This Week in Science

Science  04 Jun 2004:
Vol. 304, Issue 5676, pp. 1409
  1. Repopulating Bleached Coral

    CREDIT: LITTLE ET AL.

    Episodes of coral bleaching (loss of the symbiotic dinoflagellates), which have occurred with increasing frequency during the past two decades, can result in coral mortality. Corals can recover from such bleaching events, but the source of the repopulating symbionts has been unknown. Lewis and Coffroth (p. 1490) show that adult soft corals can be repopulated by dinoflagellates, either by taking them up from seawater or by regrowth of resident algae. Little et al. (p. 1492) show that the association between stony (scleractinian) corals and their symbionts is also flexible during the first 9 months of establishment. In this case, the genotype of dinoflagellate harbored by a coral species influences the growth of the host and changes as the coral develops. Thus, coral hosts can cope with immediate changes in the environment, which increases the likelihood of the long-term survival of corals and the reefs they create.

  2. Evidence of an End-Permian Impact

    Some end-Permian sedimentary rocks have yielded evidence that an impact may have occurred at or near the time of Earth's largest mass extinction. An earlier study of only seismic reflection data has suggested that the Bedout High, off the northwest coast of Australia, might have a morphology consistent with an impact crater. Becker et al. (p. 1469, published online 13 May 2004) analyzed two drill cores from the Bedout High. At the base of the samples, a breccia is present that contains abundant glass and what the authors suggest are shock-melted minerals. An 40Ar/39Ar age from one of the cores, as well as an earlier K-Ar age, overlap broadly the age of the Permian-Triassic boundary and are consistent with a Later Permian age based on the seismic stratigraphy. Re-interpretation of the seismic and other available data suggest that the Bedout High may be a buried impact crater and might account for the distribution of known or hypothesized impact debris.

  3. Making Use of Entanglement

    The realization of quantum information processing will require scaling the number of the particles that can be entangled (see the Perspective by Cory and Havel). Roos et al. (p. 1478) demonstrate the ability to manipulate and analyze entangled quantum states of three particles. Their quantum computer, consisting of three ions in a trap, allows them to create entangled states on demand, to manipulate them via selective operations, and to analyze them via state tomography. With the entangled state carefully prepared, they show that reading out one of the qubits need not destroy the coherence of the other two, thus presenting a building block for debugging quantum processes in a quantum computer in which the readout of an ancilla qubit can be propagated and used to switch the states of other entangled states. In a separate study that also makes use of the entangled states of three ions in a trap, Leibfried et al. (p. 1476) show that such states can be used to improve spectroscopic measurements and reduce the magnitude of the uncertainty toward that set by the Heisenberg limit.

  4. Carbon Nanotubes on a Roll

    The overlap of the π -orbital electrons helps hold together the planes of carbon atoms in graphite and the curved graphene sheets of multiwall carbon nanotubes. Hill et al. (p. 1481; see the Perspective by Blau and Fleming) functionalized hexabenzocoronene, which can be thought of as a graphene fragment consisting of 13 fused benzene rings, so that the molecules self-assemble through stacking interactions into tubular rods and coils. The nanotubes have an aspect ratio approaching 1000 and become electrically conductive upon oxidation.

  5. A Model Ecosystem

    With increasing pressure for a more ecological approach to marine fisheries and environmental management, there is a growing need to understand and predict changes in marine ecosystems. DeYoung et al. (p. 1463) review the conceptual and practical steps needed to formulate a quantitative approach to the consequences of climate change and variability in the world's oceans. The modeling of ocean-basin, multidecadal ecosystem dynamics requires the coupling of the life history and population dynamics of higher trophic levels with physical and biogeochemical dynamics. Examples from skipjack tuna and from copepods indicate how this challenge might be faced.

  6. Only One Way Out

    The virulence factors that pathogens secrete are largely unexplored in Gram-positive bacteria. Rosch and Caparon (p. 1513) have discovered that the “flesh-eating bacterium” Streptococcus pyogenes secretes its polypeptide toxins through an organelle in the cellular membrane that consists of the entire complement of the cell's general secretory (Sec) translocons. This organization of the Sec translocons may be important for the Gram-positive bacterium to organize the appropriate folding of secreted proteins.

  7. Southern Surprise

    CREDIT: LELIEVELD ET AL.

    Most of the focus on ozone production has been in Northern Hemisphere continental environments. However, Lelieveld et al. (p. 1483, published online 13 May 2004) report the results of 25 years of shipboard measurements of tropospheric air over the Atlantic Ocean, and conclude that ozone increases have actually been most dramatic in the tropics and the Southern Hemisphere. Anthropogenic nitrogen oxide emissions from fossil fuel burning in Africa have had a proportionally greater influence on air quality in the relatively pristine marine air there than the larger emissions have had in the already-polluted Northern Hemisphere.

  8. Many Ways to Make a Circadian Oscillator

    Circadian pacemakers keep cyanobacteria and eukaryotes on a 24-hour cycle that is synchronized with the environment. In Drosophila, a cryptochrome (CRY) is the primary circadian photoreceptor. It interacts with the transcription factors PERIOD (PER) and TIMELESS (TIM) that are involved in regulation of clock genes. However, the molecular mechanism of entrainment has been unclear. Busza et al. (p. 1503) show that CRY binding to TIM is light-dependent in flies. The interaction is transient, but commits TIM to proteosomal degradation. In CRY, the photolyase homology domain is involved in light detection and phototransduction, whereas the C-terminal domain regulates CRY stability and the CRY-TIM interaction. These results contrast with the functions of Arabidopsis CRY domains.

  9. Toward Tailored Cancer Therapy

    CREDIT: PAEZ ET AL.

    Lung cancer is the leading cause of cancer deaths worldwide, and more effective therapies are urgently needed. The U.S. Food and Drug Administration recently approved the drug gefitinib (also known as Iressa), a small molecule that inhibits the tyrosine kinase activity of the epidermal growth factor (EGF) receptor, which is overexpressed in many lung tumors. In clinical trials, the majority of lung cancer patients do not respond to gefitinib, but a small percentage show dramatic tumor regression. Paez et al. (p. 1497, published online 29 April 2004 with the news story by Marx; see the Perspective by Minna et al.) have found a possible molecular explanation for these clinical results: The tumors of patients who respond to gefitinib treatment are much more likely to have mutations in the EGF receptor gene than are nonresponders. This discovery may help clinicians identify which patients are most likely to benefit from gefitinib, thus bringing the concept of personalized cancer therapy a step closer to reality.

  10. A Latch for Fatty Acid Transport

    The mechanisms by which hydrophobic molecules like fatty acids enter cells remains poorly understood. Van den Berg et al. (p. 1506) present the structure of the long-chain fatty acid (LCFA) transporter FadL, which transports LCFAs across the outer membrane in Gram-negative bacteria. FadL forms a 14-stranded β barrel that is occluded by a hatch domain that can undergo conformational changes. Transport does not appear to require exogenous energy input, and it is possible that spontaneous “breathing” in the structure may release substrate from its binding site and generate a passageway through the barrel.

  11. Damage Limitation and Pathogen Resistance

    Synaptotagmins are thought to function as transducers of Ca2+ signaling in membrane fusion events. Fibroblasts and macrophages isolated from animals deficient in the synaptotagmin Syt VII are less resistant to the intracellular growth of the pathogenic bacteria Salmonella and Yersinia. Roy et al. (p. 1515) now show that the defect resides in an early form of Ca2+-dependent phagolysosome fusion, shortly after bacterial entry. The type III secretion systems of both Salmonella and Yersinia wound membranes and trigger calcium influx and lysosomal exocytosis. Type III mutants, which do not have the capacity to permeabilize host cell membranes, grow equally well in normal or Syt VII-deficient cells.

  12. Patterns of Stomatal Development in Leaves

    The pattern of stomata on plant epidermis is developmentally regulated to support even but adjustable gaseous exchange for the plant. Bergmann et al. (p. 1494; see the Perspective by Sack) now show that the MAPKK kinase, YODA, serves to regulate cell fate in the developing epidermis and manage the differentiation of stomatal guard cells. Bioinformatics analysis helped identify additional genes likely to regulate stomatal development and function, including a putative transcription factor, FAMA, which shows its highest expression in leaves.

  13. Aromatic Acids and Aerosol Formation

    Atmospheric aerosols have important effects on human health, global climate, and air quality, but the processes that control the nucleation and growth of aerosols remain poorly understood. Atmospheric aerosols contain a significant fraction of organic matter, but how organic compounds affect their formation is uncertain. Zhang et al. (p. 1487) report laboratory results on the impact of organic acids on the formation of nascent atmospheric particles. Nucleation of sulfuric acid is markedly enhanced by the presence of aromatic acids, and theoretical calculations suggest that the formation of an organic acid-sulfuric acid complex reduces the height of the energy barrier to nucleation. These results are relevant for many areas of the world, in that both organic acids and sulfuric acid are linked to the emissions caused by fossil-fuel burning.

  14. Cell Death by Another Name

    Autophagy is a process in which cells digest their own organelles and proteins in response to nutritional starvation. Yu et al. (p. 1500, published online 6 May 2004) describe a form of cell death that bears similarities to autophagy. Unlike apoptosis, which depends on activation of proteases in the caspase family, autophagic cell death in a mouse cell line was actually inhibited by caspase-8. Inhibition of expression of two genes known to function in autophagy, ATG7 and beclin 1, reduced cell death caused by inhibition of caspase-8. These findings could impact strategies for combating unwanted apoptosis that use caspase inhibitors to prevent cell death.

  15. Uncrossed Wiring

    The roundabout family of transmembrane receptors, known from studies in Drosophila and mice, supports guidance of developing axons along the midline, such that the axons cross the midline only when they should do so. Jen et al. (p. 1509, published online 22 April 2004; see the Perspective by Woods) have discovered that a rare human genetic disorder that manifests with scoliosis and aberrant eye muscle control is caused by mutations in the human gene, ROBO3. Both ascending sensory and descending corticospinal tracts are affected, but the brain nevertheless accommodates this unexpected symmetry such that the neurological defects are mild.

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