Dynamic shear stress in parallel-plate flow chambers

An in vitro model using a parallel-plate fluid flow chamber is supposed to simulate in vivo fluid shear stresses on various cell types exposed to dynamic fluid flow in their physiological environment. The metabolic response of cells in vitro is associated with the wall shear stress. However, parallel-plate flow chambers have not been characterized for dynamic fluid flow experiments. We use a dimensionless ratio h / lambda(v), in determining the exact magnitude of the dynamic wall shear stress, with its oscillating components scaled by a shear factor T. It is shown that, in order to expose cells to predictable levels of dynamic fluid shear stress, two conditions have to be met: (1) h / lambda(v) < 2, where h is the distance between the plates and lambda(v) is the viscous penetration depth; and (2) f(0) < f(c) / m, where the critical frequency f(c) is the upper threshold for this flow regime, m is the highest harmonic mode of the flow, and f(0) is the fundamental frequency of fluid flow.     

Are Ants Useful Indicators of Restoration Success in Temperate Grasslands?

Assessments of restoration are usually made through vegetation community surveys, leaving much of the ecosystem underexamined. Invertebrates, and ants in particular, are good candidates for restoration evaluation because they are sensitive to environmental change and are particularly important in ecosystem functioning. The considerable resources currently employed in restoring calcareous grassland on ex‐arable land mean that it is important to gather as much information as possible on how ecosystems change through restoration. We compared ant communities from 40 ex‐arable sites where some form of restoration work had been implemented between 2 and 60 years previously, with 40 paired reference sites of good quality calcareous grassland with no history of improvement or cultivation. A total of 11 ant species were found, but only two of these were found to be significantly different in abundance between restoration and reference sites: Myrmica sabuleti was more likely to be present in reference sites, whereas Lasius niger was more likely to be found in restoration sites. Myrmica sabuleti abundance was significantly positively correlated with age of restoration sites. The potential number of ant species found in temperate grasslands is small, limiting the information their assemblages can provide about ecosystem change. However, M. sabuleti is a good indicator species for calcareous grassland restoration success and, alongside information from the plant community, could increase the confidence with which restoration success is judged. We found the survey to be quick and simple to carry out and recommend its use.     

In situ delivery of passive immunity by lactobacilli producing single-chain antibodies

Lactobacilli have previously been used to deliver vaccine components for active immunization in vivo. Vectors encoding a single-chain Fv (scFv) antibody fragment, which recognizes the streptococcal antigen I/II (SAI/II) adhesion molecule of Streptococcus mutans, were constructed and expressed in Lactobacillus zeae (American Type Culture Collection (ATCC) 393). The scFv antibody fragments secreted into the supernatant or expressed on the surface of the bacteria showed binding activity against SAI/II in enzyme-linked immunosorbent assay (ELISA), and surface scFv-expressing lactobacilli agglutinated SAI/II-expressing S. mutans in vitro without affecting the corresponding SAI/II knockout strain. Lactobacilli expressing the scFv fragment fused to an E-tag were visualized by scanning electron microscopy (SEM) using beads coated with a monoclonal anti-E-tag antibody, and they bound directly to beads coated with SAI/II. After administration of scFv-expressing bacteria to a rat model of dental caries development, S. mutans bacteria counts and caries scores were markedly reduced. As lactobacilli are generally regarded as safe (GRAS) microorganisms, this approach may be of considerable commercial interest for in vivo immunotherapy.     

Crop residue incorporation negates the positive effect of elevated atmospheric carbon dioxide concentration on wheat productivity and fertilizer nitrogen recovery

Background and purpose

Rapid increases in atmospheric carbon dioxide concentration ([CO₂]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO₂] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO₂] on the growth, grain yield and the recovery of ¹⁵N-labeled fertilizer by wheat (Triticum aestivum L. cv. Yitpi) under controlled environmental conditions.

Methods

Residue for ambient and elevated [CO₂] treatments, obtained from wheat grown previously under ambient and elevated [CO₂], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage ¹⁵N-labeled granular urea (10.22 atom%) was applied at 50 kg?N ha^?1 and the wheat grown to maturity.

Results

When residue was not incorporated into the soil, elevated [CO₂] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO₂] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO₂] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO₂] decreased fertilizer N recovery.

Conclusions

A higher fertilizer application rate will be required under future elevated [CO₂] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO₂] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment.     

Miniaturized analytical assays in biotechnology

Biotechnology today is a well-established paradigm in many areas of human endeavor, such as the pharmaceutical industry, agriculture, management of the environment and many others. Meanwhile, biology is undergoing a spectacular transition: whereas systematic biology was replaced gradually by molecular biology, the latter is rapidly being transformed into a new systematic era in which entire genomes are being charted by ever more sophisticated analytical techniques.In the wake of this onslaught of data, new fields are germinating, such as bioinformatics in an attempt to find answers to fundamental questions, answers that may be hidden in the massive amounts of data already available today.     

A novel series of histamine H4 receptor antagonists based on the pyrido[3,2-d]pyrimidine scaffold: Comparison of hERG binding and target residence time with PF-3893787

In this work we describe the optimization of a lead compound based on the quinazoline template to give a new series of potent pyrido[3,2-d]pyrimidines as histamine H₄ receptor antagonists. The pyrido[3,2-d]pyrimidine ligands have significantly reduced hERG binding compared to clinical stage compound PF-3893787 while showing good affinities at the human and rodent histamine receptors. The receptor residence time of several of these new compounds was determined for the human H₄R and compared with JNJ7777120 and PF-3893787. The pyrido[3,2-d]pyrimidines showed residence times lower than JNJ7777120 but comparable to the residence time of PF-3893787. Overall, the pyrido[3,2-d]pyrimidines show an excellent in vitro profile that warrants their further investigation in relevant models of human disease.     

Sequestration of DROSHA and DGCR8 by Expanded CGG RNA Repeats Alters MicroRNA Processing in Fragile X-Associated Tremor/Ataxia Syndrome

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Highlights? DGCR8 binds to CGG RNA repeats, cause of the neurodegenerative FXTAS disease ? DGCR8 and its partner, DROSHA, are sequestered within CGG RNA aggregates ? DGCR8 rescues the neuronal cell death induced by expanded CGG RNA repeats ? MicroRNA processing is impaired in patients with FXTAS     

Life Expectancies of South African Adults Starting Antiretroviral Treatment: Collaborative Analysis of Cohort Studies

Background

Few estimates exist of the life expectancy of HIV-positive adults receiving antiretroviral treatment (ART) in low- and middle-income countries. We aimed to estimate the life expectancy of patients starting ART in South Africa and compare it with that of HIV-negative adults.

Methods and Findings

Data were collected from six South African ART cohorts. Analysis was restricted to 37,740 HIV-positive adults starting ART for the first time. Estimates of mortality were obtained by linking patient records to the national population register. Relative survival models were used to estimate the excess mortality attributable to HIV by age, for different baseline CD4 categories and different durations. Non-HIV mortality was estimated using a South African demographic model. The average life expectancy of men starting ART varied between 27.6 y (95% CI: 25.2–30.2) at age 20 y and 10.1 y (95% CI: 9.3–10.8) at age 60 y, while estimates for women at the same ages were substantially higher, at 36.8 y (95% CI: 34.0–39.7) and 14.4 y (95% CI: 13.3–15.3), respectively. The life expectancy of a 20-y-old woman was 43.1 y (95% CI: 40.1–46.0) if her baseline CD4 count was ≥200 cells/µl, compared to 29.5 y (95% CI: 26.2–33.0) if her baseline CD4 count was <50 cells/µl. Life expectancies of patients with baseline CD4 counts ≥200 cells/µl were between 70% and 86% of those in HIV-negative adults of the same age and sex, and life expectancies were increased by 15%–20% in patients who had survived 2 y after starting ART. However, the analysis was limited by a lack of mortality data at longer durations.

Conclusions

South African HIV-positive adults can have a near-normal life expectancy, provided that they start ART before their CD4 count drops below 200 cells/µl. These findings demonstrate that the near-normal life expectancies of HIV-positive individuals receiving ART in high-income countries can apply to low- and middle-income countries as well. Please see later in the article for the Editors'' Summary     

Independent Molecular Basis of Convergent Highland Adaptation in Maize

Convergent evolution is the independent evolution of similar traits in different species or lineages of the same species; this often is a result of adaptation to similar environments, a process referred to as convergent adaptation. We investigate here the molecular basis of convergent adaptation in maize to highland climates in Mesoamerica and South America, using genome-wide SNP data. Taking advantage of archaeological data on the arrival of maize to the highlands, we infer demographic models for both populations, identifying evidence of a strong bottleneck and rapid expansion in South America. We use these models to then identify loci showing an excess of differentiation as a means of identifying putative targets of natural selection and compare our results to expectations from recently developed theory on convergent adaptation. Consistent with predictions across a wide parameter space, we see limited evidence for convergent evolution at the nucleotide level in spite of strong similarities in overall phenotypes. Instead, we show that selection appears to have predominantly acted on standing genetic variation and that introgression from wild teosinte populations appears to have played a role in highland adaptation in Mexican maize.     

The membrane potential of Arabidopsis thaliana guard cells; depolarizations induced by apoplastic acidification

The apoplastic pH of guard cells probably acidifies in response to light, since light induces proton extrusion by both guard cells and epidermal leaf cells. From the data presented here, it is concluded that these apoplastic pH changes will affect K⁺ fluxes in guard cells of Arabidopsis thaliana (L.) Heynh. Guard cells of this species were impaled with double-barrelled microelectrodes, to measure the membrane potential (E_m) and the plasma-membrane conductance. Guard cells were found to exhibit two states with respect to their E_m, a depolarized and a hyperpolarized state. Apoplastic acidification depolarized E_m in both states, though the origin of the depolarization differed for each state. In the depolarized state, the change in E_m was the result of a combined pH effect on instantaneously activating conductances and on the slow outward rectifying K⁺ channel (s-ORC). At a more acidic apoplastic pH, the current through instantaneously activated conductances became more inwardly directed, while the maximum conductance of s-ORC decreased. The effect on s-ORC was accompanied by an acceleration of activation and deactivation of the channel. Experiments with acid loading of guard cells indicated that the effect on s-ORC was due to a lowered intracellular pH, caused by apoplastic acidification. In the hyperpolarized state, the pH-induced depolarization was due to a direct effect of the apoplastic pH on the inward rectifying K⁺ channel. Acidification shifted the threshold potential of the channel to more positive values. This effect was accompanied by a decrease in activation times and an increase of deactivation times, of the channel. From the changes in E_m and membrane conductance, the expected effect of acidification on K⁺ fluxes was calculated. It was concluded that apoplastic acidification will increase the K⁺-efflux in the depolarized state and reduce the K⁺-influx in the hyperpolarized state. Received: 28 April 1997 / Accepted: 10 November 1997