The worldwide leaf economics spectrum

Bringing together leaf trait data spanning 2,548 species and 175 sites we describe, for the first time at global scale, a universal spectrum of leaf economics consisting of key chemical, structural and physiological properties. The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves, and operates largely independently of growth form, plant functional type or biome. Categories along the spectrum would, in general, describe leaf economic variation at the global scale better than plant functional types, because functional types overlap substantially in their leaf traits. Overall, modulation of leaf traits and trait relationships by climate is surprisingly modest, although some striking and significant patterns can be seen. Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.     

Volatility forecasting with bivariate multifractal models

This paper examines volatility linkages and forecasting for stock and foreign exchange markets from a novel perspective by utilizing a bivariate Markov-switching multifractal model that accounts for possible interactions between stock and foreign exchange markets. Examining daily data from major advanced and emerging nations, we show that generalized autoregressive conditional heteroskedasticity models generally offer superior volatility forecasts for short horizons, particularly for foreign exchange returns in advanced markets. Multifractal models, on the other hand, offer significant improvements for longer horizons, consistently across most markets. Finally, the bivariate multifractal model provides superior forecasts compared to the univariate alternative in most advanced markets and more consistently for currency returns, while its benefits are limited in the case of emerging markets.     

Formation and role of exosomes in cancer

Exosomes offer new insight into cancer biology with both diagnostic and therapeutic implications. Because of their cell-to-cell communication, exosomes influence tumor progression, metastasis, and therapeutic efficacy. They can be isolated from blood and other bodily fluids to reveal disease processes occurring within the body, including cancerous growth. In addition to being a reservoir of cancer biomarkers, they can be re-engineered to reinstate tumor immunity. Tumor exosomes interact with various cells of the microenvironment to confer tumor-advantageous changes that are responsible for stromal activation, induction of the angiogenic switch, increased vascular permeability, and immune escape. Exosomes also contribute to metastasis by aiding in the epithelial-to-mesenchymal transition and formation of the pre-metastatic niche. Furthermore, exosomes protect tumor cells from the cytotoxic effects of chemotherapy drugs and transfer chemoresistance properties to nearby cells. Thus, exosomes are essential to many lethal elements of cancer and it is important to understand their biogenesis and role in cancer.     

Free-standing mesoporous silica films with tunable chiral nematic structures

Chirality at the molecular level is found in diverse biological structures, such as polysaccharides, proteins and DNA, and is responsible for many of their unique properties. Introducing chirality into porous inorganic solids may produce new types of materials that could be useful for chiral separation, stereospecific catalysis, chiral recognition (sensing) and photonic materials. Template synthesis of inorganic solids using the self-assembly of lyotropic liquid crystals offers access to materials with well-defined porous structures, but only recently has chirality been introduced into hexagonal mesostructures through the use of a chiral surfactant. Efforts to impart chirality at a larger length scale using self-assembly are almost unknown. Here we describe the development of a photonic mesoporous inorganic solid that is a cast of a chiral nematic liquid crystal formed from nanocrystalline cellulose. These materials may be obtained as free-standing films with high surface area. The peak reflected wavelength of the films can be varied across the entire visible spectrum and into the near-infrared through simple changes in the synthetic conditions. To the best of our knowledge these are the first materials to combine mesoporosity with long-range chiral ordering that produces photonic properties. Our findings could lead to the development of new materials for applications in, for example, tuneable reflective filters and sensors. In addition, this type of material could be used as a hard template to generate other new materials with chiral nematic structures.     

Clusters of iron-rich cells in the upper beak of pigeons are macrophages not magnetosensitive neurons

Understanding the molecular and cellular mechanisms that mediate magnetosensation in vertebrates is a formidable scientific problem. One hypothesis is that magnetic information is transduced into neuronal impulses by using a magnetite-based magnetoreceptor. Previous studies claim to have identified a magnetic sense system in the pigeon, common to avian species, which consists of magnetite-containing trigeminal afferents located at six specific loci in the rostral subepidermis of the beak. These studies have been widely accepted in the field and heavily relied upon by both behavioural biologists and physicists. Here we show that clusters of iron-rich cells in the rostro-medial upper beak of the pigeon Columbia livia are macrophages, not magnetosensitive neurons. Our systematic characterization of the pigeon upper beak identified iron-rich cells in the stratum laxum of the subepidermis, the basal region of the respiratory epithelium and the apex of feather follicles. Using a three-dimensional blueprint of the pigeon beak created by magnetic resonance imaging and computed tomography, we mapped the location of iron-rich cells, revealing unexpected variation in their distribution and number--an observation that is inconsistent with a role in magnetic sensation. Ultrastructure analysis of these cells, which are not unique to the beak, showed that their subcellular architecture includes ferritin-like granules, siderosomes, haemosiderin and filopodia, characteristics of iron-rich macrophages. Our conclusion that these cells are macrophages and not magnetosensitive neurons is supported by immunohistological studies showing co-localization with the antigen-presenting molecule major histocompatibility complex class II. Our work necessitates a renewed search for the true magnetite-dependent magnetoreceptor in birds.     

Crystal structure of an Hsp90-nucleotide-p23/Sba1 closed chaperone complex

Hsp90 (heat shock protein of 90 kDa) is a ubiquitous molecular chaperone responsible for the assembly and regulation of many eukaryotic signalling systems and is an emerging target for rational chemotherapy of many cancers. Although the structures of isolated domains of Hsp90 have been determined, the arrangement and ATP-dependent dynamics of these in the full Hsp90 dimer have been elusive and contentious. Here we present the crystal structure of full-length yeast Hsp90 in complex with an ATP analogue and the co-chaperone p23/Sba1. The structure reveals the complex architecture of the 'closed' state of the Hsp90 chaperone, the extensive interactions between domains and between protein chains, the detailed conformational changes in the amino-terminal domain that accompany ATP binding, and the structural basis for stabilization of the closed state by p23/Sba1. Contrary to expectations, the closed Hsp90 would not enclose its client proteins but provides a bipartite binding surface whose formation and disruption are coupled to the chaperone ATPase cycle.