This Week in Science

Science  06 Mar 2009:
Vol. 323, Issue 5919, pp. 1261
  1. A Lady Bug's Life

    CREDIT: ANTHONY R. IVES

    The responses of species to environmental change are both ecological and evolutionary. Harmon et al. (p. 1347; see the Perspective by Tylianakis) investigated how species interactions change in an invertebrate predator-prey system and how resistance to heat shock evolves in the prey. During heat-shock disturbance, which reduces aphid abundance, one ladybeetle predator of pea aphids maintained constant predation pressure, while a second ladybeetle species decreased predation pressure. Decreased predation pressure from the second ladybeetle ameliorated the impact of heat shock on aphid abundance. Tolerance to increasing frequency of heat shock evolved rapidly in aphid strains, which was mediated by Buchnera endosymbiotic bacteria. Thus, changes in population abundance depend on disturbance-induced changes in the strength of interactions with other species in a food web.

  2. Approaches to HIV Eradication

    The disappointing outcomes of recent HIV vaccine trials have led to a call for new approaches to treat and cure HIV. Richman et al. (p. 1304) review one such option: eradication of HIV infection by antilatency therapies. Antiretroviral therapies are very effective at suppressing viral replication and lowering viral loads; however, a latent reservoir of virus still persists. Therapies targeting latently infected cells aim to eliminate viral infection. The authors describe potential therapeutic targets; discuss the best experimental systems to test antilatency therapies; and suggest strategies to help researchers, clinicians, funding sources, government agencies, and industry to accomplish these goals.

  3. AMPA Receptor Modulator

    AMPA receptors are the most commonly found neurotransmitter receptors in the nervous system. They mediate fast glutamatergic signaling in many parts of the brain, and are thought to coassemble with regulatory proteins, of which the TARP (transmembrane AMPA receptor regulatory protein) family is perhaps best known. Using proteomic analysis, immunohistochemistry, and electrophysiology of native AMPA receptors from rat and mouse brain, Schwenk et al. (p. 1313; see the Perspective by Tigaret and Choquet) found that two members of the cornichon family, CNIH-2 and CNIH-3, tightly coassembled with the pore-forming subunits of the AMPA receptors. Indeed, about 70% of the AMPA receptor complexes in the mammalian brain assemble with the cornichon proteins, which promote surface expression of the AMPA receptor complexes and modulate their gating kinetics.

  4. Testing Times

    The double-pulsar system J0737-3039A/B has been shown to provide the most precise tests of general relativity. Deller et al. (p. 1327, published online 5 February; see the Perspective by D'Amico) determined the distance to this system by measuring its annual geometric parallax with the Australian Long Baseline Array of radio telescopes. Using this distance, the authors determined that with another 10 years of pulsar-timing observations, PSR J0737-3039A/B will be able to test the validity of general relativity and other theories of gravitation with an accuracy of 0.01%.

  5. Brighter Emission sans Oxygen

    Although single-walled carbon nanotubes (SWNTs) emit characteristic emissions based, for example, on their diameters and chirality, the emission for dispersed SWNTs in organic solvents is often quite weak, which is a drawback for many applications, such as sensing. Two potential causes of weak emission can both be caused by poor surface packing of surfactants: The exposure of the SWNT surface can cause reaggregation, facilitating excitation energy transfer between SWNTs, or oxygen doping, which can open up nonradiative decay pathways. Ju et al. (p. 1319) show that a flavin mononucleotide, modified with a long alkyl chain, packs tightly around SWNTs and, for dispersion in toluene, leads to quantum yields from SWNTs approaching 20%.

  6. Connecting Glass Transitions and Phase Transitions

    CREDIT: HEDGES ET AL.

    The glass transition, in which a liquid converts to an amorphous solid, differs from thermodynamic phase transitions in many ways; for example, the temperature at which the transition occurs depends on the rate of heating or cooling. Hedges et al. (p. 1309, published online 5 February) have performed numerical simulations of a two-component system that interact through a Lennard-Jones potential. They show that unlike an equilibrium phase transition, a first-order transition occurs that is controlled in trajectory space by variables that drive the system out of equilibrium. Two phases coexist heterogeneously: a mobile phase that is relaxed in finite time and an immobile phase.

  7. X-ray Probing of Magnetism

    Correlated electron systems can give rise to a number of exotic electronic and magnetic phases. While probing of the magnetic structure has usually been done with neutron scattering, recent work has shown that x-rays can also be used to probe the magnetism. Kim et al. (p. 1329) use resonant x-ray scattering to determine fully the magnetic structure of the transition metal oxide, Sr2IrO4, and unravel the quantum phase of the material. The technique should be applicable to probe the ground states of many other complex electronic systems.

  8. Ancient Domestication of Horses

    The domestication of horses changed the course of human history. The Botai Culture, present on the Eurasian Steppe from 5700 to 5100 years ago, may have been a location of at least one domestication event. The Botai Culture is known to have interacted with local horses in Northern Kazakhstan but whether the animals were husbanded or hunted has been unclear. Outram et al. (p. 1332) provide three lines of evidence suggesting that the horses were indeed domesticated: First, isotope data from fragments of pottery indicates that the horses were milked during the summer months; second, identification of bit and bridle wear suggests that horses at Botai were harnessed and ridden; and third, the Botai horses resemble later, more slender domestic Bronze Age horses, and not the sturdier wild horses in the region.

  9. Black Wolf of the Family

    Black coat color is fairly common in domestic dogs but relatively rare in their close relatives, wolves and coyotes. Anderson et al. (p. 1339, published online 5 February; see the cover) analyzed the K locus associated with black coat color in dogs, wolves, and coyotes and document the introgression of a domesticated allele into a wild species. The KB allele leads to a dominant black coat in dogs, wolves, and coyotes. Against the common flow of genes from wild to domesticated animals, the KB mutation originally occurred in dogs and later introgressed into wolves and coyotes by hybridization. Furthermore, the relatively high frequency of black wolves in Yellowstone probably reflects positive selection for the KB allele in the wild.

  10. Rot-Eat-Wheat World

    CREDIT: LYNN EPSTEIN

    Fungal diseases have a large impact on the yield of wheat crops. Some strains of wheat carry genes that make them naturally resistant. Breeders have introduced these genes into other wheat strains to share the valuable disease-resistance traits. Two papers now identify the molecular basis of some of these traits (see the Perspective by Kliebenstein and Rowe). Krattinger et al.(p. 1360, published online 19 February) used comparisons with other grass genomes to clone the gene Lr34, which resembles adenosine triphosphate-binding cassette transporters. Fu et al.(p. 1357, published online 19 February) similarly cloned the gene Yr36, which resembles a kinase. Each gene provides, to a greater or lesser extent, resistance to certain fungal pathogens that the fungi cannot overcome by genetic variation. Such durable resistance has tremendous agricultural value.

  11. Divisive Tension

    Chromosome attachments to the mitotic spindle are regulated by tension across the centromere, which ensures accurate chromosome segregation. Spindle microtubules can bind chromosomes at the kinetochore in different configurations, but only bi-oriented attachments can support accurate chromosome segregation. Tension across the centromere distinguishes correct and incorrect attachments, but how tension is sensed to regulate attachments is unclear. The mitotic kinase Aurora B is a key regulator of kinetochore-microtubule attachments, and phosphorylation of Aurora B substrates at kinetochores reduces microtubule affinity. Liu et al. (p. 1350, published online 15 January) tested to see if a tension-sensitive mechanism regulates Aurora B activity. Instead their results suggest that Aurora B kinase activity is not directly regulated by tension, but that phosphorylation of an Aurora B substrate at the kinetochore depends on its distance from the kinase at the inner centromere, and that it is this distance that is affected by tension.

  12. Form → Function

    How do proteins localize to particular sites within the bacterial cell? In many systems, biochemical features of the proteins and their target membranes specify particular localization signals. Now Ramamurthi et al. (p. 1354) report that a geometric cue—positive (convex) membrane curvature—dictates the localization of a small peripheral membrane protein during spore formation in Bacillus subtilis. Membrane curvature may represent a general cue for protein localization in bacteria in the absence of biochemically identifiable signals.

  13. Angling for Clusters

    The Periodic Table of the Elements is arranged on the basis of how electrons distribute themselves around atoms. Certain spatial arrangements, associated with different angular momenta, repeat in sequence and correlate with chemical properties. Recently, the stabilities, reactivities, and absorption spectra of various clusters comprising tens to hundreds of metal atoms have been rationalized by a similar model relying on periodic electron counts. However, it remained unclear whether the analogy extended to the actual angular distributions in space. Bartels et al. (p. 1323) used angle-resolved photoelectron spectroscopy to explore this question for clusters of 19 to 147 sodium atoms, and found that the electrons do exhibit well-defined spatial behavior along the lines observed in atomic orbitals. Preliminary modeling qualitatively support the data, but quantitative analysis will probably require consideration of multielectron correlations.

  14. A Patent Problem?

    Although there have been many complaints about the patent system's ability to promote innovation, it has been difficult to test the efficacy of alternatives. Meloso et al. (p. 1335; see the Perspective by Levine) designed experiments with human subjects to test a market-based approach, in which subjects had to combine different components into the best final results and “owned” shares in the components. The shares could be traded among participants. The proposed system performed as well as a patent-styled system, and more subjects discovered the right solution—optimal combination of components—than did so under the patent system.

  15. Carbon Sinks and Amazonian Droughts

    Amazonian forests process about 18 petagrams (18 × 1015 g) of carbon annually and, thus, changes in forest dynamics (including tree growth) have the potential to affect the concentration of atmospheric CO2 and climate. In 2005, Amazonia suffered a drought associated with elevated tropical North Atlantic sea surface temperatures. Phillips et al. (p. 1344) document the effects of this drought on the biomass of trees in an array of permanent forest plots across the Amazon basin. Censuses of the plots in years prior to the drought had indicated an accumulation of biomass (that is, a carbon sink). The rate of accumulation decreased significantly during the drought, suggesting that such events (which may become more frequent in the future) will reduce the Amazon forest's capacity to act as a carbon sink. The drought also selectively killed fast-growing trees with low wood density, which, if repeated, would affect the forest's ability to regenerate.

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