This Week in Science

Science  27 Oct 2006:
Vol. 314, Issue 5799, pp. 561
  1. Rethinking Slime Mold Taxonomy


    Despite the interest in Dictyostelium discoideum as a model system, little or no molecular data exist for the rest of this ancient and morphologically diverse group. Their current taxonomy, first described more than 50 years ago, is based purely on morphology. Schaap et al. (p. 661) have constructed a molecular phylogeny of the Dictyostelia based on two independent molecular markers that includes nearly every one of the more than 90 recognized species. The tree, which resolves into four major taxa, bears little resemblance to the morphologically based tree.

  2. Who Gains Wins?

    We are all aware that information technology can be compromised by spam e-mails, online fraud, and viruses. Computer network security must protect systems that may be internally complicated and perhaps distributed worldwide, but failures can arise simply because the enforcer does not stand to benefit from fixing the problem. Anderson and Moore (p. 610) describe how ideas from economics can be applied to information security not only to strengthen the resilience of computer systems to attack but also to optimize the design of peer-to-peer systems, program testing, online privacy, and the politics of digital-rights management.

  3. Night and Day, Far Away

    Planets that lie very near their host stars may have a wide differential in atmospheric temperature between the night and day sides. Harrington et al. (p. 623, published online 12 October; see the cover) report seeing such an effect for the innermost planet orbiting the star ν Andromedae with the Spitzer Space Telescope. They measured the sinusoidal change in the heat of the planet during its 5-day orbit, which indicates that it has distinct hot and cold sides. Because the heat does not spread throughout the atmosphere, the planet's own heat transfer properties can be measured.

  4. Brownian Motion with Twists and Turns

    The Brownian diffusion of spherical particles is well understood and goes back to the pioneering work of Einstein and Perrin, but for ellipsoidal particles, the problem becomes much harder because rotational and translational motion are coupling. This problem has been studied theoretically, but the coupling was not directly demonstrated. Han et al. (p. 626) demonstrate this coupling for a combined theoretical and experimental investigation of ellipsoidal particles, and observe the crossover from anisotropic behavior at short times to isotropic diffusion at long times.

  5. Flaring Disk


    Disks that form around young stars provide the sites for later planet formation. In stars that are more massive than the Sun, and correspondingly brighter, it has been argued that flared disks or shells of material may form instead. Lagage et al. (p. 621, published online 28 September; see the Perspective by Telesco) have detected a flared disk around the star HD 97048, whose mass is two and a half times that of the Sun's mass. By modeling the flared disk, they can measure the amount of dust and gas in the disk and suggest it may be a precursor to a debris disk. Planet formation may be difficult in this disk by gravity alone, but some planets may have formed in its inner regions.

  6. Oceanic Birth

    How did amino acids form in the prebiotic and hence pre-enzymatic world? Huber and Wächtershäuser (p. 630) show that iron and nickel particles can catalyze formation of α-amino and α-hydroxy acids by hydration of methyl thiolate and/or cyanide in basic aqueous solution with high-pressure CO when heated to 100°C. The authors argue that these conditions could have been provided in underwater volcanic vents on the early Earth. The results are consistent with a model whereby coordination of these and more complex organic reduction products to the metal centers progressively gave rise to Fe and Ni-containing hydrogenase enzymes.

  7. Dangerous Hitchhikers

    Some hazardous radionuclides in nuclear waste are transported in groundwater not as soluble ions but bound to small, nanometer-scale particles known as colloids. But the nature of likely colloids and the degree to which plutonium may be transported has been uncertain. Novikov et al. (p. 638) resolve both of these questions at a major waste site in Russia, where plutonium salts used for reprocessing have contaminated a lake connected to a groundwater system. After 55 years, plutonium is now present about 4 kilometers away, bound to iron-oxide colloids.

  8. Formation of Ion Channel Complexes

    Large-conductance Ca2+- and voltage-activated K+ (BKCa) channels play diverse and critical roles in a number of neuronal functions and provide a link between membrane potential and intracellular calcium. Previous studies suggested a tight functional coupling between BK channels and certain classes of voltage-gated Ca2+ channels in neurons. However, the molecular basis for such coupling has been unclear. Berkefeld et al. (p. 615) now confirm that BKCa channels form bimolecular complexes with voltage-gated Ca2+ channels. This bimolecular complex formation provides the basis for the fast and localized Ca2+-activated K+ signaling that controls neuronal firing pattern and release of hormones and transmitters in the central nervous system.

  9. Advancing Honey Bee Biology

    Sequencing of the genome of the Western honey bee Apis mellifera has recently been completed and has launched a variety of studies aimed at elucidating aspects of honey bee biology and evolution (see the news story by Pennisi). Whitfield et al. (p. 642), reconstructed the relationships among native Old World honey bees (Africa, Asia, and Europe), and present a fine-scale population genetic analysis of introduced New World bees (North and South America). Wang et al. (p. 645) identified DNA methyltransferase orthologs in the honey bee and demonstrated their catalytic activity. By combining genomic, proteomic, and bioinformatic approaches, Hummon et al. (p. 647) identified nearly 200 candidate neuropeptides in the honey bee genome, which provides new tools for understanding the neurobiology of this complex social organism. In Brevia, Poiner and Danforth (p. 614) describe a 100-million-year-old fossil bee, preserved in amber, along with traces of pollen associated with their role in angiosperm pollination.

  10. Alzheimer's Enzyme and Myelination


    β-Secretase activity is crucial in the production of pathological β-amyloid in Alzheimer's disease. However, its role in normal physiology is unclear, especially given the absence of an obvious phenotype in a knockout mouse for BACE1 (beta-site amyloid precursor protein-cleaving enzyme 1). Willem et al. (p. 664, published online 21 September; see the Perspective by Glabe) found that BACE1 (but not its close homolog BACE2) is required for neuregulin (NRG)-mediated peripheral nerve myelination. NRG1 was an in vivo substrate of BACE1, and the BACE-1 knockout mouse fully phenocopied hypomyelination observed in NRG1 heterozygous mutant mice. Thus, BACE-1 plays a physiological role during development in myelination.

  11. Where Has All the Sulfur Gone?

    Marine plankton produce huge amounts of dimethylsulfoniopropionate, which acts as a defensive chemical and osmolyte. One major breakdown product is the gas dimethylsulfide, which contributes to atmospheric aerosol formation at levels that could influence climate. Increasing evidence shows that heterotrophic bacteria in the plankton play an important role in regulating the partitioning of sulfur compounds between the atmosphere and the ocean (see the Perspective by Malin). Howard et al. (p. 649) have surveyed metagenome collections for genes involved in demethylation. In the open ocean, the Pelagibacter are the most important demethylators, but in coastal waters, Roseobacter take over this role. Vila-Costa et al. (p. 652) show that eukaryotic diatoms and cyanobacteria also act to retain dimethylsulfoniopropionate within plankton food webs. This activity is light-stimulated, seasonal, and appears to involve a sulfur-compound transport mechanism.

  12. Herding Olfactory Axons

    In the mammalian olfactory system, sensory neurons each express only one odorant receptor, and the axons from neurons that express the same odorant receptor somehow manage to converge on a single glomerulus in the brain. Imai et al. (p. 657, published online 21 September; see the Perspective by Dulac) have now brought both clarity and complexity to the problem. Although axon guidance was thought to depend solely on the odorant receptor, it now seems that a separate signaling system involving cyclic adenosine monophosphate contributes to guiding axons to a general position along the anteroposterior axis.

  13. A Walk Along the Grain Boundary

    The evolution of microstructure in polycrystalline materials is influenced by the motion of grain boundaries. However, measuring the mobility of a boundary is challenging, and simulations are increasingly playing a role in understanding this phenomenon. Trautt et al. (p. 632) have developed a technique that avoids the need for imposing high driving forces that make most other methods tractable, and instead determined the absolute mobilities of a flat grain boundary in the limit of zero driving force by studying the local diffusion behavior. They find much higher mobility values than previous reported, which seems to suggest that impurities enhance mobilities in the low-velocity regime to a larger extent than was previously thought.

  14. X-ray Division

    With increasing pressure, water forms a large number of ice phases that nonetheless preserve the O-H bonds. Mao et al. (p. 636) now show that radiation of ice VII with soft x-rays causes it to dissociate into H2 and O2, which together can form a novel solid alloy. This alloy is surprisingly stable over a range of pressures and to further x-ray radiation.

  15. Ring Around the Spindle Checkpoint

    The molecular role of the centrosome in the spindle checkpoint has been debated for some time. Müller et al. (p. 654) have now identified a function for a subset of core centrosomal proteins, namely, their involvement in the spindle checkpoint. Gamma-tubulin ring proteins are functionally and biochemically integrated into checkpoint control, together with two of the major players in this pathway, BubR1 and cdc20. However, the function of the γ-tubulin ring components was not linked to centrosome integrity, nor did it require localization to this organelle.

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