bluuebunny/crossref_metadata_2025 huggingface dataset:
A dry episode during the Younger Dryas and centennial‐scale weak monsoon events during the early Holocene: A high‐resolution stalagmite record from southeast of the Loess Plateau, China
Authors: Cai Binggui , Edwards R. Lawrence , Cheng Hai , Tan Ming , Wang Xu , Liu Tungsheng
Published: January 2008

A high‐resolution stalagmite oxygen isotope record from Dongshiya Cave, located southeast of the Chinese Loess Plateau, reveals detailed climatic oscillations between 12.7 and 9.0 ka BP, on centennial and decadal timescales, with a temporal resolution of 1 to 20 years. The early Younger Dryas is characterized by a gradual increase in δ18O values, which is followed by a depositional hiatus for the remainder of the Younger Dryas, between 12.1 and 11.5 ka BP, implying a weak East Asian Monsoon or a dry climate during the Younger Dryas. Eight weak monsoon events between 11.5 and 9.0 ka BP punctuate the early Holocene East Asian Monsoon, and are likely tied to cold events in Greenland, including the Pre‐boreal Oscillation and the 9.2 ky Event. The spectral analysis of the Dongshiya δ18O time series yields peaks at frequencies that have been linked to solar frequencies, indicating that solar changes may be, at least partially, responsible for changes in the intensity of the East Asian Monsoon during the early Holocene.
Faraday rotation observations of CMEs
Authors: Jensen E. A. , Russell C. T.
Published: January 2008

Simultaneous observations obtained by the Solwind coronagraph and Faraday rotation of the Helios radio frequency carrier signal in 1979 showed that CMEs produce characteristic ‘W’ or sigmoid transients in Faraday rotation observations similar to those observed by Pioneer 6 and 9 in 1968 and 1970. We demonstrate that a relaxed flux‐rope model is capable of reproducing these observations. Through fitting the model to the observations, we can obtain information on the flux rope orientation, position, size, velocity, rate of change of rope radius and pitch angle. With electron density measurements, we can also obtain a measure of the magnetic field strength. These fits demonstrate that Faraday rotation observations can provide information on the magnetic field of a CME shortly after it erupts.
Buried impact basin distribution on Mars: Contributions from crustal thickness data
Authors: Edgar Lauren A. , Frey Herbert V.
Published: January 2008

Crustal thickness data (derived from Mars Global Surveyor (MGS) gravity field and topographic data) exposes a number of circular thin areas (CTAs) that may represent deeply buried impact basins, which are often not visible in topography alone. A data set which combines quasi‐circular depressions (QCDs) revealed by the Mars Orbiter Laser Altimeter (MOLA) on the MGS spacecraft with a population of non‐QCD CTAs is a better estimate of the true crater retention ages of the buried surfaces of Mars. This study finds that all regions have older crater retention ages than previously thought based on QCDs alone. The highlands and lowlands appear to have the same basement crater retention age, but Tharsis is younger.
Channelized bottom melting and stability of floating ice shelves
Authors: Rignot E. , Steffen K.
Published: January 2008

The floating ice shelf in front of Petermann Glacier, in northwest Greenland, experiences massive bottom melting that removes 80% of its ice before calving into the Arctic Ocean. Detailed surveys of the ice shelf reveal the presence of 1–2 km wide, 200–400 m deep, sub‐ice shelf channels, aligned with the flow direction and spaced by 5 km. We attribute their formation to the bottom melting of ice from warm ocean waters underneath. Drilling at the center of one of channel, only 8 m above sea level, confirms the presence of ice‐shelf melt water in the channel. These deep incisions in ice‐shelf thickness imply a vulnerability to mechanical break up and climate warming of ice shelves that has not been considered previously.
Evaporite accumulation during the Messinian Salinity Crisis: The Suez Rift case
Authors: Gargani Julien , Moretti Isabelle , Letouzey Jean
Published: January 2008

The Mediterranean Basin may have not always been connected to the Atlantic Ocean. During the Messinian Salinity Crisis (5.96–5.33 Myr), the Mediterranean Sea reduced progressively its connection with the global Ocean by a complex combination of tectonic and glacio‐eustatic processes. During this period, deep erosion occurred on the margin and on the continent. Furthermore, a large quantity of evaporites was deposited in the basins (>1500 m). The way by which the evaporites accumulated in the various sub‐basins has not been precisely determined. Here we demonstrate by quantitative analysis that a combination of several Mediterranean sea‐level drawdown events associated with limited Atlantic sea inflow and continuous river discharge can explain the quantity of evaporites in the Mediterranean Basins and the observation of an intermediate lowstand at ∼500 m. Using a paleogeographical reconstruction and a numerical model, we show that the evaporites of the Gulf of Suez (GoS) are a consequence of the threshold which disconnected the GoS/Red Sea from the Eastern Mediterranean at the end of the Miocene.
Variability of passive gas emissions, seismicity, and deformation during crater lake growth at White Island Volcano, New Zealand, 2002–2006
Authors: Werner C. , Hurst T. , Scott B. , Sherburn S. , Christenson B. W. , Britten K. , Cole‐Baker J. , Mullan B.
Published: January 2008

We report on 4 years of airborne measurements of CO2, SO2, and H2S emission rates during a quiescent period at White Island volcano, New Zealand, beginning in 2003. During this time a significant crater lake emerged, allowing scrubbing processes to be investigated. CO2 emissions varied from a baseline of 250 to >2000 t d−1 and demonstrated clear annual cycling that was consistent with numbers of earthquake detections and annual changes in sea level. The annual variability was found to be most likely related to increases in the strain on the volcano during sea level highs, temporarily causing fractures to reduce in size in the upper conduit. SO2 emissions varied from 0 to >400 t d−1 and were clearly affected by scrubbing processes within the first year of lake development. Scrubbing caused increases of SO42− and Cl− in lake waters, and the ratio of carbon to total sulphur suggested that elemental sulphur deposition was also significant in the lake during the first year. Careful measurements of the lake level and chemistry allowed estimates of the rate of H2O(g) and HCl(g) input into the lake and suggested that the molar abundances of major gas species (H2O, CO2, SO2, and HCl) during this quiescent phase were similar to fumarolic ratios observed between earlier eruptive periods. The volume of magma estimated from CO2 emissions (0.015–0.04 km3) was validated by Cl− increases in the lake, suggesting that the gas and magma are transported from deep to shallow depths as a closed system and likely become open in the upper conduit region. The absence of surface deformation further leads to a necessity of magma convection to supply and remove magma from the degassing depths. Two models of convection configurations are discussed.
Modeling impacts of geomagnetic field variations on middle atmospheric ozone responses to solar proton events on long timescales
Authors: Winkler Holger , Sinnhuber Miriam , Notholt Justus , Kallenrode May‐Britt , Steinhilber Friedhelm , Vogt Joachim , Zieger Bertalan , Glassmeier Karl‐Heinz , Stadelmann Anja
Published: January 2008

Strength and structure of the Earth's magnetic field control the deflection of energetic charged particles of solar and cosmic origin. Therefore variations of the geomagnetic field occurring on geological timescales affect the penetration of charged particles into the atmosphere. During solar proton events (SPEs) the flux of high‐energy protons from the Sun is markedly increased. In order to investigate the impact of SPEs on the middle atmospheric ozone on longer timescales, two‐dimensional atmospheric chemistry and transport simulations have been performed using simulated time series of SPEs covering 200 years. Monte Carlo calculations were used to obtain ionization rates, which were then applied to the atmosphere under the consideration of different shielding properties of the geomagnetic field. The present‐day magnetic field configuration and four other scenarios were analyzed. For the first time, field configurations representing possible realistic situations during reversals have been investigated with respect to SPE‐caused ozone losses. With decreasing magnetic field strength the impacts on the ozone are found to significantly increase especially in the Southern Hemisphere, and subsequently, the flux of harmful ultraviolet radiation increases at the Earth's surface. The ozone destructions are most pronounced in the polar regions, and for some field configurations they exceed the values of ozone hole situations after large SPEs. In contrast to ozone holes the depletions due to SPEs are not restricted to winter and spring times but persist into polar summer.
Assessment of the wintertime performance of developmental particulate matter forecasts with the Eta‐Community Multiscale Air Quality modeling system
Authors: Mathur Rohit , Yu Shaocai , Kang Daiwen , Schere Kenneth L.
Published: January 2008

It is desirable for local air quality agencies to accurately forecast tropospheric PM2.5 concentrations to alert the sensitive population of the onset, severity, and duration of unhealthy air and to encourage the public and industry to reduce emissions‐producing activities. Since elevated particulate matter concentrations are encountered throughout the year, the accurate forecast of the day‐to‐day variability in PM2.5 and constituent concentrations over annual cycles poses considerable challenges. In efforts to characterize forecast model performance during different seasons, PM2.5 forecast simulations with the Eta‐Community Multiscale Air Quality system are compared with measurements from a variety of regional surface networks, with special emphasis on performance during the winter period. The analysis suggests that while the model can capture the average spatial trends and dynamic range in PM2.5 and constituent concentrations measured at individual sites, significant variability occurs on a day‐to‐day basis both in the measurements and the model predictions, which are generally not well correlated when paired both in space and time. Systematic overpredictions in regional PM2.5 forecasts during the cool season are noted through comparisons with measurements from different networks. The overpredictions are typically more pronounced at urban locations, with larger errors at the higher concentration range. Variability in aerosol sulfate concentrations were captured well, as well as the relative amounts of sulfur (IV) and sulfur (VI). The mix of carbon sources as represented by the ratio of organic to elemental carbon is captured well in the southeastern United States, but the total carbonaceous aerosol mass is underestimated. On average, during the wintertime the largest overpredictions among individual PM2.5 constituents were noted for the “other” category which predominantly represents primary‐emitted trace elements in the current model configuration. The systematic errors in model predictions of both total PM2.5 and its constituents during the winter period are found to arise from a combination of uncertainties in the magnitude and spatial and temporal allocation of primary PM2.5 emissions, current uncertainties in the estimation of chemical production pathways for secondary constituents (e.g., NO3−), and the representation of the impacts of boundary layer mixing on simulated concentrations, especially during nighttime conditions.
MODIS Aerosol Optical Depth Retrievals with high spatial resolution over an Urban Area using the Critical Reflectance
Authors: de Almeida Castanho Andréa D. , Vanderlei Martins J. , Artaxo Paulo
Published: January 2008

The retrieval of aerosol optical depth (τa) over land by satellite remote sensing is still a challenge when a high spatial resolution is required. This study presents a tool that uses satellite measurements to dynamically identify the aerosol optical model that best represents the optical properties of the aerosol present in the atmosphere. We use aerosol critical reflectance to identify the single scattering albedo of the aerosol layer. Two case studies show that the Sao Paulo region can have different aerosol properties and demonstrates how the dynamic methodology works to identify those differences to obtain a better τa retrieval. The methodology assigned the high single scattering albedo aerosol model (ϖo(λ = 0.55) = 0.90) to the case where the aerosol source was dominated by biomass burning and the lower ϖo model (ϖo (λ = 0.55) = 0.85) to the case where the local urban aerosol had the dominant influence on the region, as expected. The dynamic methodology was applied using cloud‐free data from 2002 to 2005 in order to retrieve τa with Moderate Resolution Imaging Spectroradiometer (MODIS). These results were compared with collocated data measured by AERONET in Sao Paulo. The comparison shows better results when the dynamic methodology using two aerosol optical models is applied (slope 1.06 ± 0.08 offset 0.01 ± 0.02 r2 0.6) than when a single and fixed aerosol model is used (slope 1.48 ± 0.11 and offset −0.03 ± 0.03 r2 0.6). In conclusion the dynamical methodology is shown to work well with two aerosol models. Further studies are necessary to evaluate the methodology in other regions and under different conditions.
Equally likely inverse solutions to a groundwater flow problem including pattern information from remote sensing images
Authors: Hendricks Franssen H. J. , Brunner P. , Makobo P. , Kinzelbach W.
Published: January 2008

Groundwater flow modeling for large areas in arid and semiarid regions, like the Chobe region in Botswana, suffers from a severe lack of data. This study addresses the usefulness of remote sensing (RS) images to constrain the recharge rate estimates for a region. The estimates derived from METEOSAT and NOAA advanced very high resolution radar (AVHRR) images are correlated with recharge rate values estimated from chloride measurements and used jointly in the generation of multiple, equally likely recharge rate realizations with the colocated cosimulation algorithm. The colocated cosimulation algorithm is very suited to generate stochastic realizations of a parameter that includes information from a correlated covariable given on a regular, dense grid as in RS information. These equally likely recharge rate realizations, together with multiple equally likely transmissivity realizations, are conditioned by inversion to hydraulic head data and a digital elevation model. For the inverse conditioning an additional penalty term was added to the objective function, penalizing too large deviations of the recharge rate pattern from the RS image. As such, the recharge rate pattern observed with the RS images is still honored by the calibrated recharge rate realizations. It was observed that conditioning to the RS information reduces significantly the estimated ensemble variance of the recharge rates.
Foxp3+regulatory T cells promiscuously accept thymic signals critical for their development
Authors: Spence Philip J. , Green E. Allison
Published: January 2008

Foxp3+regulatory T cells develop in the thymus and are essential for maintaining peripheral tolerance to self tissues. We report the critical requirement for CD154 up-regulation specifically on, and during the thymic development of, Foxp3+regulatory T cells for the induction of their clonal expansion within the medulla. In the absence of this signal, there was a severe reduction in their thymic generation and output, leading to decreased peripheral numbers. Importantly, CD40 expression on either thymic dendritic or epithelial cells was sufficient to promote the development of normal numbers of Foxp3+regulatory T cells. This work suggests that CD154-transduced signals promote Foxp3+regulatory T cell development and highlights the plasticity of the thymic stroma for supporting their generation. Crucially, this study demonstrates that Foxp3+regulatory T cells can promiscuously accept a single critical signal necessary for their thymic development from different cellular sources, redefining our understanding of their generation.
Functional plasticity of paralogous diterpene synthases involved in conifer defense
Authors: Keeling Christopher I. , Weisshaar Sabrina , Lin Roy P. C. , Bohlmann Jörg
Published: January 2008

The diversity of terpenoid compounds produced by plants plays an important role in mediating various plant–herbivore, plant–pollinator, and plant–pathogen interactions. This diversity has resulted from gene duplication and neofunctionalization of the enzymes that synthesize and subsequently modify terpenes. Two diterpene synthases in Norway spruce (
Picea abies
), isopimaradiene synthase and levopimaradiene/abietadiene synthase, provide the hydrocarbon precursors for most of the diterpene resin acids found in the defensive oleoresin of conifers. Although these paralogous enzymes are 91% identical at the amino acid level, one is a single-product enzyme, whereas the other is a multiproduct enzyme that forms completely different products. We used a rational approach of homology modeling, protein sequence comparison, domain swapping, and a series of reciprocal site-directed mutagenesis to identify the specific residues that direct the different product outcomes. A one-amino acid mutation switched the levopimaradiene/abietadiene synthase into producing isopimaradiene and sandaracopimaradiene and none of its normal products. Four mutations were sufficient to reciprocally reverse the product profiles for both of these paralogous enzymes while maintaining catalytic efficiencies similar to the wild-type enzymes. This study illustrates how neofunctionalization can result from relatively minor changes in protein sequence, increasing the diversity of secondary metabolites important for conifer defense.
Role of Epigenetics in Mental Disorders
Authors: Stuffrein-Roberts Selma , Joyce Peter R. , Kennedy Martin A.
Published: January 2008

The purpose of this paper was to selectively review the literature on the role of epigenetics in mental illnesses. Aberrant epigenetic regulation has been clearly implicated in the aetiology of some human illnesses. In recent years a growing body of evidence has highlighted the possibility that epigenetics may also play a key role in the origins and expression of mental disorders. Epigenetic phenomena may help explain some of the complexity of mental illnesses and provide a basis for discovering novel pharmacological targets to treat these disorders.
Temporal Patterns of Recovery Across Eating Disorder Subtypes
Authors: Von Holle Ann , Poyastro Pinheiro Andréa , Thornton Laura M. , Klump Kelly L. , Berrettini Wade H. , Brandt Harry , Crawford Steven , Crow Scott , Fichter Manfred M. , Halmi Katherine A. , Johnson Craig , Kaplan Allan S. , Keel Pamela , La Via Maria , Mitchell James , Strober Michael , Blake Woodside D. , Kaye Walter H. , Bulik Cynthia M.
Published: January 2008

Objective: To compare patterns of recovery in individuals with index episodes of anorexia nervosa (AN) and bulimia nervosa (BN).

Method: Using Kaplan–Meier methods and Cox proportional hazards models, comparisons were conducted that were conditional on duration of eating disorder from onset and included a conservative recovery criterion of 3 asymptomatic years. Data collection was retrospective and from two of the international Price Foundation genetic studies on 901 individuals with eating disorders.

Results: Using Kaplan–Meier methods, 11% of those with index AN and 10% of those with index BN met recovery criteria at 10 years. At 15 years, 16% of those with index AN and 25% of those with index BN met recovery criteria. In a Cox proportional hazards model the index BN group had three times the rate of recovery at 10–14 years (p=0.01) than the index AN group.

Conclusions: Initially the probability of recovery was greater for those with index AN, but as the duration of the eating disorder lengthened those with BN had higher probabilities of recovery. Replication of these results with prospective data using similarly stringent recovery criteria and methods is required to confirm trends.
Neotyphodiumendophyte infection frequency in annual grass populations: relative importance of mutualism and transmission efficiency
Authors: Gundel Pedro E , Batista William B , Texeira Marcos , Martínez-Ghersa M. Alejandra , Omacini Marina , Ghersa Claudio M
Published: January 2008

Persistence and ubiquity of vertically transmittedNeotyphodiumendophytes in grass populations is puzzling because infected plants do not consistently exhibit increased fitness. Using an annual grass population model, we show that the problems for matching endophyte infection and mutualism are likely to arise from difficulties in detecting small mutualistic effects, variability in endophyte transmission efficiency and an apparent prevalence of non-equilibrium in the dynamics of infection. Although endophytes would ultimately persist only if the infection confers some fitness increase to the host plants, such an increase can be very small, as long as the transmission efficiency is sufficiently high. In addition, imperfect transmission limits effectively the equilibrium infection level if the infected plants exhibit small or large reproductive advantage. Under frequent natural conditions, the equilibrium infection level is very sensitive to small changes in transmission efficiency and host reproductive advantage, while convergence to such an equilibrium is slow. As a consequence, seed immigration and environmental fluctuation are likely to keep local infection levels away from equilibrium. Transient dynamics analysis suggests that, when driven by environmental fluctuation, infection frequency increases would often be larger than decreases. By contrast, when due to immigration, overrepresentation of infected individuals tends to vanish faster than equivalent overrepresentation of non-infected individuals.
The largest fossil rodent
Authors: Rinderknecht Andrés , Blanco R. Ernesto
Published: January 2008

The discovery of an exceptionally well-preserved skull permits the description of the new South American fossil species of the rodent,Josephoartigasia monesisp. nov. (family: Dinomyidae; Rodentia: Hystricognathi: Caviomorpha). This species with estimated body mass of nearly 1000 kg is the largest yet recorded. The skull sheds new light on the anatomy of the extinct giant rodents of the Dinomyidae, which are known mostly from isolated teeth and incomplete mandible remains. The fossil derives from San José Formation, Uruguay, usually assigned to the Pliocene–Pleistocene (4–2 Myr ago), and the proposed palaeoenvironment where this rodent lived was characterized as an estuarine or deltaic system with forest communities.
Molecular analysis of neural crest migration
Authors: Kuriyama Sei , Mayor Roberto
Published: January 2008

The neural crest (NC) cells have been called the ‘explorers of the embryos’ because they migrate all over the embryo where they differentiate into a variety of diverse kinds of cells. In this work, we analyse the role of different molecules controlling the migration of NC cells. First, we describe the strong similarity between the process of NC migration and metastasis in tumour cells. The epithelial–mesenchymal transition process that both kinds of cells undergo is controlled by the same molecular machinery, including cadherins, connexins,SnailandTwistgenes and matrix metalloproteases. Second, we analysed the molecular signals that control the patterned migration of the cephalic and trunk NC cells. Most of the factors described so far, such as Eph/ephrins, semaphorins/neuropilins and Slit/Robo, are negative signals that prohibit the migration of NC cells into target areas of the embryo. Finally, we analyse how the direction of migration is controlled by regulation of cell polarity and how the planar cell polarity or non-canonical Wnt signalling is involved in this process.
Calcium signalling during the cleavage period of zebrafish development
Authors: Webb Sarah E , Li Wai Ming , Miller Andrew L
Published: January 2008

Imaging studies, using both luminescent and fluorescent Ca2+-sensitive reporters, have revealed that during the first few meroblastic cleavages of the large embryos of teleosts, localized elevations of intracellular Ca2+accompany positioning, propagation, deepening and apposition of the cleavage furrows. Here, we will review the Ca2+transients reported during the cleavage period in these embryos, with reference mainly to that of the zebrafish (Danio rerio). We will also present the latest findings that support the proposal that Ca2+transients are an essential feature of embryonic cytokinesis. In addition, the potential upstream triggers and downstream targets of the different cytokinetic Ca2+transients will be discussed. Finally, we will present a hypothetical model that summarizes what has been suggested to be the various roles of Ca2+signalling during cytokinesis in teleost embryos.
Impact of glycosylation on antigenicity of simian immunodeficiency virus SIV239: induction of rapid V1/V2-specific non-neutralizing antibody and delayed neutralizing antibody following infection with an attenuated deglycosylated mutant
Authors: Sugimoto Chie , Nakayama Emi E. , Shioda Tatsuo , Villinger Francois , Ansari Aftab A. , Yamamoto Naoki , Suzuki Yasuo , Nagai Yoshiyuki , Mori Kazuyasu
Published: January 2008

Infection of rhesus macaques with a deglycosylation mutant, Δ5G, derived from SIV239, a pathogenic clone of simian immunodeficiency virus (SIV), led to robust acute-phase viral replication followed by a chronic phase with undetectable viral load. This study examined whether humoral responses in Δ5G-infected animals played any role in the control of infection. Neutralizing antibodies (nAbs) were elicited more efficiently in Δ5G-infected animals than in SIV239-infected animals. However, functional nAb measured by 90 % neutralization was prominent in only two of the five Δ5G-infected animals, and only at 8 weeks post-infection (p.i.), when viral loads were already below 104 copies ml−1. These results suggest a minimal role for nAbs in the control of the primary infection. In contrast, whilst Ab responses to epitopes localized to the variable loops V1/V2 were detected in all Δ5G-infected animals at 3 weeks p.i., this response was associated with a concomitant reduction in Ab responses to epitopes in gp41 compared with those in SIV239-infected animals. These results suggest that the altered surface glycosylation and/or conformation of viral spikes induce a humoral response against SIV that is distinct from the response induced by SIV239. More interestingly, whereas V1/V2-specific Abs were induced in all animals, these Abs were associated with vigorous Δ5G-specific virion capture ability in only two Δ5G-infected animals that exhibited a functional nAb response. Thus, whereas the deglycosylation mutant infection elicited early virion capture and subsequent nAbs, the responses differed among animals, suggesting the existence of host factors that may influence the functional humoral responses against human immunodeficiency virus/SIV.
Cloning and sequencing of a highly productive, endotheliotropic virus strain derived from human cytomegalovirus TB40/E
Authors: Sinzger Christian , Hahn Gabriele , Digel Margarete , Katona Ruth , Sampaio Kerstin Laib , Messerle Martin , Hengel Hartmut , Koszinowski Ulrich , Brune Wolfram , Adler Barbara
Published: January 2008

Human cytomegalovirus (HCMV) strain TB40/E, replicates efficiently, exhibits a broad cell tropism and is widely used for infection of endothelial cells and monocyte-derived cells yet has not been available in a phenotypically homogeneous form compatible with genetic analysis. To overcome this problem, we cloned the TB40/E strain into a bacterial artificial chromosome (BAC) vector. Both highly endotheliotropic and poorly endotheliotropic virus clones, representing three distinct restriction fragment patterns, were reconstituted after transfection of BAC clones derived from previously plaque-purified strain TB40/E. For one of the highly endotheliotropic clones, TB40-BAC4, we provide the genome sequence. Two BACs with identical restriction fragment patterns but different cell tropism were further analysed in the UL128-UL131A gene region. Sequence analysis revealed one coding-relevant adenine insertion at position 332 of UL128 in the BAC of the poorly endotheliotropic virus, which caused a frameshift in the C-terminal part of the coding sequence. Removal of this insertion by markerless mutagenesis restored the highly endotheliotropic phenotype, indicating that the loss of endothelial cell tropism was caused by this insertion. In conclusion, HCMV strain TB40/E, which combines the high endothelial cell tropism of a clinical isolate with the high titre growth of a cell culture adapted strain, is now available as a BAC clone suitable for genetic engineering. The results also suggest BAC cloning as a suitable method for selection of genetically defined virus clones.
Functional entry of dengue virus into Aedes albopictus mosquito cells is dependent on clathrin-mediated endocytosis
Authors: Acosta Eliana G. , Castilla Viviana , Damonte Elsa B.
Published: January 2008

Entry of dengue virus 2 (DENV-2) intoAedes albopictusmosquito C6/36 cells was analysed using biochemical and molecular inhibitors, together with confocal and electron microscopy observations. Treatment with monodansylcadaverine, chlorpromazine, sucrose and ammonium chloride inhibited DENV-2 virus yield and protein expression, whereas nystatin, a blocker of caveolae-mediated endocytosis, did not have any effect. Using confocal microscopy, co-localization of DENV-2 E glycoprotein and the marker protein transferrin was observed at the periphery of the cytoplasm. To support the requirement of clathrin function for DENV-2 entry, overexpression of a dominant-negative mutant of Eps15 in C6/36 cells was shown to impair virus entry. The disruption of actin microfilaments by cytochalasin D also significantly affected DENV-2 replication. In contrast, microtubule disruption by colchicine treatment did not impair DENV-2 infectivity, suggesting that DENV-2 does not require transport from early to late endosomes for successful infection of mosquito cells. Furthermore, using transmission electron microscopy, DENV-2 particles of approximately 44–52 nm were found attached within electron-dense invaginations of the plasma membrane and in coated vesicles that resembled those of clathrin-coated pits and vesicles, respectively. Together, these results demonstrate for the first time that DENV-2 enters insect cells by receptor-mediated, clathrin-dependent endocytosis, requiring traffic through an acidic pH compartment for subsequent uncoating and completion of a productive infection.
Exogenous introduction of an immunodominant peptide from the non-structural IE1 protein of human cytomegalovirus into the MHC class I presentation pathway by recombinant dense bodies
Authors: Mersseman Véronique , Besold Katrin , Reddehase Matthias J. , Wolfrum Uwe , Strand Dennis , Plachter Bodo , Reyda Sabine
Published: January 2008

Exogenous introduction of particle-associated proteins of human cytomegalovirus (HCMV) into the major histocompatibility complex (MHC) class I presentation pathway by subviral dense bodies (DB) is an effective way to sensitize cells against CD8 T-cell (CTL) recognition and killing. Consequently, these particles have been proposed as a platform for vaccine development. We have developed a strategy to refine the antigenic composition of DB. For proof of principle, an HCMV recombinant (RV-VM3) was generated that encoded the immunodominant CTL determinant IE1TMYfrom the IE1 protein in fusion with the major constituent of DB, the tegument protein pp65. To generate RV-VM3, a bacterial artificial chromosome containing the HCMV genome was modified by applying positive/negative selection based on the expression of the bacterial galactokinase in conjunction withλRed-mediated homologous recombination. This method allowed the efficient and seamless insertion of the DNA sequence encoding IE1TMYin frame into the pp65 open reading frame (UL83) of the viral genome. RV-VM3 expressed its fusion protein to high levels. The fusion protein was packaged into DB and into virions. Its delivery into fibroblasts by these viral particles led to the loading of the MHC class I presentation pathway with IE1TMYand to efficient killing by specific CTLs. This demonstrated that a heterologous peptide, not naturally present in HCMV particles, can be processed from a recombinant, DB-derived protein to be subsequently presented by MHC class I. The results presented here provide a rationale for the optimization of a vaccine based on recombinant DB.
Antenatal pulmonary embolism: risk factors, management and outcomes
Authors: Knight M ,   UKOSS
Published: January 2008

Objectives  To estimate the incidence of antenatal pulmonary embolism and describe the risk factors, management and outcomes.

Design  A national matched case–control study using the UK Obstetric Surveillance System (UKOSS).

Setting  All hospitals with consultant‐led maternity units in the UK.

Participants  A total of 143 women who had an antenatal pulmonary embolism between February 2005 and August 2006. Two hundred and fifty nine matched control women.

Methods  Prospective case and control identification through the UKOSS monthly mailing.

Main outcome measures  Incidence and case fatality rates with 95% CIs. Adjusted odds ratio estimates.

Results  One hundred per cent of UK consultant‐led obstetric units contributed data to UKOSS. A total of 143 antenatal pulmonary embolisms were reported, representing an estimated incidence of 1.3 per 10 000 maternities (95% CI 1.1–1.5). Seventy per cent of women had identifiable classical risk factors for thromboembolic disease. The main risk factors for pulmonary embolism were multiparity (adjusted odds ratio [aOR] 4.03, 95% CI 1.60–9.84) and body mass index ≥ 30 kg/m2 (aOR 2.65, 95% CI 1.09–6.45). Nine women who had a pulmonary embolism should have received antenatal thromboprophylaxis with low‐molecular‐weight heparin (LMWH) according to national guidelines; only three (33%) of them did. Six women (4%) had a pulmonary embolism following antenatal prophylaxis with LMWH; three of these women (50%) were receiving lower than recommended doses. Two women had recurrent pulmonary emboli (1.4%, 95% CI 0.2–5.1%). Five women died (case fatality 3.5%, 95% CI 1.1–8.0%).

Conclusions  Significant severe morbidity from thromboembolic disease underlies the maternal deaths from pulmonary embolism in the UK. This study has shown some cases where thromboprophylaxis was not provided according to national guidelines, and there may be scope for further work on guideline implementation.
Geographic variation in ecophysiological traits of black cottonwood (Populus trichocarpa)This article is one of a selection of papers published in the Special Issue on Poplar Research in Canada.
Authors: Gornall Jemma L. , Guy Robert D.
Published: January 2008

Variation in traits related to photosynthesis and water-use were examined within and between geographic sources (provenances) of black cottonwood in two range-wide common garden experiments in British Columbia, Canada. In the first experiment, CO2 assimilation (A), stomatal conductance (gs), instantaneous intrinsic water use efficiency (WUEi), stomatal density, specific leaf area, growth height, and foliar N were measured on five 2-year-old trees of 20 clones from five widely separated provenances (i.e., 4 clones per source). Leaf disks were analysed for stable carbon isotope composition (δ13C) to provide a more long-term measure of WUE. Photosynthetic rate per unit leaf nitrogen was used as a measure of nitrogen use efficiency (NUE). A differed between (p < 0.001), but not within provenances, and increased with latitude of origin (R2 = 0.70). NUE and WUEi also varied between (p = 0.034 and p = 0.039, respectively), but not within provenances. In contrast, no variation among provenances was detected for δ13C, but there were strong differences between clones within provenances (p < 0.001). Variation in A was well correlated with foliar nitrogen, gs, and stomatal density and adaxial:abaxial distribution ratio; hence, WUEi, δ13C and NUE were mostly unrelated to latitude or associated climate variables. Species-wide patterns in stomatal density and distribution were confirmed in the second experiment which utilized 140 clones. Stomatal density on the adaxial (but not the abaxial) leaf surface was strongly correlated with latitude (p <0.001). We speculate that northern provenances may have inherently higher A and gs to compensate for shorter growing seasons.
Shoot–root defense signaling and activation of root defense by leaf damage in poplarThis article is one of a selection of papers published in the Special Issue on Poplar Research in Canada.
Authors: Major Ian T. , Constabel C. Peter
Published: January 2008

Shoot–root systemic defense signaling of hybrid poplar (Populus trichocarpa Torr. & A. Gray × Populus deltoides Bartr. ex Marsh.) was investigated with molecular techniques to extend existing knowledge of poplar defense. Treatment of roots with methyl jasmonate demonstrated that transcripts of PtdTI3, a poplar trypsin inhibitor and marker of poplar defense responses, can be induced in poplar roots as well as leaves. Moreover, simulated herbivory of poplar leaves with methyl jasmonate treatment or wounding with pliers also induced PtdTI3 mRNA in roots, which implies downward, or basipetal, systemic signaling from shoots to roots. In addition, the inducible root-defense response comprised both increased PtdTI3 protein levels and trypsin-inhibitor activity. The inducible systemic response was further investigated with comparative macroarray analyses which indicated that in addition to PtdTI3, other genes respond in roots after wounding and methyl jasmonate treatment of leaves. The majority of the 17 genes encode previously identified leaf herbivory defense genes; however, some genes strongly up-regulated in leaves were not induced in roots. The identification of multiple defense genes that are inducible in roots following leaf damage is clear evidence of a systemic defense response in roots and the presence of basipetal shoot–root defense signaling.
Poplar defense against insect herbivoresThis review is one of a selection of papers published in the Special Issue on Poplar Research in Canada.
Authors: Philippe Ryan N. , Bohlmann Jörg
Published: January 2008

The availability of a poplar ( Populus trichocarpa Torr & A. Gray, black cottonwood) genome sequence is enabling new research approaches in angiosperm tree biology. Much of the recent genomics research in poplars has been on wood formation, growth and development, resistance to abiotic stress and pathogens, motivated, at least in part, by the fact that poplars provide an important system for large-scale, short-rotation plantation forestry in the Northern Hemisphere. To sustain productivity and ecosystem health of natural and planted poplar forests it is of critical importance to also develop a better understanding of the molecular mechanisms of defense and resistance of poplars against insect pests. Previous research has established a solid foundation of the chemical ecology of poplar defense against insects. This review summarizes some of the relevant literature on defense against insect herbivores in poplars with an emphasis on molecular, biochemical, and emerging genomic research in this important field within forest biotechnology and chemical ecology. Following a general introduction, we provide a brief overview of some of the most relevant insect pests of poplars; we then describe some of the general defense strategies of poplars along with selected examples of their activities. We conclude with a summary of emerging results and perspectives from recent advances in genomics research on poplar defense against insects.
Intraspecific variation in photosynthetic traits of Populus trichocarpa
Authors: Dunlap J. M. , Braatne J. H. , Hinckley T. M. , Stettler R. F.
Published: January 2008

Three experiments were conducted to evaluate net photosynthesis in black cottonwood (Populus trichocarpa Torrey & Gray) from mesic and xeric regions of Washington. In 1986, six clones each from the lower Nisqually (mesic) and Yakima (xeric) river valleys and growing in a common garden were measured for their photosynthetic rates. On 2 clear days in summer, Yakima clones had significantly (p ≤ 0.10) higher rates (means: 32 and 25μmol CO2 m−2 s−1) than Nisqually clones (means: 25 and 22μmol CO2 m−2 s−1). The next year, cuttings from these clones were potted, grown separately for 2 months in a maritime (Puyallup, Wash.) and a continental climate (Wenatchee, Wash.), and then transferred to growth chambers in Seattle, Wash. Photosynthetic rates were determined at four light levels (200, 500, 800, and 1500 μmol m−2 s−1) and two temperatures (24 and 32 °C). Yakima plants had significantly (p ≤ 0.05) higher rates at high light (20μmol CO2 m−2 s−1) and also at moderate light in high temperature than Nisqually plants (16 μmol CO2 m−2 s−1 in high light). Significant acclimation (p ≤ 0.01) was also revealed: at the two moderate light levels in high temperatures the Wenatchee-grown plants, regardless of source, had higher rates than those grown at Puyallup. In 1991, eight clones from the lower elevation, xeric region of the Yakima and eight from the upper elevation, mesic region were selected in a Puyallup stoolbed, and their photosynthesis and water-use efficiency were measured on a clear summer day. Lower elevation plants had a higher photosynthetic rate than those from the upper elevations along the Yakima; values were similar to those of 1986. The pattern for water-use efficiency was reversed; values were 56 μmol CO2/mol H2O for the lower and 84 μmol CO2/mol H2O for the upper Yakima plants. These three experiments provide evidence for significant genetic variation in photosynthetic processes both between and within river valleys. Key words: Populus trichocarpa, black cottonwood, poplar, photosynthesis, water-use efficiency, adaptation.
Origin and development of embryo and bud primordia during maturation of embryogenic calli of Zea mays
Authors: Emons Anne Mie C. , Does Hans de
Published: January 2008

Maize genotype 4C1 calli under embryo maturation conditions give rise to somatic embryos that can be regenerated into plants. This scanning electron microscope study shows that the pattern formation is as in zygotic embryos. A globular stage somatic embryo forms a starch-containing scutellum, a coleoptile, and leaf primordia in the same order and pattern as in zygotic embryos. There is no callus tissue between shoot and root meristems, as occurs in organogenesis. However, the study also reveals a different order of events: shoot meristems with leaf primordia develop at the base of leafy structures, on the surface of the callus. Similar structures were often named somatic embryos in the plant tissue culture literature, but they are more comparable to axillary buds. A coleoptile is not present. Both structures develop into plants on regeneration medium. Maturation of somatic embryos that are attached to callus aggregates is impaired in liquid culture; fewer embryos mature and regenerate probably because their cells have less cell to cell contact than those grown on solid medium. Somatic embryos unattached to callus tissue grow in suspension culture; they lack a scutellum or have only a rudimentary one, lack a coleoptile and leaf primordia. They develop roots but do not develop into plants in the media used in this study. Key words: in vitro culture, pattern formation, scanning electron microscopy, somatic embryogenesis, suspension culture, Zea mays L.
Pollen morphology and biometry in Androcymbium (Colchicaceae)
Authors: Martín Joan , Pedrola Joan , Caujapé Juli
Published: January 2008

The pollen of 34 individuals representing the 10 species and subspecies of the section Erythrostictus (Schlecht.) Bentham and 3 species of the section Cymbanthes Bentham in the genus Androcymbium Willdenow was examined with scanning electron microscopy to investigate the degree of morphologic differentiation within and between these two sections of the genus. Diporate pollen morphology was observed for all these taxa except for Androcymbium capense (L.) Krause (section Cymbanthes), which was triporate. Given the specific importance traditionally given to this character, some doubt is cast upon the naturalness of this section. Surface sculpturing was reticulate in both sections for all of the analysed species except for Androcymbium psammophilum Sventenius (section Erythrostictus), which was rugulate-perforated. A canonical analysis of populations based upon four pollen biometrie parameters measured on the analysed individuals belonging to section Erythrostictus was run. The pattern of groups displayed by the corresponding canonical representation furnishes other evidence that supports the establishment of more accurate taxonomic relationships among the species that are presently included in the complex Androcymbium gramineum (Cav.) McBride. Key words: Colchicaceae, Androcymbium, pollen, biometry, taxonomy, canonical analysis.
Spatial and temporal patterns of balsam fir mortality in spaced and unspaced stands caused by spruce budworm defoliation
Authors: MacLean David A. , Piene Harald
Published: January 2008

Spatial and temporal patterns of balsam fir (Abiesbalsamea (L.) Mill.) mortality were studied during a spruce budworm (Choristoneurafumiferana Clem.) outbreak from 1976 to 1984 on Cape Breton Island, Nova Scotia. Natural mortality in four insecticide-protected plots was 0% in spaced and 9–15% in unspaced stands, with only the smallest trees dying. Budworm-caused mortality (i.e., total minus natural) was 31–49% and 11–32% in spaced and unspaced young fir plots, respectively, but reached 94–100% in severely defoliated spaced plots, unprecedented in the literature for young fir mortality caused by the spruce budworm. Mortality began in the fourth to sixth year of defoliation, being earliest in the severely defoliated plots. From 80 to 90% of trees that died had > 75% cumulative defoliation, and most (64–100%) of the smallest (2 cm DBH) trees died. There was no significant difference in percent mortality between 25 spaced and 13 unspaced plots (p = 0.434), although, on average, mortality was 10–22% higher in the spaced plots. About 20–30% more of the intermediate-sized and largest trees were killed in the spaced plots. High spatial plot to plot variability in mortality occurred, which was apparently related to observed differences in the amount of defoliation and especially the incidence of "back-feeding" (damage to noncurrent foliage), as well as to plot size. Because budworm-caused mortality exhibits a distribution that tends to form large "holes" in stands, the degree of between-plot variability is related to plot size, and it is recommended that small plots that may miss these patches of mortality be avoided.