Intact Core Research Articles

Comprehensive glycerol ether lipid fingerprints through a novel reversed phase liquid chromatography–mass spectrometry protocol

Glycerol ether lipid distributions have been developed as proxies for reconstructing past environmental change or, in their intact polar form, for fingerprinting the viable microbial community composition. However, due to their structural complexity, full characterization of glycerol ether lipids requires separate protocols for the analysis of the polar head groups and the alkyl chain moieties in core ether lipids. As a consequence, the valuable relationship between core ether lipid composition and specific polar head groups is often lost; this limits understanding of the diversity of ether lipids and their utility as biogeochemical proxies. Here, we report a novel reversed phase liquid chromatography–electrospray ionization-mass spectrometry (RP-ESI-MS) protocol that enables the simultaneous analysis of polar head groups (e.g. phosphocholine, phosphoglycerol, phosphoinositol, hexose and dihexose) and alkyl moieties (e.g. alkyl moieties modified with different numbers of cycloalkyl moieties, hydroxyl and alkyl groups and double bonds) in crude lipid extracts without further preparation. The protocol greatly enhances detection of archaeal intact polar lipids (IPLs) and core lipids (CLs) with double bond- and hydroxyl group-bearing alkyl moieties. With these improvements, widely used ratios that describe relative distributions of the core lipids, such as TEX86 and ring index, can now be directly determined in specific intact polar lipids (IPL-specific TEX86 and ring index). Since IPLs are the putative precursors of the environmentally persistent core lipids, their detailed examination using this protocol can potentially provide new insights into diagenetic and biological mechanisms inherent to these proxies. In a series of 12 samples from diverse settings, core and IPL-specific TEX86 values followed the order: 2G-GDGTs>core GDGTs>1G-GDGTs>1G-GDGT-PI and the ring indices followed: 1G-GDGTs≈core GDGTs>2G-GDGTs>1G-GDGT-P1G>2G-OH-GDGTs≈1G-OH-GDGTs (1G, monoglycosyl; 2G, diglycosyl; P1G, phosphomonoglycosyl; GDGT, glycerol dialkyl glycerol tetraether).

Evaluation of Pleistocene groundwater flow through fractured tuffs using a U-series disequilibrium approach, Pahute Mesa, Nevada, USA

Groundwater flow through fractured felsic tuffs and lavas at the Nevada National Security Site represents the most likely mechanism for transport of radionuclides away from underground nuclear tests at Pahute Mesa. To help evaluate fracture flow and matrix–water exchange, we have determined U-series isotopic compositions on more than 40 drill core samples from 5 boreholes that represent discrete fracture surfaces, breccia zones, and interiors of unfractured core. The U-series approach relies on the disruption of radioactive secular equilibrium between isotopes in the uranium-series decay chain due to preferential mobilization of 234U relative to 238U, and U relative to Th. Samples from discrete fractures were obtained by milling fracture surfaces containing thin secondary mineral coatings of clays, silica, Fe–Mn oxyhydroxides, and zeolite. Intact core interiors and breccia fragments were sampled in bulk. In addition, profiles of rock matrix extending 15 to 44mm away from several fractures that show evidence of recent flow were analyzed to investigate the extent of fracture/matrix water exchange.Samples of rock matrix have 234U/238U and 230Th/238U activity ratios (AR) closest to radioactive secular equilibrium indicating only small amounts of groundwater penetrated unfractured matrix. Greater U mobility was observed in welded-tuff matrix with elevated porosity and in zeolitized bedded tuff. Samples of brecciated core were also in secular equilibrium implying a lack of long-range hydraulic connectivity in these cases. Samples of discrete fracture surfaces typically, but not always, were in radioactive disequilibrium. Many fractures had isotopic compositions plotting near the 230Th-234U 1:1 line indicating a steady-state balance between U input and removal along with radioactive decay. Numerical simulations of U-series isotope evolution indicate that 0.5 to 1 million years are required to reach steady-state compositions. Once attained, disequilibrium 234U/238U and 230Th/238U AR values can be maintained indefinitely as long as hydrological and geochemical processes remain stable. Therefore, many Pahute Mesa fractures represent stable hydrologic pathways over million-year timescales. A smaller number of samples have non-steady-state compositions indicating transient conditions in the last several hundred thousand years. In these cases, U mobility is dominated by overall gains rather than losses of U.

Link Protein N-terminal Peptide Binds to Bone Morphogenetic Protein (BMP) Type II Receptor and Drives Matrix Protein Expression in Rabbit Intervertebral Disc Cells

Intervertebral disc (IVD) degeneration and associated spinal disorders are leading sources of morbidity, and they can be responsible for chronic low back pain. Treatments for degenerative disc diseases continue to be a challenge. Intensive research is now focusing on promoting regeneration of degenerated discs by stimulating production of the disc matrix. Link protein N-terminal peptide (LPP) is a proteolytic fragment of link protein, an important cross-linker and stabilizer of the major structural components of cartilage, aggrecan and hyaluronan. In this study we investigated LPP action in rabbit primary intervertebral disc cells cultured ex vivo in a three-dimensional alginate matrix. Our data reveal that LPP promotes disc matrix production, which was evidenced by increased expression of the chondrocyte-specific transcription factor SOX9 and the extracellular matrix macromolecules aggrecan and collagen II. Using colocalization and pulldown studies we further document a noggin-insensitive direct peptide-protein association between LPP and BMP-RII. This association mediated Smad signaling that converges on BMP genes leading to expression of BMP-4 and BMP-7. Furthermore, through a cell-autonomous loop BMP-4 and BMP-7 intensified Smad1/5 signaling though a feedforward circuit involving BMP-RI, ultimately promoting expression of SOX9 and downstream aggrecan and collagen II genes. Our data define a complex regulatory signaling cascade initiated by LPP and suggest that LPP may be a useful therapeutic substitute for direct BMP administration to treat IVD degeneration and to ameliorate IVD-associated chronic low back pain.

Denitrification and Potential Nitrous Oxide and Carbon Dioxide Production in Brownfield Wetland Soils

Brownfields, previously developed sites that are derelict, vacant, or underused, are ubiquitous in urban areas. Wetlands on brownfields often retain rain and stormwater longer than the surrounding landscape because they are low-lying; this increases the possibility for these areas to process waterborne contaminants from the urban environment. In the northeastern United States, atmospheric deposition of nitrate (NO) is high. Denitrification, a microbial process common in wetlands, is a means of removing excess NO. Nitrogen gas is the desired end product of denitrification, but incomplete denitrification results in the production of NO, a greenhouse gas. The goal of this study was to investigate the potential of brownfield wetlands to serve as sinks for inorganic nitrogen and sources of greenhouse gases. We examined limitations to denitrification and NO production in brownfield wetland soils in New Jersey. Soil C:N ratios were high (18-40) and intact core denitrification (-0.78 to 11.6 μg NO-N kg dry soil d) and N mineralization (0.11-2.97 mg N kg dry soil d) were low for all sites. However, soil NO increased during dry periods. Nitrate additions to soil slurries increased denitrification rates, whereas labile C additions did not, indicating that soil denitrifiers were nitrogen limited. Incubations indicated that the end product of denitrification was primarily NO and not N. These results indicate that brownfield wetlands can develop significant denitrification capacity, potentially causing NO limitation. They might be significant sinks for atmospheric NO but may also become a significant source of NO if NO deposition were to increase.

Comparing and Combining Capillary Electrophoresis Electrospray Ionization Mass Spectrometry and Nano–Liquid Chromatography Electrospray Ionization Mass Spectrometry for the Characterization of Post-translationally Modified Histones

We present the first comprehensive capillary electrophoresis electrospray ionization mass spectrometry (CESI-MS) analysis of post-translational modifications derived from H1 and core histones. Using a capillary electrophoresis system equipped with a sheathless high-sensitivity porous sprayer and nano-liquid chromatography electrospray ionization mass spectrometry (nano-LC-ESI-MS) as two complementary techniques, we characterized H1 histones isolated from rat testis. Without any pre-separation of the perchloric acid extraction, a total of 70 different modified peptides, including 50 phosphopeptides, were identified in the rat linker histones H1.0, H1a-H1e, and H1t. Out of the 70 modified H1 histone peptides, 27 peptides could be identified with CESI-MS only, and 11 solely with LC-ESI-MS. Immobilized metal-affinity chromatography enrichment prior to MS analysis yielded a total of 55 phosphopeptides; 22 of these peptides could be identified only by CESI-MS, and 19 only by LC-ESI-MS, showing the complementarity of the two techniques. We mapped 42 H1 modification sites, including 31 phosphorylation sites, of which 8 were novel sites. For the analysis of core histones, we chose a different strategy. In a first step, the sulfuric-acid-extracted core histones were pre-separated using reverse-phase high-performance liquid chromatography. Individual rat testis core histone fractions obtained in this way were digested and analyzed via bottom-up CESI-MS. This approach yielded the identification of 42 different modification sites including acetylation (lysine and N(α)-terminal); mono-, di-, and trimethylation; and phosphorylation. When we applied CESI-MS for the analysis of intact core histone subtypes from butyrate-treated mouse tumor cells, we were able to rapidly detect their degree of modification, and we found this method very useful for the separation of isobaric trimethyl and acetyl modifications. Taken together, our results highlight the need for additional techniques for the comprehensive analysis of post-translational modifications. CESI-MS is a promising new proteomics tool as demonstrated by this, the first comprehensive analysis of histone modifications, using rat testis as an example.

Separation of Intact Intestinal Epithelium from Mesenchyme

Current protocols for separating adult intestinal epithelial cells from the underlying muscular and mesenchymal tissues typically involve extended incubations, harsh mechanical treatment, and exposure to either proteases or chelating agents. The drawbacks of these approaches include fragmentation, contamination with other cell types, reduced viability, and under-representation of crypt cells. Here we describe a gentle procedure that allows harvesting of pure, fully viable sheets of murine intestinal epithelium, with intact crypts and villi, without enzymes or EDTA. The mesenchyme retains intact villus core projections, is virtually free from epithelial cells, and can be cultured in vitro.

Equine-Derived Bone Mineral Matrix for Maxillary Sinus Floor Augmentation: A Clinical, Radiographic, Histologic, and Histomorphometric Case Series

The objective of this proof-of-principle multicenter case series was to examine the bone regenerative potential of a newly introduced equine-derived bone mineral matrix (Equimatrix) to provide human sinus augmentation for the purpose of implant placement in the posterior maxilla. There were 10 patients requiring 12 maxillary sinus augmentations enrolled in this study. Histologic results at 6 months demonstrated abundant amounts of vital new bone in intimate contact with residual graft particles. Active bridging between residual graft particles with newly regenerated bone was routinely observed in intact core specimens. A mean value of 23.4% vital bone formation was observed at 6 months. This compared favorably with previous results using xenografts to produce bone in the maxillary sinus for the purpose of dental implant placement. Both the qualitative and quantitative results of this case series suggest comparable bone regenerative results at 6 months to bovine-derived xenografts.

Waveguides fabricated by femtosecond laser exploiting both depressed cladding and stress-induced guiding core

We report on the fabrication of stress-induced optical channel waveguides and waveguide splitters with laser-depressed cladding by femtosecond laser. The laser beam was focused into neodymium doped phosphate glass by an objective producing a destructive filament. By moving the sample along an enclosed routine in the horizontal plane followed by a minor descent less than the filament length in the vertical direction, a cylinder with rarified periphery and densified center region was fabricated. Lining up the segments in partially overlapping sequence enabled waveguiding therein. The refractive-index contrast, near- and far-field mode distribution and confocal microscope fluorescence image of the waveguide were obtained. 1-to-2, 1-to-3 and 1-to-4 splitters were also machined with adjustable splitting ratio. Compared with traditional femtosecond laser writing methods, waveguides prepared by this approach showed controllable mode conduction, strong field confinement, large numerical aperture, low propagation loss and intact core region.

Protein film voltammetry and co-factor electron transfer dynamics in spinach photosystem II core complex

Direct protein film voltammetry (PFV) was used to investigate the redox properties of the photosystem II (PSII) core complex from spinach. The complex was isolated using an improved protocol not used previously for PFV. The PSII core complex had high oxygen-evolving capacity and was incorporated into thin lipid and polyion films. Three well-defined reversible pairs of reduction and oxidation voltammetry peaks were observed at 4 °C in the dark. Results were similar in both types of films, indicating that the environment of the PSII-bound cofactors was not influenced by film type. Based on comparison with various control samples including Mn-depleted PSII, peaks were assigned to chlorophyll a (Chl a) (Em = -0.47 V, all vs. NHE, at pH 6), quinones (-0.12 V), and the manganese (Mn) cluster (Em = 0.18 V). PFV of purified iron heme protein cytochrome b-559 (Cyt b-559), a component of PSII, gave a partly reversible peak pair at 0.004 V that did not have a potential similar to any peaks observed from the intact PSII core complex. The closest peak in PSII to 0.004 V is the 0.18 V peak that was found to be associated with a two-electron process, and thus is inconsistent with iron heme protein voltammetry. The -0.47 V peak had a peak potential and peak potential-pH dependence similar to that found for purified Chl a incorporated into DMPC films. The midpoint potentials reported here may differ to various extents from previously reported redox titration data due to the influence of electrode double-layer effects. Heterogeneous electron transfer (hET) rate constants were estimated by theoretical fitting and digital simulations for the -0.47 and 0.18 V peaks. Data for the Chl a peaks were best fit to a one-electron model, while the peak assigned to the Mn cluster was best fit by a two-electron/one-proton model.

Liquid limit as a predictor of mudrock permeability

Measurements of bedding perpendicular permeability are made on resedimented natural mudrocks that vary widely in mineralogy and clay fraction over a porosity range of 0.25–0.75 and under effective stresses up to 40 MPa. At a given porosity, permeability varies over 2–5 orders of magnitude. We show that the permeability–porosity relationship for a mudrock can be related to its liquid limit, an easily measured index property that can be determined from highly disturbed samples and reflects the clay mineralogy and clay fraction of a mudrock. We present correlations which allow the permeability of a mudrock to be estimated based on its porosity and liquid limit. The permeabilities predicted using these correlations all fall within ±5 times the measured values and most fall within ±3 times the measured values. We compare permeability measurements made on intact core samples to those predicted using the liquid limit correlations in order to demonstrate the applicability of the correlations for estimating in situ permeability. The use of clay fraction (particles <2 μm) as a material property for predicting permeability is found to be considerably less reliable.

Overcoming neurite‐inhibitory chondroitin sulfate proteoglycans in the astrocyte matrix

Acute trauma to the central nervous system (CNS) can result in permanent damage and loss of function related to the poor regeneration of injured axons. Injured axons encounter several barriers to regeneration, such as the glial scar at the injury site. The glial scar contains extracellular matrix (ECM) macromolecules deposited by reactive astrocytes in response to injury. The scar ECM is rich in chondroitin sulfate proteoglycans (CSPGs), macromolecules that inhibit axonal growth. CSPGs consist of a core protein with attachment sites for glycosaminoglycan (GAG) chains. An extensive literature demonstrates that enzymatic removal of the GAG chains by chondroitinase ABC permits some axonal regrowth; however, the remaining intact core proteins also possess inhibitory domains. Because metalloproteinases can degrade core proteins of CSPGs, we have evaluated five matrix metalloproteinases (MMPs) and a related protease-a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4)-for their capacity to overcome CSPG inhibition of neuritic growth in culture. The metalloproteinases were selected for their known expression after CNS injuries. Of the MMPs, MMP-3, -7 and -8 reduced or abolished inhibition of neurite outgrowth on a purified CSPG substrate and on an astrocyte-derived ECM. ADAMTS-4 also attenuated CSPG inhibition of neurites and had the additional benefits of neither degrading laminin nor causing neurotoxicity. The efficacy of ADAMTS-4 matched that of blocking the EGFR signaling previously reported to mediate CSPG inhibition. These findings highlight ADAMTS-4 as a superior protease for overcoming CSPG inhibition of axonal regeneration in the CNS.

Application of two new LC–ESI–MS methods for improved detection of intact polar lipids (IPLs) in environmental samples

Intact polar lipid distributions have become a valuable tool for the study of microbial ecosystems. In order to expand the detection and interpretation of the presence of these lipids, improved analytical methods are needed. Therefore, two high pressure liquid chromatography–electrospray ionization tandem mass spectrometry (HPLC–ESI–MS2) methods, based on hydrophilic interaction chromatography (HILIC) and reversed phase (RP) chromatography were developed, taking advantage of new chromatographic possibilities such as smaller particle size and recently developed column packing material. Both were optimized to cover the broad range of compounds found in environmental samples and to cope with the associated complex sample matrices. The capabilities of the methods were tested on pure standards and an environmental sample. Both methods offer improved peak resolution and detection limit, and reduced chromatographic background at twofold shorter run time compared with the previous method based on a diol column. The HILIC method offers separation according to lipid class similar to a diol column, so can be recommended for lipid fingerprinting. The method based on RP separation offers the unique possibility of analyzing intact polar lipids and core lipids in the same chromatographic run and an alternative mode of lipid separation based mainly on side chain structure. The method is especially suitable for separation of compounds based on side chain length, degree of saturation and/or presence of acyl/ether bonds. The combination of both newly developed chromatographic methods provides a powerful tool for the analysis of lipid distributions in environmental samples at ultra-low concentration.

Estimation of Maximum Biosolids and Meat and Bone Meal Application to a Low P Index Soil and a Method to Test for Nutrient and Metal Losses

The aim of this study was to develop (1) a method for the calculation of the maximum legal rate at which meat and bone meal (MBM) and biosolids should be applied to land, which took into account the soil phosphorus (P) index, the dry solids and the nutrient and metal content of each material, and (2) a quick method to evaluate their impact, when applied at the estimated maximum and twice the maximum application rates, on the release of P and metals to surface runoff. Three types of biosolids—lime stabilised (LS), anaerobically digested (AD) and thermally dried (TD)—and two types of MBM (low and high ash) were examined. The nutrient and metal losses were examined using a 1-L capacity beaker, which contained an intact soil core. Treatments were applied at maximum and twice the maximum legal application rates and then overlain with 500 mL of water, which was stirred to simulate overland flow. At the maximum legal application rate, low ash MBM (1.14 mg L−1) and TD biosolids (2.43 mg L−1) had the highest losses of P. Thermally dried biosolids and LS biosolids exceeded maximum allowable concentrations (MAC) for manganese, but all treatments remained below the MAC for copper and iron, at the maximum legal application rate. Anaerobically digested biosolids and high and low ash MBM would appear to have potential for landspreading, but these results are indicative only and should be verified at field scale.

Effect of seasonal freeze–thaw cycle on net nitrogen mineralization of soil organic layer in the subalpine/alpine forests of western Sichuan, China

Nitrogen mineralization, a main way that soil organic nitrogen converts to mineral nitrogen, is one of the key processes in soil nitrogen cycle. The mineral nitrogen has an important role in plant growth in the growing season. It has been widely accepted that soil freezing in winter can kill a number of microorganisms, weakening soil nitrogen mineralization. However, more and more recent studies have documented that soil microorganisms still have high activity during the deep freezing period, and obvious nitrogen mineralization in winter. Seasonal freeze–thaw cycle is a common phenomenon in the subalpine/alpine forest region, which may have a strong effect on soil ecological processes. Furthermore, the changing pattern of seasonal freeze–thaw cycles might have a significant influence on soil nitrogen mineralization in this region in the scenarios of global warming. As yet, little attention has been given to nitrogen mineralization of soil organic layer as affected by changed seasonal freeze–thaw pattern, although the increasing studies have demonstrated that winter warming might give strong effects on the litter decomposition and microbial activity in the subalpine/alpine forest regions. Therefore, a method of intact soil core incubation in combination with natural environmental gradient was employed by transferring forest soils from 3582m (A1) of altitude to 3298m (A2) of altitude and 3023m (A3) of altitude in the subalpine/alpine forests of western Sichuan, respectively. The amounts and rates of net nitrogen mineralization in soil organic layer were measured. The incubation period included the growing season and the freeze–thaw season from May 24, 2010 to April 19, 2011. The results suggested that significant net nitrogen mineralization was only observed in soil organic layer at low altitude (A3) during the whole incubation period. Forest soils at higher altitudes (A1 and A2) showed obvious soil nitrogen immobilization. In comparison with the growing season which showed remarkable nitrogen immobilization characteristic, the freeze–thaw season showed obvious nitrogen mineralization at lower altitudes (A2 and A3). In contrast, the nitrogen immobilization amounts at high altitude (A1) in freeze–thaw period were less than those in the growing season. Besides, the maximum of net nitrogen mineralization amounts and rates at high altitude (A1) in soil organic layer mainly occurred in the late stage of growing season and the onset of freezing, soil nitrogen mineralization at the middle altitude (A2) mainly occurred in the onset of freezing and the deep freezing period, while the highest amount and rate of net nitrogen mineralization at low altitude (A3) occurred in the early stage of thawing and the late stage of growing season. Furthermore, the amount and rate of soil net nitrogen mineralization during the freeze–thaw season were increasing with the decrease of altitude, which correlated with soil freeze–thaw cycle and freezing process at different altitudes. These results indicated that increasing soil temperature in the future could not only significantly enhance soil nitrogen mineralization in the freeze–thaw season, but also improve soil nitrogen mineralization by increasing freeze–thaw cycle times and shortening freeze–thaw period. However, the processes were significantly influenced by soil micro-environment of subalpine/alpine forest regions.

Identification of acetate-oxidizing bacteria in a coastal marine surface sediment by RNA-stable isotope probing in anoxic slurries and intact cores

We investigated the terminal electron-accepting pathways and the acetate-oxidizing bacteria in surface sediment (0-5 mm depth) of Aarhus Bay, Denmark, in anoxic slurry and intact core incubations. In the intact cores, oxygen, nitrate, oxides of manganese and iron, and sulfate were all available and likely all used as electron acceptors by the microbial community, whereas microbial iron and sulfate reduction dominated in the slurries. The availability of electron acceptors clearly affected which organisms were labeled by 16S rRNA-stable isotope probing (SIP). Members of the Oceanospirillaceae were identified as (13) C-acetate oxidizers in both types of incubations, but bacteria related to Colwellia and Arcobacter oxidized acetate in the intact core, while members of the Desulfuromonadales and Acidithiobacillaceae did so in the slurry incubation. Desulfuromonadales sequences also dominated 16S rRNA gene clone libraries from the highest positive dilution of the acetate-oxidizing most probable number cultures with manganese and iron oxides. Thus, members of Desulfuromonadales are likely important for acetate oxidation coupled to iron and manganese reduction in situ, while the identified Gammaproteobacteria and affiliates of Arcobacter may utilize oxygen, nitrate and manganese oxides. Our study further highlights some of the biases that are associated with the use of RNA-SIP as well as slurry and intact core incubations.

Two Dimensional Broadband Electronic Spectroscopy of Photosystem II Core Complexes

Studying the energy transfer and conversion processes in natural photosystems has both fundamental importance and relevance to the development of artificial light harvesting devices. Of particular interest is the D1/D2-cyt b559 reaction center of photosystem II (D1D2 RC), where the primary charge separation events associated with the evolution of molecular oxygen in photosynthesis occur. using transient 2D electronic spectroscopy (2DES), the energy transfer and charge separation processes in this system can be studied with femtosecond temporal resolution. Previously we have reported 2DES studies of the D1D2 RC in the Qy region where the electronic transitions associated with charge separation are found. This region contains overlapping transitions from all of the constituent chlorophyll and pheophytin pigments in the D1D2 RC, complicating the interpretation of the spectroscopic dynamics. Here we present broadband 2DES data spanning 460 - 700 nm along the detection axis, enabling the use of other electronic transitions to facilitate understanding of the energy transfer and charge separation processes. We discuss preliminary 2DES results on highly functional core complexes from BBY particles, which include the D1D2 RC along with the CP43, CP47 and psbO subunits. By studying the more intact and functional core complex, we aim to determine whether more reduced systems such as D1D2 RC experience changes in excitonic couplings or fundamental charge separation as a result of purification.

Numerical Investigation of the Dynamic Mechanical State of a Coal Pillar During Longwall Mining Panel Extraction

This study presents a numerical investigation on the dynamic mechanical state of a coal pillar and the assessment of the coal bump risk during extraction using the longwall mining method. The present research indicates that there is an intact core, even when the peak pillar strength has been exceeded under uniaxial compression. This central portion of the coal pillar plays a significant role in its loading capacity. In this study, the intact core of the coal pillar is defined as an elastic core. Based on the geological conditions of a typical longwall panel from the Tangshan coal mine in the City of Tangshan, China, a numerical fast Lagrangian analysis of continua in three dimensions (FLAC3D) model was created to understand the relationship between the volume of the elastic core in a coal pillar and the vertical stress, which is considered to be an important precursor to the development of a coal bump. The numerical results suggest that, the wider the coal pillar, the greater the volume of the elastic core. Therefore, a coal pillar with large width may form a large elastic core as the panel is mined, and the vertical stress is expected to be greater in magnitude. Because of the high stresses and the associated stored elastic energy, the risk of coal bumps in a coal pillar with large width is greater than for a coal pillar with small width. The results of the model also predict that the peak abutment stress occurs near the intersection between the mining face and the roadways at a distance of 7.5 m from the mining face. It is revealed that the bump-prone zones around the longwall panel are within 7–10 m ahead of the mining face and near the edge of the roadway during panel extraction.

Mineralization of Carbon‐14‐Labeled Plant Residues in Conventional Tillage and No‐Till Systems

Tillage systems are known to influence the quantity and quality of soil organic C (SOC); however, it is unclear if tillage also changes the soil catabolic capacity (the ability to decompose C substrates). This study compared soils from two contrasting tillage systems, no‐till (NT) vs. conventional tillage (CT), with respect to their ability to catabolize a common 14C‐labeled substrate. Intact core samples from the 0‐ to 5‐cm soil depth under CT and the 0‐ to 5‐ and 10‐ to 15‐cm depths under NT were collected after 14 yr of winter wheat (Triticum aestivum L.)–corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation. Soil cores received a common substrate (14C‐labeled wheat residues) either surface applied or incorporated into the soil. Decomposition of the 14C‐labeled residues, soil mineral N concentration, and soil microbial biomass 14C (MB14C) were monitored for 86 d at 25°C. Respiration of 12CO2 from native SOC was greater at 0 to 5 cm under NT than CT but did not vary with depth under NT; there was no significant effect of tillage system or depth under NT or residue placement on respiration of residue 14CO2. Incorporation of 14C residues increased MB14C compared with surface application, indicating a greater efficiency of C utilization. For the soils and residues used in this experiment, there was no evidence of an effect of tillage system on soil catabolic capacity, and differences in soil microbial activity between tillage systems were attributed only to differences in the quantity and quality of C substrates.

Human Immunodeficiency Virus Type 1 (HIV-1) Transactivator of Transcription through Its Intact Core and Cysteine-Rich Domains Inhibits Wnt/β-Catenin Signaling in Astrocytes: Relevance to HIV Neuropathogenesis

Wnt/β-catenin is a neuroprotective pathway regulating cell fate commitment in the CNS and many vital functions of neurons and glia. Its dysregulation is linked to a number of neurodegenerative diseases. Wnt/β-catenin is also a repressor of HIV transcription in multiple cell types, including astrocytes, which are dysregulated in HIV-associated neurocognitive disorder. Given that HIV proteins can overcome host restriction factors and that perturbations of Wnt/β-catenin signaling can compromise astrocyte function, we evaluated the impact of HIV transactivator of transcription (Tat) on Wnt/β-catenin signaling in astrocytes. HIV clade B Tat, in primary progenitor-derived astrocytes and U87MG cells, inhibited Wnt/β-catenin signaling as demonstrated by its inhibition of active β-catenin, TOPflash reporter activity, and Axin-2 (a downstream target of Wnt/β-catenin signaling). Point mutations in either the core region (K41A) or the cysteine-rich region (C30G) of Tat abrogated its ability to inhibit β-catenin signaling. Clade C Tat, which lacks the dicysteine motif, did not alter β-catenin signaling, confirming that the dicysteine motif is critical for Tat inhibition of β-catenin signaling. Tat coprecipitated with TCF-4 (a transcription factor that partners with β-catenin), suggesting a physical interaction between these two proteins. Furthermore, knockdown of β-catenin or TCF-4 enhanced docking of Tat at the TAR region of the HIV long terminal repeat. These findings highlight a bidirectional interference between Tat and Wnt/β-catenin that negatively impacts their cognate target genes. The consequences of this interaction include alleviation of Wnt/β-catenin-mediated suppression of HIV and possible astrocyte dysregulation contributing to HIV neuropathogenesis.

Sediment-water oxygen, ammonium and soluble reactive phosphorus fluxes in a turbid freshwater estuary (Curonian lagoon, Lithuania): evidences of benthic microalgal activity

Seasonal measurements of total and diffusive benthic fluxes were performed during the ice-free period in the Curonian Lagoon (Lithuania). This mostly freshwater hypertrophic basin exhibits wide seasonal variations of water temperature (1-22°C) and inorganic nitrogen availability and it is subjected to dramatic blooms of diatoms and cyanobacteria (>100 μg chl a l -1 ). In this shallow lagoon, nutrient exchanges at the sediment-water interface and the regulating factors have been poorly explored. Overall aim of the present work is to demonstrate that the activity of benthic microalgae, generally neglected in turbid systems, can be a relevant regulator of sedimentary processes. To this purpose, light and dark fluxes of oxygen, ammonium and soluble reactive phosphorus were measured seasonally by intact core laboratory incubation and diffusive fluxes were calculated from sediment profiles. We investigated sandy sediments that were collected from the central area lagoon, that is representative of the most of the shallower lagoon area. Oxygen and ammonium fluxes were significantly different under light and dark incubations, suggesting an active role of benthic microalgae at the sediment-water interface. In the light net oxygen production was measured in three out of four samplings, with July as only exception, and ammonium was retained within sediments. In the dark sediment respiration displayed a temperature-dependent pattern while ammonium efflux increased from March to October. Fluxes of reactive phosphorus varied significantly with sampling seasons but were less affected by the incubation condition. Diffusive fluxes peaked in July, where highest concentration gradients at the interface and theoretical efflux of ammonium and reactive phosphorous were calculated. The marked differences between diffusive and total nutrient fluxes are probably due to photosynthetic activity by benthic microalgae, and thus oxygen production, enhancement of aerobic processes and net solute uptake at the sediment-water interface. Our findings support the hypothesis that even in highly turbid systems benthic microalgae can have a relevant role as filters for regenerated nutrients and as regulators of benthic processes.