This Week in Science

Science  17 Mar 2000:
Vol. 287, Issue 5460, pp. 1885
  1. Catalyzing C-H Bond Reactions

    The selective activation under mild conditions of the carbon-hydrogen bonds of saturated hydrocarbons, or alkanes, as well as those of aromatic compounds, such as benzene, is the focus of two reports (see the Perspective by Jones). Transition metal complexes that activate alkanes generally do so as reagents, not as catalysts. Chen et al. (p. 1995) report on a rhodium complex that catalyzes the formation of linear alkylboranes (derivatized at the end of the chain) from alkanes and commercially available boron compounds in high yield. These compounds can then be converted to alcohols or amines for use in fine chemical synthesis. Most of the catalytic routes for the activation of aromatic C-H bonds are either unselective, require a particular group to present on the ring, or encounter difficulties in catalyst regeneration. Jia et al. (p. 1992) used a palladium complex with a weakly coordinating anion as a catalyst to insert alkynes and alkenes into aromatic C-H bonds under mild room-temperature conditions, thus forming carbon-carbon bonds. The reaction with alkynes usually produces the thermodynamically less-favored cis-substituted alkenes.

  2. Changes in Io's Exosphere

    The gaseous eruptions of Io have created a broad plasma torus around Jupiter. The Galileo Orbiter made a close flyby of Io in 1995, and measurements of the ion density in the plasma confirmed that sulfur dioxide from eruptions on Io was being ionized and trapped in the torus. Russell and Kivelson (p. 1998) have analyzed new data from another close flyby of Io in October 1999, and they infer that a high density of ionized sulfur monoxide and possibly other more exotic species such as cyanogen or ionized sodium are present in a fan-shaped region extending from about 2 to 20 Io radii away from Jupiter. The authors attribute changes in the composition and shape of the ionized region since the 1995 flyby to recent eruptions from the active volcano, Pillan Patera.

  3. Swinging Sinks

    Carbon storage by natural ecosystems is a major factor in the global carbon cycle, and much recent effort has been devoted to estimating the size of such “sinks.” Recent estimates have varied widely, especially for the United States, where they have ranged over an order of magnitude. Using climatic data for the past 100 years, Schimel et al. (p. 2004) model the effects of carbon dioxide increase and climate fluctuations on carbon storage in the United States. Their models show that the carbon sink is highly variable from year to year, and that sometimes there is actually a net efflux. Forest management and agricultural abandonment appear to contribute at least as much as climate and carbon dioxide increases do to the sink.

  4. Ironing Out the Past

    Iron plays a key role in the regulation of oceanic productivity, and thus changes in paleoproductivity might be ascertained from records of the abundance and isotopic composition of iron in seawater. Zhu et al. (p. 2000) have created a seawater iron-isotopic curve for the past 6 million years by analyzing the ferromanganese crust of a deep-sea nodule. The correlation with lead isotopes that they observe indicates that the isotopic variations are of geological, not biological, origin.

  5. Ill Tidings on the Winds

    Some of the most destructive hurricanes and tropical storms affecting the United States come from the Gulf of Mexico or the western Caribbean Sea. Maloney and Hartmann (p. 2002) have analyzed the record of tropical cyclones in these areas and found that the frequency of these storms is modulated by a tropical intraseasonal variation in winds called the Madden-Julian oscillation (MJO). These hurricanes are four times more likely when these wind anomalies are westerly in the eastern Pacific than when they are easterly. This correlation could be useful in improving long-range predictions of tropical cyclone activity in this region because the MJO may be forecast up to 2 weeks into the future.

  6. Modifying Cell Surfaces Outside-and In?

    The selective chemical modification of cell surfaces could be used for working out or even engineering cell-surface interactions. The few approaches that exist usually require a condensation reaction between the chemical species to be introduced (such as a dye or a receptor) and a partner formed within the cell. If such reactions are to be specific, the partners should be “abiotic,” yet most “abiotic” organic chemistry is usually run in nonaqueous solvents. Saxon and Bertozzi (p. 2007) have modified the Staudinger reaction, the coupling of an azide and a phosphine, so that an amide linkage can form in water. Azides were introduced into cell surfaces by metabolism of an azidosugar, and these groups formed covalent adducts with a biotinylated triarylphosphine. It may be possible to extend this reaction to work in the intracellular environment as well.

  7. Still Sneaky

    The origin of snakes provides a readily perceived example of a major evolutionary transition in the vertebrates that involved extensive morphological changes associated with locomotion, feeding, and life history. Equally, it has been a subject beset with controversy in recent years and hampered by the relative poverty of the fossil record. Tchernov et al. (p. 2010; see the Perspective by Greene and Cundall) describe a new fossil snake with limbs from 95-million-year-old deposits near Jerusalem. This fossil, named Haasiophis, shows very close affinities with Pachyrhachis, which has been claimed as the sister-taxon of all snakes. However, the better preservation of the Hassiophis material indicates that these two snakes were primitive members of only the more advanced snake assemblage, the macrostomates (such as pythons and boas).

  8. Attacking Asthma

    Asthma is caused by exposure to certain substances in the environment that lead to inappropriately severe allergic reaction in the lung. These environmental antigens trigger immunoglobulin E antibodies that then activate mast cells. One of the inflammation-inducing substances released by the mast cells is prostaglandin D2, which Matsuoka et al. (p. 2013) now show to cause some of the more severe symptoms of asthma. In mice in which prostaglandin D2 has been genetically deleted, fewer T lymphocytes (which secrete TH2 cytokines) and eosinophils accumulate in the lung, and the mice did not develop the hyperreactive airways usually characteristic of asthma attacks. Thus, prostaglandin D2 could prove to be a new therapeutic target against asthma.

  9. Mitochondrial Detection of Cancer

    Cancer therapy is most effective at early stages of the disease, so there is much interest in developing sensitive and noninvasive methods of early diagnosis. Fliss et al. (p. 2017) show that human tumors contain a large number of mutations in mitochondrial DNA (mtDNA) and that these mutant mtDNAs appear to accumulate at disproportionately high levels in the tumor cells. Analysis of bodily fluids such as urine and sputum revealed that the mtDNA mutations were significantly easier to detect than were mutations in p53, a nuclear gene. These results raise the possibility that mtDNA can serve as a powerful diagnostic marker for cancer detection.

  10. Outward Bound

    DNA replication in yeast and bacteria begins at a particular site and propagates in both directions outward. In mammalian cells, the details of the events surrounding the initiation of DNA replication have remained obscure. Abdurashidova et al. (p. 2023) studied the lamin B2 gene in human cell lines and found that the leading strands of each replication fork, which head in opposite directions, initiate within very few nucleotides of each other. This initiation site falls within a region that may bind a cell cycle-regulated protein complex.

  11. Taking IP3 a Step Further

    Activation of phospholipase C causes increased production of inositol 1,4,5-trisphosphate, a second messenger that regulates release of calcium from intracellular stores. IP3 can be modified by further phosphorylation, but the signaling role, if any, of such molecules is unclear. Odom et al. (p. 2026; see the Perspective by Chi and Crabtree) report that in the yeast Saccharomyces cerevisiae, an IP3 kinase (designated Ipk2p for inositol polyphosphate kinase) that can convert IP3 to IP5 is identical to Arg82p, a protein that participates in regulation of transcription. Arg82p functions as part of a transcriptional complex that mediates the response to changes in the extracellular concentration of arginine. Ipk2p protein, but not its kinase activity, was required for proper formation of complexes on DNA promoter elements. However, activity of the enzyme and formation of I(1,4,5,6)-P4 was required for proper transcriptional regulation in response to extracellular arginine. Thus, signaling through inositol polyphosphates appears to be intimately associated with regulation of transcription in the nucleus.

  12. Retinal Regeneration in Mammals?

    The retina in some nonmammalian vertebrates, such as fish and amphibians, can continue cellular renewal throughout life and regenerate in response to damage. These abilities are, however, lost to the mammalian retina, thus increasing the susceptibility of our vision to loss or degradation through disease. Traces of the more primitive developmental flexibility may yet exist, however. Tropepe et al. (p. 2032) have now found that, in mice, certain cells from the ciliary margin of the retinal pigmented epithelium function as stem cells. In culture, these cells will proliferate and will also generate differentiated neuronal cell types typical of the retina. Tremendous potential exists if this developmental flexibility can be manipulated for therapeutic benefit.

  13. Self-Assembled Magnetic Memories

    In order to satisfy the increasing demand for yet higher memory storage density, there is a constant effort to reduce the size of magnetic elements on which the magnetic information can be stored. Some processes exist for ultrahigh density storage based on the local modification of the surface. However, these processes are relatively slow as the elements are fabricated one by one. Sun et al. (p. 1989) report on a new synthesis route for the self-assembly of two-dimensional arrays of FePt nanoparticles, which are several nanometers apart, and each element is separated by several nanometers. By controlling the synthesis process, the particle size and particle separation can be controlled. (See the news story by Service.)

  14. Addressing Memory Side Effects

    One of the challenges for psychiatric medication is to provide effective treatment with only minimal side effects. Castner et al. (p. 2020) show that a widely used antipsychotic treatment (administration of haloperidol) decreases working memory in monkeys, most likely through the down-regulation of dopamine D1 receptors in the prefrontal cortex of the brain. However, when they combined the antipsychotic treatment with short periods of D1 receptor agonist application, the working memory impairment could be completely compensated. This deficit reversal was long lasting and would still be detected more than 1 year after agonist administration.

  15. A New Beginning

    Monocular deprivation is a well-established experimental model for the study of neuronal plasticity during the early postnatal period. Trachtenberg et al. (p. 2029) combined optical imaging methods with electrophysiological recordings to determine where the initial effects of this plastic shift in ocular dominance are located. In contrast to the prevailing opinion, the synaptic remodeling does not begin in layer IV, the thalamorecipient area of the neocortex. The effects occur first in the superficial and deep cortical layers and spread only secondarily to layer IV. (See the Perspective by Cynader.)

  16. Quick as a Flash

    As fast as neural processing of visual stimuli appears to be, it still takes time. How do we allow for what happens during the time needed for processing and thus to adjust our perception of events that change with time, such as motion of an object? Eagleman and Sejnowski (p. 2036) provide a new explanation for a robust visual illusion known as the flash-lag effect. They suggest that the reason that a superimposed stationary flash of light and a moving object appear to be displaced from each other is that we extrapolate backward in time from what we see during approximately 80 milliseconds after the flash. They go on to argue against other proposals (for predictive extrapolation or for differences in processing speed of stationary and moving objects) from a series of psychophysical experiments.

  17. Kentucky 31, Far from Home

    Clay and Holah (Reports, 10 Sep., p. 1742) found that the presence of a host-specific fungal endophyte in the tall-fescue cultivar Kentucky 31 (KY-31) significantly reduced species diversity in experimental plots, and suggested that natural areas in which fescue is common and highly infected may suffer a similar loss of species richness. Saikkonen argues that these results, rather than constituting a model of endophyte-plant symbiosis, should instead be viewed as evidence of “ecosystem vulnerability to human-induced invasion” by an inbred, highly competitive exotic species. Clay and Holah respond that the experimental design of their study isolated the effect of endophyte infection from “other potentially confounding factors,” and that the well-documented success of wild endophyte-infected grasses is “clearly not predicated on being either exotic or inbred.” The full text of these comments can be seen at

Log in to view full text

Via your Institution

Log in through your institution

Log in through your institution