Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Fluctuating selection”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33Linked to original sources
PubMed2000

Laser desorption/ionization coupled to tandem mass spectrometry for real-time monitoring of paraquat on the surface of environmental particles.

Aerosol mass spectrometry with laser desorption/ionization was investigated as a possible tool for real-time monitoring of the presence of the pesticide paraquat on the surface of airborne soil particles. Laser desorption/ionization of paraquat dication produced only singly charged ions. The most abundant species were [M](+.), [M - H](+), and [M - CH3](+). Operation of the ion trap mass spectrometer in the MS(3) mode allowed the reduction of the signal dependence on laser fluence fluctuations and permitted the detection of the analyte with good sensitivity and high selectivity. The estimated limit of detection in terms of surface coverage was 0.016 monolayers, approximately 1 attomole of paraquat on the surface of a single micron-sized soil particle.

Air Pollutants↗
PubMed1995

Molecular characterization and expression patterns of a B-type nuclear lamin during sea urchin embryogenesis.

Developmentally regulated, tissue-specific patterns of nuclear lamin expression occur during vertebrate embryogenesis, but little is known regarding lamin ontogeny during the early development of other phyla. cDNA clones encoding a lamin from the sea urchins Strongylocentrotus purpuratus and Lytechinus variegatus have been identified, and the full coding region from the former has been sequenced. The predicted amino acid sequence indicates that this echinoderm lamin is more closely related to vertebrate B-type lamins than to dipteran fly and nematode lamins--the only other invertebrate lamins sequenced to date. Monoclonal and polyclonal antibodies to sea urchin lamin demonstrate that nuclei of unfertilized eggs and embryos exhibit relatively faint immunoreactivity until the differentiation of primary mesenchymal cells, the nuclear envelopes of which become strongly and selectively labeled by anti-lamin antibodies. Northern blots reveal stage-specific fluctuations in a single 4-kb lamin message during early development and, together with immunoblotting data, suggest that the increase in mesenchymal cell nuclear envelope immunoreactivity is due to a quantitative increase in a single type of lamin. These observations demonstrate that, similar to vertebrates, cell differentiation in invertebrates can be accompanied by a change in lamin expression patterns.

Amino Acid Sequence↗
PubMed1979

High frequency of mutation to tubercidin resistance in CHO cells.

The acquisition of high-level resistance to tubercidin (an adenosine analog) in CHO cells occurs in a single step at high frequency (10(-3) to 10(-4)) without mutagenesis. Analysis of a large number of independent mutants by a fluctuation test (Luria and Delbruk, 1943) indicates that they arise independently of the selection medium and all fall into the same complementation group. All mutants tested lack detectable adenosine kinase activity. An analysis of hybrids between mutant and wild-type cells indicates that resistance to tubercidin is a recessive marker which segregates as would be expected if it were a haploid locus in the parental CHO cell. Resistance to tubercidin is not linked to the X chromosome in CHO cells and appears to occur at much lower frequency in primary Chinese hamster cells and other cultured cell lines.

Animals↗
PubMed1987

Internal perfusion of guinea-pig hepatocytes with buffered Ca2+ or inositol 1,4,5-trisphosphate mimics noradrenaline activation of K+ and Cl- conductances.

External application of noradrenaline to voltage-clamped guinea-pig isolated hepatocytes evoked membrane conductance increases to K+ and Cl-. This effect was reproduced by internal perfusion of the cells with 2 microM buffered Ca2+ and with 20 microM inositol 1,4,5-trisphosphate (IP3). The kinetic properties of the K+ conductance and its selective block by the toxin apamin were the same in each case. Cyclical fluctuations of conductance observed with noradrenaline were reproduced by internal IP3 but not by Ca2+ perfusion, indicating that oscillations of intracellular free Ca2+ may arise from properties of the Ca2+ sequestration mechanism at constant IP3 concentration.

Animals↗
PubMed1981

The thymidine-kinase locus of Friend erythroleukaemic cells. 1. Mutation rates and properties of mutants.

Spontaneous mutation at the thymidine-kinase locus in clone 707 of the Friend cell line has been examined. The rate of mutation in BrdU resistance was found to be 2.6 x 10(-6) cell-1 generation-1. The rate of reversion to HAT resistance was found to vary from 1.1 x 10(-7) to 2.85 x 10(-6) cell-1 generation-1 in 4 BrdU-resistant clones. Of 14 mutant clones assayed for thymidine-kinase activity only one had greater than 13% the activity of wild-type cells. Fluctuation analysis showed that mutations occurred spontaneously and were not induced by the selective agent. The mutation rate at the thymidine-kinase locus is several orders of magnitude greater than those reported for several other cells lines. There does not appear to be a general genetic instability in this cell line as the mutation rate at the HGPRT locus is similar to those found in other established cell lines. It is suggested that the high forward mutation rate at the thymidine-kinase locus may be due to only one functional thymidine-kinase allele being present in cells of this clone.

Animals↗
PubMed1982

Effect of haloperidol and chlorpromazine on reversal learning of normal and striatectomized rats in a Y-maze.

Haloperidol (0.05-0.1 mg/kg) and chlorpromazine (0.5-1.0 mg/kg) improved reversal learning avoidance responses in a Y-maze, decreased intersessional fluctuations of errors and decreased the number of spontaneous exits from a correctly selected chamber. After bilateral lesions of the striatum this effect disappeared. Brain lesions also attenuated the ability of neuroleptics to suppress amphetamine-induced stereotypy and and accompanying defects in avoidance responses. The improvement of avoidance behavior by neuroleptics may be related to the reduction of spatial preference caused by functional asymmetry between the bilateral nigro-striatal systems.

Amphetamine↗
PubMed2004

Diurnal autonomic variations and emotional reactivity.

Diurnal temporal variations of emotional reactivity were investigated in relationship with fluctuations of psychophysiological state, evaluated by tonic autonomic activity. Neutral and unpleasant pictures, selected to constitute seven matched sets, were evaluated by 12 participants during seven sessions in the course of daytime. Skin conductance level (SCL) was recorded at the beginning of each session, whereas skin conductance responses (SCRs), affective evaluation and emotional experience were measured during or after each session. Data show significant temporal variations for SCL, SCRs and emotional experience which follow similar patterns during the daytime. Discussion highlights the role of temporal patterns of autonomic activity as an interesting basis to better understand the emotional regulation and affective disorders.

Adult↗
PubMed2005

Noncomplementing diploidy resulting from spontaneous zygogenesis in Escherichia coli.

With the aim of understanding sexual reproduction and phenotypic expression, a novel type of mating recently discovered in Escherichia coli was investigated. Termed spontaneous zygogenesis (or Z-mating), it differs from F-mediated conjugation. Its products proved phenotypically unstable, losing part of the phenotype for which they were selected. Inactivation of a parental chromosome in the zygote is strongly suggested by fluctuation tests, respreading experiments, analysis of reisolates, and segregation of non-viable cells detected by epifluorescence staining. Some phenotypically haploid subclones were interpreted as stable noncomplementing diploids carrying an inactivated co-replicating chromosome. Pedigree analysis indicated that the genetic composition of such cells consisted of parental genomes or one parental plus a recombinant genome. Inactivation of a chromosome carrying a prophage resulted in the disappearance of both the ability to produce phage particles and the immunity to superinfection. Phage production signalled transient reactivation of such a chromosome and constituted a sensitive test for stable noncomplementing diploidy. Chromosome inactivation thus appears to be a spontaneous event in bacteria.

Chromosomes, Bacterial↗
PubMed2004

Collective and local molecular dynamics in the lyotropic mesophases of decylammonium chloride: 1H and 2H NMR study.

The collective and individual dynamics of decylammonium chloride (DACl) molecules in water environment were investigated as a function of surfactant concentration and temperature. In the presence of water the DACl forms a variety of self-assembled structures, ranging from isotropic micellar systems to lyotropic liquid crystalline phases of hexagonal, nematic, and lamellar types. In order to characterize the complex molecular dynamics that occur in the DACl-water system, we applied 1H and 2H NMR techniques that cover the whole frequency range between 1 kHz and 30 MHz. The slow molecular dynamics were studied by 1H NMR fast-field-cycling T1 measurements and pulse-frequency dependence of 2H NMR transverse relaxation time, performed by means of the Carr-Purcell-Meiboom-Gill sequence. We detected a well-expressed contribution of order director fluctuations, i.e., layer undulations, with characteristic omega(-1)(L) frequency dependence of T(-1)(1) in the lamellar phase. Its presence indicates a relatively weak impact of interactions between neighboring DACl layers. The frequency dependence of proton T(-1)(1) in the hexagonal phase exhibits a different type of frequency dispersion, T(-1)(1) approximately omega(-1.32)(L). The increase in the exponent is explained with the quasi-one-dimensional character of fluctuations in elongated cylinders. Further, the T1 and T2 relaxation times of deuterons selectively attached to the C2 and C7 segments of the hydrocarbon chains of DACl were measured at a Larmor frequency of 30.7 MHz, providing quantitative information about local molecular dynamics.

Journal Article↗
PubMed2005

Kin interactions and changing social structure during a population outbreak of feral house mice.

Populations of feral house mice (Mus domesticus L.) in Australia undergo multiannual fluctuations in density, and these outbreaks may be partly driven by some change in behavioural self-regulation. In other vertebrate populations with multiannual fluctuations, changes in kin structure have been proposed as a causal mechanism for changes in spacing behaviour, which consequently result in density fluctuations. We tested the predictions of two alternative conceptual models based on kin selection in a population of house mice during such an outbreak. Both published models (Charnov & Finerty 1980; Lambin & Krebs 1991) propose that the level of relatedness between interacting individuals affects their behavioural response and that this changes with population density, though the nature of this relationship differs between the two models. Neither of the models was consistent with all observed changes in relatedness between interacting female mice; however, our results suggested that changes in kin structure still have potential for explaining why mouse outbreaks begin. Therefore, we have developed a variant of one of these conceptual models suggesting that the maintenance of female kin groups through the preceding winter significantly improves recruitment during the subsequent breeding season, and is therefore necessary for mouse outbreaks. We provide six testable predictions to falsify this hypothesis.

Alleles↗
PubMed1991

Acetylcholine receptor-reactive T lymphocytes from healthy subjects and myasthenia gravis patients.

Peripheral blood lymphocytes from 23 of 114 (20%) myasthenia gravis (MG) patients showed positive T-cell proliferative responses to native acetylcholine receptor (AChR) purified from the electric fish Torpedo, compared with two of 25 (8%) healthy or other neurologic disease controls. Responsiveness appeared to fluctuate seasonally. Long-term T-cell lines and clones could be selected as readily from the two healthy responders as from the MG cases and showed similar culture behavior, CD4+ phenotype, and HLA class II restrictions. One clone from a control cross-reacted with recombinant human AChR alpha chain (r37-429A) and with the synthetic peptide 125-143(S-S) from its sequence. Both these human antigens stimulated primary proliferative responses at substantially higher frequencies (26 to 59%) than native xeno-AChR--in both patients and controls--demonstrating that truly autoreactive T cells are not inevitably deleted during normal T-cell development.

Animals↗
PubMed2000

Developing a new model for non-insulin dependent diabetes mellitus (NIDDM) by using the Philippine wild mouse, Mus musculus castaneus.

The Philippine wild-caught castaneus mouse (Mus musculus castaneus) and laboratory mouse (C57BL/6J: B6) were used to develop a new non-insulin dependent diabetes mellitus (NIDDM) model. Offspring from the cross between a wild male and B6 female were backcrossed to the sire. One male which exhibited highest fasting hyperglycemia (190 mg/dl) among eighty-seven backcross offspring was selected at 10 weeks of age, and crossed with a B6 female to comprise the fundamental stock (F0). Thereafter, full-sib mating was performed to develop a new inbred strain named CBD (Castaneus-B6 diabetic) mouse. Mice with relatively higher fasting hyperglycemia among F0 and F1 generations were selected for breeding. From the F2 generation, mice were defined as diabetic when blood glucose levels exceeded 200 mg/dl at 120 min in intraperitoneal glucose tolerance test (IPGTT) at 10 weeks of age, and have been selectively bred. The incidence of diabetic males from the F3-F6 generation fluctuated 45-75% at 10 weeks of age and 59-72% at 20 weeks of age. Diabetic males had about two-fold higher fasting glucose and insulin levels than B6 males. Glucose-stimulated insulin secretion was impaired in diabetic CBD mice compared to B6 males at 20 weeks. Moreover, diabetic mice had slight obesity compared to B6 mice. These facts indicated that diabetic features of CBD mice resemble NIDDM in humans. The CBD strain, characterized by high incidence and early onset of diabetes with mild obesity would be of value as a new NIDDM model. The method, utilizing wild castaneus mouse of different origin from laboratory mice, maybe useful in the development of other animal models.

Animals↗
PubMed2005

Survival of the biocontrol agents Brevibacillus brevis ZJY-1 and Bacillus subtilis ZJY-116 on the spikes of barley in the field.

Fusarium head blight (FHB) caused by Fusarium graminearum is a devastating disease that results in extensive yield losses to wheat and barley. A green fluorescent protein (GFP) expressing plasmid pRP22-GFP was constructed for monitoring the colonization of two biocontrol agents, Brevibacillus brevis ZJY-1 and Bacillus subtilis ZJY-116, on the spikes of barley and their effect on suppression of FHB. Survival and colonization of the Brevibacillus brevis ZJY-1 and Bacillus subtilis ZJY-116 strains on spikes of barley were observed by tracking the bacterial transformants with GFP expression. Our field study revealed that plasmid pRP22-GFP was stably maintained in the bacterial strains without selective pressure. The retrieved GFP-tagged strains showed that the bacterial population fluctuation accorded with that of the rain events. Furthermore, both biocontrol strains gave significant protection against FHB on spikes of barley in fields. The greater suppression of barley FHB disease was resulted from the treatment of barley spikes with biocontrol agents before inoculation with F. graminearum.

Bacillus↗
PubMed1984

A genetic analysis of sow productivity traits.

Genetic and phenotypic parameters for sow productivity traits were derived from analyses of records for 999 purebred Duroc and Yorkshire litters at the Beltsville Agricultural Research Center. Included were 682 spring-farrowed litters and 317 fall-farrowed litters. Primary traits examined were number of pigs born alive in the litter (NA), litter size at 21 d of age (N21), litter weight at 21 d (W21) and an index (I21) combining the three traits. Also analyzed were total number of pigs farrowed alive or stillborn, litter weight of pigs born alive and litter size and litter weight at 42 d of age (weaning). Selection was based mainly on the sow productivity index among litters in the spring season and mainly on performance traits among fall-farrowed pigs. Select and control lines were maintained in both breeds in both seasons. Yorkshires started at higher levels of productivity than Durocs in spring 1975, showed more fluctuation and ended in spring 1982 at about their starting levels. Durocs started at lower productivity levels and recorded generally significant increases by 1982, with comparable selection differentials for the two breeds. Heritabilities, estimated from daughter-biparental (mid-dam, paternal granddam) regressions using records expressed as deviations from contemporary breed-line means, varied widely among the breed-line groups. Suggested composite heritability estimates were 5, 10 and 20% for NA, N21 and W21, respectively. Genetic correlations, computed from daughter-biparental covariances, were high and positive (.7 or above) among all traits. Based on estimated genetic gains, it was proposed that W21, alone or in combination with N21 and(or) NA in an index, be used as the primary selection criterion to bring about genetic improvement in sow productivity traits.

Animals↗
PubMed1990

Potentiation by the hypoxic cytotoxin SR 4233 of cell killing produced by fractionated irradiation of mouse tumors.

The new bioreductive drug 3-amino-1,2,4-benzotriazine 1,4-dioxide (SR 4233) shows a high selective cytotoxicity for hypoxic cells, both in vitro and in tumors in vivo. In the present experiments, we have tested the hypothesis that this selective killing of hypoxic cells might be exploited by taking advantage of the fluctuating hypoxia in tumors by use of a multidose regimen of SR 4233 with multiple small doses of X-rays. We have tested four different transplantable mouse tumors using a standard fractionated protocol of 8 x 2.5 Gy in 4 days, using a well tolerated dose of SR 4233 given with each radiation dose. All of the tumors showed a substantial enhancement of cell killing by SR 4233 over that produced by radiation alone with dose-modifying factors of 1.5 to 3.0 for the different tumors. In all four tumors, the enhancement of cell killing was greater than that produced by a large dose of the hypoxic cell sensitizer SR 2508 given before each irradiation, thereby demonstrating the superiority of the approach of using a hypoxic cytotoxic agent rather than a radiosensitizer in fractionated radiation protocols. The data suggest that SR 4233 has considerable promise as an adjunct to standard radiotherapy.

Animals↗
PubMed1981

Genetic activity of actinomycin D in Saccharomyces cerevisiae but not in Escherichia coli.

The potential of actinomycin D for induction of forward mutation (ADE-), reversion (TRP+), gene conversion, and mitotic recombination, was examined using haploid and diploid strains of yeast Saccharomyces cerevisiae. No increase in forward or reverse mutations or gene conversion was detected, but actinomycin D induced up to 13-fold increases in mitotic recombinants and a 2-fold increase in numbers of aberrant colonies, in a non-selective assay for genetic activity. Actinomycin D was non-mutagenic in a fluctuation test using Escherichia coli strain WP2 UvrA-. This furnishes an example of a mutagen which is negative in bacteria but has genetic activity in yeast, emphasizing the need for using a battery of microbial tests for determining the genetic activity of any given chemical.

Dactinomycin↗
PubMed1995

Influence of the estrus cycle on the discrimination of apparent neuroactive steroid site subtypes on the gamma-aminobutyric acidA receptor complex in the rat.

Estrus cycle-related changes in gamma-aminobutyric acid (GABA)A receptor complex (GRC) sensitivity to modulation by reduced progesterone metabolites is suggestive of a possible mechanism for maintaining brain homeostasis in the presence of fluctuating levels of these neuroactive metabolites. In addition, certain endogenously occurring pregnanediols are selective for apparent neuroactive steroid site subtypes discriminated by the progesterone metabolite 3 alpha-hydroxy-5 beta-pregnan-20-one (3 alpha,5 beta-P) on the GRC. Thus, it was of interest to evaluate the influence of gender and the estrus cycle on the ability of 3 alpha,5 beta-P and its 20-reduced analog 5 beta-pregnan-3 alpha,20 beta-diol to differentiate neuroactive steroid site subtypes. Neuroactive steroid modulation of [35S]t-butylbicyclophosphorothionate ([35S]TBPS) binding to the GRC in rats during estrus, diestrus and after ovariectomy (OVX) was measured in washed cortical P2 homogenates in the presence or absence of exogenous GABA. During diestrus, the inability of 5 beta-pregnan-3 alpha,20 beta-diol to allosterically modulate [35S]TBPS binding in the absence of GABA coincides with the inability of 3 alpha,5 beta-P to modulate [35S]TBPS binding with high potency. In contrast, the addition of GABA to the assay produced high potency inhibition of [35S]TBPS binding by each steroid. Remarkably, although findings in diestrus and OVX homogenates were no different from those observed in males, the proportions and IC50 values of the two sites discriminated by 3 alpha,5 beta-P in [35S]TBPS binding assays during the estrus phase were significantly different from male, OVX and diestrus rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Allosteric Regulation↗
PubMed1980

Ion conductance and ion selectivity of potassium channels in snail neurones.

Delayed potassium channels were studied in internally perfused neurone somata from land snails. Relaxation and fluctuation analysis of this class of ion channels revealed Hodgkin-Huxley type K channels with an average single channel conductance (gamma K) of 2.40 +/- 0.15 pS. The conductance of open channels is independent of voltage and virtually all K channels seem to be open at maximum K conductance (gk) of the membrane. Voltage dependent time constants of activation of gK, calculated from K current relaxation and from cut-off frequencies of power spectra, are very similar indicating dominant first-order kinetics. Ion selectivity of K channels was studied by ion substitution in the external medium and exhibited the following sequence: Tl+ greater than K+ greater than Rb+ greater Cs+ greater than NH4+ greater Li+ greater than Na+. The sequence of the alkali cations does not conform to any of the sequences predicted by Eisenman's theory. However, the data are well accommodated by a new theory assuming a single rate-limiting barrier that governs ion movement through the channel.

Animals↗