bluuebunny/crossref_metadata_2025 huggingface dataset:
Fuel characteristics and fire behaviour in mature Mediterranean gorse shrublands
Authors: De Luis Martín , Baeza Manuel J. , Raventós José , González-Hidalgo José C.
Published: April 2004

Since the early 1990s, Mediterranean gorse shrublands have expanded significantly in the Mediterranean regions of Spain mainly as a result of the increase in the frequency and extension of forest fires. Mediterranean gorse (Ulex parviflorus), which has been described as a degradation stage of forest communities after fire, has also been described as a fire-prone community. Thus, its presence increases the risk that new fires might occur. In spite of this evidence, there is little information on both the composition and structural characteristics of these communities or the relationship that might exist between these vegetation characteristics and fire behaviour. In this paper we present the results of a characterization of the vegetative structure (plant density, specific composition, biomass fractions, and horizontal and vertical fuel distribution) in Mediterranean gorse. We also analyse fire behaviour using indicators obtained at different scales. Our results show mature Mediterranean gorse shrublands to be communities with high biomass values (3000–4000 g m−2) and high horizontal and vertical vegetation continuity, in which the proportion of fine dead fuel fractions with low moisture content is around 50% of the total phytomass present. Ulex parviflorus is the dominant species and its degree of dominance is a key element in the behaviour of fire. Both the fire-line intensity values and the fire severity values observed can be considered high with respect to those observed in other Mediterranean communities, thus confirming Mediterranean gorse as a high-risk community.
Corrigendum to: Assessing woody vegetation cover change in north-west Australian savanna using aerial photography
Authors: Fairfax R. J. , Fensham R. J.
Published: April 2004

Models to calibrate tree and shrub cover assessed from aerial photography with field measurements were developed for a range of vegetation types in north-western Australia. The models verify previous studies indicating that woody cover can be successfully determined from aerial photography. The calibration models were applied to estimates of woody vegetation cover determined for 279 randomly located sample areas in the Ord–Victoria Rivers region using aerial photography from 1948 to 1950 and 1988 to 1997. Overstorey cover increased from a regional average of 11.5% to 13.5% and understorey cover increased from 1.3% to 2.0%. Downs, Limestone Hills and Alluvia land-types showed the most substantial increases in overstorey cover while overstorey cover in the Limestone plains land-type decreased. Relatively open structured vegetation is most susceptible to thickening. Rainfall records reveal an extreme multi-year rainfall deficit in the study area in the 1930s and relatively wet times in the 1970s and 1980s. Interpretation of a limited set of aerial photographs taken between 1964 and 1972 suggests that most of the increases in cover have occurred since this time. The study highlights the possibility that the average trend of vegetation thickening represents recovery during the relatively wet times after the 1970s. There was no relationship between structural change and a grazing intensity surrogate (distance of sample points to stock watering-points). However, the causes of structural change are undoubtedly multi-factored and the relative contributions of climate, fire and grazing vary for different landscapes and tree species.
Evolutionary conservation of a phosphate transporter in the arbuscular mycorrhizal symbiosis
Authors: Karandashov Vladimir , Nagy Réka , Wegmüller Sarah , Amrhein Nikolaus , Bucher Marcel
Published: April 2004

Arbuscular mycorrhizae are ancient symbioses that are thought to have originated >400 million years ago in the roots of plants, pioneering the colonization of terrestrial habitats. In these associations, a key process is the transfer of phosphorus as inorganic phosphate to the host plant across the fungus–plant interface. Mycorrhiza-specific phosphate transporter genes and their regulation are conserved in phylogenetically distant plant species, and they are activated selectively by fungal species from the phylum
Glomeromycota
. The potato phosphate transporter gene
StPT3
is expressed in a temporally defined manner in root cells harboring various mycorrhizal structures, including thick-coiled hyphae. The results highlight the role of different symbiotic structures in phosphorus transfer, and they indicate that cell–cell contact between the symbiotic partners is required to induce phosphate transport.
Structures of nitric oxide synthase isoforms complexed with the inhibitor AR-R17477 suggest a rational basis for specificity and inhibitor design
Authors: Fedorov Roman , Vasan Ryan , Ghosh Dipak K. , Schlichting Ilme
Published: April 2004

The high level of amino acid conservation and structural similarity of the substrate-binding sites of the oxygenase domains of the nitric oxide synthase (NOS) isoforms (eNOSoxy, iNOSoxy, nNOSoxy) make the interpretation of the structural basis of inhibitor isoform specificity a challenge, and provide few clues for the design of new selective compounds. Crystal structures of iNOSoxy and nNOSoxy complexed with the neuronal NOS-specific inhibitor AR-R17447 suggest that specificity is provided by the interaction of the chlorophenyl group with an isoform-unique substrate access channel residue (L337 in rat neuronal NOS, N115 in mouse inducible NOS). This is confirmed by biochemical analysis of site-directed mutants. Inhibitors combining guanidinium-like structural motifs with long chains specifically targeting this residue are good candidates for rational isoform-specific drug design. Based on this finding, modifications of AR-R17447 to improve the specificity for the human isoforms are suggested.
Ca
v
β-subunit displacement is a key step to induce the reluctant state of P/Q calcium channels by direct G protein regulation
Authors: Sandoz Guillaume , Lopez-Gonzalez Ignacio , Grunwald Didier , Bichet Delphine , Altafaj Xavier , Weiss Norbert , Ronjat Michel , Dupuis Alain , De Waard Michel
Published: April 2004

P/Q Ca
2+
channel activity is inhibited by G protein-coupled receptor activation. Channel inhibition requires a direct Gβγ binding onto the pore-forming subunit, Ca
v
2.1. It is characterized by biophysical changes, including current amplitude reduction, activation kinetic slowing, and an I-V curve shift, which leads to a reluctant mode. Here, we have characterized the contribution of the auxiliary β
3
-subunit to channel regulation by G proteins. The shift in I-V to a P/Q reluctant mode is exclusively observed in the presence of β
3
. Along with the observation that Gβγ has no effect on the I-V curve of Ca
v
2.1 alone, we propose that the reluctant mode promoted by Gβγ corresponds to a state in which the β
3
-subunit has been displaced from its channel-binding site. We validate this hypothesis with a β
3
-I-II
2.1
loop chimera construct. Gβγ binding onto the I-II
2.1
loop portion of the chimera releases the β
3
-binding domain and makes it available for binding onto the I-II loop of Ca
v
1.2, a G protein-insensitive channel. This finding is extended to the full-length Ca
v
2.1 channel by using fluorescence resonance energy transfer. Gβγ injection into
Xenopus
oocytes displaces a Cy3-labeled β
3
-subunit from a GFP-tagged Ca
v
2.1 channel. We conclude that β-subunit dissociation from the channel complex constitutes a key step in P/Q calcium channel regulation by G proteins that underlies the reluctant state and is an important process for modulating neurotransmission through G protein-coupled receptors.
11β-Hydroxysteroid dehydrogenase inhibition improves cognitive function in healthy elderly men and type 2 diabetics
Authors: Sandeep Thekkepat C. , Yau Joyce L. W. , MacLullich Alasdair M. J. , Noble June , Deary Ian J. , Walker Brian R. , Seckl Jonathan R.
Published: April 2004

In aging humans and rodents, inter-individual differences in cognitive function have been ascribed to variations in long-term glucocorticoid exposure. 11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) regenerates the active glucocorticoid cortisol from circulating inert cortisone, thus amplifying intracellular glucocorticoid levels in some tissues. We show that 11β-HSD1, but not 11β-HSD2, mRNA is expressed in the human hippocampus, frontal cortex, and cerebellum. In two randomized, double-blind, placebo-controlled crossover studies, administration of the 11β-HSD inhibitor carbenoxolone (100 mg three times per day) improved verbal fluency (
P
< 0.01) after 4 weeks in 10 healthy elderly men (aged 55-75 y) and improved verbal memory (
P
< 0.01) after 6 weeks in 12 patients with type 2 diabetes (52-70 y). Although carbenoxolone has been reported to enhance hepatic insulin sensitivity in short-term studies, there were no changes in glycemic control or serum lipid profile, nor was plasma cortisol altered. 11β-HSD1 inhibition may be a new approach to prevent/ameliorate cognitive decline.
Optics at critical intensity: Applications to nanomorphing
Authors: Joglekar Ajit P. , Liu Hsiao-hua , Meyhöfer Edgar , Mourou Gerard , Hunt Alan J.
Published: April 2004

Laser-induced optical breakdown by femtosecond pulses is extraordinarily precise when the energy is near threshold. Despite numerous applications, the basis for this deterministic nature has not been determined. We present experiments that shed light on the basic mechanisms of light–matter interactions in this regime, which we term “optics at critical intensity.” We find that the remarkably sharp threshold for laser-induced material damage enables the structure or properties of materials to be modified with nanometer precision. Through detailed study of the minimum ablation size and the effects of polarization, we propose a fundamental framework for describing light–matter interactions in this regime. In surprising contrast to accepted damage theory, multiphoton ionization does not play a significant role. Our results also reject the use of the Keldysh parameter in predicting the role of multiphoton effects. We find that the dominant mechanism is Zener ionization followed by a combination of Zener and Zener-seeded avalanche ionization. We predict that the minimum feature size ultimately depends on the valence electron density, which is sufficiently high and uniform, to confer deterministic behavior on the damage threshold even at the nanoscale. This behavior enables nanomachining with high precision, which we demonstrate by machining highly reproducible nanometer-sized holes and grooves in dielectrics.
Expanding the scope of asymmetric electrophilic atom-transfer reactions: Titanium- and ruthenium-catalyzed hydroxylation of β-ketoesters
Authors: Toullec Patrick Y. , Bonaccorsi Cristina , Mezzetti Antonio , Togni Antonio
Published: April 2004

The enantioselective formation of a quaternary stereogenic center coinciding with a hydroxylation process is a very rare reaction from a homogeneous catalysis point of view. Indeed, to our knowledge, no asymmetric transition-metal-catalyzed direct hydroxylation has been reported before. We describe here our initial study concerning the enantioselective α-hydroxylation of various β-ketoesters catalyzed by Lewis-acidic complexes. Specifically, it was found that the Ti complex [TiCl2((R,R)-1-Np-TADDOLato)(MeCN)2] affords the hydroxylated products in high yield and enantioselectivities up to 94% enantiomeric excess when using 2-(phenylsulphonyl)-3-(4-nitrophenyl)oxaziridine as the oxidizing agent. Chiral enantiopure compounds of the latter type have been used previously in stoichiometric asymmetric hydroxylation reactions. We also show that, in a complementary approach with H2O2as the oxidant, the Ru(II) complex [RuCl(OE2)((S,S)-PNNP)]PF6catalyzes the same type of transformation in a case of substrates showing a very substantial extent of enolization under reaction conditions; being, however, unreactive toward only weakly enolized β-ketoesters.
Copper-catalyzed asymmetric conjugate addition of Grignard reagents to cyclic enones
Authors: Feringa Ben L. , Badorrey Ramón , Peña Diego , Harutyunyan Syuzanna R. , Minnaard Adriaan J.
Published: April 2004

It is no longer necessary to use dialkylzinc reagents to obtain enantioselectivities >95% in the copper-catalyzed asymmetric conjugate addition of organometallic compounds to cyclic enones. We now report how this can be accomplished by using inexpensive and readily available Grignard reagents. Screening of bidentate ligands provided outstanding results with copper complexes of commercially available chiral ferrocenyl-based diphosphines, in particular TaniaPhos and JosiPhos derivatives. These catalysts tolerate a range of Grignard reagents and different cyclic enones as substrates, leading to high regioselectivities and unprecedented enantioselectivities. Moreover, the reactions are successful with moderate catalyst loading (5 mol %) under mild conditions and in the absence of additives.
Genetic evidence for nonredundant functional cooperativity between NPC1 and NPC2 in lipid transport
Authors: Sleat David E. , Wiseman Jennifer A. , El-Banna Mukarram , Price Sandy M. , Verot Lucie , Shen Michael M. , Tint G. Stephen , Vanier Marie T. , Walkley Steven U. , Lobel Peter
Published: April 2004

Niemann–Pick C (NPC) disease is a fatal neurodegenerative disorder characterized by a lysosomal accumulation of cholesterol and other lipids within the cells of patients. Clinically identical forms of NPC disease are caused by defects in either of two different proteins: NPC1, a lysosomal–endosomal transmembrane protein and NPC2, a soluble lysosomal protein with cholesterol binding properties. Although it is clear that NPC1 and NPC2 are required for the egress of lipids from the lysosome, the precise roles of these proteins in this process is unknown. To gain insight into the normal function of NPC2 and to investigate its interactions, if any, with NPC1, we have generated a murine NPC2 hypomorph that expresses 0–4% residual protein in different tissues and have examined its phenotype in the presence and absence of NPC1. The phenotypes of NPC1 and NPC2 single mutants and an NPC1;NPC2 double mutant are similar or identical in terms of disease onset and progression, pathology, neuronal storage, and biochemistry of lipid accumulation. These findings provide genetic evidence that the NPC1 and NPC2 proteins function in concert to facilitate the intracellular transport of lipids from the lysosome to other cellular sites.
A DNA polymerase β mutant from colon cancer cells induces mutations
Authors: Lang Tieming , Maitra Mausumi , Starcevic Daniela , Li Shu-Xia , Sweasy Joann B.
Published: April 2004

Previous investigations have shown that ≈35% of the 90 tumors analyzed to date contain mutations within the DNA polymeraseβ (pol β) gene. The existence of pol β mutations in a substantial fraction of human tumors studied suggests a link between DNA pol β and cancer. A DNA pol β variant, in which Lys-289 has been altered to Met, was identified previously in a colorectal carcinoma. The K289M protein was expressed in mouse L cells containing the λ
cII
mutational target. The λ DNA was packaged and used to infect bacterial cells to obtain the spontaneous mutation frequency. We found that expression of K289M in the mouse cells resulted in a 2.5-fold increase in the mutation frequency. What was most interesting was that expression of K289M in these cells resulted in a 16-fold increase in the frequency of C to G or G to C base substitutions at a specific site within the
cII
target. By using this
cII
target sequence, kinetic analysis of the purified K289M protein revealed that it was able to misincorporate dCTP opposite template C and dGTP opposite template G with significantly higher efficiency than the wild-type pol β protein. We provide evidence that misincorporation of nucleotides by K289M results from altered positioning of the DNA within the active site of the enzyme. Our data are consistent with the interpretation that misincorporation of nucleotides resulting from altered DNA positioning by the K289M protein has the potential to result in tumorigenesis or neoplastic progression.
Drought stress and carbon uptake in an Amazon forest measured with spaceborne imaging spectroscopy
Authors: Asner Gregory P. , Nepstad Daniel , Cardinot Gina , Ray David
Published: April 2004

Amazônia contains vast stores of carbon in high-diversity ecosystems, yet this region undergoes major changes in precipitation affecting land use, carbon dynamics, and climate. The extent and structural complexity of Amazon forests impedes ground studies of ecosystem functions such as net primary production (NPP), water cycling, and carbon sequestration. Traditional modeling and remote-sensing approaches are not well suited to tropical forest studies, because (i) biophysical mechanisms determining drought effects on canopy water and carbon dynamics are poorly known, and (ii) remote-sensing metrics of canopy greenness may be insensitive to small changes in leaf area accompanying drought. New spaceborne imaging spectroscopy may detect drought stress in tropical forests, helping to monitor forest physiology and constrain carbon models. We combined a forest drought experiment in Amazônia with spaceborne imaging spectrometer measurements of this area. With field data on rainfall, soil water, and leaf and canopy responses, we tested whether spaceborne hyperspectral observations quantify differences in canopy water and NPP resulting from drought stress. We found that hyperspectral metrics of canopy water content and light-use efficiency are highly sensitive to drought. Using these observations, forest NPP was estimated with greater sensitivity to drought conditions than with traditional combinations of modeling, remote-sensing, and field measurements. Spaceborne imaging spectroscopy will increase the accuracy of ecological studies in humid tropical forests.
Encoding for computation: Recognizing brief dynamical patterns by exploiting effects of weak rhythms on action-potential timing
Authors: Hopfield J. J.
Published: April 2004

Many stimuli have meaning only as patterns over time. Most auditory and many visual stimuli are of this nature and can be described as multidimensional, time-dependent vectors. A simple neuron can encode a single component of the vector in a firing rate. The addition of a small subthreshold oscillatory current perturbs the action-potential timing, encoding the signal also in a timing relationship, with little effect on the coexisting firing rate representation. When the subthreshold signal is common to a group of neurons, the timing-based information is significant to neurons receiving inputs from the group. This information encoding allows simple implementation of computations not readily done with rate coding. These ideas are examined by using speech to provide a realistic input signal to a biologically inspired model network of spiking neurons. The output neurons of the two-layer system are shown to specifically encode short linguistic elements of speech.
Suppressor screen in
Mpl
-/-
mice:
c-Myb
mutation causes supraphysiological production of platelets in the absence of thrombopoietin signaling
Authors: Carpinelli Marina R. , Hilton Douglas J. , Metcalf Donald , Antonchuk Jennifer L. , Hyland Craig D. , Mifsud Sandra L. , Di Rago Ladina , Hilton Adrienne A. , Willson Tracy A. , Roberts Andrew W. , Ramsay Robert G. , Nicola Nicos A. , Alexander Warren S.
Published: April 2004

Genetic screens in lower organisms, particularly those that identify modifiers of preexisting genetic defects, have been used successfully to order components of complex signaling pathways. To date, similar suppressor screens have not been used in vertebrates. To define the molecular pathways regulating platelet production, we have executed a large-scale modifier screen with genetically thrombocytopenic
Mpl

-
/
-

mice by using
N
-ethyl-
N
-nitrosourea mutagenesis. Here we show that mutations in the
c-Myb
gene cause a myeloproliferative syndrome and supraphysiological expansion of megakaryocyte and platelet production in the absence of thrombopoietin signaling. This screen demonstrates the utility of large-scale
N
-ethyl-
N
-nitrosourea mutagenesis suppressor screens in mice for the simultaneous discovery and
in vivo
validation of targets for therapeutic discovery in diseases for which mouse models are available.
Of mice and men: genetic determinants of iron status
Authors: McGregor Johanne , McKie Andrew T. , Simpson Robert J.
Published: April 2004

Fe homeostasis is maintained by regulation of Fe absorption to balance largely unregulated body Fe losses. The majority of human subjects maintain relatively constant Fe stores; however, Fe deficiency and Fe overload are common conditions. Fe overload is frequently associated with mutations in genes of Fe metabolism. The present paper summarises present knowledge of these mutations as well as indicating other genes that animal studies have implicated as candidates for influencing body Fe stores.
The quest for cardiovascular health in the genomic era: nutrigenetics and plasma lipoproteins
Authors: Ordovas Jose M.
Published: April 2004

Nutrigenetics and nutrigenomics are promising multidisciplinary fields that focus on studying the interactions between nutritional factors, genetic factors and health outcomes. Their goal is to achieve more efficient individual dietary intervention strategies aimed at preventing disease, improving quality of life and achieving healthy aging. Our studies, and those of many other investigators, using population-based and intervention studies have found evidence for interactions between dietary factors, genetic variants and biochemical markers of CVD. Now, the characterization of individuals who may respond better to one type of dietary recommendation than another can be begun. Thus, a low-fat low-cholesterol strategy may be particularly efficacious in lowering the plasma cholesterol levels of those subjects carrying the apoE4 allele at the APOE gene. HDL-cholesterol (HDL-C) levels are also modulated by dietary, behavioural and genetic factors. It has been reported that the effect of PUFA intake on HDL-C concentrations is modulated by an APOA1 genetic polymorphism. Thus, subjects carrying the A allele at the –75 G/A polymorphism show an increase in HDL-C with increased intakes of PUFA, whereas those homozygotes for the more common G allele have the expected lowering of HDL-C levels with increased intake of PUFA. Variability at the hepatic lipase gene is also associated with interactions between intake of fat and HDL-C concentrations that could shed some light on the different abilities of certain ethnic groups to adapt to new nutritional environments. This knowledge should lead to successful dietary recommendations partly based on genetic factors that may help to reduce cardiovascular risk more efficiently than the current universal recommendations.
Intestinal and placental zinc transport pathways
Authors: Ford Dianne
Published: April 2004

Mammalian members of the cation diffusion facilitator (CDF) and zrt-, irt-like protein (ZIP) families of Zn transporters, initially identified in Saccharomyces cerevisiae and Arabidopsis thalania spp., have been cloned during the last 8 years and have been classified as families SLC30 and SLC39 respectively. The cloning of human Zn transporters ZnT-like transporter 1 (hZTL1)/ZnT5 (SLC30A5) and hZIP4 (SLC39A4) were major advances in the understanding of the molecular mechanisms of dietary Zn absorption. Both transporters are localised at the enterocyte apical membrane and are, therefore, potentially of fundamental importance in dietary Zn uptake. hZTL1 mediates Zn uptake when expressed in Xenopus laevis oocytes and hZIP4 is mutated in most cases of the inherited Zn deficiency disease acrodermatitis enteropathica. Localisation of hZTL1/ZnT5 at the apical membrane of the placental syncytiotrophoblast indicates a fundamental role in the transfer of Slc30 Zn to the foetus. Observations in rodent models indicate that in the intestine increased Zn availability increases expression of Zn transporters. Human intestinal Caco-2 cells show a similar response to increasing the Zn2+ concentration of the nutrient medium in relation to the expression of mRNA corresponding to several Zn transporters and that of ZnT1 (SLC30A1) and hZTL1/ZnT5 proteins. In the human placental cell line JAR, however, expression at the mRNA level of a number of Zn transporters is not modified by Zn availability, whilst ZnT1 and hZTL1/ZnT5 proteins are reduced under Zn-supplemented conditions. These differences between Caco-2 and JAR cells in Zn transporter gene responses to Zn supply may reflect the different extracellular Zn concentrations encountered by the corresponding cell types in vitro.
Genetic modification of the effect of alcohol consumption on CHD
Authors: Hines Lisa M.
Published: April 2004

The deleterious health effects of high alcohol consumption are numerous and well recognized; however, the effect of moderate alcohol consumption on overall health continues to be a debated issue. Among the more prevalent diseases in Westernized countries, epidemiological research suggests that alcohol in moderation substantially reduces the risk of CHD, while it modestly increases the risk for certain cancers, such as breast and colon cancer. Despite the overwhelming data supporting the beneficial effect of moderate alcohol consumption on the cardiovascular system, some researchers are not convinced. Sceptics argue that the reduction in risk is attributed to a favourable lifestyle factor associated with moderate alcohol consumption, or that it may be attributed to constituents of alcoholic beverages other than ethanol, such as the antioxidants in the grapes. In order to promote overall health for the general public, it is necessary to elucidate these issues. One approach is to study population differences in alcohol metabolic efficiency, which is likely to contribute to an individual's susceptibility to alcohol-associated diseases. Among the population there is substantial variability in the efficiency to metabolize alcohol. Genetic variation among the alcohol-metabolizing genes is known to produce isoenzymes with distinct kinetic properties. Studying genetic differences that potentially influence disease susceptibility among populations may provide insight into the mechanism(s) for the relationship between risk factor and disease, such as alcohol and CHD.
Alcohol and cancer: genetic and nutritional aspects
Authors: Pöschl Gudrun , Stickel Felix , Wang Xiang D. , Seitz Helmut K.
Published: April 2004

Chronic alcohol consumption is a major risk factor for cancer of upper aero-digestive tract (oro-pharynx, hypopharynx, larynx and oesophagus), the liver, the colo-rectum and the breast. Evidence has accumulated that acetaldehyde is predominantly responsible for alcohol-associated carcinogenesis. Acetaldehyde is carcinogenic and mutagenic, binds to DNA and protein, destroys the folate molecule and results in secondary cellular hyper-regeneration. Acetaldehyde is produced by mucosal and cellular alcohol dehydrogenase, cytochrome P450 2E1 and through bacterial oxidation. Its generation and/or its metabolism is modulated as a result of polymorphisms or mutations of the genes responsible for these enzymes. Acetaldehyde can also be produced by oral bacteria. Smoking, which changes the oral bacterial flora, also increases salivary acetaldehyde. Cigarette smoke and some alcoholic beverages, such as Calvados, contain acetaldehyde. In addition, chronic alcohol consumption induces cytochrome P450 2E1 enxyme activity in mucosal cells, resulting in an increased generation of reactive oxygen species and in an increased activation of various dietary and environmental carcinogens. Deficiencies of riboflavin, Zn, folate and possibly retinoic acid may further enhance alcohol-associated carcinogenesis. Finally, methyl deficiency as a result of multiple alcohol-induced changes leads to DNA hypomethylation. A depletion of lipotropes, including methionine, choline, betaine and S-adenosylmethionine, as well as folate, results in the hypomethylation of oncogenes and may lead to DNA strand breaks, all of which are associated with increased carcinogenesis.
Ontogeny and nutritional manipulation of the hepatic prolactin–growth hormone–insulin-like growth factor axis in the ovine fetus and in neonate and juvenile sheep
Authors: Hyatt Melanie A. , Walker David A. , Stephenson Terence , Symonds Michael E.
Published: April 2004

The somatotrophic axis is the main endocrine system regulating postnatal growth; however, prenatal growth is independent of growth hormone (GH). Fetal development relies on the coordinated actions of a range of hormones, including insulin-like growth factors (IGF), and prolactin (PRL), in the control of differentiation, growth and maturation. In the sheep the abundance peaks for liver IGF-II and PRL receptors occur during late gestation while that for IGF-I receptor occurs at birth. All receptors, with the exception of GH receptor subsequently decrease by age 6 months. It has been proposed that maternal undernutrition during gestation regulates the maturation of the fetal hypothalmic–pituitary–adrenal axis and endocrine sensitivity. Critically, the timing of the nutritional insult may affect the magnitude of reprogramming. Maternal malnutrition during early to mid-gestation (3·2–3·8 MJ/d (60% total metabolisable energy requirements)v. 8·7–9·9 MJ/d (150% total metabolisable energy requirements) between 28 and 80 d of gestation) had no effect on body or liver weight. Nutrient-restricted (NR) fetuses sampled at 80 d (mid-gestation) showed up-regulation of hepatic PRL receptor, but following refeeding the normal gestational rise in PRL and GH receptors did not occur. Hepatic IGF-II receptor was down regulated in NR fetuses at both mid- and late gestation. Conversely, 6-month-old offspring showed no difference in the abundance of either GH receptor or PRL receptor, while IGF-II mRNA was increased. Offspring of ewes malnourished during late gestation (9·1 MJ/d (60% total metabolisable energy requirements)v. 12·7 MJ/d (100% total metabolisable energy requirements) from 110 d of gestation to term) showed reduced abundance of hepatic GH and PRL receptor mRNA. In conclusion, maternal undernutrition during the various stages of gestation reprogrammed the PRL–GH–IGF axis. Nutritional regulation of cytokine receptors may contribute to altered liver function following the onset of GH-dependent growth, which may be important in regulating endocrine adaptations during subsequent periods of nutritional deprivation.
Alcohol, nutrition and health maintenance: selected aspects
Authors: Suter Paolo M.
Published: April 2004

In view of the developments in health care relating to the increased prevalence and incidence of chronic diseases and the continuing increase in health-care expenditure, more attention should be paid to health maintenance and disease prevention. Any strategy that can influence health maintenance is of interest, especially lifestyle factors such as nutrition, exercise or stress control. Alcohol has an important place in the daily life of many healthy as well as sick individuals. Alcohol has three major characteristics; it is a nutrient (energy source), a psycho-active drug and a toxin. Each consumer has the choice of which of the characteristics of alcohol he/she wants to utilise. Thus, alcohol represents one of the most important self-implemented disease modifiers in our modern society. The major determinants of the health effects of alcohol are the absolute amount consumed, the consumption frequency, associated lifestyle factors (e.g. smoking, nutrient intake, substrate composition, physical activity pattern) and last, but not least, the genetic background. There are few known disease conditions that have not already been associated positively or negatively with alcohol consumption. The list of diseases includes atherosclerosis, dementia, diabetes, obesity and conditions relating to Zn metabolism. Obesity represents the most important disease modifier in the world and the prevalence rates are increasing rapidly. Evidence suggests that alcohol represents a risk factor for overweight and obesity as a result of specific effects on energy metabolism and substrate metabolism. The potential role of alcohol as an important modulator for the postprandial lipidaemia and its role in the pathogenesis of modern diseases will be discussed.
Fatty acids and the immune system: from basic science to clinical applications
Authors: Yaqoob Parveen
Published: April 2004

Over the last 25 years, the effects of fatty acids on the immune system have been characterized usingin vitro, animal and human studies. Advances in fatty acid biochemistry and molecular techniques have recently suggested new mechanisms by which fatty acids could potentially modify immune responses, including modification of the organization of cellular lipids and interaction with nuclear receptors. Possibilities for the clinical applications ofn-3 PUFA are now developing. The present review focuses on the hypothesis that the anti-inflammatory properties ofn-3 PUFA in the arterial wall may contribute to the protective effects ofn-3 PUFA in CVD, as suggested by epidemiological and secondary prevention studies. Studies are just beginning to show that dietaryn-3 PUFA can be incorporated into plaque lipid in human subjects, where they may influence the morphology and stability of the atherosclerotic lesion.
AstR–AstS, a new two-component signal transduction system, mediates swarming, adaptation to stationary phase and phenotypic variation in Photorhabdus luminescens
Authors: Derzelle Sylviane , Ngo Saravuth , Turlin Évelyne , Duchaud Éric , Namane Abdelkader , Kunst Frank , Danchin Antoine , Bertin Philippe , Charles Jean-François
Published: April 2004

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.
S-layer glycan-specific loci on the chromosome of Geobacillus stearothermophilus NRS 2004/3a and dTDP-l-rhamnose biosynthesis potential of G. stearothermophilus strains
Authors: Novotny René , Schäffer Christina , Strauss Joseph , Messner Paul
Published: April 2004

The ∼16·5 kb surface layer (S-layer) glycan biosynthesis (slg) gene cluster of the Gram-positive thermophileGeobacillus stearothermophilusNRS 2004/3a has been sequenced. The cluster is located immediately downstream of the S-layer structural genesgsEand consists of 13 ORFs that have been identified by database sequence comparisons. The cluster encodes dTDP-l-rhamnose biosynthesis (rmloperon), required for building up the polyrhamnan S-layer glycan, as well as for assembly and export of the elongated glycan chain, and its transfer to the S-layer protein. This is the first report of a gene cluster likely to be involved in the glycosylation of an S-layer protein. There is evidence that this cluster is transcribed as a polycistronic unit, whereassgsEis transcribed monocistronically. To get insights into the regulatory mechanisms underlying glycosylation of the S-layer protein, the influence of growth temperature on the S-layer was investigated in seven closely relatedG. stearothermophilusstrains, of which only strain NRS 2004/3a possessed a glycosylated S-layer. Chromosomal DNA preparations of these strains were screened for the presence of thermloperon, becausel-rhamnose is a frequent constituent of S-layer glycans. Fromrml-positive strains, flanking regions of the operon were sequenced. Comparison with theslggene cluster ofG. stearothermophilusNRS 2004/3a revealed sequence homologies between adjacent genes. The temperature inducibility of S-layer protein glycosylation was investigated in those strains by raising the growth temperature from 55 °C to 67 °C; no change of either the protein banding pattern or the glycan staining behaviour was observed on SDS-PAGE gels, although thesgsEtranscript was several-fold more abundant at 67 °C. Cell-free extracts of the strains were capable of converting dTDP-d-glucose to dtdp-l-rhamnose. Taken together, the results indicate that thermllocus is highly conserved amongG. stearothermophilusstrains, and that in the investigatedrml-containing strains, dTDP-l-rhamnose is actively synthesizedin vitro. However, in contrast to previous reports forG. stearothermophiluswild-type strains, an increase in growth temperature did not switch an S-layer protein phenotype to an S-layer glycoprotein phenotype, via thede novogeneration of a new S-layer gene sequence.
Expression of Pseudomonas aeruginosa exoS is controlled by quorum sensing and RpoS
Authors: Hogardt Michael , Roeder Maximilian , Schreff Anna Maria , Eberl Leo , Heesemann Jürgen
Published: April 2004

InPseudomonas aeruginosa, virulence determinants and biofilm formation are coordinated via a hierarchical quorum sensing cascade, which involves the transcriptional regulators LasR and RhlR and their cognate homoserine lactone activators C12-HSL [N-(3-oxododecanoyl)-l-homoserine lactone] and c4-hsl (n-butanoyl-l-homoserine lactone), which are produced by LasI and RhlI, respectively. The exoenzyme S regulon ofP. aeruginosa, comprises genes for a type III secretion system and for four anti-host effector proteins (ExoS, T, U and Y), which are translocated into host cells. It is a reasonable assumption that this ExoS regulon should be downregulated in the biofilm growth state and thus should also be under the regulatory control of the Las/Rhl system. Therefore, anexoS′-gfpreporter construct was used, and the influence of the Las and Rhl quorum sensing systems and the effect of the stationary-phase sigma factor RpoS on regulation of theexoSgene was examined. Evidence is provided for downregulation ofexoSduring biofilm formation ofP. aeruginosaPAO1. TherhlImutant PDO100 andrhlRmutant PDO111, but not thelasImutant PDO-JP1, showed approximately twofold upregulation of theexoS′-gfpreporter in comparison to PAO1. Upregulation ofexoS′-gfpin the PDO100 mutant could be repressed to normal level by adding C4-HSL autoinducer, indicating a negative regulatory effect of RhlR/C4-HSL onexoSexpression. As RhlR/C4-HSL is also involved in regulation of RpoS, theP. aeruginosa rpoSmutant SS24 was examined and theexoS′-gfpreporter was found to be fivefold upregulated in comparison to PAO1. For the first time evidence is reported for a regulatory cascade linking RhlR/RhlI and RpoS with the expression of the anti-host effector ExoS, part of the exoenzyme S regulon. Moreover, these data suggest that the exoenzyme S regulon may be downregulated inP. aeruginosabiofilms.
Low-proline environments impair growth, proline transport and in vivo survival of Staphylococcus aureus strain-specific putP mutants
Authors: Schwan William R. , Wetzel Keith J. , Gomez Timothy S. , Stiles Melissa A. , Beitlich Brian D. , Grunwald Sandra
Published: April 2004

Staphylococcus aureus is a common cause of disease in humans, particularly in hospitalized patients. This species needs to import several amino acids to survive, including proline. Previously, it was shown that an insertion mutation in the high-affinity proline uptake gene putP in strain RN6390 affected proline uptake by the bacteria as well as reducing their ability to survive in vivo. To further delineate the effect of the putP mutation on growth of S. aureus strain RN6390, a proline uptake assay that spanned less than 1 min was done to measure transport. An eightfold difference in proline levels was observed between the wild-type strain and the high-affinity proline transport mutant strain after 15 s, indicating that the defect was only in proline transport and not a combination of proline transport, metabolism and accumulation that would have been assessed with longer assays. A putP mutant of S. aureus strain RN4220 was then grown in minimal medium with different concentrations of proline. When compared to the wild-type strain, the putP mutant strain was significantly growth impaired when the level of proline was decreased to 1·74 μM. An assessment of proline concentrations in mouse livers and spleens showed proline concentrations of 7·5 μmol per spleen and 88·4 μmol per liver. To verify that the effects on proline transport and bacterial survival were indeed caused solely by a mutation in putP, the putP mutation was complemented by cloning a full-length putP gene on a plasmid that replicates in S. aureus. Complementation of the putP mutant strains restored proline transport, in vitro growth in low-proline medium, and in vivo survival within mice. These results show that the mutation in putP led to attenuated growth in low-proline media and by corollary low-proline murine organ tissues due to less efficient transport of proline into the bacteria.
Identification and cloning of the gene encoding BmpC: an outer-membrane lipoprotein associated with Brachyspira pilosicoli membrane vesicles
Authors: Trott Darren J. , Alt David P. , Zuerner Richard L. , Bulach Dieter M. , Wannemuehler Michael J. , Stasko Judi , Townsend Kirsty M. , Stanton Thaddeus B.
Published: April 2004

The intestinal spirochaeteBrachyspira pilosicolicauses colitis in a wide variety of host species. Little is known about the structure or protein constituents of theB. pilosicoliouter membrane (OM). To identify surface-exposed proteins in this species, membrane vesicles were isolated fromB. pilosicolistrain 95-1000 cells by osmotic lysis in dH2O followed by isopycnic centrifugation in sucrose density gradients. The membrane vesicles were separated into a high-density fraction (HDMV;ρ=1·18 g cm−3) and a low-density fraction (LDMV;ρ=1·12 g cm−3). Both fractions were free of flagella and soluble protein contamination. LDMV contained predominantly OM markers (lipo-oligosaccharide and a 29 kDaB. pilosicoliOM protein) and was used as a source of antigens to produce mAbs. FiveB. pilosicoli-specific mAbs reacting with proteins with molecular masses of 23, 24, 35, 61 and 79 kDa were characterized. The 23 kDa protein was only partially soluble in Triton X-114, whereas the 24 and 35 kDa proteins were enriched in the detergent phase, implying that they were integral membrane proteins or lipoproteins. All three proteins were localized to theB. pilosicoliOM by immunogold labelling using specific mAbs. The gene encoding the abundant, surface-exposed 23 kDa protein was identified by screening aB. pilosicoli95-1000 genome library with the mAb and was expressed inEscherichia coli. Sequence analysis showed that it encoded a unique lipoprotein, designated BmpC. Recombinant BmpC partitioned predominantly in the OM fraction ofE. colistrain SOLR. The mAb to BmpC was used to screen a collection of 13 genetically heterogeneous strains ofB. pilosicoliisolated from five different host species. Interestingly, only strain 95-1000 was reactive with the mAb, indicating that either the surface-exposed epitope on BmpC is variable between strains or that the protein is restricted in its distribution withinB. pilosicoli.
Bile-salt-mediated induction of antimicrobial and bile resistance in Salmonella typhimurium
Authors: Prouty A. M. , Brodsky I. E. , Falkow S. , Gunn J. S.
Published: April 2004

By DNA microarray, the Salmonella typhimurium marRAB operon was identified as being bile-activated. Transcriptional assays confirm that marRAB is activated in the presence of bile and that this response is concentration-dependent. The bile salt deoxycholate is alone able to activate transcription, while there was no response in the presence of other bile salts tested or a non-ionic detergent. Deoxycholate is able to interact with MarR and interfere with its ability to bind to the mar operator. In addition, incubation of salmonellae in the presence of sublethal concentrations of bile is able to enhance resistance to chloramphenicol and bile, by means of both mar-dependent and mar-independent pathways. To further characterize putative marRAB-regulated genes that may be important for the resistance phenotype, acrAB, which encodes an efflux pump, was analysed. In S. typhimurium, acrAB is required for bile resistance, but while transcription of acrAB is activated by bile, this activation is independent of marRAB, as well as Rob, RpoS or PhoP–PhoQ. These data suggest that bile interacts with salmonellae to increase resistance to bile and other antimicrobials and that this can occur by marRAB- and acrAB-dependent pathways that function independently with respect to bile activation.
Genetic characterization of pcpS, encoding the multifunctional phosphopantetheinyl transferase of Pseudomonas aeruginosa
Authors: Barekzi Nazir , Joshi Swati , Irwin Scott , Ontl Todd , Schweizer Herbert P.
Published: April 2004

Fatty acid synthases (primary metabolism), non-ribosomal peptide synthases and polyketide synthases (secondary metabolism) contain phosphopantetheinyl (Ppant)-dependent carrier proteins that must be made functionally active by transfer of the 4′-Ppant moiety from coenzyme A. These reactions are usually catalysed by dedicated Ppant transferases. Although rich in Ppant-dependent carrier proteins, it was previously shown that Pseudomonas aeruginosa possesses only one Ppant transferase, encoded by pcpS, which functions in both primary and secondary metabolism. Consistent with this notion are our findings that pcpS can genetically complement mutations in the Escherichia coli acpS and entD genes, encoding the apo-acyl carrier protein (ACP) synthase of fatty acid synthesis and a Ppant transferase of enterobactin synthesis, respectively. It also complements a Bacillus subtilis sfp mutation affecting a gene encoding a Ppant transferase essential for surfactin synthesis. A pcpS insertion mutant could only be constructed in a strain carrying the E. coli acpS gene on a chromosomally integrated element in trans, implying that the in vitro essentiality of pcpS is due to its requirement for activation of apo-ACP of fatty acid synthesis. The conditional pcpS mutant is non-fluorescent, does not produce pyoverdine and pyochelin, and does not grow in the presence of iron chelators. The data presented here for the first time confirm that PcpS plays an essential role in both fatty acid and siderophore metabolism.