bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupling between neighboring two-dimensional modes of water waves
Authors: Feng Z. C.
Published: July 2002

We consider two-dimensional waves in a rectangular container which is periodically excited along its length in the horizontal direction. In general a standing wave of odd mode number whose frequency is close to the forcing frequency is excited. However, we show in this paper that the neighboring even mode, though not directly excited, may be excited through an energy transfer from the odd mode. As a result, the wave response becomes superposition of two standing waves which are not in general in phase with each other. Consequently the mixed-mode wave motion is not standing waves but traveling waves. We employ a perturbation method to derive amplitude equations governing the dynamics of these two modes. Studies of the steady-state solutions and their stability lead to bifurcation diagrams showing the sequences of the events leading to the instability and the parameters for which the standing waves become unstable.
Numerical simulation of neutral gas release experiments in the ionosphere*
Authors: Okuda H. , Choueiri Edgar Y.
Published: July 2002

A two-and-one-half-dimensional electrostatic particle simulation model has been developed to study neutral gas release experiments into the ionosphere. The electrons are assumed guiding center particles, while the full dynamics of the ions (with real masses) are followed in time and space. Ionization processes of the neutral gas by charge exchange and electron impact are included by means of the Monte Carlo technique. It is shown that the model can be used to simulate the neutral gas interaction, with the ionosphere using realistic experimental parameters. The model was applied to study the critical ionization velocity (CIV) tests recently conducted as part of the ATLAS-1 [Geophys. Res. Lett. 20, 499 (1993)] xenon gas releases from the space shuttle. The simulation results show suprathermal electrons produced by an ion beam-driven lower hybrid instability, create a xenon ion population much more rapidly than the production by classical processes, indicating the prevalence of a CIV-type mechanism.
Effect of magnetic field on the distribution of ions striking a planar target
Authors: Parks P. B. , Lippmann S. I.
Published: July 2002

The angular distribution of ions striking a planar target surface which has an obliquely inclined magnetic field at the surface is considered. The results have potentially important ramification for divertor surface sputtering and impurity transport in tokamak plasmas.
Tabletop x-ray lasers*
Authors: Eder D. C. , Amendt P. , DaSilva L. B. , London R. A. , MacGowan B. J. , Matthews D. L. , Penetrante B. M. , Rosen M. D. , Wilks S. C. , Donnelly T. D. , Falcone R. W. , Strobel G. L.
Published: July 2002

Details of schemes for two tabletop size x-ray lasers that require a high-intensity short-pulse driving laser are discussed. The first is based on rapid recombination following optical-field ionization. Analytical and numerical calculations of the output properties are presented. Propagation in the confocal geometry is discussed and a solution for x-ray lasing in Li-like N at 247 Å is described. Since the calculated gain coefficient depends strongly on the electron temperature, the methods of calculating electron heating following field ionization are discussed. Recent experiments aimed at demonstrating lasing in H-like Li at 135 Å are discussed along with modeling results. The second x-ray laser scheme is based on the population inversion obtained during inner-shell photoionization by hard x rays. This approach has significantly higher-energy requirements, but lasing occurs at very short wavelengths (λ≤15 Å). Experiments that are possible with existing lasers are discussed.
Parametric instabilities of Langmuir waves in strong magnetic fields and phase transition of Langmuir turbulence
Authors: Akimoto K.
Published: July 2002

Parametric instabilities of Langmuir waves in strong magnetic fields such that Ωe≳ωe were investigated, where Ωe(ωe) denotes the electron cyclotron (plasma) frequency. It has been well established that as a plasma is more strongly magnetized, the parametric instabilities of Langmuir waves become more field aligned and thus one dimensional. Here, it is demonstrated that this trend continues only up to Ωe/ωe=1, and that above this value, most Langmuir waves decay to relatively short wavelength oblique-Langmuir and ion waves that are damped rapidly. These new parametric instabilities have growth rates greater than those of the conventional modulational and decay instabilities. Consequently, the scenario of strong Langmuir turbulence in which Langmuir solitons play a major role may not apply to the strong magnetic-field regime. In the weak Langmuir turbulence regime these decay instabilities make the turbulence more isotropic. Therefore, it is concluded that there occurs a type of phase transition in magnetized Langmuir turbulence at Ωe/ωe∼1.
The nonlinear diocotron mode in a pure electron plasma
Authors: Corngold Noel R.
Published: July 2002

The nonlinear diocotron mode, discussed by Fine, Driscoll, and Malmberg [Phys. Rev. Lett. 63, 2232 (1989)] is characterized by two equations, one describing the frequency of orbiting, the other giving the quadrupole moment, as functions of size and offset. A new analysis, based on the method of moments, which yields equations more general in their content, is presented here. For example, the new equations describe columns whose shapes are not elliptical and whose densities are not constant.
Coarse-graining and nonlocal processes in proton cyclotron resonant interactions
Authors: Siregar E. , Viñas A. F. , Goldstein M. L.
Published: July 2002

Coarse-grained information from a hybrid simulation show that previously developed quasifluid equations of state capture some aspects of proton cyclotron resonant interactions for parallel propagation in a low β plasma. Direct kinetic information is used as a closure for the information exchanged with the higher-order moment quantities. The coarse-graining procedure involves averaging over many proton-inertial lengths and looking at long time scales associated with the wave envelopes. By use of the coarse-graining prior to statistical analysis, the anticorrelations predicted by the equations of state are very high for both the single resonant wave case and for a broadband spectrum centered on a resonant wave. These anticorrelations are also consistent with what one expects from a single particle orbit analysis. A similar analysis, but done without the prior averaging procedures, shows no relevant correlations, and no simple dynamics emerges from the kinetic data in this case. A comparison is made with a model based on quasilinear theory. These results suggest that, in addition to simply taking velocity moments of particle distributions, the proper averaging of kinetic information over space and time scales lying below the range accessible to a fluid model can be essential to its success.
Global approach to the spectral problem of microinstabilities in a cylindrical plasma using a gyrokinetic model
Authors: Brunner S. , Vaclavik J.
Published: July 2002

Considering the spectral problem of microinstabilities in a curved system, methods for solving the global gyrokinetic equation are presented for the simple case of a cylindrical plasma. They prove to be efficient for computing the full unstable spectrum of ion temperature gradient (ITG) type modes and have shown to be applicable to the two-dimensional integral equation of tokamak configurations.
Excimer lasers in cardiovascular surgery: Ablation products and photoacoustic spectrum of the arterial wall
Authors: Singleton D. L. , Paraskevopoulos G. , Jolly G. S. , Irwin R. S. , McKenney D. J. , Nip W. S. , Farrell E. M. , Higginson L. A. J.
Published: July 2002

Photoacoustic spectra of normal artery wall and of atherosclerotic plaque are reported. Threshold fluences for ablative formation of gaseous products for each excimer laser line were calculated from the photoacoustic spectrum and the measured threshold for the KrF laser.
Theory of Faraday rotation by dilute suspensions of small particles
Authors: Hui P. M. , Stroud D.
Published: July 2002

We consider Faraday rotation by a dilute suspension of small particles embedded in a host. Using the Maxwell-Garnett approximation, we obtain an expression for the complex effective dielectric tensor of the composite in the low concentration limit. The Faraday coefficient becomes anomalously large near the surface plasmon frequency of the small particles. Numerical examples are given for the frequency-dependent off-diagonal part of the dielectric tensor and for the angle of rotation.
An unusual Fc receptor-related protein expressed in human centroblasts
Authors: Facchetti Fabio , Cella Marina , Festa Silvana , Fremont Daved H. , Colonna Marco
Published: July 2002

Here, we report the identification of Fc receptor homolog expressed in B cells (FREB), a unique B cell-specific molecule that is distantly related to FcγRI (receptor I for the Fc fragment of IgG) and is encoded on human chromosome 1q, within the FcγR gene region. FREB has an intracellular distribution and lacks a canonical transmembrane domain. In addition, FREB lacks bona fide Fc fragment binding regions and does not bind immunoglobulins. By using specific monoclonal antibodies, we show that FREB is preferentially expressed in germinal center centroblasts, which undergo affinity maturation and class-switch recombination. Together, these characteristics indicate that FREB may have a unique role in B cell differentiation. FREB is also expressed in some B cell lymphomas, most of which have centroblast origin. Remarkably, FREB is expressed in a subset of diffuse large B cell lymphomas, providing a unique marker for the characterization of this B cell malignancy.
The cellulose synthase gene of
Dictyostelium
Authors: Blanton Richard L. , Fuller Danny , Iranfar Negin , Grimson Mark J. , Loomis William F.
Published: July 2002

Cellulose is a major component of the extracellular matrices formed during development of the social amoeba,
Dictyostelium discoideum
. We isolated insertional mutants that failed to accumulate cellulose and had no cellulose synthase activity at any stage of development. Development proceeded normally in the null mutants up to the beginning of stalk formation, at which point the culminating structures collapsed onto themselves, then proceeded to attempt culmination again. No spores or stalk cells were ever made in the mutants, with all cells eventually lysing. The predicted product of the disrupted gene (
dcsA
) showed significant similarity to the catalytic subunit of cellulose synthases found in bacteria. Enzyme activity and normal development were recovered in strains transformed with a construct expressing the intact
dcsA
gene. Growing amoebae carrying the construct accumulated the protein product of
dcsA
, but did not make cellulose until they had developed for at least 10 hr. These studies show directly that the product of
dcsA
is necessary, but not sufficient, for synthesis of cellulose.
Telomere dysfunction alters the chemotherapeutic profile of transformed cells
Authors: Lee Kee-Ho , Rudolph K. Lenhard , Ju Yeun-Jin , Greenberg Roger A. , Cannizzaro Linda , Chin Lynda , Weiler Sarah R. , DePinho Ronald A.
Published: July 2002

Telomerase inhibition has been touted as a novel cancer-selective
therapeutic goal based on the observation of high telomerase levels in
most cancers and the importance of telomere maintenance in long-term
cellular growth and survival. Here, the impact of telomere dysfunction
on chemotherapeutic responses was assessed in normal and neoplastic
cells derived from telomerase RNA null (mTERC
−/−
) mice.
Telomere dysfunction, rather than telomerase
per se
, was
found to be the principal determinant governing chemosensitivity
specifically to agents that induced double-stranded DNA breaks (DSB).
Enhanced chemosensitivity in telomere dysfunctional cells was linked to
therapy-induced fragmentation and multichromosomal fusions, whereas
telomerase reconstitution restored genomic integrity and
chemoresistance. Loss of p53 function muted the cytotoxic effects of
DSB-inducing agents in cells with telomere dysfunction. Together, these
results point to the combined use of DSB-inducing agents and telomere
maintenance inhibition as an effective anticancer therapeutic approach
particularly in cells with intact p53-dependent checkpoint responses.
Y chromosome polymorphism is a strong determinant of male fitness in
Drosophila melanogaster
Authors: Chippindale Adam K. , Rice William R.
Published: July 2002

In many species, the Y (or W) chromosome carries relatively few
functional genes. This observation motivates the null hypothesis that
the Y will be a minor contributor to genetic variation for fitness.
Previous data and theory supported the null hypothesis, but evidence
presented here shows that the Y of
Drosophila
melanogaster
is a major determinant of a male's total fitness,
with standing genetic variation estimated to be 68% of that of an
entire X/autosome genomic haplotype. Most Y-linked genes are
expressed during spermatogenesis, and correspondingly, we found that
the Y influences fitness primarily through its effect on a male's
reproductive success (sperm competition and/or mating success) rather
than his egg-to-adult viability. But the fitness of a Y highly depended
on the genetic makeup of its bearer, reverting from high to low in
different genetic backgrounds. This pattern leads to large epistatic
(inconsistent among backgrounds) but no additive (consistent among
backgrounds) Y-linked genetic variance for fitness. On a
microevolutionary scale, the observed large epistatic variation on the
Y substantially reduces heritable variation for fitness among males,
and on a macroevolutionary scale, the Y produces strong selection for
genomic rearrangements that move interacting genes onto the
nonrecombining region of the Y.
A therapeutic agent with oriented carbohydrates for treatment of infections by Shiga toxin-producing
Escherichia coli
O157:H7
Authors: Nishikawa Kiyotaka , Matsuoka Koji , Kita Eiji , Okabe Noriko , Mizuguchi Masashi , Hino Kumiko , Miyazawa Shinobu , Yamasaki Chisato , Aoki Junken , Takashima Sachio , Yamakawa Yoshio , Nishijima Masahiro , Terunuma Daiyo , Kuzuhara Hiroyoshi , Natori Yasuhiro
Published: July 2002

Infection with Shiga toxin (Stx)-producing
Escherichia coli
O157:H7, which causes diarrhea and hemorrhagic colitis in humans, often results in fatal systemic complications, such as neurological damage and hemolytic–uremic syndrome. Because Stx circulating in the blood is a major causative factor of these complications, the development of a Stx neutralizer that functions in the circulation holds promise as a viable therapy. Here we developed a series of carbosilane dendrimers, in which trisaccharides of globotriaosyl ceramide, a receptor for Stx, were variously oriented at their termini (referred to as SUPER TWIG), and identified a SUPER TWIG with six trisaccharides as a Stx neutralizer functioning in the circulation. This SUPER TWIG specifically bound to Stx with high affinity (
K
d
= 1.1 × 10
−6
M) and inhibited the incorporation of the toxin into target cells. Intravenous administration of the SUPER TWIG along with Stx to mice substantially reduced the fatal brain damage and completely suppressed the lethal effect of Stx. Moreover, the SUPER TWIG protected mice from challenge with a fatal dose of
E. coli
O157:H7, even when administered after the establishment of the infection. The SUPER TWIG neutralized Stx
in vivo
by a mechanism in which the accumulation and immediate degradation of Stx by phagocytic macrophages present in the reticuloendothelial system were induced. Taken together, our findings indicate that this SUPER TWIG is therapeutic agent against infections by Stx-producing
E. coli
.
In vitro
trans-differentiation of adult hepatic stem cells into pancreatic endocrine hormone-producing cells
Authors: Yang Lijun , Li Shiwu , Hatch Heather , Ahrens Kim , Cornelius Janet G. , Petersen Bryon E. , Peck Ammon B.
Published: July 2002

Although organ-specific stem cells possess plasticity that permit differentiation along new lineages, production of endocrine pancreas and insulin-secreting β cells from adult nonpancreatic stem cells has not been demonstrated. We present evidence that highly purified adult rat hepatic oval “stem” cells, which are capable of differentiation to hepatocytes and bile duct epithelium, can trans-differentiate into pancreatic endocrine hormone-producing cells when cultured in a high-glucose environment. These differentiated cells can self-assemble to form three-dimensional islet cell-like clusters that express pancreatic islet cell differentiation-related transcripts detectable by reverse transcription–PCR/nested PCR (e.g., PDX-1, PAX-4, PAX-6, Nkx2.2 and Nkx6.1, insulin I, insulin II, glucose transporter 2, and glucagon) and islet-specific hormones detectable by immunocytochemistry (e.g., insulin, glucagon, and pancreatic polypeptide). In addition, these cells concomitantly lose expression of the hepatocyte protein Hep-par. When stimulated with glucose, these cells synthesize and secrete insulin, a response enhanced by nicotinamide. In a pilot study, the oval cell-derived islet cell-like clusters displayed the ability to reverse hyperglycemia in a diabetic NOD-
scid
mouse. These results indicate that primary adult liver stem cells can differentiate in a nonlineage-restricted manner. Trans-differentiation into endocrine pancreas could have significant implications for future therapies of diabetes.
Lipophosphoglycan is a virulence factor distinct from related glycoconjugates in the protozoan parasiteLeishmania major
Authors: Späth Gerald F. , Epstein Linda , Leader Ben , Singer Steven M. , Avila Herbert A. , Turco Salvatore J. , Beverley Stephen M.
Published: July 2002

Protozoan parasites of the genusLeishmaniaundergo a complex life cycle involving transmission by biting sand flies and replication within mammalian macrophage phagolysosomes. A major component of theLeishmaniasurface coat is the glycosylphosphatidylinositol (GPI)-anchored polysaccharide called lipophosphoglycan (LPG). LPG has been proposed to play many roles in the infectious cycle, including protection against complement and oxidants, serving as the major ligand for macrophage adhesion, and as a key factor mitigating host responses by deactivation of macrophage signaling pathways. However, all structural domains of LPG are shared by other major surface or secretory products, providing a biochemical redundancy that compromises the ability ofin vitrotests to establish whether LPG itself is a virulence factor. To study trulylpg−parasites, we generatedLeishmania majorlacking the geneLPG1[encoding a putative galactofuranosyl (Galf) transferase] by targeted gene disruption. Thelpg1−parasites lacked LPG but contained normal levels of related glycoconjugates and GPI-anchored proteins. Infections of susceptible mice and macrophagesin vitroshowed that theselpg−Leishmaniawere highly attenuated. Significantly and in contrast to previous LPG mutants, reintroduction ofLPG1into thelpg−parasites restored virulence. Thus, genetic approaches allow dissection of the roles of this complex family of interrelated parasite virulence factors, and definitively establish the role of LPG itself as a parasite virulence factor. Because thelpg1−mutant continue to synthesize bulk GPI-anchored Galf-containing glycolipids other than LPG, a second pathway distinct from the Golgi-associated LPG synthetic compartment must exist.
Powerful anticonvulsant action of IL-1 receptor antagonist on intracerebral injection and astrocytic overexpression in mice
Authors: Vezzani A. , Moneta D. , Conti M. , Richichi C. , Ravizza T. , De Luigi A. , De Simoni M. G. , Sperk G. , Andell-Jonsson S. , Lundkvist J. , Iverfeldt K. , Bartfai T.
Published: July 2002

IL-1β and its endogenous receptor antagonist (IL-1Ra) are rapidly induced by seizures in the rodent hippocampus. Exogenously applied IL-1β prolongs seizures in an IL-1R type I-mediated manner. This effect depends onN-methyl-d-aspartate receptor activation. We report here that intrahippocampal application of recombinant IL-1Ra or its selective endogenous overexpression in astrocytes under the control of glial acidic fibrillary protein promoter potently inhibits motor and electroencephalographic seizures induced by bicuculline methiodide in mice. Accordingly, transgenic mice show a reduced seizure-relatedc-fosmRNA expression in various forebrain areas compared with their wild-type littermates. Recombinant IL-1Ra was ineffective in mice deficient in IL-1R type I, havingper sea delayed onset to generalized convulsions. These results demonstrate that IL-1Ra mediates potent anticonvulsant effects acting on IL-1R type I and suggest that the balance between brain IL-1β and IL-1Ra represents a crucial mechanism to control seizure generalization.
Telomere dysfunction triggers extensive DNA fragmentation and evolution of complex chromosome abnormalities in human malignant tumors
Authors: Gisselsson David , Jonson Tord , Petersén Åsa , Strömbeck Bodil , Dal Cin Paola , Höglund Mattias , Mitelman Felix , Mertens Fredrik , Mandahl Nils
Published: July 2002

Although mechanisms for chromosomal instability in tumors have been described in animal and
in vitro
models, little is known about these processes in man. To explore cytogenetic evolution in human tumors, chromosomal breakpoint profiles were constructed for 102 pancreatic carcinomas and 140 osteosarcomas, two tumor types characterized by extensive genomic instability. Cases with few chromosomal alterations showed a preferential clustering of breakpoints to the terminal bands, whereas tumors with many changes showed primarily interstitial and centromeric breakpoints. The terminal breakpoint frequency was negatively correlated to telomeric TTAGGG repeat length, and fluorescence
in situ
hybridization with telomeric TTAGGG probes consistently indicated shortened telomeres and >10% of chromosome ends lacking telomeric signals. Because telomeric dysfunction may lead to formation of unstable ring and dicentric chromosomes, mitotic figures were also evaluated. Anaphase bridges were found in all cases, and fluorescence
in situ
hybridization demonstrated extensive structural rearrangements of chromosomes, with terminal transferase detection showing fragmented DNA in 5–20% of interphase cells. Less than 2% of cells showed evidence of necrosis or apoptosis, and telomerase was expressed in the majority of cases. Telomeric dysfunction may thus trigger chromosomal fragmentation through persistent bridge-breakage events in pancreatic carcinomas and osteosarcomas, leading to a continuous reorganization of the tumor genome. Telomerase expression is not sufficient for completely stabilizing the chromosome complement but may be crucial for preventing complete genomic deterioration and maintaining cellular survival.
Role of positively charged transmembrane segments in the insertion and assembly of mitochondrial inner-membrane proteins
Authors: Saint-Georges Yann , Hamel Patrice , Lemaire Claire , Dujardin Geneviève
Published: July 2002

The biogenesis of membrane oligomeric complexes is an intricate process that requires the insertion and assembly of transmembrane (TM) domains into the lipid bilayer. The Oxa1p family plays a key role in this process in organelles and bacteria. Hell
et al.
(2001,
EMBO J.
, 20, 1281–1288) recently have proposed that Oxa1p could act as part of a general membrane insertion machinery for mitochondrial respiratory complex subunits. We have previously shown that mutations in the TM domain of Cyt1p can partially compensate for the absence of Oxa1p. Here, we demonstrate that a single amino acid substitution in the TM domain of Qcr9p can bypass Oxa1p in yeast. Qcr9p and Cyt1p are two subunits of the respiratory complex
bc1
and their relative roles in the assembly of other respiratory complexes have been investigated. The mutations we have isolated in Cyt1p or Qcr9p introduce positively charged amino acids, and we show that the mutant TM domain of Cyt1p mediates the restoration of complex assembly. We propose that the positive charges introduced in Cyt1p and Qcr9p TM domains promote interactions with negatively charged TM domains of other respiratory complex subunits, allowing the coinsertion of both domains into the membrane, in the absence of Oxa1p. This model argues in favor of a role of Oxa1p in the insertion and the lateral exit of less hydrophobic TM domains from the translocation site into the lipid bilayer.
Bacteriophage lambda N protein alone can induce transcription antitermination in vitro.
Authors: Rees W A , Weitzel S E , Yager T D , Das A , von Hippel P H
Published: July 2002

Specific and processive antitermination by bacteriophage lambda N protein in vivo and in vitro requires the participation of a large number of Escherichia coli proteins (Nus factors), as well as an RNA hairpin (boxB) within the nut site of the nascent transcript. In this study we show that efficient, though nonprocessive, antitermination can be induced by large concentrations of N alone, even in the absence of a nut site. By adding back individual components of the system, we also show that N with nut+ nascent RNA is much more effective in antitermination than is N alone. This effect is abolished if N is competed away from the nut+ RNA by adding, in trans, an excess of boxB RNA. The addition of NusA makes antitermination by the N-nut+ complex yet more effective. This NusA-dependent increase in antitermination is lost when delta nut transcripts are used. These results suggest the formation of a specific boxB RNA-N-NusA complex within the transcription complex. By assuming an equilibrium model, we estimate a binding constant of 5 x 10(6) M-1 for the interaction of N alone with the transcription complex. This value can be used to estimate a characteristic dissociation time of N from the complex that is comparable to the dwell time of the complex at an average template position, thus explaining the nonprocessivity of the antitermination effect induced by N alone. On this basis, the effective dissociation rate of N should be approximately 1000-fold slower from the minimally processive (100-600 bp) N-NusA-nut+ transcription complex and approximately 10(5)-fold slower from the maximally processive (thousands of base pairs) complex containing all of the components of the in vivo N-dependent antitermination system.
Localization of alpha type II calcium calmodulin-dependent protein kinase at glutamatergic but not gamma-aminobutyric acid (GABAergic) synapses in thalamus and cerebral cortex.
Authors: Liu X B , Jones E G
Published: July 2002

The alpha subunit of type II calcium/calmodulin-dependent protein kinase (CAM II kinase-alpha) plays an important role in longterm synaptic plasticity. We applied preembedding immunocytochemistry (for CAM II kinase-alpha) and postembedding immunogold labeling [for glutamate or gamma-aminobutyric acid (GABA)] to explore the subcellular relationships between transmitter-defined axon terminals and the kinase at excitatory and inhibitory synapses in thalamus and cerebral cortex. Many (but not all) axon terminals ending in asymmetric synapses contained presynaptic CAM II kinase-alpha immunoreactivity; GABAergic terminals ending in symmetric synapses did not. Postsynaptically, CAM II kinase-alpha immunoreactivity was associated with postsynaptic densities of many (but not all) glutamatergic axon terminals ending on excitatory neurons. CAM II kinase-alpha immunoreactivity was absent at postsynaptic densities of all GABAergic synapses. The findings show that CAM II kinase-alpha is selectively expressed in subpopulations of excitatory neurons and, to our knowledge, demonstrate for the first time that it is only associated with glutamatergic terminals pre- and postsynaptically. CAM II kinase-alpha is unlikely to play a role in plasticity at GABAergic synapses.
Induction of myelination in the central nervous system by electrical activity.
Authors: Demerens C , Stankoff B , Logak M , Anglade P , Allinquant B , Couraud F , Zalc B , Lubetzki C
Published: July 2002

The oligodendrocyte is the myelin-forming cell in the central nervous system. Despite the close interaction between axons and oligodendrocytes, there is little evidence that neurons influence myelinogenesis. On the contrary, newly differentiated oligodendrocytes, which mature in culture in the total absence of neurons, synthesize the myelin-specific constituents of oligodendrocytes differentiated in vivo and even form myelin-like figures. Neuronal electrical activity may be required, however, for the appropriate formation of the myelin sheath. To investigate the role of electrical activity on myelin formation, we have used highly specific neurotoxins, which can either block (tetrodotoxin) or increase (alpha-scorpion toxin) the firing of neurons. We show that myelination can be inhibited by blocking the action potential of neighboring axons or enhanced by increasing their electrical activity, clearly linking neuronal electrical activity to myelinogenesis.
Toward antibody-directed "abzyme" prodrug therapy, ADAPT: carbamate prodrug activation by a catalytic antibody and its in vitro application to human tumor cell killing.
Authors: Wentworth P , Datta A , Blakey D , Boyle T , Partridge L J , Blackburn G M
Published: July 2002

Antibody-directed enzyme prodrug therapy, ADEPT, is a recent approach to targeted cancer chemotherapy intended to diminish the nonspecific toxicity associated with many commonly used chemotherapeutic agents. Most ADEPT systems incorporate a bacterial enzyme, and thus their potential is reduced because of the immunogenicity of that component of the conjugate. This limitation can be circumvented by the use of a catalytic antibody, which can be "humanized," in place of the bacterial enzyme catalyst. We have explored the scope of such antibody-directed "abzyme" prodrug therapy, ADAPT, to evaluate the potential for a repeatable targeted cancer chemotherapy. We report the production of a catalytic antibody that can hydrolyze the carbamate prodrug 4-[N,N-bis(2-chloroethyl)]aminophenyl-N-[(1S)-(1,3- dicarboxy)propyl]carbamate (1) to generate the corresponding cytotoxic nitrogen mustard (Km = 201 microM, kcat = 1.88 min-1). In vitro studies with this abzyme, EA11-D7, and prodrug 1 lead to a marked reduction in viability of cultured human colonic carcinoma (LoVo) cells relative to appropriate controls. In addition, we have found a good correlation between antibody catalysis as determined by this cytotoxicity assay in vitro and competitive binding studies of candidate abzymes to the truncated transition-state analogue ethyl 4-nitrophenylmethylphosphonate. This cell-kill assay heralds a general approach to direct and rapid screening of antibody libraries for catalysts.
The Gfi-1 protooncoprotein represses
Bax
expression and inhibits T-cell death
Authors: Grimes H. Leighton , Gilks C. Blake , Chan Tung O. , Porter Susan , Tsichlis Philip N.
Published: July 2002

The
Gfi-1
protooncogene encodes a nuclear
zinc-finger protein that carries a novel repressor domain, SNAG, and
functions as a position- and orientation-independent active
transcriptional repressor. The Gfi-1 repressor allows interleukin 2
(IL-2)-dependent T cells to escape G
1
arrest induced by
IL-2 withdrawal in culture and collaborates with c-
myc
and
pim-1
for the induction of retrovirus-induced
lymphomas in animals. Here we show that overexpression of
Gfi-1
also inhibits cell death induced by cultivation of
IL-2-dependent T-cell lines in IL-2-deficient media. Similarly,
induction of
Gfi-1
in primary thymocytes from mice
carrying a metal-inducible
Gfi-1
transgene inhibits cell
death induced by cultivation
in vitro
. The protein and
mRNA levels of the proapoptotic regulator
Bax
are down-regulated by Gfi-1 in both immortalized T-cell lines and
primary transgenic thymocytes. The repression is direct and depends on
several Gfi-1-binding sites in the p53-inducible
Bax
promoter. In addition to
Bax
, Gfi-1 also represses
Bak
, another apoptosis-promoting member of the
Bcl-2
gene family. Therefore, Gfi-1 may inhibit
apoptosis by means of its repression of multiple
proapoptotic regulators. The antiapoptotic properties
of
Gfi-1
provide a potential explanation for its strong
collaboration with c-
myc
during oncogenesis.
cag
, a pathogenicity island of
Helicobacter pylori,
encodes type I-specific and disease-associated virulence factors
Authors: Censini Stefano , Lange Christina , Xiang Zhaoying , Crabtree Jean E. , Ghiara Paolo , Borodovsky Mark , Rappuoli Rino , Covacci Antonello
Published: July 2002

cagA
, a gene that codes for an immunodominant
antigen, is present only in
Helicobacter pylori
strains
that are associated with severe forms of gastroduodenal disease (type I
strains). We found that the genetic locus that contains
cagA
(
cag
) is part of a 40-kb DNA
insertion that likely was acquired horizontally and integrated into the
chromosomal glutamate racemase gene. This pathogenicity island is
flanked by direct repeats of 31 bp. In some strains,
cag
is split into a right segment (
cag
I) and a left segment
(
cag
II) by a novel insertion sequence
(IS
605
). In a minority of
H. pylori
strains,
cag
I and
cag
II are separated by
an intervening chromosomal sequence. Nucleotide sequencing of the
23,508 base pairs that form the
cag
I region and the
extreme 3′ end of the
cag
II region reveals the presence
of 19 ORFs that code for proteins predicted to be mostly membrane
associated with one gene (
cagE
), which is similar to the
toxin-secretion gene of
Bordetella pertussis, ptlC,
and
the transport systems required for plasmid transfer, including the
virB4
gene of
Agrobacterium tumefaciens
.
Transposon inactivation of several of the
cag
I genes
abolishes induction of IL-8 expression in gastric epithelial cell
lines. Thus, we believe the
cag
region may encode
a novel
H. pylori
secretion system for the export of
virulence determinants.
Isolation and characterization of the chicken m2 acetylcholine receptor promoter region: Induction of gene transcription by leukemia inhibitory factor and ciliary neurotrophic factor
Authors: Rosoff Marc L. , Wei Jia , Nathanson Neil M.
Published: July 2002

We have isolated the promoter region and determined the start sites
of transcription for the gene encoding the chicken m2 (cm2) muscarinic
acetylcholine receptor. Transfection experiments, using cm2-luciferase
reporter gene constructs, demonstrated that a 789-bp genomic fragment
was sufficient to drive high level expression in chicken heart primary
cultures, while an additional 1.2-kb region was required for maximal
expression in mouse septal/neuroblastoma (SN56) cells. Treatment of
SN56 cells with the cytokines ciliary neurotrophic factor and leukemia
inhibitory factor increases expression of endogenous
muscarinic acetylcholine receptors and results in a 4- to 6-fold
induction of cm2 promoter driven luciferase expression. We have mapped
a region of the cm2 promoter that is necessary for induction by
cytokines.
HMG I(Y) interferes with the DNA binding of NF-AT factors and the induction of the interleukin 4 promoter in T cells
Authors: Klein-Hessling Stefan , Schneider Günter , Heinfling Annette , Chuvpilo Sergei , Serfling Edgar
Published: July 2002

HMG I(Y) proteins bind to double-stranded A+T oligonucleotides longer than three base pairs. Such motifs form part of numerous NF-AT-binding sites of lymphokine promoters, including the interleukin 4 (IL-4) promoter. NF-AT factors share short homologous peptide sequences in their DNA-binding domain with NF-κB factors and bind to certain NF-κB sites. It has been shown that HMG I(Y) proteins enhance NF-κB binding to the interferon β promoter and virus-mediated interferon β promoter induction. We show that HMG I(Y) proteins exert an opposite effect on the DNA binding of NF-AT factors and the induction of the IL-4 promoter in T lymphocytes. Introduction of mutations into a high-affinity HMG I(Y)-binding site of the IL-4 promoter, which decreased HMG I(Y)-binding to a NF-AT-binding sequence, the Pu-bB(or P) site, distinctly increased the induction of the IL-4 promoter in Jurkat T leukemia cells. High concentrations of HMG I(Y) proteins are able to displace NF-ATp from its binding to the Pu-bBsite. High HMG I(Y) concentrations are typical for Jurkat cells and peripheral blood T lymphocytes, whereas El4 T lymphoma cells and certain T helper type 2 cell clones contain relatively low HMG I(Y) concentrations. Our results indicate that HMG I(Y) proteins do not cooperate, but instead compete with NF-AT factors for the binding to DNA even though NF-AT factors share some DNA-binding properties with NF-kB factors. This competition between HMG I(Y) and NF-AT proteins for DNA binding might be due to common contacts with minor groove nucleotides of DNA and may be one mechanism contributing to the selective IL-4 expression in certain T lymphocyte populations, such as T helper type 2 cells.
The terminal Paleozoic fungal event: evidence of terrestrial ecosystem destabilization and collapse.
Authors: Visscher H , Brinkhuis H , Dilcher D L , Elsik W C , Eshet Y , Looy C V , Rampino M R , Traverse A
Published: July 2002

Because of its prominent role in global biomass storage, land vegetation is the most obvious biota to be investigated for records of dramatic ecologic crisis in Earth history. There is accumulating evidence that, throughout the world, sedimentary organic matter preserved in latest Permian deposits is characterized by unparalleled abundances of fungal remains, irrespective of depositional environment (marine, lacustrine, fluviatile), floral provinciality, and climatic zonation. This fungal event can be considered to reflect excessive dieback of arboreous vegetation, effecting destabilization and subsequent collapse of terrestrial ecosystems with concomitant loss of standing biomass. Such a scenario is in harmony with predictions that the Permian-Triassic ecologic crisis was triggered by the effects of severe changes in atmospheric chemistry arising from the rapid eruption of the Siberian Traps flood basalts.
Function of the pre-T-cell receptor alpha chain in T-cell development and allelic exclusion at the T-cell receptor beta locus.
Authors: Xu Y , Davidson L , Alt F W , Baltimore D
Published: July 2002

The pre-T-cell receptor, composed of the T-cell receptor (TCR) beta chain (TCRbeta), pre-Talpha (pTalpha) chain, and CD3 molecules, has been postulated to be a transducer of signals during the early stages of T-cell development. To examine the function of the transmembrane pTalpha chain during tbymocyte development, we generated pTalpha-/- embryonic stem cells and assayed their ability to differentiate into lymphoid cells in vivo after injection into recombination-activating gene (RAG)-2-deficient blastocysts. Thymocytes representing all stages of T-cell differentiation were detected in the thymus of pTalpha-/- chimeric mice, indicating that thymocyte development can occur without pTalpha. However, greatly reduced thymocyte numbers and substantially increased percentages of both CD4-CD8- thymocytes and TCRgammadelta+ thymocytes suggest that pTalpha plays a critical role in thymocyte expansion. To investigate the role of the pTalpha chain in allelic exclusion at the TCRbeta locus, a functionally rearranged TCRbeta minigene was introduced into pTalpha-/- and pTalpha+/- embryonic stem cells, which were subsequently assayed by RAG-2-deficient blastocyst complementation. In the absence of pTalpha, expression of the transgenic TCRbeta inhibited rearrangement of the endogenous TCRbeta locus to an extent similar to that seen in normal TCRbeta transgenic mice, suggesting that pTalpha may not be required for signaling allelic exclusion at the TCRbeta locus.
Crystal structures of the trimeric human immunodeficiency virus type 1 matrix protein: implications for membrane association and assembly.
Authors: Hill C P , Worthylake D , Bancroft D P , Christensen A M , Sundquist W I
Published: July 2002

The human immunodeficiency virus type 1 (HIV-1) matrix protein forms a structural shell associated with the inner viral membrane and performs other essential functions throughout the viral life cycle. The crystal structure of the HIV-1 matrix protein, determined at 2.3 angstrom resolution, reveals that individual matrix molecules are composed of five major helices capped by a three-stranded mixed beta-sheet. Unexpectedly, the protein assembles into a trimer in three different crystal lattices, burying 1880 angstrom2 of accessible surface area at the trimer interfaces. Trimerization appears to create a large, bipartite membrane binding surface in which exposed basic residues could cooperate with the N-terminal myristoyl groups to anchor the protein on the acidic inner membrane of the virus.
Development of a bovine X chromosome linkage group and painting probes to assess cattle, sheep, and goat X chromosome segment homologies.
Authors: Ponce de Leon F A , Ambady S , Hawkins G A , Kappes S M , Bishop M D , Robl J M , Beattie C W
Published: July 2002

The X chromosome linkage group is conserved in placental mammals. However, X chromosome morphological differences, due to internal chromosome rearrangements, exist among mammalian species. We have developed bovine chromosome painting probes for Xp and Xq to assess segment homologies between the submetacentric bovine X chromosome and the acrocentric sheep and goat X chromosomes. These painting probes and their corresponding DNA libraries were developed by chromosome micromanipulation, DNA micropurification, microcloning, and PCR amplification. The bovine Xp painting probe identified an interstitially located homologous segment in the sheep and goat Xq region, most probably resulting from chromosome inversion. Ten type II (microsatellite) markers obtained from the bovine Xq library and five other X chromosome assigned, but unlinked, markers were used to generate a linkage map for Xq spanning 89.4 centimorgans. The chromosome painting probes and molecular markers generated in this study would be useful for comparative mapping and tracing of internal X chromosome rearrangements in all ruminant species and would contribute to the understanding of mammalian sex chromosome evolution.
cAMP inducibility of transcriptional repressor ICER in developing and mature human T lymphocytes.
Authors: Bodor J , Spetz A L , Strominger J L , Habener J F
Published: July 2002

Stimulation of the cAMP-dependent signaling pathway exerts an inhibitory effect on the proliferation and effector functions of T cells. The ability of T cells to form high intracellular levels of cAMP is acquired during development in the human thymus and is retained by the majority of mature peripheral T lymphocytes. Here we show that elevated cAMP levels in T cells correlate with the expression of the potent transcriptional repressor ICER (inducible cAMP early repressor) previously described in the hypothalamic-pituitary-gonadal axis. Further, in transcriptional assays in vivo, ICER inhibits calcineurin-mediated expression of the interleukin 2 promoter as well as Tax-mediated transactivation of the human T-lymphotropic virus type I (HTLV-I) promoter. Thus, the induction of ICER in T cells may play an important role in the cAMP-induced quiescence and the persistent latency of HTLV-I.
Centripetal cholesterol flux from extrahepatic organs to the liver is independent of the concentration of high density lipoprotein-cholesterol in plasma.
Authors: Osono Y , Woollett L A , Marotti K R , Melchior G W , Dietschy J M
Published: July 2002

High density lipoproteins (HDLs) play a role in two processes that include the amelioration of atheroma formation and the centripetal flow of cholesterol from the extrahepatic organs to the liver. This study tests the hypothesis that the flow of sterol from the peripheral organs to the liver is dependent upon circulating HDL concentrations. Transgenic C57BL/6 mice were used that expressed variable amounts of simian cholesteryl ester-transfer protein (CETP). The rate of centripetal cholesterol flux was quantitated as the sum of the rates of cholesterol synthesis and low density lipoprotein-cholesterol uptake in the extrahepatic tissues. Steady-state concentrations of cholesterol carried in HDL (HDL-C) varied from 59 to 15 mg/dl and those of apolipoprotein AI from 138 to 65 mg/dl between the control mice (CETPc) and those maximally expressing the transfer protein (CETP+). There was no difference in the size of the extrahepatic cholesterol pools in the CETPc and CETP+ animals. Similarly, the rates of cholesterol synthesis (83 and 80 mg/day per kg, respectively) and cholesterol carried in low density lipoprotein uptake (4 and 3 mg/day per kg, respectively) were virtually identical in the two groups. Thus, under circumstances where the steady-state concentration of HDL-C varied 4-fold, the centripetal flux of cholesterol from the peripheral organs to the liver was essentially constant at approximately 87 mg/day per kg. These studies demonstrate that neither the concentration of HDL-C or apolipoprotein AI nor the level of CETP activity dictates the magnitude of centripetal cholesterol flux from the extrahepatic organs to the liver, at least in the mouse.
Elasmobranchs express separate cholecystokinin and gastrin genes
Authors: Johnsen Anders H. , Jønson Lars , Rourke Ian J. , Rehfeld Jens F.
Published: July 2002

The peptide hormone gastrin was long believed to be specific for higher vertebrates, whereas its homologue, cholecystokinin (CCK), has been assumed to represent the original ancestor of the CCK/gastrin family. To trace the divergence of the CCK/gastrin family beyond birds, reptiles, and amphibians we have now examined sharks. Distinct CCK and gastrin peptides were identified in two shark species, the spiny dogfish (
Squalus acanthias
) and the porbeagle (
Lamna cornubica
). The corresponding genes and cDNAs were isolated and sequenced from the spiny dogfish. Comparison with several vertebrate species show that the CCK gene and peptide structures have been considerably more conserved than the corresponding gastrin structures. Alignment of the dogfish prepropeptides displays similarities that support the hypothesis that they share a common ancestor. Our findings move the CCK/gastrin family segregation back to at least 350 million years ago. This event must have occurred before, or perhaps during, the evolution of cartilagenous fishes, probably concomitant with the occurrence of gastric acid secretion.
Synthesis and screening of small molecule libraries active in binding to DNA
Authors: Shipps Gerald W. , Pryor Kent E. , Xian Jun , Skyler David A. , Davidson Eric H. , Rebek Julius
Published: July 2002

Five synthetic combinatorial libraries of 2,080 components each were screened as mixtures for inhibition of DNA binding to two transcription factors. Rapid, solution-phase synthesis coupled to a gel-shift assay led to the identification of two compounds active at a 5- to 10-μM concentration level. The likely mode of inhibition is intercalation between DNA base pairs. The efficient deconvolution through sublibrary synthesis augurs well for the use of large mixtures of small, nonpeptide molecules in biological screens.