This Week in Science

Science  15 Jan 2010:
Vol. 327, Issue 5963, pp. 247
  1. Parasitoid Wasp Genomes

      CREDIT: PETER KOOMEN AND MTHIJIS ZWIER/UNIVERSITY OF GRONINGEN, NETHERLANDS

      Parasitoid wasps, which prey on and reproduce in host insect species, play important roles in plant herbivore interactions, and may provide valuable tools in the biological control of pest species. The Nasonia Genome Working Group (p. 343; see the news story by Pennisi) presents the genome of three very closely related species: Nasonia vitripennis, N. giraulti, and N. longicornis. The findings document rapid evolution between a host and endosymbiont that can cause nuclear-cytoplasmic incompatibilities that may affect speciation.

    1. Adaptive Girdle Loss in Sticklebacks

        How do molecular changes give rise to phenotypic adaptation exemplified by the repeated reduction in the pelvic girdle observed in separate populations of sticklebacks? Now Chan et al. (p. 302, published online 10 December) have identified the specific DNA changes that control this major skeletal adaptation. The key locus controlling pelvic phenotypes mapped to a noncoding regulatory region upstream of the Pituitary homeobox transcription factor 1 gene, which drives a tissue-specific pelvic enhancer. Multiple populations showed independent deletions in this region and enhancer function was inactivated. Reintroduction of the enhancer restored pelvic development in a pelvic-reduced stickleback.

      1. Planetary Midwifery

          Planets form from the materials left behind after a star is formed. Unlike the Sun, most stars are members of binary systems. Mayama et al. (p. 306, published online 19 November) present an infrared image of the protoplanetary disks around a young binary star system taken with the coronagraph mounted on the Subaru Telescope in Hawaii. Each individual disk is clearly visible around its star, and comparison with numerical simulations suggests that there could be gas flow from one disk to the other. The nature of this potential gas flow is important in determining where planets could form in binary systems.

        1. It's the Network

            Numerous reactions of small molecules and ions in the atmosphere take place in the confines of watery aerosols. Relph et al. (p. 308; see the Perspective by Siefermann and Abel) explored the specific influence of a water cluster's geometry on the transformation of solvated nitrosonium (NO+) to nitrous acid (HONO). The reaction involves (O)N–O(H) bond formation with one water molecule, concomitant with proton transfer to additional, surrounding water molecules. Vibrational spectroscopy and theoretical simulations suggest that certain arrangements of the surrounding water network are much more effective than others in accommodating this charge transfer, and thus facilitating the reaction.

          1. Heck of an Alternative

              The Mizoroki-Heck reaction is widely used in organic synthesis to link together unsaturated carbon fragments such as olefins and arenes. However, one of its drawbacks is the need to append a reactive group such as a halogen to one of the reagents beforehand. Wang et al. (p. 315, published online 26 November) present an alternative palladium-catalyzed reaction that links olefins directly to aryl acids. Oxygen added to the reaction medium concurrently oxidizes the aryl C-H bond at the linkage site, eliminating the need for prior halogenation. Introducing amino acid–derived ligands tunes the aryl site at which the reaction takes place, and efficient reactivity can be achieved across a diverse range of substrates.

            1. Measuring Methanogenesis

                After carbon dioxide, methane is the second most important greenhouse gas, and an important species in terms of its role in atmospheric chemistry. The sources and sinks of methane, particularly the natural ones, are too poorly quantified, however, even to explain why the decades-long, steady increase of its concentration in the atmosphere was interrupted between 1999 and 2006. Bloom et al. (p. 322) use a combination of satellite data, which indicate water table depth and surface temperature, and atmospheric methane concentrations to determine the location and strength of methane emissions from wetlands, the largest natural global source. The constraints placed on these sources should help to improve predictions of how climate change will affect wet-land emissions of methane.

              1. Methanol Coupling Catalyzed with Gold

                  CREDIT: WITTSTOCK ET AL.

                  Gold surfaces can be effective catalysts for partial oxidation reactions, in part because lower interaction strengths of molecules absorbed on gold allow products to desorb before further unwanted oxidations occur. One challenge in these reactions is the low rate of formation of reactive atomic surface oxygen. Wittstock et al. (p. 319; see the Perspective by Christensen and Nørskov) created high–surface area gold catalysts by leaching silver from gold-silver alloys. This material proved to be an effective catalyst for partial oxidative coupling of methanol, yielding methyl formate. Residual silver appears to play a key role in activating the dissociation of molecular oxygen.

                1. Predator Avoidance Strategy

                    Selective pressures influencing bird migration can include availability of food, pressure from parasites and pathogens, and predation risk. The importance of the last of these is revealed by McKinnon et al. (p. 326; see the Perspective by Gilg and Yoccoz), who present an experimental analysis of the benefits of long-distance migration for reproduction in arctic-nesting birds. Measurements of a controlled effect of predation risk along a 3350-kilometer north-south gradient across arctic Canada provides evidence that the risk of nest predation decreases with latitude. Thus, birds migrating further north may acquire reproductive benefits in the form of reduced predation risk.

                  1. Targeting Copper Clusters

                      Tetrathiomolybdate (TM) is a copper-depleting agent that has potential in treating copper-dependent diseases. Alvarez et al. (p. 331, published online 26 November) used spectroscopic and structural studies to show that TM inhibits the yeast copper chaperone Atx1 by forming a TM-Cu-ATx1 complex that is stabilized by a sulfur-bridged copper-molybdenum cluster. Cluster formation prevents transfer of copper from the chaperone to target enzymes. The results provide a basis for developing drugs that target metallation pathways.

                    1. To Stall or Not to Stall

                        Recent studies in mammals and Drosophila have shown that RNA polymerase II frequently stalls shortly after initiating messenger RNA synthesis and that this stalling is important for proper expression of genes. Although several protein factors that affect polymerase stalling are known, the role of DNA sequence in this process has remained unclear. Now Nechaev et al. (p. 335, published online 10 December) report that the initially transcribed sequences of many genes contain a signal that works like a stop sign for the elongating polymerase. Expression of genes may thus be regulated by a combination of a DNA signal that induces promoter-proximal stalling and protein factors that alter its duration.

                      1. Alligator Breath

                          Birds have a unidirectional system of airflow within their lungs that has been attributed to the peculiarities of flight. However, Farmer and Sanders (p. 338) provide evidence that this unidirectional and more or less continuous flow of air also occurs through parts of the alligator lung; in contrast to the tidal, biphasic system in mammals. By analyzing lung and tracheal structures, the similarities of the alligator lungs were compared with those of birds. The data suggest that the unusual properties of bird lungs originated before the divergence of the alligator line from the dinosaur or avian line.

                        1. The Art of Artemisia

                            CREDIT: THE CNAP ARTEMISIA RESEARCH PROJECT

                            As the malaria parasite, which is transmitted through mosquito vectors, develops resistance, previously useful control mechanisms are beginning to fail. Combination therapies based on the plant product artemisinin are a promising alternative. Graham et al. (p. 328; see the Perspective by Milhous and Weina) have now developed a genetic map of the plant Artemisia annua from which artemisinin is derived. The results lay the foundation for improving agricultural productivity of this natural product, which is becoming increasingly important in the fight against malaria.

                          1. Integrin G Protein

                              Adhesion molecules, known as integrins, are found on the surface of cells. When integrins adhere to components of the extracellular matrix, they act as receptors and initiate signaling events within the cell. Gong et al. (p. 340) show that they do so in part by partnering with a signal-transducing protein called Gα13. Such α subunits of heterotrimeric guanine nucleotide-binding proteins are well known for transducing signals from the large class of G protein–coupled receptors, but were not known to work with integrins. Gα13 appears to interact directly with the integrin αIIbβ3 and to transmit signals that regulate cell spreading.

                            1. Behavioral Profiling

                                The complexity of the brain makes it difficult to predict how a drug will affect behavior without direct testing in live animals. Rihel et al. (p. 348) developed a high-throughput assay to assess the effects of thousands of drugs on sleep/wake behaviors of zebrafish larvae. The data set reveals a broad conservation of zebrafish and mammalian sleep/wake pharmacology and identifies pathways that regulate sleep. Moreover, the biological targets of poorly characterized small molecules can be predicted by matching their behavioral profiles to those of well-known drugs. Thus, behavioral profiling in zebrafish offers a cost-effective way to characterize neuroactive drugs and to predict biological targets of novel compounds.

                              1. Oxalate from Air

                                  In light of increasing concerns about the consequences of excessive atmospheric carbon dioxide, there is demand for methods to use carbon dioxide in the preparation of more elaborate compounds. Though reactions with hydroxide salts to form carbonates tend to proceed fairly cleanly, reductive processes to form carboxylic acids, esters, and alcohols are often rather unselective. Angamuthu et al. (p. 313; see the news story by Service) discovered that a copper complex exhibited remarkable selectivity in reductively coupling CO2 to form oxalate through coordinative electron transfer, even in the presence of excess oxygen, normally a much more potent electron acceptor. Precipitation of the oxalate as a lithium salt and electrochemical re-reduction of the copper produced a preliminary catalytic cycle, demonstrated through six turnovers.