PubMed Health⌕ Search

Biomedical subjects

A Burt

Publications and source records attributed to A Burt.

At least 19 recordsLinked to original sources
PubMed2006

Echinacea extracts modulate the pattern of chemokine and cytokine secretion in rhinovirus-infected and uninfected epithelial cells.

Extracts of Echinacea purpurea are among the most widely used herbal medicines throughout Europe and North America for the prevention or treatment of common cold, coughs, bronchitis and other upper respiratory infections. Popular preparations include expressed juice from the aerial parts of the plant (which contain polysaccharides) and alcoholic tinctures from roots (containing caffeic acid derivatives and alkylamides). Since immune modulation has been reported for similar extracts, cytokine antibody arrays were used to investigate the changes in the pro-inflammatory cytokines and chemokines released from a cultured line of human bronchial epithelial cells exposed to Rhinovirus 14 and two different chemically characterized Echinacea extracts. Virus infection stimulated the release of at least 31 cytokine-related molecules, including several important chemokines known to attract inflammatory cells. Most of these effects were reversed by simultaneous exposure to either of the two Echinacea extracts, although the patterns of response were different for the two extracts. These results could explain the antiinflammatory properties of Echinacea extracts. Furthermore, a number of these cytokines were stimulated by the same Echinacea preparations in uninfected cells. These observations therefore provide support for the alleged beneficial uses of Echinacea extracts.

Cell Line, Transformed↗
PubMed2005

Study of apoptosis and heat shock protein (HSP) expression in hepatocytes following radiofrequency ablation (RFA).

BACKGROUND: Radiofrequency ablation (RFA) of the liver produces necrosis of the hepatocytes. Histological examination shows a sharp demarcation between ablated and normal liver tissue. This experiment was carried out to study the cellular injury produced by RFA in area surrounding the ablated tissue and effect of reperfusion on this zone. MATERIAL AND METHODS: Five pigs underwent RFA of liver parenchyma. Four pigs were sacrificed 30 min after RFA and one pig was sacrificed 5 days later. Ablated lesions including surrounding liver parenchyma was examined for apoptosis and HSP 70 expression. RESULTS: There was a zone of transition surrounding the necrotic ablated area that showed apoptosis as well as increased HSP 70 expression. This was more prevalent in the pig that was sacrificed 5 days later. CONCLUSION: RFA produces sub lethal injury in the zone of transition causing apoptosis and increase in HSP 70 expression. Increased HSP expression enhances immunogenicity of these cells that can have therapeutic implications for the treatment of liver.

Animals↗
PubMed2004

Learning difficulties in children born to male UK nuclear industry employees; analysis from the nuclear industry family study.

There has been much debate about paternal pre-conceptual exposure to low level ionising radiation and possible increased risk of ill health among the children subsequently conceived. The prevalence of reported learning difficulties was examined in over 16000 children born to UK nuclear industry workers, using fathers' information on exposure from the workers' individual employment and dosimetry records. There was no evidence that paternal exposure to low level ionising radiation at work influences the prevalence of learning difficulties in otherwise healthy children conceived after exposure.

Adolescent↗
PubMed2004

The distribution of B chromosomes across species.

In this review we look at the broad picture of how B chromosomes are distributed across a wide range of species. We review recent studies of the factors associated with the presence of Bs across species, and provide new analyses with updated data and additional variables. The major obstacle facing comparative studies of B chromosome distribution is variation among species in the intensity of cytogenetic study. Because Bs are, by definition, not present in all individuals of a species, they may often be overlooked in species that are rarely studied. We give examples of corrections for differences in study effort, and show that after a variety of such corrections, strong correlations remain. Several major biological factors are associated with the presence of B chromosomes. Among flowering plants, Bs are more likely to occur in outcrossing than in inbred species, and their presence is also positively correlated with genome size and negatively with chromosome number. They are no more frequent in polyploids than in diploids, nor in species with multiple ploidies. Among mammals, Bs are more likely to occur in species with karyotypes consisting of mostly acrocentric chromosomes. We find no evidence for an association with chromosome number or genome size in mammals, although the sample for genome size is small. The associations with breeding system and acrocentric chromosomes were both predicted in advance, but those with genome size and chromosome number were discovered empirically and we can offer only tentative explanations for the very strong associations we have uncovered. Our understanding of why B chromosomes are present in some species and absent in others is still in its infancy, and we suggest several potential avenues for future research.

Animals↗
PubMed2003

Issues in environmental water allocation--an Australian perspective.

Environmental water allocation is a critical issue in Australia and internationally. It has been prominent in Australia for a little over ten years during which time major policy and scientific advances have been made, but little implementation. This paper examines current understanding of environmental water allocation across a broad range of disciplines including the biophysical sciences, social sciences, economics, law, and policy. Development of practical methods for assessing environmental water requirements and experience with implementation in Australia are discussed. The paper concludes with thoughts on future needs.

Australia↗
PubMed2001

Outcrossed sex allows a selfish gene to invade yeast populations.

Homing endonuclease genes (HEGs) in eukaryotes are optional genes that have no obvious effect on host phenotype except for causing chromosomes not containing a copy of the gene to be cut, thus causing them to be inherited at a greater than Mendelian rate via gene conversion. These genes are therefore expected to increase in frequency in outcrossed populations, but not in obligately selfed populations. In order to test this idea, we compared the dynamics of the VDE HEG in six replicate outcrossed and inbred populations of yeast (Saccharomyces cerevisiae). VDE increased in frequency from 0.21 to 0.55 in four outcrossed generations, but showed no change in frequency in the inbred populations. The absence of change in the inbred populations indicates that any effect of VDE on mitotic replication rates is less than 1%. The data from the outcrossed populations best fit a model in which 82% of individuals are derived from outcrossing and VDE is inherited by 74% of the meiotic products from heterozygotes (as compared with 50% for Mendelian genes). These results empirically demonstrate how a host mating system plays a key role in determining the population dynamics of a selfish gene.

Chromosome Mapping↗
PubMed2001

Amplified single-nucleotide polymorphisms and a (GA)(n) microsatellite marker reveal genetic differentiation between populations of Histoplasma capsulatum from the Americas.

Histoplasma capsulatum has a worldwide distribution but is particularly concentrated in the midwestern United States and throughout Central and South America. Genetic differences between isolates resident in separate parts of the world have been reported, but the relationship between the isolates and the level of migration between different endemic foci has not been clear. In this study we used multilocus genotypes based on amplified polymorphic loci and one microsatellite to quantify the level of genetic differentiation occurring between North and South American populations of H. capsulatum. Significant genetic differentiation occurred between isolates obtained from Indiana and Alabama, and a marked division was seen between the Indiana population and the Class 1 isolates from St. Louis. Strong genetic differentiation occurred between the two North American populations and the Colombian population. This study supports the separation of North and South American H. capsulatum into different species, which has been proposed under the phylogenetic species concept.

Genetic Markers↗
PubMed2001

Gene genealogies, cryptic species, and molecular evolution in the human pathogen Coccidioides immitis and relatives (Ascomycota, Onygenales).

Previous genealogical analyses of population structure in Coccidioides immitis revealed the presence of two cryptic and sexual species in this pathogenic fungus but did not clarify their origin and relationships with respect to other taxa. By combining the C. immitis data with those of two of its closest relatives, the free-living saprophytes Auxarthron zuffianum and Uncinocarpus reesii, we show that the C. immitis species complex is monophyletic, indicating a single origin of pathogenicity. Cryptic species also were found in both A. zuffianum and U. reesii, indicating that they can be found in both pathogenic and free-living fungi. Our study, together with a few others, indicates that the current list of known fungal species might be augmented by a factor of at least two. However, at least in the C. immitis, A. zuffianum, and U. reesii complexes, cryptic species represent subdivisions at the tips of deep monophyletic clades and thus well within the existing framework of generic classification. An analysis of silent and expressed divergence and polymorphism values between and within the taxa identified by genealogical concordance did not reveal faster evolution in C. immitis as a consequence of adaptation to the pathogenic habit, nor did it show positive Darwinian evolution in a region of a dioxygenase gene (tcrP gene coding for 4-HPPD) known to cause antigenic responses in humans. Instead, the data suggested relative stasis, indicative of purifying selection against mostly deleterious mutations. Two introns in the same gene fragment were considerably more divergent than exons and were unalignable between species complexes but had very low polymorphism within taxa.

4-Hydroxyphenylpyruvate Dioxygenase↗
PubMed2000

Perspective: sex, recombination, and the efficacy of selection--was Weismann right?

The idea that sex functions to provide variation for natural selection to act upon was first advocated by August Weismann and it has dominated much discussion on the evolution of sex and recombination since then. The goal of this paper is to further extend this hypothesis and to assess its place in a larger body of theory on the evolution of sex and recombination. A simple generic model is developed to show how fitness variation and covariation interact with selection for recombination and illustrate some important implications of the hypothesis: (1) the advantage of sex and recombination can accrue both to reproductively isolated populations and to modifiers segregating within populations, but the former will be much larger than the latter; (2) forces of degradation that are correlated across loci within an individual can reduce or reverse selection for increased recombination; and (3) crossing-over (which can occur at different places in different meioses) will create more variability than having multiple chromosomes and so will have more influence on the efficacy of selection. Several long-term selection experiments support Weismann's hypothesis, including those showing a greater response to selection in populations with higher rates of recombination and higher rates of recombination evolving as a correlated response to selection for some other character. Weismann's hypothesis is also consistent with the sporadic distribution of obligate asexuality, which indicates that clones have a higher rate of extinction than sexuals. Weismann's hypothesis is then discussed in light of other patterns in the distribution of sexuality versus asexuality. To account for variation in the frequency of obligate asexuality in different taxa, a simple model is developed in which this frequency is a function of three parameters: the rate of clonal origin, the initial fitness of clones when they arise, and the rate at which that fitness declines over time. Variation in all three parameters is likely to be important in explaining the distribution of obligate asexuality. Facultative asexuality also exists, and for this to be stable it seems there must be ecological differences between the sexual and asexual propagules as well as genetic differences. Finally, the timing of sex in cyclical parthenogens is most likely set to minimize the opportunity costs of sex. None of these patterns contradict Weismann's hypothesis, but they do show that many additional principles unrelated to the function of sex are required to fully explain its distribution. Weismann's hypothesis is also consistent with what we know about the mechanics and molecular genetics of recombination, in particular the tendency for chromatids to recombine with a homolog rather than a sister chromatid at meiosis, which is opposite to what they do during mitosis. However, molecular genetic studies have shown that cis-acting sites at which recombination is initiated are lost by gene conversion as a result, a factor that can be expected to affect many fine details in the evolution of recombination. In summary, although Weismann's hypothesis must be considered the leading candidate for the function of sex and recombination, nevertheless, many additional principles are needed to fully account for their evolution.

Biological Evolution↗
PubMed1999

Recurrent invasion and extinction of a selfish gene.

Homing endonuclease genes show super-Mendelian inheritance, which allows them to spread in populations even when they are of no benefit to the host organism. To test the idea that regular horizontal transmission is necessary for the long-term persistence of these genes, we surveyed 20 species of yeasts for the omega-homing endonuclease gene and associated group I intron. The status of omega could be categorized into three states (functional, nonfunctional, or absent), and status was not clustered on the host phylogeny. Moreover, the phylogeny of omega differed significantly from that of the host, strong evidence of horizontal transmission. Further analyses indicate that horizontal transmission is more common than transposition, and that it occurs preferentially between closely related species. Parsimony analysis and coalescent theory suggest that there have been 15 horizontal transmission events in the ancestry of our yeast species, through simulations indicate that this value is probably an underestimate. Overall, the data support a cyclical model of invasion, degeneration, and loss, followed by reinvasion, and each of these transitions is estimated to occur about once every 2 million years. The data are thus consistent with the idea that frequent horizontal transmission is necessary for the long-term persistence of homing endonuclease genes, and further, that this requirement limits these genes to organisms with easily accessible germ lines. The data also show that mitochondrial DNA sequences are transferred intact between yeast species; if other genes do not show such high levels of horizontal transmission, it would be due to lack of selection, rather than lack of opportunity.

Base Sequence↗
PubMed1999

The evolutionary biology and population genetics underlying fungal strain typing.

Strain typing of medically important fungi and fungal population genetics have been stimulated by new methods of tapping DNA variation. The aim of this contribution is to show how awareness of fungal population genetics can increase the utility of strain typing to better serve the interests of medical mycology. Knowing two basic features of fungal population biology, the mode of reproduction and genetic differentiation or isolation, can give medical mycologists information about the intraspecific groups that are worth identifying and the number and type of markers that would be needed to do so. The same evolutionary information can be just as valuable for the selection of fungi for development and testing of pharmaceuticals or vaccines. The many methods of analyzing DNA variation are evaluated in light of the need for polymorphic loci that are well characterized, simple, independent, and stable. Traditional population genetic and new phylogenetic methods for analyzing mode of reproduction, genetic differentiation, and isolation are reviewed. Strain typing and population genetic reports are examined for six medically important species: Coccidioides immitis, Histoplasma capsulatum, Candida albicans, Cryptococcus neoformans, Aspergillus fumigatus, and A. flavus. Research opportunities in the areas of genomics, correlation of clinical variation with genetic variation, amount of recombination, and standardization of approach are suggested.

Biological Evolution↗
PubMed1998

Genetic conflicts in genomic imprinting.

The expression pattern of genes in mammals and plants can depend upon the parent from which the gene was inherited, evidence for a mechanism of parent-specific genomic imprinting. Kinship considerations are likely to be important in the natural selection of many such genes, because coefficients of relatedness will usually differ between maternally and paternally derived genes. Three classes of gene are likely to be involved in genomic imprinting: the imprinted genes themselves, trans-acting genes in the parents, which affect the application of the imprint, and trnas-acting genes in the offspring, which recognize and affect the expression of the imprint. We show that coefficients of relatedness will typically differ among these three classes, thus engendering conflicts of interest between Imprinter genes, imprinted genes, and imprint-recognition genes, with probable consequences for the evolution of the imprinting machinery.

Animals↗
PubMed1997

Concordance of gene genealogies reveals reproductive isolation in the pathogenic fungus Coccidioides immitis.

Simple cladogenetic theory suggests that gene genealogies can be used to detect mixis in a population and delineate reproductively isolated groups within sexual taxa. We have taken this approach in a study of Coccidioides immitis, an ascomycete fungus responsible for a recent epidemic of coccidioidomycosis (Valley fever) in California. To test whether this fungus represents a single sexual species throughout its entire geographic range, we have compared genealogies from fragments of five nuclear genes. The five genealogies show multiple incompatibilities indicative of sex, but also share a branch that partitions the isolates into two reproductively isolated taxa, one centered in California and the other outside California. We conclude that coccidioidomycosis can be caused by two distinct noninterbreeding taxa. This result should aid the future study of the disease and illustrates the utility of the genealogical approach in population genetics.

Amino Acid Sequence↗
PubMed1997

A set of electrophoretic molecular markers for strain typing and population genetic studies of Histoplasma capsulatum.

A set of eleven biallelic and three multiallelic molecular markers have been developed to analyze populations of Histoplasma capsulatum. All markers are amplified by polymerase chain reaction (PCR) and can be readily scored using minimal amounts of template DNA. The 11 biallelic loci have polymorphic restriction endonuclease sites or small insertions or deletions which may be assessed by agarose gel electrophoresis. These markers are inherited in an unambiguous manner and are ideal for assessing structure and gene flow within US populations of H. capsulatum, but are monomorphic in non-US populations. Both length and sequence variation are present in the multiallelic loci, which can be scored by direct sequencing, polyacrylamide gel electrophoresis, or single-strand conformation polymorphism (SSCP): As they are hypervariable, the multiallelic loci can be used to type isolates and to assess the level of genetic variation within populations. Preliminary results indicate that the three multiallelic markers presented are sufficient to distinguish isolates at the individual level and are polymorphic in both US and non-US populations. This collection of molecular markers will be a useful tool in population and epidemiology studies of H. capsulatum.

Alleles↗