bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma emission by a nonlinear beam instability
Authors: Yoon Peter H.
Published: July 2002

A new theory for electromagnetic radiation emission with wave frequency at the plasma frequency and/or its harmonic (known as the plasma emission) is presented. According to the new theory, the radiation emission takes place as a result of combined effects of the excitation of electrostatic waves by a nonlinear beam instability, and the concurrent conversion into electromagnetic waves by a nonlinear mode coupling process. The underlying physical mechanism for the nonlinear beam instability is an interaction of energetic electron beam with enhanced ion-acoustic or Langmuir turbulence. The turbulence, which is treated as intrinsic in the present analysis, also gives rise to the nonlinear mode coupling process between the electrostatic and electromagnetic modes. That is, the two processes (nonlinear instability and mode coupling) occur concomitantly. An important aspect of the present theory is that the effective growth rate associated with the radiation is comparable to the usual beam–plasma (or bump-in-tail) instability growth rate, which makes the radiation emission process very efficient, a feature very different from any standard theory.
Anomalous diffusion and Lévy random walk of magnetic field lines in three dimensional turbulence
Authors: Zimbardo G. , Veltri P. , Basile G. , Principato S.
Published: July 2002

The transport of magnetic field lines is studied numerically where three dimensional (3-D) magnetic fluctuations, with a power law spectrum, and periodic over the simulation box are superimposed on an average uniform magnetic field. The weak and the strong turbulence regime, δB∼B0, are investigated. In the weak turbulence case, magnetic flux tubes are separated from each other by percolating layers in which field lines undergo a chaotic motion. In this regime the field lines may exhibit Lévy, rather than Gaussian, random walk, changing from Lévy flights to trapped motion. The anomalous diffusion laws 〈Δx2i〉∝sα with α≳1 and α<1, are obtained for a number of cases, and the non-Gaussian character of the field line random walk is pointed out by computing the kurtosis. Increasing the fluctuation level, and, therefore stochasticity, normal diffusion (α≂1) is recovered and the kurtoses reach their Gaussian value. However, the numerical results show that neither the quasi-linear theory nor the two dimensional percolation theory can be safely extrapolated to the considered 3-D strong turbulence regime.
Ion-acoustic compressive and rarefactive solitons in a warm multicomponent plasma with negative ions
Authors: Mishra M. K. , Chhabra R. S.
Published: July 2002

Propagation of ion-acoustic solitons in a plasma consisting of warm positive and negative ion species with different masses, concentrations, and charge states, along with hot electrons, is studied. It is found that the finite temperatures of two ion species give rise to two types of modes, i.e., a slow ion-acoustic mode and a fast ion-acoustic mode. For all values of negative ion concentration, the slow wave mode supports compressive (rarefactive) solitons, when the negative ion species has a higher (lower) temperature than the positive ion species. The fast wave mode supports compressive solitons for low concentration of negative ions. At the critical concentration of negative ions both compressive and rarefactive modified Korteweg–de Vries solitons coexist. Above this critical concentration the system supports rarefactive solitons. The dependence of the critical concentration on the temperatures of two ion species is also discussed.
Rarefactive ion acoustic soliton excitation using a modulated high-frequency sinusoidal wave in a negative ion plasma
Authors: Yi Seungjun , Lonngren Karl E.
Published: July 2002

Experiments on the excitation of rarefactive ion acoustic solitons using a fine mesh grid in a negative ion plasma are described. The excitation is novel in that a modulated high-frequency sinusoidal wave voltage signal is applied to the grid. An interpretation of the velocity modulation and bunching of free-streaming ions that pass through the grid to which the signal is applied is given.
An analytical theory of a gas-filled diode
Authors: Uhm Han S. , Choi Eun H. , Cho Guangsup
Published: July 2002

A theory of a gas-filled diode is developed by making use of the fractional charge neutralization f originating from the ionization of neutrals in the diode. The diode voltage is self-consistently determined in terms of the gas pressure and species. Ions in the diode are created from neutral particles by the electron impact-ionization. A formula for circuit analysis is obtained, including external elements. Several points are noteworthy from the theoretical study. First, as expected, the fractional charge neutralization approaches unity rather quickly for a high gas density. Second, the profile of a gas-filled diode voltage is very different from that of the vacuum-diode voltage. Third, the strength of the gas-filled diode voltage decreases drastically as the neutral number density increases. Fourth, it is also shown that time profile of the gas-filled diode voltage deviates dramatically from the sine waveform, although the diode current is very close to the waveform. The gas-filled diode voltage is therefore very sensitive to the gas pressure in the diode.
Dynamical behavior of the soliton formation and propagation in magnetized plasma
Authors: Das G. C. , Sarma J. , Gao Yi-Tian , Uberoi C.
Published: July 2002

Despite many theoretical studies on soliton formation and its propagation in plasmas, no study with multicomponent magnetized plasma has derived the special nonlinear wave equation, called the Zakharov–Kuznetsov equation [V. E. Zakharov and E. A. Kuznetsov, Sov. Phys. JETP 39, 285 (1974)]. Thus, the main emphasis has been given to employing the hyperbolic-type method for finding the soliton features in relation to laboratory and space plasma environments. Where this method has been unsuccessful, an alternate method has been developed to yield the soliton propagation. The features of the nonlinear plasma-acoustic waves, which depend on the plasma composition, affect the coexistence of compressive and rarefactive solitary waves. Later, allowing for the higher order nonlinearity in the dynamics, one is led to further different solitary waves along with double layers. The main aim of the present study is to use a new formalism for finding the soliton propagation from the nonlinear wave equation with strong, as well as weak, nonlinearity. The coexistence of different nonlinear acoustic modes due to the interaction of multiple charges in plasma is shown. Moreover, the theoretical observations revealed many other soliton-like structures, which could be similar to the dip and hump solitons observed by the Freja Scientific Satellite and the collapsed solitons expected in the propagation of solar flares, as well as in the interplanetary space plasmas.
Plasma density behavior in the Hefei tokamak-7
Authors: Gao Xiang , Jie Y. X. , Yang Y. , Xia C. Y. , Wei M. S. , Zhang S. Y. , Cheng Y. F. , Hu L. Q. , Mao J. S. , Tong X. D. , Wan B. N. , Kuang G. L. , Li J. G. , Zhao Y. P. , Luo J. R. , Qiu N. , Yang K. , Li G. , Xie J. K. , Wan Y. X.
Published: July 2002

The density profiles were measured in the Hefei tokamak-7 (HT-7) [World Survey of Activities in Controlled Fusion Research, Nuclear Fusion Special Supplement (International Atomic Energy Agency, Vienna, 1997), p. 61] ohmic discharges by means of a new multichannel far-infrared (FIR) laser interferometer. The progress on the extension of the HT-7 ohmic discharge operation region was introduced. The experiment results at the density limit, the multifaceted asymmetric radiation from the edge (MARFE) phenomena, the rf (radio frequency) boronization experiments, and the fueling efficiency studies were reported. The plasma physics in the molecular beam injection (MBI), the pellet injection (PI), and the gas puffing (GP) fueling experiments was studied and discussed.
Extrinsic gettering via the controlled introduction of misfit dislocations
Authors: Salih A. S. , Kim H. J. , Davis R. F. , Rozgonyi G. A.
Published: July 2002

As an alternative to existing gettering techniques, extrinsic gettering by misfit dislocations is described and gettering efficiency evaluated. Uniform arrays of misfit dislocations were generated at epitaxial Si interfaces by incorporation of 0.1–1% of Ge. The dislocations were shown to be confined to the interface by means of optical and electron microscopies. The misfit dislocations were used as extrinsic gettering sinks for metallic impurities deliberately introduced and diffused towards the dislocations. Transmission electron microscopy and secondary ion mass spectrometry analyses showed the preferential precipitation of Cu and Au at the misfit dislocations.
Low-temperature liquid phase epitaxial growth of an (In,Ga,Al)Sb quaternary alloy
Authors: Ohshima Hisayoshi , Tanaka Akira , Sukegawa Tokuzo
Published: July 2002

A growth procedure was proposed to prepare the saturated growth solution at low temperature. Using the procedure, an (In,Ga,Al)Sb alloy was grown on GaSb at 450 °C successfully. The energy gap and the lattice constant of the grown layer were determined at 0.886 eV at 77 K and 6.1174 Å, respectively. The estimated value of the alloy composition from these values was In0.048Ga0.812Al0.140Sb.
Characterization study of a HgTe-CdTe superlattice by means of transmission electron microscopy and infrared photoluminescence
Authors: Harris K. A. , Hwang S. , Blanks D. K. , Cook J. W. , Schetzina J. F. , Otsuka N. , Baukus J. P. , Hunter A. T.
Published: July 2002

We report the first transmission electron microscopy (TEM) study of a HgTe-CdTe superlattice. The superlattice consists of 250 layer pairs of HgTe-CdTe on a (100) CdTe substrate and was grown at 175 °C by molecular beam epitaxy. Vertical cross-section TEM images show a highly regular structure of the superlattice from the CdTe substrate to the free surface, indicating that interdiffusion effects at interfaces are minimal. Diffraction patterns taken from the first 30 pairs of layers of the superlattice from the CdTe buffer layer show a series of satellite spots up to the sixth order. This implies that the interfacial sharpness of this HgTe-CdTe superlattice is comparable to those interfaces of high quality III-V semiconductor superlattices. The HgTe-CdTe superlattice exhibits an infrared photoluminescence peak at 357 meV, in reasonable agreement with theoretical predictions of its band gap.
Electrical transport in amorphous hydrogenated Ge/Si superlattices
Authors: Wronski C. R. , Persans P. D. , Abeles B.
Published: July 2002

Electrical conductivity measurements on a-Ge:H/a-Si:H superlattices parallel and perpendicular to the layers are explained by a simple quantum well model which yields effective electron masses 0.4m0 for a-Ge:H and 0.3m0 for a-Si:H. Space-charge-limited currents observed at high fields are used to determine the density of deep gap states in the a-Ge:H layers.
Measurement of GaAs surface oxide desorption temperatures
Authors: SpringThorpe A. J. , Ingrey S. J. , Emmerstorfer B. , Mandeville P. , Moore W. T.
Published: July 2002

Auger analysis of oxidized GaAs surfaces, heat treated in vacuo, has been used to establish an accurate value for the oxide desorption temperature Tox. Major differences are found in the value of Tox for the surface oxides produced by thermal and ozone oxidation: 582±1 °C and 638±1°C, respectively. These temperature differences are also confirmed by reflection high-energy electron diffraction observations of the thermal cleaning of GaAs substrates prior to epitaxial growth in a molecular beam epitaxy system. It is suggested that the measured temperatures can be used in establishing appropriate growth conditions for ‘‘indium-free’’ GaAs substrates during molecular beam epitaxial growth.
Determination of the atomic configuration at semiconductor interfaces
Authors: Ourmazd A. , Tsang W. T. , Rentschler J. A. , Taylor D. W.
Published: July 2002

We describe an approach based on high-resolution transmission electron microscopy (HRTEM), which is capable of directly and sensitively revealing the atomic configuration at compound semiconductor/semiconductor interfaces, and thus show that interfaces normally regarded as atomically smooth can contain significant roughness. Our technique establishes that HRTEM can simultaneously provide chemical and structural information on an atomic scale.
Thickness dependence of oxide breakdown under high field and current stress
Authors: Liang M.-S. , Choi J. Y.
Published: July 2002

The integrity of gate oxides is shown to be a strong function of both oxide thickness and applied field and current strength. Thin gate oxides show longer lifetime under low field and current stress. However, high field and current induced intrinsic breakdown is inversely proportional to oxide thickness. It is also found that the effect of polycrystalline silicon and silicon dioxide interface roughness on oxide charge-to-breakdown is independent of oxide thickness and stressing field and current level. A model of positive charge generation and recombination is applied to explain the experimental data.
Low-temperature organometallic chemical vapor deposition of platinum
Authors: Chen Yea-jer , Kaesz Herbert D. , Thridandam Hareesh , Hicks Robert F.
Published: July 2002

Impurity-free, polycrystalline films of platinum have been grown by the decomposition of cyclopentadienyl platinum trimethyl, CpPtMe3, in hydrogen and a noble gas over silicon or glass substrates heated to 180 °C. The films contain less than 1 at. % of oxygen and carbon, and no other detectable impurities, as measured by x-ray photoelectron and Auger spectroscopies after argon ion sputtering. Sheet resistivities are 50% greater than sputter-deposited platinum.
Evidence for positive selection and population structure at the human
MAO-A
gene
Authors: Gilad Yoav , Rosenberg Shai , Przeworski Molly , Lancet Doron , Skorecki Karl
Published: July 2002

We report the analysis of human nucleotide diversity at a genetic locus known to be involved in a behavioral phenotype, the monoamine oxidase A gene. Sequencing of five regions totaling 18.8 kb and spanning 90 kb of the monoamine oxidase A gene was carried out in 56 male individuals from seven different ethnogeographic groups. We uncovered 41 segregating sites, which formed 46 distinct haplotypes. A permutation test detected substantial population structure in these samples. Consistent with differentiation between populations, linkage disequilibrium is higher than expected under panmixia, with no evidence of a decay with distance. The extent of linkage disequilibrium is not typical of nuclear loci and suggests that the underlying population structure may have been accentuated by a selective sweep that fixed different haplotypes in different populations, or by local adaptation. In support of this suggestion, we find both a reduction in levels of diversity (as measured by a Hudson–Kreitman–Aguade test with the DMD44 locus) and an excess of high frequency-derived variants, as expected after a recent episode of positive selection.
Type 3 ryanodine receptors of skeletal muscle are segregated in a parajunctional position
Authors: Felder Edward , Franzini-Armstrong Clara
Published: July 2002

A key event in skeletal muscle activation is the rapid release of Ca
2+
from the sarcoplasmic reticulum (SR), the Ca
2+
storage organelle in the muscle cell. The surface membrane/transverse tubules and the SR form functional units (calcium release units containing one or two couplons or junctions), where the voltage-sensing dihydropyridine receptor of the surface membrane interacts with the SR Ca
2+
release channel [ryanodine receptor (RyR)] and depolarization of the cell membrane is converted into Ca
2+
release from the SR. Although RyR1 is the most important isoform in skeletal muscle, some muscles also express high levels of RyR3, an isoform with a wide tissue distribution. The cytoplasmic domains of RyRs are visible in the electron microscope as periodically disposed feet. We find that, in muscles containing only RyR1, feet are exclusively located over the junctional SR surface facing the surface membrane/transverse tubule. In muscles containing RyR1 as well as RyR3, additional feet are located in lateral parajunctional regions immediately adjacent to junctional SR. Biochemical content of RyR3 and content of parajunctional feet are highly correlated in different muscles and the disposition of parajunctional versus junctional feet are notably different. On the basis of these two observations, we postulate that RyR3s are restricted to the parajunctional region, and thus their activation must be indirect and derivative during excitation–contraction coupling.
Reverse engineering the (β/α)
8
barrel fold
Authors: Silverman J. A. , Balakrishnan R. , Harbury P. B.
Published: July 2002

The (β/α)
8
barrel is the most commonly
occurring fold among protein catalysts. To lay a groundwork for
engineering novel barrel proteins, we investigated the amino acid
sequence restrictions at 182 structural positions of the prototypical
(β/α)
8
barrel enzyme triosephosphate
isomerase. Using combinatorial mutagenesis and functional selection, we
find that turn sequences, α-helix capping and stop motifs, and
residues that pack the interface between β-strands and α-helices
are highly mutable. Conversely, any mutation of residues in the central
core of the β-barrel, β-strand stop motifs, and a single buried
salt bridge between amino acids R189 and D227 substantially reduces
catalytic activity. Four positions are effectively immutable:
conservative single substitutions at these four positions prevent the
mutant protein from complementing a triosephosphate isomerase knockout
in
Escherichia coli
. At 142 of the 182 positions,
mutation to at least one amino acid of a seven-letter amino acid
alphabet produces a triosephosphate isomerase with wild-type activity.
Consequently, it seems likely that (β/α)
8
barrel structures can be encoded with a subset of the 20 amino acids.
Such simplification would greatly decrease the computational burden of
(β/α)
8
barrel design.
Mechanism for antibody catalysis of the oxidation of water by singlet dioxygen
Authors: Datta Deepshikha , Vaidehi Nagarajan , Xu Xin , Goddard William A.
Published: July 2002

Wentworth
et al.
[Wentworth, P., Jones, L. H., Wentworth, A. D., Zhu, X. Y., Larsen, N. A., Wilson, I. A., Xu, X., Goddard, W. A., Janda, K. D., Eschenmoser, A. & Lerner, R. A. (2001)
Science
293, 1806–1811] recently reported the surprising result that antibodies and T cell receptors efficiently catalyze the conversion of molecular singlet oxygen (
1
O
2
) plus water to hydrogen peroxide (HOOH). Recently, quantum mechanical calculations were used to delineate a plausible mechanism, involving reaction of
1
O
2
with two waters to form HOOOH (plus H
2
O), followed by formation of HOOOH dimer, which rearranges to form HOO—HOOO + H
2
O, which rearranges to form two HOOH plus
1
O
2
or
3
O
2
. For a system with
18
O H
2
O, this mechanism leads to a 2.2:1 ratio of
16
O:
18
O in the product HOOH, in good agreement with the ratio 2.2:1 observed in isotope experiments by Wentworth
et al
. In this paper we use docking and molecular dynamics techniques (HierDock) to search various protein structures for sites that stabilize these products and intermediates predicted from quantum mechanical calculations. We find that the reaction intermediates for production of HOOH from
1
O
2
are stabilized at the interface of light and heavy chains of antibodies and T cell receptors. This inter Greek key domain interface structure is unique to antibodies and T cell receptors, but is
not
present in β
2
-microglobulin, which does
not
show any stabilization in our docking studies. This result is consistent with the experimentally observed lack of HOOH production in this system. Our results provide a plausible mechanism for the reactions and provide an explanation of the specific structural character of antibodies responsible for this unexpected chemistry.
Regulation of eye development by frizzled signaling in
Xenopus
Authors: Rasmussen Jennifer T. , Deardorff Matthew A. , Tan Change , Rao Mahendra S. , Klein Peter S. , Vetter Monica L.
Published: July 2002

Eye development in both invertebrates and vertebrates is regulated
by a network of highly conserved transcription factors. However, it is
not known what controls the expression of these factors to regulate
early eye formation and whether transmembrane signaling events are
involved. Here we establish a role for signaling via a member of the
frizzled family of receptors in regulating early eye development. We
show that overexpression of
Xenopus
frizzled 3 (Xfz3), a
receptor expressed during normal eye development, functions cell
autonomously to promote ectopic eye formation and can perturb
endogenous eye development. Ectopic eyes obtained with Xfz3
overexpression have a laminar organization similar to that of
endogenous eyes and contain differentiated retinal cell
types. Ectopic eye formation is preceded by ectopic expression of
transcription factors involved in early eye development, including
Pax6, Rx, and Otx2. Conversely, targeted overexpression of a
dominant-negative form of Xfz3 (Nxfz3), consisting of the soluble
extracellular domain of the receptor, results in suppression of
endogenous Pax6, Rx, and Otx2 expression and suppression of
endogenous eye development. This effect can be rescued by
coexpression of Xfz3. Finally, overexpression of Kermit, a protein that
interacts with the C-terminal intracellular domain of Xfz3, also blocks
endogenous eye development, suggesting that signaling
through Xfz3 or a related receptor is required for normal eye
development. In summary, we show that frizzled signaling is both
necessary and sufficient to regulate eye development in
Xenopus
.
Metal ion recognition and molecular templating in self-assembled monolayers of cyclic and acyclic polyethers
Authors: Herranz Maria Ángeles , Colonna Barbara , Echegoyen Luis
Published: July 2002

Our recent work with cyclic and acyclic polyether self-assembled monolayers (SAMs) on gold is presented. A series of dithia-crown-tetrathiafulvalene derivatives with one or two disulfide groups has been prepared, and their SAMs on gold have been characterized by electrochemistry and by reflection–absorption infrared spectroscopy. These SAMs are extremely stable on repeated electrochemical potential scans and can selectively recognize alkali metal ions. Acyclic polyether derivatives can also self-assemble on gold to yield selective metal ion recognition domains. Impedance spectroscopy data for these SAMs fit the Langmuir isotherm and allow the determination of ion association constants. Some of the SAMs prepared with new acyclic polyether derivatives are able to detect potassium cations selectively when templated in their presence. These structures are believed to be a consequence of ion “imprinting” during the process of SAM formation.
Unraveling the nanostructure of supramolecular assemblies of hydrogen-bonded rosettes on graphite: An atomic force microscopy study
Authors: Schönherr Holger , Paraschiv Vasile , Zapotoczny Szczepan , Crego-Calama Mercedes , Timmerman Peter , Frank Curtis W. , Vancso G. Julius , Reinhoudt David N.
Published: July 2002

The self-organization of multicomponent tetrarosette assemblies into ordered nanostructures on graphite surfaces has been studied by atomic force microscopy (AFM). Real-space information on the level of individual molecules allowed us to analyze the underlying structure in unprecedented detail. In highly ordered nanorod domains, tetrarosettes 1
3
⋅(DEB)
12
arrange in the form of parallel rows with a spacing of 4.6 ± 0.1 nm. High resolution AFM revealed the internal packing of the tetrarosette assemblies in these rows, which can be described by an oblique lattice with
a
= 2.5 ± 0.3 nm,
b
= 5.0 ± 0.1 nm, and γ = 122 ± 3°. The results, together with recent improvements in synthetic approaches, contribute to the development of a general strategy to develop H-bonding-based nanostructures with molecular precision.
HIV-1 gp120 and chemokines activate ion channels in primary macrophages through CCR5 and CXCR4 stimulation
Authors: Liu Qing-Hua , Williams Darlisha A. , McManus Carrie , Baribaud Frédéric , Doms Robert W. , Schols Dominique , De Clercq Erik , Kotlikoff Michael I. , Collman Ronald G. , Freedman Bruce D.
Published: July 2002

HIV type 1 (HIV-1) uses the chemokine receptors CCR5 and CXCR4 as coreceptors for entry into target cells. Here we show that the HIV-1 envelope gp120 (Env) activates multiple ionic signaling responses in primary human macrophages, which are important targets for HIV-1in vivo. Env from both CCR5-dependent JRFL (R5) and CXCR4-dependent IIIB (X4) HIV-1 opened calcium-activated potassium (KCa), chloride, and calcium-permeant nonselective cation channels in macrophages. These signals were mediated by CCR5 and CXCR4 because macrophages lacking CCR5 failed to respond to JRFL and an inhibitor of CXCR4 blocked ion current activation by IIIB. MIP-1β and SDF-1α, chemokine ligands for CCR5 and CXCR4, respectively, also activated KCaand Cl−currents in macrophages, but nonselective cation channel activation was unique to gp120. Intracellular Ca2+levels were also elevated by gp120. The patterns of activation mediated by CCR5 and CXCR4 were qualitatively similar but quantitatively distinct, as R5 Env activated the KCacurrent more frequently, elicited Cl−currents that were ≈2-fold greater in amplitude, and elevated intracellular Ca+2to higher peak and steady-state levels. Env from R5 and X4 primary isolates evoked similar current responses as the corresponding prototype strains. Thus, the interaction of HIV-1 gp120 with CCR5 or CXCR4 evokes complex and distinct signaling responses in primary macrophages, and gp120-evoked signals differ from those activated by the coreceptors' chemokine ligands. Intracellular signaling responses of macrophages to HIV-1 may modulate postentry steps of infection and cell functions apart from infection.
A power law for cells
Authors: Azevedo Ricardo B. R. , Leroi Armand M.
Published: July 2002

Darwin observed that multiple, lowly organized, rudimentary, or exaggerated structures show increased relative variability. However, the cellular basis for these laws has never been investigated. Some animals, such as the nematodeCaenorhabditis elegans, are famous for having organs that possess the same number of cells in all individuals, a property known as eutely. But for most multicellular creatures, the extent of cell number variability is unknown. Here we estimate variability in organ cell number for a variety of animals, plants, slime moulds, and volvocine algae. We find that the mean and variance in cell number obey a power law with an exponent of 2, comparable to Taylor's law in ecological processes. Relative cell number variability, as measured by the coefficient of variation, differs widely across taxa and tissues, but is generally independent of mean cell number among homologous tissues of closely related species. We show that the power law for cell number variability can be explained by stochastic branching process models based on the properties of cell lineages. We also identify taxa in which the precision of developmental control appears to have evolved. We propose that the scale independence of relative cell number variability is maintained by natural selection.
bcl-2
overexpression promotes myocyte proliferation
Authors: Limana Federica , Urbanek Konrad , Chimenti Stefano , Quaini Federico , Leri Annarosa , Kajstura Jan , Nadal-Ginard Bernardo , Izumo Seigo , Anversa Piero
Published: July 2002

To determine the influence of Bcl-2 on the developmental biology of myocytes, we analyzed the population dynamics of this cell type in the heart of transgenic (TG) mice overexpressing Bcl-2 under the control of the α-myosin heavy chain promoter. TG mice and non-TG (wild type, WT) mice were studied at 24 days, 2 months, and 4 months after birth. Bcl-2 overexpression produced a significant increase in the percentage of cycling myocytes and their mitotic index. These effects were strictly connected to the expression of the transgene, as demonstrated in isolated myocytes. The formation of mitotic spindle and contractile ring was identified in replicating cells. These typical aspects of mitosis were complemented with the demonstration of karyokinesis and cytokinesis to provide structural evidence of cell division. Apoptosis was low at all ages and was not affected by Bcl-2. The higher cell replication rate in TG was conditioned by a decrease in the expression of the cell-cycle inhibitors, p21
WAF1
and p16
INK4a
, and by an increase in Mdm2-p53 complexes. In comparison with WT, TG had 0.4 × 10
6
, 0.74 × 10
6
, and 1.2 × 10
6
more myocytes in the left ventricle at 24 days, 2 months, and 4 months, respectively. Binucleated myocytes were 12% and 25% larger in WT than in TG mice at 2 and 4 months of age. Taken together, these observations reveal a previously uncharacterized replication-enhancing function of Bcl-2 in myocytes
in vivo
in the absence of stressful conditions.
Phenotypic consequences of lung-specific inducible expression of FGF-3
Authors: Zhao Bihong , Chua Steven S. , Burcin Mark M. , Reynolds Susan D. , Stripp Barry R. , Edwards Robert A. , Finegold Milton J. , Tsai Sophia Y. , DeMayo Francesco J.
Published: July 2002

Members of the fibroblast growth factor (FGF) family play a
critical role in embryonic lung development and adult lung physiology.
The
in vivo
investigation of the role FGFs play in the
adult lung has been hampered because the constitutive pulmonary
expression of these factors often has deleterious effects and
frequently results in neonatal lethality. To circumvent these
shortcomings, we expressed FGF-3 in the lungs under the control of the
progesterone antagonist-responsive binary transgenic system. Four
binary transgenic lines were obtained that showed ligand-dependent
induction of FGF-3 with induced levels of FGF-3 expression dependent on
the levels of expression of the GLp65 regulator as well as the dose of
the progesterone antagonist, RU486, administered. FGF-3 expression in
the adult mouse lung resulted in two phenotypes depending on the levels
of induction of FGF-3. Low levels of FGF-3 expression resulted in
massive free alveolar macrophage infiltration. High levels of FGF-3
expression resulted in diffuse alveolar type II cell hyperplasia. Both
phenotypes were reversible after the withdrawal of RU486. This system
will be a valuable means of investigating the diverse roles of FGFs in
the adult lung.
Quantitative analysis of chromosomal CGH in human breast tumors associates copy number abnormalities with p53 status and patient survival
Authors: Jain Ajay N. , Chin Koei , Børresen-Dale Anne-Lise , Erikstein Bjorn K. , Lonning Per Eystein , Kaaresen Rolf , Gray Joe W.
Published: July 2002

We present a general method for rigorously identifying correlations between variations in large-scale molecular profiles and outcomes and apply it to chromosomal comparative genomic hybridization data from a set of 52 breast tumors. We identify two loci where copy number abnormalities are correlated with poor survival outcome (gain at 8q24 and loss at 9q13). We also identify a relationship between abnormalities at two loci and the mutational status of p53. Gain at 8q24 and loss at 5q15-5q21 are linked with mutant p53. The 9q and 5q losses suggest the possibility of gene products involved in breast cancer progression. The analytical techniques are general and also are applicable to the analysis of array-based expression data.
Regulation of vascular endothelial growth factor (VEGF) gene transcription by estrogen receptors α and β
Authors: Mueller Michael D. , Vigne Jean-Louis , Minchenko Alexander , Lebovic Dan I. , Leitman Dale C. , Taylor Robert N.
Published: July 2002

Vascular endothelial growth factor (VEGF) mediates angiogenic
activity in a variety of estrogen target tissues. To determine whether
estrogen has a direct transcriptional effect on VEGF gene expression,
we developed a model system by transiently transfecting human VEGF
promoter-luciferase reporter constructs into primary human endometrial
cells and into Ishikawa cells, derived from a well-differentiated human
endometrial adenocarcinoma. In primary endometrial epithelial cells,
treatment with 17β-estradiol (E
2
) resulted in a 3.8-fold
increase in luciferase activity, whereas a 3.2-fold induction was
demonstrated for stromal cells. Our Ishikawa cells had less than 100
functional estrogen receptors (ER)/cell and were therefore
cotransfected with expression vectors encoding either the α- or the
β-form of the human ER. In cells cotransfected with ERα,
E
2
induced 3.2-fold induction in VEGF-promoter luciferase
activity. A 2.3-fold increase was observed in cells cotransfected with
ERβ. Through specific deletions, the E
2
response was
restricted to a single 385-bp
Pvu
II-
Sst
I
fragment in the 5′ flanking DNA. Cotransfection of this upstream region
with a DNA binding domain ER mutant, or site-directed mutagenesis of a
variant ERE within this fragment, resulted in the loss of the
E
2
response. Electromobility shift assays demonstrated that
this same ERE sequence specifically binds estradiol-ER complexes. These
studies demonstrate that E
2
-regulated VEGF gene
transcription requires a variant ERE located 1.5 kb upstream from the
transcriptional start site. Site-directed mutagenesis of this ERE
abrogated E
2
-induced VEGF gene expression.
Histone H2A-mediated transient cytokine gene delivery induces efficient antitumor responses in murine neuroblastoma
Authors: Balicki Danuta , Reisfeld Ralph A. , Pertl Ursula , Beutler Ernest , Lode Holger N.
Published: July 2002

A major goal of cancer immunotherapy is the induction of a
cell-mediated antitumor response in poorly immunogenic malignancies. We
tested the hypothesis that this can be achieved by cytokine gene
therapy with a novel histone H2A-based transient transfection
procedure. This was tested by using cytokine genes encoding for IL-2
and a single chain IL-12 (scIL-12) fusion protein in a recently
developed murine neuroblastoma model. Here, we demonstrate that
cytokine gene transfer of IL-2 and scIL-12 with histone H2A results in
the induction of an antitumor immune response that is superior in some
respects to gene transfer with Superfect, a commercially available
activated dendrimer commonly used to effect transfection with plasmids.
Three lines of evidence support this contention. First, histone
H2A-mediated transfection of IL-2 induces a natural killer cell-induced
rejection of primary tumors in contrast to Superfect, which produces
only a partial reduction in primary tumor growth. Second, the induction
of a T cell-mediated protective tumor immunity following gene transfer
of scIL-12 is more efficient with the histone H2A-mediated gene
transfer because rejection of a lethal wild-type tumor cell challenge
is accompanied by the greatest degree of MHC class I-restricted tumor
cell killing
in vitro
. Third, histone H2A-mediated
scIL-12 gene therapy induces the greatest release of mIFN-γ from
splenocytes of vaccinated animals in contrast to Superfect and other
controls.
Th1-polarizing immunization with egg antigens correlates with severe exacerbation of immunopathology and death in schistosome infection
Authors: Rutitzky Laura I. , Hernandez Hector J. , Stadecker Miguel J.
Published: July 2002

In schistosomiasis mansoni, parasite eggs precipitate an intrahepatic granulomatous and fibrosing inflammatory process, which is mediated by, and dependent on, MHC class II-restricted CD4 T helper (Th) lymphocytes specific for schistosome egg antigens (SEA). In the mouse model of the disease, CBA mice develop large granulomas, whereas in C57BL/6 (BL/6) mice these granulomas are significantly smaller. To further investigate how the prevailing cytokine environment influences the development of the egg-induced immunopathology, we immunized the low-pathology BL/6 mice with SEA in complete Freund's adjuvant (CFA) once before, and once again during, the course of a 7-week infection. This immunization caused a pronounced Th1 shift in the SEA-specific CD4 T cell response, which was detected in the mesenteric lymph nodes (MLNs) and spleens, as well as in the granulomatous lesions themselves. The immunized mice displayed a dramatic enhancement of hepatic egg-induced immunopathology manifested by a marked increase in granuloma size and parenchymal inflammation, leading to early death. Control mice immunized with equivalent amounts of SEA or CFA alone displayed the smaller hepatic lesions in a Th2-dominant environment typically seen in the unimmunized BL/6 mice. Analysis of granuloma and MLN lymphocytes from the SEA/CFA-immunized mice revealed that the proportion of CD4 T cells was unchanged in comparison with the control BL/6 groups and remained significantly lower than that seen in the normally high-pathology CBA strain. These results suggest that the shift toward Th1-type cytokine production by a numerically stable population of CD4 T cells correlates with severe exacerbation of immunopathology in schistosomiasis.
Point mutation in the mouse glucocorticoid receptor preventing DNA binding impairs spatial memory
Authors: Oitzl Melly S. , Reichardt Holger M. , Joëls Marian , de Kloet E. Ronald
Published: July 2002

Activation of central glucocorticoid receptors caused by the stress that is associated with a learning task facilitates storage of the acquired information. The molecular mechanism underlying this phenomenon is entirely unknown. Glucocorticoid receptors can influence transcription both through DNA binding-dependent and -independent mechanisms. To assess the importance of these two modes of action for spatial memory, we here used male mutant mice in which homodimerization and DNA binding of the glucocorticoid receptor is largely prevented (GR
dim/dim
) while protein–protein interactions still can take place. These mice showed a selective impairment of spatial memory in the water maze. Locomotion and anxiety-related parameters measured in an open field and a light/dark preference task were comparable for mutant and control mice. Mutant mice released more corticosterone than control mice under basal resting conditions and in response to swimming, which could have influenced memory processes of the mice. However, mimicking the task-related increase in corticosterone by supplementary injection of corticosterone (250 μg/kg, i.p.) in adrenalectomized mice, resulting in equal plasma corticosterone concentrations in both genotypes, improved spatial memory of control mice but had no effect on mutant mice. These findings suggest that task-related facilitating effects of corticosterone on spatial memory indeed depend on DNA binding of the glucocorticoid receptor rather than on protein–protein interactions of the receptor with other transcription factors. Although it cannot be excluded that both processes are involved in a coordinated way, interrupting the DNA-binding capacity of the receptor is sufficient to induce impairment.
Retinoblastoma protein directly interacts with and activates the transcription factor NF-IL6.
Authors: Chen P L , Riley D J , Chen-Kiang S , Lee W H
Published: July 2002

The biological function of the retinoblastoma protein (RB) in the cell division cycle has been extensively documented, but its apparent role in differentiation remains largely unexplored. To investigate how RB is involved in differentiation, the U937 large-cell lymphoma line was induced to differentiate along a monocyte/macrophage lineage. During differentiation RB was found to interact directly through its simian virus 40 large tumor antigen (T antigen)-binding domain with NF-IL6, a member of the CAAT/enhancer-binding protein (C/EBP) family of transcription factors. NF-IL6 utilizes two distinct regions to bind to the hypophosphorylated form of RB in vitro and in cells. Wild-type but not mutant RB enhanced both binding activity of NF-IL6 to its cognate DNA sequences in vitro and promoter transactivation by NF-IL6 in cells. These findings indicate a novel biochemical function of RB: it activates, by an apparent chaperone-like activity, specific transcription factors important for differentiation. This contrasts with its sequestration and inactivation of other transcription factors, such as E2F-1, which promote progression of the cell cycle. Such disparate mechanisms may help to explain the dual role of RB in cell differentiation and the cell division cycle.
Identification and characterization of an alternative cytotoxic T lymphocyte-associated protein 4 binding molecule on B cells.
Authors: Murakami M , Takahashi Y , Isashi Y , Kon S , Jia W Y , Inobe M , Abe R , Uede T
Published: July 2002

To determine whether alternative cytotoxic T lymphocyte-associated protein 4 (CTLA4) binding proteins exist on B cells, we constructed (i) mCTLA4hIgG consisting of the extracellular region of a mouse CTLA4 molecule and the Fc portion of a human IgG1 molecule and (ii) PYAAhIgG, a mutant mCTLA4hIgG, having two amino acid substitutions on the conserved MYPPPY motif in the complementarity-determining region 3-like region and lacking detectable binding to both B7-1 and B7-2 molecules. Using these fusion proteins (mCTLA4hIgG and PYAAhIgG), we demonstrated that a mouse immature B-cell line, WEHI231 cells, expressed alternative CTLA4 binding molecules (ACBMs) that were distinct from both B7-1 and B7-2. ACBMs were 130-kDa disulfide-linked proteins. More importantly, ACBMs were able to provide costimulatory signal for T-cell proliferation in the presence of anti-CD3 monoclonal antibodies. In addition, we demonstrated that more than 20% of B220+ cells obtained from normal mouse spleen expressed ACBMs.
Chiral molecular self-assembly of phospholipid tubules: A circular dichroism study
Authors: Spector Mark S. , Easwaran Kalpathy R. K. , Jyothi Ghanta , Selinger Jonathan V. , Singh Alok , Schnur Joel M.
Published: July 2002

We report on spectroscopic studies of the chiral structure in
phospholipid tubules formed in mixtures of alcohol and water. Synthetic
phospholipids containing diacetylenic moieties in the acyl chains
self-assemble into hollow, cylindrical tubules in appropriate
conditions. Circular dichroism provides a direct measure of chirality
of the molecular structure. We find that the CD spectra of tubules
formed in mixtures of alcohol and water depends strongly on the alcohol
used and the lipid concentration. The relative spectral intensity of
different circular dichroism bands correlates with the number of
bilayers observed using microscopy. The results provide experimental
evidence that tubule formation is based on chiral packing of the lipid
molecules and that interbilayer interactions are important to the
tubule structure.
In vitro
V(D)J recombination: Signal joint formation
Authors: Cortes Patricia , Weis-Garcia Frances , Misulovin Ziva , Nussenzweig Andre , Lai Jiann-Shiun , Li Gloria , Nussenzweig Michel C. , Baltimore David
Published: July 2002

The first step of V(D)J recombination, specific cleavage at the
recombination signal sequence (RSS), can be carried out by the
recombination activating proteins RAG1 and RAG2.
In
vivo
, the cleaved coding and signal ends must be rejoined to
generate functional antigen receptors and maintain chromosomal
integrity. We have investigated signal joint formation using deletion
and inversion substrates in a cell free system. RAG1 and RAG2 alone or
in combination were unable to generate signal joints. However, RAG1 and
RAG2 complemented with nuclear extracts were able to recombine an
extrachromosomal substrate and form precise signal joints. The
in vitro
reaction resembled authentic V(D)J
recombination in being Ku-antigen-dependent.
Correlation between the effects of bombesin antagonists on cell proliferation and intracellular calcium concentration in Swiss 3T3 and HT-29 cell lines.
Authors: Casanueva F F , Perez F R , Casabiell X , Camiña J P , Cai R Z , Schally A V
Published: July 2002

Bombesin (BN) acts as an autocrine mitogen in various human cancers. Several pseudononapeptide BN-(6-14) analogs with a reduced peptide bond between positions 13 and 14 have been shown to suppress the mitogenic activity of BN or gastrin-releasing peptide (GRP) when assessed by radioreceptor or proliferation assays and may have significant clinical applications. The search for potent and safe BN antagonists requires the evaluation of a large series of analogs in radioreceptor and proliferation assays. In this paper, we report that the ability of BN analogs to inhibit BN-induced calcium transients in Swiss 3T3 cells shows a high correlation with their inhibitory potency as evaluated by classical proliferation tests. The assay of calcium transients allows a rapid characterization of new BN analogs (in terms of minutes rather than days) and can be adapted as a labor and cost-effective screening step in the selection of potentially relevant BN antagonists for further characterization in cell proliferation systems. We also observed that results from the assay of calcium transients in Swiss 3T3 cells can be correlated with the results of the proliferative response in HT-29 cells, a cell line that does not seem to use the same early transmembrane ionic signal system. This result suggests that the calcium pathway is not mandatory for triggering cell division by the BN receptor.
Azotobacter vinelandii NIFL is a flavoprotein that modulates transcriptional activation of nitrogen-fixation genes via a redox-sensitive switch.
Authors: Hill S , Austin S , Eydmann T , Jones T , Dixon R
Published: July 2002

The NIFL regulatory protein controls transcriptional activation of nitrogen fixation (nif) genes in Azotobacter vinelandii by direct interaction with the enhancer binding protein NIFA. Modulation of NIFA activity by NIFL, in vivo occurs in response to external oxygen concentration or the level of fixed nitrogen. Spectral features of purified NIFL and chromatographic analysis indicate that it is a flavoprotein with FAD as the prosthetic group, which undergoes reduction in the presence of sodium dithionite. Under anaerobic conditions, the oxidized form of NIFL inhibits transcriptional activation by NIFA in vitro, and this inhibition is reversed when NIFL is in the reduced form. Hence NIFL is a redox-sensitive regulatory protein and may represent a type of flavoprotein in which electron transfer is not coupled to an obvious catalytic activity. In addition to its ability to act as a redox sensor, the activity of NIFL is also responsive to adenosine nucleotides, particularly ADP. This response overrides the influence of redox status on NIFL and is also observed with refolded NIFL apoprotein, which lacks the flavin moiety. These observations suggest that both energy and redox status are important determinants of nif gene regulation in vivo.