Border of Notch activity establishes a boundary between the two dorsal appendage tube cell types

Boundaries establish and maintain separate populations of cells critical for organ formation. We show that Notch signaling establishes the boundary between two types of post-mitotic epithelial cells, the Rhomboid- and the Broad-positive cells. These cells will undergo morphogenetic movements to generate the two sides of a simple organ, the dorsal appendage tube of the Drosophila egg chamber. The boundary forms due to a difference in Notch levels in adjacent cells. The Notch expression pattern mimics the boundary; Notch levels are high in Rhomboid cells and low in Broad cells. Notch(-) mutant clones generate an ectopic boundary: ectopic Rhomboid cells arise in Notch(+) cells adjacent to the Notch(-) mutant cells but not further away from the clonal border. Pangolin, a component of the Wingless pathway, is required for Broad expression and for rhomboid repression. We further show that Broad represses rhomboid cell autonomously. Our data provide a foundation for understanding how a single row of Rhomboid cells arises adjacent to the Broad cells in the dorsal appendage primordia. Generating a boundary by the Notch pathway might constitute an evolutionarily conserved first step during organ formation in many tissues.     

Lrrn1 is required for formation of the midbrain-hindbrain boundary and organiser through regulation of affinity differences between midbrain and hindbrain cells in chick

The midbrain–hindbrain boundary (MHB) acts as an organiser/signalling centre to pattern tectal and cerebellar compartments. Cells in adjacent compartments must be distinct from each other for boundary formation to occur at the interface. Here we have identified the leucine-rich repeat (LRR) neuronal 1 (Lrrn1) protein as a key regulator of this process in chick. The Lrrn family is orthologous to the Drosophila tartan/capricious (trn/caps) family. Differential expression of trn/caps promotes an affinity difference and boundary formation between adjacent compartments in a number of contexts; for example, in the wing, leg and eye imaginal discs. Here we show that Lrrn1 is expressed in midbrain cells but not in anterior hindbrain cells. Lrrn1 is down-regulated in the anterior hindbrain by the organiser signalling molecule FGF8, thereby creating a differential affinity between these two compartments. Lrrn1 is required for the formation of MHB — loss of function leads to a loss of the morphological constriction and loss of Fgf8. Cells overexpressing Lrrn1 violate the boundary and result in a loss of cell restriction between midbrain and hindbrain compartments. Lrrn1 also regulates the glycosyltransferase Lunatic Fringe, a modulator of Notch signalling, maintaining its expression in midbrain cells which is instrumental in MHB boundary formation. Thus, Lrrn1 provides a link between cell affinity/compartment segregation, and cell signalling to specify boundary cell fate.     

Interaction of lubricin with type II collagen surfaces: Adsorption,friction, and normal forces

One of the major constituents of the synovial fluid that is thought to be responsible for chondroprotection and boundary lubrication is the glycoprotein lubricin (PRG4); however, the molecular mechanisms by which lubricin carries out its critical functions still remain largely unknown. We hypothesized that the interaction of lubricin with type II collagen, the main component of the cartilage extracellular matrix, results in enhanced tribological and wear properties. In this study, we examined: (i) the molecular details by which lubricin interacts with type II collagen and how binding is related to boundary lubrication and adhesive interactions; and (ii) whether collagen structure can affect lubricin adsorption and its chondroprotective properties. We found that lubricin adsorbs strongly onto denatured, amorphous, and fibrillar collagen surfaces. Furthermore, we found large repulsive interactions between the collagen surfaces in presence of lubricin, which increased with increasing lubricin concentration. Lubricin attenuated the large friction and also the long-range adhesion between fibrillar collagen surfaces. Interestingly, lubricin adsorbed onto and mediated the frictional response between the denatured and native amorphous collagen surfaces equally and showed no preference on the supramolecular architecture of collagen. However, the coefficient of friction was lowest on fibrillar collagen in the presence of lubricin. We speculate that an important role of lubricin in mediating interactions at the cartilage surface is to attach to the cartilage surface and provide a protective coating that maintains the contacting surfaces in a sterically repulsive state.     

Correlation of conodont and ammonoid successions across the Viséan–Serpukhovian boundary — A review of occurrences in the South Urals,Cantabrian Mountains,western Ireland and the Rhenish Mountains

Lochriea ziegleri is the conodont species that bears the highest potential to be the index for the base of Serpukhovian. Proposed phylogenetic lineages within the genus Lochriea, particularly the lineage L. nodosa–L. ziegleri, can be confirmed by the latest studies of the succession of the respective species in sections of north-western Ireland and the Rhenish Mountains of Germany; in these regions the first occurrence datum (FOD) of L. ziegleri is in the P2a zone or the comparable Neoglyphioceras suerlandense ammonoid zone. In the Cantabrian Mountains and the South Urals, the FODs of L. ziegleri are possibly located within ammonoid zones characterized by the genera Revilloceras and early representatives of Dombarites zones with falcatoid ornament.     

Local–regional boundary shifts in oribatid mite (Acari: Oribatida) communities: species–area relationships in arboreal habitat islands of a coastal temperate rain forest, Vancouver Island, Canada

Aim This study investigates the species–area relationship (SAR) for oribatid mite communities of isolated suspended soil habitats, and compares the shape and slope of the SAR with a nested data set collected over three spatial scales (core, patch and tree level). We investigate whether scale dependence is exhibited in the nested sampling design, use multivariate regression models to elucidate factors affecting richness and abundance patterns, and ask whether the community composition of oribatid mites changes in suspended soil patches of different sizes. Location Walbran Valley, Vancouver Island, Canada. Methods A total of 216 core samples were collected from 72 small, medium and large isolated suspended soil habitats in six western redcedar trees in June 2005. The relationship between oribatid species richness and habitat volume was modelled for suspended soil habitat isolates (type 3) and a nested sampling design (type 1) over multiple spatial scales. Nonlinear estimation parameterized linear, power and Weibull function regression models for both SAR designs, and these were assessed for best fit using R² and Akaike's information criteria (ΔAIC) values. Factors affecting oribatid mite species richness and standardized abundance (number per g dry weight) were analysed by anova and linear regression models. Results Sixty‐seven species of oribatid mites were identified from 9064 adult specimens. Surface area and moisture content of suspended soils contributed to the variation in species richness, while overall oribatid mite abundance was explained by moisture and depth. A power‐law function best described the isolate SAR (S = 3.97 × A^0.12, R² = 0.247, F_1,70 = 22.450, P < 0.001), although linear and Weibull functions were also valid models. Oribatid mite species richness in nested samples closely fitted a power‐law model (S = 1.96 × A^0.39, R² = 0.854, F_1,18 = 2693.6, P < 0.001). The nested SAR constructed over spatial scales of core, patch and tree levels proved to be scale‐independent. Main conclusions Unique microhabitats provided by well developed suspended soil accumulations are a habitat template responsible for the diversity of canopy oribatid mites. Species–area relationships of isolate vs. nested species richness data differed in the rate of accumulation of species with increased area. We suggest that colonization history, stability of suspended soil environments, and structural habitat complexity at local and regional scales are major determinants of arboreal oribatid mite species richness.     

Gradient and zonal analysis of understorey suppression by Eucalyptus wandoo

Gradients, zones and boundaries can be recognized on the basis of biotic, abiotic, field and experimentally-determined attributes along transects through isolated patches of Eucalyptus wandoo trees. The patch zone (corresponding to the tree canopy) could be defined on numerous environmental grounds. The suppression zone (with few shrubs) which embraced the patch zone, could only be distinguished from the surrounding scrub zone (with a dense shrub cover) on vegetation grounds. Site relationships, including identification of boundaries, were analyzed with the aid of a range-standardized dissimilarity measure and metric multidimensional scaling. Differences in availability of nutrients and phytotoxic substances from wandoo leaves, roots and litter had some effects on growth in pot trials but it is concluded that their role in explaining understorey suppression in the field is negligible. Competition for water at depth between the extensive lateral root system of wandoo trees and the roots of adult shrubs is shown to be the most likely explanation for genesis of the suppression zone and location of its boundary. Factors affecting seedling establishment, mainly surface water availability, are more concerned with maintenance of the suppression zone once it is formed.     

Azethoxyl nitroxide spin labels. ESR studies involving thiourea crystals, model membrane systems and chromatophores, and chemical reduction with ascorbate and dithiothreitol

Trans- and cis-azethoxyl nitroxides , , and can be trapped in the cavities of thiourea crystals. The presence of a single gauche conformation on either side of the pyrrolidine ring within the crystals was indicated by the ESR spectra. Rotation about the long molecular axis then corresponds approximately to y-axis motion of the nitroxide moiety. Proxyl nitroxides in which the nitroxide group is located on the penultimate carbon of long chain lipids can also be trapped and were shown to adopt the azethoxyl conformation in the thiourea crystals.The measured ΔA values (A_| − A) of oriented egg lecithin multilayers containing trans- and cis-azethoxyl nitroxides and were quite small, consistent with the unique orientation of the nitroxide principal axes with respect to the long axis of the molecule. The ΔA values for a series of lipids bearing a label near the terminus of the chain were very similar to that of , showing that the azethoxyl conformation is likely the predominant one in these labels in orienting systems.Computer simulations of the ESR spectra of and in egg lecithin vesicles provided values for molecular orientation and motion parameters consistent with those expected from a consideration of molecular models in the extended (all trans) conformation.Azethoxyl nitroxides have also proven useful in the investigation of motion restricted (boundary) lipid in a lipid-protein system. Thus, the values (69 ± 10%) for the amount of boundary lipid in the chromatophore membranes from Rhodopseudomonas sphaeroides as determined using trans- and cis- are in good agreement with values using 16-doxylstearic acid (64 ± 3%). The fact that all three labels show about the same fraction of boundary lipid in this system indicates that the lipid binding sites are relatively insensitive to the geometry of the lipid chain. Also, both and appear to be able to detect a third lipid environment not seen with the doxyl fatty acid. The apparent fluidity of this component lies between that of boundary and bilayer lipid. The unique orientation of the nitroxide principal axes with respect to the long molecular axis in azethoxyl nitroxides and allows detection of hindrance to rotation about the long molecular axis, in contrast to the analogous doxyl and proxyl fatty acids.Comparative reduction studies using ascorbate and dithiothreitol indicate that azethoxyl nitroxides are slightly more resistant toward reduction than proxyl nitroxides and much more resistant than doxyl nitroxides.     

Bridging science and practice in conservation: Deficits and challenges from a research perspective

Biodiversity is being lost at alarming rates in spite of efforts to conserve ecosystems, species and genetic diversity. There is broad consensus that biodiversity conservation needs to become more effective, and this requires an analysis of the causes that have prevented previous efforts from reaching their goal. A lack of knowledge exchange and cooperation between science and practice has been identified as a key issue in this context. Scientific knowledge frequently does not find its way into conservation practice, and information requirements by practitioners are often not considered appropriately by scientists. Here, we summarize deficits and challenges in the relationship between science and practice in conservation and outline approaches to achieving more effective knowledge exchange and collaboration at the interface between both. We propose that existing platforms for communication need to be complemented by independent institutions in particular at national and sub-national levels to facilitate successful co-production of knowledge as a prerequisite for effective conservation measures.