Editors' Choice

Science  17 Mar 2006:
Vol. 311, Issue 5767, pp. 1523

    The Best Laid Plans

    The invasive weed Centaurea maculosa (spotted knapweed) has become widespread in North America. Gall flies (Urophora spp.) have been introduced in an attempt at biological control of the plant. The gall flies lay their eggs in the flower heads, where the larvae induce the formation of galls in which they overwinter. The presence of the galls ultimately results in the plants producing fewer seeds. Although the flies have successfully dispersed throughout populations of the invasive weed, they have not proved to be effective control agents, and the weed continues to spread, particularly in areas disturbed by human activity.

    Pearson and Callaway have discovered that therein lies a deeper threat. The fly grubs have proved to be an attractive food source for Peromyscus (deer) mice and bolster mouse populations during otherwise lean winter months. This genus of mice are reservoir hosts for the human pathogenic hantavirus, Sin Nombre, and, worryingly, the authors found that the abundance of hantavirus-seropositive mice is elevated in zones of high abundance of weed and flies. Deer mice also act as reservoir hosts for Lyme disease and potentially for plague and other zoonotic pathogens. — CA

    Ecol. Lett. 10.1111/j.1461-0248.2006.00896.x (2006).


    Hide and SECIS

    Insertion of the 21st amino acid, selenocysteine, into selenoproteins occurs at what is usually a translation stop codon, UGA. This creates something of a dilemma in eukaryotic cells, because mRNAs carrying a premature stop codon are normally subject to nonsense-mediated decay (NMD). NMD is a process that destroys the mRNA and prevents the cell from synthesizing potentially dangerous truncated proteins. Indeed, when selenoprotein synthesis is limiting, selenoprotein mRNAs can be degraded by NMD.

    In eukaryotes, recoding of the UGA stop codon is achieved through a secondary structure, the SECIS element, in the 3′ untranslated region of the selenoprotein mRNA. This element binds a complex of the SECIS binding protein (SBP2) and the elongation factor EFsec. De Jesus et al. investigated the subcellular location of these two proteins. Both proteins possess functional nuclear localization and nuclear export signals, and SBP2 is capable of shuttling between the cytoplasm and the nucleus. SBP2 and EFsec co-localize, suggesting that SBP2 may contribute to nuclear retention of EFsec. Furthermore, the level of the SBP2 protein correlates with the level of selenoprotein mRNAs, suggesting that it might stabilize these mRNAs. Thus, the prompt nuclear deposition of the two proteins on the SECIS element may play a role in protecting the selenoprotein mRNA from the unwanted attentions of the NMD machinery. — GR

    Mol. Cell. Biol. 26, 1795 (2006).


    Penultimate Monsoons

    Analysis of stalagmites has provided remarkably detailed records of precipitation patterns and particularly of changes in monsoonal rainfall. Some stalagmites have been used to chronicle variations of the Asian monsoon for most of the past 160,000 years, revealing close connections between these variations and regional climate behavior in distant locations. The data also help to deepen understanding of how climate dynamics have operated in the past.

    Cheng et al. add to this body of knowledge with a record of oxygen isotopes from three stalagmites in Hulu Cave, China, characterizing most of the interval between 128,000 and 178,000 years ago. Most of the penultimate deglaciation period—during which atmospheric CO2 concentration rose and much of the accompanying rise in atmospheric methane took place—occurred during a time of weak Asian monsoons, when the high northern latitudes likely were cold. Thus, the penultimate deglaciation seems to have been a two-phase process driven by orbital forcing in both hemispheres. — HJS

    Geology 34, 217 (2006).


    Pulled but not Distorted

    Single-molecule force spectroscopy can be used to examine the potential energy landscape of displacement reactions. Such analysis assumes that the reaction mechanism remains the same when the dissociation step is assisted by mechanical force. Kersey et al. explored this question by attaching substituted pyridines to a substrate and an atomic force microscope tip, and then bridging the tip and substrate using a molecule with square-planar Pd centers that could bind each pyridine. They then measured force-extension curves for various loading rates that captured bond rupture events in which dimethyl-sulfoxide (DMSO) solvent displaced the pyridine ligands from Pd. The thermal rates extrapolated from the data corresponded well with rates measured by nuclear magnetic resonance for the analogous displacement reaction in free solution. Thus, the same bimolecular mechanism appears to operate in both the thermal and nonequilibrium applied stress regimes, with the observed stress-induced acceleration (approximately a 10-fold rate increase for a 50-piconewton force) arising from a lower-energy transition state for Pd-pyridine bond scission and Pd-DMSO bond formation. — PDS

    J. Am. Chem. Soc. 10.1021/ja058516b (2006).


    Black Hole Encryption

    What happens to the quantum information ingested by a black hole? In 1997, Thorne and Hawking argued that information swallowed by a black hole is forever hidden, despite the fact that these dense objects do emit a peculiar kind of radiation and eventually evaporate. Preskill countered that for quantum mechanics to remain valid, the theory mandates that the information has to be released from the evaporating black hole in some fashion. Although Hawking conceded in 2004, the disagreement between Preskill and Thorne still stands.

    Smolin and Oppenheim now find that one of the main assertions made about black holes may be flawed. It is often assumed that as the black hole evaporates, all of the information gets stored in the remnant until the very end, at which point the information is either released or else disappears forever. Instead, Smolin and Oppenheim suggest that the information is distributed among the quanta that escape during evaporation, but is encrypted and thus effectively locked away.

    The catch is that it can only be accessed with the help of the quanta released when the black hole disappears, in much the same way as a cryptographic key unlocks a coded message. The result offers a link between general relativity and quantum cryptography. — DV

    Phys. Rev. Lett. 96, 081302 (2006).


    Dendritic Cells Diversify

    Dendritic cells act as pivotal coordinators of the immune response, inducing T cells to develop specific effector functions, such as the killing of tumor cells.

    Chan et al. present evidence that at least one new lineage of dendritic cells may, in fact, be tasked with an even broader remit than previously thought. After stimulation through innate immune receptors, a subpopulation of cells could be induced to display major features of conventional dendritic cells. However, before arriving at this point, they first transited through a phenotype more akin to that of a natural killer (NK) cell, including being able to produce interferon gamma (IFN-γ) and to kill NK-sensitive target cells. These interferon-producing killer dendritic cells (IKDCs) displayed similar properties in vivo, and after activation were seen to migrate to lymph nodes to carry out their antigen-presenting functions. Taieb et al. also observed that IKDCs were a principal source of IFN-γ and also used expression of the pro-apoptotic ligand TRAIL to kill malignant cells and reduce the tumor burden in a mouse melanoma model. Both studies raise questions about the relationships between the cellular components that sense, regulate, and execute tumor immunity. — SJS

    Nat. Med. 12, 207; 214 (2006).


    Plant Wars

    In plant ecology, it is commonly observed that some plant species will facilitate the establishment or persistence of other species. Weir and Vivanco have uncovered the biochemical basis of such facilitation in North American grasslands invaded by Centaurea maculosa (spotted knapweed). The invading species produces a phytotoxin, catechin, which induces oxidative stress in many native plants and often thereby eliminates them entirely from the local ecological community. A few native species, such as Gaillardia grandiflora, are able to resist knapweed invasion, and several of these species, including Lupinus sericeus, facilitate the resistance of native grasses to the invader. Lupinus secretes oxalate from its root tissues in response to catechin exposure. By blocking reactive oxygen species, oxalate affords protection to neighboring vulnerable plants against the toxic effects of catechin. These results suggest strategies for controlling a serious invader and also provide insight into the multiplicity of facilitation mechanisms involved as plant communities develop. — AMS

    Planta 10.1007/s00425-005-0192-x (2006).