bluuebunny/crossref_metadata_2025 huggingface dataset:
Tissue factor- and factor X-dependent activation of protease-activated receptor 2 by factor VIIa
Authors: Camerer Eric , Huang Wei , Coughlin Shaun R.
Published: July 2002

Protease-activated receptor 2 (PAR2) is expressed by vascular endothelial cells and other cells in which its function and physiological activator(s) are unknown. Unlike PAR1, PAR3, and PAR4, PAR2 is not activatable by thrombin. Coagulation factors VIIa (FVIIa) and Xa (FXa) are proteases that act upstream of thrombin in the coagulation cascade and require cofactors to interact with their substrates. These proteases elicit cellular responses, but their receptor(s) have not been identified. We asked whether FVIIa and FXa might activate PARs if presented by their cofactors. Co-expression of tissue factor (TF), the cellular cofactor for FVIIa, together with PAR1, PAR2, PAR3, or PAR4 conferred TF-dependent FVIIa activation of PAR2 and, to lesser degree, PAR1. Responses to FXa were also observed but were independent of exogenous cofactor. The TF/FVIIa complex converts the inactive zymogen Factor X (FX) to FXa. Strikingly, when FX was present, low picomolar concentrations of FVIIa caused robust signaling in cells expressing TF and PAR2. Responses in keratinocytes and cytokine-treated endothelial cells suggested that PAR2 may be activated directly by TF/FVIIa and indirectly by TF/FVIIa-generated FXa at naturally occurring expression levels of TF and PAR2. These results suggest that PAR2, although not activatable by thrombin, may nonetheless function as a sensor for coagulation proteases and contribute to endothelial activation in the setting of injury and inflammation. More generally, these findings highlight the potential importance of cofactors in regulating PAR function and specificity.
Synaptophysin regulates clathrin-independent endocytosis of synaptic vesicles
Authors: Daly Christopher , Sugimori Mutsuyuki , Moreira Jorge E. , Ziff Edward B. , Llinás Rodolfo
Published: July 2002

The GTPase dynamin I is required for synaptic vesicle (SV) endocytosis. Our observation that dynamin binds to the SV protein synaptophysin in a Ca
2+
-dependent fashion suggested the possibility that a dynamin/synaptophysin complex functions in SV recycling. In this paper we show that disruption of the dynamin/synaptophysin interaction by peptide injection into the squid giant synapse preterminal results in a decrease in transmitter release during high-frequency stimulation, indicating an inhibition of SV recycling. Electron microscopy of these synapses reveals a depletion of SVs, demonstrating a block of vesicle retrieval after fusion. In addition, we observed an increase in clathrin-coated vesicles, indicating that the peptide does not block clathrin-dependent endocytosis. We conclude that the dynamin/synaptophysin complex functions in a clathrin-independent mechanism of SV endocytosis that is required for efficient synaptic transmission.
Spermatogonial stem cell enrichment by multiparameter selection of mouse testis cells
Authors: Shinohara Takashi , Orwig Kyle E. , Avarbock Mary R. , Brinster Ralph L.
Published: July 2002

The spermatogonial stem cell initiates and maintains spermatogenesis in the testis. To perform this role, the stem cell must self replicate as well as produce daughter cells that can expand and differentiate to form spermatozoa. Despite the central importance of the spermatogonial stem cell to male reproduction, little is known about its morphological or biochemical characteristics. This results, in part, from the fact that spermatogonial stem cells are an extremely rare cell population in the testis, and techniques for their enrichment are just beginning to be established. In this investigation, we used a multiparameter selection strategy, combining thein vivocryptorchid testis model within vitrofluorescence-activated cell sorting analysis. Cryptorchid testis cells were fractionated by fluorescence-activated cell sorting analysis based on light-scattering properties and expression of the cell surface molecules α6-integrin, αv-integrin, and the c-kit receptor. Two important observations emerged from these analyses. First, spermatogonial stem cells from the adult cryptorchid testis express little or no c-kit. Second, the most effective enrichment strategy, in this study, selected cells with low side scatter light-scattering properties, positive staining for α6-integrin, and negative or low αv-integrin expression, and resulted in a 166-fold enrichment of spermatogonial stem cells. Identification of these characteristics will allow further purification of these valuable cells and facilitate the investigation of molecular mechanisms governing spermatogonial stem cell self renewal and hierarchical differentiation.
Cloning and expression of a novel human antibody–antigen pair associated with Felty's syndrome
Authors: Ditzel Henrik J. , Masaki Yasufumi , Nielsen Heidi , Farnaes Lauge , Burton Dennis R.
Published: July 2002

An increasing number of studies suggest the importance of antibodies in the pathogenesis of most systemic and organ-specific autoimmune diseases, although there is considerable controversy over the precise role of the autoantibodies involved. In humans, a major obstacle to progress is the identification and cloning of the relevant autoantibodies and autoantigens. Here, an approach based on the sequential use of antibody phage display and antigen expression libraries is developed and applied to a donor suffering from rheumatoid arthritis (RA), splenomegaly, and peripheral destruction of neutrophils leading to neutropenia (Felty's syndrome). An antibody phage display library was constructed from bone marrow from the donor and a high-affinity human mAb, ANA15, selected by panning against fresh neutrophils and independently by panning against a fixed cell line. The antibody showed strong staining of neutrophils and a number of cell lines. Probing of a λgt11 expression library from an induced myelomonocytic cell line with the mAb ANA15 identified the eukaryotic elongation factor 1A-1 (eEF1A-1) as a novel autoantigen. The specificity of ANA15 was confirmed by reactivity with both purified and recombinant eEF1A-1. Screening of a large panel of sera revealed that 66% of patients with Felty's syndrome had elevated levels of anti-eEF1A-1 antibodies. The cloning of this antibody–antigen pair should permit rational evaluation of any pathogenicity resulting from the interaction and its significance in neutropenia.
A dynamic model of social network formation
Authors: Skyrms Brian , Pemantle Robin
Published: July 2002

We consider a dynamic social network model in which agents play
repeated games in pairings determined by a stochastically evolving
social network. Individual agents begin to interact at random, with the
interactions modeled as games. The game payoffs determine which
interactions are reinforced, and the network structure emerges as a
consequence of the dynamics of the agents' learning behavior. We study
this in a variety of game-theoretic conditions and show that the
behavior is complex and sometimes dissimilar to behavior in the absence
of structural dynamics. We argue that modeling network structure as
dynamic increases realism without rendering the problem of analysis
intractable.
Diffusion of nitric oxide can facilitate cerebellar learning: A simulation study
Authors: Schweighofer Nicolas , Ferriol Gabriel
Published: July 2002

The gaseous second messenger nitric oxide (NO), which readily
diffuses in brain tissue, has been implicated in cerebellar long-term
depression (LTD), a form of synaptic plasticity thought to be involved
in cerebellar learning. Can NO diffusion facilitate cerebellar
learning? The inferior olive (IO) cells, which provide the error
signals necessary for modifying the granule cell–Purkinje cell (PC)
synapses by LTD, fire at ultra-low firing rates
in vivo
,
rarely more than 2–4 spikes within a second. In this paper, we show
that NO diffusion can improve the transmission of sporadic IO error
signals to PCs within cerebellar cortical functional units, or
microzones. To relate NO diffusion to adaptive behavior, we add NO
diffusion and a “volumic” LTD learning rule, i.e., a learning
rule that depends both on the synaptic activity and on the NO
concentration at the synapse, to a cerebellar model for arm movement
control. Our results show that biologically plausible diffusion leads
to an increase in information transfer of the error signals to the PCs
when the IO firing rate is ultra-low. This, in turn, enhances
cerebellar learning as shown by improved performance in an arm-reaching
task.
Nitric oxide prevents cardiovascular disease and determines survival in polyglobulic mice overexpressing erythropoietin
Authors: Ruschitzka Frank T. , Wenger Roland H. , Stallmach Thomas , Quaschning Thomas , de Wit Cor , Wagner Klaus , Labugger Ralf , Kelm Malte , Noll Georg , Rülicke Thomas , Shaw Sidney , Lindberg Raija L. P. , Rodenwaldt Barbara , Lutz Hans , Bauer Christian , Lüscher Thomas F. , Gassmann Max
Published: July 2002

Nitric oxide (NO) induces vasodilatatory, antiaggregatory, and
antiproliferative effects
in vitro
. To delineate
potential beneficial effects of NO in preventing vascular disease
in vivo
, we generated transgenic mice overexpressing
human erythropoietin. These animals induce polyglobulia known to be
associated with a high incidence of vascular disease. Despite
hematocrit levels of 80%, adult transgenic mice did not develop
hypertension or thromboembolism. Endothelial NO synthase levels,
NO-mediated endothelium-dependent relaxation and circulating and
vascular tissue NO levels were markedly increased. Administration of
the NO synthase inhibitor
N
G
-nitro-L-arginine methyl
ester (L-NAME) led to vasoconstriction of peripheral resistance
vessels, hypertension, and death of transgenic mice, whereas wild-type
siblings developed hypertension but did not show increased mortality.
L-NAME-treated polyglobulic mice revealed acute left ventricular
dilatation and vascular engorgement associated with pulmonary
congestion and hemorrhage. In conclusion, we here unequivocally
demonstrate that endothelial NO maintains normotension, prevents
cardiovascular dysfunction, and critically determines survival
in vivo
under conditions of increased hematocrit.
Skeletal muscle deformity and neuronal disorder in Trio exchange factor-deficient mouse embryos
Authors: O'Brien Stephen P. , Seipel Katja , Medley Quintus G. , Bronson Roderick , Segal Rosalind , Streuli Michel
Published: July 2002

Dbl-homology guanine nucleotide exchange factors (DH-GEFs) regulate
actin cytoskeletal reorganization, cell adhesion, and gene
transcription via activation of Rho GTPases. However, little is known
about the physiological role of mammalian DH-GEFs during development.
The DH-GEF family member Trio is of particular interest because it is a
multifunctional protein possessing two GEF domains, as well as a
protein serine/threonine kinase domain, and trio-like genes in
Caenorhabditis elegans
and
Drosophila
were shown to function in neural migration
and axon guidance. To determine the role of Trio during mammalian
development, we generated a mouse trio loss-of-function mutation
(
trio
−/−
). Trio function is essential
during late embryonic development as genotype analysis indicated that
trio
−/−
embryos died between embryonic day
(E)-15.5 and birth, or shortly thereafter. In the trio
−/−
embryos, primary skeletal myofibers were relatively normal at E14.5,
but by E18.5 highly unusual spherical myofibers accumulated. Trio
deficiency may cause a defect in secondary myogenesis, as the
appearance of the abnormal
trio
−/−
skeletal myofibers temporally coincided with the onset of secondary
myogenesis, and smaller secondary myofibers located adjacent to the
primary myofibers were absent. The proliferation of
trio
−/−
secondary myoblasts appeared
normal, suggesting that Trio may regulate secondary myoblast alignment
or fusion.
trio
−/−
embryos also displayed
aberrant organization in several regions within the brain, including
the hippocampal formation and olfactory bulb. We thus conclude that
Trio is essential for late embryonic development, and that Trio
functions in fetal skeletal muscle formation and in the organization of
neural tissues.
Compositional genomes: Prebiotic information transfer in mutually catalytic noncovalent assemblies
Authors: Segré Daniel , Ben-Eli Dafna , Lancet Doron
Published: July 2002

Mutually catalytic sets of simple organic molecules have been suggested to be capable of self-replication and rudimentary chemical evolution. Previous models for the behavior of such sets have analyzed the global properties of short biopolymer ensembles by using graph theory and a mean field approach. In parallel, experimental studies with the autocatalytic formation of amphiphilic assemblies (e.g., lipid vesicles or micelles) demonstrated self-replication properties resembling those of living cells. Combining these approaches, we analyze here the kinetic behavior of small heterogeneous assemblies of spontaneously aggregating molecules, of the type that could form readily under prebiotic conditions. A statistical formalism for mutual rate enhancement is used to numerically simulate the detailed chemical kinetics within such assemblies. We demonstrate that a straightforward set of assumptions about kinetically enhanced recruitment of simple amphiphilic molecules, as well as about the spontaneous growth and splitting of assemblies, results in a complex population behavior. The assemblies manifest a significant degree of homeostasis, resembling the previously predicted quasi-stationary states of biopolymer ensembles (Dyson, F. J. (1982)J. Mol. Evol. 18, 344–350). Such emergent catalysis-driven, compositionally biased entities may be viewed as having rudimentary “compositional genomes.” Our analysis addresses the question of how mutually catalytic metabolic networks, devoid of sequence-based biopolymers, could exhibit transfer of chemical information and might undergo selection and evolution. This computed behavior may constitute a demonstration of natural selection in populations of molecules without genetic apparatus, suggesting a pathway from random molecular assemblies to a minimal protocell.
Paxgene diversity in the basal cnidarianAcropora millepora(Cnidaria, Anthozoa): Implications for the evolution of thePaxgene family
Authors: Miller David J. , Hayward David C. , Reece-Hoyes John S. , Scholten Ingo , Catmull Julian , Gehring Walter J. , Callaerts Patrick , Larsen Jill E. , Ball Eldon E.
Published: July 2002

Paxgenes encode a family of transcription factors, many of which play key roles in animal embryonic development but whose evolutionary relationships and ancestral functions are unclear. To address these issues, we are characterizing thePaxgene complement of the coralAcropora millepora, an anthozoan cnidarian. As the simplest animals at the tissue level of organization, cnidarians occupy a key position in animal evolution, and the Anthozoa are the basal class within this diverse phylum. We have identified fourPaxgenes inAcropora: two (Pax-AamandPax-Bam) are orthologs of genes identified in other cnidarians; the others (Pax-CamandPax-Dam) are unique toAcropora. Pax-Aammay be orthologous withDrosophila Pox neuro, andPax-Bamclearly belongs to thePax-2/5/8class. The Pax-Bam Paired domain binds specifically and preferentially to Pax-2/5/8 binding sites. The recently identifiedAcroporagenePax-Dambelongs to thePax-3/7class. Clearly, substantial diversification of thePaxfamily occurred before the Cnidaria/higher Metazoa split. The fourthAcropora Paxgene,Pax-Cam, may correspond to the ancestral vertebratePaxgene and most closely resemblesPax-6. The expression pattern ofPax-Cam, in putative neurons, is consistent with an ancestral role of thePaxfamily in neural differentiation and patterning. We have determined the genomic structure of eachAcropora Paxgene and show that some splice sites are shared both between the coral genes and between these andPaxgenes in triploblastic metazoans. Together, these data support the monophyly of thePaxfamily and indicate ancient origins of several introns.
Human Values and Social Identities among Samples of White and Black South Africans
Authors: Heaven Patrick C.L. , Simbayi Leickness , Stones Christopher , Roux Anda Le
Published: July 2002

We examined the value correlates of different social identities among two groups of South Africans, those identifying themselves as white Afrikaners or as black South Africans. Respondents indicated the importance of their membership of different groups and also completed indices of National strength and order, and International harmony and equality. Multiple regression analyses showed that the social identities associated with both values for self‐identified Afrikaners were mainly linked with ethnic language (Afrikaans) and religion. Among self‐identified black South Africans, however, the social identities were more encompassing, including the notion of global citizen and South African. The findings are discussed in the light of ongoing political and social change in South Africa and the nature of changing identities, as well as the role of cultural symbols in facilitating in‐group identification among white Afrikaners.
Learning Careers: Continuity and change in young people's dispositions to learning
Authors: Bloomer Martin , Hodkinson Phil
Published: July 2002

Despite an extensive literature on the subject of learning, very little has been written about the ways in which young people's dispositions to learning transform over time. This article draws upon a longitudinal research project which focused on such transformations. The article centres on the case of Amanda Ball and considers the implications which her story holds for our understanding of learning. It is shown that dispositions can transform in a short period of time and that such transformations are often linked, in complex ways, to wider social, economic and cultural contexts.
Motor development as foundation and future of developmental psychology
Authors: Thelen Esther
Published: July 2002

The study of how infants and children come to control their bodies is perhaps the oldest topic in scientific developmental psychology. Yet, for many years the study of motor development lay dormant. In the last two decades, however, there has been an enormous resurgence of interest. As at the time of the very beginnings of our field, the contemporary study of motor development is contributing both empirically and theoretically to the larger questions in development and especially to our understanding of developmental change. In this essay, I trace the course of the changing fortunes of motor development, evaluate where we have been, what we are doing, and speculate on some critical issues for the future. The purpose of this essay is to comment on the general themes and influences that have been a part of motor development’s “rise-fall-and-rise-again” history. For a more comprehensive review of substantive topic areas in motor development, readers are referred to the authoritative treatment recently published by Bertenthal and Clifton (1998) and to the excellent monograph by Goldfield (1995).
Distinguishing One’s Own Voice from Those of Others: A Function for Private Speech?
Authors: Fernyhough Charles , Russell James
Published: July 2002

The aim of the study reported here was to test a new hypothesis about the function of private speech, namely that children’s private speech in social contexts presents them with an opportunity to distinguish their own voices from those of others. Data on the social and private speech of 22 five-year-olds were collected during single hour-long group play sessions. In a later session, children heard extracts from an audio recording of an earlier group discussion, and were asked to state which of each pair of extracts contained their own speech. It was found that children’s performance on this speech recognition task was positively correlated with both proportional and frequency measures of private speech. There was no relationship between the speech recognition measure and frequencies of social speech or overall verbosity; and performance on a test of children’s ability to recognise their own speech in isolation was no better than chance. We suggest that these findings are consistent with private speech having a specific function in the development of an understanding of oneself as a speaking agent among other such speakers.
The Estimation of Reliability in Longitudinal Models
Authors: DeShon Richard P. , Ployhart Robert E. , Sacco Joshua M.
Published: July 2002

Despite the increasing attention devoted to the study and analysis of longitudinal data, relatively little consideration has been directed toward understanding the issues of reliability and measurement error. Perhaps one reason for this neglect has been that traditional methods of estimation (e.g. generalisability theory) require assumptions that are often not tenable in longitudinal designs. This paper first examines applications of generalisability theory to the estimation of m easurement error and reliability in longitudinal research, and notes how factors such as missing data, correlated errors, and true score instability prohibit traditional variance com ponent estimation. Next, we discuss how estimation methods using restricted maximum likelihood can account for these factors, thereby providing m any advantages over traditional estimation methods. Finally, we provide a substantive exam ple illustrating these advantages, and include brief discussions of programming and software considerations.
Information and action in punching a falling ball
Authors: Michaels Claire F. , Zeinstra Edzard B. , Oudejans Raôul R. D.
Published: July 2002

Lee, Young, Reddish, Lough, and Clayton (1983) reported that the timing control of jumping and vertically punching a dropping ball exploits the inverse of the rate of change of optical expansion, τ (r). We raise a number of methodological and logical criticisms against their experiment and conclusions and attempt to rectify them by examining elbow joint angles only, in seated punchers, under both monocular and binocular conditions, with two ball sizes, dropped from two heights. Differences between the binocular and monocular cases suggest the exploitation of different information. We present several techniques to help determine the operative variable(s) controlling the action. The optical variable used to initiate and guide flexion appeared to be expansion velocity (looming), rather than τ (r); extension appeared to be under the control of different variables in the monocular and binocular cases. Simulations using single variables and single perceptuo-motor intervals were of mixed success.
Timing goals in bimanual coordination
Authors: Semjen A. , Summers J.J.
Published: July 2002

Phase coupling between movement trajectories has been proposed as the basic mechanism of hand coordination in the production of bimanual rhythmic movements with a 1:2 frequency ratio. Here a central temporal coupling view is proposed as an alternative. Extending previous models of two-handed synchronic and alternate-hand tapping, we hypothesized that 1:2 tapping is performed under the control of a single internal timekeeper set at the frequency required for the fast hand. The fast hand is assumed to use every signal and the slow hand every other signal of the timekeeper, to produce actions coordinated in time. The model's predictions for the variance-covariance pattern of tap timing within and across hands were tested in an experiment that required tapping with both hands with 1:1 or 1:2 frequency ratio. The finger contact on the response plate was to be short or long, according to instruction. Prolonged finger contact entailed profound modifications in the movement trajectories but failed to modify the variance-covariance pattern of the tap timing. This pattern proved to conform to predictions under both the short and the long contact conditions, thus supporting the central temporal coupling hypothesis.
Responding under time pressure: Testing two animal learning models and a model of visual categorization
Authors: Kinder Annette , Lachnit Harald
Published: July 2002

Two experiments are reported, which employed a Pavlovian eyelid conditioning procedure with human participants. The experiments tested the predictions of three models of the time-course of processing under time pressure. These were the extended generalized context model (Lamberts, 1998), and two variants of the Rescorla-Wagner model (Rescorla & Wagner, 1972), which were activated in cascade mode. Reinforcement schedules in the experiments were equivalent either to an AND rule or to an XOR rule. The time available for processing the conditioned stimulus and initiating a conditioned response was manipulated by varying the interval from the onset of the conditioned stimulus to the onset of the unconditioned stimulus. The results were in accord with the predictions of one of the two variants of the Rescorla-Wagner model.
Attention to local form information can prevent access to semantic information
Authors: Murray Janice E. , Jones Craig
Published: July 2002

Humphreys and Boucart (1997) have shown that when processing of local form is required for response, surrounding global information is automatically processed to a semantic level. The generality of this effect was investigated in two experiments in which the perceptual load of the relevant local form information was manipulated, as was uncertainty about perceptual load. Participants attended to a single line segment inside a picture of an animal or a vehicle and then decided which of two pictures in the target/distractor display that followed contained a line segment that matched the first in orientation. The perceptual load of the relevant local form information was either low (the matching line segment was one of the solitary line segments presented in the centre of the target and distractor pictures), or high (the matching line segment was part of one of the solitary letters presented in the centre of the target and distractor pictures). The semantic relations among the pictures were manipulated, and when perceptual load remained constant across trials, semantic relations affected performance in the low-load but not in the high-load condition. When perceptual load varied from trial to trial, there was no evidence of any semantic processing on either low- or high-load trials. The results suggest that in form-matching tasks, attentional priority can be given to local information, thus preventing access to semantic information derived from global shape. They further suggest that the distribution of attention is not dictated entirely by the actual perceptual demands of the relevant stimulus, indicating an important role for top-down processing.
Limits of rhythm perception
Authors: Demany Laurent , Semal Catherine
Published: July 2002

To what extent are listeners sensitive to the time intervals separating non-consecutive events in sound sequences? The subjects of Experiment 1 were presented with sequences of 20 identical tones in which the 10 odd-numbered tones or the 10 even-numbered tones made up an isochronous sub-sequence (with a periodicity of 0.5-1 s) whereas the other tones, acting as distractors, occurred at random moments. Such sequences appeared to be very difficult to discriminate from sequences without any timing regularity, which revealed a lack of perceptual sensitivity to their “second-order” intervals. Experiment 2 employed repetitive sequences in which the first-order intervals (separating consecutive tones) took two possible values, forming a ratio that subjects had to classify as larger or smaller than 2. The results of this experiment suggest that subjects were able to make use of second-order intervals in their task, but mainly due to the predictable nature of the sequences; the relative positions of subjective accents (Povel & Essens, 1985) had no significant effect on performance. It is concluded that the perception of subtle timing details in “ordinary” music may rest on nothing more than a sensitivity to the relations between first-order intervals (within a given auditory stream).
Children's reading of words, pseudohomophones, and other nonwords
Authors: Laxon Veronica , Masterson Jackie , Gallagher Alison , Pay Julia
Published: July 2002

In Experiment 1 children aged 8-9 and 9-10 years were tested for neighbourhood and pseudohomophone effects in nonword reading. Neighbourhood effects (N effects) were robust irrespective of group or type of nonword. Pseudohomophones were read more accurately than other nonwords but this finding was robust only for the younger 8-9-year-olds. High-frequency words were read more accurately than low-frequency words, but the reverse applied to pseudohomophones based on high- and low-frequency words, although this was not robust. Error rates for the 9-10-year-olds in Experiment 1 were low, and so it was difficult to interpret the lack of a pseudohomophone advantage for reading nonwords in this age group. Experiment 2 was therefore carried out, which consisted of a replication of the first study with a further group of 9- 10-year-olds, but pronunciation latencies were measured, as well as accuracy. All the effects obtained in Experiment 1 were replicated but, in addition, an advantage for pseudohomophones in terms of pronunciation latencies was observed. The implications for accounts of reading development are discussed.
Process Dissociation Procedure: Double Dissociations following Divided Attention and Speeded Responding
Authors: Dehn M. Doris , Engelkamp Johannes
Published: July 2002

The validity of the process dissociation procedure was examined by manipulating attention and speed of responding in a recognition task. Both manipulations were expected to decrease the probability of controlled memory processes, c, while leaving the probability of automatic memory processes, a, unaffected. In order to estimate c and a, a multinomial processing tree model was fitted to the data. Contrary to expectation, a double dissociation (i.e.a decrease inc coupled with an increase in a) was obtained, suggesting that a does not accurately measure the probability of automatic processes. The results are discussed with reference to the independence assumption in the process dissociation procedure.
Glucocorticoids: mechanisms of action and anti‐inflammatory potential in asthma
Authors: van der Velden V. H. J.
Published: July 2002

Glucocorticoids are potent inhibitors of inflammatory processes and are widely used in the treatment of asthma. The anti‐inflammatory effects are mediated either by direct binding of the glucocorticoid/glucocorticoid receptor complex to glucocorticoid responsive elements in the promoter region of genes, or by an interaction of this complex with other transcription factors, in particular activating protein‐1 or nuclear factor‐κB. Glucocorticoids inhibit many inflammation‐associated molecules such as cytokines, chemokines, arachidonic acid metabolites, and adhesion molecules. In contrast, anti‐inflammatory mediators often are up‐regulated by glucocorticoids. In vivo studies have shown that treatment of asthmatic patients with inhaled glucocorticoids inhibits the bronchial inflammation and simultaneously improves their lung function. In this review, our current knowledge of the mechanism of action of glucocorticoids and their anti‐inflammatory potential in asthma is described. Since bronchial epithelial cells may be important targets for glucocorticoid therapy in asthma, the effects of glucocorticoids on epithelial expressed inflammatory genes will be emphasized.
Illness behaviour among Norwegian physicians
Authors: Rosvold Elin O. , Bjertness Espen
Published: July 2002

Background: Information on physicians' illness behaviour is to a large extent based on studies of selected groups of physicians. The objective of this paper is to study self-treatment and help-seeking behaviour in a nationwide representative sample of physicians. Results: In total, 70% of 1,476 physicians answered a mailed, anonymous questionnaire as a part of the Norwegian Medical Association's health survey. Of these, 75% had performed self-treatment during the last three years. Treatment by spouse, friends, and colleagues was also frequent. Of those who used prescription medicine, 73% were self-prescribing it; 13% of the physicians had negative experiences with self-treatment. Some 56% stated that they would prefer to seek help for somatic problems from a physician to whom they had no personal ties, and 50% would seek help for mental problems elsewhere than in the mental health care facilities located where they lived. Conclusion: Most physicians practise self-treatment when they are ill, and although they prefer to be treated by a physician they do not have personal ties to, many contact friends and colleagues when they need help from another physician.
Cells on the Move: A Dialogue Between Polarization and Motility
Authors: Manes Santos , Mira Emilia , Gomez‐Mouton Concepcion , Lacalle Rosa Ana , Martinez‐A Carlos
Published: July 2002

Throughout evolution, both prokaryotic and eukaryotic cells have developed a variety of biochemical mechanisms to define the direction and proximity of extracellular stimuli. This process is essential for the cell to reply properly to the environmental cues that determine cell migration, proliferation, and differentiation. Chemotaxis is the cellular response to chemical attractants that direct cell migration, a process that plays a central role in many physiological situations, such as host immune responses, angiogenesis, wound healing, embryogenesis, and neuronal patterning, among others. In addition, cell migration takes part in pathological states, including inflammation and tumor metastasis. Indeed, tumor progression to invasion and metastasis depends on the active motility of the invading cancer cells and the endothelial cell bed during tumor neovascularization. Cell migration switches “off” and “on” based on quantitative differences in molecular components such as adhesion receptors, cytoskeletal linking proteins, and extracellular matrix ligands, and by regulating the affinity of membrane‐bound chemoattractant receptors. A clear understanding of how cells sense chemoattractants is, therefore, of pivotal importance in the biology of the normal cell as well as in prevention of malignant cell invasion. Here we offer a perspective on cell migration that emphasizes the relationship between cell polarization and cell movement and the importance of the equilibrium between the signals that drive each process for the control of tumor cell invasion.
Xenopus Actin Depolymerizing Factor/Cofilin (XAC) Is Responsible for the Turnover of Actin Filaments in Listeria monocytogenes Tails
Authors: Rosenblatt Jody , Agnew Brian J. , Abe Hiroshi , Bamburg James R. , Mitchison Timothy J.
Published: July 2002

In contrast to the slow rate of depolymerization of pure actin in vitro, populations of actin filaments in vivo turn over rapidly. Therefore, the rate of actin depolymerization must be accelerated by one or more factors in the cell. Since the actin dynamics in Listeria monocytogenes tails bear many similarities to those in the lamellipodia of moving cells, we have used Listeria as a model system to isolate factors required for regulating the rapid actin filament turnover involved in cell migration. Using a cell-free Xenopus egg extract system to reproduce the Listeria movement seen in a cell, we depleted candidate depolymerizing proteins and analyzed the effect that their removal had on the morphology of Listeria tails. Immunodepletion of Xenopus actin depolymerizing factor (ADF)/cofilin (XAC) from Xenopus egg extracts resulted in Listeria tails that were approximately five times longer than the tails from undepleted extracts. Depletion of XAC did not affect the tail assembly rate, suggesting that the increased tail length was caused by an inhibition of actin filament depolymerization. Immunodepletion of Xenopus gelsolin had no effect on either tail length or assembly rate. Addition of recombinant wild-type XAC or chick ADF protein to XAC-depleted extracts restored the tail length to that of control extracts, while addition of mutant ADF S3E that mimics the phosphorylated, inactive form of ADF did not reduce the tail length. Addition of excess wild-type XAC to Xenopus egg extracts reduced the length of Listeria tails to a limited extent. These observations show that XAC but not gelsolin is essential for depolymerizing actin filaments that rapidly turn over in Xenopus extracts. We also show that while the depolymerizing activities of XAC and Xenopus extract are effective at depolymerizing normal filaments containing ADP, they are unable to completely depolymerize actin filaments containing AMPPNP, a slowly hydrolyzible ATP analog. This observation suggests that the substrate for XAC is the ADP-bound subunit of actin and that the lifetime of a filament is controlled by its nucleotide content.
Transport and Localization Elements in Myelin Basic Protein mRNA
Authors: Ainger Kevin , Avossa Daniela , Diana Amy S. , Barry Christopher , Barbarese Elisa , Carson John H.
Published: July 2002

Myelin basic protein (MBP) mRNA is localized to myelin produced by oligodendrocytes of the central nervous system. MBP mRNA microinjected into oligodendrocytes in primary culture is assembled into granules in the perikaryon, transported along the processes, and localized to the myelin compartment. In this work, microinjection of various deleted and chimeric RNAs was used to delineate regions in MBP mRNA that are required for transport and localization in oligodendrocytes. The results indicate that transport requires a 21-nucleotide sequence, termed the RNA transport signal (RTS), in the 3′ UTR of MBP mRNA. Homologous sequences are present in several other localized mRNAs, suggesting that the RTS represents a general transport signal in a variety of different cell types. Insertion of the RTS from MBP mRNA into nontransported mRNAs, causes the RNA to be transported to the oligodendrocyte processes. Localization of mRNA to the myelin compartment requires an additional element, termed the RNA localization region (RLR), contained between nucleotide 1,130 and 1,473 in the 3′ UTR of MBP mRNA. Computer analysis predicts that this region contains a stable secondary structure. If the coding region of the mRNA is deleted, the RLR is no longer required for localization, and the region between nucleotide 667 and 953, containing the RTS, is sufficient for both RNA transport and localization. Thus, localization of coding RNA is RLR dependent, and localization of noncoding RNA is RLR independent, suggesting that they are localized by different pathways.
Spatial Organization of Large-Scale Chromatin Domains in the Nucleus: A Magnified View of Single Chromosome Territories
Authors: Ferreira João , Paolella Giovanni , Ramos Carlos , Lamond Angus I.
Published: July 2002

We have analyzed the spatial organization of large scale chromatin domains in chinese hamster fibroblast, human lymphoid (IM-9), and marsupial kidney epithelial (PtK) cells by labeling DNA at defined stages of S phase via pulsed incorporation of halogenated deoxynucleosides. Most, if not all, chromosomes contribute multiple chromatin domains to both peripheral and internal nucleoplasmic compartments. The peripheral compartment contains predominantly late replicating G/Q bands, whereas early replicating R bands preferentially localize to the internal nucleoplasmic compartment. During mitosis, the labeled chromatin domains that were separated in interphase form a pattern of intercalated bands along the length of each metaphase chromosome. The transition from a banded (mitotic) to a compartmentalized (interphasic) organization of chromatin domains occurs during the late telophase/early G1 stage and is independent of transcriptional activation of the genome. Interestingly, generation of micronuclei with a few chromosomes showed that the spatial separation of early and late replicating chromatin compartments is recapitulated independently of chromosome number, even in micronuclei containing only a single chromosome. Our data strongly support the notion that the compartmentalization of large-scale (band size) chromatin domains seen in the intact nucleus is a magnified image of a similar compartmentalization occurring in individual chromosome territories.
Nuclear Localization of Cyclin B1 Controls Mitotic Entry After DNA Damage
Authors: Jin Pei , Hardy Stephen , Morgan David O.
Published: July 2002

Mitosis in human cells is initiated by the protein kinase Cdc2-cyclin B1, which is activated at the end of G2 by dephosphorylation of two inhibitory residues, Thr14 and Tyr15. The G2 arrest that occurs after DNA damage is due in part to stabilization of phosphorylation at these sites. We explored the possibility that entry into mitosis is also regulated by the subcellular location of Cdc2-cyclin B1, which is suddenly imported into the nucleus at the end of G2. We measured the timing of mitosis in HeLa cells expressing a constitutively nuclear cyclin B1 mutant. Parallel studies were performed with cells expressing Cdc2AF, a Cdc2 mutant that cannot be phosphorylated at inhibitory sites. Whereas nuclear cyclin B1 and Cdc2AF each had little effect under normal growth conditions, together they induced a striking premature mitotic phenotype. Nuclear targeting of cyclin B1 was particularly effective in cells arrested in G2 by DNA damage, where it greatly reduced the damage-induced G2 arrest. Expression of nuclear cyclin B1 and Cdc2AF also resulted in significant defects in the exit from mitosis. Thus, nuclear targeting of cyclin B1 and dephosphorylation of Cdc2 both contribute to the control of mitotic entry and exit in human cells.
Regulation of Organelle Movement in Melanophores by Protein Kinase A (PKA), Protein Kinase C (PKC), and Protein Phosphatase 2A (PP2A)
Authors: Reilein Amy R. , Tint Irina S. , Peunova Natalia I. , Enikolopov Grigori N. , Gelfand Vladimir I.
Published: July 2002

We used melanophores, cells specialized for regulated organelle transport, to study signaling pathways involved in the regulation of transport. We transfected immortalized Xenopus melanophores with plasmids encoding epitope-tagged inhibitors of protein phosphatases and protein kinases or control plasmids encoding inactive analogues of these inhibitors. Expression of a recombinant inhibitor of protein kinase A (PKA) results in spontaneous pigment aggregation. α-Melanocyte-stimulating hormone (MSH), a stimulus which increases intracellular cAMP, cannot disperse pigment in these cells. However, melanosomes in these cells can be partially dispersed by PMA, an activator of protein kinase C (PKC). When a recombinant inhibitor of PKC is expressed in melanophores, PMA-induced pigment dispersion is inhibited, but not dispersion induced by MSH. We conclude that PKA and PKC activate two different pathways for melanosome dispersion. When melanophores express the small t antigen of SV-40 virus, a specific inhibitor of protein phosphatase 2A (PP2A), aggregation is completely prevented. Conversely, overexpression of PP2A inhibits pigment dispersion by MSH. Inhibitors of protein phosphatase 1 and protein phosphatase 2B (PP2B) do not affect pigment movement. Therefore, melanosome aggregation is mediated by PP2A.
AnkyrinG Is Required for Clustering of Voltage-gated Na Channels at Axon Initial Segments and for Normal Action Potential Firing
Authors: Zhou Daixing , Lambert Stephen , Malen Peter L. , Carpenter Scott , Boland Linda M. , Bennett Vann
Published: July 2002

Voltage-gated sodium channels (NaCh) are colocalized with isoforms of the membrane-skeletal protein ankyrinG at axon initial segments, nodes of Ranvier, and postsynaptic folds of the mammalian neuromuscular junction. The role of ankyrinG in directing NaCh localization to axon initial segments was evaluated by region-specific knockout of ankyrinG in the mouse cerebellum. Mutant mice exhibited a progressive ataxia beginning around postnatal day P16 and subsequent loss of Purkinje neurons. In mutant mouse cerebella, NaCh were absent from axon initial segments of granule cell neurons, and Purkinje cells showed deficiencies in their ability to initiate action potentials and support rapid, repetitive firing. Neurofascin, a member of the L1CAM family of ankyrin-binding cell adhesion molecules, also exhibited impaired localization to initial segments of Purkinje cell neurons. These results demonstrate that ankyrinG is essential for clustering NaCh and neurofascin at axon initial segments and is required for physiological levels of sodium channel activity.
Heterotrimeric Kinesin II Is the Microtubule Motor Protein Responsible for Pigment Dispersion in Xenopus Melanophores
Authors: Tuma M. Carolina , Zill Andrew , Le Bot Nathalie , Vernos Isabelle , Gelfand Vladimir
Published: July 2002

Melanophores move pigment organelles (melanosomes) from the cell center to the periphery and vice-versa. These bidirectional movements require cytoplasmic microtubules and microfilaments and depend on the function of microtubule motors and a myosin. Earlier we found that melanosomes purified from Xenopus melanophores contain the plus end microtubule motor kinesin II, indicating that it may be involved in dispersion (Rogers, S.L., I.S. Tint, P.C. Fanapour, and V.I. Gelfand. 1997. Proc. Natl. Acad. Sci. USA. 94: 3720–3725). Here, we generated a dominant-negative construct encoding green fluorescent protein fused to the stalk-tail region of Xenopus kinesin-like protein 3 (Xklp3), the 95-kD motor subunit of Xenopus kinesin II, and introduced it into melanophores. Overexpression of the fusion protein inhibited pigment dispersion but had no effect on aggregation. To control for the specificity of this effect, we studied the kinesin-dependent movement of lysosomes. Neither dispersion of lysosomes in acidic conditions nor their clustering under alkaline conditions was affected by the mutant Xklp3. Furthermore, microinjection of melanophores with SUK4, a function-blocking kinesin antibody, inhibited dispersion of lysosomes but had no effect on melanosome transport. We conclude that melanosome dispersion is powered by kinesin II and not by conventional kinesin. This paper demonstrates that kinesin II moves membrane-bound organelles.
Membrane Expansion Increases Endocytosis Rate during Mitosis
Authors: Raucher Drazen , Sheetz Michael P.
Published: July 2002

Mitosis in mammalian cells is accompanied by a dramatic inhibition of endocytosis. We have found that the addition of amphyphilic compounds to metaphase cells increases the endocytosis rate even to interphase levels. Detergents and solvents all increased endocytosis rate, and the extent of increase was in direct proportion to the concentration added. Although the compounds could produce a variety of different effects, we have found a strong correlation with a physical alteration in the membrane tension as measured by the laser tweezers. Plasma membrane tethers formed by latex beads pull back on the beads with a force that was related to the in-plane bilayer tension and membrane– cytoskeletal adhesion. We found that as cells enter mitosis, the membrane tension rises as the endocytosis rate decreases; and as cells exited mitosis, the endocytosis rate increased as the membrane tension decreased. The addition of amphyphilic compounds decreased membrane tension and increased the endocytosis rate. With the detergent, deoxycholate, the endocytosis rate was restored to interphase levels when the membrane tension was restored to interphase levels. Although biochemical factors are clearly involved in the alterations in mitosis, we suggest that endocytosis is blocked primarily by the increase in apparent plasma membrane tension. Higher tensions inhibit both the binding of the endocytic complex to the membrane and mechanical deformation of the membrane during invagination. We suggest that membrane tension is an important regulator of the endocytosis rate and alteration of tension is sufficient to modify endocytosis rates during mitosis. Further, we postulate that the rise in membrane tension causes cell rounding and the inhibition of motility, characteristic of mitosis.