The netrin receptor UNC5B mediates guidance events controlling morphogenesis of the vascular system

Blood vessels and nerves are complex, branched structures that share a high degree of anatomical similarity. Guidance of vessels and nerves has to be exquisitely regulated to ensure proper wiring of both systems. Several regulators of axon guidance have been identified and some of these are also expressed in endothelial cells; however, the extent to which their guidance functions are conserved in the vascular system is still incompletely understood. We show here that the repulsive netrin receptor UNC5B is expressed by endothelial tip cells of the vascular system. Disruption of the Unc5b gene in mice, or of Unc5b or netrin-1a in zebrafish, leads to aberrant extension of endothelial tip cell filopodia, excessive vessel branching and abnormal navigation. Netrin-1 causes endothelial filopodial retraction, but only when UNC5B is present. Thus, UNC5B functions as a repulsive netrin receptor in endothelial cells controlling morphogenesis of the vascular system.     

Influence of PPCA inhibitor on CaCO3 scale surface deposition and bulk precipitation at elevated temperature

Scale formation is a serious and costly problem encountered in the oil and gas industry. Polyphosphinocarboxylic acid (PPCA) is a common commercial organic scale inhibitor used in the oil and gas industry which is normally referred to a nucleation inhibitor. In this paper, the effect of PPCA on calcium carbonate scale is studied systematically and some new insights into the mechanisms of PPCA inhibition are given. Traditionally, the studies of scale formation and inhibition have focused on bulk precipitation or surface deposition. Few studies have focused on the difference between surface deposition and bulk precipitation processes. In this paper, the effect of PPCA inhibitor on calcium carbonate scale formation is studied both in the bulk solution and on the metal surface in supersaturated scale formation solutions which represent typical waters encountered in oil and gas production. It is clear that PPCA inhibits both bulk precipitation and surface deposition but to a different degree. At 4 ppm PPCA, the inhibition efficiency of surface deposition is greater than the inhibition efficiency of bulk precipitation. It is assumed that the inhibitor film formed on the metal surface at the highest concentration of PPCA (4 ppm) prevent the adsorption of scale crystals on the metal surface. In addition, PPCA suppresses aragonite and calcite crystal formation and results in the least stable vaterite crystal dominating the scale.     

A deletion in the gene encoding sphingomyelin phosphodiesterase 3 (Smpd3) results in osteogenesis and dentinogenesis imperfecta in the mouse

The mouse mutation fragilitas ossium (fro) leads to a syndrome of severe osteogenesis and dentinogenesis imperfecta with no detectable collagen defect. Positional cloning of the locus identified a deletion in the gene encoding neutral sphingomyelin phosphodiesterase 3 (Smpd3) that led to complete loss of enzymatic activity. Our knowledge of SMPD3 function is consistent with the pathology observed in mutant mice and provides new insight into human pathologies.     

Antagonism between Ca and Na ions at neurohypophysial nerve terminals

Résumé La secrétion hormonale de neurohypophyses isolées de rat a été estimée à l'aide d'un test d'éjection du lait. Au moment de la dépolarisation des terminaisons neurosecrétrices, il y a compétition entre le sodium et le calcium externes pour d'hypothétiques sites membranaires. Pour des concentrations de calcium inférieures ou égales à la concentration physiologique, la libération hormonale est fonction du rapport [Ca²⁺]/[Na⁺]² dans le milieu externe.

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This work was supported by grants from the Swiss National Science Foundation No. 5340.3 and 3.556.71 and the F. Hoffmann-La-Roche Foundation No. 117.     

Active transport of Cl− across the isolated intestinal mucosa ofTestudo hermanni

Riassunto Nel digiuno diTestudo hermanni in assenza di gradienti elettrochimici esiste un trasporto netto di Cl^– dal mezzo serosale a quello mucosale. Il trattamento con DNP riduce significativamente il flusso sierosamucosa di Cl^–, per cui si conferma l'esistenza di un trasporto attivo di questo ione. Anche il flusso mucosasierosa di Cl^– è inibito dal DNP, per cui è probabile che anche questo flusso sia dovuto in parte a un trasporto attivo.     

Explaining the excess of rare species in natural species abundance distributions

The observation that a few species in ecological communities are exceptionally abundant, whereas most are rare, prompted the development of species abundance models. Nevertheless, despite the large literature on the commonness and rarity of species inspired by these pioneering studies, some widespread empirical patterns of species abundance resist easy explanation. Notable among these is the observation that in large assemblages there are more rare species than the log normal model predicts. Here we use a long-term (21-year) data set, from an estuarine fish community, to show how an ecological community can be separated into two components. Core species, which are persistent, abundant and biologically associated with estuarine habitats, are log normally distributed. Occasional species occur infrequently in the record, are typically low in abundance and have different habitat requirements; they follow a log series distribution. These distributions are overlaid, producing the negative skew that characterizes real data sets.     

Low-temperature processing of 'baroplastics' by pressure-induced flow

The manufacturing of plastics traditionally involves melt processing at temperatures typically greater than 200 degrees C-to enable extrusion or moulding under pressure into desired forms-followed by solidification. This process consumes energy and can cause substantial degradation of polymers and additives (such as flame retardants and ultraviolet stabilizers), limiting plastics performance and recyclability. It was recently reported that the application of pressure could induce melt-like behaviour in the block copolymer polystyrene-block-poly(n-butyl methacrylate) (PS-b-PBMA), and this behaviour has now been demonstrated in a range of other block copolymer systems. These polymers have been termed baroplastics. However, in each case, the order-to-disorder transition, which gives rise to the accompanying change in rheology from soft solid to melt, was observed at temperatures far exceeding the glass transition temperatures (T(g)) of both components. Here we show that baroplastic systems containing nanophase domains of one high-T(g) and one low-T(g) component can exhibit melt-like flow under pressure at ambient temperature through an apparent semi-solid partial mixing mechanism that substantially preserves the high-T(g) phase. These systems were shredded and remoulded ten times with no evident property degradation. Baroplastics with low-temperature formability promise lower energy consumption in manufacture and processing, reduced use of additives, faster production and improved recyclability, and also provide potential alternatives to current thermoplastic elastomers, rubber-modified plastics, and semi-crystalline polymers.