This Week in Science

Science  31 Oct 2014:
Vol. 346, Issue 6209, pp. 596
  1. Volcanology

    Imaging before an unimaginable eruption

    1. Brent Grocholski
    Lake Toba, northern SumatraCREDIT: BARRY KUSUMA/GETTY IMAGES

    Volcanic super-eruptions eject thousands of times the volume of the largest documented eruptions over human history. Several “supervolcanoes” capable of this type of unimaginable devastation dot the surface of Earth today. Jaxybulatov et al. use seismic background noise to estimate the size and maturity of one of the world's largest volcanic reservoirs, the Toba caldera in northern Sumatra. Magma storage under the caldera occurs slowly over time, in the form of horizontal layers of magma injected into the crust. These magmatic sills are documented to 20 kilometers below the surface, but more sills could exist even deeper. The characterization of magma storage in large volcanic systems may help us to prepare for future volcanic super-eruptions.

    Science, this issue p. 617

  2. Earth History

    Low oxygen limited the rise of animals

    1. Nicholas S. Wigginton

    Oxygen levels in Earth's early atmosphere had an important influence on the evolution of complex life. Planavsky et al. analyzed the isotopic signature of chromium in sedimentary rocks from across the globe—a proxy for past oxygen levels. Oxygen levels in the mid-Proterozoic (1.6 billion to 900 million years ago) were very low: less than 0.1% of the modern atmosphere. These low levels were probably below the minimum oxygen requirements for the earliest animals, delaying their emergence and diversification.

    Science, this issue p. 635

  3. Nuclear Physics

    Scattering electrons off nuclear targets

    1. Jelena Stajic

    Atomic nuclei consist of fermions—protons and neutrons—bound together by interactions. Because two identical fermions cannot occupy the same quantum state, both protons and neutrons have a broad range of momenta inside the nucleus. Hen et al. scattered electrons off nuclei of varying sizes to study the distribution of the protons' and neutrons' momenta. Protons formed high-momentum pairs with neutrons much more frequently than with other protons. Thus, surprisingly, the average momentum of a neutron was lower than that of a proton, even in nuclei with a larger number of neutrons than protons.

    Science, this issue p. 614

  4. Early Solar System

    History recorded in asteroid's water

    1. Margaret M. Moerchen

    Astronomers know that interstellar water is abundantly available to young planetary systems—our blue planet collected (or accreted) plenty of it. Still, the details of water's movement in the inner solar system are elusive. Sarafian et al. measured water isotopes in meteorite samples from the asteroid Vesta for clues to the timing of water accretion. Their samples have the same isotopic fingerprint of volatiles as both Earth and carbonaceous chondrites, some of the most primitive meteorites. The findings suggest that Earth received most of its water relatively early from chondrite-like bodies.

    Science, this issue p. 623

  5. Wildlife Disease

    A new, yet old, threat to amphibians

    1. Sacha Vignieri

    Globally, populations of amphibians have been severely affected by a disease caused by the fungus Batrachochytrium dendrobatidis. Recently, some European salamander populations were decimated by the emergence of a new, related chytrid fungus, B. salamandrivorans. Martel et al. screened amphibians across continents. This newly emerging threat seems to have originated in Asia and traveled to Europe with salamanders transported as part of the pet trade. Asian salamanders have evolved resistance to the pathogen, but salamanders from other parts of the world are highly susceptible.

    Science, this issue p. 630

  6. Neurodegeneration

    Hunting for the effects of huntingtin

    1. Leslie K. Ferrarelli

    Huntington's disease (HD) is associated with a mutant form of the protein huntingtin (Htt). HD-associated symptoms are alleviated by inhibition of the kinase mTOR, which activates protein synthesis when amino acids are plentiful. In mouse striatal neurons, Pryor et al. found that wild-type Htt stimulated amino acid–induced mTOR signaling by enhancing its interaction with an activating protein. Mutant Htt promoted this interaction even when amino acid availability was not increased. In a mouse model of HD, activating mTOR in striatal neurons accelerated the onset of symptoms.

    Sci. Signal. 7, ra103 (2014).

  7. Plant Genetics

    Y male plants affect female development

    1. Laura M. Zahn

    Persimmons separate the sexes


    Although most plants have both male and female organs within a single flower, some produce separate male and female plants. In some cases, such as persimmons, males are determined by a Y chromosome. Akagi et al. examined the gene transcript differences between male and female persimmons. A gene on the Y chromosome regulated a non–sex chromosome–linked small RNA that suppresses female organ development. This small RNA was localized to male flowers and could affect female development in other plant species. The evolutionary history of these genes suggests that they are tied to the origin of the separation of sexes in the persimmon family.

    Science, this issue p. 646

  8. Behavioral Economics

    How to increase charitable donations

    1. Gilbert Chin

    Charities could raise more money from more people if they were to announce that a startup grant had been used to defray overhead expenses. Gneezy et al. told 40,000 potential donors that an initial donation (half of the target amount) would be used as seed money, as a source of matching funds, or for covering administrative and fundraising costs. When the money was assigned to cover administration, twice as many people made donations.

    Science, this issue p. 632

  9. Nanomedicine

    Nanoparticles for molecular cancer imaging

    1. MLF

    Tiny particles can be coated with antibodies or peptides to target a molecule specific to cancer, improving diagnostic accuracy and patient stratification. Yet these decorated nanoparticles have been slow in making it to clinical trials. Now, Phillips et al. describe the translation of ultrasmall (<10 nm) inorganic nanoparticles, called “C dots,” from animals to patients. The nanoparticles were not toxic in a small group of five patients with metastatic melanoma and were excreted intact via the kidneys and bladder. In contrast, larger or uncoated particles often get lodged in the liver. Many more studies in patients will be needed to confirm lack of toxicity and to optimize tumor targeting, but now that such ultrasmall nanoparticles can be tested in people, a new era of molecular cancer imaging has begun.

    Sci. Transl. Med. 6, 260ra149 (2014).

  10. Nanomaterials

    Supported nanoparticles make the reaction faster

    1. Phil Szuromi

    Several techniques now allow surface structures used as catalysts to be probed during exposure to reactive gases, as opposed to under vacuum conditions. Divins et al. used near-ambient-pressure x-ray photoelectron spectroscopy to compare the effect of reaction gases on unsupported palladium-rhodium nanoparticles versus ones on a reducible cerium oxide support. For the reaction of ethanol with steam to produce hydrogen, the supported nanoparticles were more reactive and less prone to reduction and surface rearrangement.

    Science, this issue p. 620

  11. Topological Matter

    A possible sighting of Majorana states

    1. Jelena Stajic

    Nearly 80 years ago, the Italian physicist Ettore Majorana proposed the existence of an unusual type of particle that is its own antiparticle, the so-called Majorana fermion. The search for a free Majorana fermion has so far been unsuccessful, but bound Majorana-like collective excitations may exist in certain exotic superconductors. Nadj-Perge et al. created such a topological superconductor by depositing iron atoms onto the surface of superconducting lead, forming atomic chains (see the Perspective by Lee). They then used a scanning tunneling microscope to observe enhanced conductance at the ends of these chains at zero energy, where theory predicts Majorana states should appear.

    Science, this issue p. 602; see also p. 547

  12. Conservation

    How to achieve win-win outcomes for biodiversity

    1. Julia Fahrenkamp-Uppenbrink

    Ecosystems serve many functions, such as helping to guard against flooding or ensuring pollination by wild bees. Can efforts to conserve biodiversity rely on the economic benefits from such “ecosystem services”? In a Perspective, Adams argues that win-win outcomes are possible where economic and conservation benefits align. He cautions, however, that the ecosystem service concept is not a conservation measure in itself and that numerous conditions must be met for ecosystem service values to favor conservation.

    Science, this issue p. 549

  13. Membrane Trafficking

    You've got to pick a Golgi tether or two

    1. Stella M. Hurtley

    The inside of the cell contains a large variety of different membrane transport vesicles, each of which needs to find and fuse with its correct target destination. The detailed mechanism specifying which vesicle can fuse with which target membrane has been the subject of an enormous amount of research. An additional layer of specificity in intracellular membrane trafficking across the Golgi complex is thought to involve particular membrane “tethers.” However, the importance of these tethers has been unclear. Wong and Munro used a clever trick to reveal how specific tethers can indeed ensure correct vesicle destination. Tether proteins experimentally expressed on mitochondria hijacked different transport vesicles and diverted them from their normal destination to the mitochondria.

    Science, this issue 10.1126/science.1256898

  14. Gene Regulation

    Repressing the right (and not the wrong) mRNA

    1. Guy Riddihough

    MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression by targeting a repressor complex to specific messenger RNAs (mRNAs). Schirle et al. determined structures of a miRNA bound to both the central component of the repressor complex, the protein Argonaute-2 (Ago2), and a target mRNA (see the Perspective by Patel). The miRNA in the complex first recognizes a short region of complementary sequence in the mRNA. This initial interaction promotes structural changes that allow the complex to bind additional target sequences. The authors suggest that in the absence of extensive miRNA-mRNA pairing, the repressor complex active site is rendered inactive, preventing repression of nontarget mRNAs.

    Science, this issue p. 608; see also p. 542

  15. Neurodevelopment

    Making dendritic arbors during development

    1. Pamela J. Hines

    Developing axons are known to compete for limiting, target-derived neurotrophins for survival and growth in the peripheral nervous system. Joo et al. suggest that an additional, reciprocal model is involved in the development of dendritic arbors of cerebellar Purkinje cells. Working in mice, the authors show that growing dendrites of Purkinje neurons require presynaptic partner-derived neurotrophins during competitive dendritic growth in the central nervous system.

    Science, this issue p. 626

  16. Chemical Biology

    Epigenetics: It's all about the individual

    1. Paula A. Kiberstis

    The bromodomain and extraterminal domain (BET) proteins are a family of epigenetic regulators that affect transcription through interactions with acetylated chromatin. These proteins have attracted interest as drug targets because of their roles in human diseases, including cancer. Parsing out the biological functions of individual family members is important for drug development but has been challenging because of the proteins' shared structural domains. In a proof-of-concept study, Baud et al. used a chemical genetics strategy to design a highly selective small-molecule probe that inhibits the chromatin binding activity of one family member. Extension of this approach may help elucidate the function of individual BET proteins and prioritize them as drug targets.

    Science, this issue p. 638

  17. Cell Adhesion

    Pulling me apart only makes me stronger

    1. Stella M. Hurtley

    Tension transmitted between neighboring cells can exert profound effects on cell proliferation, differentiation, and tissue organization. Exactly how intercellular mechanical tension is sensed at the molecular level is unknown. One attractive hypothesis is that a linkage between the cell-cell adhesion molecule E-cadherin, its binding partners α- and β-catenin, and actin filaments may act as a tension sensor. However, how this linkage is established at the molecular level is not known. Buckley et al. used optical tweezers to determine how mechanical load influences interactions of the cadherin/catenin complex with single actin filaments. The data support a model in which force shifts the interaction from a force-independent, weakly bound state to a highly force-sensitive, strongly bound state. The findings may explain how cells maintain tissue integrity while still being able to move and change shape.

    Science, this issue 10.1126/science.1254211

  18. Innate Immunity

    Overcoming staph infections is hardwired

    1. Stella M. Hurtley

    Several evolutionarily conserved components of antistaphylococcal immunity have been identified, using Drosophila as a model organism. However, no vertebrate ortholog has been identified for the Toll ligand Spaetzle, which plays a key role in controlling gram-positive infection in flies. Hepburn et al. have now identified NGF-β as a functional equivalent to Spaetzle in vertebrates. NGF-β acts as a paracrine “alarmin” orchestrating macrophage and neutrophil responses to S. aureus infection. People with deleterious mutations in genes encoding NGF-β or its high-affinity receptor TRKA are predisposed to recurrent and severe staph infections. S. aureus proteins selectively trigger macrophage production of NGF-β, which enhances uptake and superoxide-dependent killing of S. aureus, stimulates proinflammatory cytokine production, and promotes neutrophil recruitment. Moreover, TrkA silencing in vivo increases susceptibility to S. aureus. Thus, the NGF-β–TRKA pathway is a critical, evolutionarily conserved component of vertebrate immunity to S. aureus infection.

    Science, this issue p. 641

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