This Week in Science

Science  02 Sep 2011:
Vol. 333, Issue 6047, pp. 1199
  1. Woollies Ready for the Ice Age


    Cold-adapted megafaunal species, such as woolly mammoths and woolly rhinos of the Pleistocene, were thought to have evolved gradually, in situ, from less cold-tolerant forms. A newly discovered ancestral species of woolly rhino from the pre–Ice Age Tibetan plateau described by Deng et al. (p. 1285) displays adaptations to a cold, snowy climate. This description and the accompanying descriptions of a community of cold-adapted megafaunal species, including leopards, sheep, and bovids, indicates that this region could have been a cradle of adaptation to cold, which may have facilitated multiple range expansions of these species as the climate cooled.

  2. Biggish Bang

    Supernova 1987A has become the best-studied stellar explosion and a template for all supernovae of its kind because it happened in one of our neighboring galaxies. Supernovae are the chemical factories of our universe and drive the physical and chemical evolution of galaxies. Matsuura et al. (p. 1258; see the Perspective by McKee) report observations, obtained with the Herschel Space Telescope, of supernova 1987A in the far-infrared and submillimeter wavelengths. The data indicate that a large quantity of dust, as much as 0.4 to 0.7 times the mass of the Sun, must have condensed in the ejecta of this supernova and suggest that the large amounts of dust observed in young galaxies originate from similar explosions.

  3. Fantastic Ferroelectric Elastic Lattice

    Multiferroic compounds in which magnetic and electric orders coexist are a subject of intense interest in material science because of their technological potential. Knowledge of the ferroelectric ordering of these compounds has been incomplete; proposals have been put forward that attribute it to either lattice or electronic distortions. Now, Walker et al. (p. 1273) use x-ray scattering to study the lattice ionic displacements caused by the application of a magnetic field. The displacements are found to be in the femtometer range and can account for roughly a quarter of the measured ferroelectric polarization, giving support to the class of theories that attribute the ferroelectric order to lattice distortions.

  4. Sheer Shear Sphere

    Fluids with entrapped particles or polymers, such as tomato paste or mayonnaise, exhibit complex fluid behavior when subject to shearing flows. While this behavior is well understood at high particle concentrations where jamming of the particles dominates, the particle behavior at lower concentrations is less well understood. Cheng et al. (p. 1276, published online 12 August; see the Perspective by Brown and Jaeger) study the origins of shear thinning and shear thickening in moderately concentrated hard-sphere suspensions using confocal rheology and are able to observe the role of particle interactions in these phenomena.

  5. Dark Metabolisms

    Marine microorganisms in the dark regions of the oceans below 800-meters depth are presumed to mediate a large proportion of carbon dioxide fixation in the oceans. This autotrophy is thought to be driven by archaea and fueled by ammonia oxidation (nitrification), but carbon fixation in the deep ocean is spatially variable and it is possible that other organisms contribute. Swan et al. (p. 1296) embarked on a single-cell genomics study of sites in the South Atlantic and North Pacific to look for bacterial lineages with inorganic carbon fixation machinery and found that about a third of identifiable bacterial cells carried genes for components of the carbon fixation apparatus and for oxidation of reduced organic sulfur compounds. It is not immediately obvious where the sulfur compounds originate for the energy-generating reaction, although, feasibly, they come from other organisms, such as the ubiquitous osmolyte dimethylsulfoniopropionates.

  6. Taste Maps


    During the past 50 years, the anatomical and functional organization of how the brain processes the classical senses has largely been worked out. Vision, hearing, and touch are mapped topographically in the cortex, whereas the sense of smell has been shown to use a distributed code. Taste, however, has remained a mystery. Through in vivo two-photon calcium imaging, Chen et al. (p. 1262) simultaneously analyzed the taste-evoked activity of neurons in the primary taste cortex within the brain area called the insula. Single-cell resolution experiments led to a clear picture of the central representation of taste, in which individual basic tastes are represented by finely tuned cells organized in a precise and spatially ordered way that encodes each taste quality in its own specific field.

  7. Intracellular Therapy Tool

    One goal of synthetic biology is to integrate a genetic circuit into mammalian cells that can detect a diseased state and then trigger a therapeutic appropriate response. Xie et al. (p. 1307) have engineered a regulatory circuit that specifically triggers apoptosis if it detects a micro-RNA profile characteristic of HeLa cancer cells. Programmed biological actuation in response to complex intracellular conditions could be valuable in applications such as drug screening, although to realize its full therapeutic potential, the technology will have to overcome major challenges, such as in vivo DNA delivery.

  8. All at Once

    Efficient implementation and characterization of quantum information protocols will rely on the ability to measure multiple qubits individually and simultaneously. In an electrical setup, Nowack et al. (p. 1269) show that the electronic spin stored on two separate but coupled quantum dots can be read out individually without destroying the spin on the other dot. The coupled-spin system is a strong contender for becoming the basic building block in scalable quantum information processing architectures. The ability to read out the spins and observe the correlations between them once they have interacted and have been separated, may provide a route for implementing more complex quantum circuits.

  9. Traffic Report

    The first step in fermentative biofuels production is degradation of the biomass into soluble sugars. Understanding more precisely how enzymes degrade cellulose could help improve the efficiency of this process—a critical step in moving beyond food crop feedstocks to more recalcitrant grasses. To this end, Igarashi et al. (p. 1279) have tracked the movements of individual enzymes on cellulose surfaces using high-speed atomic force microscopy. They observe collective dynamics akin to traffic jams and highlight the synergistic action of two different families of enzyme in enhancing degradation.

  10. Chimeric Channels

    Ligand-gated ion channels (LGICs) regulate ionic conductances into cells, thereby regulating cellular behavior. Several tools have been developed to modulate conductance and thus probe function; however, most of these indirectly target ion channels. Magnus et al. (p. 1292) used genetic and chemical engineering to design chimeric LGICs comprising modular combinations of pharmacologically selective ligand-binding domains and diverse ion-pore domains. By using this approach, they constructed LGIC-ligand pairs that are orthogonal to naturally occurring systems and used them selectively to manipulate neuron activity in mouse brains in vivo.

  11. Variable Entrainment

    The biochemical circuits in cells that function as biological clocks can produce steady oscillations and be entrained by external cues to run faster or slower, or stay in sync with the 24-hour light-dark cycle. Mondragón-Palomino et al. (p. 1315) explored how such entrainment works with a synthetic cellular oscillator in bacteria that allowed them to monitor transcriptional activity of clock genes in populations of bacteria, held within a microfluidic device, when external cues vary. The results indicate that a positive feedback loop in the oscillator is critical for entrainment and that variation in the period of the oscillators among individual cells is advantageous because it assures that at least some individuals will be entrained when environmental cues change.

  12. No Laughing Matter

    On a global scale, microorganisms in the oceans strongly influence the composition of the atmosphere, for example, by producing large quantities of greenhouse gases. Nitrous oxide (N2O) is formed through the oxidation of ammonia in a process thought to be dominated by nitrifying bacteria; however, the isotopic signature of N2O in the atmosphere suggests that the bacteria are not the sole source of the gas. By studying enrichment cultures from the Pacific Ocean, Santoro et al. (p. 1282, published online 28 July) show that marine archaea can also produce large quantities of N2O. The nitrogen and oxygen isotope signatures measured in these experiments indicate that the major source of this gas emissions from the oceans may in fact be the ammonia-oxidizing archaea.

  13. Land to Spare or Share?

    Maintaining the food supply for a growing population and ensuring the conservation of global biodiversity are important challenges facing humanity, but there is debate over how to best to achieve these two goals simultaneously. Phalan et al. (p. 1289; see the Perspective by Godfray) investigate whether land sparing (designating protected areas separately from intensive farming) or land sharing (allowing biodiversity and agriculture to coexist in the landscape) would be a more efficient approach to conserve biodiversity. The findings regarding birds and trees from Ghana and India indicate that land sparing is a more effective strategy than land sharing for reconciling food production with biodiversity conservation.

  14. Tet Conversions

    DNA methylation is a critical regulatory event in gene imprinting, X-chromosome inactivation, and transposon silencing. In plants, a DNA repair-based mechanism is used to remove DNA methyl marks. How DNA is demethylated in animals is less well understood, although it is known that 5-methylcytosine bases (5mC) can be converted to 5-hydroxymethyl C (5hmC) by the Tet family of enzymes. Two papers from Ito et al. (p. 1300) and He et al. (p. 1303. Both published online 12 August; see the Perspective by Nabel and Kohli) show that Tet enzymes not only convert 5mC to 5hmC but can convert 5hmC to 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC), as well. Both groups find evidence of low levels of the Tet-dependent modifications in vivo, and He et al. show that 5caC can be targeted for removal from DNA by thymine-DNA glycosylase.

  15. Prevent Fem Silencing

    Increasingly, noncoding RNAs are being found that play important regulatory roles in biological processes. In the nematode roundworm, Caenorhabditis elegans, the fem-1 gene is needed for male development; however, genetic crossing suggested that the maternal contribution is dispensible for maleness. Now, Johnson and Spence (p. 1311) show that maternal fem-1 is required for male offspring. They found mutants that disrupt the coding potential of the RNA do not prevent the mutant RNA from promoting maleness in offspring, and it appears that the active component is fem-1 RNA. Defects in zygotic fem-1 expression are heritable, which suggests that the RNA functions to prevent the silencing of the zygotic fem-1 gene by interfering with the deposition of a repressive epigenetic mark.

  16. For Transparency—Nothing Works

    Quantum information technology based on optical circuits will require the ability to manipulate and switch single photons. A cloud of atoms can be made transparent to an otherwise absorbed probe beam by selectively controlling the transitions between the energy levels of the atoms with a control beam. However, this electromagnetic induced transparency typically requires many photons to achieve the effect. Tanji-Suzuki et al. (p. 1266; see the Perspective by Fleischhauer) placed the atom cloud in a high-finesse optical cavity to show that the light-matter interaction can be enhanced so that the vacuum field of the cavity itself can induce transparency at the single-photon level. Moreover, they show that the effect of vacuum-induced transparency is strongly nonlinear, thereby making it an attractive candidate for optical control.

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