This Week in Science

Science  17 Jun 2011:
Vol. 332, Issue 6036, pp. 1355
  1. Glassy Crystals

    Glassy materials have been thought to possess little or no structure order, but recent experiments have confirmed ordering over short- and medium-length scales. When mixed in a 3:1 ratio, cerium and aluminum will form a glass because of the severe mismatch in size and electronegativity of the atoms. Zeng et al. (p. 1404) studied this metallic glass and found no evidence of long-range structural order. However, when the material was forced to crystallize at high pressure, a large single crystal was formed, which suggests that the glassy material must have had an undetected form of long-range order.

  2. A Measure of Separation

    Under the right conditions, the optical response of two particles can be used to provide a measure of the separation between the particles. Because such an optical ruler is inherently one-dimensional, it cannot provide three-dimensional information about complex changes to the local structure or spatial environment, which limits real-world applications. Liu et al. (p. 1407; see the Perspective by Sönnichsen) designed and fabricated a nanostructure, the optical response of which can be used to determine spatial distance in three dimensions. The technique should be useful for monitoring structural changes in biological samples or chemical reactions.

  3. Iron Superconductor Symmetry

    CREDIT: SONG ET AL.

    The mechanism and symmetry of electron pairing are central issues in superconductivity research. Despite intense investigation, the pairing symmetry in the recently discovered iron-based superconductors remains elusive. Song et al. (p. 1410) studied the simplest example, iron selenide (FeSe), by scanning tunneling microscopy and spectroscopy. A gap function and evidence of nodal lines was observed in high-quality stoichiometric and superconducting FeSe single crystalline films. When inhomogeneities were created (for example, by using magnetic fields), a twofold symmetry in the quasiparticle-excited states of the superconducting state was observed, which could be accounted for in terms of orbital ordering effects.

  4. Deep Impact on Hartley 2

    CREDIT: NASA/JPL/UMD/LINDLER

    After carrying out an impact experiment on comet 9P/Tempel 1 in 2005, the Deep Impact satellite flew by comet Hartley 2 in November 2010 as part of its extended mission. The goals were to understand the diversity of morphology and topography of cometary nuclei by going to a comet with a much smaller nucleus than those of the comets previously visited by spacecraft. The nucleus of Hartley 2 is the fifth to be observed up close by a spacecraft. A'Hearn et al. (p. 1396) provide an overview of the findings from this encounter. Hartley 2 is an unusually active comet, and produces more water per unit time than possible by simple sublimation from its surface. It appears that the release of CO2 and other volatiles, which “drag” ice out of the comet's nucleus, are the primary drivers of this activity.

  5. Saturn's Early Storm

    Every saturnian year (∼ every 30 Earth years) a storm erupts in the atmosphere of Saturn. Normally, it occurs after the summer solstice, but in December 2010 a storm was detected in Saturn's northern springtime hemisphere. This storm is the largest seen on Saturn to date and occurred about 20 years earlier than expected. Fletcher et al. (p. 1413, published online 19 May) determined its vertical structure using thermal-infrared images from the Very Large Telescope in Chile and infrared spectroscopy from the Cassini spacecraft. Atmospheric motions associated with the storm generated thermal anomalies that modified Saturn's atmospheric circulation. The storm has altered the atmospheric structure and composition from the deep atmosphere to the upper troposphere and may affect Saturn's northern hemisphere for years to come.

  6. The Quake That Rocked Japan

    The 11 March 2011 magnitude 9.0 Tohoku-Oki megathrust earthquake just off the Eastern coast of Japan was one of the largest earthquakes in recorded history. Japan's considerable investment in seismic and geodetic networks allowed for the collection of rapid and reliable data on the mechanics of the earthquake and the devastating tsunami that followed (see the Perspective by Heki). Sato et al. (p. 1395, published online 19 May) describe the huge displacements from ocean bottom transponders—previously placed directly above the earthquake's hypocenter—communicating with Global Positioning System (GPS) receivers aboard a ship. Simons et al. (p. 1421, published online 19 May) used land-based GPS receivers and tsunami gauge measurements to model the kinematics and extent of the earthquake, comparing it to past earthquakes in Japan and elsewhere. Finally, Ide et al. (p. 1426, published online 19 May) used finite-source imaging to model the evolution of the earthquake's rupture that revealed a strong depth dependence in both slip and seismic energy. These initial results provide fundamental insights into the behavior of rare, very large earthquakes that may aid in preparation and early warning efforts for future tsunamis following subduction zone earthquakes.

  7. Ramping Up AMPK

    The adenosine monophosphate (AMP)–activated protein kinase (AMPK) senses depletion of energy stores (the accumulation of AMP) and activates appropriate metabolic responses to control cellular and organismal energy balance. But its name does not tell the whole story. The energy status of a cell is reflected in the “adenylate charge” or ratio of the concentration of adenosine triphosphate (ATP) to those of adenosine diphosphate (ADP) and AMP. Oakhill et al. (p. 1433; see the Perspective by Bland and Birnbaum) show that activity of AMPK is also highly sensitive to the concentration of ADP, as well as that of AMP. Like AMP, ADP bound to AMPK and promoted its activating phosphorylation by other protein kinases. ADP also inhibited dephosphorylation of AMPK, which inactivates the kinase. Because AMP can be rapidly deaminated in cells, sensing of ADP, as well as AMP, may be critical for the control of AMPK, which regulates a broad spectrum of biological responses from metabolism and metabolic diseases to the growth of cancer.

  8. Molecular Clockwork

    Although the basic transcriptional feedback loop that makes up the mammalian clock has been described, fundamental pieces of the clock's workings continue to be discovered. The oscillator depends on a transcriptional mechanism in which the transcription factor CLOCK-BMAL enhances transcription of its own inhibitor, PER. Duong et al. (p. 1436) clarified the biochemical mechanism by which PER inhibits its own transcription by purifying proteins that associated with PER. The protein PSF, a transcriptional corepressor protein was identified, which helped to recruit another protein, the SIN3–histone deacetylase complex (SIN3-HDAC) to the Per1 promoter. The resulting histone deacetylation inhibits the transcription promoted by CLOCK-BMAL1. Depleting cells of PSF or SIN3-HDAC shortened the length of the circadian period, consistent with their roles as part of the fundamental clock mechanism.

  9. Coordinating Autophagy and Lysosome Regulation

    CREDIT: SETTEMBRE ET AL.

    Autophagy involves the degradation of intracellular proteins and organelles and is often promoted as a response to starvation that allows for the reuse of constituent amino acids. How do cells coordinate protein degradation and recycling processes? Settembre et al. (p. 1429, published online 26 May; see the Perspective by Cuervo) identified a biological mechanism that regulates, in a coordinated fashion, the function of two cellular organelles, autophagosomes and lysosomes, whose synergy is required for an efficient autophagic process. During starvation, cells activated a transcriptional program that controls all major steps of the autophagic pathway, including autophagosome formation, autophagosome-lysosome fusion, and substrate degradation. The transcription factor EB (TFEB), a master gene for lysosomal biogenesis, coordinated this program by driving expression of both autophagy and lysosomal genes. Furthermore, TFEB activity was regulated by the mitogen-activated protein (MAP) kinase ERK2, which implicates the kinase signaling pathway in the control of autophagy.

  10. An End to Plant Defenses

    When defending against bacterial pathogens, plants make use of an innate immunity system that detects molecular signatures of bacteria. The plant defense response depends on receptors including the pattern recognition receptor FLAGELLIN-SENSING 2 (FLS2) and initiates a cascade of responses that deflect bacterial attack. However, always being on the defensive does not work out well for plants: Once activated, defense systems need to be turned off. Studying Arabidopsis, Lu et al. (p. 1439; see the Perspective by O'Neill) have now analyzed this shut-down protocol. Once FLS2 is activated by binding to bacterial flagellin and to coreceptors, it becomes the target for a ubiquitination cascade that results in its degradation.

  11. Keeping an Eye On Your Enemy

    During binocular rivalry, different images presented simultaneously to two eyes alternate in consciousness so that, for example, we first see a face shown to the left eye and then a house shown to the right eye. The duration with which one stimulus is perceived is affected by a number of factors, such as its relative brightness, and is generally not under conscious control. Anderson et al. (p. 1446, published online 19 May) demonstrate that negative social information about a person increases the duration of “seeing” that person's face in a binocular rivalry protocol; other kinds of social information and negative information did not display this effect, illustrating the privileged link between human social evaluations and vision.

  12. Plant Cell Wall Development

    A glycoprotein network helps make up the plant cell wall. The core proteins include extensins, arabinogalactan-proteins, and proline-rich proteins. In order to acquire their carbohydrate side chains, the proteins must first be hydroxylated on serial proline residues. Velasquez et al. (p. 1401; see the Perspective by Mohnen and Tierney) analyzed the developmental and biochemical phenotypes when this hydroxylation and glycosylation pathway is disrupted in Arabidopsis. With these pathways disrupted, root hair cells could not grow as long and, in some genetic settings, were not initiated as often. The findings elucidate the biochemical interactions required for self-assembly of the plant cell wall, which is crucial in the normal development of plant cells.

  13. Chile's Movements Tracked from Above

    Ground-based seismometers are integral components to earthquake monitoring systems across the globe, but satellite-based monitoring systems provide complementary information. In February 2010, Central Chile ruptured along the Concepción-Constitución gap during a magnitude 8.8 earthquake, and stretch of the fault contained a dense network of seismometers and Global Positioning System (GPS) receiver stations. The continuous GPS data, as described by Vigny et al. (p. 1417, published online 28 April; see the Perspective by Heki) provide independent and, in some cases, higher-resolution information about the rupture process when compared to data collected on the ground. For example, the location of the earthquake's epicenter differed by 40 kilometers from ground-based data. Furthermore, the GPS data revealed that the rupture propagated bilaterally at speeds of up to 3.1 kilometers per second.

  14. Sirtuin 6 and DNA Repair

    The mammalian silent chromatin regulator family of proteins (sirtuins, or SIRT) are involved in stress response and genome maintenance pathways. They have dual enzymic activities, functioning as both deacetylases and mono-ADP-ribosyltransferases. Mao et al. (p. 1443) show that SIRT6 functions in double-strand-break (DSB) DNA repair, through the homologous recombination and nonhomologous end joining repair pathways. The repair activity is highly stimulated under conditions of stress, when SIRT6 is rapidly recruited to sites of DNA damage. SIRT6 then associates with, and mono-ADP-ribosylates, the poly-ADP ribose polymerase 1 (PARP1), thereby activating PARP1 to poly-ADP-ribosylate other break-associated proteins, facilitating recruitment of additional DNA repair factors. Because PARP1 is involved in both base excision repair and DSB repair through PARP1, SIRT6 integrates DNA repair and stress signaling pathways.

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