This Week in Science

Science  17 Aug 2012:
Vol. 337, Issue 6096, pp. 775
  1. Mechanical Chameleon

    CREDIT: STEPHEN MORIN/HARVARD UNIVERSITY

    A wide range of animals can adapt their color patterns as a means of camouflage or otherwise changing their appearance. This is accomplished through changes in coloration, contrast, patterning, or shape. Morin et al. (p. 828) show at a basic level that some of these features can be added as microfluidic layers attached to mobile, flexible, soft machines. By pumping different fluids through the channels, the robots were able to change their coloration or overall contrast and could thus blend into the background of the surface they were lying upon. Conversely, by pumping through fluids of different temperature, the infrared profile of the robot could be changed without changing its visible coloration.

  2. A State of High Tc Superconductivity

    There are strong indications that high-temperature superconductivity in the cuprates is formed amid competing orders, but only two have been observed unambiguously. The so-called stripe order has been observed in a Lanthanum-based cuprate family and consists of coexisting charge-and-spin modulations and occurs at a characteristic dopant concentration in which the critical temperature Tc has a dip. Now, Ghiringhelli et al. (p. 821, published online 12 July; see the Perspective by Tranquada) have used resonant inelastic x-ray scattering to uncover a related but apparently two-dimensional charge order in the much cleaner YBCO cuprate family. The charge fluctuations were not commensurate with the lattice and did not originate in the characteristic oxygen chains of YBCO. The order appeared only in a narrow interval of dopant concentrations and competed with superconductivity, which provides a natural explanation for a plateau in Tc observed in the same range.

  3. Amorphous Crystals

    One usually thinks of a crystal as containing atoms, molecules, or other ordered units arranged in a periodic fashion to make a larger structure. L. Wang et al. (p. 825; see the Perspective by D. Wang and Fernandez-Martinez) compressed a solvate of xylene in C60 (fullerene) to very high pressures at room temperature, which caused the fullerene molecules to collapse and form amorphous clusters but with each cluster retaining its position in the original crystal lattice because of the interaction with the intercalated xylene molecules. Thus, a crystal was formed from amorphous constituents. On heating at atmospheric pressure, the xylene disappeared and the sample became completely amorphous.

  4. Water In, Ozone Out

    The danger of stratospheric ozone loss burst into public awareness in the 1980s, when the Antarctic ozone hole was discovered and described. Since then, the specter of ozone depletion in other locations, notably the Arctic, has been identified. Ozone loss is not confined to high latitudes, however, nor is it only the result of the addition of anthropogenic compounds containing chlorine and bromine in the stratosphere, as Anderson et al. (p. 835, published online 26 July; see the Perspective by Ravishankara) now demonstrate. Data from the atmosphere above the continental United States revealed that convective injection of water vapor into the stratosphere affects the free radical chemistry involving the (mostly anthropogenic) chlorine and bromine, thus accelerating ozone loss. This process could become important in the stratospheric ozone budget if the frequency and intensity of these water-injection events, which are most common in the summer, increase as a result of global warming.

  5. Synchronize Your Watches

    In mammals, a central circadian clock in the suprachiasmatic nucleus (SCN) of the brain coordinates circadian changes in physiology and synchronizes other peripheral clocks. T. A. Wang et al. (p. 839, published online 2 August; see the Perspective by Belle and Piggins) report that daily changes in electrical activity of neurons in the SCN are coupled to the circadian clock through changes in metabolism—in particular, changes in reduction and oxidation state within the cell that reflect daily cycles of metabolism. The conductance of two kinds of potassium channels in the neurons was sensitive to redox state, thus linking the membrane potential and firing rate of the neurons to cycles of metabolic activity.

  6. Ditching Invading DNA

    CREDIT: ADAM STEINBERG/ARTFORSCIENCE.COM

    Bacteria and archaea protect themselves from invasive foreign nucleic acids through an RNA-mediated adaptive immune system called CRISPR (clustered regularly interspaced short palindromic repeats)/CRISPR-associated (Cas). Jinek et al. (p. 816, published online 28 June; see the Perspective by Brouns) found that for the type II CRISPR/Cas system, the CRISPR RNA (crRNA) as well as the trans-activating crRNA—which is known to be involved in the pre-crRNA processing—were both required to direct the Cas9 endonuclease to cleave the invading target DNA. Furthermore, engineered RNA molecules were able to program the Cas9 endonuclease to cleave specific DNA sequences to generate double-stranded DNA breaks.

  7. Take Another Cap

    Selective cytosolic protein degradation is mediated primarily by the proteasome, which is comprised of a core peptidase and a regulatory cap. Current dogma holds that the 20S core peptidase of the proteasome functions exclusively with the 19S regulatory particle in eukaryotes, with PAN in archaea, and with Mpa in mycobacteria. Barthelme and Sauer (p. 843, published online 26 July 2012; see the Perspective by Matouschek and Finley) now suggest that another type of proteasome can assemble in archaea consisting of the double-ring AAA+ protein, Cdc48, in complex with the 20S core protease.

  8. Biology Made Me Do It

    Introducing evidence of a biological basis of dysfunctional behavior might induce a judge to impose a lighter sentence upon defendants on the grounds that their innate biology lessened personal responsibility for their actions. On the other hand, it might also plausibly lead to a longer sentence on the grounds that this biological predisposition would imply a higher risk of future criminal acts. Aspinwall et al. (p. 846) analyzed sentencing opinions from a nationwide group of judges in the United States of a scenario closely modeled on a real-life case. Varying two factors—whether evidence for a biological basis was presented and whether it was offered by the defense or by the prosecution—revealed an overall lessening of sentences when biology was invoked.

  9. Cleaning Diesel Exhaust

    CREDIT: W. WANG ET AL.

    One strategy for removing pollutants from diesel engine exhaust is to trap the unburned carbon soot and then to combust the soot with the NO2 that is generated from NO; the two pollutants are then converted to N2 and CO2. Diesel exhaust is relatively cold, compared to gasoline engine exhaust, and conversion of NO to NO2 has required the use of platinum catalysts. W. Wang et al. (p. 832) now report that a more earth-abundant catalyst, based on Mn-mullite (Sm, Gd)Mn2O5 metal oxides was able to oxidize NO in simulated diesel exhaust at temperatures as low as 75°C. Spectroscopic studies and quantum chemical modeling suggested that Mn-nitrates formed on Mn-Mn dimer sites were the key intermediates responsible for NO2 formation.

  10. How to Make a Place Cell

    Hippocampal place cells have been studied for more than 40 years, yet the mechanisms underlying their remarkable spatial tuning are still not established. Using whole-cell patch-clamp recordings in freely moving rats, Lee et al. (p. 849) changed the baseline membrane potential in hippocampal pyramidal neurons. Place fields arose spontaneously in otherwise silent pyramidal cells after depolarization when the membrane voltage reached a threshold. Place cells in the hippocampus and grid cells in the entorhinal cortex are thought to provide the framework for spatial navigation in an animal. However, it is still unclear how the hexagonal symmetry that is so prominent in grid cells emerges. While recording from the entorhinal cortex and in the pre- and parasubiculum during spatial behavior in the rat, Krupic et al. (p. 853) discovered that many forms of spatial periodicity exist in neurons in these structures. The grid cells seem to reflect a subset of this larger set, generated by self-organized dynamics.

  11. All TOGether Now

    αβ-Tubulin is the polymerizing subunit of microtubules, which are dynamic polymers that have essential roles in cell division and intracellular organization. TOG domains are αβ-tubulin binding modules that occur in the evolutionarily conserved Stu2p/XMAP215 family of proteins and promote microtubule elongation. Ayaz et al. (p. 857) used crystallographic and biochemical experiments to reveal that the TOG1 domain interacts with guanosine triphosphate–bound αβ-tubulin in a conformation-selective manner, binding preferentially to a “curved,” microtubule-incompatible conformation. The binding mode apparently excludes analogous binding of a second TOG domain to the same heterodimer and may help to ensure polarized growth of microtubules.

  12. Truthful Embellishments

    Exaggerated ornaments such as beetle horns, deer antlers, and extreme tail lengths in birds are typically assumed to be subject to sexual selection because they signal the quality of an individual's breeding status—but how? Emlen et al. (p. 860, published online 26 July) present a general mechanistic model for the evolution of exaggerated traits, proposing that sensitivity to the insulin response pathway can explain variation among individuals. The exaggerated size of such ornaments and their increased variability between individuals are a result of sexual selection for traits that are honest signals of the fitness of the individual.

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