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At least 811 records · Page 45Linked to original sources
PubMed1986

Antigenic variation in the phase I lipopolysaccharide of Coxiella burnetii isolates.

Coxiella burnetii isolates from a variety of clinical and geographical sources were screened for antigenic variation of lipopolysaccharides (LPSs) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis coupled with silver staining or immunoblotting. All isolates from chronic Q fever or other sources possessed a phase I-type LPS. These LPSs appeared to fall into three groups based on the sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile or on reactivity with rabbit anti-C. burnetti antisera. The LPS of one group was identified on isolates from milk, ticks, or primary Q fever. The two remaining groups were found almost exclusively on isolates from human cases of chronic Q fever.

Antigens, Bacterial↗
PubMed2005

Circadian variation of the cell proliferation in the jejunal epithelium of rats at weaning phase.

Circadian variation in cell proliferation of the jejunal epithelium of 18-day-old rats was studied using the 2-h arrested metaphase score and crypt isolation method. A continuous decrease in the arrested metaphases occurred from 07.00 h to 13.00 h. From 17.00 h arrested metaphase values increased and were maintained at the higher level during the dark period as showed by Cosinor analyses (P < 0.05). These results indicate that in the young rat there is already a circadian variation in jejunal epithelial cell proliferation as early as 18 days. We can even suggest that the presence of a circadian rhythm at weaning contributes to the steady state of cell proliferation in the intestinal epithelium observed in adult life.

Animals↗
PubMed2004

AstR-AstS, a new two-component signal transduction system, mediates swarming, adaptation to stationary phase and phenotypic variation in Photorhabdus luminescens.

Photorhabdus luminescens is an insect-pathogenic bacterium that forms a symbiosis with specific entomopathogenic nematodes. In this bacterium, a symbiosis-'deficient' phenotypic variant (known as the secondary variant or form II) arises at a low frequency during prolonged incubation. A knock-out mutant was generated of the regulator of a newly identified two-component regulatory system, designated AstR-AstS. Interestingly, this mutation altered the timing of phenotypic switching. Variant cells arose in the mutant strain several days before they did in the wild-type population, suggesting that AstRS is directly or indirectly involved in the genetic mechanism underlying variant cell formation. This mutation also affected motility and antibiotic synthesis. To identify AstRS-regulated genes, a comparative analysis using two-dimensional gel electrophoresis was performed. Seventeen proteins with modified synthesis in stationary phase were identified by mass spectrometry and shown to be involved in electron-transport systems, energy metabolism, iron acquisition and stress responses. The results imply that AstRS is involved in the adaptation of cells to the stationary phase, whilst negatively affecting the competitive advantage of form I cells. The link between AstRS-dependent stationary-phase adaptation and phenotypic variation is discussed.

Adaptation, Physiological↗
PubMed1995

An audit of pulmonary function laboratories in the West Midlands.

BACKGROUND: Pulmonary function testing has become an integral part of the assessment and follow-up of patients with pulmonary disease. Many factors can influence the results produced by a laboratory. This audit was performed to examine the extent of variation in the pulmonary function test results amongst all laboratories in the West Midlands. This was followed by an attempt to determine the cause of this variation. METHODS: Phase 1. Three normal healthy subjects each underwent a set of pulmonary function tests in all 22 laboratories in the West Midlands. Information regarding technicians' qualifications, training and seniority, protocol and equipment used were obtained in the form of a questionnaire. Phase 2. All 22 laboratories were asked to calculate the predicted values on the same nine sets of demographic data. These data included both sexes, ethnic minorities and range of ages. In addition technical aspects of each laboratory were investigated including the assessment of volume and gas analysers with standard gases containing known concentrations of helium and carbon monoxide. RESULTS: Phase 1. Significant variations (P < 0.05) were observed in all measured values of pulmonary function tests of the three subjects. Significant variations (P < 0.05) were also observed in all predicted values except total lung capacity. Phase 2. There were significant variations (P < 0.05) amongst laboratories in calculating the predicted values of all components of pulmonary function tests. No significant differences were observed in the measurement of volume or concentration of carbon monoxide or helium.

Adult↗
PubMed1994

Sequence changes in the pilus subunit lead to tropism variation of Neisseria gonorrhoeae to human tissue.

Pili of Neisseria gonorrhoeae are correlated with increased bacterial attachment to epithelial cells and undergo both phase and antigenic variation. Phase variation of gonococcal pili can be brought about by recombination events in the pilin structural gene, pilE, or by the on/off switch in expression of PilC, a pilus biogenesis protein for which two loci exist. We have studied the binding to epithelial cell lines and to fixed tissue sections of N. gonorrhoeae MS11 derivatives and mutants carrying structurally defined PilE and PilC proteins. In situ binding studies of N. gonorrhoeae to formalin-fixed tissue sections resulted in a binding pattern similar to that obtained using viable epithelial cell lines of different origin. Piliated gonococcal clones, containing different pilE sequences, varied dramatically from one another in their efficiencies at binding to corneal and conjunctival tissue, but bound equally well to cervical and endometrial tissues. Further, the binding data suggested that PilC expression by itself, i.e. without pili, cannot confer bacterial binding and that expression of either PilC1 or PilC2 does not confer different binding properties to the bacterial cells. Possible receptors for piliated gonococci were expressed in human tissues, such as cervix, endometrium, cornea, intestine, stomach, mid-brain and meninges, but not in human kidney. Pretreatment of the target tissues with Proteinase K decreased the gonococcal binding dramatically, whereas pretreatment with neuraminidase and meta-periodate, which cleave carbon-carbon linkages between vicinal hydroxyl groups in carbohydrates, did not affect attachment of gonococci. These data argue that pilus-dependent attachment of N. gonorrhoeae to human tissue may be mediated by a eukaryotic receptor having protein characteristics, and that the pilus subunit sequence may play an important role in the interaction with human cornea.

Amino Acid Sequence↗
PubMed1985

Estimation of circadian variations in cell cycle phase durations in murine epidermal basal cells.

Circadian variations in the proliferative activity of squamous epithelia are well known. However, circadian variations in the duration of the various cell cycle phases (S, G2 and mitosis) have been disputed. The percent labelled mitoses method, which is traditionally used to obtain duration of cell cycle phases, is poorly suited for identification of circadian variations. Therefore methods combining changes in compartment size (cell cycle phase) and cellular flux through the compartments have been used. Three different methods using such data are presented. These incorporate various simplifying assumptions that cause methodological errors. Limits for use of the different methods are indicated. The use of all three methods gives comparable and pronounced circadian variations in the duration of S and G2 phase. These results are also compatible with circadian variations in the mitotic duration, but they may also represent artefacts due to sensitivity to model errors.

Animals↗
PubMed1987

Common mechanism controlling phase and antigenic variation in pathogenic neisseriae.

The expression of the Neisseria gonorrhoeae opacity protein (Op, protein II), a major antigenic determinant of the outer membrane, is subject to frequent phase transitions. At least nine expression loci (opaE) are involved in the production of a large number of serologically distinct Op types. Using opa-specific oligonucleotides as probes in genomic blots, we detect Op-related gene sequences (opr) in N. meningitidis as well as in N. lactamica. DNA sequence analysis of such opr genes derived from N. meningitidis reveals distinct regions of homology with gonococcal opa E genes. As shown in the immunoblot, the proteins encoded by opa and opr are serologically related. Like the opaE genes, the 5'-coding sequences of the opr genes include a repetitive sequence composed of pentameric CTCTT units. The number of these coding repeat (CR) units is variable. This finding, together with the observation that all opr genes are constitutively transcribed, regardless of the status of protein production, suggests a translational control mechanism identical to that of the opa genes in gonococci. The related structures and control mechanisms of opa and opr genes imply a general significance of their gene products for the pathogenic character of the investigated Neisseria species.

Amino Acid Sequence↗
PubMed1997

DNA topology in hyperthermophilic archaea: reference states and their variation with growth phase, growth temperature, and temperature stresses.

In order to address the dynamics of DNA topology in hyperthermophilic archaea, we analysed the topological state of several plasmids recently discovered in Thermococcales and Sulfolobales. All of these plasmids were from relaxed to highly positively supercoiled in vitro, i.e. they exhibited a significant linking excess compared to the negatively supercoiled plasmids from mesophilic organisms (both Archaea and Bacteria). In the two archaeal orders, plasmid linking number (Lk) decreased as growth temperature was lowered from its optimal value, i.e. positively supercoiled plasmids were relaxed whereas relaxed plasmids became negatively supercoiled. Growth temperatures above the optimum correlated with higher positive supercoiling in Sulfolobales (Lk increase) but with relaxation of positive supercoils in Thermococcus sp. GE31. The topological variation of plasmid DNA isolated from cells at different growth phases were found to be species specific in both archaeal orders. In contrast, the direction of topological variation under temperature stress was the same, i.e. a heat shock correlated with an increase in plasmid positive supercoiling, whilst a cold shock induced negative supercoiling. The kinetics of these effects were analysed in Sulfolobales. In both temperature upshift (from 80 to 85 degrees C) and downshift (from 80 to 65 degrees C), a transient sharp variation of Lk occurred first, and then DNA supercoiling progressively reached levels typical of steady-state growth at the final temperature. These results indicate that DNA topology can change with physiological states and environmental modifications in hyperthermophilic archaea.

Archaea↗
PubMed1984

ELISA plaque assay for the detection of antibody secreting cells: observations on the nature of the solid phase and on variations in plaque diameter.

This report examines the basis for variations in the size and number of ELISA plaques detected in vitro. The nature and concentration of antigen used to coat the solid phase is shown to be critical, high concentrations of polymerized antigen being optimal for low molecular weight proteins, while coating conditions for high molecular weight multideterminant antigens are similar to conventional liquid ELISA. Variations in plaque diameter are shown to reflect maturational changes in the immune response, and probably indicate differences in the affinity of antibody being secreted within a population of plasma cells.

Animals↗
PubMed2000

Relationship between membrane damage and cell death in pressure-treated Escherichia coli cells: differences between exponential- and stationary-phase cells and variation among strains.

The relationship between membrane damage and loss of viability following pressure treatment was examined in Escherichia coli strains C9490, H1071, and NCTC 8003. These strains showed high, medium, and low resistance to pressure, respectively, in stationary phase but similar resistance to pressure in exponential phase. Loss of membrane integrity was measured as loss of osmotic responsiveness or as increased uptake of the fluorescent dye propidium iodide. In exponential-phase cells, loss of viability was correlated with a permanent loss of membrane integrity in all strains, whereas in stationary-phase cells, a more complicated picture emerged in which cell membranes became leaky during pressure treatment but resealed to a greater or lesser extent following decompression. Strain H1071 displayed a very unusual pressure response in stationary phase in which survival decreased to a minimum at 300 MPa but then increased at 400 to 500 MPa before decreasing again. Membranes were unable to reseal after treatment at 300 MPa but could do so after treatment at higher pressures. Membrane damage in this strain was thus typical of exponential-phase cells under low-pressure conditions but of stationary-phase cells under higher-pressure conditions. Heat shock treatment of strain H1071 cells increased pressure resistance under low-pressure conditions and also allowed membrane damage to reseal. Growth in the presence of IPTG (isopropyl-beta-D-thiogalactopyranoside) increased resistance under high-pressure conditions. The mechanisms of inactivation may thus differ at high and low pressures. These studies support the view that membrane damage is an important event in the inactivation of bacteria by high pressure, but the nature of membrane damage and its relation to cell death may differ between species and phases of growth.

Cell Membrane↗
PubMed2001

Reproductive phase depedent circadian variation in the pineal biochemical constituents of Indian palm squirrel, Funambulus pennanti.

In mammals, pineal gland is intimately concerned with the co-ordination of rhythm physiology. Biochemical characteristics of pineal gland in man and other mammals may provide strong, yet sometimes elusive support for the belief in functional individuality and probable importance of this tiny gland. In seasonal breeding animals, pineal gland function is very much dependent on the reproductive status. Therefore, the aim of this experiment is to note the circadian rhythmicity of different biochemical constituents of pineal gland during active and inactive phases of reproductive cycle of a seasonally breeding rodent, F. pennanti. In the present study, pineal biochemical constituents i.e. protein and cholesterol showed higher values during daytime (1400 h). The plasma melatonin level presented two peaks during active (April; at 1800 h and 0200 h) and inactive (December; at 1400 h and 0200 h) phases of reproductive cycle. The pineal protein, cholesterol and plasma melatonin values in term of basal and peak levels were higher during the reproductive inactive/pineal active phase. Therefore, pineal--also known to have antigonadotropic properties and cholesterol which appears conjugated with pineal serotonin, presented circadian rhythmicity along with the plasma level of melatonin. This rhythmicity noted in present study was dependent on the reproductive and pineal activity status, and might be regulated by the sex steroid receptor present on the pineal gland.

Animals↗
PubMed1979

Variation in S phase in synchronous human cell lines.

Growth parameters of diploid and trisomic human fibroblasts were determined. The rate of growth of both classes of cells was examined in asynchronous cultures, and diploid and trisomic cells had similar growth rates. Synchronous cultures were developed using simple mitotic selection. The patterns and length of the DNA synthetic period (S phase) were found to be altered in trisomy 21 cells when compared to diploid human or to heteroploid HeLa cells. Early S-phase synthesis was absent or reduced and the overall length of the S phase was extended. However, the trisomic cells have apparently normal rates of DNA chain elongation and normal replicon sizes.

Cell Cycle↗
PubMed1986

Opacity genes in Neisseria gonorrhoeae: control of phase and antigenic variation.

The chromosome of N. gonorrhoeae contains several complete expression genes coding for variant opacity proteins. DNA sequence analysis of two opacity genes derived from the same locus (opaE1) of two isogenic gonococcal variants reveals common and variable regions in these genes. Genomic blotting experiments using synthetic probes suggest gene conversion as a principle for the assembly of variant sequence information in opacity genes. The 5' region of opacity genes is composed of identical pentameric pyrimidine units (CTCTT) encoding the hydrophobic portion of the opacity leader peptide. This coding repeat is variable in a given locus with respect of the number of pentameric units. While all expression loci in a single cell are constitutively transcribed, the production of opacity proteins is determined by the coding repeat sequence on the translational level.

Amino Acid Sequence↗
PubMed1993

Phase and antigenic variation--the impact on strategies for bacterial vaccine design.

Many pathogens have the ability to vary the antigenic composition of surface-associated antigens. Often, this variation is mediated by the regulation of gene expression. By varying its antigenicity, the pathogen is able to avoid host immune responses more efficiently; however, this makes the design of vaccines against pathogens that exhibit antigenic variation difficult. In this review, we use the pathogenic Neisseria as an example of antigenically variable bacteria and discuss some attempts to overcome the problems of vaccine design posed by such organisms.

Antigenic Variation↗
PubMed2005

Systematic variation of interfacial phase reactivity in dental nanocomposites.

This study was designed to determine the effect of varying the chemistry of the interfacial phase on critical composite properties in dental nanocomposite materials. Silica nanoparticles were silanized with varying ratios of 3-methacryloxypropyltrimethoxysilane (MPTMS) and octyltrimethoxysilane (OTMS) while keeping the total amount of silane constant at 10% by mass fraction relative to the mass of filler. The silanized nanoparticles were mixed into a dimethacrylate resin (60% filler by mass fraction). The mechanical properties of the uncured pastes were assessed by compression testing between parallel plates. The composites were photo-cured and tested by biaxial flexure and three-point bend flexure testing. Fracture surfaces were analyzed by field-emission scanning electron microscopy (FE-SEM). At maximized filler mass fractions, the workabilities of the uncured pastes were better maintained as the fraction of OTMS in the interphase increased relative to MPTMS. The flexure strengths and moduli of the MPTMS silanized and dual silanized composites were similar but decreased as OTMS mass fractions in the silane mixture increased to 7.5% and 10%. FE-SEM images revealed evidence for phase separation in the composites containing silica silanized with high fractions of OTMS. Among the potential practical benefits of dual silanized nanoparticles are the improved workability of composite pastes with higher filler loadings that should lead to higher modulus composites with lower polymerization shrinkage.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2000

Fluid phase endocytosis in oral epithelia: variation with site and effect of cancer.

The structure of the oral mucosa has been extensively studied but its cell physiology has been less well characterised. This study aimed to show the range in variation in fluid phase endocytic capability in biopsies from different oral sites. Oral epithelial cells were obtained from both biopsies and single-cell suspensions obtained by brushing the oral cavity. Biopsies in organ culture and single cells in suspension were incubated with fluorescent microspheres of 0.02, 0.1 or 1.0 microm diameter. Endocytosis of fluorescent microspheres was quantitated by flow cytometry and visualised by confocal microscopy. Epithelial cells from all oral sites that were sampled internalised 0.02 microm and 0.1 microm but not 1.0 microm microspheres, with no significant differences observed between oral regions. Single cells from non-cancer patients endocytosed significantly more 0.02 microm microspheres than cells removed from patients with oral cancer. This model may be used to study integrated oral cell function both in health and disease.

Biopsy↗
PubMed2001

Training effects of amortization phase with eccentric/concentric variations--the vertical jump.

The purpose of this study was to find if the performance of the vertical jump is improved by the result of increasing the force, velocity, and muscle adaptation(s). For the experiment, there were four groups (Gr): three groups did the training programs and the fourth group was the control group (CG). In order to establish improvements in force and velocity, the groups performed three variations using eccentric (Ecc) and concentric (Con) movement. Finally, the leg presses, squat jumps (SJ) and countermovement jumps (CJ) were used to determine the changes in the muscle adaptations before and after the training program. For measuring the force, four force transducers were used. In determining the velocity, a displacement transducer was used. A surface EMG was used to measure the muscle activations during all of the tests that were performed. After eight weeks of training, Gr 1 and Gr 2 improved the isometric force and the power during the Con. movement for the leg press. For the SJ, Gr. 1 and 2 increased their height, muscle activity, force, and power, but only group one improved the velocity. However, group three improved the isometric force and power for the leg presses, the squat jump and the countermovement jump. For both of the jumps, they also increased velocity, muscle activity and height. There were no changes observed for group four. Although the three combinations of Ecc/Con movements existed during the training program, the force, velocity and muscle adaptations increased, but not all of the improvements were of the same degree.

Adaptation, Physiological↗