This Week in Science

Science  07 Apr 2006:
Vol. 312, Issue 5770, pp. 15
  1. Repeating Ring Properties


    Two new outer rings and moons were recently discovered around Uranus. Using the infrared Keck adaptive optics system, de Pater et al. (p. 92) show that the rings are blue and red like Saturn's E and G rings. Blue ring R1 is associated with moon Mab, and Saturn's E ring hosts the active moon Enceladus. This correspondence suggests that Mab may be the source of ring material and the blue color, because only small grains survive gravitational forces, solar radiation pressure, and electromagnetic forces. Ring R2 is as red as Saturn's G ring and shows the same forward- and back-scattered light ratios. Both the uranian and saturnian rings are also at similar locations in planetary radii.

  2. Beginning with C-H Bonds

    Carbon-hydrogen bonds in organic molecules and biopolymers are among the least reactive chemical groups, and in chemical synthesis, a C-H bond is first activated by oxygenation or halogenation reactions that can be unselective or difficult to control. Godula and Sames (p. 67) review recent progress in transition metal catalysis that has allowed direct, selective formation of carbon-carbon bonds from isolated C-H bonds. These synthetic routes offer great potential for increased synthetic efficiency in preparing complex molecules such as drug precursors.

  3. From Quantum Kittens to Flying Cats

    Quantum information processing will require the reliable preparation of quantum states of matter. While these are easy to specify theoretically, experimental realization of such states has been difficult, especially the type of “flying” states that are expected to be useful for quantum communication purposes. By subtracting a single photon from a squeezed coherent optical pulse, Ourjoumtsev et al. (p. 83, published online 9 March; see the Perspective by Gisin) report on the production of small Schrödinger cat states, or Schrödinger kittens, and show that these kittens can be grown into cats through a suitable amplification and distillation process.

  4. Superalloying Cobalt

    Superalloys, which are based on iron, cobalt, or most commonly nickel, can be safely used at temperatures in excess of 0.7 of the absolute melting temperature, unlike conventional alloys, which are prone to creep and oxidation. Through the addition of solutes like aluminum or titanium, or both, a two-phase equilibrium microstructure forms that consists of γ and γ′ phases; the latter phase is largely responsible for the elevated-temperature strength of the material and its incredible resistance to creep. Cobalt superalloys typically have lower strengths than those based on nickel, which is why the latter has dominated in applications. However, Sato et al. (p. 90) now show than a ternary cobalt alloy based on the addition of aluminum and tungsten has properties that compete with those of the nickel superalloys.

  5. H2 Leaves Pt Unexcited


    The Born-Oppenheimer (B-O) approximation, which treats nuclear and electronic motion independently during chemical interactions, is a cornerstone of computational modeling. Without it, theoretical analysis of even small molecule reactions in the gas phase would prove dauntingly complex. However, the ease with which electrons can be excited at metal surfaces has cast doubt on the validity of the approximation for simulating molecule-surface collisions, which play a major role in industrial catalysis. Nieto et al. (p. 86, published online 9 February; see the Perspective by Wodtke) show that data for scattering and dissociative adsorption of H2 at a platinum surface are well predicted with a density functional theory approach with the B-O criteria intact. The absence of Pt electronic excitation during the H2 interaction suggests that accurate modeling of a wide range of heterogeneous reactions should be feasible.

  6. Hunting Hurricane Causes

    A number of different factors can affect the formation and development of hurricanes, including sea surface temperature (SST), lower tropospheric humidity, vertical wind shear, and large-scale atmospheric circulation patterns. Which of these factors are most important and which are responsible for the increase in global hurricane intensity observed since 1970? Hoyos et al. (p. 94, published online 16 March) use a method based on Bayesian statistics and information theory to isolate the causes of the trend from short-term variability, for all of the major ocean basins where these storms occur. They conclude that only rising tropical SSTs have had a significant influence on the recent multi-decadal trend.

  7. No Pain, No Gain

    Societal behavior is complex and multifaceted. One complicated question is the conditions under which we cooperate with others for mutual gain. Experimental results using a public goods game suggest that the threat of costly punishment of free-riders by altruistically minded souls suffices to maintain groupwide compliance. Gürerk et al. (p. 108; see the Perspective by Henrich) show that if allowed to choose freely, individuals first elect to join a sanction-free game where punishment is not permitted. As successive rounds are played, they come to appreciate that cooperation yields greater rewards, so they switch to the sanctioning regime where punishment (which makes free-riding costly) is allowed and themselves become active monitors of compliance.

  8. Ant Family Tree

    Ants are a dominant feature of terrestrial ecosystems and yet we know surprisingly little about their evolutionary history. Moreau et al. (p. 101; see the cover) sequenced DNA from multiple genes for a representative sample of ant species from around the world to reconstruct an ant family tree. A single group, the Leptanillinae, lies at the base of the tree, while all the other groups fall into two major clusters. By using fossils to calibrate the rates of DNA evolution in ants, they conclude that present-day ants arose approximately 140 to 168 million years ago. However, ant diversification only took off ∼100 million years ago, immediately after the rise of flowering plants, the angiosperms.

  9. MicroRNAs in Embryogenesis


    Early in animal development, the embryo switches from using maternally provided messenger RNA (mRNA) transcripts to expressing mostly zygotic genes. During this maternal-to-zygotic transition, a large number of maternal mRNAs are somehow eliminated. Giraldez et al. (p. 75, published online 16 February; see the Perspective by Cohen and Brennecke) examined possible microRNA (miRNA)-based mechanisms and identified 203 putative targets for the zebrafish miRNA miR-430, which is specifically expressed at the maternal-to-zygotic transition. Hundreds of miR-430 target mRNAs are maternally expressed during early development, and miR-430 can promote their deacetylation and decay. Thus, during the maternal-to-zygotic transition in zebrafish embryogenesis, miR-430 plays a critical role.

  10. Serotonin and Liver Regeneration

    The liver can regenerate after severe injury or surgery, even when up to 70% of the tissue has been removed. Lesurtel et al. (p. 104) report that in a mouse model, serotonin carried by platelets circulating in the blood plays a role in the regenerative process. Liver was found to express serotonin receptors. Mice with impaired platelet function had a reduced regenerative response, but when treated with a serotonin receptor agonist, hepatocyte proliferation was restored. Liver regeneration in mice lacking peripheral serotonin was also restored when their platelets were reloaded with serotonin. Therapeutic treatment with serotonin receptor agonists may thus be useful in tissue recovery.

  11. Limits to Evolutionary Flexibility

    Genetic mutations are the substrate for evolution. Genes conferring fitness can accumulate multiple mutations during a period of selection. There are, of course, many potential evolutionary trajectories for the appearance of these mutations. However, it is likely that not all trajectories are available because the fitness of individual mutations may depend on the genetic background in which they appear. Weinreich et al. (p. 111) chart the available evolutionary trajectories for five mutations in β-lactamase in Escherichia coli, which together confer a 100,000-fold increased resistance to the antibiotic cefotaxime. Only 18 of a potential 120 routes to high fitness are accessible to selection, due to pleiotropic effects of the mutations on the enzyme.

  12. Therapy for Marfan Syndrome

    Marfan syndrome (MFS) is a hereditary disorder characterized by systemwide defects in connective tissue. People with MFS have a greatly increased risk of developing an aortic aneurysm, a bulge in the wall of the aorta that can rupture and cause life-threatening internal bleeding. Studying a mouse model of MFS, Habashi et al. (p. 117; see the news story by Travis) found that aneurysm formation is accompanied by activation of the transforming growth factor-β (TGF-β) signaling pathway in the aortic wall. Treatment of the MFS mice with losartan, a drug recently shown to antagonize TGF-β signaling in other disease states, almost completely normalized the aortic phenotype in the MFS mice, even after an aneurysm had formed. Losartan is already widely used to control high blood pressure, and the authors suggest that a prospective clinical trial in MFS patients is warranted.

  13. Tropical Pacific Climate Evolution

    During the early Pliocene epoch (5 million to 3 million years ago), there was little or no permanent ice in the Northern Hemisphere, and global mean surface temperatures were several degrees centigrade warmer than today. Around 3 million years ago, permanent continental ice sheets began to form in the Northern Hemisphere and the variability of high-latitude climate increased dramatically. How these changes are related to corresponding changes in tropical climate change has been a topic of vigorous debate. Lawrence et al. (p. 79) present a 5-million-year record of sea surface temperature and productivity variations from the eastern equatorial Pacific Ocean and find that cooling began about 4 million years ago, long before the intensification of Northern Hemisphere glaciation. Thus, high-latitude processes in the Southern Hemisphere helped drive ocean surface conditions in the eastern equatorial Pacific during the Pliocene and Pleistocene.

  14. Prescient Hormone Receptor Evolution?

    Highly integrated biological systems can provide a challenge in terms of understanding how such systems arose during the course of evolution. One such system involves the mineralocorticoid receptor (MR) and glucocorticoid receptor (GR), which arose from a gene duplication deep in the vertebrate lineage. MR binds to and is activated by the hormone aldosterone, which only appeared much later, in the lineage leading to tetrapods, raising the question of how each component “anticipated” the presence of the other. Bridgham et al. (p. 97; see the Perspective by Adami) analyze the evolution of this system by reconstructing the ancestral hormone receptor (AncCR) that gave rise to MR and GR and show that it already had substantial affinity for aldosterone, as a consequence of its affinity for other more ancient hormones, possibly including 11-deoxycorticosterone. Furthermore, two single-nucleotide mutations in the AncCR yield a GR-like receptor with present-day low affinity for aldosterone.

  15. Make Space

    Maintaining strict control over T cell numbers is essential for proper immune function, although many questions remain about how relative lymphocyte abundance is regulated. Hataye et al. (p. 114, published online 2 March) found that when a large number of identical T cells were present, the resulting population over time was unstable, with a considerably reduced half-life compared with smaller numbers of the same clonal population. In normal polyclonal T cell populations, such intraclonal jostling keeping numbers of particular clonal populations low would help to ensure that the greatest number of diverse clones can coexist at a given time.