An apparently normal gamma-ray burst with an unusually low luminosity

Much of the progress in understanding gamma-ray bursts (GRBs) has come from studies of distant events (redshift z approximately 1). In the brightest GRBs, the gamma-rays are so highly collimated that the events can be seen across the Universe. It has long been suspected that the nearest and most common events have been missed because they are not as collimated or they are under-energetic (or both). Here we report soft gamma-ray observations of GRB 031203, the nearest event to date (z = 0.106; ref. 2). It had a duration of 40 s and peak energy of >190 keV, and therefore appears to be a typical long-duration GRB. The isotropic gamma-ray energy of < or =10(50) erg, however, is about three orders of magnitude smaller than that of the cosmological population. This event--as well as the other nearby but somewhat controversial GRB 980425--is a clear outlier from the isotropic-energy/peak-energy relation and luminosity/spectral-lag relations that describe the majority of GRBs. Radio calorimetry shows that both of these events are under-energetic explosions. We conclude that there does indeed exist a large population of under-energetic events.     

The DNA sequence and analysis of human chromosome 13

Chromosome 13 is the largest acrocentric human chromosome. It carries genes involved in cancer including the breast cancer type 2 (BRCA2) and retinoblastoma (RB1) genes, is frequently rearranged in B-cell chronic lymphocytic leukaemia, and contains the DAOA locus associated with bipolar disorder and schizophrenia. We describe completion and analysis of 95.5 megabases (Mb) of sequence from chromosome 13, which contains 633 genes and 296 pseudogenes. We estimate that more than 95.4% of the protein-coding genes of this chromosome have been identified, on the basis of comparison with other vertebrate genome sequences. Additionally, 105 putative non-coding RNA genes were found. Chromosome 13 has one of the lowest gene densities (6.5 genes per Mb) among human chromosomes, and contains a central region of 38 Mb where the gene density drops to only 3.1 genes per Mb.     

The role of barren stalk1 in the architecture of maize

The architecture of higher plants is established through the activity of lateral meristems--small groups of stem cells formed during vegetative and reproductive development. Lateral meristems generate branches and inflorescence structures, which define the overall form of a plant, and are largely responsible for the evolution of different plant architectures. Here, we report the isolation of the barren stalk1 gene, which encodes a non-canonical basic helix-loop-helix protein required for the initiation of all aerial lateral meristems in maize. barren stalk1 represents one of the earliest genes involved in the patterning of maize inflorescences, and, together with the teosinte branched1 gene, it regulates vegetative lateral meristem development. The architecture of maize has been a major target of selection for early agriculturalists and modern farmers, because it influences harvesting, breeding strategies and mechanization. By sampling nucleotide diversity in the barren stalk1 region, we show that two haplotypes entered the maize gene pool from its wild progenitor, teosinte, and that only one was incorporated throughout modern inbreds, suggesting that barren stalk1 was selected for agronomic purposes.     

Trichomonas hydrogenosomes contain the NADH dehydrogenase module of mitochondrial complex I

Hydrogenosomes are double-membraned ATP-producing and hydrogen-producing organelles of diverse anaerobic eukaryotes. In some versions of endosymbiotic theory they are suggested to be homologues of mitochondria, but alternative views suggest they arose from an anaerobic bacterium that was distinct from the mitochondrial endosymbiont. Here we show that the 51-kDa and 24-kDa subunits of the NADH dehydrogenase module in complex I, the first step in the mitochondrial respiratory chain, are active in hydrogenosomes of Trichomonas vaginalis. Like mitochondrial NADH dehydrogenase, the purified Trichomonas enzyme can reduce a variety of electron carriers including ubiquinone, but unlike the mitochondrial enzyme it can also reduce ferredoxin, the electron carrier used for hydrogen production. The presence of NADH dehydrogenase solves the long-standing conundrum of how hydrogenosomes regenerate NAD+ after malate oxidation. Phylogenetic analyses show that the Trichomonas 51-kDa homologue shares common ancestry with the mitochondrial enzyme. Recruitment of complex I subunits into a H2-producing pathway provides evidence that mitochondria and hydrogenosomes are aerobic and anaerobic homologues of the same endosymbiotically derived organelle.     

Public health vaccination policies for containing an anthrax outbreak

Concern about biological weapons has raised questions about the most effective public health policies to contain an anthrax outbreak. We developed a probability model to predict the impact of different anthrax antibiotic and vaccination policies. An anthrax outbreak can be significantly contained by minimizing the delay until initiation of antibiotic prophylaxis. However, even if mass distribution of antibiotics is completed within six days of the initial exposure, then at most about 70% of cases can be prevented. Post-exposure vaccination will not significantly increase that prevention rate if adherence to antibiotic regimens is similar or higher than that attained in the 2001 US outbreak. However, post-exposure vaccination can be useful either in shortening the duration of a prolonged antibiotic regimen, in the event of an antibiotic-resistant strain, or if antibiotic adherence rates are very low. Here we show that a mass pre-exposure vaccination programme for the general population would require very high population coverage rates to significantly increase prevention rates from that achieved with targeted and rapid post-exposure prophylaxis programmes.     

Neurolinguistics: structural plasticity in the bilingual brain

Humans have a unique ability to learn more than one language--a skill that is thought to be mediated by functional (rather than structural) plastic changes in the brain. Here we show that learning a second language increases the density of grey matter in the left inferior parietal cortex and that the degree of structural reorganization in this region is modulated by the proficiency attained and the age at acquisition. This relation between grey-matter density and performance may represent a general principle of brain organization.     

Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes

The Atlantic meridional overturning circulation is widely believed to affect climate. Changes in ocean circulation have been inferred from records of the deep water chemical composition derived from sedimentary nutrient proxies, but their impact on climate is difficult to assess because such reconstructions provide insufficient constraints on the rate of overturning. Here we report measurements of 231Pa/230Th, a kinematic proxy for the meridional overturning circulation, in a sediment core from the subtropical North Atlantic Ocean. We find that the meridional overturning was nearly, or completely, eliminated during the coldest deglacial interval in the North Atlantic region, beginning with the catastrophic iceberg discharge Heinrich event H1, 17,500 yr ago, and declined sharply but briefly into the Younger Dryas cold event, about 12,700 yr ago. Following these cold events, the 231Pa/230Th record indicates that rapid accelerations of the meridional overturning circulation were concurrent with the two strongest regional warming events during deglaciation. These results confirm the significance of variations in the rate of the Atlantic meridional overturning circulation for abrupt climate changes.     

Structural basis for allostery in integrins and binding to fibrinogen-mimetic therapeutics

Integrins are important adhesion receptors in all Metazoa that transmit conformational change bidirectionally across the membrane. Integrin alpha and beta subunits form a head and two long legs in the ectodomain and span the membrane. Here, we define with crystal structures the atomic basis for allosteric regulation of the conformation and affinity for ligand of the integrin ectodomain, and how fibrinogen-mimetic therapeutics bind to platelet integrin alpha(IIb)beta3. Allostery in the beta3 I domain alters three metal binding sites, associated loops and alpha1- and alpha7-helices. Piston-like displacement of the alpha7-helix causes a 62 degrees reorientation between the beta3 I and hybrid domains. Transmission through the rigidly connected plexin/semaphorin/integrin (PSI) domain in the upper beta3 leg causes a 70 A separation between the knees of the alpha and beta legs. Allostery in the head thus disrupts interaction between the legs in a previously described low-affinity bent integrin conformation, and leg extension positions the high-affinity head far above the cell surface.     

A single population of olfactory sensory neurons mediates an innate avoidance behaviour in Drosophila

All animals exhibit innate behaviours in response to specific sensory stimuli that are likely to result from the activation of developmentally programmed neural circuits. Here we observe that Drosophila exhibit robust avoidance to odours released by stressed flies. Gas chromatography and mass spectrometry identifies one component of this 'Drosophila stress odorant (dSO)' as CO2. CO2 elicits avoidance behaviour, at levels as low as 0.1%. We used two-photon imaging with the Ca2+-sensitive fluorescent protein G-CaMP to map the primary sensory neurons governing avoidance to CO2. CO2 activates only a single glomerulus in the antennal lobe, the V glomerulus; moreover, this glomerulus is not activated by any of 26 other odorants tested. Inhibition of synaptic transmission in sensory neurons that innervate the V glomerulus, using a temperature-sensitive Shibire gene (Shi(ts)), blocks the avoidance response to CO2. Inhibition of synaptic release in the vast majority of other olfactory receptor neurons has no effect on this behaviour. These data demonstrate that the activation of a single population of sensory neurons innervating one glomerulus is responsible for an innate avoidance behaviour in Drosophila.