This Week in Science

Science  21 Jun 2013:
Vol. 340, Issue 6139, pp. 1373
  1. Watching Organic Reactions

    CREDIT: ALEXANDER RISS AND SEBASTIAN WICKENBURG

    Single-molecule studies can overcome the difficulty of inferring the various outcomes of reactions in ensemble measurements. De Oteyza et al. (p. 1434, published online 30 May; see the Perspective by Giessibl) used a variation of noncontact atomic force microscopy in which the imaging tip was derivatized with a single CO molecule to obtain subnanometer-resolution images of conjugated organic molecules undergoing reaction on a silver surface. Different thermally induced cyclization reactions of oligo- (phenylene-1,2-ethynylenes) were observed.

  2. Furthering Exfoliation

    In addition to graphene, a wide range of layered materials, including oxides, chalcogenides, and clays are of interest because of their optical, electrical, and mechanical properties. While many methods can be used to cleave layered sheets from the bulk material, they are difficult to scale up. Liquid exfoliation routes may hold the best promise for making materials in large quantities. Nicolosi et al. (p. 1226419) review progress in developing exfoliation routes, both aqueous and nonaqueous for a wide range of starting materials.

  3. From Russia with Lovely Data

    Climate and the atmospheric concentration of CO2 are closely linked. Brigham-Grette et al. (p. 1421, published online 9 May) present data from Lake El'gygytgyn, in northeast Arctic Russia, that shows how climate varied between 3.6 and 2.2 million years ago, an important interval in the global cooling trend that accelerated rapidly at the end of the Miocene. Summer temperatures were about 10°C warmer than today, even though the concentration of atmospheric CO2 was similar.

  4. Coherence in Photosynthesis

    It is unclear how energy absorbed by pigments in antenna proteins is transferred to the central site of chemical catalysis during photosynthesis. Hildner et al. (p. 1448) observed coherence—prolonged persistence of a quantum mechanical phase relationship—at the single-molecule level in light-harvesting complexes from purple bacteria. The results bolster conclusions from past ensemble measurements that coherence plays a pivotal role in photosynthetic energy transfer. Hayes et al. (p. 1431, published online 18 April) examined a series of small molecules comprised of bridged chromophores that also manifest prolonged coherence.

  5. GPR15 Gets Tregs to Guard the Gut

    The large intestine is the site that is typically most inflamed in Crohn's disease and ulcerative colitis, which are thought to result when the immune system is not able to keep the peace with trillions of resident gut microbes. The immune system does this by recruiting specific cell populations, like regulatory T cells (Tregs), to the gut. Kim et al. (p. 1456, published online 9 May) now suggest that the orphan G protein–coupled receptor GPR15 is expressed by Tregs and required for Treg homing to the large intestine in mice.

  6. Influencing Influenza

    Currently, there is anxiety that the avian H5N1 influenza virus will reassort with the highly transmissible and epidemic H1N1 subtype to trigger a virulent human pandemic. Y. Zhang et al. (p. 1459, published online 2 May) used reverse genetics to make all possible reassortants between a virulent bird H5N1 with genes from a human pandemic H1N1. Virulence was tested in mice and transmissibility was tested between guinea pigs, which have both avian- and human-like airway influenza virus receptors. To assess what is happening to the receptor-ligand interactions as a result of these mutations, W. Zhang et al. (p. 1463, published online 2 May) probed the structure of both wild-type and mutant hemagglutinin of H5 in complex with analogs of the avian and human receptor types. Certain mutations in the receptor-binding site changed binding affinity.

  7. The Equations Underlying Cities

    Cities are complex systems of which functioning depends upon many social, economic, and environmental factors. Bettencourt (p. 1438; see the cover; see the Perspective by Batty) developed a theory to explain the quantitative relationships observed between various aspects of cities and population size or land area.

  8. Genetic College

    Many genomic elements in humans are associated with behavior, including educational attainment. In a genome-wide association study including more than 100,000 samples, Rietveld et al. (p. 1467, published online 30 May; see the Perspective by Flint and Munafò) looked for genes related to educational attainment in Caucasians. Small genetic effects at three loci appeared to impact educational attainment.

  9. Reconstructing the Human Brain

    CREDIT: AMUNTS ET AL.

    Reference brains have become a standard tool in human brain research. Reference brains presently in the public domain provide a spatial framework at the macroscopic level. Amunts et al. (p. 1472) present a high-resolution (20 µm) three-dimensional reconstruction of a human brain. The tool will be freely available to help with interpreting functional neuroimaging studies, fiber tract analyses, and assigning molecular and gene expression data.

  10. Dendritic Pruning

    During metamorphosis, Drosophila sensory neurons eliminate their dendritic trees, but axons and soma remain intact. Kanamori et al. (p. 1475, published online 30 May) demonstrate that compartmentalized calcium transients in dendrites function as the spatiotemporal cue for pruning of unwanted branches. Such a localized calcium signal, induced by a local elevation of branch excitability, activates calcium-dependent proteinases and eventually causes branch death.

  11. Graphene, Gapped and Butterflied

    The remarkable transport properties of graphene, such as the high electron mobility, make it a promising material for electronics. However, unlike semiconductors such as silicon, graphene's electronic structure lacks a band gap, and a transistor made out of graphene would not have an “off” state. Hunt et al. (p. 1427, published online 16 May; see the Perspective by Fuhrer) modulated the electronic properties of graphene by building a heterostructure consisting of a graphene flake resting on hexagonal boron nitride (hBN), which has the same honeycomb structure as graphene, but consists of alternating boron and nitrogen atoms instead of carbons. The natural mismatch between the graphene and hBN lattices led to a moire pattern with a large wavelength, causing the opening of a band gap, the formation of an elusive fractional quantum Hall state, and, at high magnetic fields, a fractal phenomenon in the electronic structure called the Hofstadter butterfly.

  12. Feather Features

    CREDIT: IMAGE IS CREATED BY J. FOLEY WITH PHOTOS FROM J. LEGENDRE, G. BRERETON, NEIL GRASSBAUGH, AND D. AKERS

    Diversification of feather pigment patterns is essential for avian speciation and adaptation. Yet the identity of feather pigment progenitor cells and the cellular and molecular basis for feather pigment pattern formation is poorly understood. Lin et al. (p. 1442, published online 25 April) report that, compared to the localized pigment cell niche in hair, a more dispersed circular topology of the feather pigment progenitor niche loosens spatial constraints and allows for more freedom in patterning possibilities. Multiple cellular mechanisms are co-opted and choreographed in this multidimensional space to create patterns.

  13. Lord of the Ring Canal

    In Drosophila, some cells maintain direct cytoplasmic connections with their siblings by intercellular bridges known as ring canals that arise from mitotic cleavage furrows. In ovarian follicle cells and imaginal discs, McLean and Cooley (p. 1445, published online 23 May) found that ring canals allowed diffusion of cytoplasmic proteins between cells and across mitotic clone boundaries, which may suggest a role in compensating for transcriptional variation between cells.

  14. Parkin Enhanced?

    Inactivation of parkin, an E3 ubiquitin ligase, is responsible for a familial form of Parkinson's disease and may be involved in sporadic forms as well. Trempe et al. (p. 1451, published online 9 May) present the crystal structure of full-length parkin in an autoinhibited configuration. Guided by the structure, mutations were designed that activated parkin both in vitro and in cells. Because parkin is neuroprotective, the structure provides a framework for enhancing parkin function as a therapeutic strategy in Parkinson's disease.

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