This Week in Science

Science  18 Jan 2013:
Vol. 339, Issue 6117, pp. 249
  1. All Together Now

    CREDIT: NICOLAS LECOMTE/NORWEGIAN POLAR INSTITUTE

    Environmental drivers, such as extreme weather events, impact population dynamics and can synchronize such dynamics across populations within a species. Given that many species depend on similar resources, such events might also be expected to synchronize dynamics across species, but the complexity of multispecies communities makes it difficult to reveal potential drivers in common. Hansen et al. (p. 313) took advantage of the simplicity of the year-round community on the high-arctic island of Spitsbergen to test for the presence of synchrony. Population fluctuations were synchronized across the three herbivore species (Svalbard reindeer, Svalbard rock ptarmigan, and sibling vole) and the single resident predator, the arctic fox, was in lagged synchrony. The driver of these fluctuations appears to be extreme winter rain-on-snow events that reduce the availability of winter forage due to ice cover.

  2. Putting a C in Cytochrome

    Cytochrome P450 enzymes oxidize hydrocarbons using a highly reactive iron oxo intermediate. Much research has focused on tuning the protein structure to broaden the range of hydrocarbons that can be functionalized. Coelho et al. (p. 307, published online 20 December; see the Perspective by Narayan and Sherman) substituted a carbene source for the oxygen to make a P450 mutant a cyclopropanation catalyst whereby a carbon fragment is transferred in place of oxygen. Though carbene activation by iron is chemically analogous to the native oxygen activation pathway, the overall reaction is completely different from any known enzymatic transformation.

  3. Wet Mercury

    Radar observations of Mercury's poles in the 1990s revealed regions of high backscatter that were interpreted as indicative of thick deposits of water ice; however, other explanations have also been proposed (see the Perspective by Lucey). MESSENGER neutron data reported by Lawrence et al. (p. 292, published online 29 November) in conjunction with thermal modeling by Paige et al. (p. 300, published online 29 November) now confirm that the primary component of radar-reflective material at Mercury's north pole is water ice. Neumann et al. (p. 296, published online 29 November) analyzed surface reflectance measurements from the Mercury Laser Altimeter onboard MESSENGER and found that while some areas of high radar backscatter coincide with optically bright regions, consistent with water ice exposed at the surface, some radar-reflective areas correlate with optically dark regions, indicative of organic sublimation lag deposits overlying the ice. Dark areas that fall outside regions of high radio backscatter suggest that water ice was once more widespread.

  4. A Well-Defined Path

    Although chemokines have long been thought to direct immune cell movements within tissues, a formal in vivo demonstration and detailed understanding are lacking. By tracking dendritic cell movements in the ears of mice, Weber et al. (p. 328) were able to provide both. Endogenous gradients of the chemokine CCL21 were observed in ear tissue and, at distances of up 90 µm, dendritic cells were able to use these gradients to migrate directionally toward lymphatic vessels. The CCL21 gradient was immobilized on heparan sulfates and disruption of the gradient inhibited dendritic cell migration.

  5. Defeat, Distress, and Glucocorticoids

    Understanding how individuals control emotions and cope with stressful events is a major clinical concern and of importance for the treatment of psychiatric illnesses (see the Perspective by McEwen). Barik et al. (p. 332) discovered that aggressive defeat stress in mice caused glucocortioid release and increased activity in the dopamine system. Deleting the glucocorticoid receptors in dopaminoceptive neurons completely prevented the social avoidance that usually follows aggressive defeat. How the combination of genetic factors and environmental stressors during adolescence determines adult behavior and how their disturbance results in neuropsychiatric disorders is poorly understood. Niwa et al. (p. 335) found that isolation stress during adolescence, which does not cause any long-lasting changes in wild-type mice, induced significant neurochemical and behavioral alterations in mutant mice expressing a dominant-negative variant of the disrupted in schizophrenia 1 gene under the control of the prion protein promoter. These deficits could be reversed by a glucocorticoid receptor antagonist.

  6. Compressed Sampling

    CREDIT: HUNT ET AL.

    It is often said that a picture is worth a thousand words. But images often contain a lot of redundant information—effectively creating huge data files of meaningless information. While algorithms can compress the size of a file without loss of information, such processing is done after the picture has been taken. Hunt et al. (p. 310) used a metamaterial sensor to compress the sampled scene directly, obviating the need for postprocessing. Tuning the response of the metamaterial allowed imaging of a scene with a 40:1 compression ratio, which may mean that finding that needle in a haystack may be much easier using a metamaterial camera.

  7. A Shift in Cancer's Inflammatory Balance

    One of the many factors that contribute to the initiation and progression of cancer is inflammation. Inflammation can support tumor development, both directly and indirectly, and tumors can promote a chronic inflammatory environment that results in immunosuppression, which benefits the tumor. Coussens et al. (p. 286) review the components of the immune system that contribute to the chronic inflammation seen in tumors. Potential therapies might shift this inflammatory environment toward one more characteristic of an acute, resolving inflammation, similar to what is observed during a pathogenic infection. Such a shift would relieve immunosuppression and drive antitumor immunity that, when combined with other therapies, may ultimately result in tumor cell clearance.

  8. Bicyclic Bridge to Improvement

    Polymers of intrinsic microporosity are a recently developed class of contorted rigid glassy ladderlike polymers having very high free volume (open internal spaces). The intrinsic porosity of these materials has made them of interest for ultrahigh permeability gas separation membranes. However, while the polymers show good gas permeability, they have only moderate gas selectivity. Carta et al. (p. 303; see the Perspective by Guiver and Lee) hypothesized that if they could replace the dioxin-like rings in their polymers with stiffer bridged bicyclic rings, they could improve the membrane properties of the polymer. By exploiting reactions connected to the formation of Tröger's base to form the multiple covalent bonds needed to make the bicyclic rings, the resulting polymers showed significantly improved selectivity and permeability.

  9. The Scale of Plant Invasions

    Many studies have shown large effects of invasive species on native species diversity, but at the same time, invaders (especially plants) have rarely been implicated in the extinctions of native species. Powell et al. (p. 316) noted that studies showing large effects have tended to be focused on smaller spatial scales, while those showing smaller effects have usually been on broader spatial scales. For such a scale-dependent effect to occur, invasive species must alter the shape of the species-area relationship (SAR). Comparing the differences in SARs with invaded and uninvaded communities of plants in three different ecosystem types in the United States revealed smaller effects of invasive species on biodiversity at increasingly broader spatial scales. Empirical data and simulations suggested that the observed patterns result from disproportionately greater influences of invasive species on common relative to rare species that result from a combination of sampling effects and differential responses to invasion.

  10. Recognizing a Stem-Loop Structure

    Metazoan histone messenger RNAs (mRNAs) have a conserved stem-loop (SL) structure at their 3′-end. The stem-loop is bound by the stem-loop binding protein (SLBP), which is required for histone mRNA 3′-end processing, export, stability, and translation. The 3′-5′ exonuclease 3′hExo also binds the SL and trims off three nucleotides. Tan et al. (p. 318) determined the high-resolution structure of the SL bound by the RNA-binding domain (RBD) of human SLBP together with human 3′hExo. The conformation of the loop differed substantially from other RNA tetraloops and the SLBP RBD may function as a ruler that can measure the length of the stem. Although the SLBP directly recognizes the guanine base of the second nucleotide of the stem, it appears that SLBP and 3′hExo recognize the unique shape of the SL.

  11. Anonymity Compromised

    The balance between maintaining individual privacy and sharing genomic information for research purposes has been a topic of considerable controversy. Gymrek et al. (p. 321; see the Policy Forum by Rodriguez et al.) demonstrate that the anonymity of participants (and their families) can be compromised by analyzing Y-chromosome sequences from public genetic genealogy Web sites that contain (sometimes distant) relatives with the same surname. Short tandem repeats (STRs) on the Y chromosome of a target individual (whose sequence was freely available and identified in GenBank) were compared with information in public genealogy Web sites to determine the shortest time to the most recent common ancestor and find the most likely surname, which, when combined with age and state of residency identified the individual. When STRs from 911 individuals were used as the starting points, the analysis projected a success rate of 12% within the U.S. male population with Caucasian ancestry. Further analysis of detailed pedigrees from one collection revealed that families of individuals whose genomes are in public repositories could be identified with high probability.

  12. Signaling Differentiation

    The six-transmembrane protein GDE2 promotes differentiation through extracellular glycerophosphodiester phosphodiesterase (GDPD) activity and induces neuronal differentiation through inhibition of Notch signaling—a major pathway that maintains stem or progenitor cell states and is implicated in multiple cancers. How then, does GDPD activity inhibit Notch signaling, given that GDPD enzymes are known to metabolize glycerophosphodiesters into glycerol-3-phosphate and corresponding alcohols? Park et al. (p. 324) show that the six-transmembrane GDPDs such as GDE2, do not function as conventional GDPD enzymes, but instead cleave the glycosylphosphatidylinositol (GPI) anchors of GPI-anchored proteins. GDE2 GDPD activity cleaves and inactivates the GPI-anchored protein RECK, which normally acts to prevent shedding of the Notch ligand Delta. Accordingly, RECK inactivation stimulates Delta shedding leading to Notch inactivation in progenitors and the initiation of cellular differentiation.

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