bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling the Disruptive Effects of Irrelevant Speech on Order Information
Authors: Neath Ian
Published: July 2002

The feature model (Nairne, 1990) is extended to include order information by incorporating aspects of Estes' (1972, 1997) perturbation theory. Order information is encoded with other cues in primary memory and precision is gradually lost due to drift along the appropriate dimension. Recall begins with the cue whose positional uncertainty gradient indicates it was in the first position with the highest probability. Order errors occur primarily because cues can “perturb” to adjacent positions: Although the appropriate secondary memory target is sampled, it is sampled out of order. However, cues that have not perturbed can also sample an incorrect secondary memory item, which is then recalled out of order. Thus, both order errors and item errors can give rise to recalling an item from the list in an incorrect position. A simulation shows that with the addition of the perturbation mechanism, the feature model can produce the appropriate order error gradients for short and long words recalled in quiet, accompanied by irrelevant speech, or accompanied by articulatory suppression.
The Employment Generation Potential of Mature SMEs in Different Geographical Environments
Authors: North David , Smallbone David
Published: July 2002

Using a longitudinal database, this paper compares the employment performance over the 1979-90 period of mature SMEs in three contrasting geographical environments—i.e. London, outer metropolitan locations in the South East, and remote rural locations in northern England. The performance of SMEs in London locations is shown to be inferior to that of similar firms in remote rural locations, but this is found not to result from them having a weaker performance in output terms. Whilst it is the most rapidly growing firms which have the greatest employment generation potential in all locations, London-based SMEs are more likely to achieve growth in ways which minimise the number of additional workers employed directly by the firm. These urban-rural differences can be explained by the different 'strategies' for business growth adopted by managers in responding to the various opportunities and constraints existing in different geographical environments.
Investigating the Patterns of Differential Attainment of Boys and Girls at School
Authors: Gorard Stephen , Rees Gareth , Salisbury Jane
Published: July 2002

Abstract Recent research on the differential attainment of boys and girls at school has produced findings in significant contrast to the standard account on which most previous explanations of the differences between boys and girls were based. Put simply, much previous research may have been attempting to explain differences whose nature was incompletely understood. The result, if these new findings are accepted, is that further research is now necessary to discover the potential socio‐economic, classroom and individual determinants of these gender gaps. In addition, it is important before such research takes place that the nature of the actual differences between the ‘performance’ of boys and girls is more clearly understood. This article is intended to be a part of that advance. It details differential attainment by gender for all students in Wales over 6 years and at every level of assessment from Key Stage 1 to A level. There are few significant gender differences in mathematics and the sciences (i.e. the majority of the core subjects). For all other subjects, there are no significant gender differences at the lowest level of any assessment. Otherwise, the gap in attainment between boys and girls rises with every grade or level in an assessment, leading to the conclusion that the problem, if indeed it is a problem, is one mainly facing mid‐to high‐attainers. Proportionately more girls are attaining high grades and more boys are attaining middle grades than might be expected. Trends over time reveal no great change in this picture at the subject level over 6 years, but in terms of aggregate scores such as government benchmarks, the gap between boys and girls is decreasing.
Single‐sex Teaching in a Co‐educational Comprehensive School in England: An evaluation based upon students' performance and classroom interactions
Authors: Younger Mike , Warrington Molly
Published: July 2002

Abstract This article focuses on single‐sex teaching in co‐educational schools, through a case study of one such school where single‐sex teaching has been the norm since the school was established in the early 1970s. The long‐established nature of this mode of organisation gives scope to discuss the long‐term effectiveness of such single‐sex groupings on students' learning, through an analysis of achievement levels in the school at 16 +, and through a consideration of the nature of classroom interactions and the engagement of girls and boys in mathematics and geography lessons. Analysis of students' performance since the introduction of the General Certificate of Secondary Education examination reveals that, in most years, girls have consistently achieved better results than boys in most subjects, but that the relative improvement levels of both girls and boys over time are similar, and significantly higher than the national average. Interviews with staff and students, and analysis of patterns of classroom interactions, suggest that both girls and boys benefit from having their own learning space, although there are issues about the reintegration of students, particularly boys, when mixed lessons are provided in the foundation subjects in years 10 and 11. The evidence suggests that some teachers do explicitly adjust their teaching styles when teaching boys' classes or girls' classes, but many do not explicitly do so. It is argued that single‐sex teaching has potential to raise achievement levels in some contexts, but that this potential will only be maximised when differential teaching approaches are systematically planned and explicitly implemented, monitored and evaluated.
Measured lives: the rise of assessment as the engine of change in English schools
Authors: James Mary
Published: July 2002

The year 2000 marks the end of compulsory education for the first cohort of students to experience the National Curriculum throughout their school careers. This article describes their experience of assessment and compares it with the testing regime that those children who start school in 2000 are likely to experience. Changes in policy from the early Task Group on Assessment and Testing proposals are analysed, especially the increasing priority given to the use of assessment for monitoring and evaluating the performance of teachers, schools and local education authorities. This shift is interpreted in terms of underlying assumptions about effective strategies for change. While Conservative and Labour governments have pursued somewhat different goals, they have used a similar change strategy. This explains why the general thrust of policy has continued in a broadly similar direction — towards ever more testing in schools and the use of results as performance indicators. It is argued, however, that this strategy cannot be pursued indefinitely. After a point, further improvements will only be made if teachers are helped to work ‘smarter’, not just harder. Policy‐makers need, therefore, to look again at the contribution that formative assessment — or assessment for learning as part of pedagogy — can make to lifelong learning, in a more coherent, balanced and ‘educational’ system.
Book Reviews
Authors: GOSSOP MICHAEL
Published: July 2002

Book reviewed in this article:

Suicide in Alcoholism GEPRGE E. MURPHY

Criminalizing the Drink‐Driver ROY LIGHT

Appetite: Neural & Behavioural Bases CHARLES R. LEGG & D. A. BOOTH (Eds)

Beyond Adolescence: Problem Behaviour and Young Adult Development RICHARD JESSOR, JOHN E. DONOVAN & FRANCIS M. COSTA

Substance Misuse in Adolescence THOMAS P. GULOTTA, GERALD R. ADAMS & R. MONTEMEYER

A World of Opportunities: Lifestyle and Economic Behaviour of Heroin Addicts in Amsterdam MARTIN GRAPENDAAL, ED LEUW & HANS NELEN
Subtle Neuromuscular Defects in Utrophin-deficient Mice
Authors: Grady R. Mark , Merlie John P. , Sanes Joshua R.
Published: July 2002

Utrophin is a large cytoskeletal protein that is homologous to dystrophin, the protein mutated in Duchenne and Becker muscular dystrophy. In skeletal muscle, dystrophin is broadly distributed along the sarcolemma whereas utrophin is concentrated at the neuromuscular junction. This differential localization, along with studies on cultured cells, led to the suggestion that utrophin is required for synaptic differentiation. In addition, utrophin is present in numerous nonmuscle cells, suggesting that it may have a more generalized role in the maintenance of cellular integrity. To test these hypotheses we generated and characterized utrophin-deficient mutant mice. These mutant mice were normal in appearance and behavior and showed no obvious defects in muscle or nonmuscle tissue. Detailed analysis, however, revealed that the density of acetylcholine receptors and the number of junctional folds were reduced at the neuromuscular junctions in utrophin-deficient skeletal muscle. Despite these subtle derangements, the overall structure of the mutant synapse was qualitatively normal, and the specialized characteristics of the dystrophin-associated protein complex were preserved at the mutant neuromuscular junction. These results point to a predominant role for other molecules in the differentiation and maintenance of the postsynaptic membrane.
Surrogate Antigen Processing Mediated by TAP-dependent Antigenic Peptide Secretion
Authors: Gabathuler Reinhard , Alimonti Judie , Zhang Qian-Jin , Kolaitis Gerassimos , Reid Gregor , Jefferies Wilfred A.
Published: July 2002

MHC class I proteins assemble with peptides in the ER. The peptides are predominantly generated from cytoplasmic proteins, probably by the action of the proteasome, a multicatalytic proteinase complex. Peptides are translocated into the ER by the transporters associated with antigen processing (TAP), and bind to the MHC class I molecules before transport to the cell surface. Here, we use a new functional assay to demonstrate that peptides derived from vesicular stomatitis virus nucleoprotein (VSV-N) antigen are actively secreted from cells. This secretion pathway is dependent on the expression of TAP transporters, but is independent of the MHC genotype of the donor cells. Furthermore, the expression and transport of MHC class I molecules is not required. This novel pathway is sensitive to the protein secretion inhibitors brefeldin A (BFA) and a temperature block at 21°C, and is also inhibited by the metabolic poison, azide, and the protein synthesis inhibitor, emetine. These data support the existence of a novel form of peptide secretion that uses the TAP transporters, as opposed to the ER translocon, to gain access to the secretion pathway. Finally, we suggest that this release of peptides in the vicinity of uninfected cells, which we term surrogate antigen processing, could contribute to various immune and secretory phenomena.
Pheromone-regulated Genes Required for Yeast Mating Differentiation
Authors: Erdman Scott , Lin Li , Malczynski Michael , Snyder Michael
Published: July 2002

Yeast cells mate by an inducible pathway that involves agglutination, mating projection formation, cell fusion, and nuclear fusion. To obtain insight into the mating differentiation of Saccharomyces cerevisiae, we carried out a large-scale transposon tagging screen to identify genes whose expression is regulated by mating pheromone. 91,200 transformants containing random lacZ insertions were screened for β-galactosidase (β-gal) expression in the presence and absence of α factor, and 189 strains containing pheromone-regulated lacZ insertions were identified. Transposon insertion alleles corresponding to 20 genes that are novel or had not previously been known to be pheromone regulated were examined for effects on the mating process. Mutations in four novel genes, FIG1, FIG2, KAR5/ FIG3, and FIG4 were found to cause mating defects. Three of the proteins encoded by these genes, Fig1p, Fig2p, and Fig4p, are dispensible for cell polarization in uniform concentrations of mating pheromone, but are required for normal cell polarization in mating mixtures, conditions that involve cell–cell communication. Fig1p and Fig2p are also important for cell fusion and conjugation bridge shape, respectively. The fourth protein, Kar5p/Fig3p, is required for nuclear fusion. Fig1p and Fig2p are likely to act at the cell surface as Fig1:: β-gal and Fig2::β-gal fusion proteins localize to the periphery of mating cells. Fig4p is a member of a family of eukaryotic proteins that contain a domain homologous to the yeast Sac1p. Our results indicate that a variety of novel genes are expressed specifically during mating differentiation to mediate proper cell morphogenesis, cell fusion, and other steps of the mating process.
The LDL Receptor Clustering Motif Interacts with the Clathrin Terminal Domain in a Reverse Turn Conformation
Authors: Kibbey Richard G. , Rizo Josep , Gierasch Lila M. , Anderson Richard G.W.
Published: July 2002

Previously the hexapeptide motif FXNPXY807 in the cytoplasmic tail of the LDL receptor was shown to be essential for clustering in clathrin-coated pits. We used nuclear magnetic resonance line-broadening and transferred nuclear Overhauser effect measurements to identify the molecule in the clathrin lattice that interacts with this hexapeptide, and determined the structure of the bound motif. The wild-type peptide bound in a single conformation with a reverse turn at residues NPVY. Tyr807Ser, a peptide that harbors a mutation that disrupts receptor clustering, displayed markedly reduced interactions. Clustering motif peptides interacted with clathrin cages assembled in the presence or absence of AP2, with recombinant clathrin terminal domains, but not with clathrin hubs. The identification of terminal domains as the primary site of interaction for FXNPXY807 suggests that adaptor molecules are not required for receptor-mediated endocytosis of LDL, and that at least two different tyrosine-based internalization motifs exist for clustering receptors in coated pits.
CD44 Occupancy Prevents Macrophage Multinucleation
Authors: Sterling Hyacinth , Saginario Charles , Vignery Agnès
Published: July 2002

Cells of the mononuclear phagocyte lineage have the capability to adhere to and fuse with each other and to differentiate into osteoclasts and giant cells. To investigate the macrophage adhesion/fusion mechanism, we focused our attention on CD44, a surface glycoprotein known to play a role in hematopoietic cell–cell adhesion. We report that CD44 expression by macrophages is highly and transiently induced by fusogenic conditions both in vitro and in vivo. We show that CD44 ligands, hyaluronic acid, chondroitin sulfates, and osteopontin prevent macrophage multinucleation. In addition, we report that the recombinant extracellular domain of CD44 binds fusing macrophages and prevents multinucleation in vitro. These data suggest that CD44 may control the mononucleated status of macrophages in tissues by virtue of mediating cell–cell interaction.
Isolation of a Ribonucleoprotein Complex Involved in mRNA Localization in Drosophila Oocytes
Authors: Wilhelm James E. , Mansfield Jennifer , Hom-Booher Nora , Wang Shengxian , Turck Christoph W. , Hazelrigg Tulle , Vale Ronald D.
Published: July 2002

Localization of bicoid (bcd) mRNA to the anterior and oskar (osk) mRNA to the posterior of the Drosophila oocyte is critical for embryonic patterning. Previous genetic studies implicated exuperantia (exu) in bcd mRNA localization, but its role in this process is not understood. We have biochemically isolated Exu and show that it is part of a large RNase-sensitive complex that contains at least seven other proteins. One of these proteins was identified as the cold shock domain RNA-binding protein Ypsilon Schachtel (Yps), which we show binds directly to Exu and colocalizes with Exu in both the oocyte and nurse cells of the Drosophila egg chamber. Surprisingly, the Exu–Yps complex contains osk mRNA. This biochemical result led us to reexamine the role of Exu in the localization of osk mRNA. We discovered that exu-null mutants are defective in osk mRNA localization in both nurse cells and the oocyte. Furthermore, both Exu/Yps particles and osk mRNA follow a similar temporal pattern of localization in which they transiently accumulate at the oocyte anterior and subsequently localize to the posterior pole. We propose that Exu is a core component of a large protein complex involved in localizing mRNAs both within nurse cells and the developing oocyte.
Dynamic Localization of Protein Phosphatase Type 1 in the Mitotic Cell Cycle of Saccharomyces cerevisiae
Authors: Bloecher Andrew , Tatchell Kelly
Published: July 2002

Protein phosphatase type I (PP1), encoded by the single essential gene GLC7 in Saccharomyces cerevisiae, functions in diverse cellular processes. To identify in vivo subcellular location(s) where these processes take place, we used a functional green fluorescent protein (GFP)–Glc7p fusion protein. Time-lapse fluorescence microscopy revealed GFP–Glc7p localizes predominantly in the nucleus throughout the mitotic cell cycle, with the highest concentrations in the nucleolus. GFP–Glc7p was also observed in a ring at the bud neck, which was dependent upon functional septins. Supporting a role for Glc7p in bud site selection, a glc7-129 mutant displayed a random budding pattern. In α-factor treated cells, GFP–Glc7p was located at the base of mating projections, again in a septin-dependent manner. At the start of anaphase, GFP–Glc7p accumulated at the spindle pole bodies and remained there until cytokinesis. After anaphase, GFP–Glc7p became concentrated in a ring that colocalized with the actomyosin ring. A GFP–Glc7-129 fusion was defective in localizing to the bud neck and SPBs. Together, these results identify sites of Glc7p function and suggest Glc7p activity is regulated through dynamic changes in its location.
Extracellular-Regulated Kinase Activation and Cas/Crk Coupling Regulate Cell Migration and Suppress Apoptosis during Invasion of the Extracellular Matrix
Authors: Cho Samuel Y. , Klemke Richard L.
Published: July 2002

Regulation of cell migration/invasion is important for embryonic development, immune function, and angiogenesis. However, migratory cells must also coordinately activate survival mechanisms to invade the extracellular matrix and colonize foreign sites in the body. Although invasive cells activate protective programs to survive under diverse and sometimes hostile conditions, the molecular signals that regulate these processes are poorly understood. Evidence is provided that signals that induce cell invasion also promote cell survival by suppressing apoptosis of migratory cells. Extracellular-regulated kinase (ERK) activation and molecular coupling of the adaptor proteins p130 Crk-associated substrate (CAS) and c-CrkII (Crk) represent two distinct pathways that induce cell invasion and protect cells from apoptosis in a three-dimensional collagen matrix. CAS/Crk-mediated cell invasion and survival requires activation of the small GTPase Rac, whereas ERK-induced cell invasion, but not survival requires myosin light chain kinase activation and myosin light chain phosphorylation. Uncoupling CAS from Crk or inhibition of ERK activity prevents migration and induces apoptosis of invasive cells. These findings provide molecular evidence that during invasion of the extracellular matrix, cells coordinately regulate migration and survival mechanisms through ERK activation and CAS/Crk coupling.
Imaging Constitutive Exocytosis with Total Internal Reflection Fluorescence Microscopy
Authors: Schmoranzer Jan , Goulian Mark , Axelrod Dan , Simon Sanford M.
Published: July 2002

Total internal reflection fluorescence microscopy has been applied to image the final stage of constitutive exocytosis, which is the fusion of single post-Golgi carriers with the plasma membrane. The use of a membrane protein tagged with green fluorescent protein allowed the kinetics of fusion to be followed with a time resolution of 30 frames/s. Quantitative analysis allowed carriers undergoing fusion to be easily distinguished from carriers moving perpendicularly to the plasma membrane. The flattening of the carriers into the plasma membrane is seen as a simultaneous rise in the total, peak, and width of the fluorescence intensity. The duration of this flattening process depends on the size of the carriers, distinguishing small spherical from large tubular carriers. The spread of the membrane protein into the plasma membrane upon fusion is diffusive. Mapping many fusion sites of a single cell reveals that there are no preferred sites for constitutive exocytosis in this system.
The Cortical Protein Num1p Is Essential for Dynein-Dependent Interactions of Microtubules with the Cortex
Authors: Heil-Chapdelaine Richard A. , Oberle Jessica R. , Cooper John A.
Published: July 2002

In budding yeast, the mitotic spindle moves into the neck between the mother and bud via dynein-dependent sliding of cytoplasmic microtubules along the cortex of the bud. How dynein and microtubules interact with the cortex is unknown. We found that cells lacking Num1p failed to exhibit dynein-dependent microtubule sliding in the bud, resulting in defective mitotic spindle movement and nuclear segregation. Num1p localized to the bud cortex, and that localization was independent of microtubules, dynein, or dynactin. These data are consistent with Num1p being an essential element of the cortical attachment mechanism for dynein-dependent sliding of microtubules in the bud.
The Phagosome Proteome
Authors: Garin Jérome , Diez Roberto , Kieffer Sylvie , Dermine Jean-François , Duclos Sophie , Gagnon Etienne , Sadoul Remy , Rondeau Christiane , Desjardins Michel
Published: July 2002

Phagosomes are key organelles for the innate ability of macrophages to participate in tissue remodeling, clear apoptotic cells, and restrict the spread of intracellular pathogens. To understand the functions of phagosomes, we initiated the systematic identification of their proteins. Using a proteomic approach, we identified >140 proteins associated with latex bead–containing phagosomes. Among these were hydrolases, proton pump ATPase subunits, and proteins of the fusion machinery, validating our approach. A series of unexpected proteins not previously described along the endocytic/phagocytic pathways were also identified, including the apoptotic proteins galectin3, Alix, and TRAIL, the anti-apoptotic protein 14-3-3, the lipid raft-enriched flotillin-1, the anti-microbial molecule lactadherin, and the small GTPase rab14. In addition, 24 spots from which the peptide masses could not be matched to entries in any database potentially represent new phagosomal proteins. The elaboration of a two-dimensional gel database of >160 identified spots allowed us to analyze how phagosome composition is modulated during phagolysosome biogenesis. Remarkably, during this process, hydrolases are not delivered in bulk to phagosomes, but are instead acquired sequentially. The systematic characterization of phagosome proteins provided new insights into phagosome functions and the protein or groups of proteins involved in and regulating these functions.
The erbB2 gene is required for the development of terminally differentiated spinal cord oligodendrocytes
Authors: Park Song-Kyu , Miller Robert , Krane Ian , Vartanian Timothy
Published: July 2002

Development of oligodendrocytes and the generation of myelin internodes within the spinal cord depends on regional signals derived from the notochord and axonally derived signals. Neuregulin 1 (NRG)-1, localized in the floor plate as well as in motor and sensory neurons, is necessary for normal oligodendrocyte development. Oligodendrocytes respond to NRGs by activating members of the erbB receptor tyrosine kinase family. Here, we show that erbB2 is not necessary for the early stages of oligodendrocyte precursor development, but is essential for proligodendroblasts to differentiate into galactosylcerebroside-positive (GalC+) oligodendrocytes. In the presence of erbB2, oligodendrocyte development is normal. In the absence of erbB2 (erbB2−/−), however, oligodendrocyte development is halted at the proligodendroblast stage with a >10-fold reduction in the number of GalC+ oligodendrocytes. ErbB2 appears to function in the transition of proligodendroblast to oligodendrocyte by transducing a terminal differentiation signal, since there is no evidence of increased oligodendrocyte death in the absence of erbB2. Furthermore, known survival signals for oligodendrocytes increase oligodendrocyte numbers in the presence of erbB2, but fail to do so in the absence of erbB2. Of the erbB2−/− oligodendrocytes that do differentiate, all fail to ensheath neurites. These data suggest that erbB2 is required for the terminal differentiation of oligodendrocytes and for development of myelin.
Cod1p/Spf1p is a P-type ATPase involved in ER function and Ca2+ homeostasis
Authors: Cronin Stephen R. , Rao Rajini , Hampton Randolph Y.
Published: July 2002

The internal environment of the ER is regulated to accommodate essential cellular processes, yet our understanding of this regulation remains incomplete. Cod1p/Spf1p belongs to the widely conserved, uncharacterized type V branch of P-type ATPases, a large family of ion pumps. Our previous work suggested Cod1p may function in the ER. Consistent with this hypothesis, we localized Cod1p to the ER membrane. The cod1Δ mutant disrupted cellular calcium homeostasis, causing increased transcription of calcium-regulated genes and a synergistic increase in cellular calcium when paired with disruption of the Golgi apparatus–localized Ca2+ pump Pmr1p. Deletion of COD1 also impaired ER function, causing constitutive activation of the unfolded protein response, hypersensitivity to the glycosylation inhibitor tunicamycin, and synthetic lethality with deletion of the unfolded protein response regulator HAC1. Expression of the Drosophila melanogaster homologue of Cod1p complemented the cod1Δ mutant. Finally, we demonstrated the ATPase activity of the purified protein. This study provides the first biochemical characterization of a type V P-type ATPase, implicates Cod1p in ER function and ion homeostasis, and indicates that these functions are conserved among Cod1p's metazoan homologues.
Asynchronous Coreceptor Downregulation after Positive Thymic Selection: Prolonged Maintenance of the Double Positive State in CD8 Lineage Differentiation Due to Sustained Biosynthesis of the CD4 Coreceptor
Authors: Barthlott Thomas , Kohler Hubertus , Eichmann Klaus
Published: July 2002

In several experimental systems analyzing the generation of single positive (SP) thymocytes from double positive (DP) thymocytes, CD4 SP cells have been shown to appear before CD8 SP cells. This apparent temporal asymmetry in the maturation of CD4 SP and CD8 SP thymocytes could either be due to divergent molecular differentiation programs of the two T cell lineages, or merely to slower degradation kinetics of the CD4 protein. To study this question in unmanipulated in vivo differentiation, we developed a four-color flow cytometry protocol which identifies a recently activated TCRintCD69pos thymocyte population containing DP cells and early CD4 SP cells but no CD8 SP cells. We show that these TCRintCD69pos thymocytes represent a transitory stage in the mainstream αβ T cell lineage. The precursors of the CD8 SP cells are contained in this population as incompletely selected DP cells. Moreover, we show that expression of both coreceptors in the TCRintCD69pos population depends on transcriptional and translational activity, thus excluding differences in turnover rates of the CD4 and CD8 proteins as the cause of the asynchrony in differentiation of the CD4 and CD8 lineages.
Productive Infection of Neonatal CD8+ T Lymphocytes by HIV-1
Authors: Yang Liang Peng , Riley James L. , Carroll Richard G. , June Carl H. , Hoxie James , Patterson Bruce K. , Ohshima Yusei , Hodes Richard J. , Delespesse Guy
Published: July 2002

CD8+ T lymphocytes confer significant but ultimately insufficient protection against HIV infection. Here we report that activated neonatal CD8+ T cells can be productively infected in vitro by macrophage-tropic (M-tropic) HIV-1 isolates, which are responsible for disease transmission, whereas they are resistant to T cell–tropic (T-tropic) HIV strains. Physiological activation of CD8-α/β+ CD4− T cell receptor–α/β+ neonatal T cells, including activation by allogeneic dendritic cells, induces the accumulation of CD4 messenger RNA and the expression of CD4 Ag on the cell surface. The large majority of anti-CD3/B7.1–activated cord blood CD8+ T cells coexpress CD4, the primary HIV receptor, as well as CCR5 and CXCR4, the coreceptors used by M- and T-tropic HIV-1 strains, respectively, to enter target cells. These findings are relevant to the rapid progression of neonatal HIV infection. Infection of primary HIV-specific CD8+ T cells may compromise their survival and thus significantly contribute to the failure of the immune system to control the infection. Furthermore, these results indicate a previously unsuspected level of plasticity in the neonatal immune system in the regulation of CD4 expression by costimulation.
The Interleukin 2 Receptor α Chain/CD25 Promoter Is a Target for Nuclear Factor of Activated T Cells
Authors: Schuh Kai , Twardzik Thomas , Kneitz Burkhard , Heyer Jörg , Schimpl Anneliese , Serfling Edgar
Published: July 2002

The expression of the murine interleukin (IL)-2 receptor α chain/CD25 is strongly induced at the transcriptional level after T cell activation. We show here that nuclear factor of activated T cell (NF-AT) factors are involved in the control of CD25 promoter induction in T cells. NF-ATp and NF-ATc bind to two sites around positions −585 and −650 located upstream of the proximal CD25 promoter. Immediately 3′ from these NF-AT motifs, nonconsensus sites are located for the binding of AP-1–like factors. Mutations of sites that suppress NF-AT binding impair the induction and strong NF-ATp–mediated transactivation of the CD25 promoter in T cells. In T lymphocytes from NF-ATp–deficient mice, the expression of CD25 is severely impaired, leading to a delayed IL-2 receptor expression after T cell receptor (TCR)/CD3 stimulation. Our data indicate an important role for NF-AT in the faithful expression of high affinity IL-2 receptors and a close link between the TCR-mediated induction of IL-2 and IL-2 receptor α chain promoters, both of which are regulated by NF-AT factors.
Supraoptimal Peptide–Major Histocompatibility Complex Causes a Decrease in Bcl-2 Levels and Allows Tumor Necrosis Factor α Receptor II–mediated Apoptosis of Cytotoxic T Lymphocytes
Authors: Alexander-Miller Martha A. , Derby Michael A. , Sarin Apurva , Henkart Pierre A. , Berzofsky Jay A.
Published: July 2002

Cytotoxic T lymphocytes (CTLs) are primary mediators of viral clearance, but high viral burden can result in deletion of antigen-specific CTLs. We previously reported a potential mechanism for this deletion: tumor necrosis factor (TNF)-α–mediated apoptosis resulting from stimulation with supraoptimal peptide–major histocompatibility complex. Here, we show that although death is mediated by TNF-α and its receptor (TNF-RII), surprisingly neither the antigen dose dependence of TNF-α production nor that of TNF-RII expression can account for the dose dependence of apoptosis. Rather, a previously unrecognized effect of supraoptimal antigen in markedly decreasing levels of the antiapoptotic protein Bcl-2 was discovered and is likely to account for the gain in susceptibility or competence to sustain the death signal through TNF-RII. This decrease requires a signal through the TCR, not just through TNF-RII. Although death mediated by TNF-RII is not as widely studied as that mediated by TNF-RI, we show here that it is also dependent on proteolytic cleavage by caspases and triggered by a brief initial encounter with antigen. These results suggest that determinant density can regulate the immune response by altering the sensitivity of CTLs to the apoptotic effects of TNF-α by decreasing Bcl-2 levels.
Osteoprotegerin Reverses Osteoporosis by Inhibiting Endosteal Osteoclasts and Prevents Vascular Calcification by Blocking a Process Resembling Osteoclastogenesis
Authors: Min Hosung , Morony Sean , Sarosi Ildiko , Dunstan Colin R. , Capparelli Casey , Scully Sheila , Van Gwyneth , Kaufman Steve , Kostenuik Paul J. , Lacey David L. , Boyle William J. , Simonet W. Scott
Published: July 2002

High systemic levels of osteoprotegerin (OPG) in OPG transgenic mice cause osteopetrosis with normal tooth eruption and bone elongation and inhibit the development and activity of endosteal, but not periosteal, osteoclasts. We demonstrate that both intravenous injection of recombinant OPG protein and transgenic overexpression of OPG in OPG−/2 mice effectively rescue the osteoporotic bone phenotype observed in OPG-deficient mice. However, intravenous injection of recombinant OPG over a 4-wk period could not reverse the arterial calcification observed in OPG−/− mice. In contrast, transgenic OPG delivered from mid-gestation through adulthood does prevent the formation of arterial calcification in OPG−/− mice. Although OPG is normally expressed in arteries, OPG ligand (OPGL) and receptor activator of NF-κB (RANK) are not detected in the arterial walls of wild-type adult mice. Interestingly, OPGL and RANK transcripts are detected in the calcified arteries of OPG−/− mice. Furthermore, RANK transcript expression coincides with the presence of multinuclear osteoclast-like cells. These findings indicate that the OPG/OPGL/RANK signaling pathway may play an important role in both pathological and physiological calcification processes. Such findings may also explain the observed high clinical incidence of vascular calcification in the osteoporotic patient population.
The Activation-induced Deaminase Functions in a Postcleavage Step of the Somatic Hypermutation Process
Authors: Papavasiliou F. Nina , Schatz David G.
Published: July 2002

Activation of B cells by antigen fuels two distinct molecular modifications of immunoglobulin (Ig) genes. Class-switch recombination (CSR) replaces the Igμ heavy chain constant region with a downstream constant region gene, thereby altering the effector function of the resulting antibodies. Somatic hypermutation (SHM) introduces point mutations into the variable regions of Ig genes, thereby changing the affinity of antibody for antigen. Mechanistic overlap between the two reactions has been suggested by the finding that both require the activation-induced cytidine deaminase (AID). It has been proposed that AID initiates both CSR and SHM by activating a common nuclease. Here we provide evidence that cells lacking AID, or expressing a dominant negative form of the protein, are still able to incur DNA lesions in SHM target sequences. The results indicate that an intact cytidine deaminase motif is required for AID function, and that AID acts downstream of the initial DNA lesions in SHM.
On the Mechanism by which 4-Aminopyridine Occludes Quinidine Block of the Cardiac K+ Channel, hKv1.5
Authors: Chen Fred S.P. , Fedida David
Published: July 2002

4-Aminopyridine (4-AP) binds to potassium channels at a site or sites in the inner mouth of the pore and is thought to prevent channel opening. The return of hKv1.5 off-gating charge upon repolarization is accelerated by 4-AP and it has been suggested that 4-AP blocks slow conformational rearrangements during late closed states that are necessary for channel opening. On the other hand, quinidine, an open channel blocker, slows the return or immobilizes off-gating charge only at opening potentials (>−25 mV). The aim of this study was to use quini-dine as a probe of open channels to test the kinetic state of 4-AP-blocked channels. In the presence of 0.2–1 mM 4-AP, quinidine slowed charge return and caused partial charge immobilization, corresponding to an increase in the Kd of ∼20-fold. Peak off-gating currents were reduced and decay was slowed ∼2- to 2.5-fold at potentials negative to the threshold of channel activation and during depolarizations shorter than normally required for channel activation. This demonstrated access of quinidine to 4-AP-blocked channels, a lack of competition between the two drugs, and implied allosteric modulation of the quinidine binding site by 4-AP resident within the channel. Single channel recordings also showed that quinidine could modulate the 4-AP-induced closure of the channels, with the result that frequent channel reopenings were observed when both drugs were present. We propose that 4-AP-blocked channels exist in a partially open, nonconducting state that allows access to quinidine, even at more negative potentials and during shorter depolarizations than those required for channel activation.
Analysis of a cell-vertex finite volume method for convection-diffusion problems
Authors: Morton K. , Stynes Martin , Süli Endre
Published: July 2002

A cell-vertex finite volume approximation of elliptic convection-dominated diffusion equations is considered in two dimensions. The scheme is shown to be stable and second-order convergent in a mesh-dependent

L
2

L_2

-norm.
Selective and Signal-dependent Recruitment of Membrane Proteins to Secretory Granules Formed by Heterologously Expressed von Willebrand Factor
Authors: Blagoveshchenskaya Anastasia D. , Hannah Matthew J. , Allen Simon , Cutler Daniel F.
Published: July 2002

von Willebrand factor (vWF) is a large, multimeric protein secreted by endothelial cells and involved in hemostasis. When expressed in AtT-20 cells, vWF leads to the de novo formation of cigar-shaped organelles similar in appearance to the Weibel-Palade bodies of endothelial cells in which vWF is normally stored before regulated secretion. The membranes of this vWF-induced organelle, termed the pseudogranule, are uncharacterized. We have examined the ability of these pseudogranules, which we show are secretagogue responsive, to recruit membrane proteins. Coexpression experiments show that the Weibel-Palade body proteins P-selectin and CD63, as well as the secretory organelle membrane proteins vesicle-associated membrane protein-2 and synaptotagmin I are diverted away from the endogenous adrenocorticotropic hormone-containing secretory granules to the vWF-containing pseudogranules. However, transferrin receptor, lysosomal-associated membrane protein 1, and sialyl transferase are not recruited. The recruitment of P-selectin is dependent on a tyrosine-based motif within its cytoplasmic domain. Our data show that vWF pseudogranules specifically recruit a subset of membrane proteins, and that in a process explicitly driven by the pseudogranule content (i.e., vWF), the active recruitment of at least one component of the pseudogranule membrane (i.e., P-selectin) is dependent on residues of P-selectin that are cytosolic and therefore unable to directly interact with vWF.
Symmetry observations in long nucleotide sequences: a
commentary on the Discovery Note of Qi and Cuticchia
Authors: Forsdyke D. R.
Published: July 2002

The relative quantities of bases in DNA were determined chemically many years before sequencing technologies permitted direct counting of bases. Apparently unaware of the rich literature on the topic, bioinformaticists are today rediscovering the ‘wheels’ of Chargaff, Wyatt and other biochemists. It follows from Chargaff’s second parity rule (%A = %T, %G = %C for single stranded DNA) that the symmetries observed for the two pairs of complementary mononucleotide bases, should also apply to the eight pairs of complementary dinucleotide bases, the thirty-two pairs of complementary trinucleotide bases, etc. This was made explicit by Prabhu in 1993 in a study of complete genomes and long genome segments from a wide range of taxa, and was rediscovered by Qi and Cuticchia in 2001 in a study of complete genomes. It follows from Chargaff’s GC-rule (%GC tends to be uniform and species specific) that, within a species, oligonucleotides of the same GC% will be at approximately equal quantities in single stranded DNA. Thus, for example, while quantities of CAT and ATG (reverse complements) will be closely correlated because of both of the above Chargaff rules, CAT and GTA (forward complements) will show some correlation only because of the latter rule. The need for complete genomic sequences in bioinformatic analyses may have been somewhat overplayed.
Lyn and Syk tyrosine kinases are not activated in B‐lineage lymphoid cells exposed to low‐energy electromagnetic fields
Authors: Woods Margaret , Bobanovic Fedja , Brown David , R. Alexander Denis
Published: July 2002

Exposure of B‐lineage lymphoid cells to a 100 μΤ 60 Hz AC magnetic field has been reported to stimulate the rapid activation of Lyn and Syk tyrosine kinases and the induction of protein tyrosine phosphorylation. These findings are significant because of the critical role played by these B cell signaling events in the control of growth and differentiation, and therefore the potential of electromagnetic field (EMF) exposure to induce cancer. We report the first study carried out with the aim of reproducing the reported EMF effects on Lyn and Syk tyrosine kinases. The system used enabled EMF exposure conditions to be carefully controlled and also allowed experiments to be performed blind. The effects of a 100 μT 60 Hz AC magnetic field on protein tyrosine phosphorylation and on Lyn and Syk tyrosine kinase activities were investigated in Nalm‐6 and DT40 B cells in the absence and presence of a 46 μT DC magnetic field. However, no significant effects of low‐energy electromagnetic fields on tyrosine kinase activities or protein phosphorylation were observed.—Woods, M., Bobanovic, F., Brown, D., Alexander, D. R. Lyn and Syk tyrosine kinases are not activated in B‐lineage lymphoid cells exposed to low‐energy electromagnetic fields. FASEB J. 14, 2284‐2290 (2000)
A note on solitary and periodic waves of a new kind
Authors: Montagu E. L. , Norbury John
Published: July 2002

The operator
B
ϵ
2
=(
W
− ϵ
2
∂

x

2
)
–1
, where
W
(
x
) = 1 – 2
γ
|
x
| +
x
2
,
x
ϵ
R
and
γϵ
(0, 1) is shown to converge strongly to the limit operator
W
–1
, as ϵ
2
→ 0 This key result was omitted from the proof of existence of solitary waves in the recently published paper by Professor T. B. Benjamin.
Sexual conflict and speciation
Authors: Parker G. A. , Partridge L.
Published: July 2002

We review the significance of two forms of sexual conflict (different evolutionary interests of the two sexes) for genetic differentiation of populations and the evolution of reproductive isolation. Conflicting selection on the alleles at a single locus can occur in males and females if the sexes have different optima for a trait, and there are pleiotropic genetic correlations between the sexes for it. There will then be selection for sex limitation and hence sexual dimorphism. This sex limitation could break down in hybrids and reduce their fitness. Pleiotropic genetic correlations between the sexes could also affect the likelihood of mating in interpopulation encounters. Conflict can also occur between (sex–limited) loci that determine behaviour in males and those that determine behaviour in females. Reproductive isolation may occur by rapid coevolution of male trait and female mating preference. This would tend to generate assortative mating on secondary contact, hence promoting speciation. Sexual conflict resulting from sensory exploitation, polyspermy and the cost of mating could result in high levels of interpopulation mating. If females evolve resistance to male pre– and postmating manipulation, males from one population could be more successful with females from the other, because females would have evolved resistance to their own (but not to the allopatric) males. Between–locus sexual conflict could also occur as a result of confict between males and females of different populations over the production of unfit hybrids. We develop models which show that females are in general selected to resist such matings and males to persist, and this could have a bearing on both the initial level of interpopulation matings and the likelihood that reinforcement will occur. In effect, selection on males usually acts to promote gene flow and to restrict premating isolation, whereas selection on females usually acts in the reverse direction. We review theoretical models relevant to resolution of this conflict. The winning role depends on a balance between the ‘value of winning’ and ‘power’ (relating to contest or armament costs): the winning role is likely to correlate with high value of winning and low costs. Sperm–ovum (or sperm–female tract) conflicts (and their plant parallels) are likely to obey the same principles. Males may typically have higher values of winning, but it is difficult to quantify ‘power’, and females may often be able to resist mating more cheaply than males can force it. We tentatively predict that sexual conflict will typically result in a higher rate of speciation in ‘female–win’ clades, that females will be responsible for premating isolation through reinforcement, and that ‘female–win’ populations will be less genetically diverse.
Memory, consciousness and neuroimaging
Authors:   The American Association for Research into Nervous and Mental Diseases, Schacter D. L. , Buckner R. L. , Koutstaal W.
Published: July 2002

Neuroimaging techniques that allow the assessment of memory performance in healthy human volunteers while simultaneously obtaining measurements of brain activityin vivomay offer new information on the neural correlates of particular forms of memory retrieval and their association with consciousness and intention. We consider evidence from studies with positron emission tomography and functional magnetic resonance imaging indicating that priming, a form of implicit retrieval, is associated with decreased activity in various cortical regions. We also consider evidence concerning the question of whether two components of explicit retrieval—intentional or effortful search and successful conscious recollection— are preferentially associated with increased activity in prefrontal and medial temporal regions, respectively. Last, we consider recent efforts to probe the relation between the phenomenological character of remembering and neural activity. In this instance we broaden our scope to include studies employing event–related potentials and consider evidence concerning the neural correlates of qualitatively different forms of memory, including memory that is specifically associated with a sense of self, and the recollection of particular temporal or perceptual features that might contribute to a rich and vivid experience of the past.
How to study consciousness scientifically
Authors:   The American Association for Research into Nervous and Mental Diseases, Searle J. R.
Published: July 2002

The neurosciences have advanced to the point that we can now treat consciousness as a scientific problem like any other. The problem is to explain how brain processes cause consciousness and how consciousness is realized in the brain. Progress is impeded by a number of philosophical mistakes, and the aim of this paper is to remove nine of those mistakes: (i) consciousness cannot be defined; (ii) consciousness is subjective but science is objective; (iii) brain processes cannot explain consciousness; (iv) the problem of ‘qualia’ should be set aside; (v) consciousness is epiphenomenal; (vi) consciousness has no evolutionary function; (vii) a causal account of consciousness is necessarily dualistic; (viii) science is reductionistic, so a scientific account of consciousness would show it reducible to something else; and (ix) an account of consciousness must be an information processing account.