Morphological effects of the nanostructured ceria support on the activity and stability of CuO/CeO2 catalysts for the water-gas shift reaction.

Three CuO/CeO2 catalyst with different morphologies of ceria, namely nanospheres, nanorods and nanocubes, were synthesized and used to catalyze the water-gas shift (WGS) reaction. The reactivity tests showed that the Cu supported on the ceria nanospheres exhibited both the highest activity and superior stability when compared with the nanocube and nanorod ceria catalysts. Operando X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) methods were used to characterize these catalysts in their working state. High resolution electron microscopy (HRTEM, STEM) was used to look at the local atomic structure and nano-scale morphology. Our results show that the morphology of the ceria support, which can involve different crystal faces and concentrations of defects and imperfections, has a critical impact on the catalytic properties and influences: (1) the dispersion of CuO in the as-synthesized catalyst; (2) the particle size of metallic Cu upon reduction during the WGS reaction, (3) the stability of the metallic Cu upon variations of temperature, and (4) the dissociation of water on the ceria support. The nanosphere ceria catalyst showed an excellent water dissociation capability, the best dispersion of Cu and a strong Cu-Ce interaction, therefore delivering the best performance among the three WGS catalysts. The metallic Cu, which is the active species during the WGS reaction, was more stabilized on the nanospheres than on the nanorods and nanocubes and thus led to a better stability of the nanosphere catalyst than the other two architectures. Each catalyst exhibited a distinctive line-shape in the 800-1600 cm(-1) region of the DRIFTS spectra, pointing to the existence of different types of carbonate or carboxylate species as surface intermediates for the WGS.

Operando DRIFTS study of the redox and catalytic properties of CuO/Ce(1-x)Tb(x)O(2-δ) (x = 0-0.5) catalysts: evidence of an induction step during CO oxidation.

Catalysts of 1 wt% copper oxide supported on cerium oxide or cerium-terbium mixed oxides are comparatively examined with respect to their redox and catalytic properties for CO oxidation. Characterization of the catalysts had shown that they contain highly dispersed CuO-type entities on the corresponding nanostructured fluorite supports with copper dispersion increasing with increasing amounts of terbium in the support. In contrast, the CO oxidation catalytic activity decreases with increasing amounts of terbium in the support. On the basis of operando-DRIFTS experiments, one of the factors that could explain such behaviour is related to the greater difficulty in generating reduced copper sites active for the reaction in the presence of terbium, which in turn is evidenced to constitute an induction stage. Analysis of the redox properties is complemented by XPS which confirms the greater resistance to copper reduction in the presence of terbium.

Inverse CeO2/CuO catalyst as an alternative to classical direct configurations for preferential oxidation of CO in hydrogen-rich stream.

A novel inverse CeO(2)/CuO catalyst for preferential oxidation of CO in H(2)-rich stream (CO-PROX) has been developed on the basis of a hypothesis extracted from previous work of the group (JACS 2007, 129, 12064). Possible separation of the two competing oxidation reactions involved in the process (of CO and H(2), respectively) is the key to modulation of overall CO-PROX activity and is based on involvement of different sites as most active ones for each of the two reactions. Achievement of large size CuO particles and adequate CeO(2)-CuO interfacial configurations in the inverse catalyst apparently allows appreciable enhancement of the catalytic properties of this kind of system for CO-PROX, constituting an interesting alternative to classic direct configurations so far explored for this process. Reasons for such behavior are analyzed on the basis of operando-XRD, -XAFS, and -DRIFTS studies.

Redox behaviour of Pd-based TWCs under dynamic conditions: analysis using dispersive XAS and mass spectrometry.

The redox behaviour of Pd-based TWCs is studied under dynamic, cycling conditions (e.g. lambda oscillations) on a 50 millisecond scale. Pd temporal response to gas inlet mixture changes is governed by metal-promoter interface properties.

Nanostructured Ti-W mixed-metal oxides: structural and electronic properties.

In this article, the structural and electronic properties of Ti-W binary mixed oxide nanoparticles are investigated by using X-ray diffraction, Raman, X-ray absorption spectroscopies (XAS; near edge XANES and extended EXAFS), UV-vis spectroscopy, and density functional calculations. A series of Ti-W binary oxide samples having W content below 20 atom % and with particle size between 8 and 13 nm were prepared by a microemulsion method. The atoms in these nanoparticles adopted the anatase-type structure with a/b lattice constants rather similar to those of the single TiO(2) reference and with a c cell parameter showing a noticeable expansion upon doping. Within the anatase structure, W occupies substitutional positions, while Ti atoms only suffer minor structural perturbations. A change in the W local order at first neighboring distance is observed when comparing samples having a W content below and above 15 atom %. Charge neutrality is mostly achieved by formation of cation vacancies located at the first cation distance of W centers. Upon addition of W to the TiO(2) structure, the Ti charge is not strongly modified, while changes in the W-O interaction appear to drive a modest modification of the W d-electron density throughout the Ti-W series. A combination of these geometrical and electronic effects produced Ti K- and W L(I)/L(III)-edge XANES/EXAFS spectra with distinctive features. UV-vis spectra show a nonlinear decrease of the band gap in the Ti-W solid solutions with a characteristic turning point at a W content of ca. 15 atom %. The relationship between local/long-range order and electronic parameters is discussed on the basis of these experimental results.

Mechanisms of epithelial fusion and repair.

One of the principal functions of any epithelium in the embryonic or adult organism is to act as a self-sealing barrier layer. From the earliest stages of development, embryonic epithelia are required to close naturally occurring holes and to fuse wherever two free edges are brought together, and at the simplest level that is precisely what the epidermis must do to repair itself wherever it is damaged. Parallels can be drawn between the artificially triggered epithelial movements of wound repair and the naturally occurring epithelial movements that shape the embryo during morphogenesis. Recent in vitro and in vivo wound-healing studies and analysis of paradigm morphogenetic movements in genetically tractable embryos, like those of Drosophila and Caenorhabditis elegans, have begun to identify both the signals that initiate these movements and the cytoskeletal machinery that drives motility. We are also gaining insight into the nature of the brakes and stop signals, and the mechanisms by which the confronting epithelial sheets knit together to form a seam.

Drosophila puckered regulates Fos/Jun levels during follicle cell morphogenesis.

puckered (puc) encodes a VH1-like phosphatase that down-regulates Jun kinase (JNK) activity during dorsal closure of the Drosophila embryo. We report a role for puc in follicle cell morphogenesis during oogenesis. puc mRNA accumulates preferentially in the centripetally migrating follicle cells and cells of the elongating dorsal appendages. Proper levels of Puc activity in the follicle cells are critical for the production of a normal egg: either reduced or increased Puc activity result in incomplete nurse cell dumping and aberrant dorsal appendages. Phenotypes associated with puc mutant follicle cells include altered DE-cadherin expression in the follicle cells and a failure of nurse cell dumping to coordinate with dorsal appendage elongation, leading to the formation of cup-shaped egg chambers. The JNK pathway target A251-lacZ showed cell-type-specific differences in its regulation by puc and by the small GTPase DRac1. puc mutant cells displayed region-specific ectopic expression of the A251-lacZ enhancer trap whereas overexpression of a transgene encoding Puc was sufficient to suppress lacZ expression in a cell autonomous fashion. Strikingly, decreased or increased puc function leads to a corresponding increase or decrease, respectively, of Fos and Jun protein levels. Taken together, these data indicate that puc modulates gene expression responses by antagonizing a Rho GTPase signal transduction pathway that stabilizes the AP-1 transcription factor. Consistent with this, overexpression of a dominant negative DRac1 resulted in lower levels of Fos/Jun.

Wnt signalling: a theme with nuclear variations.

Wnt proteins are involved in a large number of events during development and disease. The crucial element in the transduction of the signal elicited by Wnt is the state and activity of beta-catenin. There are two pools of beta-catenin, one associated with cadherins at the cell surface and a soluble one in the cytolasm, whose state and concentration are critical for Wnt signalling. In the absence of Wnt, the cytoplasmic pool is low due to targetted degradation of beta-catenin. Upon Wnt signalling, beta-catenin is stabilized. As a consequence, it can access the nucleus where it interacts with members of the Tcf family of transcription factors to modulate the expression of defined targets. Recent reports indicate that, in addition to Tcfs, beta-catenin can interact with other nuclear proteins raising the possibility that Wnt signalling has a wider modulatory effect on transcription than is mediated by its interactions with Tcfs. BioEssays 23:311-318, 2001.

Dynamic actin-based epithelial adhesion and cell matching during Drosophila dorsal closure.

BACKGROUND: The adhesion of two epithelial sheets is a fundamental process that occurs throughout embryogenesis and during wound repair. Sealing of the dorsal epidermis along the midline of the Drosophila embryo provides a genetically tractable model to analyse the closure of such holes. Several studies indicate that the actin cytoskeleton plays a critical role in dorsal closure. Although many components of the signalling cascade directing this process have been identified, the precise cell-biological events upon which these signals act remain poorly described. RESULTS: By confocal imaging of living fly embryos expressing green fluorescent protein (GFP)-tagged actin, we found that dorsal closure relies on the activity of dynamic filopodia and lamellipodia that extend from front-row cells to actively zipper the epithelial sheets together. As these epithelial fronts approach one another, we observed long, thin filopodia, apparently 'sampling' cells on the opposing face. When the assembly of these actin-based protrusions was blocked (by interfering with the activities of Cdc42 and Jun N-terminal kinase signalling), the adhesion and fusion of opposing epithelial cells was prevented and their ability to 'sense' correct partners was also blocked, leading to segment misalignment along the midline seam. CONCLUSIONS: Dynamic, actin-based protrusions (filopodia and lamellae) are critical, both in the mechanics of epithelial adhesion during dorsal closure and in the correct 'matching' of opposing cells along the fusion seam.

[Introduction of Bacillus sphaericus strain-2362 (GRISELESF) for biological control of malaria vectors in Guatemala]. / Introducción del Bacillus sphaericus cepa-2362 (GRISELESF) para el control biológico de vectores maláricos en Guatemala.

Malaria continues to be an important health problem in a number of countries of Central and South America where it is considered as a highly prevent endemic disease. The objective of this paper is to assess the entomo-epidemiological impact of a pilot program for the biological control of malaria-transmitting vectors, which was implemented in 1998 in Escuintla, Republic of Guatemala. This program was based on the use of 20,000 L of biolarvicide Bacillus sphaericus- strain-2362 (GRISELESF) which was applied in the 46 localities of highest epidemiological risk at a rate of 10 mL/m2 of effective area of breeding. The entomologic effectiveness of this biolarvicide was monitored from the first 72 hours to 4 months after the application. There was a total larval reduction of 94.57 in the maturity stage of the water phase of Anopheles albimanus vector. The epidemiological analysis was carried out by comparing the rate of malaria prevalence (per 1000 pop) during 1997 and 1998. The five treated municipalities showed a statistically significant reduction of 50% (p 0.01). The results obtained in this paper coincided with those reported by comparable studies, so, this allowed us to recommend the use of the biolarvicide Bacillus sphaericus (strain-2362) as part of a comprehensive program of malaria-transmitting vector control in the Republic of Guatemala and other countries of the region.

Two different activities of Suppressor of Hairless during wing development in Drosophila.

The Notch pathway plays a crucial and universal role in the assignation of cell fates during development. In Drosophila, Notch is a transmembrane protein that acts as a receptor of two ligands Serrate and delta. The current model of Notch signal transduction proposes that Notch is activated upon binding its ligands and that this leads to the cleavage and release of its intracellular domain (also called Nintra). Nintra translocates to the nucleus where it forms a dimeric transcription activator with the Su(H) protein. In contrast with this activation model, experiments with the vertebrate homologue of Su(H), CBF1, suggest that, in vertebrates, Nintra converts CBF1 from a repressor into an activator. Here we have assessed the role of Su(H) in Notch signalling during the development of the wing of Drosophila. Our results show that, during this process, Su(H) can activate the expression of some Notch target genes and that it can do so without the activation of the Notch pathway or the presence of Nintra. In contrast, the activation of other Notch target genes requires both Su(H) and Nintra, and, in the absence of Nintra, Su(H) acts as a repressor. We also find that the Hairless protein interacts with Notch signalling during wing development and inhibits the activity of Su(H). Our results suggest that, in Drosophila, the activation of Su(H) by Notch involve the release of Su(H) from an inhibitory complex, which contains the Hairless protein. After its release Su(H) can activate gene expression in absence of Nintra.

Structural requirements for notch signalling with delta and serrate during the development and patterning of the wing disc of Drosophila.

The delta and Serrate proteins interact with the extracellular domain of the Notch receptor and initiate signalling through the receptor. The two ligands are very similar in structure and have been shown to be interchangeable experimentally; however, loss of function analysis indicates that they have different functions during development and analysis of their signalling during wing development indicates that the Fringe protein can discriminate between the two ligands. This raises the possibility that the signalling of delta and Serrate through Notch requires different domains of the Notch protein. Here we have tested this possibility by examining the ability of delta and Serrate to interact and signal with Notch molecules in which different domains had been deleted. This analysis has shown that EGF-like repeats 11 and 12, the RAM-23 and cdc10/ankyrin repeats and the region C-terminal to the cdc10/ankyrin repeats of Notch are necessary for both delta and Serrate to signal via Notch. They also indicate, however, that delta and Serrate utilise EGF-like repeats 24-26 of Notch for signalling, but there are significant differences in the way they utilise these repeats.

The informational content of gradients of Wnt proteins.

This perspective tackles the issues facing developmental biologists and cell biologists regarding how the molecular mechanisms for specifying cell fate are defined. This perspective focuses on members of the Wnt family. The author proposes that Wnt proteins may act as stabilizing signals for earlier inductive events in certain systems, for example, in Caenorhabditis elegans during the migration of two neurons and in Drosophila melanogaster during the patterning of the wing.

Antagonist activity of DWnt-4 and wingless in the Drosophila embryonic ventral ectoderm and in heterologous Xenopus assays.

Wnt genes encode secreted signalling molecules involved in a number of basic developmental processes. In Drosophila, wingless and DWnt-4 are two physically clustered Wnt genes, which are transcribed in overlapping patterns during embryogenesis and, in several instances, are controlled by the same regulatory molecules. To address the question of the functional relationship of wingless and DWnt-4, we analysed how embryonic cells respond when they are exposed, simultaneously or not, to the encoded Wnt signals. We show that DWnt-4 has the capacity to antagonise Wingless signalling both in the Drosophila ventral epidermis and in a heterologous system, the Xenopus embryo. We provide evidence that DWnt-4 inhibits the Wingless/Wnt-1 signalling pathway upstream of the activation of transcriptional targets. This is the first report that antagonising Wnt signals exist in Drosophila.

An activity of Notch regulates JNK signalling and affects dorsal closure in Drosophila.

BACKGROUND: The Drosophila Notch protein is a receptor that controls cell fate during embryonic development, particularly in lateral inhibition, a process that acts on groups of cells that share a particular developmental potential to restrict the number of cells that will adopt that cell fate. The process of lateral inhibition is implemented by the nuclear protein Suppressor of Hairless (Su(H)) and is triggered by the ligand Delta. Recent results have shown that the interaction between Delta and Notch triggers the cleavage of the intracellular domain of Notch which then translocates to the nucleus and binds to Su(H). RESULTS: We find that Notch plays a role in the patterning of the dorsal epidermis of the Drosophila embryo and that this function of Notch is independent of Su(H), requires Notch at the plasma membrane and targets the c-Jun N-terminal kinase (JNK) signalling pathway. Notch mutants show high levels of JNK activity and can rescue the effects of lowered JNK signalling resulting from mutations in the hemipterous and basket genes. Two regions of the intracellular domain of Notch are involved: the Cdc10/ankyrin repeats, which downregulate signalling through the JNK pathway, and a region carboxy-terminal to these repeats, which regulates this negative function. CONCLUSIONS: Our results reveal a novel signalling activity of Notch that does not require its cleavage and acts by modulating signalling through the JNK pathway. In the Drosophila embryo, this activity plays an important role in the morphogenetic movements that drive dorsal closure.

Interactions between Wingless and Notch during the assignment of cell fates in Drosophila.

A large number of observations suggest that, during Drosophila development there are close functional interactions between the activity of Notch receptor and that of a signaling molecule encoded by wingless gene. In this essay, I summarize these interactions and discuss the possibility that Wingless acts as a ligand for Notch as part of a switch that is iteratively involved in the assignation of cell fates during development.

Wing development and specification of dorsal cell fates in the absence of apterous in Drosophila.

The development and patterning of the Drosophila wing relies on interactions between cell populations that have the anteroposterior (AP) axis and dorsoventral (DV) axis of the wing imaginal disc as frames of reference [1-3]. Each of these cell populations gives rise to a compartment - a group of cells that have their fates restricted by cell lineage - within which cells acquire specific identities through the expression of 'selector' genes [1,2,4]. The genes engrailed (en) and invected (inv), for example, label cells in the posterior compartment and mediate a set of cell interactions that direct the patterning and growth of the wing along the AP axis [1,2,4]. A similar situation has been proposed to exist across the DV axis, along with apterous (ap) as a dorsal selector gene [5], mediating cell interactions by regulating the expression of Serrate (Ser) [6] [7] and fringe (fng) [8]. In ap mutants, the wing is lost [5] [9], and here we report that this phenotype can be rescued by ectopic expression of either Ser or fng and that, surprisingly, the resulting wings have both dorsal and ventral cell fates.

puckered encodes a phosphatase that mediates a feedback loop regulating JNK activity during dorsal closure in Drosophila.

The activation of MAPKs is controlled by the balance between MAPK kinase and MAPK phosphatase activities. The latter is mediated by a subset of phosphatases with dual specificity (VH-1 family). Here, we describe a new member of this family encoded by the puckered gene of Drosophila. Mutations in this gene lead to cytoskeletal defects that result in a failure in dorsal closure related to those associated with mutations in basket, the Drosophila JNK homolog. We show that puckered mutations result in the hyperactivation of DJNK, and that overexpression of puc mimics basket mutant phenotypes. We also show that puckered expression is itself a consequence of the activity of the JNK pathway and that during dorsal closure, JNK signaling has a dual role: to activate an effector, encoded by decapentaplegic, and an element of negative feedback regulation encoded by puckered.