bluuebunny/crossref_metadata_2025 huggingface dataset:
Probing the magnetic states in mesoscopic rings by synchronous transport measurements in ring-wire hybrid configuration
Authors: Jain S. , Adeyeye A. O.
Published: May 2008

The magnetization reversal of individual rings has been mapped using synchronous magnetotransport measurement of ring-wire hybrid structures. This method of characterization eliminates the effect of both short circuiting introduced by placing the electrical contact probes directly on the ring and the dependence of the magnetotransport response on the contact configuration used. We have characterized the switching behavior of circular and elliptical ring elements and observed clearly distinguishable spin states for different ring shapes.
Residual strain in ZnO nanowires grown by catalyst-free chemical vapor deposition on GaN/sapphire (0001)
Authors: Tsao F. C. , Chen J. Y. , Kuo C. H. , Chi G. C. , Pan C. J. , Huang P. J. , Tun C. J. , Pong B. J. , Hsueh T. H. , Chang C. Y. , Pearton S. J. , Ren F.
Published: May 2008

ZnO nanowires were grown on 2-μm-thick GaN templates by chemical vapor deposition without employing any metal catalysts. The GaN template was deposited by metal-organic chemical vapor deposition on a c-plane sapphire substrate. The diameters of the resulting nanowires were in the range of 40–250nm depending on growth time. The ZnO nanowires were vertically well aligned with uniform length, diameter, and distribution density as revealed by electron microscopy. X-ray diffraction spectra showed that ZnO grew in single c-axis orientation with the c axis normal to the GaN basal plane, indicating a heteroepitaxial relationship of (0002)ZnO‖(0002)GaN. The lattice constant of the c axis of the ZnO nanowires with diameter of 40nm was 5.211Å, which is larger than that of bulk ZnO (5.207Å). The ZnO nanowires exhibit a residual tensile strain along the c axis, which decreases with increasing diameter.
Crystal and defect chemistry influences on band gap trends in alkaline earth perovskites
Authors: Lee Soonil , Woodford William H. , Randall Clive A.
Published: May 2008

A number of perovskites with A-site alkaline earth chemistries being Ca, Sr, and Ba, and tetravalent cations including Ce, Zr, and Ti are measured for optical band gap and found to vary systematically with tolerance factor and lattice volume within limits defined by the chemistry of the octahedral site. This paper also focuses on the BaTiO3 system, considering equilibrated nonstoichiometries, and determines the changes in band gap with respect to Ba∕Ti ratios. It was found that the optical band gap changes in the solid solution regime and is invariant in the second phase regions, as would be expected. In the cases of Ba∕Ti<1.0, the variation in band gap scales with lattice volume, but in the Ba∕Ti>1.0 stoichiometries, there is a distinct Urbach tail and the trend with lattice volume no longer holds. It is inferred that the VTi⁗−2VO•• partial Schottky complex controls the band gap trend with Ba-rich nonstoichiometries.
Characterization of piezoelectric single crystal YCa4O(BO3)3 for high temperature applications
Authors: Zhang Shujun , Fei Yiting , Chai Bruce H. T. , Frantz Eric , Snyder David W. , Jiang Xiaoning , Shrout Thomas R.
Published: May 2008

Operation at temperatures well above ambient is desired for applications such as smart structures integrated within aircraft and space vehicles. Piezoelectric yttrium calcium oxyborate single crystal YCa4O(BO3)3 (YCOB) was found to exhibit no phase transition until its melting temperature around ∼1500°C. The temperature characteristics of the resonance frequency, electromechanical coupling, and dielectric permittivity were studied in the temperature range of 30–950°C for different orientations. The electrical resistivity at 800°C was found to be greater than 2×108Ωcm. Together with its temperature independent electromechanical coupling factor (∼12%) and engineered resonance frequency behavior, these make YCOB crystals excellent candidates for sensing applications at ultra high temperatures.
Preparation and thermoelectric properties of high-performance Sb additional Yb0.2Co4Sb12+y bulk materials with nanostructure
Authors: Li Han , Tang Xinfeng , Su Xianli , Zhang Qingjie
Published: May 2008

High-performance Sb excess Yb0.2Co4Sb12+y (y=0,0.3,0.6,1.0) bulk materials with nanostructure have been prepared by combining melt spinning technique with spark plasma sintering. Average grain size of the bulk samples is about 150nm when y=0 and 0.3, and the grain size increases with the increase of y. Moderately superfluous Sb may improve the electrical transport properties effectively and the thermal conductivity of the bulk samples decreases markedly due to the nanostructure. The thermoelectric performance of the samples is significantly improved, and the maximum figure of the merit reaches 1.26 for the Yb0.2Co4Sb12.3 compound at 800K.
Cubic GaN∕AlN multiple quantum well photodetector
Authors: DeCuir E. A. , Manasreh M. O. , Tschumak Elena , Schörmann J. , As D. J. , Lischka K.
Published: May 2008

Photodetectors based on intersubband transitions in molecular beam epitaxially grown cubic GaN∕AlN multiple quantum wells were fabricated and tested. The presence of the intersubband transition was confirmed by using the optical absorption technique for structures with different well widths. Samples were polished into waveguide configuration on which the devices were fabricated. The photoresponse spectra were collected in the temperature range of 77–215K under the influence of small bias voltages. All devices exhibit photovoltaic effect where the photoresponse is observed at zero bias voltage. Theoretical calculations of the intersubband transition were performed and found to be in agreement with the observed results.
AlInN-based ultraviolet photodiode grown by metal organic chemical vapor deposition
Authors: Senda S. , Jiang H. , Egawa T.
Published: May 2008

AlInN, one of the III-nitride semiconductors, is expected to find its application as transistors, sensors, light emitters of electronic, and optoelectronic devices. When the lattice alignment of AlInN is made similar to GaN, a great deal of crack-free AlInN film growth is possible on GaN layers. We have successfully grown AlInN and AlGaN films by metal organic chemical vapor deposition. The structural analysis for the metal organic chemical vapor deposition grown films show that they have the same structure and were used to produce AlInN and AlGaN-based ultraviolet (UV) photodiodes. This paper describes the growth and fabrication of AlGaN and AlInN-based UV photodiodes and analyzes their device performance. For an AlInN, the peak responsivity at zero bias was measured to be 140mA∕W at 230nm, corresponding to an external quantum efficiency of 74%. AlInN was found to be more suitable than AlGaN for UV photodiodes with a cutoff wavelength in the UV-C range.
Characterization of Mn1.56Co0.96Ni0.48O4 films for infrared detection
Authors: Hou Yun , Huang Zhiming , Gao Yanqing , Ge Yujian , Wu Jing , Chu Junhao
Published: May 2008

Mn 1.56 Co 0.96 Ni 0.48 O 4 films with spinel structure were prepared on Al2O3 substrate by chemical solution deposition method. The microstructure of the films was studied by atomic force microscope and field-emission scanning electron microscope. The current-voltage characteristics showed Ohmic conductivity in the temperature range of 245–295K. The conduction was described by a variable range hopping model for a parabolic density of states. The advantages of high characteristic temperature, as well as high transition temperature (201K) between ferromagnetic and paramagnetic phases make the Mn1.56Co0.96Ni0.48O4 films very promising for infrared detection, especially for functional devices by integrating magnetic and electronic properties of the materials.
Plasma dispersion effect in heavily doped antimony-based passive optical waveguides
Authors: Lim C. G.
Published: May 2008

Theoretical analysis showed that the refractive-index change induced by plasma dispersion effect in heavily doped antimony-based optical waveguides can be pushed beyond the saturated value attainable with high absorption by shifting the absorption peak to the lower wavelength side of the pump wavelength. The efficiency of the resulting cross-phase modulation is dependent on the offset of the subband energy levels from the conduction band edge. For a given subband structure, the cross-phase modulation efficiency increases as the subband structure is placed closer to the conduction band edge.
Miniaturization of photonic waveguides by the use of left-handed materials
Authors: Tassin Philippe , Sahyoun Xavier , Veretennicoff Irina
Published: May 2008

We propose the use of a left-handed material in an optical waveguide structure to reduce its thickness well below the wavelength of light. We demonstrate that a layer of left-handed material, added to the cladding of a planar waveguide rather than to its core, allows for good light confinement in a subwavelength thin waveguide. We attribute the observed behavior to the change in phase evolution of electromagnetic waves in the guide. This technique can be used for the miniaturization of photonic integrated circuits.
Moderate to large magneto-optical signals in high Tc double perovskites
Authors: Das Hena , De Raychaudhury Molly , Saha-Dasgupta T.
Published: May 2008

Using first-principles density functional calculations, we have computed the optical and magneto-optical properties of the Cr-based double perovskite compounds, Sr2CrB′O6 with B′=W,Re,Os. Our computed magneto-optic spectra show substantially large Kerr rotations of about −2° to −2.5° for Sr2CrWO6 and Sr2CrReO6 and a moderately large Faraday rotation of about −0.25×106deg∕cm in insulating Sr2CrOsO6, indicating possible industrial applications. Our study should motivate experimental investigations in this yet to be explored area of Sr2CrB′O6 compounds.
Self-sputtering runaway in high power impulse magnetron sputtering: The role of secondary electrons and multiply charged metal ions
Authors: Anders André
Published: May 2008

Self-sputtering runaway in high power impulse magnetron sputtering is closely related to the appearance of multiply charged ions. This conclusion is based on the properties of potential emission of secondary electrons and energy balance considerations. The effect is especially strong for materials whose sputtering yield is marginally greater than unity. The absolute deposition rate increases ∼Q1∕2, whereas the rate normalized to the average power decreases ∼Q−1∕2, with Q being the mean ion charge state number.
Interfacial magnetic domain wall formation in perpendicular-anisotropy, exchange-spring films
Authors: Watson S. M. , Hauet T. , Borchers J. A. , Mangin S. , Fullerton Eric E.
Published: May 2008

Using magnetometry and polarized neutron reflectometry (PNR), we have mapped the reversal processes of the antiferromagnetically coupled, hard/soft system, TbFeCo∕[Co∕Pd(tPd)]15, with perpendicular anisotropy. The magnitude of the exchange coupling within the [Co∕Pd] layer can be tuned by varying Pd thickness. Since PNR is insensitive to moments perpendicular to the plane, a scattering geometry with polarization parallel to the scattering vector was used to isolate in-plane magnetization components and characterize the behavior of a domain wall near the bilayer interface. Consistent with predictions from a micromagnetic calculation, the characteristics of the domain wall vary with field and exchange stiffness in the Co∕Pd.
Effects of interlayers on phosphorescent blue organic light-emitting diodes
Authors: Lee Jonghee , Lee Jeong-Ik , Song Ki-Im , Lee Su Jin , Chu Hye Yong
Published: May 2008

We demonstrate that the electroluminescence efficiencies of blue organic light-emitting diodes can be significantly enhanced by the incorporation of interlayers at the hole transporting layer (HTL)/emitting layer (EML) and/or EML/electron transporting layer (ETL) interfaces. Blue light-emitting iridium(III)bis(4,6-difluorophenyl)-pyridinato-N,C2′) picolinate was doped in an m-bis-(triphenylsilyl)benzene (UGH3) host and hole transporting wide band gap materials were introduced between the HTL and the EML as interlayers in order to block triplet exciton quenching and reduce electron overflow. The effects of adding a second undoped UGH3 interlayer at the EML/ETL interface were also studied. When the appropriate interlayers were added, the device performances were found to be dramatically enhanced, with peak external quantum and power efficiencies of 20.1% and 29.2lm∕W.
Energy transfer and enhanced luminescence in metal oxide nanoparticle and rare earth codoped silica
Authors: Wan Neng , Xu Jun , Lin Tao , Zhang Xiangao , Xu Ling
Published: May 2008

A significant enhancement of photoluminescence from Eu3+ embedded in SiO2 matrix is observed by codoping with wide band-gap In2O3 nanoparticles. The enhanced photoluminescence characteristics are strongly influenced by the postannealing temperature and the In3+ concentration. Synchronous scanning photoluminescence technique was used to understand the excitation and luminescence behavior in codoped silica films. Based on the experimental results, we argue that the enhancement of photoluminescence is associated with the effective energy transfer process from In2O3 nanoparticles to the charge transfer band of O2+–Eu3+ instead of the direct transfer to the rare-earth energy levels.
Carbohydrate-Based Tolylsulfonyl Hydrazines: Effective Catalysts for the Mannich Reaction and the Syntheses of Bisindolylalkanes in Water
Authors: Wu Peng , Wan Yiqian , Cai Jiwen
Published: May 2008

Three carbohydrate-based tolylsulfonyl hydrazines were used to catalyze the three-component Mannich reaction, as well as the adduct reaction of aldehyde and indole to prepare bisindolylalkanes in water. Moderate to good yields were achieved. The results demonstrate that carbohydrate derivatives can be employed as effective catalysts in water, and an environmentally benign methodology was developed to synthesize bioactive bisindolylalkanes and the β-amino carbonyl framework.
Manganese(II) Complexes with a Bulky Anthracene-Based Dicarboxylic Ligand: Syntheses, Crystal Structures, and Magnetic Properties
Authors: Liu Chun-Sen , Sañudo E. Carolina , Wang Jun-Jie , Chang Ze , Yan Li-Fen , Bu Xian-He
Published: May 2008

To investigate the influence of the bulky aromatic ring skeleton with a large conjugated π-system on the structures and properties of its complexes, two MnII complexes with the anthracene-based dicarboxylic ligand anthracene-9,10-dicarboxylic acid (H2L) and different 2,2′-bipyridyl-like chelating ligands were synthesized and characterized: {[Mn2(L)2(bipy)2(H2O)2]}∞ (1) and {[Mn(L)(phen)2](H2O)2.5}∞ (2) (L = anthracene-9,10-dicarboxylate, bipy = 2,2′-bipyridine, and phen = 1,10-phenanthroline). Complex 1 has a (4,4) two-dimensional (2D) sheet structure that is further assembled to form a three-dimensional (3D) supramolecular network by the co-effects of C–H···π and O–H···O hydrogen-bonding interactions. Complex 2 adopts a one-dimensional (1D) polymeric chain structure by using the chelating phen instead of bipy in 1, which is further interlinked by interchain C–H···π interactions, which results in a higher-dimensional supramolecular network from the different crystallographic directions. The relevant results reveal that the steric bulk of the anthracene ring in H2L may play an important role in the formation of 1 and 2. Moreover, the magnetic properties of 1 and 2 show that the long Mn···Mn intermetallic separations result in weak magnetic coupling, along with the corresponding coupling constant J parameters related to their structural characteristics, –0.35 cm–1 for 1 and –3.0 cm–1 for 2.
Incorporating a Transition Metal Complex into Polymeric Iodoplumbate: Structure Characterization, Properties and Theoretical Study of a Unprecedented Hybrid Semiconductor: {[Cu(en)2][Pb2I6]}n
Authors: Li Hao-Hong , Sun Ling-Guo , Chen Zhi-Rong , Wang Yun-Jie , Li Jun-Qian
Published: May 2008

A hybrid semiconductor {[Cu(en)2][Pb2I6]}n (1) (en = ethylenediamine) templated by a transition metal complex was synthesized and structurally characterized. The title compound consists of discrete structure-directing molecules (transition metal complex) and an inorganic iodoplumbate polymer. The iodoplumbate polymer could be described as a three-dimensional network constructed from a [Pb2I8]n4– double chain bridged by iodine. [Cu(en)2]2+ structure-directing cations are discrete, and interact with the inorganic moiety by strong static attraction and the H-bond of N–H···I to give a so-called hybrid structure. Experimental and theoretical optical property investigations indicate that 1 possesses semiconductor properties. A density functional theory calculation was executed to probe the regulation effect on the introduction of a second metal.
DNA-Binding and Photocleavage Behaviour of [Ru(bpy)2(MDPZ)]2+
Authors: Tan Lifeng , Chao Hui , Fei Junjie , Su Guojun , Zhang Sheng , Xia Yue , Ji Liangnian
Published: May 2008

The new ligand MDPZ (MDPZ = 7,7′-methylenedioxyphenyldipyrido[3,2-a:2′,3′-c]-phenazine and its RuII complex [Ru(bpy)2(MDPZ)]2+ (phen = 1,10-phenanthroline) was synthesized and characterized by elemental analysis, mass spectrometry, and 1H NMR spectroscopy. The DNA-binding properties of [Ru(bpy)2(MDPZ)]2+ were investigated by different spectrophotometric methods and viscosity measurements. The results suggest that the complex binds to CT-DNA through intercalation, and can enantioselectively interact with CT-DNA. Although the [Ru(bpy)2(MDPZ)]2+ complex does not show the characteristics of a molecular ‘light switch’ for DNA, [Ru(phen)2(MDPZ)]2+ may serve as a sensitive luminescent probe for DNA. Also, when irradiated at 365 nm, the complex promotes the photocleavage of pBR 322 DNA.
N,N-Dialkyl-N′-Chlorosulfonyl Chloroformamidines in Heterocyclic Synthesis. VI. The Preparation of Some Fused [1,4,2,6]Dithiadiazine Dioxides
Authors: Cablewski Teresa , Francis Craig L. , Liepa Andris J.
Published: May 2008

N,N-Dialkyl-N′-chlorosulfonylchloroformamidines 1 were treated with 2-mercaptobenzimidazoles 2 to give [1,4,2,6]dithiadiazino[2,3-a]benzimidazole 1,1-dioxides 3. 3-Mercapto[1,2,4]triazoles 5 afforded [1,2,4]triazolo[2,3-b][1,4,2,6]dithiadiazine 1,1-dioxides 6 and [1,2,4]triazolo[4,3-b][1,4,2,6]dithiadiazine 1,1-dioxides 7. These products are derivatives of new or very rare heterocycles.
Entrapment of an Ionic Liquid in a Metallic Silver Matrix through Precipitation
Authors: Neouze Marie-Alexandra , Litschauer Marco
Published: May 2008

Entrapment of an ionic liquid within metallic silver by means of physical caging is described. Thermal analysis of this new silver-based composite material allows estimation of the 1-butyl-3-methylimidazolium nitrate entrapment efficiency at 98%.
Modularity of stress response evolution
Authors: Singh Amoolya H. , Wolf Denise M. , Wang Peggy , Arkin Adam P.
Published: May 2008

Responses to extracellular stress directly confer survival fitness by means of complex regulatory networks. Despite their complexity, the networks must be evolvable because of changing ecological and environmental pressures. Although the regulatory networks underlying stress responses are characterized extensively, their mechanism of evolution remains poorly understood. Here, we examine the evolution of three candidate stress response networks (chemotaxis, competence for DNA uptake, and endospore formation) by analyzing their phylogenetic distribution across several hundred diverse bacterial and archaeal lineages. We report that genes in the chemotaxis and sporulation networks group into well defined evolutionary modules with distinct functions, phenotypes, and substitution rates as compared with control sets of randomly chosen genes. The evolutionary modules vary in both number and cohesiveness among the three pathways. Chemotaxis has five coherent modules whose distribution among species shows a clear pattern of interdependence and rewiring. Sporulation, by contrast, is nearly monolithic and seems to be inherited vertically, with three weak modules constituting early and late stages of the pathway. Competence does not seem to exhibit well defined modules either at or below the pathway level. Many of the detected modules are better understood in engineering terms than in protein functional terms, as we demonstrate using a control-based ontology that classifies gene function according to roles such as “sensor,” “regulator,” and “actuator.” Moreover, we show that combinations of the modules predict phenotype, yet surprisingly do not necessarily correlate with phylogenetic inheritance. The architectures of these three pathways are therefore emblematic of different modes and constraints on evolution.
Overcoming retinoic acid-resistance of mammary carcinomas by diverting retinoic acid from PPARβ/δ to RAR
Authors: Schug Thaddeus T. , Berry Daniel C. , Toshkov Illia A. , Cheng Le , Nikitin Alexander Yu , Noy Noa
Published: May 2008

Retinoic acid (RA) displays potent anticarcinogenic activities that are mediated by the nuclear retinoic acid receptors (RARs). However, use of RA in oncology is limited by RA resistance acquired during carcinogenesis. Moreover, in some cancers, RA facilitates rather than inhibits growth. A clue to this paradoxical behavior was recently suggested by the findings that RA also activates PPARβ/δ, a receptor involved in mitogenic and anti-apoptotic activities. The observations that partitioning of RA between its two receptors is regulated by two intracellular lipid-binding proteins—CRABP-II, which targets RA to RAR, and FABP5, which delivers it to PPARβ/δ—further suggest that RA resistance may stem from the deregulation of the binding proteins, resulting in activation of PPARβ/δ rather than RAR. Here, we show that, in the RA-resistant mouse model of breast cancer
MMTV-neu
, RA indeed activates the nonclassical RA receptor PPARβ/δ. This behavior was traced to an aberrantly high intratumor FABP5/CRABP-II ratio. Decreasing this ratio in mammary tissue diverted RA from PPARβ/δ to RAR and suppressed tumor growth. The data demonstrate the existence of a mechanism that underlies RA resistance in tumors, indicate that CRABP-II functions as a tumor suppressor, and suggest that the inhibition of FABP5 may comprise a therapeutic strategy for overcoming RA resistance in some tumors.
Biochemical visualization of cell surface molecular clustering in living cells
Authors: Kotani Norihiro , Gu Jianguo , Isaji Tomoya , Udaka Keiko , Taniguchi Naoyuki , Honke Koichi
Published: May 2008

Many plasma membrane-resident molecules cluster with other molecules to collaborate in a variety of biological events. We herein report a sensitive and simple method to identify components of cell surface molecular clusters in living cells. This method includes a recently established reaction, called the enzyme-mediated activation of radical source (EMARS), to label molecules within a limited distance (≈200–300 nm) from the probed molecule on which HRP is set. Because the size of this active area is close to that of the reported membrane clusters, it is suggested that the labeled molecules cluster with the probed molecule in the same membrane domain. A combination of the EMARS reaction and antibody array analysis demonstrated that many kinds of receptor tyrosine kinases (RTKs) formed clusters with β1 integrin in HeLa S3 cells. A similar antibody array analysis after the EMARS reaction with three HRP-labeled antibodies against growth factor receptors showed the patterns of biotinylated RTKs to be substantially different from each other. These results suggest that different types of cell surface molecular clusters can thus be distinguished using the EMARS reaction. Therefore, the present “biochemical visualization” method is expected to be a powerful tool to elucidate molecular clustering on the cell surface of living cells in various contexts.
Crystal structure and thermoelastic properties of (Mg
0.91
Fe
0.09
)SiO
3
postperovskite up to 135 GPa and 2,700 K
Authors: Shim Sang-Heon , Catalli Krystle , Hustoft Justin , Kubo Atsushi , Prakapenka Vitali B. , Caldwell Wendel A. , Kunz Martin
Published: May 2008

Intriguing seismic observations have been made for the bottom 400 km of Earth's mantle (the D″ region) over the past few decades, yet the origin of these seismic structures has not been well understood. Recent theoretical calculations have predicted many unusual changes in physical properties across the postperovskite transition, perovskite (Pv) → postperovskite (PPv), that may provide explanations for the seismic observations. Here, we report measurements of the crystal structure of (Mg
0.91
Fe
0.09
)SiO
3
-PPv under quasi-hydrostatic conditions up to the pressure (
P
)–temperature (
T
) conditions expected for the core-mantle boundary (CMB). The measured crystal structure is in excellent agreement with the first-principles calculations. We found that bulk sound speed (
V
Φ
) decreases by 2.4 ± 1.4% across the PPv transition. Combined with the predicted shear-wave velocity (

V
S

) increase, our measurements indicate that lateral variations in mineralogy between Pv and PPv may result in the anticorrelation between the
V
Φ
and

V
S

anomalies at the D″ region. Also, density increases by 1.6 ± 0.4% and Grüneisen parameter decreases by 21 ± 15% across the PPv transition, which will dynamically stabilize the PPv lenses observed in recent seismic studies.
Reproductive mode plasticity: Aquatic and terrestrial oviposition in a treefrog
Authors: Touchon Justin Charles , Warkentin Karen Michelle
Published: May 2008

Diversification of reproductive mode is a major theme in animal evolution. Vertebrate reproduction began in water, and terrestrial eggs evolved multiple times in fishes and amphibians and in the amniote ancestor. Because oxygen uptake from water conflicts with water retention in air, egg adaptations to one environment typically preclude development in the other. Few animals have variable reproductive modes, and no vertebrates are known to lay eggs both in water and on land. We report phenotypic plasticity of reproduction with aquatic and terrestrial egg deposition by a frog. The treefrogDendropsophus ebraccatus, known to lay eggs terrestrially, also lays eggs in water, both at the surface and fully submerged, and chooses its reproductive mode based on the shade above a pond. Under unshaded conditions, in a disturbed habitat and in experimental mesocosms, these frogs lay most of their egg masses aquatically. The same pairs also can lay eggs terrestrially, on vegetation over water, even during a single night. Eggs can survive in both aquatic and terrestrial environments, and variable mortality risks in each may make oviposition plasticity adaptive. Phylogenetically,D. ebraccatusbranches from the basal node in a clade of terrestrially breeding species, nested within a larger lineage of aquatic-breeding frogs. Reproductive plasticity inD. ebraccatusmay represent a retained ancestral state intermediate in the evolution of terrestrial reproduction.
Deletion of a gene encoding an amino acid transporter in the midgut membrane causes resistance to a
Bombyx
parvo-like virus
Authors: Ito Katsuhiko , Kidokoro Kurako , Sezutsu Hideki , Nohata Junko , Yamamoto Kimiko , Kobayashi Isao , Uchino Keiro , Kalyebi Andrew , Eguchi Ryokitsu , Hara Wajiro , Tamura Toshiki , Katsuma Susumu , Shimada Toru , Mita Kazuei , Kadono-Okuda Keiko
Published: May 2008

Bombyx mori
densovirus type 2 (BmDNV-2), a parvo-like virus, replicates only in midgut columnar cells and causes fatal disease. The resistance expressed in some silkworm strains against the virus is determined by a single gene,
nsd-2
, which is characterized as nonsusceptibility irrespective of the viral dose. However, the responsible gene has been unknown. We isolated the
nsd-2
gene by positional cloning. The virus resistance is caused by a 6-kb deletion in the ORF of a gene encoding a 12-pass transmembrane protein, a member of an amino acid transporter family, and expressed only in midgut. Germ-line transformation with a wild-type transgene expressed in the midgut restores susceptibility, showing that the defective membrane protein is responsible for resistance. Cumulatively, our data show that the membrane protein is a functional receptor for BmDNV-2. This is a previously undescribed report of positional cloning of a mutant gene in
Bombyx
and isolation of an absolute virus resistance gene in insects.
Transcription factor Ap2δ associates with Ash2l and ALR, a trithorax family histone methyltransferase, to activate
Hoxc8
transcription
Authors: Tan Cheryl C. , Sindhu K. V. , Li SiDe , Nishio Hitomi , Stoller Jason Z. , Oishi Kimihiko , Puttreddy Sahitya , Lee Tamara J. , Epstein Jonathan A. , Walsh Martin J. , Gelb Bruce D.
Published: May 2008

The family of Ap2 transcription factors comprises five members with highly conserved DNA-binding domains. Among the family members, Ap2δ is the most divergent, because it lacks highly conserved residues within the transactivation domain (TAD) and has weak affinity for known Ap2 binding sites. To identify specific Ap2δ coactivators/regulators during development, we performed a yeast two-hybrid screen, using Ap2δ's TAD. We identified the trithorax superfamily member, Ash2l, as a binding partner that interacts exclusively with Ap2δ. We showed that Ash2l positively mediates Ap2δ transactivation in a dose-dependent manner. Given the known role of Ash2l in histone modification, we determined whether Ap2δ was able to form a complex with that activity. Our results showed that Ap2δ associates with endogenous ASH2L and a member of the MLL family of histone lysine methyltransferases (HKMTs), MLL2 (ALR), forming a complex that methylates lysine 4 of histone H3 (H3K4). Additionally, we showed that Ap2δ is necessary for recruitment of Ash2l and Alr to the
Hoxc8
locus and that recruitment of this complex leads to H3K4 trimethylation (H3K4me3) and subsequent gene activation. Altogether, we provide evidence of an association between a highly restricted gene-specific transcription factor and a Su(var), Enhancer of Zeste, Trithorax (SET)1/trithorax-like complex with H3K4 methyltransferase activity. Our studies also document a functional role for Ap2δ in recruiting histone methyltransferases (HMTs) to specific gene targets, such as
Hoxc8
. This role provides a mechanism through which these transcription factors can have diverse effects despite nearly identical DNA-binding motifs.
Hydrodynamic metamaterials: Microfabricated arrays to steer, refract, and focus streams of biomaterials
Authors: Morton Keith J. , Loutherback Kevin , Inglis David W. , Tsui Ophelia K. , Sturm James C. , Chou Stephen Y. , Austin Robert H.
Published: May 2008

We show that it is possible to direct particles entrained in a fluid along trajectories much like rays of light in classical optics. A microstructured, asymmetric post array forms the core hydrodynamic element and is used as a building block to construct microfluidic metamaterials and to demonstrate refractive, focusing, and dispersive pathways for flowing beads and cells. The core element is based on the concept of deterministic lateral displacement where particles choose different paths through the asymmetric array based on their size: Particles larger than a critical size are displaced laterally at each row by a post and move along the asymmetric axis at an angle to the flow, while smaller particles move along streamline paths. We create compound elements with complex particle handling modes by tiling this core element using multiple transformation operations; we show that particle trajectories can be bent at an interface between two elements and that particles can be focused into hydrodynamic jets by using a single inlet port. Although particles propagate through these elements in a way that strongly resembles light rays propagating through optical elements, there are unique differences in the paths of our particles as compared with photons. The unusual aspects of these modular, microfluidic metamaterials form a rich design toolkit for mixing, separating, and analyzing cells and functional beads on-chip.
Structure of the membrane proximal oxidoreductase domain of human Steap3, the dominant ferrireductase of the erythroid transferrin cycle
Authors: Sendamarai Anoop K. , Ohgami Robert S. , Fleming Mark D. , Lawrence C. Martin
Published: May 2008

The daily production of 200 billion erythrocytes requires 20 mg of iron, accounting for nearly 80% of the iron demand in humans. Thus, erythroid precursor cells possess an efficient mechanism for iron uptake in which iron loaded transferrin (Tf) binds to the transferrin receptor (TfR) at the cell surface. The Tf:TfR complex then enters the endosome via receptor-mediated endocytosis. Upon endosomal acidification, iron is released from Tf, reduced to Fe
2+
by Steap3, and transported across the endosomal membrane by divalent metal iron transporter 1. Steap3, the major ferrireductase in erythrocyte endosomes, is a member of a unique family of reductases. Steap3 is comprised of an N-terminal cytosolic oxidoreductase domain and a C-terminal heme-containing transmembrane domain. Cytosolic NADPH and a flavin are predicted cofactors, but the NADPH/flavin binding domain differs significantly from those in other eukaryotic reductases. Instead, Steap3 shows remarkable, although limited homology to FNO, an archaeal oxidoreductase. We have determined the crystal structure of the human Steap3 oxidoreductase domain in the absence and presence of NADPH. The structure reveals an FNO-like domain with an unexpected dimer interface and substrate binding sites that are well positioned to direct electron transfer from the cytosol to a heme moiety predicted to be fixed within the transmembrane domain. Here, we discuss possible gating mechanisms for electron transfer across the endosomal membrane.
Complementary dimerization of microtubule-associated tau protein: Implications for microtubule bundling and tau-mediated pathogenesis
Authors: Rosenberg Kenneth J. , Ross Jennifer L. , Feinstein H. Eric , Feinstein Stuart C. , Israelachvili Jacob
Published: May 2008

Tau is an intrinsically unstructured microtubule (MT)-associated protein capable of binding to and organizing MTs into evenly spaced parallel assemblies known as “MT bundles.” How tau achieves MT bundling is enigmatic because each tau molecule possesses only one MT-binding region. To dissect this complex behavior, we have used a surface forces apparatus to measure the interaction forces of the six CNS tau isoforms when bound to mica substrates
in vitro
. Two types of measurements were performed for each isoform: symmetric configuration experiments measured the interactions between two tau-coated mica surfaces, whereas “asymmetric” experiments examined tau-coated surfaces interacting with a smooth bare mica surface. Depending on the configuration (of which there were 12), the forces were weakly adhesive, strongly adhesive, or purely repulsive. The equilibrium spacing was determined mainly by the length of the tau projection domain, in contrast to the adhesion force/energy, which was determined by the number of repeats in the MT-binding region. Taken together, the data are incompatible with tau acting as a monomer; rather, they indicate that two tau molecules associate in an antiparallel configuration held together by an electrostatic “zipper” of complementary salt bridges composed of the N-terminal and central regions of each tau monomer, with the C-terminal MT-binding regions extending outward from each end of the dimeric backbone. This tau dimer determines the length and strength of the linker holding two MTs together and could be the fundamental structural unit of tau, underlying both its normal and pathological action.
Functional analysis of theArabidopsiscentromere by T-DNA insertion-induced centromere breakage
Authors: Murata Minoru , Yokota Etsuko , Shibata Fukashi , Kashihara Kazunari
Published: May 2008

Two minichromosomes (α and δ) in addition to two other aberrant chromosomes (β and γ) were found in a transgenicArabidopsisplant produced by anin plantavacuum infiltration technique. The minichromosomes were successfully separated by successive crossing and selfing and added to wild-type Columbia (Col-0) as a supernumerary chromosome. FISH indicated that both of the two minichromosomes originated from the short arm of chromosome 2. The mini α chromosome contained the whole short-arm 2S and a truncated centromere (180-bp repeat cluster), whereas mini δ lacked the terminal region including telomere repeats. Pachytene FISH clearly revealed that mini δ comprised a ring chromosome carrying two copies of the region from the 180-bp repeat cluster to BAC-F3C11. Both of the 180-bp clusters (each ≈500 kb in length) were thought to possess normal centromere functions because the centromere-specific histone H3 variant (HTR12) was detected on both clusters. Notwithstanding this dicentric and ring form, mini δ was stably transmitted to the next generations, perhaps because of its compact size (<4 Mb). Chromosome β also comprised a dicentric-like structure, with one of the two 180-bp repeat sites derived from chromosome 1 and the other from chromosome 2. However, the latter was quite small and failed to bind HTR12. The data obtained in this study indicated that 500 kb of the 180-bp array of the chromosome 2 centromere, from the edge of the 180-bp array on the short-arm side, is sufficient to form a functional domain.
Modulation of auditory processing by cortico-cortical feed-forward and feedback projections
Authors: Tang Jie , Suga Nobuo
Published: May 2008

The auditory center in the cerebrum, the auditory cortex, consists of multiple interconnected areas. The functional role of these interconnections is poorly understood. The auditory cortex of the mustached bat consists of at least nine areas, including the frequency modulation–frequency modulation (FF) and dorsal fringe (DF) areas. The FF and DF areas consist of neurons tuned to specific echo delays carrying target-distance information. The DF area is hierarchically at a higher level than the FF area. Here, we show that the feedback projection from the DF area to the FF area shifts the delay-tuning of FF neurons toward that of the stimulated DF neurons. In contrast, the feed-forward projection from the FF area to the DF area shifts the delay-tuning of DF neurons away from that of the stimulated FF neurons. The lateral projection within the DF area shifts the delay-tuning of DF neurons toward that of the stimulated DF neurons. In contrast, the lateral projection within the FF area shifts the delay-tuning of FF neurons away from that of the stimulated FF neurons. The delay-tuning shift evoked by the DF stimulation was 2.5 times larger than that evoked by the FF stimulation. Our data indicate that the FF–DF feed-forward and FF–FF lateral projections shape the highly selective neural representation of the tuning of the excited DF neurons, whereas the DF–FF feedback and DF–DF lateral projections enhance the representation of the selected tuning, perhaps, for focal processing of information carried by the excited FF neurons.
A drug-controllable tag for visualizing newly synthesized proteins in cells and whole animals
Authors: Lin Michael Z. , Glenn Jeffrey S. , Tsien Roger Y.
Published: May 2008

Research on basic cellular processes involving local production or delivery of proteins, such as activity-dependent synaptic modification in neurons, would benefit greatly from a robust, nontoxic method to visualize selectively newly synthesized copies of proteins of interest within cells, tissues, or animals. We report a technique for covalent labeling of newly synthesized proteins of interest based on drug-dependent preservation of epitope tags. Epitope tags are removed from proteins of interest immediately after translation by the activity of a sequence-specific protease until the time a protease inhibitor is added, after which newly synthesized protein copies retain their tags. This method, which we call TimeSTAMP for time-specific tagging for the age measurement of proteins, allows sensitive and nonperturbative visualization and quantification of newly synthesized proteins of interest with exceptionally tight temporal control. We demonstrate applications of TimeSTAMP in retrospectively identifying growing synapses in cultured neurons and in visualizing the distribution of recently synthesized proteins in intact fly brains.
Elucidation of a TRPC6-TRPC5 Channel Cascade That Restricts Endothelial Cell Movement
Authors: Chaudhuri Pinaki , Colles Scott M. , Bhat Manjunatha , Van Wagoner David R. , Birnbaumer Lutz , Graham Linda M.
Published: May 2008

Canonical transient receptor potential (TRPC) channels are opened by classical signal transduction events initiated by receptor activation or depletion of intracellular calcium stores. Here, we report a novel mechanism for opening TRPC channels in which TRPC6 activation initiates a cascade resulting in TRPC5 translocation. When endothelial cells (ECs) are incubated in lysophosphatidylcholine (lysoPC), rapid translocation of TRPC6 initiates calcium influx that results in externalization of TRPC5. Activation of this TRPC6–5 cascade causes a prolonged increase in intracellular calcium concentration ([Ca2+]i) that inhibits EC movement. When TRPC5 is down-regulated with siRNA, the lysoPC-induced rise in [Ca2+]iis shortened and the inhibition of EC migration is lessened. When TRPC6 is down-regulated or EC from TRPC6−/−mice are studied, lysoPC has minimal effect on [Ca2+]iand EC migration. In addition, TRPC5 is not externalized in response to lysoPC, supporting the dependence of TRPC5 translocation on the opening of TRPC6 channels. Activation of this novel TRPC channel cascade by lysoPC, resulting in the inhibition of EC migration, could adversely impact on EC healing in atherosclerotic arteries where lysoPC is abundant.
An Essential Role for MCL-1 in ATR-mediated CHK1 Phosphorylation
Authors: Jamil Sarwat , Mojtabavi Shadi , Hojabrpour Payman , Cheah Stefanie , Duronio Vincent
Published: May 2008

Here we report a novel role for myeloid cell leukemia 1 (Mcl-1), a Bcl-2 family member, in regulating phosphorylation and activation of DNA damage checkpoint kinase, Chk1. Increased expression of nuclear Mcl-1 and/or a previously reported short nuclear form of Mcl-1, snMcl-1, was observed in response to treatment with low concentrations of etoposide or low doses of UV irradiation. We showed that after etoposide treatment, Mcl-1 could coimmunoprecipitate with the regulatory kinase, Chk1. Chk1 is a known regulator of DNA damage response, and its phosphorylation is associated with activation of the kinase. Transient transfection with Mcl-1 resulted in an increase in the expression of phospho-Ser345 Chk1, in the absence of any evidence of DNA damage, and accumulation of cells in G2. Importantly, knockdown of Mcl-1 expression abolished Chk1 phosphorylation in response to DNA damage. Mcl-1 could induce Chk1 phosphorylation in ATM-negative (ataxia telangectasia mutated) cells, but this response was lost in ATR (AT mutated and Rad3 related)-defective cells. Low levels of UV treatment also caused transient increases in Mcl-1 levels and an ATR-dependent phosphorylation of Chk1. Together, our results strongly support an essential regulatory role for Mcl-1, perhaps acting as an adaptor protein, in controlling the ATR-mediated regulation of Chk1 phosphorylation.
Connexin Hemichannel Composition Determines the FGF-1–induced Membrane Permeability and Free [Ca2+]iResponses
Authors: Schalper Kurt A. , Palacios-Prado Nicolás , Retamal Mauricio A. , Shoji Kenji F. , Martínez Agustín D. , Sáez Juan C.
Published: May 2008

Cell surface hemichannels (HCs) composed of different connexin (Cx) types are present in diverse cells and their possible role on FGF-1–induced cellular responses remains unknown. Here, we show that FGF-1 transiently (4–14 h, maximal at 7 h) increases the membrane permeability through HCs in HeLa cells expressing Cx43 or Cx45 under physiological extracellular Ca2+/Mg2+concentrations. The effect does not occur in HeLa cells expressing HCs constituted of Cx26 or Cx43 with its C-terminus truncated at aa 257, or in parental nontransfected HeLa cells. The increase in membrane permeability is associated with a rise in HC levels at the cell surface and a proportional increase in HC unitary events. The response requires an early intracellular free Ca2+concentration increase, activation of a p38 MAP kinase-dependent pathway, and a regulatory site of Cx subunit C-terminus. The FGF-1–induced rise in membrane permeability is also associated with a late increase in intracellular free Ca2+concentration, suggesting that responsive HCs allow Ca2+influx. The cell density of Cx26 and Cx43 HeLa transfectants cultured in serum-free medium was differentially affected by FGF-1. Thus, the FGF-1–induced cell permeabilization and derived consequences depend on the Cx composition of HCs.
Molecular Dissection of the Structural Machinery Underlying the Tissue-invasive Activity of Membrane Type-1 Matrix Metalloproteinase
Authors: Li Xiao-Yan , Ota Ichiro , Yana Ikuo , Sabeh Farideh , Weiss Stephen J.
Published: May 2008

Membrane type-1 matrix metalloproteinase (MT1-MMP) drives cell invasion through three-dimensional (3-D) extracellular matrix (ECM) barriers dominated by type I collagen or fibrin. Based largely on analyses of its impact on cell function under two-dimensional culture conditions, MT1-MMP is categorized as a multifunctional molecule with 1) a structurally distinct, N-terminal catalytic domain; 2) a C-terminal hemopexin domain that regulates substrate recognition as well as conformation; and 3) a type I transmembrane domain whose cytosolic tail controls protease trafficking and signaling cascades. The MT1-MMP domains that subserve cell trafficking through 3-D ECM barriers in vitro or in vivo, however, remain largely undefined. Herein, we demonstrate that collagen-invasive activity is not confined strictly to the catalytic, hemopexin, transmembrane, or cytosolic domain sequences of MT1-MMP. Indeed, even a secreted collagenase supports invasion when tethered to the cell surface in the absence of the MT1-MMP hemopexin, transmembrane, and cytosolic tail domains. By contrast, the ability of MT1-MMP to support fibrin-invasive activity diverges from collagenolytic potential, and alternatively, it requires the specific participation of MT-MMP catalytic and hemopexin domains. Hence, the tissue-invasive properties of MT1-MMP are unexpectedly embedded within distinct, but parsimonious, sequences that serve to tether the requisite matrix-degradative activity to the surface of migrating cells.
More Than a Repair Enzyme:Aspergillus nidulansPhotolyase-like CryA Is a Regulator of Sexual Development
Authors: Bayram Özgür , Biesemann Christoph , Krappmann Sven , Galland Paul , Braus Gerhard H.
Published: May 2008

Cryptochromes are blue-light receptors that have presumably evolved from the DNA photolyase protein family, and the genomes of many organisms contain genes for both types of molecules. Both protein structures resemble each other, which suggests that light control and light protection share a common ancient origin. In the genome of the filamentous fungus Aspergillus nidulans, however, only one cryptochrome/photolyase-encoding gene, termed cryA, was identified. Deletion of the cryA gene triggers sexual differentiation under inappropriate culture conditions and results in up-regulation of transcripts encoding regulators of fruiting body formation. CryA is a protein whose N- and C-terminal synthetic green fluorescent protein fusions localize to the nucleus. CryA represses sexual development under UVA350-370 nmlight both on plates and in submerged culture. Strikingly, CryA exhibits photorepair activity as demonstrated by heterologous complementation of a DNA repair-deficient Escherichia coli strain as well as overexpression in an A. nidulans uvsBΔ genetic background. This is in contrast to the single deletion cryAΔ strain, which does not show increased sensitivity toward UV-induced damage. In A. nidulans, cryA encodes a novel type of cryptochrome/photolyase that exhibits a regulatory function during light-dependent development and DNA repair activity. This represents a paradigm for the evolutionary transition between photolyases and cryptochromes.