Editors' Choice

Science  25 Mar 2005:
Vol. 307, Issue 5717, pp. 1841

    Imaging Surface Plasmons

    The drive to integrate optics with nanoelectronics presents a number of problems, one of which is the several orders of magnitude mismatch in the size of the respective components. For example, optical waveguides are typically of micrometer size, whereas active structures such as quantum dots tend to measure only several nanometers. Surface plasmons, which are coupled excitations of light and electrons that propagate on metallic surfaces and that are much smaller than the photon wavelength, are one route being pursued to bridge this gap in scale. Tetz et al. present an imaging technique for studying the excitation and propagation of surface plasmons. The ability to observe directly how these excitations propagate should provide an important step forward in coupling them to nanoscale structures. — ISO

    Appl. Phys. Lett. 86, 111110 (2005).


    Dating Service

    Radiocarbon dating is the preeminent method for determining the age of carbonaceous materials younger than about 50,000 years. The determination of accurate calendar ages from radiocarbon ages requires a calibration curve, though, because the production of 14C and its distribution between atmospheric, oceanic, and terrestrial carbon reservoirs both vary with time.

    Charged with the task of producing the official calibration curve for terrestrial radiocarbon dating, the IntCal working group has just released the latest version, IntCal04. Reimer et al. present this new curve, which replaces the previous version that has been in effect since 1998. IntCal04 extends the calibration backward by 2000 years, to 26,000 calendar years before the present (cal yr B.P., where the present is defined as 1950), increases the resolution of the period earlier than 11,400 cal yr B.P., and considers the uncertainty in both the calendar age and the 14C age in the calibration. Tree ring data contribute the bulk of the ages in the interval between today and 12,400 cal yr B.P., and marine data from corals and foraminifera provide the calibration for samples older than 12,400 years. Associated papers in the same issue describe the details of this impressive and valuable achievement. — HJS

    Radiocarbon 46, 1029 (2005).


    Taking the Low Road

    Listeria monocytogenes bacteria are well known among cell biologists for their spectacular hijacking of the actin cytoskeleton early after infection, which enables them to zoom around inside target cells, propelled by actin comet tails. At later stages of infection, Listeria use another clever strategy to spread between host cells without risking exposure to the host immune system: They invade neighboring cells by inducing bacteria-containing cellular protrusions that somehow transfer the bacteria to the neighboring cell without it ever being exposed to the extracellular milieu.

    Pust et al. examined the process of cell-cell transfer of Listeria and found that in addition to the actin cytoskeleton, the bacteria exploit the cellular protein ezrin, which functions as a plasma membrane-cytoskeleton linker. Interfering with the phosphorylation of ezrin leads to short collapsed protrusions that fail to deliver bacteria efficiently between cells. — SMH

    EMBO J. 10.1038/sj.emboj.7600595 (2005).


    A Signal for Suppression

    T cells with a dedicated regulatory function (T-reg) maintain a crucial balance in immune responses and prevent autoimmune responses by effector T cells. Although the cytokine transforming growth factor-β (TGF-β) is central to T-reg cell activity, key questions remain about how T-reg cells use this mediator.

    Fahlén et al. explored the role of TGF-β using a model of colitis, in which pathogenic T cells induce severe intestinal inflammation after transfer to healthy lymphocyte-deficient mice; the inflammatory response can be suppressed if T-reg cells are cotransferred. In animals that received pathogenic T cells expressing a nonfunctional TGF-β receptor, T-reg cells were unable to prevent colitis, demonstrating that pathogenic effector T cells must receive TGF-β signals directly. However, the critical source of TGF-β appeared not to be the T-reg cells themselves, indicating that TGF-β is furnished by a distinct population of cells and that the role of T-reg cells is to provide an unidentified signal that acts in conjunction with TGF-β. Furthermore, in the absence of TGF-β, T-reg cells developed normally and retained the ability to suppress effector T cells. These results address the function and source of TGF-β in T-reg cell activity and point to unexplored pathways involved in mediating regulatory events. — SJS

    J. Exp. Med. 201, 737 (2005).


    A Boron Bridge

    Boron compounds have been of continued fundamental interest because of their tendency to adopt unusual electron-deficient bonding. Unlike carbon, boron can form so-called 3-center, 2-electron bonds with two other atoms. Braunschweig et al. have now coaxed boron into a different arrangement, which resembles that of the central carbon in allene. They prepared two compounds in which a lone B atom bridges two transition metal centers: a pentamethylcyclopentadienyl iron dicarbonyl on one side, and either iron tetracarbonyl or chromium pentacarbonyl on the other. X-ray crystallography confirmed an essentially linear bridge structure in both compounds. Density functional theory suggests that the boron forms a traditional 2-electron σ bond with each metal, as well as a partial π bond. Similar compounds have been prepared with the heavier group 13 elements (gallium and thallium), but in those cases π bonding is absent. — JSY

    Angew. Chem. Int. Ed. 44, 1658 (2005).


    The Difference a Week Makes

    Migration is well established as a mechanism by which animals cope with seasonal variations in food supply. It is has also been suggested as a possible way of reducing the burden of parasitism in a range of hosts, either by weeding out infected individuals or by allowing them to escape from environments in which parasites have accumulated. Bradley and Altizer provide evidence that one of the more spectacular examples of migration—that of the monarch butterfly in the North America—may have evolved at least in part as such a mechanism.

    Not all monarch populations migrate, and parasite prevalence is known to be lower in the migratory monarch populations. Butterflies from migratory populations inoculated with a protozoan parasite showed reductions in flight performance and endurance in experimental cages, probably because the parasite influenced metabolic processes associated with flight (there were no changes in wing morphology associated with the presence of the parasite). The authors estimate that the impairment would lengthen the migratory journey from 9 to 10 weeks. Under these conditions, parasitized butterflies would likely suffer a reduced chance of reaching their destination, thus accounting for the differences in parasite burden between migrant and nonmigrant monarchs. Because habitat loss and climate change are expected to affect migrant populations more severely, the prevalence of parasites is likely to increase. — AMS

    Ecol. Lett. 8, 290 (2005).


    First In, Last Out

    In a first-price auction, players submit sealed bids for a known item, which is then sold to the highest bidder at the price of that bid. In a seller's English clock auction, the initial price is high and decreases at a steady rate; players choose not to buy by exiting, and the auction ends when the item is sold to the last player at the price at which the penultimate player exited.

    Berg et al. have modified these two types of auction protocols to explore risk-phobic and risk-philic behavior of subjects. In their version of the first-price auction, the winning bidder is then awarded a monetary sum equal to the difference between the resale price of the item and their bid (generally less than the resale price); for the English clock auction, the last player receives a sum equal to the sale price, whereas the other players receive the same sum but only with a known, non-zero probability (i.e., in some cases they would receive nothing). The authors find that subjects in the first-price auction do not risk making low bids in the hope of gaining a larger payoff and do, in fact, place their bids somewhere between the risk-neutral threshold and the actual resale price. However, in the English clock auction, subjects are more apt to play the gamble, so that they exit the auction earlier than expected value would predict. — GJC

    Proc. Natl. Acad. Sci. U.S.A. 102, 4209 (2005).