Editors' Choice

Science  14 Feb 2003:
Vol. 299, Issue 5609, pp. 979

    Suspended Animation

    1. Stella M. Hurtley

    A continuous supply of oxygen generally is required to maintain energy supplies in aerobic organisms. Drosophila embryos, however, are capable of withstanding profound oxygen deprivation. Teodoro and O'Farrell find that, as soon as severe hypoxia begins, embryos arrest development, but they remain capable of resuming development even after several days in the absence of oxygen. This “suspended animation” phase did not result in the turning on of stress-related genes, but it did rely on the stabilization of RNAs (and proteins) of developmental patterning genes like engrailed. Surviving oxygen deprivation involved nitric oxide (NO) metabolism, and entry into stasis could be triggered by adding NO donors. In addition, scavenging NO increased the likelihood that embryos would not survive prolonged hypoxia. — SMH

    EMBO J.22, 580 (2003).


    Punctuated Glaciation

    1. Brooks Hanson

    Sea level rose more than 150 m following the last glacial maximum about 20,000 years ago, and similarly during the previous interglacial, about 130,000 years ago. The rise was episodic, with periods of rapid melting of large ice sheets in Antarctica and the Northern Hemisphere. The sea level fluctuations during large ice sheet formation from about 120,000 to 20,000 years ago also contain information about climate and ice sheet dynamics, but it has been difficult to extract because many corals—the best recorders of past sea levels—are now buried underwater.

    Cutler et al. provide a detailed view of sea level history by accurately dating corals, some from underwater drill cores, in Barbados and Papua New Guinea. These records indicate that sea level fell and rose cyclically, at rates as high as 60 m over 6000 years after the end of the previous interglacial, before falling just prior to the last glacial maximum to more than 100 m below the current level. Notably, the periods when sea level dropped rapidly correspond to times when moisture transport toward the poles was enhanced and to declines in deep-ocean temperatures. — BH

    Earth Planet. Sci. Lett.206, 253 (2003).


    RNAi Makes Plants Ill

    1. Guy Riddihough

    Plants use a number of strategies to repel viral invaders, including targeting viral RNA for degradation, a mechanism known as RNA silencing. In turn, many plant viruses defend themselves by endeavoring to suppress RNA silencing. Successful infection often results in developmental defects, and Kasschau et al. report that these defects may be a consequence of this warfare.

    RNA silencing is part of a set of pathways that includes microRNAs (miRNAs)—small genome-encoded RNAs that posttranscriptionally repress expression of their target messenger RNAs during normal growth. Abrogation of RNA silencing in Arabidopsis by a turnip mosaic virus suppressor protein results in the dysfunction of a number of miRNAs and the mis-regulation of their target genes, which control a range of developmental processes. It is likely that the ectopic expression of these (and other) genes causes many of the disease symptoms seen in Arabidopsis and in many other viral plant diseases. — GR

    Dev. Cell4, 205 (2003).


    CRP Screening: Taking No Risks

    1. Paula A. Kiberstis

    Only some individuals who develop coronary artery disease have high cholesterol levels, and there has been considerable interest in markers that would identify high-risk individuals who might be missed in cholesterol screens. Over the past decade, C-reactive protein (CRP), a liver-derived inflammatory protein, has emerged as a strong and independent predictive marker of future cardiovascular disease (News Focus, 12 April 2002, p. 242). Importantly, CRP levels can be measured in a simple and relatively inexpensive blood test.

    Whether and how CRP tests should be incorporated into clinical practice are questions being discussed in the cardiovascular research community, as described in several articles, which include the official set of recommendations from an expert panel assembled by the American Heart Association and the U. S. Centers for Disease Control and Prevention. Although Pearson et al. acknowledge that the CRP test may provide helpful data in cases where other risk factors are present (e.g., for individuals who have high blood pressure and/or moderately high levels of cholesterol), they did not endorse widespread use of the test and stressed the need for studies to determine whether interventions that lower CRP levels will, in fact, lower the rate of heart disease. — PAK

    Circulation107, 499 (2003).


    Give and Take

    1. Caroline Ash

    Parasitoid wasps lay eggs within the bodies of insects, and when the larvae hatch, they consume the insect from within and kill it. These kinds of wasps are exploited as biocontrol agents, but even easily visible parasitoid targets, such as aphids, are not sitting ducks. Oliver et al. have shown that some secondary bacterial symbionts protect pea aphids against the ravages of parasitoid attack. They exposed aphids, inoculated with three different secondary symbionts, to adult wasps. Two of the secondary symbiont types killed 25 to 41% of the developing parasitoid larvae a few days after oviposition. These aphids continued to reproduce and transmit the protective symbionts to their daughters, hence maintaining the symbiont population. But it's not a perfect partnership, as there seems to be a cost borne from pathogenic effects of the symbionts that ultimately compromises aphid fecundity and longevity. — CA

    Proc. Natl. Acad. Sci. U.S.A.100, 1803 (2003).


    Creepy Mantle

    1. Linda Rowan

    Periclase (MgO) is a minor component of Earth's lower mantle, yet it may be essential for understanding the rheological and chemical characteristics of solid-state creep (mantle convection) because of its elastic anisotropy and ionic conductivity. Van Orman et al. measured lattice and grain boundary diffusion of 25Mg and 18O in isotopically marked, synthetic periclase at 2273 kelvin and 25 gigapascals in a multianvil device, and then extrapolated to conditions (∼4500 kelvin and 140 gigapascals) at the core-mantle boundary (CMB). A transition from dislocation creep to diffusion creep is predicted to occur near the CMB for grains smaller than 1 mm and shear stresses of 1 to 10 megapascals. Substantial chemical exchange near the CMB is allowed by the relatively fast rate of diffusion in periclase. In particular, grain boundary diffusion is very efficient, and over the 4.5 billion years of Earth's history, a mixed layer of 100 kilometers in thickness could have formed. Thus, the rheological and chemical properties of the mantle are consistent with the seismically observed D” layer at the CMB. — LR

    Geophys. Res. Lett.30, 1056, 10.1029/2002GL016343 (2003).


    A Bit of a Stretch

    1. Marc S. Lavine

    Gold is a malleable metal, but just how far can it be stretched before breaking? In a diatomic gold molecule, the Au-Au bond length is 2.48 Å. On the other hand, for mechanically stressed, single atom-thick Au nanowires, Au-Au distances as large as 4.0 Å have been measured by transmission electron microscopy and cluster around 3.6 Å, yet calculations for pure Au wires have yielded a maximum of 3.1 Å.

    Using total energy density functional theory, Novaes et al. calculated the effect of impurity atoms on stressed gold nanowires. Single H, B, C, N, O, or S atoms, which probably would not have been observable in micrographs of nanowires due to insufficient contrast, were inserted at various positions. The relaxed wires were then pulled until they ruptured, which always occurred at an Au-Au bond. The addition of a carbon atom led to a Au-C-Au distance of 3.7 Å for the unstressed wire, which increased to 3.9 Å just prior to breaking; wires containing B, N, and O displayed even larger distances when stretched. However, the addition of H produced a distance of 3.6 Å, consistent with the experimentally observed cluster, and an anomalously large distance of 4.8 Å could be explained as the separation between gold atoms in an Au-S-Au nanowire. — MSL

    Phys. Rev. Lett.90, 036101 (2003).


    The Strain of Fusing

    1. Phil D. Szuromi

    One way to generate an “anti-aromatic” system, in which the overall π-bonding network is destabilizing, is to add two electrons to an aromatic network. Aprahamian et al. have done that in two strained pyrene systems; a large ring bridges the ends of pyrene and bends the π-bonded network out of a single plane without disrupting aromaticity. Nuclear magnetic resonance spectroscopy revealed that adding two electrons did not yield an anti-aromatic molecule. Instead, a new σ bond formed across one of the six-membered rings, creating fused cyclopropyl and cyclopentyl rings. This alternative not only diminishes the induced ring strain in the pyrene network, but it also allows the two added electrons to localize and distance themselves. Thus, although strain does not reduce aromaticity in these pyrenes, it does affect their reactivity. — PDS

    J. Am. Chem. Soc. 10.1021/ja0291991 (2003).