This Week in Science

Science  19 Apr 2013:
Vol. 340, Issue 6130, pp. 247
  1. Controlling Light Propagation


    Surface plasmons are light-induced collective electronic excitations in a metal that offer the possibility of manufacturing optoelectronic devices at nanometer scale. Before such shrinking can be achieved, the propagation direction and lifetime of the plasmonic excitations have to be controlled (see the Perspective by Miroshnichenko and Kivshar). Rodríguez-Fortuño et al. (p. 328) show how this is done using polarized light. Alternatively, using an array of metallic nanoantennae (in this case, slits) patterned into a thin gold film, Lin et al. (p. 331) present a further improvement on current plasmonic coupling schemes that has the potential to encode information contained in both the intensity and polarization of light.

  2. Sticky Responses

    A textbook example of an unaccounted-for consequence (externality) of commercial or industrial activity is the production of pollutants where neither the producer nor the buyer bears the cost of using common environmental resources. Dasgupta and Ehrlich (p. 324) offer a theoretical analysis of externalities in two other areas of modern life—human fertility and material consumption. For example, when fertility decline lags mortality decline, the consequence could be environmental crash, the likelihood of which is greater if the environmental effects of consumption or population growth are external to the market.

  3. Tuning Mesopores

    Porous materials are of interest for catalysis and filtration because the open channels lend themselves to separating materials or function. Suteewong et al. (p. 337) report on a method to make branched mesoporous silica nanoparticles that contain cubic (core) and hexagonally structured (branch) parts within one particle. Controlling the extent of the branched structure is achieved by tuning the concentration of additives in a simple, one-pot reaction system.

  4. Dissolving Charcoal

    Biomass burning produces 40 to 250 million tons of charcoal per year worldwide. Much of this is preserved in soils and sediments for thousands of years. However, the estimated production rate of charcoal is significantly larger than that of decomposition, and Jaffe et al. (p. 345; see the Perspective by Masiello and Louchouarn) calculate that a large fraction of the charcoal produced by fires is lost from the land through dissolution and transport to the oceans.

  5. History Matters

    Fishery-induced mortality is not the sole driver of fish population dynamics, and shifts in population abundance are also subject to ecological impacts. In a meta-analysis, Neubauer et al. (p. 347) showed how some fish-stock recoveries have been slower than theoretically predicted. They discovered that a species' exploitation history is also an important predictor of recovery. The data indicate that even extreme limitations in harvest pressure may not allow for the timely recovery of collapsed stocks.

  6. Sliding Restriction

    Helicase enzymes access the genetic information stored in double-helical DNA and RNA by opening the individual strands. Pseudo-helicases, including bacterial Type III restriction enzymes, use adenosine triphosphate (ATP) hydrolysis to communicate between two distant restriction sites on the same DNA and excise it only if the DNA is sensed as “foreign.” Schwarz et al. (p. 353) show that the bacterial Type III restriction enzyme, EcoP15I, undergoes an ATP-dependent conformational switch that promotes sliding along the DNA to allow the enzyme to localize to its target.

  7. Turn Off Youth

    Our neurons regenerate better when we are young than when we are more mature. Studying the mechanosensory anterior ventral microtubule (AVM) neuron of the nematode Caenorhabditis elegans, Zou et al. (p. 372; see the Perspective by Nix and Bastiani) found that worms lacking microRNA machinery had unusually robust axon regeneration and youthful-looking growth cones. Under- and overexpression of let-7 microRNA confirmed its involvement in depressing axon regeneration.

  8. Bats, Grids, and Oscillations


    Nearly all animals move around in a three-dimensional (3D) world; however, very little is known about the neural circuitry underlying the representation of 3D space (see the Perspective by Barry and Doeller). Using whole-cell patch recordings in slices of entorhinal cortex, Heys et al. (p. 363) found that bat entorhinal stellate cells must generate grid patterns without theta-frequency oscillatory mechanisms. In another study, Yartsev and Ulanovsky (p. 367) used telemetry to record activity from the hippocampus of bats while they were flying around. They found that active pyramidal cells—or place cells—in hippocampal area CA1 fired in positions, depending on where the animals were in the room.

  9. Consciousness Arrives

    Neurophysiological measures in human adults correspond to the transition between very brief, “unnoticeable,” and slightly longer-lived visual stimuli that penetrate deeply enough to leave a conscious imprint that subjects report they can “see.” Kouider et al. (p. 376) have performed parallel behavioral and neurophysiological studies in infants to identify a similar neural signal that appears to mark the development of visual consciousness.

  10. Splitting Singlets


    Solar cell efficiency is limited because light at wavelengths shorter than the cell's absorption threshold does not channel any of its excess energy into the generated electricity. Congreve et al. (p. 334) have developed a method to harvest the excess energy in carbon-based absorbers through a process termed “singlet fission.” In this process, high-energy photons propel two current carriers, rather than just one, by populating a singlet state that spontaneously divides into a pair of triplet states. Although it works in a functioning organic solar cell, the efficiency needs improving.

  11. Southern Change

    Antarctica has been mostly covered by ice since the inception of large-scale continental glaciation during the Oligocene, which profoundly altered the isotopic and mineralogical records of the sediments surrounding the continent. Houben et al. (p. 341) found records of the corresponding living systems in the fossil marine dinoflagellate cysts, which revealed that a microplankton ecosystem, similar to the one that exists today, appeared simultaneously with the first major Antarctic glaciation approximately 34 million years ago.

  12. Cargo-Motor Interaction

    Kinesin-1 directs a diverse array of functions within axons by interacting with many proteins. To understand the mechanisms underpinning kinesin-cargo recognition, Pernigo et al. (p. 356, published online 21 March) solved the crystal structure of the tetratricopeptide repeat of kinesin light chain 2 bound to a W-acidic cargo peptide from SKIP—a critical host determinant in Salmonella pathogenesis that controls lysosome positioning.

  13. To Fuse or Not to Fuse?

    Cell-cell fusion is poorly understood, although we know that in the nematode, Caenorhabditis elegans, it involves cell-surface fusogens and in the fly, Drosophila, the actin cytoskeleton plays a role. Shilagardi et al. (p. 359) reconstituted a high-efficiency, inducible cell-fusion culture system, in which they found that the C. elegans fusogen, Eff-1, induced a low level of cell-cell fusion that was enhanced by coexpression with a cell adhesion molecule, Sticks and stones (Sns), required for myoblast fusion in Drosophila. Sns-enhanced cell-cell fusion was mediated by dynamic actin polymerization that generated invasive membrane protrusions at sites of fusion.

  14. Red in Cell and Marrow

    About one hundred billion new red cells are released every day from the adult human bone marrow—the result of a complex differentiation pathway. Barde et al. (p. 350, published online 14 March) show that an essential step in this process, the elimination of mitochondria from maturing erythroblasts through mitophagy, is controlled through the timely induction of specific members of the large family of KRAB-containing zinc finger proteins (KRAB-ZFPs), which, together with their cofactor KAP1, repress the expression of micro-RNAs targeting the transcripts of mitophagy effector genes. This multilayered and combinatorial regulation system provides a level of modularity that may be shared by other physiological processes.