This Week in Science

Science  23 Oct 2009:
Vol. 326, Issue 5952, pp. 498
  1. Croaking Frogs


    The global amphibian decline has been attributed, among other causes, to an amphibian skin disease chytridiomycosis caused by the fungus Batrachochytrium dendrobatidis. However, how this pathogen causes mortality has been unclear. Voyles et al. (p. 582) show that this superficial skin infection may lead to cardiac failure owing to changes caused by lowered ion transport through the skin and consequent electrolyte reduction in the blood.

  2. Drosophila Body Color

    Fly body color is controlled by a variety of genes and alleles. Now Wittkopp et al. (p. 540) describe how two genes at the ebony and tan genetic loci control body color among two closely related species, Drosophila americana and D. novamexicana. Variations at the tan locus and linked to the ebony locus also contribute to intraspecific pigmentation changes with geography in D. americana. The sequencing of multiple isolates suggests that some strains of D. americana carry alleles of tan and ebony that are more closely related to the D. novamexicana alleles than they are to other D. americana alleles. Thus, the genetic determinants of both inter- and intraspecies color variation is due to shared alleles.

  3. Yeast Joins RNAi Club


    RNA interference (RNAi) silences gene expression via small interfering (si) RNAs that bind to target sequences. RNAi has been found in almost all eukaryotes examined, with the notable exception of the budding yeast, Saccharomyces cerevisiae, one of the most prominent organisms used in the study of molecular biology. Indeed, RNAi has been thought to be missing from all budding yeast. Drinnenberg et al. (p. 544, published online 10 September; see the Perspective by Moazed) now show that several species of budding yeast do possess RNAi, which seems to act primarily on transposable elements and subtelomeric repeats. A noncanonical Dicer protein generates siRNAs that are loaded onto Ago1 protein in S. castellii. Introduction of these two genes into S. cerevisiae was sufficient to reconstitute RNAi, where it also acted to dampen the activity of transposons.

  4. Measuring Magnetic Light

    Compared to its electric component, the coupling between the magnetic field component of light and matter is usually extremely weak. With no effective way to measure it, we are effectively blind to light's magnetic component. Burresi et al. (p. 550, published online 1 October; see the Perspective by Giessen and Vogelgesang) coupled a metamaterial split-ring resonator to the tip of a scanning probe to measure the magnetic field vector of light at optical frequencies. The ability to measure the magnetic component of light should prove useful for the nanoscale characterization of optical waveguides and other optical devices.

  5. Lunar Water

    The Moon has been thought to be primarily anhydrous, although there has been some evidence for accumulated ice in permanently shadowed craters near its poles (see the Perspective by Lucey, published online 24 September). By analyzing recent infrared mapping by Chandrayaan-1 and Deep Impact, and reexamining Cassini data obtained during its early flyby of the Moon, Pieters et al. (p. 568, published online 24 September), Sunshine et al. (p. 565, published online 24 September), and Clark et al. (p. 562, published online 24 September) reveal a noticeable absorption signal for H2O and OH across much of the surface. Some variability in water abundance is seen over the course of the lunar day. The data imply that solar wind is depositing and/or somehow forming water and OH in minerals near the lunar surface, and that this trapped water is dynamic.

  6. Life in Dead Zones

    Oxygen minimum zones, or oceanic “dead zones,” are expanding. Marine dead zone expansion and intensification results in amplification of biological nitrogen and greenhouse gas production, with implications for marine fisheries' productivity and for climate balance. Little is known about the microbial communities mediating the underlying biogeochemistry of dead zones. Walsh et al. (p. 578) present metagenomic analyses of a ubiquitous, abundant, and uncultivated bacterium in oceanic dead zones. Similar bacteria, related to chemoautotrophic gill symbionts of deep-sea clams and mussels, play a role in sulfide detoxification in African shelf waters. Reconstruction of the carbon and energy metabolism of this enigmatic lineage revealed a metabolic repertoire mediating carbon sequestration, sulfur-detoxification, and biological nitrogen loss in oxygen-deficient oceanic waters.

  7. Observing Unrevealed Preferences

    Ideally, it would be possible to design a system of incentives for the production and allocation of public goods with the following properties: (i) it would be budget-balanced; (ii) people would participate willingly because they would not be made worse off by doing so; (iii) it would be easy for each participant to find his or her optimal strategy; and (iv) the equilibrium solution would yield the optimal production of the public good. Sadly, this set of conditions cannot be satisfied simultaneously because it requires that self-interested individuals reveal voluntarily and truthfully how much they value the public good. Krajbich et al. (p. 596, published online 10 September) ask whether a neuroimaging measurement can be used to circumvent this reliance on observed behavior by decoding individual valuations. A decoding accuracy of 55% would be sufficient, and, in a laboratory experiment, an optimal provision of public goods was indeed achieved.

  8. Methane Loosely Bound

    For the most part, molecular bonds involve sharing of electrons between two discrete atoms. In certain cases, however, a third atom can also attract a portion of the electron density without fully cleaving the bond. Such loose complexes between C-H bonds and transition metals are often invoked as short-lived intermediates in metal-catalyzed reactions of hydrocarbons, though they are rarely observed directly. Bernskoetter et al. (p. 553) glimpse this coordination motif for methane (CH4) and rhodium (Rh) using low-temperature nuclear magnetic resonance spectroscopy after protonation of an Rh-CH3 precursor. Kinetics measurements revealed a half-life of just over 80 minutes at −87°C.

  9. A Smooth(ened) Path to Drug Resistance

    The Hedgehog (Hh) signaling pathway has emerged as a key contributor to the growth of medulloblastoma, an aggressive brain tumor. GDC-0449, a drug that ramps down this signaling pathway by binding to the Hh pathway component Smoothened, was recently shown to induce rapid and dramatic tumor regression in a patient with metastatic medulloblastoma, but the tumor eventually developed resistance to the drug. Yauch et al. (p. 572, published online 3 September) show that resistance arose because the tumor acquired a mutation in Smoothened that disrupts binding of the drug. Identification of this resistance mechanism may facilitate the design of next-generation drugs for this type of cancer.

  10. Stretching Carbene Versatility


    Stable N-heterocyclic carbene (NHC) molecules are versatile catalysts for organic reactions (see the Perspective by Albrecht). Lavallo and Grubbs (p. 559) now show that these molecules can also catalyze organometallic transformations. Specifically, the carbenes induce coupling of monomeric iron olefin complexes to form clusters incorporating three or four bonded iron centers. Initial coordination of carbene to iron may facilitate formation of an iron-iron bond with a second complex. In a related development, Aldeco-Perez et al. (p. 556) prepared an NHC isomer in which the divalent carbon is shifted so that it no longer lies between the nitrogens. The compound forms stable complexes with both gold and CO2.

  11. Viral Link to Chronic Fatigue

    Chronic fatigue syndrome (CFS) is a complex and debilitating disorder that is often linked to immune system dysfunction but whose cause(s) remain mysterious. Lombardi et al. (p. 585, published online 8 October; see the Perspective by Coffin and Stoye) now present a tantalizing new lead. In blood samples from 101 patients with well-documented CFS, over two-thirds (68) contained DNA from a recently described human gammaretrovirus, xenotropic murine leukemia virus–related virus (XMRV), which possesses sequence similarity to a murine leukemia virus. Cell culture assays confirmed that XMRV derived from CFS patient plasma and from T and B lymphocytes was infectious. Although the correlation with CFS is striking, whether the virus plays a causal role in the disorder remains to be determined. Interestingly, nearly 4% of the 218 healthy donors tested were positive for XMRV, which suggests that this virus—whose pathogenic potential is unknown—may be present in a significant proportion of the general population.

  12. Dissecting Megaenzyme Mechanisms

    Filamentous fungi contain a class of multidomain enzymes, the highly-reducing iterative polyketide synthases (HR-IPKSs), which produce important natural products such as the cholesterol-lowering drug lovastatin. To produce their complex products, these megasynthases use multiple catalytic domains repeatedly in different combinations, but mechanistic details remain unclear. Ma et al. (p. 589) now report in vitro reconstitution of the complete catalytic function of lovastatin nonaketide synthase (LovB), the megasynthase that works together with a partner enzyme LovC to complete nearly 40 chemical steps required to construct the core of lovastatin. Analyses of the dependency of enzyme function on cofactors and on the partner enzyme elucidate the programming rules for this system.

  13. Experimental Economics

    The disciplines of social science, with the notable exception of psychology, have traditionally steered clear of laboratory. The field of economics, and in particular econometrics, has amassed an imposing arsenal of quantitative and statistical methods for analyzing observational data in assessing economic theory and in making causal inferences. More recently, laboratory experiments carried out under controlled conditions and randomized field experiments carried out under natural conditions have gained some currency as complementary approaches. Falk and Heckman (p. 535) review the strengths and shortfalls of these recent developments.

  14. Cdc20-APC in Synapse Formation

    The E3 ubiquitin ligase Cdc20-anaphase promoting complex (Cdc20-APC) has important roles in the control of the cell division cycle. Yang et al. (p. 575) now show that Cdc20-APC also appears to be required for proper formation of synapses by developing neurons in the rat brain. When Cdc20-APC was depleted from cultured neurons or in the brains of developing rat pups, synapse formation was inhibited. The brain-enriched transcription factor NeuroD2 was shown to be a possible target of Cdc20-APC–stimulated degradation. NeuroD2 may act by promoting synthesis of Complexin II, a protein that regulates synaptic vesicle fusion.

  15. Toward Neuronal Regeneration

    Neurons in the central nervous system that are severed or crushed do not regenerate well. Part of the problem derives from the glial scars left behind after such damage. The scar tissue contains sulfated proteoglycans that seem to inhibit axon regeneration. Shen et al. (p. 592, published online 15 October) have now identified a protein tyrosine phosphatase (PTP) in mouse neuronal membranes that functions as a receptor for the proteoglycans. Neurons that lacked this particular PTP showed improved regeneration. Regeneration remained incomplete, presumably due to other inhibitory factors in the way of complete axon regeneration.

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