This Week in Science

Science  04 Dec 2009:
Vol. 326, Issue 5958, pp. 1315
  1. CO2 and Miocene Climate Change


    Atmospheric carbon dioxide is a powerful greenhouse gas believed to be one of the most important determinants of climate. Ice cores provide a detailed and direct record of CO2 concentrations over the past 800,000 years, but not earlier. Tripati et al. (p. 1394, published online 8 October) report B/Ca measurements of planktonic foraminifera, from which they can infer atmospheric CO2 concentrations, for the past 20 million years. The concentration of atmospheric CO2 was similar to preindustrial values for the past 10 millions years, but between 15 and 20 million years ago, during the warm lower Miocene epoch, CO2 was more abundant, and major climate transitions toward cooler conditions occurred when CO2 decreased substantially.

  2. Zeroing in on Zoonoses

    Influenza, plague, and Lyme disease are classic examples of zoonoses—diseases that circulate in livestock and wildlife, as well as in humans. When a pathogen transfers among multiple hosts, the dynamics of circulation, transmission, and outbreak are complex. Lloyd-Smith et al. (p. 1362) review the use of analytical mathematical tools, particularly modeling, in the development of control policies and research agendas. Significant gaps are highlighted in analytical efforts during spillover transmission from animals into humans. Moreover, the tendency has been to focus on pathogens with simpler life cycles and of immediate global urgency, such as influenza, whereas insect-transmitted pathogens with complex, multihost life cycles are less well understood.

  3. Nascent Chains Revealed

    Detailed analysis of protein translation and translocation across membranes requires the identification and structural analysis of intermediates involved in these processes (see the Perspective by Kampmann and Blobel). Seidelt et al. (p. 1412, published online 29 October) report the visualization by cryo-electron microscopy of a nascent polypeptide chain in the tunnel of the ribosome at 5.8 angstroms. This resolution allows analysis of the conformation and distinct contacts of the nascent chain within the ribosomal tunnel, which suggests a mechanism by which translational stalling is induced by this peptide. Protein translocation across cellular membranes involves the Sec61 protein, a component of a protein-conducting channel. Whether Sec61 acts as a monomer or as an oligomer during protein translocation has been unclear. Becker et al. (p. 1369, published online 29 October) describe active yeast and mammalian ribosome-Sec61 structures that show the Sec61 complex interacting with the ribosome and a nascent secretory protein signal sequence. The analysis unambiguously reveals that the active protein-conducting channel is a single Sec61 copy with its central pore serving as conduit for the nascent polypeptide.

  4. ABA Receptor Up Close

    Plants face a variety of environmental stresses, including drought, salinity, and cold. In the face of such stresses, the plant hormone abscisic acid (ABA) triggers adaptive physiological responses. Nishimura et al. (p. 1373, published online 22 October; see the Perspective by Sussman and Phillips) have now analyzed the crystal structure of one member of the ABA receptor family, PYR1 (pyrabactin resistance 1). The ABA molecule binds within an internal pocket of PYR1, where it probably induces a conformational change.

  5. Elliptical Galaxy Evolution

    Our closest elliptical galaxy, M32, represents a rare class of elliptical galaxies that are too compact for their luminosities. Only a handful of elliptical galaxies with luminosities and sizes comparable to M32 have been found, making it difficult to understand how they evolved. Chilingarian et al. (p. 1379, published online 1 October) present a sample of 21 compact elliptical galaxies gathered through automated data mining of the Hubble Space Telescope Legacy Archive and other databases by means of virtual observatory tools. The results suggest that tidal stripping of more massive progenitor galaxies produces compact elliptical galaxies.

  6. Earth's Plume Plumbing

    Volcanic hot spots, such as the one that continues to build the Hawaiian Islands, are thought to form by one of two mechanisms: Either mantle plumes bring hot, buoyant material to the surface from deep within the Earth's interior, or extensive processing of the upper mantle by plate tectonics causes localized volcanism in stressed or heterogeneous crust. Wolfe et al. (p. 1388; see the cover; see the news story by Kerr) used an extensive array of ocean-bottom and land-based seismometers to reveal the structure of the mantle beneath Hawaii. These high-resolution images reveal a high-temperature plume originating from the lower mantle.

  7. Biofuel Backfire


    For compelling economical, geopolitical, and environmental reasons, biofuels are considered an attractive alternative to fossil fuels for meeting future global energy demands. Melillo et al. (p. 1397, published online 22 October), however, suggest that a few serious drawbacks related to land use need to be considered. Based on a combined biogeochemistry and economic model, indirect land use (for example, clearing forested land for food crops to compensate for increased biofuel crop production on current farmlands) is predicted to generate more soil carbon loss than directly harvesting biofuel crops. Furthermore, increased fertilizer use for biofuels will add large amounts of nitrous oxide—a more effective heat-trapping molecule than carbon dioxide—to the atmosphere. Policy decisions regarding land and crop management thus need to consider the long-term implications of increased biofuel production.

  8. Mitigating Nitrogen Enrichment?

    Nitrogen enrichment reduces the species diversity of plants in herbaceous communities. By contrast, the effects of increasing CO2 on plant species richness is poorly documented, and the interaction of both N deposition and CO2 elevation are unknown. Reich (p. 1399; see the Perspective by Collins) performed a 10-year open-air field experiment in a North American perennial grassland assemblage. Reductions in plant species richness resulting from N deposition were half as large under elevated CO2 concentrations as under ambient atmospheric CO2. Given that both N and CO2 are projected to increase globally, these results provide a pointer to the types of ecological change that could be expected, at least in relatively simple plant communities.

  9. Metamorphosis Receptor Identified


    One of the challenges facing many multicellular organisms is when to change from the juvenile stage to the reproductively mature adult. In insects, this metamorphosis is activated by the brain-derived neuropeptide, prothoracicotropic hormone (PTTH), when larvae reach a characteristic weight. Almost a century after this brain hormone was discovered, Rewitz et al. (p. 1403) have identified the PTTH receptor and its signaling cascade. The PTTH receptor is Torso (a receptor tyrosine kinase that signals through Ras/Raf/Erk), which patterns the embryonic termini during early development in response to the distantly related PTTH factor, Trunk.

  10. For the Love of Science

    Which is a better predictor of a student's continued participation in science, facile understanding or personal interest? Hulleman and Harackiewicz (p. 1410) designed an experiment to find out what drives high-school students. First-year high-school students were asked either to write about what they had just learned or about how what they had just learned connected to some facet of their personal lives. Connections of personal relevance were stronger than good grades for predicting interest in further science courses and future science careers. This low-cost intervention seemed to have its largest effect on students who began the class with the least amount of confidence in their abilities.

  11. Targeting DNA Gyrase

    DNA gyrase, an enzyme that unwinds double-stranded DNA, is essential in bacteria, but missing in humans, and is thus an important antibiotic target. DNA gyrase is inhibited by the well-known fluoroquinolines and aminocoumarins antibiotics, as well as by symocyclinones—bifunctional antibiotics comprising an aminocoumarin and a polyketide group. Surprisingly, symocyclinones, unlike aminocoumarin inhibitors, do not inhibit DNA gyrase GTPase activity, but instead inhibit binding to DNA. Now Edwards et al. (p. 1415) use biochemical and structural studies to show that the two functional groups of the antibiotic bind in separate pockets on the gyrase. Each group is a relatively weak inhibitor that together potently inhibit DNA binding.

  12. Coordinating Neuronal Assemblies

    Theoretical models predict the existence of so-called hub neurons—highly connected cells that strongly influence the synchronization of spiking activity in a large group of neurons. However, experimental evidence for the existence of these neuronal hubs is lacking. Bonifazi et al. (p. 1419) used high-resolution, two-photon calcium imaging to measure spontaneous calcium fluctuations in hundreds of neurons simultaneously and determined the relative timing of these fluctuations. Examination of functional connectivity maps, based on temporal correlation measurements, revealed a subpopulation of GABAergic hub neurons displaying a remarkably widespread axonal arborization that orchestrated network synchrony in developing hippocampal networks. Spontaneous network synchronizations in developing hippocampus caused giant depolarizing potentials in individual neurons, and manipulating the spike activity in potential hub cells influenced network activity.

  13. One More Vibration

    The beryllium dimer has puzzled chemists for the better part of a century because its bond, though weak by molecular standards, is much stronger than standard bonding frameworks would predict. Recent spectroscopic measurements have characterized the molecule in great detail, but leave open the question of whether a high-energy vibrational state might lie just below the threshold for scission of the bond. Patkowski et al. (p. 1382) have now derived a potential energy function, based on high-level theoretical calculations and, by slightly modifying it through fitting to the experimental data, obtained strong evidence for the presence of the upper vibrational state. Taken together with the measured spectra, these results offer a well-grounded basis for understanding the unusual molecule.

  14. Electrolysis at Nickel

    One drawback of solar and wind power is the need for an efficient storage system to release accumulated energy when neither source is readily available (during still nights, for example). Hydrogen derived from electrolysis of water is potentially a useful medium for this purpose, but catalyzing the interconversion efficiently at large scale would currently require a substantial amount of the scarce precious metal platinum. An alternative approach would be to mimic natural enzymatic reactions, which accomplish the interconversion using hydrogenases that incorporate the more abundant metals iron and nickel. In this vein, Le Goff et al. (p. 1384; see the Perspective by Hambourger and Moore) have lightly modified a hydrogenase-inspired nickel complex in order to append it to a conductive carbon nanotube support. The resulting hybrid material shows promising catalytic efficiency for reversible aqueous electrolysis in a standard apparatus.

  15. A Happy Marriage

    The fluxes of CO2 between the atmosphere and ocean are large and variable, and understanding why the concentration of atmospheric CO2 changes as it does, depends on accurately determining the details of those fluxes. One of the major obstacles in the way of quantifying this exchange is that there are too few measurements available, both temporally and geographically. Watson et al. (p. 1391) report results from a happy marriage of science and commerce—data collected by instruments fitted onto commercial ships plying the waters of the North Atlantic Ocean—that has generated the largest and most comprehensive set of measurements of ocean pCO2 ever collected. These data allow the oceanic CO2 sink to be monitored with unprecedented accuracy and will help researchers precisely map regional interannual air-sea fluxes.

  16. Hedgehog, Flatworms, and Regeneration

    The Hedgehog (Hh) signaling pathway plays pivotal roles during embryonic development, post-embryonic tissue maintenance, and disease. In spite of having at its core a collection of highly conserved components, the Hh pathway displays unusual differences in signal transduction mechanisms among flies, fish, and mammals. Using planarians (nonparasitic flatworms), Rink et al. (p. 1406, published online 22 October) report a key role for Hh signaling during adult regeneration and provide evidence that the perplexing diversity of transduction mechanisms may have arisen from animal-specific losses of an ancestral association between cilia and Hh signaling.

  17. Medulloblastoma and Atoh1

    The Atoh1 transcription factor is needed for normal brain development and is also implicated in some cancers of the brain. In order to study the latter function and avoid the perinatal lethality that follows early disruption of the Atoh1 gene, Flora et al. (p. 1424) knocked out the Atoh1 gene in mice after birth. A few days after the genetic knockout, cells at the surface of the cerebellum had begun to differentiate earlier than normal. Overexpression of Atoh1, on the other hand, led to excessive cell growth and even preneoplastic lesions at the surface of the cerebellum. Atoh1 was found to regulate expression of the Gli2 gene, and thereby Sonic Hedgehog signaling, which normally keeps cerebellar precursor cells undifferentiated.