This Week in Science

Science  14 Sep 2012:
Vol. 337, Issue 6100, pp. 1271
  1. Cooling Year-Round

    CREDIT: GOOGLE EARTH

    Ice cores from Greenland show that several abrupt cooling events occurred during the last glacial period and early Holocene—two of the most dramatic being the Younger Dryas [which lasted from around 12.9 to 11.7 thousand years ago (ka)] and 8.2-ka event (which began around 8200 years ago and lasted for ∼150 years). Wintertime temperatures in Greenland during the Younger Dryas seem to have been relatively lower than summertime temperatures although it is not clear if the 8.2-ka event experienced the same pattern of seasonal cooling. Young et al. (p. 1330) report observations of the positions of the leading edge of the Laurentide Ice Sheet and mountain glaciers on Baffin Island during the 8.2-ka event and find that mountain glaciers were larger than their predecessors during the Younger Dryas. It seems that cooling during the 8.2-ka event was more evenly distributed across the seasons than it was during that earlier cold period.

  2. An Eight-Noded Monster

    In superconductors, electrons are bound into pairs, and the exact form of that pairing and the resulting energy gap can vary, depending on the details of the electron-electron interaction and the band structure of the material. The energy gaps of the recently discovered iron-based superconductors exhibit a variety of pairing functions. KFe2As2 has been suggested to have a d-wave gap, similar to cuprate superconductors. Okazaki et al. (p. 1314) use laser-based angle-resolved photoemission spectroscopy (ARPES) to map out the superconducting gap on three Fermi surfaces (FS) of the compound. They find a different gap structure on each, with the middle FS gap vanishing at eight distinct positions (nodes). It appears that the gap respects the tetragonal symmetry of the crystal, indicating (although the details may vary) the all iron-based superconductors have an extended s-wave–symmetric pairing—a finding that will help understanding of unconventional superconductivity.

  3. Killer Eradication

    Rinderpest is the second disease to be eradicated globally after smallpox. Mariner et al. (p. 1309) review the technical and social challenges that were overcome during the course of eradication. Key achievements were the development of a thermostable vaccine, the recruitment of the pastoralists themselves for training and administration of vaccine, and complete vaccination coverage, despite occasionally hazardous environmental and political conditions. Although these achievements offer important lessons for future human and animal health programs, institutional memories are surprisingly short-lived, and it is important to document these lessons for the next eradication campaign.

  4. Visualizing Bond Order

    Bond lengths in conjugated molecules closely reflect individual bond order and are usually determined by diffraction methods. It is valuable to know bond order for rationalizing aromaticity, and reactivity and for chemical structure determination. Gross et al. (p. 1326; see the Perspective by Perez and the cover) differentiated the bond orders in individual molecules in the fullerene C60 and in polyaromatic hydrocarbons by imaging with noncontact atomic force microscopy (AFM). The molecules were adsorbed onto a copper surface, and the AFM tip was decorated with a CO molecule, which was used to measure tip frequency shifts above the bonds and their apparent lengths. Multiple bonds appeared brighter in the images because of stronger Pauli repulsion, and their shorter length was amplified by bending of the CO at the tip apex.

  5. Conquering Rice Sterility

    The hybrid sterility occurring among rice species has long been a puzzle and hampers progress in breeding crops with improved performance and yield characteristics. Yang et al. (p. 1336) have identified three linked genes encoding a killer, a partner, and a protector protein. The killer and partner work together to kill female gametes not carrying the functional protector, resulting in preferential transmission of gametes carrying the functional protector, which also causes segregation distortion in the progeny. This explanation for how reproductive isolation is maintained among species of rice, and perhaps other organisms, also offers approaches for boosting yields by intersubspecific heterosis.

  6. Fluorine's Smooth Introduction

    CREDIT: LIU ET AL.

    Carbon-fluorine bonds are emerging as increasingly versatile constituents of drugs, agrochemicals, and positron emission tomography tracers. Elemental F2 gas is in principle an efficient reagent for their preparation, but its extreme reactivity requires special handling precautions. Substantial research has therefore focused on promoting selective reactivity of more conveniently handled fluoride ion salts. Liu et al. (p. 1322) present a manganese catalyst that transfers fluoride to a range of hydrocarbons in conjunction with a hypervalent iodine-based oxidant. Mechanistic studies implicate a manganese difluoride intermediate that reacts with alkyl radicals generated by a preceding manganese oxo.

  7. Infectious Phenotype

    The pathogenic yeast Candida albicans needs to adopt a filamentous form to invade tissues. The distantly related yeast species Saccharomyces cerevisiae also takes on a filamentous form for nutrient foraging. Comparing genome-wide deletion libraries between the two species, Ryan et al. (p. 1353) identified genes involved in three different filamentous yeast phenotypes and found unique genes for each of these phenotypes. However, in addition, core genes, including a previously unknown conserved regulator, appear to have homologous roles in regulating filamentous growth in these distantly related yeast species.

  8. Dissecting SNARE Zippering

    The SNARE complex is critical for vesicle fusion, notably during release of neurotransmitters at synapses. Understanding the biophysics of SNARE assembly has been the object of several structural studies, and yet much remains to be understood about the mechanisms. Now, Gao et al. (p. 1340, published online 16 August; see the Perspective by Rizo) describe the results of cell-free experiments using optical tweezers to elucidate assembly and disassembly of the SNARE complex. Direct observations of SNARE intermediates revealed multiple steps of the assembly process, along with the associated energetics and kinetics. Applying forces similar to those occurring during fusion, an intermediate was stabilized, and the derived mechanism indicates how neurotransmitter release may be regulated.

  9. Influenza Antibodies, Part B

    CREDIT: DREYFUS ET AL.
    CREDIT: DREYFUS ET AL.

    With its ability to reassort in animal hosts like pigs and birds, and to cause pandemics, influenza A viruses are often in the spotlight. However, a substantial portion of the annual flu burden is also the result of influenza B virus, which is a single influenza type that is characterized by two antigenically and genetically distinct lineages. Dreyfus et al. (p. 1343, published online 9 August) identify three monoclonal human antibodies that are able to protect against lethal infection with both lineages of influenza B virus in mice. Two antibodies, which bind to distinct regions of the viral hemagluttinin (HA) molecule, neutralize multiple strains from both lineages of influenza B virus, whereas the third antibody binds to the stem region of HA and is able to neutralize both influenza A and B strains. The structural data from these antibodies bound to HA, together with already known antibodies targeting influenza A, may provide clues for designing a universal vaccine to protect against both influenza virus types.

  10. A Critical Period for Glia

    The brain develops in fits and starts—while one system is completed, another system may still be under construction. Such transient states are known as critical periods, and during these specific aspects of brain development may become more sensitive to outside agents than they would be later. Makinodan et al. (p. 1357) observed the effect of environmental conditions on the brains of mice bioengineered to develop fluorescent oligodendrocytes. The mice were exposed to a variety of social conditions during rearing, ranging from isolation to a normal laboratory cage setting, or to settings enriched with extra buddies and a steady rotation of new play toys. The results show that social isolation leaves a developmental trace that persists into adulthood. Specifically, they found that oligodendrocytes, which produce the myelin that insulates neurons, were underdeveloped, suggesting that there may be a critical period that governs development of these glial oligodendrocyte cells.

  11. Intergenerational Transposable Shutdown

    Transposable elements (TEs) are a potential threat, especially to the germline genome. In many eukaryotes, TEs are shut down by DNA methylation and/or small-RNA–mediated silencing. Therefore, it seems counterintuitive that results obtained by Ibarra et al. (p. 1360) on Arabidopsis showed that in the cells of this plant's sexual apparatus, many small TEs are demethylated by DEMETER (DME) DNA glycosylase and become activated. But it turns out that activation of the TEs triggers the formation of small-interfering RNAs, which in these experiments were seen to travel from the surrounding cells to the egg. Thus, activation of TEs in the companion cells “immunizes” the gametes via the interfering RNAs that shutdown the TEs in the gametes permanently.

  12. Prethermalization

    When a physical system is subjected to a rapid change of conditions (for example, a gas of atoms is allowed to occupy a volume twice the size of the original container), it quickly achieves a new temperature (thermalizes) through collisions. However, in some quantum systems many conserved variables inhibit thermalization; understanding the phases the systems go through in the slowing process is of great interest to cosmologists and physicists. Gring et al. (p. 1318, published online 31 August) separate an ultracold one-dimensional gas of bosonic atoms into two nearly identical halves, and follow how local differences in phase between the halves evolve in time by examining their interference. Initially, the local phases are almost identical, but a rapid decoherence ensues, followed by a very slow further decay. The authors analyze the relative state reached after the initial fast decay and find that it can be described by an equilibrium function with an effective temperature several times less than the initial temperature. Because this cannot be the final state of the system, the authors term the initial process prethermalization.

  13. It's the Pits

    Cellular shape is tied to the cytoskeleton, with specialized regions of the plasma membrane attracting or repelling microtubules, a process mediated by the microtubule binding protein MIDD1. In plants, individual xylem cells are peppered with open pits that facilitate fluid transport and so Oda and Fukuda (p. 1333) studied ROP “Rho family guanosine triphosphatases of plants” proteins from xylem cells to investigate how pits develop. Formation of the pits seems to depend on MIDD1 to destabilize the microtubules at that point. A cascade of ROP proteins establishes the point at which MIDD1 functions, and reverse inhibition of one of the ROP proteins keeps the pit formation focused on a point.

  14. Dynamic Assembly

    Structural characterization of protein complexes has yielded significant insight into biological function; however, most structural techniques require stable, homogenous samples. This presents a challenge in characterizing transient signaling complexes. Herzog et al. (p. 1348) used chemical cross-linking and mass spectroscopy (XL-MS) to characterize the modular and dynamic interaction network involving phosphatase 2A (PP2A), which interacts with tens of regulatory and adaptor proteins in diverse signaling pathways. They found 176 interprotein and 569 intraprotein distance restraints that delineated the topology of the network. The study establishes the importance of XL-MS in the suite of structural methods used to characterize dynamic assemblies.

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