Effects of web-based support for the construction of competence maps.

Stoof, A., Martens, R.L., & Van Merriënboer, J.J.G. (2006). Effects of web-based support for the construction of competence maps. Instructional Science, 34, 189-211Educationalists experience difficulties with the construction of competence maps that describe final attainment levels of educational programs. Web-based support was developed with three supportive aids: A construction kit, a phenomenarium, and an information bank. Each supportive aid was expected to improve perceived process and product quality as well as learning. In a factorial experiment, 266 educational science students constructed a competence map, whether or not supported by each of the three supportive aids. The availability of the construction kit and the phenomenarium had positive effects on perceived process quality and learning. Furthermore, if there was no phenomenarium with example materials, the absence of the construction kit greatly diminished experienced support (i.e., one aspect of process quality); if a phenomenarium was present, the availability of the construction kit had relatively little effect on perceived support. In general, this study indicates that well-designed Web-based support helps to construct competence maps

Nickel Homeostasis in Helicobacter Species

Gastric Helicobacter species are adapted to colonize the acidic environment of the stomach. Colonization with H pylori is life long if untreated, and can lead to gastritis, peptic ulcer disease and eventually to gastric cancer. Although H pylori is sensitive to many antibiotics in vitro, only a limited number of antibiotics can be used in vivo while increasing resistance against these therapeutics significantly impairs the treatment of H pylori infection. Metals play an essential role in the metabolism of all living organisms, including gastric Helicobacter species, but can also be deleterious when metal availability is either too low or too high. Therefore cells need to maintain homeostasis of intracellular metal concentrations to allow survival and growth. A better understanding of metal homeostasis in gastric Helicobacter species may allow for the knowledge-led development of therapeutics which are based on disturbing the balance of the intracellular metal concentrations to either toxicity or restriction. The focus of this PhD-thesis is on nickel metabolism, since this metal is the cofactor of the urease enzyme and hydrogenase enzyme, both essential for colonization of gastric Helicobacter species. The high expression level of the urease enzyme mediates acid resistance in the presence of urea, but also necessitates the import of relatively high concentrations of nickel. Although transcriptional regulation by the nickel-dependent regulator NikR has been studied, relative little is known about which proteins are involved in actual transport of nickel. The genome era has opened the possibility of functional genomics investigations, using the information from the genomes of different Helicobacter species. Many of the genes of Helicobacter species do not yet have a predicted function, or have been assigned a putative function only based on homology with genes from other bacterial species. Comparison of the genomic content of different Helicobacter species and transcriptional and functional characterization of the genes putatively involved in nickel homeostasis, as presented in this thesis, will provide more insight in how these bacteria are able to acquire sufficient concentrations of nickel

Web-based support for constructing competence maps: design and formative evaluation

Stoof, A., Martens, R. L., & Van Merriënboer, J. J. G. (2007). Web-based support for constructing competence maps: Design and formative evaluation. Educational Technology, Research and Development, 55(4), 347-368.This article describes the design and formative evaluation of a Web-based tool that supports curriculum developers in constructing competence maps. Competence maps describe final attainment levels of educational programs in terms of - interrelated - competencies. Key requirements for the supportive tool were validity and practicality. Validity refers to internal consistency and meaningful links to the external realities represented. Practicality refers to a design approach of evolutionary prototyping, in which feedback from intended users and domain experts was collected throughout the development process. Formative evaluations of four prototypes were conducted. Measures of design, appeal, goal, content, confidence and relevance showed that the tool is practical. The article describes the formative evaluation process and concludes with a description of the final tool from the perspective of the user and the instructional designer

Cooling curves for neutron stars with hadronic matter and quark matter

The thermal evolution of isothermal neutron stars is studied with matter both in the hadronic phase as well as in the mixed phase of hadronic matter and strange quark matter. In our models, the dominant early-stage cooling process is neutrino emission via the direct Urca process. As a consequence, the cooling curves fall too fast compared to observations. However, when superfluidity is included, the cooling of the neutron stars is significantly slowed down. Furthermore, we find that the cooling curves are not very sensitive to the precise details of the mixing between the hadronic phase and the quark phase and also of the pairing that leads to superfluidity.Comment: 19 pages, 25 figure

NikR mediates nickel-responsive transcriptional induction of urease expression in Helicobacter pylori

The important human pathogen Helicobacter pylori requires the abundant expression and activity of its urease enzyme for colonization of the gastric mucosa. The transcription, expression, and activity of H. pylori urease were previously demonstrated to be induced by nickel supplementation of growth media. Here it is demonstrated that the HP1338 protein, an ortholog of the Escherichia coli nickel regulatory protein NikR, mediates nickel-responsive induction of urease expression in H. pylori. Mutation of the HP1338 gene (nikR) of H. pylori strain 26695 resulted in significant growth inhibition of the nikR mutant in the presence of supplementation with NiCl(2) at > or =100 microM, whereas the wild-type strain tolerated more than 10-fold-higher levels of NiCl(2). Mutation of nikR did not affect urease subunit expression or urease enzyme activity in unsupplemented growth media. However, the nickel-induced increase in urease subunit expression and urease enzyme activity observed in wild-type H. pylori was absent in the H. pylori nikR mutant. A similar lack of nickel responsiveness was observed upon removal of a 19-bp palindromic sequence in the ureA promoter, as demonstrated by using a genomic ureA::lacZ reporter gene fusion. In conclusion, the H. pylori NikR protein and a 19-bp operator sequence in the ureA promoter are both essential for nickel-responsive induction of urease expression in H. pylori

Transcriptional profiling of Helicobacter pylori Fur- and iron-regulated gene expression

Intracellular iron homeostasis is a necessity for almost all living organisms, since both iron restriction and iron overload can result in cell death. The ferric uptake regulator protein, Fur, controls iron homeostasis in most Gram-negative bacteria. In the human gastric pathogen Helicobacter pylori, Fur is thought to have acquired extra functions to compensate for the relative paucity of regulatory genes. To identify H. pylori genes regulated by iron and Fur, we used DNA array-based transcriptional profiling with RNA isolated from H. pylori 26695 wild-type and fur mutant cells grown in iron-restricted and iron-replete conditions. Sixteen genes encoding proteins involved in metal metabolism, nitrogen metabolism, motility, cell wall synthesis and cofactor synthesis displayed iron-dependent Fur-repressed expression. Conversely, 16 genes encoding proteins involved in iron storage, respiration, energy metabolism, chemotaxis, and oxygen scavenging displayed iron-induced Fur-dependent expression. Several Fur-regulated genes have been previously shown to be essential for acid resistance or gastric colonization in animal models, such as those encoding the hydrogenase and superoxide dismutase enzymes. Overall, there was a partial overlap between the sets of genes regulated by Fur and those previously identified as growth-phase, iron or acid regulated. Regulatory patterns were confirmed for five selected genes using Northern hybridization. In conclusion, H. pylori Fur is a versatile regulator involved in many pathways essential for gastric colonization. These findings further delineate the central role of Fur in regulating the unique capacity of H. pylori to colonize the human stomach

Deciphering the complex three-way interaction between the non-integrin laminin receptor, galectin-3 and Neisseria meningitidis

The non-integrin laminin receptor (LAMR1/RPSA) and galectin-3 (Gal-3) are multi-functional host molecules with roles in diverse pathological processes, particularly of infectious or oncogenic origins. Using bimolecular fluorescence complementation and confocal imaging, we demonstrate that the two proteins homo- and heterodimerize, and that each isotype forms a distinct cell surface population. We present evidence that the 37 kDa form of LAMR1 (37LRP) is the precursor of the previously described 67 kDa laminin receptor (67LR), whereas the heterodimer represents an entity that is distinct from this molecule. Site-directed mutagenesis confirmed that the single cysteine (C173) of Gal-3 or lysine (K166) of LAMR1 are critical for heterodimerization. Recombinant Gal-3, expressed in normally Gal-3-deficient N2a cells, dimerized with endogenous LAMR1 and led to a significantly increased number of internalized bacteria (Neisseria meningitidis), confirming the role of Gal-3 in bacterial invasion. Contact-dependent cross-linking determined that, in common with LAMR1, Gal-3 binds the meningococcal secretin PilQ, in addition to the major pilin PilE. This study adds significant new mechanistic insights into the bacterial–host cell interaction by clarifying the nature, role and bacterial ligands of LAMR1 and Gal-3 isotypes during colonization

The role of the ferric uptake regulator (Fur) in regulation of Helicobacter pylori iron uptake

Background. Availability of the essential nutrient iron is thought to vary greatly in the gastric mucosa, and thus the human gastric pathogen Helicobacter pylori requires regulatory responses to these environmental changes. Bacterial iron-responsive regulation is often mediated by Ferric Uptake Regulator (Fur) homologs, and in this study we have determined the role of H. pylori Fur in regulation of H. pylori iron uptake. Methods. Wild-type H. pylori and fur mutant derivatives were compared after growth in ironrestricted and iron-replete conditions. Iron-uptake was measured using 55Fe-labeled iron, whereas gene expression was mon

Differential regulation of amidase- and formamidase-mediated ammonia production by the Helicobacter pylori fur repressor.

The production of high levels of ammonia allows the human gastric pathogen Helicobacter pylori to survive the acidic conditions in the human stomach. H. pylori produces ammonia through urease-mediated degradation of urea, but it is also able to convert a range of amide substrates into ammonia via its AmiE amidase and AmiF formamidase enzymes. Here data are provided that demonstrate that the iron-responsive regulatory protein Fur directly and indirectly regulates the activity of the two H. pylori amidases. In contrast to other amidase-positive bacteria, amidase and formamidase enzyme activities were not induced by medium supplementation with their respective substrates, acrylamide and formamide. AmiE protein expression and amidase enzyme activity were iron-repressed in H. pylori 26695 but constitutive in the isogenic fur mutant. This regulation was mediated at the transcriptional level via the binding of Fur to the amiE promoter region. In contrast, formamidase enzyme activity was not iron-repressed but was significantly higher in the fur mutant. This effect was not mediated at the transcriptional level, and Fur did not bind to the amiF promoter region. These roles of Fur in regulation of the H. pylori amidases suggest that the H. pylori Fur regulator may have acquired extra functions to compensate for the absence of other regulatory systems