, and the appearance of acetylcholine receptors) and biochemical analysis of muscle protein synthesis (creatine kinase, alpha-actin, tropomyosin, and myosin light chains). Our approach eliminates the variability in cellular composition that has complicated studies of primary muscle to date. We can now study in a controlled fashion the interactions and contributions of different cell types to the development of normal and genetically dystrophic human muscle.

Actins↗