This Week in Science

Science  22 Jul 2011:
Vol. 333, Issue 6041, pp. 383
  1. Diamonds Are (Almost) Forever

    CREDIT: STEPHEN RICHARDSON

    Over Earth's history, the ocean basins have cycled between periods of opening and closing as the continents disperse and reassemble due to plate tectonic processes. When this cycle originated is uncertain, but it has a direct bearing on models of Earth's evolution. Shirey and Richardson (p. 434; see the Perspective by Van Kranendonk) compiled chemical data of thousands of tiny mineral inclusions inside diamonds that were in the mantle billions of years ago. The diamonds suggest a marked compositional change between 3.0 and 3.2 billion years ago, from rocks that have a strong mantle signature to rocks that bear the signature of crust mixing with the mantle at subduction zones—a hallmark of plate tectonics and ocean basin cycles.

  2. Hope for Coral Reefs

    Coral reefs have been predicted to go into irreversible decline within the next few decades because of climate warming and ocean acidification. Pandolfi et al. (p. 418) review both paleontological and current data that suggest potential variability among species, populations, and geographic regions in coral responses to effects of global changes in ocean temperatures and pH. While reefs are highly threatened, predictions of inevitable demise in the near term should be tempered. Nevertheless, protection from local threats is essential to reduce the strong selection imposed by anthropogenic impacts at the local level and to lessen constraints on adaptation to global environmental changes.

  3. Coupling of Coexisting Quantum States

    The pseudogap states of high-critical-temperature superconductors develop at temperatures above that of the superconducting state. Their electronic ordering can be complex and resemble that of nematic and smectic liquid crystals. Mesaros et al. (p. 426) studied the underdoped smectic phase in Bi2Sr2CaCu2O8+δ using scanning tunneling microscopy and were able to separate the components of smectic and nematic ordering. A Ginzburg-Landau free energy diagram could account for the coupling of smectic and nematic ordering.

  4. Extinction Links

    The end-Triassic mass extinction about 200 million years ago has been attributed to volcanic activity during the break-up of Pangaea, which is thought to have caused a massive release of carbon dioxide and a resulting warming of climate. Confirming this link, Ruhl et al. (p. 430) present a compound-specific, carbon-isotope record derived from waxes of land plants. The injection of carbon into the environment lasted less than 20,000 years, and at least 12,000 gigatons of isotopically depleted carbon was added to the atmosphere as methane. Furthermore, concurrent vegetation changes reflect strong warming and an enhanced hydrological cycle.

  5. Metal-Free Crystal Cages

    There has been much progress in the synthesis of diverse metal organic framework structures, in which multifunctional organic ligands bridge metal ion nodes to create a highly porous crystal lattice. Liu et al. (p. 436; see the Perspective by Lauher) showcase a complementary approach, with hydrogen bonding replacing metal-ligand coordination in crystalline cage assemblies. Crystallization of solids with well-defined truncated octahedral pores was observed when guanidinium H-bond donors were combined with geometrically matched benzene sulfonate acceptors in solution.

  6. Cool Dinosaurs

    Sauropod dinosaurs were the largest terrestrial animals in Earth's history. Although dinosaurs were originally assumed to be cold-blooded, recent evidence suggests that they may have been warm-blooded. However, this potentially would have caused the largest dinosaurs to experience high body temperatures. Using an emerging technique based on isotope-based paleothermometry of fossil teeth, Eagle et al. (p. 443, published online 23 June) show that sauropods had body temperatures of 36° to 38°C. This range is comparable with modern mammals and birds, suggesting that large dinosaurs must have avoided overheating by slowing their metabolic rate or by developing adaptations that allowed heat to be dissipated.

  7. All Four Atoms

    CREDIT: XIAO ET AL.

    To a certain extent, it is possible to model and measure reaction mechanisms that involve scores of atoms; for instance, transformations within an enzyme's active site. Analysis at the highest level of quantum mechanical detail, however—an accounting of every incremental vibrational motion associated with every angular trajectory—is still confined to much simpler systems involving three atoms. Xiao et al. (p. 440) now extend full-dimensional predictions of state-to-state reaction probabilities to a four-atom system: the reaction of OH and HD to form water (H2O) and a deuterium (D) atom.

  8. Use It, Then Lose It

    Pathogenic bacteria encode effector proteins that AMPylate (covalently attach adenosine monophosphate to) target host factors such as Rho or Rab guanosine triphosphatases. AMPylation interferes with downstream signaling events, thereby promoting microbial infection. How AMPylation of host factors is regulated during infection and if it can be reversed within cells is unclear. Neunuebel et al. (p. 453, published online 16 June) have now discovered that Legionella pneumophila, in addition to secreting an AMPylation enzyme, also translocates a de-AMPylase, SidD, into host cells. SidD thus represents the missing link between the processes of early Rab1 accumulation and subsequent Rab1 removal from Legionella-containing vacuoles during infection.

  9. Keeping the Beat

    In eukaryotes, arrays of cilia display periodic beating that can propel cells or move fluid across tissue surfaces. The arrays are comprised of axonemes in which dynein motors bind two microtubules and cause them to slide relative to each other. How the activity of dynein is regulated to drive self-sustained beating of individual axonemes and, ultimately, coordinated beating of cilia arrays, remains unclear. Sanchez et al. (p. 456) show that microtubule bundles can spontaneously beat and synchronize under the influence of the molecular motor kinesin, which cross-links the microtubules. This minimal system should provide insight into the mechanisms that drive oscillation of biological nanomachines.

  10. Enzyme Exploitation

    Type II topoisomerases transiently cleave DNA as they alter topology in processes such as replication, transcription, and chromosome condensation. Some antibiotics and anticancer drugs act by stabilizing the cleavage complexes, promoting the formation of cytotoxic DNA lesions. Wu et al. (p. 459) present a high-resolution structure of the DNA-binding and cleavage core of human Topoisomerase 2β in complex with DNA and the anticancer drug etoposide. The structure provides a basis for known drug structure-activity relation and provides useful information for developing isoform-specific drugs.

  11. Built to Invade

    Apicomplexan parasites cause diseases that include malaria and toxoplasmosis. Key to invasion is a moving junction (MJ) complex that links the parasite and host cell membranes. Two key proteins in this complex are both provided by the parasite—the receptor, RON2—which integrates into the host cell membrane and its ligand, apical membrane antigen 1 (AMA1). Tonkin et al. (p. 463; see the Perspective by Baum and Cowman) have determined the crystal structure of RON2 bound to AMA1. The complex has an extensive buried surface area that probably enables the MJ complex to resist the mechanical forces of host cell invasion.

  12. Dicty Tiger Nixes Cheaters

    CREDIT: HIROSE ET AL.

    Cells within aggregates of the social amoeba, Dictyostelium discoideum, differentiate to form fruiting bodies containing a mixture of spores from different strains (genotypes). In the process of forming the stalk of the fruiting body, cells die. So what is to stop some strains from “cheating” by not participating in the sacrificial donation of cells to the dying stalk? Hirose et al. (p. 467, published online 23 June) studied an amoeba that possesses polymorphic genes called tiger, which mediate self-recognition, signaling, and developmental regulation. In a series of deletion and replacement experiments, a complementary pair of tiger alleles was sufficient to exclude cheaters from the fruiting body.

  13. Form and Function

    Structural and spatial organization of pathways in both eukaryotic and prokaryotic cells ensures the robustness and efficiency of essential reactions. Delebecque et al. (p. 470, published online 23 June; see the cover; see the Perspective by Thodey and Smolke) now describe a platform to achieve de novo spatial organization of multienzymatic pathways in vivo. RNA was programmed to assemble into discrete, one- and two-dimensional assemblies that displayed binding sites that could spatially organize proteins in vivo. Using this strategy, bacterial hydrogen biosynthesis could be fine-tuned and increased as a function of scaffold architecture.

  14. Toddler Wisdom

    Children learn an impressive number of cognitive skills in their early years of life. Perner et al. (p. 474) assessed the “theory of mind” (via a standard false-belief task) and the understanding of identity statements (in which, for example, different names can refer to the same object or person) in children aged 3 to 6. Children acquired both of these abilities between the ages of 3 and 4. The findings suggest that children's reasoned predictions about a person's behavior do not develop within an isolated domain of understanding mental states, but develop in unison with other domains of understanding that share needed conceptual abilities.

  15. Cool Parasites

    The metabolic theory of ecology explains variation in species abundance by the scaling of metabolism with body size and temperature and is considered to be a key underpinning to all biological processes at all levels of organization. For example, small-bodied organisms tend to have higher mass-specific metabolic rates than larger-bodied organisms. But what about parasites, which account for at least half of the world's biodiversity? Parasites tend to be smaller than their hosts, and metabolic scaling theory cannot fully account for the abundance of parasitic species. By taking into account the flow of energy between trophic levels, Hechinger et al. (p. 445) found that the expected scaling exponent (an average of ¾ scaling of metabolic rate with body size) still applies, using data collected from three estuarine food webs.

  16. Seeing the Trees for the Forest

    Knowledge of the phylogenetic relationships between species is important for comparative studies of taxa, but analyses quickly become computationally intensive when multiple taxa are examined for multiple characteristics. Sanderson et al. (p. 448, published online 16 June; see the Perspective by Kubatko and Pearl) help to address this problem by identifying “terraces” within the phylogenetic space composed of trees with identical values. By identifying these terraces, one can more easily reduce the number of trees to be examined and more quickly find the best relationships within a data set.

  17. Black Sea Reconstruction

    It is possible to reconstruct plankton communities from fossils and chemical signatures in the sedimentary record—even fossil virus particles can be discerned. However, this record may be truncated or contain gaps because physicochemical conditions may have hindered preservation. Despite the incomplete fossil record, Coolen (p. 451) traced a 7000-year DNA record preserved in a sediment core taken from the Black Sea. The ubiquitous phytoplankton, Emiliana huxleyi, and the viruses that have assaulted it over past millennia were analyzed. Stable phytoplankton-virus communities existed for centuries punctuated by sudden shifts caused by changes in hydrological and nutrient regimes resulting from increasing river discharge during climate shifts.