bluuebunny/crossref_metadata_2025 huggingface dataset:
Antifolate-resistant mutants of
Plasmodium falciparum
dihydrofolate reductase
Authors: Sirawaraporn Worachart , Sathitkul Tanajit , Sirawaraporn Rachada , Yuthavong Yongyuth , Santi Daniel V.
Published: July 2002

Single and multiple mutations at residues 16, 51, 59, 108, and 164 of
Plasmodium falciparum
dihydrofolate reductase (pfDHFR) have been linked to antifolate resistance in malaria. We prepared and characterized all seven of the pfDHFR mutants found in nature, as well as six mutants not observed in nature. Mutations involving residues 51, 59, 108, or 164 conferred cross resistance to both the antifolates pyrimethamine and cycloguanil, whereas mutation of residue 16 specifically conferred resistance to cycloguanil. The antifolate resistance of enzyme mutants found in nature correlated with
in vivo
antifolate resistance; however, mutants not found in nature were either poorly resistant or had insufficient catalytic activity to support DNA synthesis. Thus, specific combinations of multiple mutations at target residues were selected in nature to optimize resistance. Further, the resistance of multiple mutants was more than the sum of the component single mutations, indicating that residues were selected for their synergistic as well as intrinsic effects on resistance. Pathways inferred for the evolution of pyrimethamine-resistant mutants suggested that all multiple mutants emerged from stepwise selection of the single mutant, S108N. Thus, we propose that drugs targeted to both the wild-type pfDHFR and S108N mutant would have a low propensity for developing resistance, and hence could provide effective antimalarial agents.
A complex major histocompatibility complexDlocus variant generated by an unusual recombination mechanism in mice
Authors: Yun Theodore J. , Melvold Roger W. , Pease Larry R.
Published: July 2002

A spontaneous variant of the mouse class I major histocompatibility complexDbgene, designatedDbm28, is characterized. This mutation consists of a cluster of nucleotide substitutions in exon 3 that resembles the product of a classical gene conversion event in that the substituted nucleotides appear to be templated. However,Dbm28is distinctive, because no single donor gene containing the nucleotide sequence of the mutation exists in the genome of the parent strain. The mutation is consistent with the expected result of an interaction of two donor genes at the target locus during a single recombination event. While no known genetic mechanism gives rise to this class of mutation, we have established that 10 percent of spontaneous class I mutations in the mouse major histocompatibility complex have this complex phenotype. This process occurs at theDlocus and theKlocus. The significance of this kind of genetic interaction may extend beyond the major histocompatibility complex and have importance in shaping other multigene families.
A novel bHLH-PAS factor with close sequence similarity to hypoxia-inducible factor 1α regulates the
VEGF
expression and is potentially involved in lung and vascular development
Authors: Ema Masatsugu , Taya Shinichiro , Yokotani Noboru , Sogawa Kazuhiro , Matsuda Youichi , Fujii-Kuriyama Yoshiaki
Published: July 2002

We have isolated and characterized a cDNA for a novel Per-Arnt/AhR-Sim basic helix–loop–helix (bHLH-PAS) factor that interacts with the Ah receptor nuclear translocator (Arnt), and its predicted amino acid sequence exhibits significant similarity to the hypoxia-inducible factor 1α (HIF1α) and
Drosophila trachealess
(
dTrh
) gene product. The HIF1α-like factor (HLF) encoded by the isolated cDNA bound the hypoxia-response element (HRE) found in enhancers of genes for erythropoietin, vascular endothelial growth factor (VEGF), and various glycolytic enzymes, and activated transcription of a reporter gene harboring the HRE. Although transcription-activating properties of HLF were very similar to those reported for HIF1α, their expression patterns were quite different between the two factors; HLF mRNA was most abundantly expressed in lung, followed by heart, liver, and other various organs under normoxic conditions, whereas HIF1α mRNA was ubiquitously expressed at much lower levels. In lung development around parturition, HLF mRNA expression was markedly enhanced, whereas that of HIF1α mRNA remained apparently unchanged at a much lower level. Moreover, HLF mRNA expression was closely correlated with that of VEGF mRNA. Whole mount
in situ
hybridization experiments demonstrated that HLF mRNA was expressed in vascular endothelial cells at the middle stages (9.5 and 10.5 days postcoitus) of mouse embryo development, where HIF1α mRNA was almost undetectable. The high expression level of HLF mRNA in the O
2
delivery system of developing embryos and adult organs suggests that in a normoxic state, HLF regulates gene expression of VEGF, various glycolytic enzymes, and others driven by the HRE sequence, and may be involved in development of blood vessels and the tubular system of lung.
Impaired B-lymphopoiesis, myelopoiesis, and derailed cerebellar neuron migration in CXCR4- and SDF-1-deficient mice
Authors: Ma Qing , Jones Dan , Borghesani Paul R. , Segal Rosalind A. , Nagasawa Takashi , Kishimoto Tadamitsu , Bronson Roderick T. , Springer Timothy A.
Published: July 2002

The chemokine stromal cell-derived factor 1, SDF-1, is an important regulator of leukocyte and hematopoietic precursor migration and pre-B cell proliferation. The receptor for SDF-1, CXCR4, also functions as a coreceptor for T-tropic HIV-1 entry. We find that mice deficient for CXCR4 die perinatally and display profound defects in the hematopoietic and nervous systems. CXCR4-deficient mice have severely reduced B-lymphopoiesis, reduced myelopoiesis in fetal liver, and a virtual absence of myelopoiesis in bone marrow. However, T-lymphopoiesis is unaffected. Furthermore, the cerebellum develops abnormally with an irregular external granule cell layer, ectopically located Purkinje cells, and numerous chromophilic cell clumps of abnormally migrated granule cells within the cerebellar anlage. Identical defects are observed in mice lacking SDF-1, suggesting a monogamous relationship between CXCR4 and SDF-1. This receptor-ligand selectivity is unusual among chemokines and their receptors, as is the function in migration of nonhematopoietic cells.
5-Hydroxytryptamine
2A
serotonin receptors in the primate cerebral cortex: Possible site of action of hallucinogenic and antipsychotic drugs in pyramidal cell apical dendrites
Authors: Jakab Robert L. , Goldman-Rakic Patricia S.
Published: July 2002

To identify the cortical sites where 5-hydroxytryptamine
2A
(5-HT
2A
) serotonin receptors respond to the action of hallucinogens and atypical antipsychotic drugs, we have examined the cellular and subcellular distribution of these receptors in the cerebral cortex of macaque monkeys (with a focus on prefrontal areas) by using light and electron microscopic immunocytochemical techniques. 5-HT
2A
receptor immunoreactivity was detected in all cortical layers, among which layers II and III and layers V and VI were intensely stained, and layer IV was weakly labeled. The majority of the receptor-labeled cells were pyramidal neurons and the most intense immunolabeling was consistently confined to their parallelly aligned proximal apical dendrites that formed two intensely stained bands above and below layer IV. In double-label experiments, 5-HT
2A
label was found in calbindin D28k-positive, nonphosphorylated-neurofilament-positive, and immuno-negative pyramidal cells, suggesting that probably all pyramidal cells express 5-HT
2A
receptors. 5-HT
2A
label was also found in large- and medium-size interneurons, some of which were immuno-positive for calbindin. 5-HT
2A
receptor label was also associated with axon terminals. These findings reconcile the data on the receptor’s cortical physiology and localization by (
i
) establishing that 5-HT
2A
receptors are located postsynaptically and presynaptically, (
ii
) demonstrating that pyramidal neurons constitute the major 5-HT
2A
-receptor-expressing cells in the cortex, and (
iii
) supporting the view that the apical dendritic field proximal to the pyramidal cell soma is the “hot spot” for 5-HT
2A
-receptor-mediated physiological actions relevant to normal and “psychotic” functional states of the cerebral cortex.
Mitochondrial reactive oxygen species trigger hypoxia-induced transcription
Authors: Chandel N. S. , Maltepe E. , Goldwasser E. , Mathieu C. E. , Simon M. C. , Schumacker P. T.
Published: July 2002

Transcriptional activation of erythropoietin, glycolytic enzymes, and vascular endothelial growth factor occurs during hypoxia or in response to cobalt chloride (CoCl
2
) in Hep3B cells. However, neither the mechanism of cellular O
2
sensing nor that of cobalt is fully understood. We tested whether mitochondria act as O
2
sensors during hypoxia and whether hypoxia and cobalt activate transcription by increasing generation of reactive oxygen species (ROS). Results show (
i
) wild-type Hep3B cells increase ROS generation during hypoxia (1.5% O
2
) or CoCl
2
incubation, (
ii
) Hep3B cells depleted of mitochondrial DNA (ρ
0
cells) fail to respire, fail to activate mRNA for erythropoietin, glycolytic enzymes, or vascular endothelial growth factor during hypoxia, and fail to increase ROS generation during hypoxia; (
iii
) ρ
0
cells increase ROS generation in response to CoCl
2
and retain the ability to induce expression of these genes; and (
iv
) the antioxidants pyrrolidine dithiocarbamate and ebselen abolish transcriptional activation of these genes during hypoxia or CoCl
2
in wild-type cells, and abolish the response to CoCl
2
in ρ° cells. Thus, hypoxia activates transcription via a mitochondria-dependent signaling process involving increased ROS, whereas CoCl
2
activates transcription by stimulating ROS generation via a mitochondria-independent mechanism.
Phospholipase D activity is required for suppression of yeast phosphatidylinositol transfer protein defects
Authors: Xie Zhigang , Fang Min , Rivas Marcos P. , Faulkner Alexander J. , Sternweis Paul C. , Engebrecht JoAnne , Bankaitis Vytas A.
Published: July 2002

Yeast phosphatidylinositol transfer protein (Sec14p) function is essential for production of Golgi-derived secretory vesicles, and this requirement is bypassed by mutations in at least seven genes. Analyses of such ‘bypass Sec14p’ mutants suggest that Sec14p acts to maintain an essential Golgi membrane diacylglycerol (DAG) pool that somehow acts to promote Golgi secretory function.
SPO14
encodes the sole yeast phosphatidylinositol-4,5-bisphosphate-activated phospholipase D (PLD). PLD function, while essential for meiosis, is dispensable for vegetative growth. Herein, we report specific physiological circumstances under which an unanticipated requirement for PLD activity in yeast vegetative Golgi secretory function is revealed. This PLD involvement is essential in ‘bypass Sec14p’ mutants where normally Sec14p-dependent Golgi secretory reactions are occurring in a Sec14p-independent manner. PLD catalytic activity is necessary but not sufficient for ‘bypass Sec14p’, and yeast operating under ‘bypass Sec14p’ conditions are ethanol-sensitive. These data suggest that PLD supports ‘bypass Sec14p’ by generating a phosphatidic acid pool that is somehow utilized in supporting yeast Golgi secretory function.
Characteristics of virus-specific CD8+T cells in the liver during the control and resolution phases of influenza pneumonia
Authors: Belz Gabrielle T. , Altman John D. , Doherty Peter C.
Published: July 2002

Dissection of the primary and secondary response to an influenza A virus established that the liver contains a substantial population of CD8+T cells specific for the immunodominant epitope formed by H-2Dband the influenza virus nucleoprotein peptide fragment NP366–374(DbNP366). The numbers of CD8+DbNP366+cells in the liver reflected the magnitude of the inflammatory process in the pneumonic lung, though replication of this influenza virus is limited to the respiratory tract. Analysis of surface phenotypes indicated that the liver CD8+DbNP366+cells tended to be more “activated” than the set recovered from lymphoid tissue but generally less so than those from the lung. The distinguishing characteristic of the lymphocytes from the liver was that the prevalence of the CD8+DbNP366+set was always much higher than the percentage of CD8+T cells that could be induced to synthesize interferon γ after short-term,in vitrostimulation with the NP366–374peptide, whereas these values were generally comparable for virus-specific CD8+T cells recovered from other tissue sites. Also, the numbers of apoptotic CD8+T cells were higher in the liver. The results overall are consistent with the idea that antigen-specific CD8+T cells are destroyed in the liver during the control and resolution phases of this viral infection, though this destruction is not necessarily an immediate process.
A neuronal model of a global workspace in effortful cognitive tasks
Authors: Dehaene Stanislas , Kerszberg Michel , Changeux Jean-Pierre
Published: July 2002

A minimal hypothesis is proposed concerning the brain processes underlying effortful tasks. It distinguishes two main computational spaces: a unique global workspace composed of distributed and heavily interconnected neurons with long-range axons, and a set of specialized and modular perceptual, motor, memory, evaluative, and attentional processors. Workspace neurons are mobilized in effortful tasks for which the specialized processors do not suffice. They selectively mobilize or suppress, through descending connections, the contribution of specific processor neurons. In the course of task performance, workspace neurons become spontaneously coactivated, forming discrete though variable spatio-temporal patterns subject to modulation by vigilance signals and to selection by reward signals. A computer simulation of the Stroop task shows workspace activation to increase during acquisition of a novel task, effortful execution, and after errors. We outline predictions for spatio-temporal activation patterns during brain imaging, particularly about the contribution of dorsolateral prefrontal cortex and anterior cingulate to the workspace.
Thiazolidinediones and insulin resistance: Peroxisome proliferatoractivated receptor γ activation stimulates expression of the
CAP
gene
Authors: Ribon Vered , Johnson John H. , Camp Heidi S. , Saltiel Alan R.
Published: July 2002

c-Cbl-associated protein (CAP) is a signaling protein that interacts with both c-Cbl and the insulin receptor that may be involved in the specific insulin-stimulated tyrosine phosphorylation of c-Cbl. The restricted expression of CAP in cells metabolically sensitive to insulin suggests an important potential role in insulin action. The expression of CAP mRNA and proteins are increased in 3T3-L1 adipocytes by the insulin sensitizing thiazolidinedione drugs, which are activators of the peroxisome proliferator-activated receptor γ (PPARγ). The stimulation of CAP expression by PPARγ activators results from increased transcription. This increased expression of CAP was accompanied by a potentiation of insulin-stimulated c-Cbl tyrosine phosphorylation. Administration of the thiazolidinedione troglitazone to Zucker (
fa
/
fa
) rats markedly increased the expression of the major CAP isoform in adipose tissue. This effect was sustained for up to 12 weeks of treatment and accompanied the ability of troglitazone to prevent the onset of diabetes and its complications. Thus, CAP is the first PPARγ-sensitive gene identified that participates in insulin signaling and may play a role in thiazolidinedione-induced insulin sensitization.
Low density lipoprotein receptor-negative mice expressing human apolipoprotein B-100 develop complex atherosclerotic lesions on a chow diet: No accentuation by apolipoprotein(a)
Authors: Sanan D. A. , Newland D. L. , Tao R. , Marcovina S. , Wang J. , Mooser V. , Hammer R. E. , Hobbs H. H.
Published: July 2002

We have generated mice with markedly elevated plasma levels of human low density lipoprotein (LDL) and reduced plasma levels of high density lipoprotein. These mice have no functional LDL receptors [
LDLR
−/−
] and express a human apolipoprotein B-100 (apoB) transgene [
Tg(apoB
+/+
)] with or without an apo(a) transgene [
Tg(apoa
+/−
)]. Twenty animals (10 males and 10 females) of each of the following four genotypes were maintained on a chow diet: (
i
)
LDLR
−/−
, (
ii
)
LDLR
−/−
;
Tg(apoa
+/−
), (iii
)
LDLR
−/−
;
Tg(apoB
+/+
),
and (
iv
)
LDLR
−/−
;
Tg(apoB
+/+
);Tg(apo
+/−
).
The mice were killed at 6 mo, and the percent area of the aortic intimal surface that stained positive for neutral lipid was quantified. Mean percent areas of lipid staining were not significantly different between the
LDLR
−/−
and
LDLR
−/−
;
Tg(apoa
+/−
)
mice (1.0 ± 0.2% vs. 1.4 ± 0.3%). However, the
LDLR
−/−
;
Tg(apoB
+/+
)
mice had ≈15-fold greater mean lesion area than the
LDLR
−/−
mice. No significant difference was found in percent lesion area in the
LDLR
−/−
;
Tg(apoB
+/+
)
mice whether or not they expressed apo(a) [18.5 ± 2.5%, without lipoprotein(a), Lp(a), vs. 16.0 ± 1.7%, with Lp(a)]. Histochemical analyses of the sections from the proximal aorta of
LDLR
−/−
;
Tg(apoB
+/+
)
mice revealed large, complex, lipid-laden atherosclerotic lesions that stained intensely with human apoB-100 antibodies. In mice expressing Lp(a), large amounts of apo(a) protein colocalized with apoB-100 in the lesions. We conclude that
LDLR
−/−
;
Tg(apoB
+/+
)
mice exhibit accelerated atherosclerosis on a chow diet and thus provide an excellent animal model in which to study atherosclerosis. We found no evidence that apo(a) increased atherosclerosis in this animal model.
Monoclonal antibodies against oxidized low-density lipoprotein bind to apoptotic cells and inhibit their phagocytosis by elicited macrophages: Evidence that oxidation-specific epitopes mediate macrophage recognition
Authors: Chang Mi-Kyung , Bergmark Claes , Laurila Aino , Hörkkö Sohvi , Han Ki-Hoon , Friedman Peter , Dennis Edward A. , Witztum Joseph L.
Published: July 2002

Apoptosis is recognized as important for normal cellular homeostasis in multicellular organisms. Although there have been great advances in our knowledge of the molecular events regulating apoptosis, much less is known about the receptors on phagocytes responsible for apoptotic cell recognition and phagocytosis or the ligands on apoptotic cells mediating such recognition. The observations that apoptotic cells are under increased oxidative stress and that oxidized low-density lipoprotein (OxLDL) competes with apoptotic cells for macrophage binding suggested the hypothesis that both OxLDL and apoptotic cells share oxidatively modified moieties on their surfaces that serve as ligands for macrophage recognition. To test this hypothesis, we used murine monoclonal autoantibodies that bind to oxidation-specific epitopes on OxLDL. In particular, antibodies EO6 and EO3 recognize oxidized phospholipids, including 1-palmitoyl 2-(5-oxovaleroyl) phosphatidylcholine (POVPC), and antibodies EO12 and EO14 recognize malondialdehyde-lysine, as in malondialdehyde-LDL. Using FACS analysis, we demonstrated that each of these EO antibodies bound to apoptotic cells but not to normal cells, whereas control IgM antibodies did not. Confocal microscopy demonstrated cell-surface expression of the oxidation-specific epitopes on apoptotic cells. Furthermore, each of these antibodies inhibited the phagocytosis of apoptotic cells by elicited peritoneal macrophages, as did OxLDL. In addition, an adduct of POVPC with BSA also effectively prevented phagocytosis. These data demonstrate that apoptotic cells express oxidation-specific epitopes—including oxidized phospholipids—on their cell surface, and that these serve as ligands for recognition and phagocytosis by elicited macrophages.
The alternative oxidase lowers mitochondrial reactive oxygen production in plant cells
Authors: Maxwell Denis P. , Wang Yong , McIntosh Lee
Published: July 2002

Besides the cytochrome
c
pathway, plant mitochondria have an alternative respiratory pathway that is comprised of a single homodimeric protein, alternative oxidase (AOX). Transgenic cultured tobacco cells with altered levels of AOX were used to test the hypothesis that the alternative pathway in plant mitochondria functions as a mechanism to decrease the formation of reactive oxygen species (ROS) produced during respiratory electron transport. Using the ROS-sensitive probe 2′,7′-dichlorofluorescein diacetate, we found that antisense suppression of AOX resulted in cells with a significantly higher level of ROS compared with wild-type cells, whereas the overexpression of AOX resulted in cells with lower ROS abundance. Laser-scanning confocal microscopy showed that the difference in ROS abundance among wild-type and AOX transgenic cells was caused by changes in mitochondrial-specific ROS formation. Mitochondrial ROS production was exacerbated by the use of antimycin A, which inhibited normal cytochrome electron transport. In addition, cells overexpressing AOX were found to have consistently lower expression of genes encoding ROS-scavenging enzymes, including the superoxide dismutase genes
SodA
and
SodB
, as well as glutathione peroxidase. Also, the abundance of mRNAs encoding salicylic acid-binding catalase and a pathogenesis-related protein were significantly higher in cells deficient in AOX. These results are evidence that AOX plays a role in lowering mitochondrial ROS formation in plant cells.
Killing of
Caenorhabditis elegans
by
Pseudomonas aeruginosa
used to model mammalian bacterial pathogenesis
Authors: Tan Man-Wah , Mahajan-Miklos Shalina , Ausubel Frederick M.
Published: July 2002

We show that a single clinical isolate of the human opportunistic pathogen
Pseudomonas aeruginosa
(strain PA14), which previously was shown to be pathogenic in mice and plants, also kills
Caenorhabditis elegans
. The rate of PA14-mediated killing of
C. elegans
depends on the composition of the agar medium on which PA14 is grown. When PA14 is grown on minimal medium, killing occurs over the course of several days and is referred to as “slow” killing. When PA14 is grown on high-osmolarity medium, killing occurs over the course of several hours and is referred to as “fast” killing. Several lines of evidence, including the fact that heat-killed bacteria are still capable of fast but not slow killing of
C. elegans
, indicate that fast and slow killing occur by distinct mechanisms. Slow killing involves an infection-like process and correlates with the accumulation of PA14 within worm intestines. Among 10 PA14 virulence-related mutants that had been shown previously to affect pathogenicity in plants and mice, 6 were less effective in killing
C. elegans
under both fast- and slow-killing conditions, indicating a high degree of commonalty among the
P. aeruginosa
factors required for pathogenicity in disparate eukaryotic hosts. Thus, we show that a
C. elegans
pathogenicity model that is genetically tractable from the perspectives of both host and pathogen can be used to model mammalian bacterial pathogenesis.
Pharmacological plasticity of cardiac ATP-sensitive potassium channels toward diazoxide revealed by ADP
Authors: D’hahan Nathalie , Moreau Christophe , Prost Anne-Lise , Jacquet Hélène , Alekseev Alexey E. , Terzic André , Vivaudou Michel
Published: July 2002

The pharmacological phenotype of ATP-sensitive potassium (K
ATP
) channels is defined by their tissue-specific regulatory subunit, the sulfonylurea receptor (SUR), which associates with the pore-forming channel core, Kir6.2. The potassium channel opener diazoxide has hyperglycemic and hypotensive properties that stem from its ability to open K
ATP
channels in pancreas and smooth muscle. Diazoxide is believed not to have any significant action on cardiac sarcolemmal K
ATP
channels. Yet, diazoxide can be cardioprotective in ischemia and has been found to bind to the presumed cardiac sarcolemmal K
ATP
channel-regulatory subunit, SUR2A. Here, in excised patches, diazoxide (300 μM) activated pancreatic SUR1/Kir6.2 currents and had little effect on native or recombinant cardiac SUR2A/Kir6.2 currents. However, in the presence of cytoplasmic ADP (100 μM), SUR2A/Kir6.2 channels became as sensitive to diazoxide as SUR1/Kir6.2 channels. This effect involved specific interactions between MgADP and SUR, as it required Mg
2+
, but not ATP, and was abolished by point mutations in the second nucleotide-binding domain of SUR, which impaired channel activation by MgADP. At the whole-cell level, in cardiomyocytes treated with oligomycin to block mitochondrial function, diazoxide could also activate K
ATP
currents only after cytosolic ADP had been raised by a creatine kinase inhibitor. Thus, ADP serves as a cofactor to define the responsiveness of cardiac K
ATP
channels toward diazoxide. The present demonstration of a pharmacological plasticity of K
ATP
channels identifies a mechanism for the control of channel activity in cardiac cells depending on the cellular ADP levels, which are elevated under ischemia.
Epigenetic phenotypes distinguish microsatellite-stable and -unstable colorectal cancers
Authors: Kuismanen Shannon A. , Holmberg Mari T. , Salovaara Reijo , Schweizer Pascal , Aaltonen Lauri A. , de la Chapelle Albert , Nyström-Lahti Minna , Peltomäki Päivi
Published: July 2002

Aberrant DNA methylation is a common phenomenon in human cancer, but its patterns, causes, and consequences are poorly defined. Promoter methylation of the DNA mismatch repair gene MutL homologue (MLH1) has been implicated in the subset of colorectal cancers that shows microsatellite instability (MSI). The present analysis of four
Msp
I/
Hpa
II sites at the MLH1 promoter region in a series of 89 sporadic colorectal cancers revealed two main methylation patterns that closely correlated with the MSI status of the tumors. These sites were hypermethylated in tumor tissue relative to normal mucosa in most MSI(+) cases (31/51, 61%). By contrast, in the majority of MSI(−) cases (20/38, 53%) the same sites showed methylation in normal mucosa and hypomethylation in tumor tissue. Hypermethylation displayed a direct correlation with increasing age and proximal location in the bowel and was accompanied by immunohistochemically documented loss of MLH1 protein both in tumors and in normal tissue. Similar patterns of methylation were observed in the promoter region of the calcitonin gene that does not have a known functional role in tumorigenesis. We propose a model of carcinogenesis where different epigenetic phenotypes distinguish the colonic mucosa in individuals who develop MSI(+) and MSI(−) tumors. These phenotypes may underlie the different developmental pathways that are known to occur in these tumors.
Ca
2+
/calmodulin-kinase II enhances channel conductance of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate type glutamate receptors
Authors: Derkach Victor , Barria Andres , Soderling Thomas R.
Published: July 2002

The ability of central glutamatergic synapses to change their strength in response to the intensity of synaptic input, which occurs, for example, in long-term potentiation (LTP), is thought to provide a cellular basis for memory formation and learning. LTP in the CA1 field of the hippocampus requires activation of Ca
2+
/calmodulin-kinase II (CaM-KII), which phosphorylates Ser-831 in the GluR1 subunit of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate glutamate receptor (AMPA-R), and this activation/phosphorylation is thought to be a postsynaptic mechanism in LTP. In this study, we have identified a molecular mechanism by which CaM-KII potentiates AMPA-Rs. Coexpression in HEK-293 cells of activated CaM-KII with GluR1 did not affect the glutamate affinity of the receptor, the kinetics of desensitization and recovery, channel rectification, open probability, or gating. Single-channel recordings identified multiple conductance states for GluR1, and coexpression with CaM-KII or a mutation of Ser-831 to Asp increased the contribution of the higher conductance states. These results indicate that CaM-KII can mediate plasticity at glutamatergic synapses by increasing single-channel conductance of existing functional AMPA-Rs or by recruiting new high-conductance-state AMPA-Rs.
La roca magica: Uses of natural zeolites in agriculture and industry
Authors: Mumpton Frederick A.
Published: July 2002

For nearly 200 years since their discovery in 1756, geologists considered the zeolite minerals to occur as fairly large crystals in the vugs and cavities of basalts and other traprock formations. Here, they were prized by mineral collectors, but their small abundance and polymineralic nature defied commercial exploitation. As the synthetic zeolite (molecular sieve) business began to take hold in the late 1950s, huge beds of zeolite-rich sediments, formed by the alteration of volcanic ash (glass) in lake and marine waters, were discovered in the western United States and elsewhere in the world. These beds were found to contain as much as 95% of a single zeolite; they were generally flat-lying and easily mined by surface methods. The properties of these low-cost natural materials mimicked those of many of their synthetic counterparts, and considerable effort has made since that time to develop applications for them based on their unique adsorption, cation-exchange, dehydration–rehydration, and catalytic properties. Natural zeolites (i.e., those found in volcanogenic sedimentary rocks) have been and are being used as building stone, as lightweight aggregate and pozzolans in cements and concretes, as filler in paper, in the take-up of Cs and Sr from nuclear waste and fallout, as soil amendments in agronomy and horticulture, in the removal of ammonia from municipal, industrial, and agricultural waste and drinking waters, as energy exchangers in solar refrigerators, as dietary supplements in animal diets, as consumer deodorizers, in pet litters, in taking up ammonia from animal manures, and as ammonia filters in kidney-dialysis units. From their use in construction during Roman times, to their role as hydroponic (zeoponic) substrate for growing plants on space missions, to their recent success in the healing of cuts and wounds, natural zeolites are now considered to be full-fledged mineral commodities, the use of which promise to expand even more in the future.
Scaling in animal group-size distributions
Authors: Bonabeau Eric , Dagorn Laurent , Fréon Pierre
Published: July 2002

An elementary model of animal aggregation is presented. The group-size distributions resulting from this model are truncated power laws. The predictions of the model are found to be consistent with data that describe the group-size distributions of tuna fish, sardinellas, and African buffaloes.
Experimental removal of sexual selection reverses intersexual antagonistic coevolution and removes a reproductive load
Authors: Holland Brett , Rice William R.
Published: July 2002

Although sexual selection can provide benefits to both sexes, it also can be costly because of expanded opportunities for intersexual conflict. We evaluated the role of sexual selection in a naturally promiscuous species,Drosophila melanogaster. In two replicate populations, sexual selection was removed through enforced monogamous mating with random mate assignment or retained in promiscuous controls. Monogamous mating constrains the reproductive success of mates to be identical, thereby converting prior conflicts between mates into opportunities for mutualism. Random mate assignment removes the opportunity for females to choose beneficial qualities in their mate. The mating treatments were maintained for 47 generations, and evolution was allowed to proceed naturally within the parameters of the design. In the monogamous populations, males evolved to be less harmful to their mates, and females evolved to be less resistant to male-induced harm. The monogamous populations also evolved a greater net reproductive rate than their promiscuous controls. These results indicate a potentially widespread cost of sexual selection caused by conflicts inherent to promiscuity.
Clustered DNA damages induced in isolated DNA and in human cells by low doses of ionizing radiation
Authors: Sutherland Betsy M. , Bennett Paula V. , Sidorkina Olga , Laval Jacques
Published: July 2002

Clustered DNA damages—two or more closely spaced damages (strand breaks, abasic sites, or oxidized bases) on opposing strands—are suspects as critical lesions producing lethal and mutagenic effects of ionizing radiation. However, as a result of the lack of methods for measuring damage clusters induced by ionizing radiation in genomic DNA, neither the frequencies of their production by physiological doses of radiation, nor their repairability, nor their biological effects are known. On the basis of methods that we developed for quantitating damages in large DNAs, we have devised and validated a way of measuring ionizing radiation-induced clustered lesions in genomic DNA, including DNA from human cells. DNA is treated with an endonuclease that induces a single-strand cleavage at an oxidized base or abasic site. If there are two closely spaced damages on opposing strands, such cleavage will reduce the size of the DNA on a nondenaturing gel. We show that ionizing radiation does induce clustered DNA damages containing abasic sites, oxidized purines, or oxidized pyrimidines. Further, the frequency of each of these cluster classes is comparable to that of frank double-strand breaks; among all complex damages induced by ionizing radiation, double-strand breaks are only about 20%, with other clustered damage constituting some 80%. We also show that even low doses (0.1–1 Gy) of high linear energy transfer ionizing radiation induce clustered damages in human cells.
Sensitivity and rapidity of vegetational response to abrupt climate change
Authors: Peteet Dorothy
Published: July 2002

Rapid climate change characterizes numerous terrestrial
sediment records during and since the last glaciation. Vegetational
response is best expressed in terrestrial records near ecotones, where
sensitivity to climate change is greatest, and response times are as
short as decades.
Gamma rhythms and beta rhythms have different synchronization properties
Authors: Kopell N. , Ermentrout G. B. , Whittington M. A. , Traub R. D.
Published: July 2002

Experimental and modeling efforts suggest that rhythms in the CA1 region of the hippocampus that are in the beta range (12–29 Hz) have a different dynamical structure than that of gamma (30–70 Hz). We use a simplified model to show that the different rhythms employ different dynamical mechanisms to synchronize, based on different ionic currents. The beta frequency is able to synchronize over long conduction delays (corresponding to signals traveling a significant distance in the brain) that apparently cannot be tolerated by gamma rhythms. The synchronization properties are consistent with data suggesting that gamma rhythms are used for relatively local computations whereas beta rhythms are used for higher level interactions involving more distant structures.
Evidence for a requirement for ATP hydrolysis at two distinct steps during a single turnover of the catalytic cycle of human P-glycoprotein
Authors: Sauna Zuben E. , Ambudkar Suresh V.
Published: July 2002

P-glycoprotein (Pgp) is an ATP-dependent hydrophobic natural product anticancer drug efflux pump whose overexpression confers multidrug resistance to tumor cells. The work reported here deals with the elucidation of the energy requirement for substrate interaction with Pgp during the catalytic cycle. We show that the
K
d
(412 nM) of the substrate analogue [
125
I]iodoarylazidoprazoin for Pgp is not altered by the presence of the nonhydrolyzable nucleotide 5′-adenylylimididiphosphate and vanadate (
K
d
= 403 nM). Though binding of nucleotide
per se
does not affect interactions with the substrate, ATP hydrolysis results in a dramatic conformational change where the affinity of [
125
I]iodoarylazidoprazoin for Pgp trapped in transition-state conformation (Pgp⋅ADP⋅vanadate) is reduced >30-fold. To transform Pgp from this intermediate state of low affinity for substrate to the next catalytic cycle, i.e., a conformation that binds substrate with high affinity, requires conditions that permit ATP hydrolysis. Additionally, there is an inverse correlation (
R
2
= 0.96) between 8AzidoADP (or ADP) release and the recovery of substrate binding. These results suggest that the release of nucleotide is necessary for reactivation but not sufficient. The hydrolysis of additional molecule(s) of ATP (or 8AzidoATP) is obligatory for the catalytic cycle to advance to completion. These data are consistent with the observed stoichiometry of two ATP molecules hydrolyzed for the transport of every substrate molecule. Our data demonstrate two distinct roles for ATP hydrolysis in a single turnover of the catalytic cycle of Pgp, one in the transport of substrate and the other in effecting conformational changes to reset the pump for the next catalytic cycle.
Islam and Nation Building in Tatarstan and Dagestan of the Russian Federation
Authors: Yemelianova Galina M.
Published: July 2002

This article is based on the preliminary results of a project on “Islam, Ethnicity and Nationalism in Post-Soviet Tatarstan and Dagestan,” which began in March 1997 and ended in September 1999. These two out of Russia's 21 autonomous republics were chosen for comparative research because, although they are both Muslim, there are obvious geographical, ethnic, cultural, and political differences between them. Each republic also represents a distinctive model of the evolution of Muslim society and its relations with Russian culture in general and with the Russian political center in particular.
Risk factors for inhalant abuse in juvenile offenders: the case of Mexico
Authors: TAPIA‐CONYER ROBERTO , CRAVIOTO PATRICIA , DE LA ROSA BLANCA , VELEZ CARINA
Published: July 2002

During the last two decades the abuse of inhalants and other addictive substances has received considerable attention in Mexico. Although substance abuse seems to affect everyone, adolescents seem to be at higher risk, and although researchers have identified the links between substance abuse and delinquency, there is not enough scientific information to explain the reason. A cross‐sectional study was designed to examine the relationship between known risk factors and inhalant abuse among a group of Mexican juvenile offenders. Of the 626 subjects studied, 58% reported use of different drugs, and of them 23% abused inhalants. Gender, low socio‐economic level and labor status were the principal risk factors associated with inhalant abuse. According to attributable risks calculated, and taking into account the methodological limitations of the study, the authors suggest some preventive actions to decrease inhalant abuse in the population studied.
Book Reviews
Authors: GOSSOP MICHAEL
Published: July 2002

Book reviewed in this article:

The Stop Smoking Workbook: your guide to healthy quitting

Alcoholics Anonymous as a Mutual‐Help Movement: a study in eight societies

Substance Use among Children and Adolescents: its nature, extent, and effects from conception to adulthood

Addiction Treatment for Older Adults: evaluation of an innovative client‐centered approach

Psychiatric Services for Addicted Patients: a task force report of die American Psychiatric Association
Digital terrestrial television
Authors: Pilati Antonio , Poli Emanuela
Published: July 2002

In Italy, as in much of Europe, the beginning of the new century has brought a crucial period of change to the television system. The change affects technology, strategies and regulation of the medium. This article starts by reconstructing the current situation and the emerging trends at a global level. It then analyses the state of the Italian television industry on the eve of the introduction of digital terrestrial broadcasting, setting out the opportunities and potential developments this opens up.
Online journalism: Information and culture in the Italian technological imaginary
Authors: Sorice Michele
Published: July 2002

The Italian imaginary has been populated in recent years by a swarm of objects with high technological content, from mobile phones to palmtop organizers, from satellite dishes to sophisticated digital audio and video equipment. The computer, by contrast, has remained in the shadows. Although it has been central to the discourse of specialists, it has entered everyday life only very gradually over the last two years. This paradox accounts for the fact that online journalism still lags substantially behind in Italy, despite the fact that the first Internet newspapers appeared several years ago. The first part of this article is descriptive: it analyses the Italian situation in the light of the massive investments made in the online sector. The second part reviews the peculiarities of Italian online journalism, both more innovative than its paper counterpart and at the same time potentially more constrained by advertising. The article concludes with an analysis of the most recent tendencies in the Italian information system. From integration to convergence, technologies and the products of the communications system are producing a new context of use for consumers and may be introducing new social scenarios.
The Composition of a Primary T Cell Response Is Largely Determined by the Timing of Recruitment of Individual T Cell Clones
Authors: Bousso Philippe , Levraud Jean-Pierre , Kourilsky Philippe , Abastado Jean-Pierre
Published: July 2002

Primary T cell responses rely on the recruitment and proliferation of antigen-specific T cell precursors. The extent of expansion of each individual T cell clone may depend on (a) its frequency before immunization, (b) its proliferative capacity, and (c) the time at which it first encounters its cognate antigen. In this report, we have analyzed the relative contribution of each of these parameters to the shaping of immune repertoires in the T cell response specific for the epitope 170-179 derived from HLA-Cw3 and presented by Kd. By means of hemisplenectomy, we compared immune and naive repertoires in the same animal and found that the frequency of all expanded T cell clones was extremely low before immunization. In particular, the most expanded clones did not derive from high-frequency precursors. In addition, recruited T cells were found to proliferate at the same rate, irrespective of their T cell antigen receptor sequence. Finally, we showed that only T cells that encounter the antigen at early time points account for a significant part of the specific response. Therefore, the contribution of a T cell clone to the immune response is mostly determined by the time of its entry into the immune repertoire, i.e., the time of first cell division after antigen encounter.
pH-dependent Peptide Binding Properties of the Type I Diabetes–associated I-Ag7 Molecule: Rapid Release of CLIP at an Endosomal pH
Authors: Hausmann Dorothee H.F. , Yu Bei , Hausmann Stefan , Wucherpfennig Kai W.
Published: July 2002

MHC class II molecules and invariant chain assemble at a neutral pH in the endoplasmic reticulum and are transported to a low pH compartment where the invariant chain is trimmed to the class II–associated invariant chain peptide (CLIP). For many major histocompatibility complex class II molecules, DM is required for rapid removal of CLIP, which allows binding of antigenic peptides. Since I-Ag7 confers susceptibility to type I diabetes in NOD mice, the biochemical requirements for peptide loading were examined using soluble I-Ag7 expressed in insect cells. I-Ag7 formed long-lived complexes with naturally processed peptides from transferrin and albumin, whereas several peptides that represent T cell epitopes of islet autoantigens were poor binders. I-Ag7–peptide complexes were not sodium dodecyl sulfate (SDS) resistant, indicating that SDS sensitivity may be an intrinsic property of I-Ag7. Complexes of I-Ag7 and CLIP formed at a neutral pH, but rapidly dissociated at pH 5. This rapid dissociation was due to a poor fit of M98 of CLIP in the P9 pocket of I-Ag7, since substitution of M98 by a negatively charged residue greatly enhanced the stability of the complex. These biochemical properties of I-Ag7 result in the rapid generation of empty molecules at an endosomal pH and have a global effect on peptide binding by I-Ag7.
Presentation of Antigen in Immune Complexes Is Boosted by Soluble Bacterial Immunoglobulin Binding Proteins
Authors: Léonetti Michel , Galon Jérome , Thai Robert , Sautès-Fridman Catherine , Moine Gervaise , Ménez André
Published: July 2002

Using a snake toxin as a proteic antigen (Ag), two murine toxin–specific monoclonal antibodies (mAbs), splenocytes, and two murine Ag–specific T cell hybridomas, we showed that soluble protein A (SpA) from Staphylococcus aureus and protein G from Streptococcus subspecies, two Ig binding proteins (IBPs), not only abolish the capacity of the mAbs to decrease Ag presentation but also increase Ag presentation 20–100-fold. Five lines of evidence suggest that this phenomenon results from binding of an IBP–Ab–Ag complex to B cells possessing IBP receptors. First, we showed that SpA is likely to boost presentation of a free mAb, suggesting that the IBP-boosted presentation of an Ag in an immune complex results from the binding of IBP to the mAb. Second, FACS® analyses showed that an Ag–Ab complex is preferentially targeted by SpA to a subpopulation of splenocytes mainly composed of B cells. Third, SpA-dependent boosted presentation of an Ag–Ab complex is further enhanced when splenocytes are enriched in cells containing SpA receptors. Fourth, the boosting effect largely diminishes when splenocytes are depleted of cells containing SpA receptors. Fifth, the boosting effect occurs only when IBP simultaneously contains a Fab and an Fc binding site. Altogether, our data suggest that soluble IBPs can bridge immune complexes to APCs containing IBP receptors, raising the possibility that during an infection process by bacteria secreting these IBPs, Ag-specific T cells may activate IBP receptor–containing B cells by a mechanism of intermolecular help, thus leading to a nonspecific immune response.
Numerical solution of isospectral flows
Authors: Calvo Mari , Iserles Arieh , Zanna Antonella
Published: July 2002

In this paper we are concerned with the problem of solving numerically isospectral flows. These flows are characterized by the differential equation
\[

L
′

=
[
B
(
L
)
,
L
]
,

L
(
0
)
=

L
0

,

L’ = [B(L), L], \quad L(0)=L_0,

\]
where

L
0

L_0

is a

d
×
d

d\times d

symmetric matrix,

B
(
L
)

B(L)

is a skew-symmetric matrix function of

L
L

and

[
B
,
L
]

[B,L]

is the Lie bracket operator. We show that standard Runge–Kutta schemes fail in recovering the main qualitative feature of these flows, that is isospectrality, since they cannot recover arbitrary cubic conservation laws. This failure motivates us to introduce an alternative approach and establish a framework for generation of isospectral methods of arbitrarily high order.
Gaussian measures in traditional and not so traditional settings
Authors: Stroock Daniel
Published: July 2002

This article is intended to provide non-specialists with an introduction to integration theory on pathspace.
Polish group actions: Dichotomies and generalized elementary embeddings
Authors: Becker Howard
Published: July 2002

We prove that any Polish group which admits a complete left-invariant metric satisfies the Topological Vaught Conjecture. We also generalize some theorems of model theory from the logic actions to other Polish group actions.
The Dolbeault complex in infinite dimensions I
Authors: Lempert László
Published: July 2002

In this paper we introduce certain basic notions concerning infinite dimensional complex manifolds, and prove that the Dolbeault cohomology groups of infinite dimensional projective spaces, with values in finite rank vector bundles, vanish. Some applications of such vanishing theorems are discussed; e.g., we classify vector bundles of finite rank over infinite dimensional projective spaces. Finally, we prove a sharp theorem on solving the inhomogeneous Cauchy–Riemann equations on affine spaces.