bluuebunny/crossref_metadata_2025_split huggingface dataset:
Extracellular phosphatases in a Mediterranean reservoir: seasonal, spatial and kinetic heterogeneity
Authors: NEDOMA J. , GARCÍA J. C. , COMERMA M. , ŠIMEK K. , ARMENGOL J. 
Published: June 2006

Summary1. Epilimnetic alkaline phosphatase activity (APA) was measured in longitudinal profiles of the canyon‐shaped, eutrophic Sau Reservoir (Catalonia, Spain) during the autumn, winter and spring periods of 1997–2000.2. The spatial pattern of APA depended on lake circulation. During periods of stable stratification, when the ratio of mixed to euphotic depth (zmix/zeu < 1.7) was low and the Chlorophyll a (Chl a) concentration high, APA was also comparatively high (0.5–3.4 μmol L−1 h−1) and located mostly in the >2‐μm size‐fraction. APA increased towards the dam at the same time as the concentration of soluble reactive phosphorus (SRP) decreased. In periods of unstable stratification, deep mixing (zmix/zeu > 2.4) and low Chl a concentration, APA was low (<0.1 μmol L−1 h−1) and without longitudinal changes, consistent with a high and stable SRP concentration.3. A high input of mostly dissolved (in the <0.2‐μm size‐fraction) phosphatases from the river Ter was found in 1997–98. At the river inflow, independently of season and despite a continuously high SRP concentration, APA was approximately 0.7 μmol L−1 h−1 and decreased towards the dam within the inflowing, canyon‐like part of the reservoir.4. Analysis of saturation kinetics revealed the kinetic heterogeneity of APA. Low‐affinity APA was localised in the >2‐μm (algal) size‐fraction while, in the <2‐μm (picoplankton, mainly bacteria + dissolved) size‐fraction, high‐affinity APA, or a mixture of both, was found. The presence of two kinetic components, whose substrate affinities (i.e. in Michaelis constants, Km) differed, was confirmed statistically in 13 of 18 cases analysed. The range of KmH values of the high‐affinity component was 0.15–2.4 μmol L−1, KmL values of the low‐affinity component ranged from 18 to 275 μmol L−1.
Forest ecosystems of an ArizonaPinus ponderosalandscape: multifactor classification and implications for ecological restoration
Authors: Abella Scott R. , Covington W. Wallace 
Published: June 2006

AbstractAim We developed an ecosystem classification within a 110,000‐ha ArizonaPinus ponderosaP. & C. Lawson (ponderosa pine) landscape to support ecological restoration of these forests. Specific objectives included identifying key environmental variables constraining ecosystem distribution and comparing plant species composition, richness and tree growth among ecosystems.Location The Coconino National Forest and the Northern Arizona University Centennial Forest, in northern Arizona, USA.Methods We sampled geomorphology, soils and vegetation on 66 0.05‐ha plots in open stands containing trees of pre‐settlement (c. 1875) origin, and on 26 plots in dense post‐settlement stands. Using cluster analysis and ordination of vegetation and environment matrices, we classified plots into ecosystem types internally similar in environmental and vegetational characteristics.Results We identified 10 ecosystem types, ranging from dry, black cinders/Phaceliaecosystems to moist aspen/Lathyrusecosystems. Texture, organic carbon and other soil properties reflecting the effects of parent materials structured ecosystem distribution across the landscape, and geomorphology was locally important. Plant species composition was ecosystem‐specific, with C3Festuca arizonicaVasey (Arizona fescue), for instance, abundant in mesic basalt/Festucaecosystems. MeanP. ponderosadiameter increments ranged from 2.3–4.3 mm year−1across ecosystems in stands of pre‐settlement origin, and the ecosystem classification was robust in dense post‐settlement stands.Main conclusions Several lines of evidence suggest that although species composition may have been altered since settlement, the same basic ecosystems occurred on this landscape in pre‐settlement forests, providing reference information for ecological restoration. Red cinders/Bahiaecosystems were rare historically and > 30% of their area has been burned by crown fires since 1950, indicating that priority could be given to restoring this ecosystem's remaining mapping units. Ecosystem classifications may be useful as data layers in gap analyses to identify restoration and conservation priorities. Ecosystem turnover occurs at broad extents on this landscape, and restoration must accordingly operate across large areas to encompass ecosystem diversity. By incorporating factors driving ecosystem composition, this ecosystem classification represents a framework for estimating spatial variation in ecological properties, such as species diversity, relevant to ecological restoration.
Long‐term effects of forest fragmentation on Amazonian ant communities
Authors: Vasconcelos Heraldo L. , Vilhena José M. S. , Magnusson William E. , Albernaz Ana L. K. M 
Published: June 2006

AbstractAim  To analyse the effects of forest fragmentation on ant communities in an Amazonian landscape that has been fragmented for over a century.Location  The region surrounding the village of Alter do Chão in the Brazilian Amazonian state of Pará (2°30′ S, 54°57′ W).Methods  Collection of ants and measurements of tree density were performed along transects established in eight sites in continuous forest and in 24 forest fragments surrounded by savanna vegetation. Data on size, perimeter, and degree of isolation (distance to continuous forest and distance to nearest area of forest > 5 ha) of each fragment were obtained from a georeferenced Landsat image of the study area.Results  There were significant differences in species richness and composition between fragments and continuous forest, and these differences were not related to intersite variation in vegetation structure (tree density). Fragments supported fewer ant species per plot, and these species tended to represent a nested subset of those found in continuous forests. Fragments had significantly fewer rare species and fewer ant genera. However, fragments and continuous forest had similar numbers of species that also occur in the savanna matrix (i.e. that are not forest specialists). Multiple linear regression analyses indicated that species richness and composition in the fragments are significantly affected by fragment area, but not by fragment shape and degree of isolation. More species were found in larger fragments.Main conclusions  Forest fragmentation influences the organization of ant communities in Amazonian savanna/forest landscapes. Forest fragments harboured, on average, 85% of the species found in continuous forest. That these fragments, despite their long history of isolation, support a relatively large complement of the species found in continuous forest is surprising, especially given that in some recently fragmented landscapes the proportion of species surviving in the fragments is lower. Differences in inter‐fragment distance and type of matrix between Alter do Chão and these other landscapes may be involved. The fact that fragments at Alter do Chão are surrounded by a natural (rather than an anthropogenic) habitat, and that most of them are less than 300 m from another forest area, may have helped to ameliorate the adverse effects of forest fragmentation.
Historical biogeography of South American freshwater fishes
Authors: Hubert Nicolas , Renno Jean‐François 
Published: June 2006

AbstractAim To investigate biogeographical patterns of the obligate freshwater fish order Characiformes.Location South America.Methods Parsimony analysis of endemicity, likelihood analysis of congruent geographical distribution, and partition Bremer support were used.Results Areas of endemism are deduced from parsimony analysis of endemicity, and putative dispersal routes from a separate analysis of discordant patterns of distribution.Main conclusions Our results demonstrate the occurrence of 11 major areas of endemism and support a preferential eastern–western differentiation of the characiforms in the Amazonian region, contrasting with the southern–northern differentiation of terrestrial organisms. The areas of endemism identified seem to be deeply influenced by the distribution of the emerged land during the 100‐m marine highstand that occurred during the late Miocene and allow us to hypothesize the existence of eight aquatic freshwater refuges at that time. The raw distribution of non‐endemic species supports nine patterns of species distribution across the 11 areas of endemism, two of which support a southern–northern differentiation in the eastern part of the Amazon. This result shows that the main channel of the Amazon limited dispersal between tributaries from each bank of the river. The levels of endemism further demonstrate that the aquatic freshwater refuges promoted allopatric speciation and later allowed the colonization of the lowlands. By contrast, the biogeographical pattern found in the western part of the Amazon is identified as a result of the Miocene Andean foreland dynamic and the uplift of the palaeoarches that promoted allopatric divergence across several sedimentary basins by the establishment of disconnected floodplains. The assessment of conflicting species distributions also shows the presence of seven putative dispersal routes between the Amazon, Orinoco and Paraná rivers. Our findings suggest that, rather than there being a single predominant process, the establishment of the modern South American freshwater fish biotas is the result of an interaction between marine incursions, uplift of the palaeoarches, and historical connections allowing cross‐drainage dispersal.
Does specialty board certification influence clinical outcomes?
Authors: Grosch Eric N. 
Published: June 2006

AbstractBackground  The public seems to crave a simplistic index of ‘quality’, analogous to ‘The Good Housekeeping Seal of Approval’, for the complex endeavour of clinical medicine. The American Board of Medical Specialties (ABMS) and its member boards have purported to fill the vacuum in an effort that bears many of the earmarks of a public relations publicity campaign. The author examined the validity of the evidence touted in support of that effort.Methods  By applying Hill’s causal epidemiologic criteria and logical and statistical inference, the author evaluated: (i) published data sources consisting of the most comprehensive collection of studies yet gathered that purports to provide evidence of the relevance of board certification to clinical outcomes, a collection presented by Sharp et al. apparently with the advice and consent of ABMS, that they posited as containing ‘relevant findings’, to what purpose they left unspecified; and (ii) the review article of Sharp et al.Results  The data that Sharp et al. presented provided no credible link between specialty board certification and outcomes or ‘quality’ of clinical care. Sharp et al. ignored the evidence of absent evidence they found and proposed enthusiastic but unjustified conclusions in support of specialty board certification as an index of clinical ‘expertise’.Conclusions  No evidence supports the touted clinical benefit of specialty board certification. Specialists in clinical medicine and surgery are unamenable to simplistic evaluation by examination, yet specialty board certification remains an ersatz standard of doctors’ clinical quality in the absence of supporting evidence.
Surface anchoring of a bacterial adhesin secreted by the two‐partner secretion pathway
Authors: Buscher Amy Z. , Grass Susan , Heuser John , Roth Robyn , St. Geme Joseph W. 
Published: June 2006

SummaryIn Gram‐negative bacteria, most surface‐associated proteins are present as integral outer‐membrane proteins. Exceptions include the Haemophilus influenzae HMW1 and HMW2 adhesins and a subset of other proteins secreted by the two‐partner secretion system. In the present study we sought to determine the mechanism by which HMW1 is anchored to the bacterial surface. In initial experiments we found that HMW1 forms hair‐like fibres on the bacterial surface and is usually present as pairs that appear to be joined together at one end. Further analysis established that HMW1 is anchored to the multimeric HMW1B outer membrane translocator, resulting in a direct correlation between the level of surface‐associated HMW1 and the quantity of HMW1B in the outer membrane. Mutagenesis and polyethylene glycol maleimide labelling revealed that anchoring of HMW1 requires the C‐terminal 20 amino acids of the protein and is dependent upon disulphide bond formation between two conserved cysteine residues in this region. Immunolabelling studies demonstrated that the immediate C‐terminus of HMW1 is inaccessible to surface labelling, suggesting that it remains in the periplasm or is buried in HMW1B. Coexpression of HMW1 lacking the C‐terminal 20 amino acids and wild‐type HMW1 supported the conclusion that the C‐terminus of HMW1 occupies the HMW1B pore. These observations may have broad relevance to proteins secreted by the two‐partner secretion system, especially given the conservation of C‐terminal cysteine residues among surface‐associated proteins in this family.
A lesson in efficient killing from two‐component lantibiotics
Authors: Breukink Eefjan 
Published: June 2006

SummaryThe combined activity of the constituents of two‐component antibiotic systems is always significantly higher than the sum of the activities of the individual pieces. Understanding the principles behind this phenomenon might provide new ways to design new antibiotics. In this issue of Molecular Microbiology, Wiedemann and coworkers have made a big step towards understanding the mechanism of action of the two‐component lanthionine‐containing antibiotic lacticin 3147. It has now become clear that this two‐component system specifically targets the bacterial cell wall precursor Lipid II. This makes this essential bacterial lipid one of the most sought‐after targets in nature. Surprisingly, in view of its small size (MW 1875 Da), this is now the fifth different way that this key molecule is known to be targeted.
Progressive segregation of the Escherichia coli chromosome
Authors: Nielsen Henrik J. , Li Yongfang , Youngren Brenda , Hansen Flemming G. , Austin Stuart 
Published: June 2006

SummaryWe have followed the fate of 14 different loci around the Escherichia coli chromosome in living cells at slow growth rate using a highly efficient labelling system and automated measurements. Loci are segregated as they are replicated, but with a marked delay. Most markers segregate in a smooth temporal progression from origin to terminus. Thus, the overall pattern is one of continuous segregation during replication and is not consistent with recently published models invoking extensive sister chromosome cohesion followed by simultaneous segregation of the bulk of the chromosome. The terminus, and a region immediately clockwise from the origin, are exceptions to the overall pattern and are subjected to a more extensive delay prior to segregation. The origin region and nearby loci are replicated and segregated from the cell centre, later markers from the various positions where they lie in the nucleoid, and the terminus region from the cell centre. Segregation appears to leave one copy of each locus in place, and rapidly transport the other to the other side of the cell centre.
Alteration of T‐cell Receptor Repertoires During Thymic T‐cell Development
Authors: Matsutani T. , Ohmori T. , Ogata M. , Soga H. , Yoshioka T. , Suzuki R. , Itoh T. 
Published: June 2006

AbstractThe majority of thymocytes die in the thymus, whereas small populations of T cells that are able to specifically recognize an antigen are considered to survive. Although the thymic selection is thought to have a profound effect on T‐cell receptor (TCR) repertoire, little is known how TCR repertoire is formed during the thymocyte developmental process. We examined TCRα‐ and β‐chain variable regions (TCRAV and TCRBV) repertoire in thymic T‐cell subpopulations from mice bearing different major histocompatibility (MHC) haplotypes. In Balb/c mice, but not C57BL/6, remarkable alterations of the TCR repertoire were observed in mature T‐cell subpopulations as previously reported. In contrast, there were no significant differences of TCRBV repertoire between DN3 (CD25+CD44−) and DN4 (CD25−CD44−), and between DN4 and DP. These results suggest that (1) TCR repertoire of mature T cells was formed mainly under the influence of endogenous superantigens, while MHC haplotypes played the least role; (2) the ‘β‐selection’ process during immature stages had little impact on TCRBV repertoire formation; and (3) TCR repertoire in immature T‐cell subpopulations was extremely similar between different strains of mice. We thus consider that pre‐selection TCR repertoire in immature T cells could be determined by some genetic factors conserved among different strains.
Extrusion vs. accretion at the frictional–viscous décollement transition in experimental thrust wedges: the role of convergence velocity
Authors: Luján María , Storti Fabrizio , Rossetti Federico , Crespo‐Blanc Ana 
Published: June 2006

AbstractIn many cases, thrust wedges accreted at shallow crustal levels show an across‐strike rheological variability along the basal décollement, notably from brittle to ductile behaviour. In this paper, we illustrate the results of sandbox analogue modelling research devoted to studying the influence of convergence velocity on wedge architecture when laterally juxtaposed frictional and viscous materials occur along the basal décollement of accreting thrust wedges. Our results show that slow convergence favours a near symmetrical distribution of thrust vergence within wedge sectors accreted above viscous décollement material, whereas fast convergence favours vergence asymmetry. In particular, at fast convergence rates the hinterlandward extrusion of viscous décollement material at the toe of the frictional wedge is favoured and contributed to accommodate a significant amount of the total contraction.Terra Nova, 18, 241–247, 2006
Phloem flow strongly influences the systemic spread of silencing in GFP Nicotiana benthamiana plants
Authors: Tournier Barthélémy , Tabler Martin , Kalantidis Kriton 
Published: June 2006

SummaryThe term ‘RNA silencing’ describes a process that results in the specific degradation of an RNA target. In plants, silenced tissues can initiate the spreading of the process into non‐silenced regions by a mobile signal that can be transmitted over long distances. In the present work, we made use of a modified grafting approach to elucidate the driving force behind long‐distance transport of the silencing signal. We made reciprocal grafts of two GFP‐transgenic Nicotiana benthamiana lines, the non‐silenced line 16c (sensor) and the silenced line 6.4 (inducer). We show that the direction of systemic spread of silencing from inducer to sensor can be manipulated by altering sink/source relations in the plant. Using radioactive phosphate as a phloem tracer, we demonstrated that plants that transmitted silencing from silenced scion to non‐silenced rootstock had developed a persisting phloem flow from scion to rootstock. These data provide experimental proof of what has been hypothesized so far, that the silencing signal travels via phloem from source to sink. We present here evidence that the appearance of systemic silencing is not an accidental stochastic process, but can be predicted on the basis of the direction of phloem flow.
Two cell‐cycle regulated SET‐domain proteins interact with proliferating cell nuclear antigen (PCNA) in Arabidopsis
Authors: Raynaud Cécile , Sozzani Rosangela , Glab Nathalie , Domenichini Séverine , Perennes Claudette , Cella Rino , Kondorosi Eva , Bergounioux Catherine 
Published: June 2006

SummaryThe proliferating cell nuclear antigen (PCNA) functions as a sliding clamp for DNA polymerase, and is thus a key actor in DNA replication. It is also involved in DNA repair, maintenance of heterochromatic regions throughout replication, cell cycle regulation and programmed cell death. Identification of PCNA partners is therefore necessary for understanding these processes. Here we identify two Arabidopsis SET‐domain proteins that interact with PCNA: ATXR5 and ATXR6. A truncated ATXR5Δex2, incapable of interacting with PCNA, also occurs in planta. ATXR6, upregulated during the S phase, is upregulated by AtE2F transcription factors, suggesting that it is required for S‐phase progression. The two proteins differ in their subcellular localization: ATXR5 has a dual localization in plastids and in the nucleus, whereas ATXR6 is solely nuclear. This indicates that the two proteins may play different roles in plant cells. However, overexpression of either ATXR5 or ATXR6 causes male sterility because of the degeneration of defined cell types. Taken together, our results suggest that both proteins may play a role in the cell cycle or DNA replication, and that the activity of ATXR5 may be regulated via its subcellular localization.
Fracture toughness analysis of laser‐beam‐welded superalloys Inconel 718 and 625
Authors: YENI C. , KOÇAK M. 
Published: June 2006

ABSTRACTIn this study, two 3.2‐mm thick Ni‐base superalloys, Inconel 718 and 625, have been laser‐beam‐welded by a 6‐kW CO2 laser and their room temperature fracture toughness properties have been investigated. Fracture toughness behaviour of the base metal (BM), fusion zone (FZ) and heat affected zone (HAZ) regions was determined in terms of crack tip opening displacement (CTOD) using compact tension‐type (C(T)) specimens. Laser‐beam‐weld regions showed no significant strength overmatching in both alloys. Ductile crack growth analysis (R‐curve) also showed that both materials exhibited similar behaviour. Compared to the BM there is a slight decrease in fracture toughness of the fusion and the HAZ.
Mesodermal cell types induce neurogenesis from adult human hippocampal progenitor cells
Authors: Hermann Andreas , Maisel Martina , Liebau Stefan , Gerlach Manfred , Kleger Alexander , Schwarz Johannes , Kim Kwang‐Soo , Antoniadis Gregor , Lerche Holger , Storch Alexander 
Published: June 2006

AbstractNeurogenesis in the adult human brain occurs within two principle neurogenic regions, the hippocampus and the subventricular zone (SVZ) of the lateral ventricles. Recent reports demonstrated the isolation of human neuroprogenitor cells (NPCs) from these regions, but due to limited tissue availability the knowledge of their phenotype and differentiation behavior is restricted. Here we characterize the phenotype and differentiation capacity of human adult hippocampal NPCs (hNPCs), derived from patients who underwent epilepsy surgery, on various feeder cells including fetal mixed cortical cultures, mouse embryonic fibroblasts (MEFs) and PA6 stromal cells. Isolated hNPCs were cultured in clonal density by transferring the cells to serum‐free media supplemented with FGF‐2 and EGF in 3% atmospheric oxygen. These hNPCs showed neurosphere formation, expressed high levels of early neuroectodermal markers, such as the proneural genes NeuroD1 and Olig2, the NSC markers Nestin and Musashi1, the proliferation marker Ki67 and significant activity of telomerase. The phenotype was CD15low/–, CD34–, CD45– and CD133–. After removal of mitogens and plating them on poly d‐lysine, they spontaneously differentiated into a neuronal (MAP2ab+), astroglial (GFAP+), and oligodendroglial (GalC+) phenotype. Differentiated hNPCs showed functional properties of neurons, such as sodium channels, action potentials and production of the neurotransmitters glutamate and GABA. Co‐culture of hNPCs with fetal cortical cultures, MEFs and PA6 cells increased neurogenesis of hNPCs in vitro, while only MEFs and PA6 cells also led to a morphological and functional neurogenic maturation. Together we provide a first detailed characterization of the phenotype and differentiation potential of human adult hNPCs in vitro. Our findings reinforce the emerging view that the differentiation capacity of adult hNPCs is critically influenced by non‐neuronal mesodermal feeder cells.