This Week in Science

Science  28 May 1999:
Vol. 284, Issue 5419, pp. 1429
  1. Putting the Squeeze on Silica

    The most common form of silica is quartz. With increasing pressure, quartz eventually transforms to stishovite, which has been identified in highly shocked rocks and has been thought to be important in Earth's lower mantle. The occurrence of phases at higher pressure has been suggested; Sharp et al. (p. 1511) have now found such a phase in a highly shocked meteorite from Mars. Electron diffraction data imply that the phase has a structure similar to that of lead oxide. The new phase may be the stable silica phase in Earth's lower mantle and may have been missed in other highly shocked rocks because of its conversion at lower pressures to other phases.

  2. Superconducting Nanotubes

    Carbon single-walled nanotubes, depending on their diameter and helicity, can be semiconducting or metallic, and those that are only about 10 nanometers in diameter are expected to behave as one-dimensional conductors. Kasumov et al. (p. 1508) now show that individual carbon nanotubes about 1 nanometer in diameter (as well as bundles of about 100 of these nanotubes) can carry supercurrents. The nanotubes are connected between two superconducting electrodes; at the low temperatures used to make the electrodes superconducting (1 kelvin), they find that if the resistance of the nanotube is sufficiently low, a supercurrent can flow through it.

  3. Europan Nights

    The Galileo spacecraft has a photopolarimeter-radiometer (PPR) that maps the thermal radiation from the surface of a satellite. Spencer et al. (p. 1514) derived a map of the nighttime surface temperatures of Europa from PPR data and found that the temperatures vary with latitude, in some regions by as much as 5 kelvin. An explanation for these temperature variations remains to be determined, but the intriguing possibilities include either a change in the thermal inertia of the ice, which would be related to the changes in temperatures between daytime and nighttime, or an unresolved heat source from within Europa.

  4. The Highs and Lows of Mars

    The topography of a planet can reveal much about its evolution. Smith et al. (p. 1495; see the cover and the news story by Wuethrich) have obtained a high-resolution global view of the topography of Mars from Mars Global Surveyor. The data confirm that the high elevations of the southern hemisphere reflect internal processes and show that a widespread deposit from an impact crater forms much of the high elevations. Surface water over much of the planet would have drained into a large basin in the northern hemisphere.

  5. Younger, Faster, Lighter

    The universe developed rapidly in the first second after the Big Bang, and so has the pace of results that are helping astrophysicists understand the structure and evolution of the universe (see the news story by Glanz). Bahcall et al. (p. 1481) review the latest theoretical and observational results and simplify the description of the universe to three characteristics, the density of matter, the expansion rate, and the shape, which they represent with a “cosmic triangle.” Their review suggests that the universe is lightweight, accelerating, and flat. In a related research article, Lineweaver (p. 1503; see the news story by Finkbeiner) synthesizes similar recent data related to the “cosmic triangle” and calculates a best estimate for the age of the universe. He gets a youthful 13.4 billion years old, about 1 billion years younger than some previous estimates, but still old enough to allow the creation of galaxies like our own.

  6. Saving Fisheries

    There are two approaches to ensuring the sustainability and biodiversity of fisheries: One is the use of catch limits, as is currently practiced, and the other is the setting up of marine reserves to protect stocks. The introduction of reserves has been hampered by a lack of information of relative yields from the two systems. Hastings and Botsford (p. 1537) used a simplifying set of assumptions to show that yields are similar and that, under some circumstances, marine reserves offer significant advantages over catch quotas.

  7. A Graceful Exit

    Many viruses kill the cell in which they reproduced by lysing the cell wall, but filamentous phage f1 exits Escherichia coli without killing the bacterium. Marciano et al. (p. 1516; see the Perspective by Zimmerberg) have purified a bacteriophage-encoded protein, pIV, and showed that it acts as a channel for f1 to exit its bacterial host. Differences between mutant and wild-type protein activity indicate that pIV is a gated channel and that changes in channel properties could affect sensitivity to the antibiotic vancomycin. Protein pIV is a member of a family of proteins involved in secretion of virulence factors from Gram-negative bacterial pathogens.

  8. Understanding an Old Vaccine

    The Bacille Calmette-Guérin (BCG) family of vaccines against tuberculosis was derived serendipitously after continuous passage of bovine tubercle bacilli in guinea pigs in 1921. However, as a result of the passage history, current strains are different from the original progenitor strain, which may explain the vaccine's variable efficacy in different parts of the world. Behr et al. (p. 1520; see the Perspective by Young and Robertson) compared the genomes of BCG strains with that of Mycobacterium tuberculosis and M. bovis by microarray assay and fluorescent in situ hybridization and found a series of deletions in BCG strains that made it possible to follow their evolution. These results should help in the efforts to design new tuberculosis vaccines.

  9. Sending Sugars Against Staph Infections

    Bacterial pathogens keep a set of genes in reserve that are only activated when they enter their hosts. Because these genes are thought to be particularly useful for bacterial survival and infection promotion, they may make ideal vaccine targets. Not only would the vaccine be specific for the microbe, but it may interfere with a virulence system crucial for the bacteria's survival. McKenney et al. (p. 1523) report the primarily in vivo expression of a surface polysaccharide called PNSG during Staphylococcus aureus infection. Purified PNSG protected mice from lethal S. aureus infections by inducing an antibody response. Because of the growing prevalence of antibiotic-resistant S. aureus strains, a preventative strategy may provide a needed alternative approach.

  10. In Sync

    Some extracellular signaling molecules bind to their cell surface receptors and trigger a release of calcium (Ca2+) from intracellular stores through inositol 1,4,5-trisphosphate (IP3)-gated Ca2+ release channels. The freed Ca2+ is then available to regulate various cellular responses such as secretion, proliferation, and gene expression. Hirose et al. (p. 1527) used a probe tagged with green fluorescent protein to monitor IP3 concentration and show that in a single cell, the mobilization of Ca2+ into oscillations or propagating waves occurs in synchrony with changes in IP3 concentration and localization. The concurrence of these events in space and time indicates that IP3 dynamics support Ca2+ signaling patterns.

  11. Paying Attention?

    Learning with awareness utilizes different brain structures than learning without awareness. Although the prefrontal cortex has been shown to play a crucial role for the awareness of associations, a competing hypothesis is that awareness needs the interaction of multiple separate brain regions within a large-scale neuronal system. McIntosh et al. (p. 1531) asked people to perform a visual discrimination task while simultaneously presenting tones to them. After some time, one group consciously noticed an association between the tones and the visual stimuli. Subjects who became aware not only scored better in the test, but showed different patterns of brain activity during positron emission tomography scans. Although the left prefrontal cortex showed the highest level of activity, there were several other regions that also showed an increase that could be correlated with awareness.

  12. Losing Muscle

    Patients with hereditary hemorrhagic telangiectasia, a disease characterized by disruptions of the vascular system, have mutations in the gene encoding endoglin, a protein that binds to transforming growth factor-b (TGF-b). Li et al. (p. 1534) investigated the role of endoglin in vascular development by studying endoglin-deficient mice. Although the early stages of vasculogenesis occurred normally, the mice died in utero because the endothelial tubes were not remodeled into mature blood vessels. This remodeling defect was caused by a failure in vascular smooth muscle development, a finding that may in part explain the pathogenesis of the human disease.

  13. Intense Lasers Enlighten Stellar Physics

    The nuclear fusion reactions and dynamics of a stellar explosion can be modeled theoretically, but a complementary approach is to develop laboratory analogs for these large-scale energetic processes. Remington et al. (p. 1488) review the recent development of intense lasers that produce large amounts of energy within small areas that astrophysicists now use to study stellar reactions in a controlled laboratory setting. Laser experiments, combined with observations and models, have improved our understanding of supernova explosions, the mechanisms that produce gamma ray bursts, and the formation of giant planets.

  14. Responding in the Red

    Plant phytochromes, which serve as receptors for light in the red end of the spectrum, initiate signal transduction chains that result in developmental and physiological alterations in the plant. Fankhauser et al. (p. 1539) have identified a phytochrome binding protein, PKS1, that is active at one of the earliest steps in these pathways. PKS1 is phosphorylated in the presence of phytochromes in a light-dependent manner, which suggests that phytochromes may initiate their signals with phosphorylation.

  15. Polymorphisms Not Found in the IL-13 Gene Promoter

    M. Wills-Karp et al. (Reports, 18 Dec. p. 2258) studied the role of the type 2 cytokine interleukin-13 (IL-13) in a mouse model of asthma. They concluded that IL-13 “was necessary and sufficient for the expression of allergic asthma.”

    K. L. Anderson et al. “examined the IL-13 promoter region” on the human genome “in 129 individuals from a population in the United Kingdom.” They found “an absence of polymorphisms” in the subset of asthma patients, leading them to “doubt the significance of the IL-13 promoter as a susceptibility locus for atopy or any of the associated conditions….”

    In response, Wills-Karp and L. L. Rosenwasser state that they have also found “no significant population-based polymorphisms in this region” of the genome, but that other “possible mechanisms” may exist that involve “polymorphisms in downstream receptor and signaling molecules.”

    The full text of these comments can be seen at www.sciencemag.org/cgi/content/full/284/5419/1431a

  16. Fas, p53, and Apoptosis

    M. Bennett et al. (Reports, 9 Oct. p. 290) studied the gene p53, which “acts as a tumor suppressor by inducing both growth arrest and apoptosis.” They concluded that “p53 can mediate apoptosis through [tumor necrosis factor] Fas transport from cytoplasmic stores.”

    L. O'Connor and A. Strasser comment that they “and others have established that Fas is not required for p53-activated cell death…” and “that p53 is not required for Fas-induced apoptosis….”

    In response, Bennett et al. state that these studies “are not directly comparable. Evidently, p53 and Fas may interact at multiple levels to induce apoptosis in many different cell types.”

    The full text of these comments can be seen at www.sciencemag.org/cgi/content/full/284/5419/1431b

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