Editors' Choice

Science  24 Mar 2006:
Vol. 311, Issue 5768, pp. 1675

    Seasonal Tastes

    1. Caroline Ash

    The mosquito-borne West Nile virus (WNV) has caused repeated human epidemics in North America and is a zoonotic virus transmitted by Culex mosquitoes whose preferred host is the emblematic American robin (Turdus migratorius). Kilpatrick et al. have shown that the mosquitoes exhibit a shift in feeding behavior when the robins disperse after breeding. In early summer (May and June), about half of the mosquitoes' blood meals come from the robin, despite house sparrows (Passer domesticus) being common and susceptible to infection. In late summer (July to September), the robins disperse and the Culex shift to feeding on humans, again despite the ubiquity of house sparrows. Integrating available data into a model based on a shift in mosquito feeding preference leads to the prediction that the peak transmission of WNV to humans should occur by late July to mid-August and then decline in early October when cold weather hampers mosquito activity. Seasonal shifts in mosquito feeding behavior occur across the United States and appear to intensify epidemics of several avian zoonotic viruses, not only WNV but also Western equine encephalitis virus, St. Louis encephalitis virus, and possibly other vector-borne pathogens. — CA

    PloS Biol. 4, e82 (2006).


    A Collapsing Umbrella

    1. Brooks Hanson

    Observations of volcanic plumes have provided fundamental insight into volcanic processes, one notable instance being Pliny the Younger's descriptions of Vesuvius in 79 AD. Large eruptions, like nuclear explosions, often form an umbrella-shaped plume. The top of the umbrella forms when hot gases and particles in a central eruption column reach neutral bouyancy and mix with cold dense air that is being driven upward; this process helps to stabilize the umbrella, allowing ash to fall gradually. Most such plumes have a cauliflower-shaped outer surface.

    Chakraborty et al. describe a more ordered umbrella that formed during the November 2002 eruption of Reventador in Ecuador. In this instance, the edge of the umbrella formed large regular undulations approximately every 0.7 km, producing a shape similar to the edge of a scallop. The authors ascribe this phenomenon to an instability that occurs when the outer rim of the umbrella becomes too dense to be neutrally buoyant, a plausible result of this relatively cool eruption. Such a loss of buoyancy could lead to collapse of the umbrella, which would produce another type of volcanic flow. — BH

    Geophys. Res. Lett. 33, L05313 (2006).


    Misjudging Priors

    1. Gilbert Chin

    Mental models or simulations of future outcomes can be extremely helpful in planning and guiding our behavior, as when a forward model of a reaching movement is used to reduce the variance in the trajectory of the arm. In situations where several outcomes with associated likelihoods exist, there is a known tendency, referred to as hindsight bias, for the actual outcome to inflate our post-outcome estimates of the initial likelihoods.

    One arena where this bias comes into play is in the forensic reconstructions of traffic accidents, and Roese et al. have examined whether using computerized simulations (versus text and diagram visual aids) elicits these overestimates. They find that animated sequences exacerbate hindsight bias and, more intriguingly, that the bias reverses when the post-outcome estimate is compared to one made just before the time of collision. This so-called propensity effect describes our sense that the collision is destined to occur before it takes place, something we are surprisingly less certain about after the collision has actually occurred. — GJC

    Psychol. Sci. 17, 305 (2006).


    Small-Scale Synergy

    1. Marc Lavine

    In metallic and semiconductor nanoparticles, the material properties can be tuned simply by changing the particle size. Shi et al. have explored the additional dimension of varying nanoparticle composition to incorporate multiple kinds of materials—specifically magnetic-metallic, magnetic-semiconducting, and semiconducting-metallic hybrids, as well as ternary combinations.

    The synthetic strategy involved spontaneous epitaxial nucleation and growth of the second and third components onto seed particles in high-temperature organic solutions. For the magnetic-metallic particles (Fe3O4 grown on gold), solvent choice influenced the particle morphology, with good electron donors leading to core-shell geometries and poor electron donors yielding peanut-shaped fused particles. For Au-PbS particles, which combine a metal and a semiconductor, the choice of solvent did not influence the particle morphology, but the concentration of gold seed particles was critical. Finally, heating strategy and seed particle dimensions were the key variables for setting the ternary particle morphologies. The optical and magnetic properties of the particles were influenced by the hybrid interface. For example, the Au plasmon resonances were red-shifted in the hybrid particles; at the same time, the magnetization saturation field of the Fe3O4-Au particles was an order of magnitude greater than that of pure magnetite. — MSL

    Nano Lett. 6, 10.1021/nl0600833 (2006).


    Switching Philicity

    1. Jake Yeston

    The immiscibility of organic and aqueous solutions (such as oil and vinegar) underlies a wide range of practical chemical separations. For versatility, liquid fluorocarbons have come into increasing use over the past decade as a third solvent phase, into which highly fluorinated solutes partition from both water and the more traditional organic solvents.

    Orita et al. were therefore surprised to find that a hydrated distannoxane complex bearing linear fluorocarbon tails—an Sn-O-Sn core with two C6F13C2H4 chains and a perfluorooctane sulfonate chain appended to each Sn—failed to dissolve in common fluorous solvents such as FC-72. The compound did dissolve in polar organic liquids (ethyl acetate, acetone, and tetrahydrofuran), and subsequently partitioned into the fluorous phase upon addition of FC-72 to the solution. The authors explain these observations by suggesting that the waters of hydration initially bound to the tin repel the fluorous solvent but can be displaced by polar organics, which in turn allows the fluorous liquid to approach. The compound proved useful as a homogenizing agent for fluorous and organic solvents, with 1.7 g nearly tripling the solubility of ethyl acetate in FC-72. — JSY

    J. Am. Chem. Soc. 128, 10.1021/ja058105v (2006).


    More Is Bigger

    1. Guy Riddihough

    Multicellular organisms can grow by making more cells or by making larger ones. The nematode Caenorhabditis elegans uses both methods: Cell proliferation drives worm growth until sexual maturity, whereas cell growth (mainly of epidermal cells) accounts for the twofold increase in size during adulthood. Growing adult cells also undergo endoreduplication, wherein genomic DNA is replicated repeatedly without cell division, resulting in each cell containing multiple copies of the genome (polyploidy) rather than just two.

    Lozano et al. address the question of whether endoreduplication is directly responsible for adult growth in the worm. Blocking endoreduplication after the final larval molt results in dwarf worms that are roughly half the size of wild-type adults, whereas in a tetraploid strain, adult worms are roughly 40% larger than normal. Cyclin E is involved in the control of endoreduplication in a number of organisms, including C. elegans, and adult worms mutant for cye-1 have both reduced epidermal ploidy and are dwarfed, often to less than half the size of comparable wild-type adults. Although it is clear that endoreduplication can account for the growth of polyploid somatic cells in worms, cells that remain diploid in the adult are presumably stimulated to grow by their polyploid neighbors. — GR

    Curr. Biol. 16, 493 (2006).

  7. STKE

    Larger Pipe, Lower Resistance

    1. Elizabeth Adler

    The pathogenesis of hypertension—a risk factor for heart disease, kidney disease, and stroke—is complex and poorly understood. Zacchigna et al. find that mice lacking elastin microfibril interface-located protein 1 (Emilin1), a secreted extracellular matrix protein expressed in the cardiovascular system, had high blood pressure in conjunction with decreased blood vessel diameter and increased peripheral resistance. Emilin1 contains a cysteine-rich domain, as do other proteins involved in the regulation of growth factor signaling, leading the authors to investigate the relationship between Emilin1 and transforming growth factor-β (TGF-β), which plays a critical role in vascular development and pathophysiology. Emilin1 blocked TGF-β signaling upstream of receptor activation and did not interfere with ligand/receptor binding or signaling in response to mature TGF-β1. Rather, Emilin1 bound to proTGF-β1, preventing its proteolytic processing and the production of biologically active TGF-β1. TGF-β signaling was enhanced in the aortic wall of the mice lacking Emilin1, and inactivation of one TGF-β1 allele in Emilin1 knockout mice restored normal blood vessel diameter and blood pressure. Thus, the authors conclude that Emilin1 acts to regulate blood pressure by modulating TGF-β processing and thus the availability of the biologically active form. — EMA

    Cell 124, 929 (2006).

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