bluuebunny/crossref_metadata_2025 huggingface dataset:
Cerebral Glutamine and Glutamate Levels in Relation to Compromised Energy Metabolism: A Microdialysis Study in Subarachnoid Hemorrhage Patients
Authors: Samuelsson Carolina , Hillered Lars , Zetterling Maria , Enblad Per , Hesselager Göran , Ryttlefors Mats , Kumlien Eva , Lewén Anders , Marklund Niklas , Nilsson Pelle , Salci Konstantin , Ronne-Engström Elisabeth
Published: January 2007

Astrocytic glutamate (Glt) uptake keeps brain interstitial Glt levels low. Within the astrocytes Glt is converted to glutamine (Gln), which is released and reconverted to Glt in neurons. The Glt–Gln cycle is energy demanding and impaired energy metabolism has been suggested to cause low interstitial Gln/Glt ratios. Using microdialysis (MD) measurements from visually noninjured cortex in 33 neurointensive care patients with subarachnoid hemorrhage, we have determined how interstitial Glt and Gln, as a reflection of the Glt–Gln cycle turnover, relate to perturbed energy metabolism. A total of 3703 hourly samples were analyzed. The lactate/pyruvate (L/P) ratios correlated to the Gln/Glt ratios ( r = −0.66), but this correlation was not stronger than the correlation between L/P and Glt ( r = 0.68) or the correlation between lactate and Glt ( r = 0.65). A novel observation was a linear relationship between interstitial pyruvate and Gln ( r = 0.52). There were 13 periods (404 h) of ‘energy crisis’, defined by L/P ratios above 40. All were associated with high interstitial Glt levels. Periods with L/P ratios above 40 and low pyruvate levels were associated with decreased interstitial Gln levels, suggesting ischemia and failing astrocytic Gln synthesis. Periods with L/P ratios above 40 and normal or high pyruvate levels were associated with increased interstitial Gln levels, which may represent an astrocytic hyperglycolytic response to high interstitial Glt levels. The results imply that moderately elevated L/P ratios cannot always be interpreted as failing energy metabolism and that interstitial pyruvate levels may discriminate whether or not there is sufficient astrocytic capacity for Glt–Gln cycling in the brain.
Impaired Firing and Sodium Channel Function in CA1 Hippocampal Interneurons after Transient Cerebral Ischemia
Authors: Zhan Ren-Zhi , Nadler J Victor , Schwartz-Bloom Rochelle D
Published: January 2007

Although interneurons in area CA1 of the hippocampus are less vulnerable to cerebral ischemia than CA1 pyramidal cells, it is not clear whether their relatively intact cellular morphology implies preservation of normal function. As maintenance of cellular excitability and firing properties is essential for interneurons to regulate neural networks, we investigated these aspects of interneuronal function after transient cerebral ischemia in rats. Cerebral ischemia in rats was induced for 8 mins by a combination of bilateral common carotid artery occlusion and hypovolemic hypotension, and whole cell patch clamp recordings were made in hippocampal slices prepared 24 h after reperfusion. Interneurons located within stratum pyramidale of area CA1 exhibited normal membrane properties and action potentials under these conditions. However, their excitability had declined, as evidenced by an increased action potential threshold and a rightward shift in the relationship between injected depolarizing current and firing rate. Voltage–clamp experiments revealed that transient cerebral ischemia reduced the peak Na+ current and shifted Na+ channel activation to more depolarized values, but did not alter steady-state inactivation of the channel. Double immunofluorescence cytochemistry showed that transient cerebral ischemia also reduced Nav1.1 subunit immunoreactivity in interneurons that coexpressed parvalbumin. We conclude that transient cerebral ischemia renders CA1 interneurons less excitable, that depressed excitability involves impaired Na+ channel activation and that Na+ channel dysfunction is explained, at least in part, by reduced expression of the Nav1.1 subunit. These changes may promote interneuron survival, but might also contribute to pyramidal cell death.
Effective nonlinear coefficients of strongly nonlinear dielectric composites
Authors: Thongsee Jatuporn , Natenapit Mayuree
Published: January 2007

The effective medium theory is used to model a two-phase strongly nonlinear dielectric composite. More general effective nonlinear coefficients are determined which are not limited to the case of dilute inclusions. Our results obtained by using the decoupling technique and the variational method are compared and are in agreement with the experimental results by Gehr et al. [J. Opt. Soc. Am. B 14, 2310 (1997)].
Luminescent properties and electronic structures of rare earth and alkaline earth borates of REBa3B9O18 (RE=Lu,Y)
Authors: Duan Cheng-Jun , Wang Xiao-Jun , Zhao Jing-Tai
Published: January 2007

The samples of LuBa3B9O18 and YBa3B9O18 have been prepared by the solid-state reaction technique at high temperature and their luminescent properties were investigated for both under x-ray and vuv excitation. It is believed that the lattice defects have played an important role on the luminescent performances of the two compounds and the thermoluminescence measurement confirmed the existence of lattice defects in them. The corresponding thermoactivation energy E is estimated to be about 0.36eV for YBa3B9O18 and 0.24eV LuBa3B9O18, respectively, by the total glow peak method. The electronic structure of YBa3B9O18 was calculated using the CASTEP code. The results showed that it is an insulator with a band gap of 5.3eV. The calculated total and partial densities of states indicate that the top of valence bands is mainly built upon O 2p states and the low of conduction bands mostly originate from B 2s and 2p states. Considering the luminescent properties and electronic band structures of the two compounds, the potential applications of them are discussed.
Damage accumulation in nitrogen implanted 6H-SiC: Dependence on the direction of ion incidence and on the ion fluence
Authors: Zolnai Z. , Ster A. , Khánh N. Q. , Battistig G. , Lohner T. , Gyulai J. , Kótai E. , Posselt M.
Published: January 2007

The influence of crystallographic orientation and ion fluence on the shape of damage distributions induced by 500keV N+ implantation at room temperature into 6H-SiC is investigated. The irradiation was performed at different tilt angles between 0° and 4° with respect to the ⟨0001⟩ crystallographic axis in order to consider the whole range of beam alignment from channeling to random conditions. The applied implantation fluence range was 2.5×1014–3×1015cm−2. A special analytical method, 3.55MeV He+4 ion backscattering analysis in combination with channeling technique (BS∕C), was employed to measure the disorder accumulation simultaneously in the Si and C sublattices of SiC with good depth resolution. For correct energy to depth conversion in the BS∕C spectra, the average electronic energy loss per analyzing He ion for the ⟨0001⟩ axial channeling direction was determined. It was found that the tilt angle of nitrogen implantation has strong influence on the shape of the induced disorder profiles. Significantly lower disorder was found for channeling than for random irradiation. Computer simulation of the measured BS∕C spectra showed the presence of a simple defect structure in weakly damaged samples and suggested the formation of a complex disorder state for higher disorder levels. Full-cascade atomistic computer simulation of the ion implantation process was performed to explain the differences in disorder accumulation on the Si and C sublattices. The damage buildup mechanism was interpreted with the direct-impact, defect-stimulated amorphization model in order to understand damage formation and to describe the composition of structural disorder versus the ion fluence and the implantation tilt angle.
Experimental and theoretical analysis of direct-write laser micromachining of polymethyl methacrylate by CO2 laser ablation
Authors: Yuan Dajun , Das Suman
Published: January 2007

C O 2 laser micromachining provides a flexible and low-cost means for the rapid prototyping and manufacturing of miniaturized polymer systems such as polymethyl methacrylate (PMMA) microfluidic chip devices. In this paper, the relationships between the process variables (profile and depth of laser-ablated channels) and the process parameters (laser power and scanning velocity) are investigated. In contrast with the fabrication of 100–500μm wide channels reported in previous work, we focus on the fabrication of narrower channels using low laser power which can reduce the cost of the fabrication system and low scanning speeds. In this work, the laser power used for channel fabrication ranged from 0.45to1.35W and the scanning speeds ranged from 2to14mm∕s. The width of fabricated channels ranged from 44to240μm and their depths ranged from 22to130μm. Physical models were developed for predicting the depth and the profile of laser-ablated channels. The profile model incorporates the threshold fluence for CO2 laser ablation of PMMA to account for the partial ablation across the beam diameter. Our models are in excellent agreement with experimental results, with a maximum deviation of approximately 5%.
Bulk photoconductive gain in poly(phenylene vinylene) based diodes
Authors: Campbell I. H. , Crone B. K.
Published: January 2007

We observe large, bulk photoconductive gain (>100) in organic polymer diodes. Photoconductive gain was measured in diode structures employing the soluble polymer poly[2-methoxy,5-(2′-ethyl-hexyloxy)-1, 4-phenylene vinylene] (MEH-PPV) as the active layer. The MEH-PPV layer was either undoped or doped by incorporation of a soluble C60 derivative or PbSe quantum dots. The gain characteristics of the doped and undoped diodes are similar. We present the spectral response, transient response, and bias dependence of the gain. The photoconductive gain is due to the circulation of hole carriers through the diode in response to electrons trapped in the polymer layer. The bulk photoconductive gain reported here is distinct from the previous observations of gain in organic diodes that has been attributed to charge trapping near electrodes which increases the charge injection from that contact. The observed gain is consistent with estimates using previously established charge transport parameters of MEH-PPV.
Imaging concentric modulations in transverse modes of a vertical-cavity surface emitting laser using a scanning near-field optical microscope
Authors: Holton M. D. , Rees P. , Dunstan P. R.
Published: January 2007

Concentric standing waves have been spatially imaged in the near-field regime within the optical aperture of a vertical-cavity surface emitting laser (VCSEL) using a scanning near-field optical microscope. Using the microscope’s near-field collection mode and subsequent detection via a spectrometer it has been possible to design an experiment to determine the spatial location of multiple lasing modes in addition to concentric standing waves. At low injection current above threshold the standing waves influence and modulate the optical emission from multiple transverse modes. These results are discussed in relation to cavity and aperture effects, and pattern formation in VCSELs. Surface defects arising in the aperture are also seen to affect the optical output and are briefly discussed.
Effects of charge and size on condensation of supersaturated water vapor on nanoparticles of SiO2
Authors: Chen Chin-Cheng , Cheng Hsiu-Chin
Published: January 2007

The effects of size and charge on the condensation of a supersaturated water vapor on monodisperse nanoparticles of SiO2 were investigated in a flow cloud chamber. The dependences of the critical supersaturation Scr on particle size at diameters of 10, 12, and 15nm as well as on charge and charge polarity are determined experimentally. A novel electrospray aerosol generator was developed to generate a high concentration of SiO2 nanoparticles of less than 10nm by electrospraying silicon tetraethoxide (STE) ethanol solution followed by the thermal decomposition of STE. The effects of liquid flow rate, liquid concentration, flow rate of carrier gas, and liquid conductivity on the particle size distribution and concentration were examined. For charged particles, the nucleation occurs at a critical supersaturation Scr lower than that on neutral particles, and the charge effect fades away as particle size increases. The charge effect is stronger than the theoretical predictions. In addition, a sign preference is detected, i.e., water vapor condenses more readily on negatively charged particle, a trend consistent with those observed on ions. However, both effects of charge and charge polarity on Scr are stronger than that predicted by Volmer’s theory for ion-induced nucleation.
Observation of a Griffiths-like phase in bilayered manganites
Authors: Yang Ren-Fu , Sun Young , He Wei , Li Qing-An , Cheng Zhao-Hua
Published: January 2007

The authors report the observation of a Griffiths-like phase in La2−2xSr1+2xMn2O7 (x=0.30, 0.33, and 0.40) and (La0.8Eu0.2)2−2xSr1+2xMn2O7 (x=0.33) single crystals by means of electron spin resonance, magnetic susceptibility, and magnetoresistance measurements. In the temperature region TC<T<350K, the resonance signal consists of a ferromagnetic resonance line and a paramagnetic resonance line, which suggests that the system is not in a pure paramagnetic phase. The ferromagnetic resonance signal disappears and the magnetic susceptibility starts to deviate from the Curie-Weiss law at the same temperature T*≈350K, independent of doping level and anisotropy. These results indicate that a Griffiths-like phase exists at TC<T<T* in bilayered manganites, which is due to intrinsic inhomogeneity caused by quenched disorder.
Temperature dependent photoluminescence with spontaneous piezoelectric field in ZnO∕Zn0.74Mg0.26O single quantum wells
Authors: Cui Jian
Published: January 2007

Temperature dependent time integrated and time resolved photoluminescence spectra of ZnO∕Zn0.74Mg0.26O single quantum wells with and without spontaneous piezoelectric field are measured. The piezoelectric field can exist up to room temperature. The enhancement of piezoelectric field at low temperature reduces the optical transition energy by 75meV from room temperature to 77K, and correspondingly the lifetime increases from 1to66ns. The nonradiative process is also weaker than the sample without piezoelectric field. A model in combination with piezoelectric field, free electrons in the well and quantum confinement is proposed and can be successfully used to explain the experimental data. The temperature dependent electron density is carried out with a donor density of 1.03×1020cm−3 and an activation energy of 61.6meV.

At the request of the authors and editor, this article is being retracted effective 17 May 2007.
Postgrowth band gap trimming of InAs∕InAlGaAs quantum-dash laser
Authors: Djie H. S. , Wang Y. , Negro D. , Ooi B. S.
Published: January 2007

The authors demonstrate the selective postgrowth band gap engineering and the fabrication of band gap tuned laser in InAs–InAlGaAs quantum-dash lasers grown on InP substrate. The process utilizes nitrogen implantation to induce local defects and to enhance the group-III intermixing rate spatially upon the thermal annealing. Compared with the as-grown laser, intermixed laser with wavelength shifted by 127nm shows a 36% reduction in threshold current density and produces a comparable slope of efficiency. The integrity of the intermixed material is retained suggesting that intermixing process paves way to planar, monolithic integration of quantum-dash-based devices.
Mapping the electrostatic potential across AlGaN∕AlN∕GaN heterostructures using electron holography
Authors: Wu Z. H. , Stevens M. , Ponce F. A. , Lee W. , Ryou J. H. , Yoo D. , Dupuis R. D.
Published: January 2007

Electron holography has been used to study the properties of a nominally undoped AlGaN∕AlN∕GaN heterostructures. Important characteristics such as the electrostatic potential and the two-dimensional electron gas (2DEG) distribution have been determined with high spatial resolution across the thin film structure. The origin of 2DEG electrons is directly probed by analyzing the charge distribution in the AlGaN layer. It is shown that the contribution of residual donors is trivial and the ionized donorlike surface states are the major source of the 2DEG electrons.
Plastic deformation modes of gallium arsenide in nanoindentation and nanoscratching
Authors: Wasmer K. , Parlinska-Wojtan M. , Gassilloud R. , Pouvreau C. , Tharian J. , Micher J.
Published: January 2007

The mechanical deformation by nanoindentation and scratching of gallium arsenide has been investigated using cross-sectional transmission electron microscopy. Twinning was found to be the main deformation process occurring during indentation while only slip bands and perfect dislocations are observed during scratching. This behavior is explained, in the authors’ experiments, with the strain rate in scratching being hundred times greater than in indentation. Hence, the low indentation velocity allows twins to be nucleated and propagated from surface inhomogeneities, whereas in scratching, the deformation occurs first in front of the indenter and the scratching speed allows only perfect α dislocation to propagate.
Complete suppression of large InAs island formation on GaAs by metal organic chemical vapor deposition with periodic AsH3 interruption
Authors: Lee Youngsoo , Ahn Eungjin , Kim Jungsub , Moon Pilkyung , Yang Changjae , Yoon Euijoon , Lim Hyunjin , Cheong Hyeonsik
Published: January 2007

Self-assembled InAs quantum dots (QDs) on GaAs substrates were grown by metal organic chemical vapor deposition with periodic AsH3 interruption. In contrast to the conventional InAs QD growth method, AsH3 was interrupted periodically while TMIn was introduced into the reactor continuously. By interrupting AsH3 periodically, the growth surface is modulated between As-stabilized surface and In-stabilized one, resulting in complete suppression of relaxed large island formation and significant improvement in photoluminescence intensity. With further optimization of growth parameters, the authors obtained the emission at 1.32μm and narrow linewidth of 32meV at room temperature.
Decoding the neural substrates of reward-related decision making with functional MRI
Authors: Hampton Alan N. , O'Doherty John P.
Published: January 2007

Although previous studies have implicated a diverse set of brain regions in reward-related decision making, it is not yet known which of these regions contain information that directly reflects a decision. Here, we measured brain activity using functional MRI in a group of subjects while they performed a simple reward-based decision-making task: probabilistic reversal-learning. We recorded brain activity from nine distinct regions of interest previously implicated in decision making and separated out local spatially distributed signals in each region from global differences in signal. Using a multivariate analysis approach, we determined the extent to which global and local signals could be used to decode subjects' subsequent behavioral choice, based on their brain activity on the preceding trial. We found that subjects' decisions could be decoded to a high level of accuracy on the basis of both local and global signals even before they were required to make a choice, and even before they knew which physical action would be required. Furthermore, the combined signals from three specific brain areas (anterior cingulate cortex, medial prefrontal cortex, and ventral striatum) were found to provide all of the information sufficient to decode subjects' decisions out of all of the regions we studied. These findings implicate a specific network of regions in encoding information relevant to subsequent behavioral choice.
Activity-based probes for proteomic profiling of histone deacetylase complexes
Authors: Salisbury Cleo M. , Cravatt Benjamin F.
Published: January 2007

Histone deacetylases (HDACs) are key regulators of gene expression that require assembly into larger protein complexes for activity. Efforts to understand how associated proteins modulate the function of HDACs would benefit from new technologies that evaluate HDAC activity in native biological systems. Here, we describe an active site-directed chemical probe for profiling HDACs in native proteomes and live cells. This probe, designated SAHA-BPyne, contains structural elements of the general HDAC inhibitor suberoylanilide hydroxamic acid (SAHA), as well as benzophenone and alkyne moieties to effect covalent modification and enrichment of HDACs, respectively. Both class I and II HDACs were identified as specific targets of SAHA-BPyne in proteomes. Interestingly, multiple HDAC-associated proteins were also enriched by SAHA-BPyne, even after denaturation of probe-labeled proteomes. These data indicate that certain HDAC-associated proteins are directly modified by SAHA-BPyne, placing them in close proximity to HDAC active sites where they would be primed to regulate substrate recognition and activity. We further show that SAHA-BPyne can be used to measure differences in HDAC content and complex assembly in human disease models. This chemical proteomics probe should thus prove valuable for profiling both the activity state of HDACs and the binding proteins that regulate their function.
Long latency of evoked quantal transmitter release from somata of locus coeruleus neurons in rat pontine slices
Authors: Huang H.-P. , Wang S.-R. , Yao W. , Zhang C. , Zhou Y. , Chen X.-W. , Zhang B. , Xiong W. , Wang L.-Y. , Zheng L.-H. , Landry M. , Hökfelt T. , Xu Z.-Q. D. , Zhou Z.
Published: January 2007

The locus coeruleus (LC) harbors a compact group of noradrenergic cell bodies projecting to virtually all parts of the central nervous system. By using combined measurements of amperometry and patch-clamp, quantal vesicle release of noradrenaline (NA) was detected as amperometric spikes, after depolarization of the LC neurons. After a pulse depolarization, the average latency of amperometric spikes was 1,870 ms, whereas the latency of glutamate-mediated excitatory postsynaptic currents was 1.6 ms. A substantial fraction of the depolarization-induced amperometric spikes originated from the somata. In contrast to glutamate-mediated excitatory postsynaptic currents, NA secretion was strongly modulated by the action potential frequency (0.5–50 Hz). Somatodendritic NA release from LC upon enhanced cell activity produced autoinhibition of firing and of NA release. We conclude that, in contrast to classic synaptic transmission, quantal NA release from LC somata is characterized by a number of distinct properties, including long latency and high sensitivity to action potential frequency.
The hallmark of AGC kinase functional divergence is its C-terminal tail, a cis-acting regulatory module
Authors: Kannan Natarajan , Haste Nina , Taylor Susan S. , Neuwald Andrew F.
Published: January 2007

The catalytic activities of eukaryotic protein kinases (EPKs) are regulated by movement of the C-helix, movement of the N and C lobes upon ATP binding, and movement of the activation loop upon phosphorylation. Statistical analysis of the selective constraints associated with AGC kinase functional divergence reveals conserved interactions between these regulatory regions and three regions of the C-terminal tail (C-tail): the N-lobe tether (NLT), the active-site tether (AST), and the C-lobe tether (CLT). The NLT serves as a docking site for an upstream kinase PDK1 and, upon activation, positions the C-helix within the ATP binding pocket. The AST directly interacts with the ATP binding pocket, and the CLT interacts with the interlobe linker and the αC–β4 loop, which appears to serve as a hinge for C-helix movement. The C-tail is a hallmark of AGC functional divergence inasmuch as most of the conserved core residues that distinguish AGC kinases from other EPKs are associated with the NLT, AST, or CLT. Moreover, several AGC catalytic core conserved residues that interact with the C-tail strikingly diverge from the canonical residues observed at corresponding positions in nearly all other EPKs, suggesting that the catalytic core may have coevolved with the C-tail in AGC kinases. These observations, along with the fact that the C-tail is needed for catalytic activity suggests that the C-tail is a cis-acting regulatory module that can also serve as a regulatory “handle,” to which trans-acting cellular components can bind to modulate activity.
BIG1, a brefeldin A-inhibited guanine nucleotide-exchange protein, is required for correct glycosylation and function of integrin β1
Authors: Shen Xiaoyan , Hong Myoung-Soon , Moss Joel , Vaughan Martha
Published: January 2007

Glycosylation of β1 integrin (β1) in the Golgi complex has been related to its function in multiple cell processes, e.g., invasiveness, matrix adhesion, and migration. Brefeldin A-inhibited guanine nucleotide-exchange proteins (BIG) 1 and BIG2 activate human ADP-ribosylation factors (ARF) 1 and ARF3 by catalyzing the replacement of ARF-bound GDP with GTP to regulate Golgi vesicular transport. We show here a requirement for BIG1 (but not BIG2) in glycosylation and function of β1. In HepG2 cells treated for 48 or 72 h with BIG1, but not BIG2, siRNA, both the amount and electrophoretic mobility of the initially 130-kDa β1 were increased. BIG1 content had risen by 48 h after removal of BIG1 siRNA, and the faster-migrating, aberrant 130-kDa β1 was not seen. PeptideN-glycosidase F, but not endoglycosidase H, digestion converted all β1 to an ≈85-kDa (core protein) form. By electron microscopy, Golgi membranes in BIG1-depleted cells were less sharply defined than those in mock or BIG2 siRNA-treated cells, with more vesicle-like structures at the transface. Amounts of active RhoA-GTP also were decreased in such cells and restored by overexpression of HA-BIG1. Aberrant β1 was present on the cell surface, but its function in cell spreading, adhesion, and migration was impaired. By immunofluorescence microscopy, BIG1 siRNA-treated cells showed less spreading and concentration of β1 at the cell surface. These results indicate a previously unrecognized role for BIG1 in the glycosylation of β1 by Golgi enzymes, which is critical for its function in developmental and other vital cell processes.
Core-controlled polymorphism in virus-like particles
Authors: Sun Jingchuan , DuFort Chris , Daniel Marie-Christine , Murali Ayaluru , Chen Chao , Gopinath Kodetham , Stein Barry , De Mrinmoy , Rotello Vincent M. , Holzenburg Andreas , Kao C. Cheng , Dragnea Bogdan
Published: January 2007

This study concerns the self-assembly of virus-like particles (VLPs) composed of an icosahedral virus protein coat encapsulating a functionalized spherical nanoparticle core. The recent development of efficient methods for VLP self-assembly has opened the way to structural studies. Using electron microscopy with image reconstruction, the structures of several VLPs obtained from brome mosaic virus capsid proteins and gold nanoparticles were elucidated. Varying the gold core diameter provides control over the capsid structure. The number of subunits required for a complete capsid increases with the core diameter. The packaging efficiency is a function of the number of capsid protein subunits per gold nanoparticle. VLPs of varying diameters were found to resemble to three classes of viral particles found in cells (
T
= 1, 2, and 3). As a consequence of their regularity, VLPs form three-dimensional crystals under the same conditions as the wild-type virus. The crystals represent a form of metallodielectric material that exhibits optical properties influenced by multipolar plasmonic coupling.
Constitutively high dNTP concentration inhibits cell cycle progression and the DNA damage checkpoint in yeast
Saccharomyces cerevisiae
Authors: Chabes Andrei , Stillman Bruce
Published: January 2007

In eukaryotic cells the concentration of dNTP is highest in S phase and lowest in G
1
phase and is controlled by ribonucleotide reductase (RNR). RNR activity is eliminated in all eukaryotes in G
1
phase by a variety of mechanisms: transcriptional regulation, small inhibitory proteins, and protein degradation. After activation of RNR upon commitment to S phase, dATP feedback inhibition ensures that the dNTP concentration does not exceed a certain maximal level. It is not apparent why limitation of dNTP concentration is necessary in G
1
phase. In principle, dATP feedback inhibition should be sufficient to couple dNTP production to utilization. We demonstrate that in
Saccharomyces cerevisiae
constitutively high dNTP concentration transiently arrests cell cycle progression in late G
1
phase, affects activation of origins of replication, and inhibits the DNA damage checkpoint. We propose that fluctuation of dNTP concentration controls cell cycle progression and the initiation of DNA replication.
Aberrant monomethylation of histone H4 lysine 20 activates the DNA damage checkpoint inDrosophila melanogaster
Authors: Sakaguchi Ayako , Steward Ruth
Published: January 2007

PR-Set7 is a histone methyltransferase that specifically monomethylates histone H4 lysine 20 (K20) and is essential for cell proliferation. Our results show that in PR-Set7 mutants, the DNA damage checkpoint is activated. This phenotype is manifested by reduction in both the mitotic and the S phase indexes, a delay in the progression through early mitosis, and strong reduction of cyclin B. Furthermore, in a double mutant of PR-Set7 and mei-41 (the fly ATR orthologue), the abnormalities of mitotic progression and the cyclin B protein level were rescued. PR-Set7 also showed a defect in chromosome condensation that was enhanced in the double mutant. We therefore propose that monomethylated H4K20 is involved in the maintenance of proper higher order structure of DNA and is consequently essential for chromosome condensation.
Loss of APC induces polyploidy as a result of a combination of defects in mitosis and apoptosis
Authors: Dikovskaya Dina , Schiffmann David , Newton Ian P. , Oakley Abigail , Kroboth Karin , Sansom Owen , Jamieson Thomas J. , Meniel Valerie , Clarke Alan , Näthke Inke S.
Published: January 2007

Mutations in the adenomatous polyposis coli (APC) tumor suppressor gene initiate a majority of colorectal cancers. Acquisition of chromosomal instability is an early event in these tumors. We provide evidence that the loss of APC leads to a partial loss of interkinetochore tension at metaphase and alters mitotic progression. Furthermore, we show that inhibition of APC in U2OS cells compromises the mitotic spindle checkpoint. This is accompanied by a decrease in the association of the checkpoint proteins Bub1 and BubR1 with kinetochores. Additionally, APC depletion reduced apoptosis. As expected from this combination of defects, tetraploidy and polyploidy are consequences of APC inhibition in vitro and in vivo. The removal of APC produced the same defects in HCT116 cells that have constitutively active β-catenin. These data show that the loss of APC immediately induces chromosomal instability as a result of a combination of mitotic and apoptotic defects. We suggest that these defects amplify each other to increase the incidence of tetra- and polyploidy in early stages of tumorigenesis.
Hematopoietic reconstitution by multipotent adult progenitor cells: precursors to long-term hematopoietic stem cells
Authors: Serafini Marta , Dylla Scott J. , Oki Masayuki , Heremans Yves , Tolar Jakub , Jiang Yuehua , Buckley Shannon M. , Pelacho Beatriz , Burns Terry C. , Frommer Sarah , Rossi Derrick J. , Bryder David , Panoskaltsis-Mortari Angela , O'Shaughnessy Matthew J. , Nelson-Holte Molly , Fine Gabriel C. , Weissman Irving L. , Blazar Bruce R. , Verfaillie Catherine M.
Published: January 2007

For decades, in vitro expansion of transplantable hematopoietic stem cells (HSCs) has been an elusive goal. Here, we demonstrate that multipotent adult progenitor cells (MAPCs), isolated from green fluorescent protein (GFP)-transgenic mice and expanded in vitro for >40–80 population doublings, are capable of multilineage hematopoietic engraftment of immunodeficient mice. Among MAPC-derived GFP+CD45.2+ cells in the bone marrow of engrafted mice, HSCs were present that could radioprotect and reconstitute multilineage hematopoiesis in secondary and tertiary recipients, as well as myeloid and lymphoid hematopoietic progenitor subsets and functional GFP+ MAPC-derived lymphocytes that were functional. Although hematopoietic contribution by MAPCs was comparable to control KTLS HSCs, approximately 103-fold more MAPCs were required for efficient engraftment. Because GFP+ host-derived CD45.1+ cells were not observed, fusion is not likely to account for the generation of HSCs by MAPCs.
Helper T cell IL-2 production is limited by negative feedback and STAT-dependent cytokine signals
Authors: Villarino Alejandro V. , Tato Cristina M. , Stumhofer Jason S. , Yao Zhengju , Cui Yongzhi K. , Hennighausen Lothar , O'Shea John J. , Hunter Christopher A.
Published: January 2007

Although required for many fundamental immune processes, ranging from self-tolerance to pathogen immunity, interleukin (IL)-2 production is transient, and the mechanisms underlying this brevity remain unclear. These studies reveal that helper T cell IL-2 production is limited by a classic negative feedback loop that functions autonomously or in collaboration with other common γ chain (IL-4 and IL-7) and IL-6/IL-12 family cytokines (IL-12 and IL-27). Consistent with this model for cytokine-dependent regulation, they also demonstrate that the inhibitory effect can be mediated by several signal transducer and activator of transcription (STAT) family transcription factors, namely STAT5, STAT4, and STAT6. Collectively, these findings establish that IL-2 production is limited by a network of autocrine and paracrine signals that are readily available during acute inflammatory responses and, thus, provide a cellular and molecular basis for its transient pattern of expression.
The Role of S4 Charges in Voltage-dependent and Voltage-independent KCNQ1 Potassium Channel Complexes
Authors: Panaghie Gianina , Abbott Geoffrey W.
Published: January 2007

Voltage-gated potassium (Kv) channels extend their functional repertoire by coassembling with MinK-related peptides (MiRPs). MinK slows the activation of channels formed with KCNQ1 α subunits to generate the voltage-dependent IKs channel in human heart; MiRP1 and MiRP2 remove the voltage dependence of KCNQ1 to generate potassium “leak” currents in gastrointestinal epithelia. Other Kv α subunits interact with MiRP1 and MiRP2 but without loss of voltage dependence; the mechanism for this disparity is unknown. Here, sequence alignments revealed that the voltage-sensing S4 domain of KCNQ1 bears lower net charge (+3) than that of any other eukaryotic voltage-gated ion channel. We therefore examined the role of KCNQ1 S4 charges in channel activation using alanine-scanning mutagenesis and two-electrode voltage clamp. Alanine replacement of R231, at the N-terminal side of S4, produced constitutive activation in homomeric KCNQ1 channels, a phenomenon not observed with previous single amino acid substitutions in S4 of other channels. Homomeric KCNQ4 channels were also made constitutively active by mutagenesis to mimic the S4 charge balance of R231A-KCNQ1. Loss of single S4 charges at positions R231 or R237 produced constitutively active MinK-KCNQ1 channels and increased the constitutively active component of MiRP2-KCNQ1 currents. Charge addition to the CO2H-terminal half of S4 eliminated constitutive activation in MiRP2-KCNQ1 channels, whereas removal of homologous charges from KCNQ4 S4 produced constitutively active MiRP2-KCNQ4 channels. The results demonstrate that the unique S4 charge paucity of KCNQ1 facilitates its unique conversion to a leak channel by ancillary subunits such as MiRP2.
Importance of Hydration and Dynamics on the Selectivity of the KcsA and NaK Channels
Authors: Noskov Sergei Yu. , Roux Benoît
Published: January 2007

Fundamental concepts governing ion selectivity in narrow pores are reviewed and the microscopic factors responsible for the lack of selectivity of the NaK channel, which is structurally similar to the K+-selective KcsA channel, are elucidated on the basis of all-atom molecular dynamics free energy simulations. The results on NaK are contrasted and compared with previous studies of the KcsA channel. Analysis indicates that differences in hydration of the cation in the pore of NaK is at the origin of the lack of selectivity of NaK.
Anharmonicity of Lattice Vibrations in Zinc by Measurement of "Forbidden" Reflexions
Authors: M Merisalo  , M Järvinen  , J Kurittu
Published: January 2007

The "almost forbidden" reflexions (301) and (303) in zinc have been measured at 300 K using MoK
α radiation. Careful check for the absence of multiple Bragg events was made. The results are discussed in terms of the anharmonic atomic vibrations using the effective one-particle potential formalism. A significant value for α33 = - (1.5 ± 0.3) × 10-12 erg Å-3 was determined for the force constant of the cubic term of the potential.
Velocity- and Z-Dependence of Transient Magnetic Fields in Ferromagnetic Gd
Authors: C Fahlander  , K Johansson  , E Karlsson  , L O Norlin  , G Possnert
Published: January 2007

The ion-implantation perturbed angular correlation technique (IMPAC) was applied to the study of properties of Gd as stopping material. The transient magnetic fields at Fe, Ge, Mo, Ru, Pd, Cd and Te nuclei implanted into ferromagnetic Gd at 80 K were measured. The static magnetic hyperfine fields for Ru and Pd were deduced to be + 65 ± 25 kG and -45 ± 23 kG, respectively. The Z
1-dependence could be fitted by the adjusted Lindhard-Winther theory except for the case of implanted Fe-nuclei. The deviating behaviour for the 56Fe isotope was investigated in a separate experiment, where the dependence of the transient field was found to be directly proportional to the velocity of the recoiling ion. This result is in contradiction to the Lindhard-Winther model.
First Order Magnetic Phase Transition in Fe2P
Authors: Leif Lundgren  , Gulzar Tarmohamed  , Olof Beckman  , Bertil Carlsson  , Stig Rundqvist
Published: January 2007

The magnetic properties of stoichiometric Fe2P and non-stoichiometric Fe2-xP (0 < × ⩽ 0.06) have been studied by means of magnetic susceptibility. Measurements on pure stoichiometric Fe2P samples show that there is a first order magnetic phase transition from a ferro- to a paramagnetic state at 216 ± 1 K. The transition is accompanied by a discontinuous change in the dimensions of the hexagonal unit cell with a decrease in thea-axis of 0.06% and an increase in thec-axis of 0.08% for increasing temperature. The transition is interpreted to be of magnetoelastic origin with an exchange energy critically sensitive to the interatomic spacing. Measurements on single crystals show that the spins are directed along the hexagonalc-axis with an exceedingly high axial anisotropy. The saturation moment is 1.46 μB/iron atom and the anisotropy energy as estimated from low field data is ∼ 2.5 × 106J m-3(2.5 × 107erg cm-3). The transition behaviour is very sensitive to the magnitude of the external field as well as to the presence of impurities and deviations from the ideal stoichiometry in the samples.
Measurement of Free-Atom K-Shell Binding Energies of Light Elements
Authors: P Bisgaard  , R Bruch  , P Dahl  , B Fastrup  , M Rødbro
Published: January 2007

K-shell binding energies in free atoms for Be, B, and C have been obtained to within a few tenths of an eV by applying Auger spectroscopy to fast Be, B, and C ion beams being core-excited in single collisions with CH4and He. The present values, which correspond to the lowest possible ionization energy, i.e., for B, BE1 S=E(1s2s22p)3P0-E(1s22s22p)2P0, are considerably higher than previous values derived from measurements where solid or molecular samples have been used, while good agreement is found with recent free-atom theoretical data.
An Analysis of Hyperfine Interactions in the Electronic Spectrum of AIF
Authors: J M Brown  , I Kopp  , C Malmberg  , B Rydh
Published: January 2007

Lines in theb3Σ+-a3II andc3Σ+-a3II systems of AlF show partially resolved hyperfine structure. This structure has been attributed to magnetic interactions involving the27Al nucleus for whichI= 5/2. About twenty unblended lines from the (0, 0) bands of the two systems have been analysed in detail, using a computer programme to simulate the profiles by calculating the frequencies and intensities of individual hyperfine transitions. For low values of the rotational quantum number, the lines show a simple triplet structure, which reflects the case (bβS) coupling in the3Σ states. Analysis of these lines gives values for the Fermi contact parameters in the two states involved (bF= 0.049 cm-1and 0.057 cm-1in theb3Σ+andc3Σ+states respectively). As the rotational quantum number increases, the hyperfine patterns become less regular, indicating a departure from case (bβS) coupling in the3Σ states and from case (aβ) coupling in the3II state. By reproducing the details of these line-shapes, it has also proved possible to determine values for the electron spin-spin and spin-rotation parameters in the two3Σ states:

b3Σ+λ = -0.025(10)cm-1γ = 0.0000(3)cm-1

c3Σ+λ = 0.00(1)cm-1γ = 0.0015(10)cm-1

The experimental values for the Fermi contact parameter of AlF in thea3II andb3Σ+states are well produced by a simple single configuration molecular orbital calculation but the value for thec3Σ state is rather larger than expected on this basis.
Spin Rotation in Fe5SiB2
Authors: T Ericsson  , L Häggström  , R Wäppling
Published: January 2007

The magnetic structure of Fe5SiB2 has been investigated using Mössbauer spectroscopy. In the temperature region 140 K-784 K the compound is found to be a simple ferromagnet with the spins parallel to the c-axis. At lower temperatures the spins are located in or close to the ab-plane and there are indications that the pure ferromagnetic coupling is partly destroyed. The spin rotation seems to take place relatively abruptly, but at different temperatures in different parts of the sample thus indicating that the transition temperature is composition dependent.
On the Volume and Structure Dependence of Electric Field Gradients in Close-Packed Metals. I
Authors: T Butz
Published: January 2007

The presently available data on electric field gradientsqin close-packed metals as a function of hydrostatic and uniaxial pressure are reviewed. Data on close-packed binary alloys are included. These data indicate, thatqdepends on the unit cell volume asV-αwith α ranging from 3 to 6, in sharp contrast to conventional lattice sum predictions. Furthermore,qis found to depend linearly on the deviation from ideal close-packing. The consequences for the various contributions toqare discussed.
Search for High-Spin Isomers in 150Dy
Authors: M Piiparinen  , L Carlén  , H Ryde  , S A Hjorth  , A Johnson  , Th Lindblad
Published: January 2007

A search for yrast traps in 150Dy has been made by studying the γ-ray decay following the 144Nd (12C, 6n) 150Dy and 146Nd (12C, 8n) reactions. Although an average value of about 30 units of angular momentum is imparted to the final nucleus using these reactions, no evidence is found for the existence of isomers with half-lives longer than 10 ns.
Lifetimes of Some Levels in Neutral Carbon, Nitrogen and Oxygen
Authors: Jan Bromander  , Nada Duric  , Peter Erman  , Mats Larsson
Published: January 2007

Radiative lifetimes of a number of transitions to excited levels in neutral C, N and O have been directly measured using the High Frequency Deflection technique. With one exception, these lifetimes have not been experimentally studied earlier. The results are compared to Coulomb approximation calculations and to semi-empirical estimates as well as to very recent calculations including configuration interactions. A number of these visible and near infrared transitions have been utilized for estimating the solar C, N, and O abundances, and slight modifications are now suggested in some cases in view of the newf-values.
Beam-Foil Studies of Ionized Sulfur
Authors: B I Dynefors  , I Martinson
Published: January 2007

We have investigated the beam-foil spectra of sulfur (1050-5500 Å), obtained with 100-700 keV ions. Several lines are classified as transitions in S II-S VII. Lifetime data for some selected levels in S III-S VI are also presented.
Optical Emission-Line Spectra of Seyfert Galaxies and Radio Galaxies
Authors: Donald E Osterbrock
Published: January 2007

Many radio galaxies have strong emission lines in their optical spectra, similar to the emission lines in the spectra of Seyfert galaxies. The range of ionization extends from [O I] and [N I] through [Ne V] and [Fe VII] to [Fe X]. The emission-line spectra of radio galaxies divide into two types, narrow-line radio galaxies whose spectra are indistinguishable from Seyfert 2 galaxies, and broad-line radio galaxies whose spectra are similar to Seyfert 1 galaxies. However on the average the broad-line radio galaxies have steeper Balmer decrements, stronger [O III] and weaker Fe II emission than the Seyfert 1 galaxies, though at least one Seyfert 1 galaxy not known to be a radio source has a spectrum very similar to typical broad-line radio galaxies. Intermediate-type Seyfert galaxies exist that show various mixtures of the Seyfert 1 and Seyfert 2 properties, and the narrow-line or Seyfert 2 property seems to be strongly correlated with radio emission.
Emission-Line Spectra of QSOs and their Redshifts
Authors: E M Burbidge
Published: January 2007

A brief review of work on the emission-line spectra of QSOs is given. Data on radio-emitting and radio-quiet objects are discussed, with sections dealing with the lines that are observed, the distributions of redshifts obtained from the emission lines, and a selection of particular problems posed by current observations. These include a discussion of QSOs with atypical spectra, the Lyman/Balmer/Paschen relative line strengths, the abundances of the elements,rrelations of observed properties, and gas flow within the emission-line region.
Radio Observations of Active and Normal Nuclei
Authors: R D Ekers
Published: January 2007

At the centre of our Galaxy and in most other spiral galaxies there is a region of enhanced non-thermal radio emission of a few hundred parsecs in extent. The Seyfert galaxies have similar but somewhat more intense radio emission. Elliptical galaxies, radio galaxies and quasars have smaller and variable nuclear radio sources with complex spectral characteristics attributed to self-absorption effects. Using the clear differences between the nuclei of spiral and Seyfert galaxies on the one hand and elliptical and radio galaxies on the other, it can be argued that the quasars are extremely active manifestations of the elliptical and radio galaxies rather than of the Seyfert galaxies.