bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of the cell death program by inhibition of proteasome function
Authors: Drexler Hannes C. A.
Published: July 2002

Activation of proteolytic enzymes, including cysteine proteases of the ced-3/ICE family, is a characteristic feature of the apoptotic program. In contrast, the role of the proteasome as the major nonlysosomal machinery to degrade or process proteins by ATP/ubiquitin-dependent proteolysis in this process is less clear. In human leukemic HL60 cells, inhibition of proteasome-mediated proteolysis by specific proteasomal inhibitors leads to the rapid induction of apoptosis as judged by morphological changes as well as by nuclear condensation and DNA fragmentation. HL60 apoptosis is due to activation of CPP32, a member of the ced-3/ICE family of cysteine proteases, and appears to occur independently from ICE activity. HL60 apoptosis is accompanied by an increase in the concentration of the cyclin-dependent kinase inhibitor p27
Kip1
. Labeling of the cells by the TUNEL technique demonstrates that HL60 cells undergoing apoptosis are primarily in the G
1
phase of the cell cycle. Proteasomal activity therefore appears to be required in proliferating, but not in quiescent, HL60 cells for cell survival as well as normal progression through the cell cycle.
In vivo
control of respiration by cytochrome
c
oxidase in wild-type and mitochondrial DNA mutation-carrying human cells
Authors: Villani Gaetano , Attardi Giuseppe
Published: July 2002

The metabolic control of respiration is still poorly understood, due mainly to the lack of suitable approaches for studying it
in vivo
. Experiments on isolated mammalian mitochondria have indicated that a relatively small fraction of each of several components of the electron transport chain is sufficient to sustain a normal O
2
consumption rate. These experiments, however, may not reflect accurately the
in vivo
situation, due to the lack in the mitochondrial fraction of essential cytosolic components and to the use of excess of substrates in the
in vitro
assays. An approach is described here whereby the control of respiration by cytochrome
c
oxidase (COX; EC
1.9.3.1
) was analyzed in intact cultured human osteosarcoma 143B.TK
−
cells and other wild-type cells and in mitochondrial DNA mutation-carrying human cell lines. Surprisingly, in wild-type cells, only a slightly higher COX capacity was detected than required to support the endogenous respiration rate, pointing to a tighter
in vivo
control of respiration by COX than generally assumed. Cell lines carrying the MERRF mitochondrial tRNA
Lys
gene mutation, which causes a pronounced decrease in mitochondrial protein synthesis and respiration rates, revealed, in comparison, a significantly greater COX capacity relative to the residual endogenous respiration rate, and, correspondingly, a higher COX inhibition threshold above which the overall respiratory flux was affected. The observed relationship between COX respiratory threshold and relative COX capacity and the potential extension of the present analysis to other respiratory complexes have significant general implications for understanding the pathogenetic role of mutations in mtDNA-linked diseases and the tissue specificity of the mutation-associated phenotype.
Cytokine manipulation of primitive human hematopoietic cell self-renewal
Authors: Zandstra P. W. , Conneally E. , Petzer A. L. , Piret J. M. , Eaves C. J.
Published: July 2002

Previous studies have shown that primitive human hematopoietic cells detectable as long-term culture-initiating cells (LTC-ICs) and colony-forming cells (CFCs) can be amplified when CD34
+
CD38
−
marrow cells are cultured for 10 days in serum-free medium containing flt3 ligand (FL), Steel factor (SF), interleukin (IL)-3, IL-6, and granulocyte colony-stimulating factor. We now show that the generation of these two cell types in such cultures is differentially affected at the single cell level by changes in the concentrations of these cytokines. Thus, maximal expansion of LTC-ICs (60-fold) was obtained in the presence of 30 times more FL, SF, IL-3, IL-6, and granulocyte colony-stimulating factor than could concomitantly stimulate the near-maximal (280-fold) amplification of CFCs. Furthermore, the reduced ability of suboptimal cytokine concentrations to support the production of LTC-ICs could be ascribed to a differential response of the stimulated cells since this was not accompanied by a change in the number of input CD34
+
CD38
−
cells that proliferated. Reduced LTC-IC amplification in the absence of a significant effect on CFC generation also occurred when the concentrations of FL and SF were decreased but the concentration of IL-3 was high (as compared with cultures containing high levels of all three cytokines). To our knowledge, these findings provide the first evidence suggesting that extrinsically acting cytokines can alter the self-renewal behavior of primary human hematopoietic stem cells independent of effects on their viability or proliferation.
Neurotrophins inhibit major histocompatibility class II inducibility of microglia: Involvement of the p75 neurotrophin receptor
Authors: Neumann Harald , Misgeld Thomas , Matsumuro Kenji , Wekerle Hartmut
Published: July 2002

Major histocompatibility complex (MHC) molecules are rare in the healthy brain tissue, but are heavily expressed on microglial cells after inflammatory or neurodegenerative processes. We studied the conditions leading to the induction of MHC class II molecules in microglia by using explant cultures of neonatal rat hippocampus, a model of interacting neuronal networks. Interferon-γ (IFN-γ)-dependent MHC class II inducibility in microglia cells was very low, but strongly increased in the hippocampal slices after the blockade of neuronal activity by neurotoxins [tetrodotoxin (TTX), ω-conotoxin] or glutamate antagonists. None of these agents acted directly on isolated microglia cells. We found that neurotrophins modulate microglial MHC class II expression. MHC class II inducibility was enhanced by neutralization of neurotrophins produced locally within the cultured tissues and was inhibited by the addition of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), or neurotrophin-3 (NT3). NGF and, to a lower extent, NT3 acted directly on isolated microglia via the p75 neurotrophin receptor and inhibited MHC class II inducibility as shown by blockade of the p75 neurotrophin receptor with antibodies. Our data suggest that neurotrophins secreted by electrically active neurons control the antigen-presenting potential of microglia cells, and indicate that this effect is mediated partly via the p75 neurotrophin receptor.
Directed seed dispersal by bellbirds in a tropical cloud forest
Authors: Wenny Daniel G. , Levey Douglas J.
Published: July 2002

A fundamental goal of plant population ecology is to understand the consequences for plant fitness of seed dispersal by animals. Theories of seed dispersal and tropical forest regeneration suggest that the advantages of seed dispersal for most plants are escape from seed predation near the parent tree and colonization of vacant sites, the locations of which are unpredictable in space and time. Some plants may gain in fitness as a fortuitous consequence of disperser behavior if certain species of dispersers nonrandomly place seeds in sites predictably favorable for seedling establishment. Such patterns of directed dispersal by vertebrates long have been suggested but never demonstrated for tropical forest trees. Here we report the pattern of seed distribution and 1-year seedling survival generated by five species of birds for a neotropical, shade-tolerant tree. Four of the species dispersed seeds to sites near the parent trees with microhabitat characteristics similar to those at random locations, whereas the fifth species, a bellbird, predictably dispersed seeds under song perches in canopy gaps. The pattern of seedling recruitment was bimodal, with a peak near parent trees and a second peak, corresponding to bellbird song perches, far (>40 m) from parent trees. Seedling survival was higher for seeds dispersed by bellbirds than by the other species, because of a reduction in seedling mortality by fungal pathogens in gaps. Thus, bellbirds play a significant role in seed dispersal by providing directed dispersal to favorable sites and therefore may influence plant recruitment patterns and species diversity in Neotropical forests.
Cholesterol depletion inhibits the generation of β-amyloid in hippocampal neurons
Authors: Simons Mikael , Keller Patrick , De Strooper Bart , Beyreuther Konrad , Dotti Carlos G. , Simons Kai
Published: July 2002

The amyloid precursor protein (APP) plays a crucial role in the pathogenesis of Alzheimer’s disease. During intracellular transport APP undergoes a series of proteolytic cleavages that lead to the release either of an amyloidogenic fragment called β-amyloid (Aβ) or of a nonamyloidogenic secreted form consisting of the ectodomain of APP (APP
sec
). It is Aβ that accumulates in the brain lesions that are thought to cause the disease. By reducing the cellular cholesterol level of living hippocampal neurons by 70% with lovastatin and methyl-β-cyclodextrin, we show that the formation of Aβ is completely inhibited while the generation of APP
sec
is unperturbed. This inhibition of Aβ formation is accompanied by increased solubility in the detergent Triton X-100 and is fully reversible by the readdition of cholesterol to previously depleted cells. Our results show that cholesterol is required for Aβ formation to occur and imply a link between cholesterol, Aβ, and Alzheimer’s disease.
A transient outward-rectifying K
+
channel current down-regulated by cytosolic Ca
2+
in
Arabidopsis thaliana
guard cells
Authors: Pei Zhen-Ming , Baizabal-Aguirre Victor M. , Allen Gethyn J. , Schroeder Julian I.
Published: July 2002

Sustained (noninactivating) outward-rectifying K
+
channel currents have been identified in a variety of plant cell types and species. Here, in
Arabidopsis thaliana
guard cells, in addition to these sustained K
+
currents, an inactivating outward-rectifying K
+
current was characterized (plant A-type current:
I
AP
).
I
AP
activated rapidly with a time constant of 165 ms and inactivated slowly with a time constant of 7.2 sec at +40 mV.
I
AP
was enhanced by increasing the duration (from 0 to 20 sec) and degree (from +20 to −100 mV) of prepulse hyperpolarization. Ionic substitution and relaxation (tail) current recordings showed that outward
I
AP
was mainly carried by K
+
ions. In contrast to the sustained outward-rectifying K
+
currents, cytosolic alkaline pH was found to inhibit
I
AP
and extracellular K
+
was required for
I
AP
activity. Furthermore, increasing cytosolic free Ca
2+
in the physiological range strongly inhibited
I
AP
activity with a half inhibitory concentration of ≈ 94 nM. We present a detailed characterization of an inactivating K
+
current in a higher plant cell. Regulation of
I
AP
by diverse factors including membrane potential, cytosolic Ca
2+
and pH, and extracellular K
+
and Ca
2+
implies that the inactivating
I
AP
described here may have important functions during transient depolarizations found in guard cells, and in integrated signal transduction processes during stomatal movements.
Identification of a family of zinc transporter genes fromArabidopsisthat respond to zinc deficiency
Authors: Grotz Natasha , Fox Tama , Connolly Erin , Park Walter , Guerinot Mary Lou , Eide David
Published: July 2002

Millions of people worldwide suffer from nutritional imbalances of essential metals like zinc. These same metals, along with pollutants like cadmium and lead, contaminate soils at many sites around the world. In addition to posing a threat to human health, these metals can poison plants, livestock, and wildlife. Deciphering how metals are absorbed, transported, and incorporated as protein cofactors may help solve both of these problems. For example, edible plants could be engineered to serve as better dietary sources of metal nutrients, and other plant species could be tailored to remove metal ions from contaminated soils. We report here the cloning of the first zinc transporter genes from plants, theZIP1,ZIP2, andZIP3genes ofArabidopsis thaliana. Expression in yeast of these closely related genes confers zinc uptake activities. In the plant,ZIP1andZIP3are expressed in roots in response to zinc deficiency, suggesting that they transport zinc from the soil into the plant. Although expression ofZIP2has not been detected, a fourth relatedArabidopsisgene identified by genome sequencing,ZIP4, is induced in both shoots and roots of zinc-limited plants. Thus, ZIP4 may transport zinc intracellularly or between plant tissues. These ZIP proteins define a family of metal ion transporters that are found in plants, protozoa, fungi, invertebrates, and vertebrates, making it now possible to address questions of metal ion accumulation and homeostasis in diverse organisms.
In vivo
transfer of barley stripe mosaic hordeivirus ribonucleotides to the 5′ terminus of maize stripe tenuivirus RNAs
Authors: Estabrook Elizabeth M. , Tsai James , Falk Bryce W.
Published: July 2002

The
Tenuivirus
maize stripe virus (MStV) shares many properties with viruses in the genus
Phlebovirus
of the family
Bunyaviridae
. Besides genome organization and gene expression strategies, one property shared by these plant- and vertebrate-infecting viruses is that transcription gives rise to virus-specific mRNAs containing nonviral 5′-terminal nucleotide sequences. The 5′-terminal nucleotides are believed to be derived from host mRNA sequences as a result of “cap-snatching.” We investigated whether specific nucleotide sequences could serve as primer donors for cap-snatching
in vivo
. Barley (
Hordeum vulgare
) plants were singly and doubly infected with MStV and the
Hordeivirus
barley stripe mosaic virus (BSMV). A reverse transcription–PCR assay was used to identify chimeric BSMV/MStV RNAs. Specific reverse transcription–PCR products were detected from doubly infected plants by using one PCR primer corresponding to the 5′ termini of the BSMV RNAs (α, β, and γ) and a second primer complementary to MStV RNA 4. The resulting cDNAs were cloned, and nucleotide sequence analysis showed them to be chimeric, containing BSMV 5′-terminal sequences as well as MStV RNA 4 sequences. All clones contained the BSMV RNA 5′ primer nucleotide sequence, but they also showed characteristics common to
Tenuivirus
mRNAs. More than 80% of the clones contained BSMV RNA nucleotides not present on the PCR primer. Several lacked the exact 5′ terminus of MStV RNA 4, a feature also seen for viruses in the
Bunyaviridae
. These data show that heterologous virus RNAs (BSMV) can serve as primer donors for MStV mRNA capped RNA-primed transcription in doubly infected plants.
Two modes of transvection: Enhancer action intransand bypass of a chromatin insulator incis
Authors: Morris James R. , Chen Ji-long , Geyer Pamela K. , Wu C.-ting
Published: July 2002

Ed Lewis introduced the term “transvection” in 1954 to describe mechanisms that can cause the expression of a gene to be sensitive to the proximity of its homologue. Transvection since has been reported at an increasing number of loci inDrosophila, where homologous chromosomes are paired in somatic tissues, as well as at loci in other organisms. At theDrosophila yellowgene, transvection can explain intragenic complementation involving theyellow2allele (y2). Here, transvection was proposed to occur by enhancers of one allele acting intranson the promoter of a paired homologue. In this report, we describe twoyellowalleles that strengthen this model and reveal an unexpected, second mechanism for transvection. Data suggest that, in addition to enhancer action intrans, transvection can occur by enhancer bypass of a chromatin insulator incis. We propose that bypass results from the topology of paired genes. Finally, transvection atyellowcan occur in genotypes not involvingy2, implying that it is a feature ofyellowitself and not an attribute of one particular allele.
Simultaneous formation of functional leading and lagging strand holoenzyme complexes on a small, defined DNA substrate
Authors: Berdis Anthony J. , Benkovic Stephen J.
Published: July 2002

The biochemical characterization of leading and lagging strand DNA synthesis by bacteriophage T4 replication proteins has been addressed utilizing a small, defined primer/template. The ATP hydrolysis activity of 44/62, the clamp loading complex responsible for holoenzyme assembly, was monitored during assembly of both the leading and lagging strand holoenzyme complex. The ATPase activity of 44/62 diminishes once a functional holoenzyme is assembled on both the leading and lagging strand. The assembly of the lagging strand holoenzyme is facilitated by several factors including biotinylated streptavidin blocks at the end of the fork strands, preassembly of the leading strand holoenzyme, and by the presence of the DNA primase with ribonucleoside triphosphates. The resultant minimal replicative complex consists of two holoenzymes and a primase nested on a model replication fork derived from a 62-mer template/34-mer primer/36-mer lagging strand in an apparent 2:2:1:1 ratio of 45 protein:polymerase:primase:forked DNA. The 44/62 protein complex does not remain associated with the complex. The primase alone slowly synthesizes pentaribonucleotides on the forked DNA when the lagging strand contains a nonannealed TTG initiation site with the rate of synthesis greatly stimulated by the addition of the 41 helicase. The addition of deoxy-NTPs to this complex results in leading strand synthesis, but extension of the synthesized RNA primer does not occur. DNA synthesis in both the leading and lagging strand directions is achieved, however, when a 6-mer DNA primer is annealed to the primase recognition site of the forked DNA substrate. A model is presented that describes how leading and lagging strand DNA synthesis might be coordinated as well as the associated molecular interactions of the replicative proteins.
The three yeast A kinases have specific signaling functions in pseudohyphal growth
Authors: Robertson Laura S. , Fink Gerald R.
Published: July 2002

The three yeast A kinase catalytic subunit isoforms are redundant for viability. We demonstrate that they have dramatically different roles in pseudohyphal development: Tpk2 is essential, whereas Tpk3 inhibits. Tpk1 has no discernible effect. Two-hybrid analysis identified the transcription factor Sfl1 as a protein that interacts specifically with Tpk2, but not Tpk1 or Tpk3. Deletion of
SFL1
enhances pseudohyphal and invasive growth. Flo11, a cell surface flocculin required for pseudohyphal development, is transcriptionally regulated by Tpk2 and Sfl1. Genetic evidence indicates that Tpk2 acts upstream of Sfl1 in the regulation of Flo11.
Drought-induced shift of a forest–woodland ecotone: Rapid landscape response to climate variation
Authors: Allen Craig D. , Breshears David D.
Published: July 2002

In coming decades, global climate changes are expected to produce large shifts in vegetation distributions at unprecedented rates. These shifts are expected to be most rapid and extreme at ecotones, the boundaries between ecosystems, particularly those in semiarid landscapes. However, current models do not adequately provide for such rapid effects—particularly those caused by mortality—largely because of the lack of data from field studies. Here we report the most rapid landscape-scale shift of a woody ecotone ever documented: in northern New Mexico in the 1950s, the ecotone between semiarid ponderosa pine forest and piñon–juniper woodland shifted extensively (2 km or more) and rapidly (<5 years) through mortality of ponderosa pines in response to a severe drought. This shift has persisted for 40 years. Forest patches within the shift zone became much more fragmented, and soil erosion greatly accelerated. The rapidity and the complex dynamics of the persistent shift point to the need to represent more accurately these dynamics, especially the mortality factor, in assessments of the effects of climate change.
CREB-binding protein cooperates with transcription factor GATA-1 and is required for erythroid differentiation
Authors: Blobel Gerd A. , Nakajima Toshihiro , Eckner Richard , Montminy Marc , Orkin Stuart H.
Published: July 2002

The transcription factor GATA-1 coordinates multiple events during terminal erythroid cell maturation. GATA-1 participates in the transcription of virtually all erythroid-specific genes, blocks apoptosis of precursor cells, and controls the balance between proliferation and cell cycle arrest. Prior studies suggest that the function of GATA-1 is mediated in part through association with transcriptional cofactors. CREB-binding protein (CBP) and its close relative p300 serve as coactivators for a variety of transcription factors involved in growth control and differentiation. We report here that CBP markedly stimulates GATA-1’s transcriptional activity in transient transfection experiments in nonhematopoietic cells. GATA-1 and CBP also coimmunoprecipitate from nuclear extracts of erythroid cells. Interaction mapping pinpoints contact sites to the zinc finger region of GATA-1 and to the E1A-binding region of CBP. Expression of a conditional form of adenovirus E1A in murine erythroleukemia cells blocks differentiation and expression of endogenous GATA-1 target genes, whereas mutant forms of E1A unable to bind CBP/p300 have no effect. Our findings add GATA-1, and very likely other members of the GATA family, to the growing list of molecules implicated in the complex regulatory network surrounding CBP/p300.
Codominant interference, antieffectors, and multitarget drugs
Authors: Varshavsky Alexander
Published: July 2002

The insufficient selectivity of drugs is a bane of present-day therapies. This problem is significant for antibacterial drugs, difficult for antivirals, and utterly unsolved for anticancer drugs, which remain ineffective against major cancers, and in addition cause severe side effects. The problem may be solved if a therapeutic agent could have a multitarget, combinatorial selectivity, killing, or otherwise modifying, a cell if and only if it contains a predetermined set of molecular targets and lacks another predetermined set of targets. An earlier design of multitarget drugs [Varshavsky, A. (1995)
Proc. Natl. Acad. Sci. USA
92, 3663–3667] was confined to macromolecular reagents such as proteins, with the attendant difficulties of intracellular delivery and immunogenicity. I now propose a solution to the problem of drug selectivity that is applicable to small (≤1 kDa) drugs. Two ideas, codominant interference and antieffectors, should allow a therapeutic regimen to possess combinatorial selectivity, in which the number of positively and negatively sensed macromolecular targets can be two, three, or more. The nature of the effector and interference moieties in a multitarget drug determines its use: selective killing of cancer cells or, for example, the inhibition of a neurotransmitter-inactivating enzyme in a specific subset of the enzyme-containing cells. The
in vivo
effects of such drugs would be analogous to the outcomes of the Boolean operations “and,” “or,” and combinations thereof. I discuss the logic and applications of the antieffector and interference/codominance concepts, and the attendant problem of pharmacokinetics.
Fatty acid-induced β cell apoptosis: A link between obesity and diabetes
Authors: Shimabukuro Michio , Zhou Yan-Ting , Levi Moshe , Unger Roger H.
Published: July 2002

Like obese humans, Zucker diabetic fatty (ZDF) rats exhibit early β cell compensation for insulin resistance (4-fold β cell hyperplasia) followed by decompensation (>50% loss of β cells). In prediabetic and diabetic ZDF islets, apoptosis measured by DNA laddering is increased 3- and >7-fold, respectively, compared with lean ZDF controls. Ceramide, a fatty acid-containing messenger in cytokine-induced apoptosis, was significantly increased (
P
< 0.01) in prediabetic and diabetic islets. Free fatty acids (FFAs) in plasma are high (>1 mM) in prediabetic and diabetic ZDF rats; therefore, we cultured prediabetic islets in 1 mM FFA. DNA laddering rose to 19.6% vs. 4.6% in lean control islets, preceded by an 82% increase in ceramide. C
2
-Ceramide without FFA induced DNA laddering, but fumonisin B
1
, a ceramide synthetase inhibitor, completely blocked FFA-induced DNA laddering in cultured ZDF islets. [
3
H]Palmitate incorporation in [
3
H]ceramide in ZDF islets was twice that of controls, but [
3
H]palmitate oxidation was 77% less. Triacsin C, an inhibitor of fatty acyl-CoA synthetase, and troglitazone, an enhancer of FFA oxidation in ZDF islets, both blocked DNA laddering. These agents also reduced inducible nitric oxide (NO) synthase mRNA and NO production, which are involved in FFA-induced apoptosis. In ZDF obesity, β cell apoptosis is induced by increased FFA via
de novo
ceramide formation and increased NO production.
Receptor-triggered membrane association of a model retroviral glycoprotein
Authors: Damico Rachel L. , Crane Joanne , Bates Paul
Published: July 2002

Current models of retroviral entry hypothesize that interactions between the viral envelope protein and the host receptor(s) induce conformational changes in the envelope protein that activate the envelope protein and initiate fusion. We employed a liposome-binding assay to demonstrate directly and characterize the activation of a model retroviral envelope protein (EnvA) from Rous sarcoma virus (RSV). In the presence of purified viral receptor, the trimeric ectodomain of EnvA was converted from a water-soluble form to a membrane-associated form, consistent with conversion of the envelope protein to its fusogenic state. This activation was nonlinear with respect to receptor concentration, suggesting cooperativity within the trimeric envelope protein. The activated EnvA was stably associated with the target membrane through hydrophobic interactions, behaving like an intrinsic membrane protein. The ability of EnvA to associate with membrane was coincident with a loss of receptor-binding activity, suggesting that during viral entry activated EnvA dissociates from the receptor to facilitate membrane fusion. These results provide direct evidence that receptor binding triggers conversion of the EnvA protein to a membrane-binding form, illustrating that RSV is a useful model for the study of retroviral entry and activation of pH-independent fusion proteins.
Sympathetic neurons can produce and respond to interleukin 6
Authors: März Pia , Cheng Jr-Gang , Gadient Reto A. , Patterson Paul H. , Stoyan Tanja , Otten Uwe , Rose-John Stefan
Published: July 2002

Neuronal expression of cytokines is an area of active investigation in the contexts of development, disease, and normal neural function. Although cultured rat sympathetic neurons respond very weakly to exogenous interleukin 6 (IL-6), we find that addition of soluble IL-6 receptor (sIL-6R) and IL-6 enhances neuronal survival in the absence of nerve growth factor. Neutralizing monoclonal antibodies against IL-6 block these effects. Addition of IL-6 and sIL-6R also induces a subset of neuropeptide and transmitter synthetic enzyme mRNAs identical to that demonstrated for leukemia inhibitory factor, ciliary neurotrophic factor, and oncostatin M. Both of these effects are duplicated by addition of a highly active fusion protein of sIL-6R and IL-6, covalently linked by a flexible peptide chain, which is designated H-IL-6. In addition, we show that sympathetic neurons produce IL-6.In situhybridization indicates a neuronal localization of IL-6 mRNA in superior cervical ganglia, and bioactive IL-6 protein is detected in ganglion culture supernatants. Interestingly, the IL-6 produced by sympathetic neurons does not lead to survival of these cells in culture unless sIL-6R is added. Thus, sympathetic neurons can produce IL-6 and may respond to it in an autocrine/paracrine manner if sIL-6R is present. Moreover, the prior findings of sIL-6R in serum and inflammatory fluids now have added interest in the context of neuro–immune interactions.
Signaling among relatives. III. Talk is cheap
Authors: Bergstrom Carl T. , Lachmann Michael
Published: July 2002

The Sir Philip Sidney game has been used by numerous authors to show how signal cost can facilitate honest signaling among relatives. Here, we demonstrate that, in this game, honest cost-free signals are possible as well, under very general conditions. Moreover, these cost-free signals are better for all participants than the previously explored alternatives. Recent empirical evidence suggests that begging is energetically inexpensive for nestling birds; this finding led some researchers to question the applicability of the costly signaling framework to nestling begging. Our results show that cost-free or inexpensive signals, as observed empirically, fall within the framework of signaling theory.
Nitrogen management and the future of food: Lessons from the management of energy and carbon
Authors: Socolow Robert H.
Published: July 2002

The food system dominates anthropogenic disruption of the nitrogen cycle by generating excess fixed nitrogen. Excess fixed nitrogen, in various guises, augments the greenhouse effect, diminishes stratospheric ozone, promotes smog, contaminates drinking water, acidifies rain, eutrophies bays and estuaries, and stresses ecosystems. Yet, to date, regulatory efforts to limit these disruptions largely ignore the food system. There are many parallels between food and energy. Food is to nitrogen as energy is to carbon. Nitrogen fertilizer is analogous to fossil fuel. Organic agriculture and agricultural biotechnology play roles analogous to renewable energy and nuclear power in political discourse. Nutrition research resembles energy end-use analysis. Meat is the electricity of food. As the agriculture and food system evolves to contain its impacts on the nitrogen cycle, several lessons can be extracted from energy and carbon: (i) set the goal of ecosystem stabilization; (ii) search the entire production and consumption system (grain, livestock, food distribution, and diet) for opportunities to improve efficiency; (iii) implement cap-and-trade systems for fixed nitrogen; (iv) expand research at the intersection of agriculture and ecology, and (v) focus on the food choices of the prosperous. There are important nitrogen-carbon links. The global increase in fixed nitrogen may be fertilizing the Earth, transferring significant amounts of carbon from the atmosphere to the biosphere, and mitigating global warming. A modern biofuels industry someday may produce biofuels from crop residues or dedicated energy crops, reducing the rate of fossil fuel use, while losses of nitrogen and other nutrients are minimized.
The Rpd3 histone deacetylase is required for segmentation of the
Drosophila
embryo
Authors: Mannervik Mattias , Levine Michael
Published: July 2002

Previous studies have implicated histone deacetylation and chromatin condensation as critical mechanisms of transcription repression in yeast and mammals. A specific histone deacetylase, Rpd3, interacts with a variety of sequence-specific transcriptional repressors, including Mad–Max heterodimers and members of the nuclear receptor superfamily. Here, we present evidence that a strong hypomorphic mutation in the
Drosophila
Rpd3 gene causes embryonic lethality and a specific pair-rule segmentation phenotype. The analysis of a number of segmentation genes suggests that the repressor function of Even-skipped (Eve) may be diminished, causing an indirect loss of Ftz-mediated activation of engrailed. The relatively mild defects observed in Rpd3 mutants suggest that the recently identified Groucho and dCtBP corepressor proteins do not function solely through the recruitment of histone deacetylases. We discuss the possibility that Eve mediates multiple mechanisms of repression, so that Rpd3 mutants disrupt the regulation of just a subset of Eve target genes.
Phytoremediation of methylmercury pollution:
merB
expression in
Arabidopsis thaliana
confers resistance to organomercurials
Authors: Bizily Scott P. , Rugh Clayton L. , Summers Anne O. , Meagher Richard B.
Published: July 2002

Methylmercury is an environmental toxicant that biomagnifies and causes severe neurological degeneration in animals. It is produced by bacteria in soils and sediments that have been contaminated with mercury. To explore the potential of plants to extract and detoxify this chemical, we engineered a model plant,
Arabidopsis thaliana,
to express a modified bacterial gene,
merBpe
, encoding organomercurial lyase (MerB) under control of a plant promoter. MerB catalyzes the protonolysis of the carbon—mercury bond, removing the organic ligand and releasing Hg(II), a less mobile mercury species. Transgenic plants expressing
merBpe
grew vigorously on a wide range of concentrations of monomethylmercuric chloride and phenylmercuric acetate. Plants lacking the
merBpe
gene were severely inhibited or died at the same organomercurial concentrations. Six independently isolated transgenic lines produced
merBpe
mRNA and MerB protein at levels that varied over a 10- to 15-fold range, and even the lowest levels of
merBpe
expression conferred resistance to organomercurials. Our work suggests that native macrophytes (e.g., trees, shrubs, grasses) engineered to express
merBpe
may be used to degrade methylmercury at polluted sites and sequester Hg(II) for later removal.
Suppression of the heterotrimeric G protein causes abnormal morphology, including dwarfism, in rice
Authors: Fujisawa Yukiko , Kato Teruhisa , Ohki Shizuka , Ishikawa Atsushi , Kitano Hidemi , Sasaki Takuji , Asahi Tadashi , Iwasaki Yukimoto
Published: July 2002

Transgenic rice containing an antisense cDNA for the α subunit of rice heterotrimeric G protein produced little or no mRNA for the subunit and exhibited abnormal morphology, including dwarf traits and the setting of small seeds. In normal rice, the mRNA for the α subunit was abundant in the internodes and florets, the tissues closely related to abnormality in the dwarf transformants. The position of the α-subunit gene was mapped on rice chromosome 5 by mapping with the restriction fragment length polymorphism. The position was closely linked to the locus of a rice dwarf mutant, Daikoku dwarf (
d-1
), which is known to exhibit abnormal phenotypes similar to those of the transformants that suppressed the endogenous mRNA for the α subunit by antisense technology. Analysis of the cDNAs for the α subunits of five alleles of Daikoku dwarf (
d-1
), ID-1, DK22, DKT-1, DKT-2, and CM1361–1, showed that these dwarf mutants had mutated in the coding region of the α-subunit gene. These results show that the G protein functions in the formation of normal internodes and seeds in rice.
The signature of balancing selection: Fungal mating compatibility gene evolution
Authors: May Georgiana , Shaw Frank , Badrane Hassan , Vekemans Xavier
Published: July 2002

A key problem in evolutionary biology has been distinguishing the contributions of current and historical processes to the maintenance of genetic variation. Because alleles at self-recognition genes are under balancing selection, they exhibit extended residence times in populations and thus may provide unique insight into population demographic history. However, evidence for balancing selection and extended residence times has almost exclusively depended on identification of transspecific polymorphisms; polymorphisms retained in populations through speciation events. We present a broadly applicable approach for detecting balancing selection and apply it to the
b1
mating type gene in the mushroom fungus
Coprinus cinereus
. The comparison of neutral molecular variation within and between allelic classes was used to directly estimate the strength of balancing selection. Different allelic classes are defined as encoding different mating compatibility types and are thus potentially subject to balancing selection. Variation within an allelic class, where all alleles have the same mating compatibility type, provided an internal standard of neutral evolution. Mating compatibility in this organism is determined by the complex
A
mating type locus, and
b1
is one of several redundantly functioning genes. Consequently, we conducted numerical simulations of a model with two subloci and varying levels of recombination to show that balancing selection should operate at each sublocus. Empirical data show that strong balancing selection has indeed occurred at the
b1
locus. The widespread geographic distribution of identical
b1
alleles suggests that their association with differing
A
mating types is the result of recent recombination events.
Identification of a zinc finger protein whose subcellular distribution is regulated by serum and nerve growth factor
Authors: Chittka Alexandra , Chao Moses V.
Published: July 2002

A subclass of zinc finger proteins containing a unique protein motif called the positive regulatory (PR) domain has been described. The members include the PRDI-BF1/Blimp-1 protein, the
Caenorhabditis elegans
egl-43 and EVI1 gene products, and the retinoblastoma interacting protein RIZ. Here we describe a member of this family, SC-1, that exhibits several distinctive features. First, SC-1 interacts with the p75 neurotrophin receptor and is redistributed from the cytoplasm to the nucleus after nerve growth factor (NGF) treatment of transfected COS cells. The translocation of SC-1 to the nucleus was specific for p75, as NGF binding to the TrkA receptor did not lead to nuclear localization of SC-1. Thus, SC-1 provides a downstream transducer for the effects of NGF through the p75 neurotrophin receptor. Under normal growth conditions, SC-1 was found predominantly in the cytoplasm. On serum-starvation, SC-1 also translocated into the nucleus. A direct correlation between nuclear expression of SC-1 with the loss of BrdUrd incorporation was observed. These results imply that SC-1 may be involved in events associated with growth arrest.
The curvature of a Hilbert module over ℂ[
z
1
, … ,

z
d

]
Authors: Arveson William
Published: July 2002

A notion of curvature is introduced in multivariable operator theory. The curvature invariant of a Hilbert module over ℂ[
z
1
, … , 

z
d

] is a nonnegative real number which has significant extremal properties, which tends to be an integer, and which is hard to compute directly. It is shown that for graded Hilbert modules, the curvature agrees with the Euler characteristic of a certain finitely generated algebraic module over the appropriate polynomial ring. This result is a higher dimensional operator-theoretic counterpart of the Gauss–Bonnet formula which expresses the average Gaussian curvature of a compact oriented Riemann surface as the alternating sum of the Betti numbers of the surface, and it solves the problem of calculating the curvature of graded Hilbert modules. The proof of that result is based on an asymptotic formula which expresses the curvature of a Hilbert module in terms that allow its comparison to a corresponding asymptotic expression for the Euler characteristic.
Measuring the amplification of attention
Authors: Blaser Erik , Sperling George , Lu Zhong-Lin
Published: July 2002

An ambiguous motion paradigm, in which the direction of apparent motion is determined by salience (i.e., the extent to which an area is perceived as figure versus ground), is used to assay the amplification of color by attention to color. In the red–green colored gratings used in these experiments, without attention instructions, salience depends on the chromaticity difference between colored stripes embedded in the motion sequence and the yellow background. Selective attention to red (or to green) alters the perceived direction of motion and is found to be equivalent to increasing the physical redness (or greenness) by 25–117%, depending on the observer and color. Whereas attention to a color drastically alters the salience of that color, it leaves color appearance unchanged. A computational model, which embodies separate, parallel pathways for object perception and for salience, accounts for 99% of the variance of the experimental data.
PV-1 is a component of the fenestral and stomatal diaphragms in fenestrated endothelia
Authors: Stan Radu-Virgil , Kubitza Marion , Palade George E.
Published: July 2002

PV-1 is a novel endothelial protein shown by immunocytochemical tests to be specifically associated with the stomatal diaphragms of caveolae in lung endothelium. Although the highest expression levels of both mRNA and protein are in the lung, PV-1 also has been found to be expressed in other organs. Using a specific antibody to the extracellular domain of PV-1, we have extended the survey on the presence of this protein at light and electron microscope level in several rat organs. Here we show that by immunofluorescence the antibody recognizes with high specificity the endothelium of the fenestrated peritubular capillaries of the kidney and those of the intestinal villi, pancreas, and adrenals. By immunolocalization at electron microscope level, the antibody recognizes specifically the diaphragms of the fenestrae and the stomatal diaphragms of caveolae and transendothelial channels in the endothelia of these vascular beds. No signal was detected in the continuous endothelium of the heart, skeletal muscle, intestinal muscularis, or brain capillaries or the nondiaphragmed fenestrated endothelium of kidney glomeruli. Taken together, our findings define the only antigen to be localized thus far in fenestral diaphragms. They also show that the stomatal diaphragms of caveolae and transendothelial channels and the fenestral diaphragms might be biochemically related, in addition to being morphologically similar structures.
Compelling transgenetic evidence for transmission of bovine spongiform encephalopathy prions to humans
Authors: Scott Michael R. , Will Robert , Ironside James , Nguyen Hoang-Oanh B. , Tremblay Patrick , DeArmond Stephen J. , Prusiner Stanley B.
Published: July 2002

There is growing concern that bovine spongiform encephalopathy (BSE) may have passed from cattle to humans. We report here that transgenic (Tg) mice expressing bovine (Bo) prion protein (PrP) serially propagate BSE prions and that there is no species barrier for transmission from cattle to Tg(BoPrP) mice. These same mice were also highly susceptible to a new variant of Creutzfeldt–Jakob disease (nvCJD) and natural sheep scrapie. The incubation times (≈250 days), neuropathology, and disease-causing PrP isoforms in Tg(BoPrP)Prnp
0/0
mice inoculated with nvCJD and BSE brain extracts were indistinguishable and differed dramatically from those seen in these mice injected with natural scrapie prions. Our findings provide the most compelling evidence to date that prions from cattle with BSE have infected humans and caused fatal neurodegeneration.
In vivo
transposition of
mariner
-based elements in enteric bacteria and mycobacteria
Authors: Rubin Eric J. , Akerley Brian J. , Novik Veronica N. , Lampe David J. , Husson Robert N. , Mekalanos John J.
Published: July 2002

mariner
family transposons are widespread among
eukaryotic organisms. These transposons are apparently horizontally
transmitted among diverse eukaryotes and can also transpose
in
vitro
in the absence of added cofactors. Here we show that
transposons derived from the
mariner
element
Himar1
can efficiently transpose in bacteria
in
vivo
. We have developed simple transposition systems by using
minitransposons, made up of short inverted repeats flanking antibiotic
resistance markers. These elements can efficiently transpose after
expression of transposase from an appropriate bacterial promoter. We
found that transposition of
mariner
-based elements in
Escherichia coli
produces diverse insertion mutations in
either a targeted plasmid or a chromosomal gene. With
Himar1
-derived transposons we were able to isolate
phage-resistant mutants of both
E. coli
and
Mycobacterium smegmatis
.
mariner-
based
transposons will provide valuable tools for mutagenesis and genetic
manipulation of bacteria that currently lack well developed genetic
systems.
An intronic enhancer containing an N-box motif is required for synapse- and tissue-specific expression of the acetylcholinesterase gene in skeletal muscle fibers
Authors: Chan Roxanne Y. Y. , Boudreau-Larivière Céline , Angus Lindsay M. , Mankal Fawzi A. , Jasmin Bernard J.
Published: July 2002

mRNAs encoding acetylcholinesterase (AChE; EC
3.1.1.7
) are highly concentrated within the postsynaptic sarcoplasm of adult skeletal muscle fibers, where their expression is markedly influenced by nerve-evoked electrical activity and trophic factors. To determine whether transcriptional regulatory mechanisms account for the synaptic accumulation of AChE transcripts at the mammalian neuromuscular synapse, we cloned a 5.3-kb DNA fragment that contained the 5′ regulatory region of the rat AChE gene and generated several constructs in which AChE promoter fragments were placed upstream of the reporter gene
lacZ
and a nuclear localization signal (nls). Using a recently described transient expression assay system in intact skeletal muscle, we show that this AChE promoter fragment directs the synapse-specific expression of the reporter gene. Deletion analysis revealed that a 499-bp fragment located in the first intron of the AChE gene is essential for expression in muscle fibers. Further analysis showed that sequences contained within this intronic fragment were (
i
) functionally independent of position and orientation and (
ii
) inactive in hematopoietic cells. Disruption of an N-box motif located within this DNA fragment reduced by more than 80% the expression of the reporter gene in muscle fibers. In contrast, mutation of an adjacent CArG element had no effect on nlsLacZ expression. Taken together, these results indicate that a muscle-specific enhancer is present within the first intron of the AChE gene and that an intronic N-box is essential for the regulation of AChE along skeletal muscle fibers.
A neuronal morphologic type unique to humans and great apes
Authors: Nimchinsky Esther A. , Gilissen Emmanuel , Allman John M. , Perl Daniel P. , Erwin Joseph M. , Hof Patrick R.
Published: July 2002

We report the existence and distribution of an unusual type of projection neuron, a large, spindle-shaped cell, in layer Vb of the anterior cingulate cortex of pongids and hominids. These spindle cells were not observed in any other primate species or any other mammalian taxa, and their volume was correlated with brain volume residuals, a measure of encephalization in higher primates. These observations are of particular interest when considering primate neocortical evolution, as they reveal possible adaptive changes and functional modifications over the last 15–20 million years in the anterior cingulate cortex, a region that plays a major role in the regulation of many aspects of autonomic function and of certain cognitive processes. That in humans these unique neurons have been shown previously to be severely affected in the degenerative process of Alzheimer’s disease suggests that some of the differential neuronal susceptibility that occurs in the human brain in the course of age-related dementing illnesses may have appeared only recently during primate evolution.