Atrial natriuretic peptide inhibits angiotensin-stimulated proximal tubular sodium and water reabsorption

The discovery that atrial extracts have potent diuretic and natriuretic properties revealed a possible endocrine function of the heart in the regulation of extracellular fluid volume. Since that first report intense research activity has been directed towards determining the mechanism of action of the active atrial natriuretic polypeptides (ANP) found in these extracts. Despite these efforts it remains controversial whether the renal actions of ANP are exerted solely on the process of glomerular filtration or involve additional direct actions on tubular transport. We have investigated the possibility that atrial natriuretic polypeptides may induce natriuresis by suppression of proximal tubular sodium and water reabsorption. Using shrinking split-drop micropuncture combined with simultaneous capillary perfusion in anaesthetized rats we report that 20 nanomolar alpha-rANP (the main component of ANP in rat plasma) added to the peritubular fluid had no direct effect on proximal fluid uptake whereas picomolar angiotensin II had a marked stimulatory action as reported. The stimulatory effect of angiotensin II on fluid reabsorption was inhibited by peritubular ANP at physiological concentrations and abolished by higher concentrations of ANP. Thus at physiological concentrations ANP acts within the kidney to decrease proximal reabsorption by inhibition of angiotensin-stimulated sodium and water transport.     

A fossil entomogenous fungus from Dominican amber

Summary A worker ant (Formicidae: Hymenoptera) embedded in amber (25 million years old) from the Dominican Republic was covered with an entomogenous fungus containing characters very similar to present day strains ofBeauveria bassiana. This represents the first report of a fossil insect-pathogenic fungus belonging to the class Deuteromycetes.     

Remobilization of southern African desert dune systems by twenty-first century global warming

Although desert dunes cover 5 per cent of the global land surface and 30 per cent of Africa, the potential impacts of twenty-first century global warming on desert dune systems are not well understood. The inactive Sahel and southern African dune systems, which developed in multiple arid phases since the last interglacial period, are used today by pastoral and agricultural systems that could be disrupted if climate change alters twenty-first century dune dynamics. Empirical data and model simulations have established that the interplay between dune surface erodibility (determined by vegetation cover and moisture availability) and atmospheric erosivity (determined by wind energy) is critical for dunefield dynamics. This relationship between erodibility and erosivity is susceptible to climate-change impacts. Here we use simulations with three global climate models and a range of emission scenarios to assess the potential future activity of three Kalahari dunefields. We determine monthly values of dune activity by modifying and improving an established dune mobility index so that it can account for global climate model data outputs. We find that, regardless of the emission scenario used, significantly enhanced dune activity is simulated in the southern dunefield by 2039, and in the eastern and northern dunefields by 2069. By 2099 all dunefields are highly dynamic, from northern South Africa to Angola and Zambia. Our results suggest that dunefields are likely to be reactivated (the sand will become significantly exposed and move) as a consequence of twenty-first century climate warming.     

The phylogenetic position of the 'giant deer' Megaloceros giganteus

The giant deer, or 'Irish elk', has featured extensively in debates on adaptation, sexual selection, and extinction. Its huge antlers--the largest of any deer species, living or extinct--formed a focus of much past work. Yet the phylogenetic position of the giant deer has remained an enigma. On the basis of its flattened antlers, the species was previously regarded as closely related to the living fallow deer. Recent morphological studies, however, have challenged that view and placed the giant deer closer to the living red deer or wapiti. Here we present a new phylogenetic analysis encompassing morphological and DNA sequence evidence, and find that both sets of data independently support a sister-group relationship of giant and fallow deer. Our results include the successful extraction and sequencing of DNA from this extinct species, and highlight the value of a joint molecular and morphological approach.     

Structural characterization of the molecular platform for type III secretion system assembly

Type III secretion systems (TTSSs) are multi-protein macromolecular 'machines' that have a central function in the virulence of many Gram-negative pathogens by directly mediating the secretion and translocation of bacterial proteins (termed effectors) into the cytoplasm of eukaryotic cells. Most of the 20 unique structural components constituting this secretion apparatus are highly conserved among animal and plant pathogens and are also evolutionarily related to proteins in the flagellar-specific export system. Recent electron microscopy experiments have revealed the gross 'needle-shaped' morphology of the TTSS, yet a detailed understanding of the structural characteristics and organization of these protein components within the bacterial membranes is lacking. Here we report the 1.8-A crystal structure of EscJ from enteropathogenic Escherichia coli (EPEC), a member of the YscJ/PrgK family whose oligomerization represents one of the earliest events in TTSS assembly. Crystal packing analysis and molecular modelling indicate that EscJ could form a large 24-subunit 'ring' superstructure with extensive grooves, ridges and electrostatic features. Electron microscopy, labelling and mass spectrometry studies on the orthologous Salmonella typhimurium PrgK within the context of the assembled TTSS support the stoichiometry, membrane association and surface accessibility of the modelled ring. We propose that the YscJ/PrgK protein family functions as an essential molecular platform for TTSS assembly.     

A resolved outflow of matter from a brown dwarf

The birth of stars involves not only accretion but also, counter-intuitively, the expulsion of matter in the form of highly supersonic outflows. Although this phenomenon has been seen in young stars, a fundamental question is whether it also occurs among newborn brown dwarfs: these are the so-called 'failed stars', with masses between stars and planets, that never manage to reach temperatures high enough for normal hydrogen fusion to occur. Recently, evidence for accretion in young brown dwarfs has mounted, and their spectra show lines that are suggestive of outflows. Here we report spectro-astrometric data that spatially resolve an outflow from a brown dwarf. The outflow's characteristics appear similar to, but on a smaller scale than, outflows from normal young stars. This result suggests that the outflow mechanism is universal, and perhaps relevant even to the formation of planets.