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A Ridley

Publications and source records attributed to A Ridley.

At least 19 recordsLinked to original sources
PubMed2001

Protein kinase C-delta C2-like domain is a binding site for actin and enables actin redistribution in neutrophils.

Neutrophils play a key role in host-defence mechanisms against invading pathogens, using their capacity to migrate, engulf micro-organisms and produce toxic radicals. Protein kinase C (PKC) isotypes are important intracellular regulators of these processes in neutrophils. PKC isotypes themselves are controlled by interactions with lipids, Ca(2+) and proteins. The C2-like domain of PKC-delta (deltaC2) has been identified as a protein-interaction domain in this PKC isotype. In the present paper we have investigated the contribution of protein interactions at this domain to the regulation/function of PKC-delta in neutrophils. Using affinity chromatography we identified actin as a deltaC2 binding partner in these cells. Fluorescein-labelled deltaC2, microinjected into immobilized neutrophils, interacts with filamentous actin (F-actin) inside the cell. PKC-delta co-localizes with F-actin in neutrophils, in lamellipodia at the leading edge of the cell. Stimulation with phorbol ester or IgG-opsonized Staphylococcus aureus results in co-ordinated redistribution of PKC-delta and F-actin, and a PKC-delta inhibitor inhibits these changes. Microinjection of deltaC2 also inhibits F-actin redistribution. Thus PKC-delta binds to F-actin through its C2 domain, and these interactions are important in regulating actin redistribution in neutrophils.

Actins↗
PubMed2001

Evidence for a genetically stable strain of Campylobacter jejuni.

The genetic stability of selected epidemiologically linked strains of Campylobacter jejuni during outbreak situations was investigated by using subtyping techniques. Strains isolated from geographically related chicken flock outbreaks in 1998 and from a human outbreak in 1981 were investigated. There was little similarity in the strains obtained from the different chicken flock outbreaks; however, the strains from each of three chicken outbreaks, including strains isolated from various environments, were identical as determined by fla typing, amplified fragment length polymorphism (AFLP) analysis, and pulsed-field gel electrophoresis, which confirmed the genetic stability of these strains during the short time courses of chicken flock outbreaks. The human outbreak samples were compared with strain 81116, which originated from the same outbreak but has since undergone innumerable laboratory passages. Two main AFLP profiles were recognized from this outbreak, which confirmed the serotyping results obtained at the time of the outbreak. The major type isolated from this outbreak (serotype P6:L6) was exemplified by strain 81116. Despite the long existence of strain 81116 as a laboratory strain, the AFLP profile of this strain was identical to the profiles of all the other historical P6:L6 strains from the outbreak, indicating that the genotype has remained stable for almost 20 years. Interestingly, the AFLP profiles of the P6:L6 group of strains from the human outbreak and the strains from one of the recent chicken outbreaks were also identical. This similarity suggests that some clones of C. jejuni remain genetically stable in completely different environments over long periods of time and considerable geographical distances.

Animals↗
PubMed2000

What initiates actin polymerization?

For those working on the actin cytoskeleton, a major theme of the 39th annual meeting of the American Society for Cell Biology [http://www.faseb.org/ascb/meetings/am99/+ ++main99mtg.htm] (Washington DC, December 11-15, 1999) was the elucidation of how actin polymerization is initiated. The emphasis was on the regulation and localization of the Arp2/3 complex, which over the last two years has been shown to stimulate actin nucleation, and on the identification of additional proteins that interact with actin and Arp2/3 in a variety of organisms.

Actins↗
PubMed1999

Sema3A-induced growth-cone collapse is mediated by Rac1 amino acids 17-32.

BACKGROUND: Neurons project their axons along specific pathways in order to establish appropriate connections with their target cells. The rate and direction of axonal growth is determined by interactions between the highly motile growth cone and environmental cues that can act in either an attractive or a repulsive manner. Locomotion is ultimately dependent upon the reorganisation of the actin cytoskeleton and an established role for the Rho family of small GTPases in regulating this process in non-neuronal cells identifies them as candidate signalling molecules in growth cones. An inactive form of Rac1 has recently been shown to inhibit the 'growth-cone collapse' response induced by chick Sema3A, a protein that has recently been established as an important guidance cue. The molecular basis for this inhibition remains unclear. RESULTS: We have made a series of overlapping peptides from the amino-terminal region of Rac1 and rendered them cell permeable by synthesis in tandem with an established internalisation vector. We report here that a peptide encompassing Rac1 amino acids 17-32 binds directly to the established Rac1-interacting molecules PAK, WASP, 3BP-1 and p85beta(P13K), but not to p67(Phox). Furthermore, the peptide can compete with activated Rac1 for target binding, and inhibits Sema3A-induced growth-cone collapse. We also synthesised cell-permeable peptides that correspond to the Cdc42/Rac1-binding (CRIB) motifs present in PAK and N-WASP. Our results show that a CRIB-containing peptide from PAK, but not that from N-WASP, inhibits growth-cone collapse and that the inhibitory activity correlates with binding to Rac1 and not to Cdc42. CONCLUSIONS: Our results suggest that Sema3A-induced growth-cone collapse is mediated by Rac1 amino acids 17-32, and demonstrate the feasibility of designing new cell-permeable inhibitors of small GTPases.

Amino Acid Sequence↗
PubMed1999

Rac and Rho.

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Animals↗
PubMed1998

Molecular epidemiology of antibiotic resistance genes in multiresistant epidemic Salmonella typhimurium DT 104.

The epidemiology of antibiotic resistance genes in epidemic multiresistant S. typhimurium DT 104 of human and animal origin was investigated. DNA prepared from 45 human and 21 animal strains isolated between 1984 and 1997, including eight isolated in other European countries, the USA, Trinidad, and South Africa and resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides, spectinomycin, tetracyclines (R-type ACSSuSpT) were examined for the presence of integrons by PCR. Integron hot spots were observed in all strains conferring resistance to ACSSuSpT in two copies, determined by two discrete bands of approximately 1.0 and 1.2 kb. Direct nucleotide sequencing of the individual amplicons of selected strains indicated that the 1.0 kb gene product was ant (3")-Ia, responsible for resistance to streptomycin and spectinomycin; the 1.2 kb amplicon contained the gene blaPSE-1, encoding the beta-lactamase PSE-1 (CARB-2). Both integrons were encoded on a single XbaI macrorestriction fragment of approximately 10 kb. All isolates of DT 104 of this resistance phenotype contained the same inserted gene cassettes, irrespective of source and country of origin, supporting the suggestion of the spread of an epidemic clone. Sequence analysis of the quinolone resistance determining region (QRDR) of gyrA of 15 multiresistant strains conferring additional resistance to nalidixic acid and ciprofloxacin (R-type ACSSuSpTNxCp) identified two discrete base substitutions at codon Asp-87. Conversion of Asp-87 --> Asn was most commonly observed, in 7/10 human and 4/5 animal isolates, suggesting that this codon plays a major role in the development of ciprofloxacin resistance in multiresistant S. typhimurium DT 104.

Animals↗
PubMed1997

Role of phosphoinositide 3-OH kinase in cell transformation and control of the actin cytoskeleton by Ras.

The pathways by which mammalian Ras proteins induce cortical actin rearrangement and cause cellular transformation are investigated using partial loss of function mutants of Ras and activated and inhibitory forms of various postulated target enzymes for Ras. Efficient transformation by Ras requires activation of other direct effectors in addition to the MAP kinase kinase kinase Raf and is inhibited by inactivation of the PI 3-kinase pathway. Actin rearrangement correlates with the ability of Ras mutants to activate PI 3-kinase. Inhibition of PI 3-kinase activity blocks Ras induction of membrane ruffling, while activated PI 3-kinase is sufficient to induce membrane ruffling, acting through Rac. The ability of activated Ras to stimulate PI 3-kinase in addition to Raf is therefore important in Ras transformation of mammalian cells and essential in Ras-induced cytoskeletal reorganization.

3T3 Cells↗
PubMed1996

WHO-sponsored international collaborative study to evaluate methods for subtyping Listeria monocytogenes: restriction fragment length polymorphism (RFLP) analysis using ribotyping and Southern hybridization with two probes derived from L. monocytogenes chromosome.

Seven laboratories participated in a WHO-sponsored international collaborative study, to evaluate methods for subtyping Listeria monocytogenes, by performing restriction fragment length polymorph sm (RFLP) analysis-based subtyping of an international study set of 80 strains of L. monocytogenes that included 22 epidemiologically related groups. The RFLP analysis was done by Southern hybridization with one of two types of probes found in multiple copies on the chromosome of L. monocytogenes. Six laboratories performed ribotyping. These laboratories used EcoRI enzyme to restrict the L. monocytogenes DNA and ribosomal RNA or DNA as the probe for Southern hybridizations. The seventh laboratory used Ncil to restrict the DNA, and two probes, one randomly cloned and the other containing repeat sequences cloned from L. monocytogenes DNA. The overall discriminating power of ribotyping, as estimated by calculation of Simpson's index of diversity, ranged from 0.83 to 0.88 for the six laboratories. The discriminating power of the combination of two probes used by Laboratory 7 was 0.91. Ribotyping and the cloned probes used by Laboratory 7 discriminated poorly between serotype 4b strains. Neither method identified three atypical strains (identified by other subtyping methods) included in three apparently epidemiologically related groups. Ribotyping did not discriminate between strains of serotypes 4b and 4b(X) in one epidemiologically related group of strains; one cloned probe used by Laboratory 7 discriminated between these strains. Intra-laboratory reproducibilities for the seven laboratories ranged from 80.0 to 100%. as determined by their abilities to correctly identify 11 pairs of duplicate strains included in the study set. Inter-laboratory reproducibilities were generally very good considering that no attempt was made to standardize protocols used by the participants.

Bacterial Typing Techniques↗
PubMed1995

CpG islands in human ZFX and ZFY and mouse Zfx genes: sequence similarities and methylation differences.

The human ZFX, human ZFY, and mouse Zfx genes have CpG islands near their 5; ends. These islands are typical in that they span about 1.5 kb, contain transcription initiation sites, and encompass some 5' untranslated exons and introns. However, comparitive nucleotide sequencing of these human and mouse islands provided evidence of evolutionary conservation to a degree unprecedented among mammalian 5' CpG islands. In one stretch of 165 nucleotides containing 19 CpGs, mouse Zfx and human ZFX are identical to each other and differ from human ZFY at only 9 nucleotides. In contrast, we found no evidence of homologous CpG islands in the mouse Zfy genes, whose transcription is more circumscribed than that of human ZFX, human ZFY, and mouse Zfx. Using the isoschizomers HpaII and MspI to examine a highly conserved segment of the ZFX CpG island, we detected methylation on inactive mouse X chromosomes but not on inactive human X chromosomes. These observations parallel the previous findings that mouse Zfx undergoes X inactivation while human ZFX escapes it.

Animals↗
PubMed1990

Homologous ribosomal protein genes on the human X and Y chromosomes: escape from X inactivation and possible implications for Turner syndrome.

We have isolated two genes on the human sex chromosomes, one on the Y and one on the X, that appear to encode isoforms of ribosomal protein S4. These predicted RPS4Y and RPS4X proteins differ at 19 of 263 amino acids. Both genes are widely transcribed in human tissues, suggesting that the ribosomes of human males and females are structurally distinct. Transcription analysis revealed that, unlike most genes on the X chromosome, RPS4X is not dosage compensated. RPS4X maps to the long arm of the X chromosome (Xq), where no other genes are known to escape X inactivation. Curiously, RPS4X maps near the site from which the X-inactivating signal is thought to emanate. On the Y chromosome, RPS4Y maps to a 90 kb segment that has been implicated in Turner syndrome. We consider the possible role of RPS4 haploinsufficiency in the etiology of the Turner phenotype.

Amino Acid Sequence↗
PubMed1987

Omnipause neurons in two cases of opsoclonus associated with oat cell carcinoma of the lung.

Opsoclonus is an involuntary eye movement disorder in which there are chaotic, usually conjugate, multidimensional saccadic eye movements. In this paper 2 cases of opsoclonus are reported, as a paraneoplastic phenomenon in association with oat cell carcinoma of the lung. It has previously been hypothesized that opsoclonus results from dysfunction of a group of premotor neurons in the brainstem called omnipause neurons. We describe the location of these cells in man by homology with animal studies, and describe the light microscopic appearance of these neurons in the 2 cases of opsoclonus. Although these neurons appeared normal it is still possible that their function was disturbed as a result of metabolic or neurotransmitter abnormalities.

Aged↗
PubMed1982

Treatment of the Guillain-Barré syndrome by plasma exchange.

Twelve consecutive patients with Guillain-Barré syndrome were treated with plasma exchange. Examination two weeks after treatment was commenced showed that three had not improved. Five showed only a minimal improvement, which was considered to be compatible with the natural history of the disease. The remaining four patients showed a more substantial improvement which could have been related to the plasma exchange.

Adult↗
PubMed1981

Lymphocyte-mediated cytotoxicity against gliomas.

The effects of peripheral blood lymphocytes from patients with glioma on glioma cells grown in culture was studied using an in vitro microcytotoxicity test. Lymphocytes from 12 of the 20 patients studied showed significant cytotoxic activity against their own tumour cells. Four of them reacted against heterologous glioma cells and 4 also showed some reactivity against foetal brain cells. An attempt to correlate in vitro cytotoxicity with the degree of lymphocytic infiltration of the tumour suggested an association, but the number of cases examined was too small to achieve statistical significance.

Adult↗