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R Williamson

Publications and source records attributed to R Williamson.

539 records · Page 30Linked to original sources
PubMedDate not supplied

Atomic force microscopy imaging of DNA-cationic liposome complexes optimised for gene transfection into neuronal cells.

BACKGROUND: Cationic liposomes represent an important gene delivery system due to their low immunogenicity, but are relatively inefficient, with optimisation of DNA-liposome complexes (lipoplexes) for transfection necessary for each cell type of interest. There have been few studies examining optimisation in neuronal cell types or determining how the structure of lipoplexes affects transfection efficiency. METHODS: Four commercially available cationic liposome formulations were used to optimise transfection efficiency in neuronal cells. The DNA to liposome ratio and the amount of DNA used in transfections were varied. Transfection efficiency was determined by the percentage of cells positive for the micro-galactosidase reporter gene product. The structure of lipoplexes was studied using atomic force microscopy. Lipoplexes were characterised further using dynamic light scattering to determine size and fluorescence techniques to show DNA compaction. RESULTS: Optimal transfection conditions were found to differ between immortalised cell lines and primary cells. High transfection efficiencies in immortalised cell lines were achieved predominantly with multivalent cationic liposomes while primary neuronal cells showed optimal transfection efficiency with monovalent cationic liposomes. The structure of lipoplexes was observed with atomic force microscopy and showed globular complexes for multivalent cationic liposomes, while monovalent liposomes gave less compact structures. In support of this finding, high levels of DNA compaction with multivalent liposomes were observed using fluorescence quenching measurements for all DNA to liposome ratios tested. One monovalent liposome showed increasing levels of compaction with increasing liposome amount. Dynamic light scattering showed little change in complex size when the different lipoplexes were studied. CONCLUSIONS: Optimisation of transfection efficiency was different for cell lines and primary neurons. Immortalised cells showed optimal transfection with multivalent liposomes while primary neurons showed optimal transfection with monovalent liposomes. The charge ratio of the monovalent liposome was below one, suggesting a different mechanism of lipoplex binding and uptake in primary neurons. The structure of lipoplexes, as

Animals↗
PubMedDate not supplied

Use of community genetic screening to prevent HFE-associated hereditary haemochromatosis.

HFE-associated hereditary haemochromatosis is a recessive, iron-overload disorder that affects about one in 200 north Europeans and that can be easily prevented. However, genetic screening for this disease is controversial, and so we assessed whether such screening was suitable for communities. Cheek-brush screening for the Cys282Tyr HFE mutation was offered to individuals in the workplace. Outcomes were assessed by questionnaires before and after testing. 11,307 individuals were screened. We recorded no increase in anxiety in individuals who were homozygous for the Cys282Tyr mutation or non-homozygous. Self-reported tiredness before testing was significantly higher in homozygous participants than in non-homozygous participants (chi2 test, p=0.029). Of the 47 homozygous individuals identified, 46 have taken steps to treat or prevent iron accumulation. Population genetic screening for HFE-associated hereditary haemochromatosis can be practicable and acceptable.

Adult↗
PubMedDate not supplied

Localization of cystic fibrosis locus to human chromosome 7cen-q22.

Cystic fibrosis (CF) is the most common genetic disease in Caucasian populations, with an incidence of 1 in 2,000 live births in the United Kingdom, and a carrier frequency of approximately 1 in 20. The biochemical basis of the disease is not known, although membrane transport phenomena associated with CF have been described recently. Consanguinity studies have shown that the inheritance of CF is consistent with it being a recessive defect caused by a mutation at a single autosomal locus. Eiberg et al. have reported a genetic linkage between the CF locus and a polymorphic locus controlling activity of the serum aryl esterase paraoxonase (PON). The chromosomal location of PON, however, is not known. Linkage to a DNA probe, DOCR1-917, was also recently found at a genetic distance of approximately 15 centimorgans (L.-C. Tsui and H. Donnis-Keller, personal communication), but no chromosomal localization was given. Here we report tight linkage between the CF locus and an anonymous DNA probe, pJ3.11, which has been assigned to chromosome 7cen-q22.

Chromosome Mapping↗
PubMedDate not supplied

Linkage of an X-chromosome cleft palate gene.

Many congenital malformations, such as cleft palate and neural tube defects, have a multifactorial origin involving both environmental and genetic factors. Conditions such as these may be exclusively monogenic, polygenic or environmental, but in most cases both genetic and environmental factors are involved. This study describes the sub-chromosomal localization of a single gene defect causing cleft palate and ankyloglossia (tongue-tied) in a large Icelandic family. This defect is a model for the analysis of other neural-crest malformations that show a more complex multifactorial inheritance pattern.

Cleft Palate↗
PubMedDate not supplied

Valuable libraries.

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Cloning, Molecular↗
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Plasmid-mediated beta-lactamase (TEM-7) involved in resistance to ceftazidime and aztreonam.

TEM-7, a novel TEM-type beta-lactamase (pI 5.41) encoded on a plasmid of approximately 85 kilobases, was found in a clinical isolate of Citrobacter freundii. Strains containing this enzyme exhibited decreased susceptibility to ceftazidime (64-fold) and aztreonam (16-fold) but not to other third-generation cephalosporins. Addition of a beta-lactamase inhibitor--clavulanic acid, sulbactam, or YTR 830--restored normal susceptibility to associated compounds such as ampicillin, piperacillin, ceftazidime, and aztreonam. DNA-DNA hybridization of an intragenic probe of TEM-1 occurred with a 19-kilobase EcoRI fragment of the plasmid encoding TEM-7. A TEM-2 derivative, TEM-201, with characteristics similar to those of TEM-7 was selected spontaneously in the presence of ceftazidime in vitro.

Aztreonam↗
PubMedDate not supplied

Some properties of Serratia marcescens, Salmonella paratyphi A, and Enterobacter cloacae with non-enzyme-dependent multiple resistance to beta-lactam antibiotics, aminoglycosides, and quinolones.

Non-enzyme-dependent multiple-drug resistance occurs preferentially in some genera of Enterobacteriaceae, such as Serratia, Klebsiella, Enterobacter, and Salmonella. Susceptibility to beta-lactam antibiotics, aminoglycosides, quinolones, trimethoprim, and chloramphenicol may be affected in various combinations in different mutants. Proteins from the outer and inner membranes and lipopolysaccharides may be altered concomitantly. Although porin alterations have been observed in all resistant mutants studied, these modifications alone do not seem sufficient to explain the various cross-resistance phenotypes.

4-Quinolones↗
PubMedDate not supplied

Ultrasound-guided gene transfer to hepatocytes in utero.

OBJECTIVES: Several inherited liver diseases are associated with a progressive course that begins early in life. Such disorders may be amenable to treatment with gene transfer in the fetal or neonatal period. METHODS: We used ultrasound guidance to deliver an adenoviral vector to the liver of 28-day gestation fetal rabbits by cardiocentesis. beta-Galactosidase reporter gene expression in hepatocytes was analyzed 3, 7, and 21 days after vector delivery. Using this nonsurgical approach, the viral vector was efficiently delivered into the fetal circulation. RESULTS: The liver was the main organ targeted by this route of administration with up to 40% of the hepatocytes beta-galactosidase positive in some animals. The beta-galactosidase expression in hepatocytes gradually declined between 3 and 21 days following gene transfer. Associated with the decline in gene expression, an increased number of inflammatory cells were noted in the livers of adenoviral vector treated animals. This suggests that an immune response limits the duration of gene expression in the fetal rabbit, similar to the findings in postnatal animals. CONCLUSIONS: This animal model and vector delivery method may be useful for evaluating gene transfer to the fetus with viral and nonviral vectors. Further modifications of the adenoviral vector to reduce immunogenicity may enhance the duration of expression.

Adenoviridae↗
PubMedDate not supplied

Localization of a mutant gene for cleft palate and ankyloglossia in an X-linked Icelandic family.

Common congenital malformations such as cleft lip and cleft palate are in most cases multifactorial in origin, involving both environmental and genetic components. Molecular biology techniques have enabled the successful chromosomal localization of many mutant genes from disorders that exhibit simple Mendelian segregation, whether autosomally dominant (e.g., Huntington's disease), autosomal recessive (e.g., cystic fibrosis), or X-linked (e.g., Duchenne muscular dystrophy). Studying the genetic aspect of multifactorial disorders is more complex. It requires a model family or families within which the common multifactorial phenotype is displayed as a single gene defect. Such a model has been recently exploited in the form of a large Icelandic family (over 280 members) exhibiting X-linked secondary cleft palate (CP) and ankyloglossia (A) (tongue-tied) as a single gene mutation. Using this family and the large bank of well-characterized DNA probes available for the human X chromosome, the gene for CP + A was localized by linkage analysis to Xq13-q21.1 (LOD score = 3.07, linked to anonymous probe DXYS1). Further fine mapping, using other X probes from this region (confirmed by analysis of DNA from a deletion cell-line) has placed the gene between markers DXYS12 and DXS17 (LOD score = 4.1) at Xq21.3-q22. The approximate distance between these two probes is 5 centimorgans (cM), equivalent to approximately 5 million base pairs. Now that the limits of genetic linkage have been fully tested and there are two markers flanking the defect locus, strategies are being pursued to clone the gene responsible.(ABSTRACT TRUNCATED AT 250 WORDS)

Cleft Palate↗
PubMedDate not supplied

In vivo and in vitro emergence of simultaneous resistance to both beta-lactam and aminoglycoside antibiotics in a strain of Serratia marcescens.

In a patient with Serratia marcescens bacteraemia, a variant resistant to cefotaxime and amikacin was isolated in a blood culture under combined treatment with cefotaxime and amikacin. In addition, in vitro selection on cefotaxime and/or amikacin yielded resistant mutants from the sensitive parent strain. These mutants displayed the same type of cross-resistance as the clinical strain to all beta-lactam and aminoglycoside antibiotics. The mechanism for this resistance was a decrease in the permeability of the cell. To our knowledge, the isolation of such strains from blood cultures and the mechanism responsible for this "broad-spectrum resistance" have not been previously described.

Aminoglycosides↗
PubMedDate not supplied

Clinical management of galvanic current between gold and amalgam.

Placing a strip of rubber dam or similar insulator between the contacting dissimilar restorations is a diagnostic technique for relieving and evaluating painful galvanic currents. Treatment modalities vary according to severity of pain. In cases of little or no pain, nothing is done, and corrosion products are allowed to form an insulating cover over the offending restoration. For patients with severe pain that does not improve, treatment may consist of placing a composite restoration in the amalgam restoration to break the interproximal dissimilar-metal contact. For painful currents caused by occluding restorations, a coating of unfilled light-cured resin over the offending amalgam breaks the metal contact and allows corrosion product buildup. Galvanic currents can occur and cause pain, but this is generally shortlived and should not influence the dentist's choice of an appropriate restorative material.

Adult↗