Showing papers by "Université de Sherbrooke published in 2001"

An emerging ground-based aerosol climatology: Aerosol optical depth from AERONET

Abstract: Long-term measurements by the AERONET program of spectral aerosol optical depth, precipitable water, and derived Angstrom exponent were analyzed and compiled into an aerosol optical properties climatology. Quality assured monthly means are presented and described for 9 primary sites and 21 additional multiyear sites with distinct aerosol regimes representing tropical biomass burning, boreal forests, midlatitude humid climates, midlatitude dry climates, oceanic sites, desert sites, and background sites. Seasonal trends for each of these nine sites are discussed and climatic averages presented.

A standardized protocol for the determination of specific leaf area and leaf dry matter content

Abstract: Summary 1 The impact of sample preparation, rehydration procedure and time of collection on the determination of specific leaf area (SLA, the ratio of leaf area to leaf dry mass) and leaf dry matter content (LDMC, the ratio of leaf dry mass to fresh mass) of mature leaves was studied in three wild species growing in the field, chosen for their contrasting SLA and LDMC. 2 Complete rehydration was achieved 6 h after samples were placed into water, but neither of the procedures tested – preparation of samples before rehydration or temperature applied during rehydration – had a significant effect on the final values of SLA or LDMC. 3 As expected, water-saturated leaves had a lower LDMC than non-rehydrated leaves; more surprisingly, their SLA was also higher. The impact of rehydration on SLA was especially important when the SLA of the species was high. 4 There was no significant effect of time of sampling on either trait in any species over the time period covered (09·00–16·30 h). 5 These results suggest that SLA and LDMC obtained on water-saturated leaves (SLASAT and LDMCSAT) can be used for species comparisons. We propose a standardized protocol for the measurement of these traits. This would allow for better consistency in data collection, a prerequisite for the constitution of large databases of functional traits.

Current status of phthalocyanines in the photodynamic therapy of cancer

Abstract: Photodynamic therapy is a binary treatment now accepted in clinic for various malignancies in several countries around the world. Phthalocyanine molecules are second-generation photosensitizers with enhanced photophysical and photochemical properties over those of porphyrins. They have been shown to be phototoxic against a number of cell types and tumor models. A great deal of research has been devoted to the elucidation of their mechanism of action and mode of cell death. The present paper reviews phthalocyanine pre-clinical anti-cancer research with emphasis on phthalocyanine induced apoptosis using a silicon phthalocyanine, Pc4. A brief summary of the latest clinical results using phthalocyanines is presented.

Energetic and fitness costs of mismatching resource supply and demand in seasonally breeding birds.

Abstract: By advancing spring leaf flush and ensuing food availability, climatic warming results in a mismatch between the timing of peak food supply and nestling demand, shifting the optimal time for reproduction in birds. Two populations of blue tits (Parus caeruleus) that breed at different dates in similar, but spatially distinct, habitat types in Corsica and southern France provide a unique opportunity to quantify the energetic and fitness consequences when breeding is mismatched with local productivity. As food supply and demand become progressively mismatched, the increased cost of rearing young pushes the metabolic effort of adults beyond their apparent sustainable limit, drastically reducing the persistence of adults in the breeding population. We provide evidence that the economics of parental foraging and limits to sustainable metabolic effort are key selective forces underlying synchronized seasonal breeding and long-term shifts in breeding date in response to climatic change.

H2A.Z Is Required for Global Chromatin Integrity and for Recruitment of RNA Polymerase II under Specific Conditions

Abstract: Evolutionarily conserved variant histone H2A.Z has been recently shown to regulate gene transcription in Saccharomyces cerevisiae. Here we show that loss of H2A.Z in this organism negatively affects the induction of GAL genes. Importantly, fusion of the H2A.Z C-terminal region to S phase H2A without its corresponding C-terminal region can mediate the variant histone's specialized function in GAL1-10 gene induction, and it restores the slow-growth phenotype of cells with a deletion of HTZ1. Furthermore, we show that the C-terminal region of H2A.Z can interact with some components of the transcriptional apparatus. In cells lacking H2A.Z, recruitment of RNA polymerase II and TATA-binding protein to the GAL1-10 promoters is significantly diminished under inducing conditions. Unexpectedly, we also find that H2A.Z is required to globally maintain chromatin integrity under GAL gene-inducing conditions. We hypothesize that H2A.Z can positively regulate gene transcription, at least in part, by modulating interactions with RNA polymerase II-associated factors at certain genes under specific cell growth conditions.

Birthdate, mass and survival in mountain goat kids: effects of maternal characteristics and forage quality

Abstract: In temperate environments, early-born ungulates may enjoy a longer growth period before winter, and so attain a higher body mass and an increased probability of survival compared to late-born ones. We assessed the effects of maternal characteristics, forage quality and population density on kid birthdate, mass and survival in a population of marked mountain goats (Oreamnos americanus) in Alberta. The duration and timing of the birth season were similar in all years. Births were highly synchronised: 80% of kids were born within 2 weeks of the first birth. Maternal age, maternal social rank and density did not affect kid birthdate or mass. Previous breeding experience was not related to kid birthdate, but kids born to pluriparous mothers were heavier during summer than kids born to primiparous mothers. Male and female kids had similar mass and accumulated mass linearly during summer. Early-born kids were heavier than late-born kids. Faecal crude protein (FCP) in late spring and maternal mass were positively related to kid mass. Survival to weaning appeared higher for males (90%) than for females (78%), but survival to 1 year was 65% for both sexes. FCP in late spring, density, birthdate and mass did not affect kid survival to weaning in either sex. Survival to 1 year increased with FCP in late spring for females, but not for males. Survival to 1 year was independent of birthdate for both sexes, but heavy females survived better than light ones. Multiple logistic regression revealed a positive effect of mass on survival to 1 year when the sexes were pooled. Our results suggest that mountain goats are constrained to give birth in a short birth season synchronised with forage productivity.

Impact of Motor, Cognitive, and Perceptual Disorders on Ability to Perform Activities of Daily Living After Stroke

Abstract: Background and Purpose— Using confirmatory factor analysis, this study evaluates the relative impact of motor, cognitive, and perceptual deficits on functional autonomy with 100 elderly (aged 55 to 79 years) victims of stroke. Methods— Two different approaches were used for measuring functional autonomy: the Functional Autonomy Measurement System (Systeme de Mesure de l’Autonomie Fonctionnelle [SMAF]) and the Assessment of Motor and Process Skills (AMPS). Results— The results of the confirmatory factor analysis show that motor, cognitive, and perceptual factors all make a significant contribution to the variation in functional autonomy and confirm the accuracy of the model (93% of the variance is explained when the SMAF is used to measure functional autonomy, and 64% of the variance is explained when the AMPS is used). Conclusions— The factors that make the greatest contribution in explaining the variance in functional autonomy are, in order of importance, the motor factor, the perceptual factor, and the...

Multiscale MAP filtering of SAR images

Abstract: Synthetic aperture radar (SAR) images are disturbed by a multiplicative noise depending on the signal (the ground reflectivity) due to the radar wave coherence. Images have a strong variability from one pixel to another reducing essentially the efficiency of the algorithms of detection and classification. We propose to filter this noise with a multiresolution analysis of the image. The wavelet coefficient of the reflectivity is estimated with a Bayesian model, maximizing the a posteriori probability density function. The different probability density function are modeled with the Pearson system of distributions. The resulting filter combines the classical adaptive approach with wavelet decomposition where the local variance of high-frequency images is used in order to segment and filter wavelet coefficients.

Evidence that Furin Is an Authentic Transforming Growth Factor-β1-Converting Enzyme

Abstract: Transforming growth factor (TGF)-β1 plays an essential role in cell growth and differentiation. It is also considered as a gatekeeper of immune homeostasis with gene disruption leading to autoimmune and inflammatory diseases. TGF-β1 is produced as an inactive precursor polypeptide that can be efficiently secreted but correct proteolytic cleavage is an essential step for its activation. Assessment of the cleavage site has revealed a unique R-H-R-R sequence reminiscent of proprotein convertase (PC) recognition motifs and has previously demonstrated that this PC-like cleavage site is correctly cleaved by furin, a member of the PC family. Here we report that among PC members, furin more closely satisfies the requirements needed to fulfill the role of a genuine TGF-β1 convertase. Even though six members of the PC family have the ability to cleave TGF-β1, ectopic expression of α1-antitrypsin Portland (α1-AT-PDX), a potent furin inhibitor, blocked 80% of TGF-β1 processing mediated by endogenous enzymes as demonstrated in an in vitro digestion assay. Genetic complementation of a furin-deficient LoVo cell line with the wild-type gene restores the production of mature and bioactivable TGF-β1. Moreover, both furin and TGF-β are coordinately expressed and regulated in vitro and in vivo in the hematopoietic and immune system, an important tissue target. These results demonstrate for the first time that furin is an authentic and adaptive TGF-β1-converting enzyme whereas other members of the PC family might substitute or supplement furin activity. Our study advances our comprehension of the complexity of the TGF-β system and should facilitate the development of therapeutically useful TGF-β inhibitors.

Double-blind, randomized trial of an anti-CD18 antibody in conjunction with recombinant tissue plasminogen activator for acute myocardial infarction: limitation of myocardial infarction following thrombolysis in acute myocardial infarction (LIMIT AMI) study.

Abstract: Background Inhibition of leukocyte adhesion can reduce myocardial infarct size in animals. This study was designed to define the safety and efficacy of a recombinant, humanized, monoclonal antibody to the CD18 subunit of the β2 integrin adhesion receptors (rhuMAb CD18), in reducing infarct size in patients treated with a thrombolytic agent. Methods and Results The Limitation of Myocardial Infarction following Thrombolysis in Acute Myocardial Infarction Study (LIMIT AMI) was a randomized, double-blind, placebo-controlled, multicenter study conducted in 60 centers in the United States and Canada. A total of 394 subjects who presented within 12 hours of symptom onset with ECG findings (ST-segment elevation) consistent with AMI were treated with recombinant tissue plasminogen activator and were also given an intravenous bolus of 0.5 or 2.0 mg/kg rhuMAb CD18 or placebo. Coronary angiography was performed at 90 minutes, 12-lead ECGs were obtained at baseline, 90, and 180 minutes, and resting sestamibi scans were performed at ≥120 hours. Adjunctive angioplasty and use of glycoprotein IIb/IIIa antiplatelet agents at the time of angiography were discretionary. There were no treatment effects on coronary blood flow, infarct size, or the rate of ECG ST-segment elevation resolution, despite the expected induction of peripheral leukocytosis. A slight trend toward an increase in bacterial infections was observed with rhuMAb CD18 ( P =0.33). Conclusions RhuMAb CD18 was well tolerated but not effective in modifying cardiac end points. Received February 28, 2001; revision received September 25, 2001; accepted September 28, 2001.

"Actinomycetes, promising tools to control plant diseases and to promote plant growth"

Abstract: Les actinomycetes representent une grande proportion de la biomasse microbienne du sol et ont la capacite de produire une large variete d’antibiotiques et d’enzymes extracellulaires. Plusieurs souches d’actinomycetes s’averent capables de proteger les plantes contre des maladies. Cette revue se penche sur le potentiel des actinomycetes comme (a) source de composes agronomiques, (b) agents stimulant la croissance des plantes et (c) agents de lutte biologique. La revue donne aussi des exemples de lutte biologique contre les agents phytopathogenes bacteriens et fongiques par l’utilisation d’especes d’actinomycetes deja disponibles sur le marche ou qui le seront probablement au cours des prochaines annees.

Inherent inhomogeneities in tunneling spectra of Bi 2 Sr 2 CaCu 2 O 8 − x crystals in the superconducting state

Abstract: Scanning tunneling spectroscopy on cleaved BSCCO(2212) single crystals reveals inhomogeneities on length scales of $\ensuremath{\sim}30 \AA{}.$ While most of the surface yields spectra consistent with a d-wave superconductor, small regions show a doubly gapped structure with both gaps lacking coherence peaks and the larger gap having a size typical of the respective pseudogap for the same sample.

Neutrophil-mediated epithelial injury during transmigration: role of elastase

Abstract: Neutrophil-mediated injury to gut epithelium may lead to disruption of the epithelial barrier function with consequent organ dysfunction, but the mechanisms of this are incompletely characterized. Because the epithelial apical junctional complex, comprised of tight and adherens junctions, is responsible in part for this barrier function, we investigated the effects of neutrophil transmigration on these structures. Using a colonic epithelial cell line, we observed that neutrophils migrating across cell monolayers formed clusters that were associated with focal epithelial cell loss and the creation of circular defects within the monolayer. The loss of epithelial cells was partly attributable to neutrophil-derived proteases, likely elastase, because it was prevented by elastase inhibitors. Spatially delimited disruption of epithelial junctional complexes with focal loss of E-cadherin, beta-catenin, and zonula occludens 1 was observed adjacent to clusters of transmigrating neutrophils. During neutrophil transmigration, fragments of E-cadherin were released into the apical supernatant, and inhibitors of neutrophil elastase prevented this proteolytic degradation. Addition of purified leukocyte elastase also resulted in release of E-cadherin fragments, but only after opening of tight junctions. Taken together, these data demonstrate that neutrophil-derived proteases can mediate spatially delimited disruption of epithelial apical junctions during transmigration. These processes may contribute to epithelial loss and disruption of epithelial barrier function in inflammatory diseases.

IL-13 and IL-4 up-regulate cysteinyl leukotriene 1 receptor expression in human monocytes and macrophages.

Abstract: The cysteinyl (Cys) leukotrienes (LT)C(4), LTD(4), and LTE(4), are lipid mediators that have been implicated in the pathogenesis of asthma. The human LTD(4) receptor (CysLT(1)R) was recently cloned and characterized. The present work was undertaken to study the potential modulation of CysLT(1)R expression by the Th2 cytokines IL-13 and IL-4. In this study, we report that IL-13 up-regulates CysLT(1)R mRNA levels, with consequently enhanced CysLT(1)R protein expression and function in human monocytes and monocyte-derived macrophages. CysLT(1)R mRNA expression was augmented 2- to 5-fold following treatment with IL-13 and was due to enhanced transcriptional activity. The effect was observed after 4 h, was maximal by 8 h, and maintained at 24 h. IL-4, but not IFN-gamma, induced a similar pattern of CysLT(1)R up-regulation. Monocytes pretreated with IL-13 or IL-4 for 24 h showed enhanced CysLT(1)R protein expression, as assessed by flow cytometry using a polyclonal anti-CysLT(1)R Ab. They also showed enhanced responsiveness to LTD(4), but not to LTB(4), in terms of Ca(2+) mobilization, as well as augmented chemotactic activity. Our findings suggest a possible mechanism by which IL-13 and IL-4 can modulate CysLT(1)R expression on monocytes and macrophages, and consequently their responsiveness to LTD(4), and thus contribute to the pathogenesis of asthma and allergic diseases.

The epidemiology and control of human African trypanosomiasis.

Abstract: Human African trypanosomiasis is caused by Trypanosoma brucei gambiense in West and Central Africa, and by Trypanosoma brucei rhodesiense in East and southern Africa. In recent years there has been a dramatic resurgence of Gambian trypanosomiasis in Central Africa, especially in the Democratic Republic of Congo, Angola and Sudan. The disease is quiescent in most of West Africa, as is Rhodesian trypanosomiasis the other side of the continent. The epidemiology of Gambian trypanosomiasis is reviewed in detail. The long duration of infection in human hosts with cycles of intermittent parasitaemia, the vectors' feeding habits and the intensity of human-fly contact are the major determinants of the dynamics of transmission of this parasite. The development of immunity may lead to a reduction in the fraction of the population that is susceptible to infection and the burning out of epidemics after 20 to 30 years. So far, the acquired immune deficiency syndrome pandemic has had no impact on the epidemiology of Gambian trypanosomiasis. A brief review of the epidemiology of Rhodesian trypanosomiasis highlights the differences from Gambian trypanosomiasis that, to some extent, explain its lower propensity to cause epidemics: it is a more aggressive disease that rapidly kills its human host, and its transmission involves mostly domestic and game animals, humans being in most circumstances an accidental host. The various methods and strategies for the surveillance and control of both diseases are reviewed.

Association between personal and environmental factors and the occurrence of handicap situations following a stroke.

Abstract: Background and purpose : Little is known about the potential role of environmental factors in the handicap creation process following a stroke. The objective of this study was to explore the presence of a relationship between environmental factors and the occurrence of handicap following a stroke, taking into consideration age and the level of impairments and disabilities. Methods : This is a cross-sectional study where data were collected 6 months after discharge from an intensive functional rehabilitation unit. A convenience sample of 51 participants was recruited at the time of their admission to the rehabilitation unit for rehabilitation post-stroke. Perceived influence of environmental factors was measured using the Measure of the Quality of the Environment (MQE). Handicap situations were measured with the Assessment of Life Habits (LIFE-H). Impairments and disabilities comprised six domains (cognition, perception, depression, communication, sensorimotor function and comorbidity) assessed using a var...

Breakdown of Fermi-liquid theory in a copper-oxide superconductor

Abstract: The behaviour of electrons in solids is well described by Landau's Fermi-liquid theory, which predicts that although electrons in a metal interact, they can still be treated as well defined fermions, which are called 'quasiparticles'. At low temperatures, the ability of quasiparticles to transport heat is given strictly by their ability to transport charge, as described by a universal relation known as the Wiedemann-Franz law, which hitherto no material has been known to violate. High-temperature superconductors have long been thought to fall outside the realm of Fermi-liquid theory, as suggested by several anomalous properties, but this has yet to be shown conclusively. Here we report an experimental test of the Wiedemann-Franz law in the normal state of a copper-oxide superconductor, (Pr,Ce)2CuO4, which reveals that the elementary excitations that carry heat in this material are not fermions. This is compelling evidence for the breakdown of Fermi-liquid theory in high-temperature superconductors.

Measurement of clinical reflective capacity early in training as a predictor of clinical reasoning performance at the end of residency: an experimental study on the script concordance test.

Abstract: Background The script concordance (SC) test was conceived to measure knowledge organization, the presence of links between items of knowledge which allow for interpretation of data in clinical decision making situations. Earlier studies have shown that the SC test has good psychometric qualities and overcomes some of the limitations of simulation clinical testing. This study explores the predictive validity of the test. Objectives To verify whether scores obtained by students at the end of clerkship predict their clinical reasoning performance at the end of residency. Design Comparison of scores obtained on a SC test taken at the end of clerkship with those obtained 2 years later at the end of residency on two clinical reasoning assessments of known validity, called the short-answer management problems (SAMPs) and the simulated office orals (SOOs), and an objective structured clinical examination (OSCE) aimed at assessing hands-on skills and clinical reasoning. Data were treated by Pearson correlation analysis. Subjects and setting A cohort of 24 students from a medical school in Quebec was followed up to the end of their residency in family medicine, completed in several schools across Quebec. Results The observed Pearson correlation coefficients of the SC test were statistically significant (0AE451, Pa 0AE013; 0AE447; Pa 0AE015) when compared with the SAMPs and the SOOs, respectively. They were not statistically significant (0AE340, Pa 0AE052) when compared with the OSCE. Conclusion The authors assumed that the richness of knowledge organization, as indicated by SC test scores, would predict part of the performance on the measures of clinical reasoning (SAMP and SOO), but would predict less well performance on the OSCE which measures both clinical skills and clinical reasoning. Data found in the study are coherent with this hypothesis. This is evidence in favour of the construct validity of the SC test. It also indicates that, in the context of certification assessment, if a candidate has shown good organization of clinical knowledge at an early point in training, it can be expected that he/she will show good organization at subsequent measurements of this kind of knowledge. This appears to be true even if the later measures bear on a wider clinical domain.