This Week in Science

Science  10 Jan 2014:
Vol. 343, Issue 6167, pp. 116
  1. Computational Metamaterials


    Optical signal processing of light waves can represent certain mathematical functions and perform computational tasks on signals or images in an analog fashion. However, the complex systems of lenses and filters required are bulky. Metamaterials can perform similar optical processing operations but with materials that need only be a wavelength thick. Silva et al. (p. 160; see the Perspective by Sihvola) present a simulation study that shows how an architecture based on such metamaterials can be designed to perform a suite of mathematical functions to create ultrathin optical signal and data processors.

  2. Collective Coherent Spin Dynamics

    Ultracold gases have shown considerable promise for the quantum simulation of more complicated systems, such as correlated electrons in solids. Usually, researchers use two hyperfine states of the atoms to correspond to the spin up and down states of the electrons; however, these gases typically have a much richer internal state structure. Krauser et al. (p. 157) observed the coherent behavior of a gas of potassium-40 atoms that had 10 accessible internal spin states and that evolved through collisions. The spin state of the system oscillated as a whole, a surprising finding given that the atoms are fermions.

  3. Soft, Selective CO Sorption

    Many industrial processes produce CO, which could be used as a chemical feedstock, but separation of CO from other gases, especially N2, is too difficult to be economically viable. Sato et al. (p. 167, published online 12 December 2013) now report that a porous coordination polymer containing Cu2+ ions can selectivity bind CO through serial structural changes reminiscent of allosteric effects in proteins. The separation of CO-N2 mixtures can be achieved with a low input energy for CO desorption.

  4. Europa's Plumes

    Jupiter's moon Europa has a subsurface ocean and a relatively young icy surface. Roth et al. (p. 171, published online 12 December 2013; see the Perspective by Spencer) analyzed spectral images taken by the Hubble Space Telescope that show ultraviolet emissions from the moon's atmosphere, and report a statistically significant emission signal extending above the satellite's southern hemisphere. This emission is consistent with two 200-km-high plumes of water vapor. Tidal stresses likely play a role in opening and closing fractures at the surface.

  5. Cancer Immunosurveillance Gone Bad?

    A subset of patients who develop scleroderma, a debilitating autoimmune disease, have an elevated risk of developing cancer. These patients harbor autoantibodies to RPC1, an RNA polymerase subunit encoded by the POLR3A gene. Joseph et al. (p. 152, published online December 5; see the Perspective by Teng and Smyth) explored whether the RPC1 autoantibodies target a “foreign” antigen derived from a mutated POLR3A gene. Sequence analysis revealed that POLR3A mutations were present in tumors from six of eight patients with RPC1 autoantibodies but in no tumors from eight control patients who lacked RPC1 autoantibodies. Cell culture data suggested that the POLR3A mutations triggered cellular and humoral immune responses in the patients. These results provide support for the “immunosurveillance” hypothesis, which posits the continual eradication of nascent tumor cells via immune responses.

  6. Make Way for the Emerging Rootlet

    Plant cells are immobilized by their rigid cells walls, and the root endodermal cell layer maintains a impervious perimeter seal made of an indigestible irregular polymer. Despite these mechanical obstacles, lateral root primordia, which initiate in the deep layers of the root, manage to break through to the surface. Vermeer et al. (p. 178; see the cover) used live-tissue imaging and genetics to show that signals are exchanged between the root primordium and the handful of cells overlying it, which then cave in on themselves to open up a channel for the growing root primordium.

  7. Back with a Vengeance

    After surgery, gliomas (a type of brain tumor) recur in nearly all patients and often in a more aggressive form. Johnson et al. (p. 189, published online 12 December 2013) used exome sequencing to explore whether recurrent tumors harbor different mutations than the primary tumors and whether the mutational profile in the recurrences is influenced by postsurgical treatment of patients with temozolomide (TMZ), a chemotherapeutic drug known to damage DNA. In more than 40% of cases, at least half of the mutations in the initial glioma were undetected at recurrence. The recurrent tumors in many of the TMZ-treated patients bore the signature of TMZ-induced mutagenesis and appeared to follow an evolutionary path to high-grade glioma distinct from that in untreated patients.

  8. Out with the Old, In with the New


    In adult animals, resident stem or progenitor cells residing in niches replenish old tissues with new cells, but how they form new tissue is not well understood. Chen and Krasnow (p. 186) examined how progenitor cells in the fruit fly form new tracheae as the old tracheae are destroyed during metamorphosis. Proliferating progenitors move out of their niche by crawling along the surface of decaying tracheal branches. The decaying branches express the chemoattractant FGF (fibroblast growth factor) and create a track that directs progenitors.

  9. Spinal Circuit Complexity in Fish

    Rapid coordination of opposing muscle groups helps zebrafish zip through water. Bagnall and McLean (p. 197) now describe the neuronal circuits that stabilize swimming fish in their three-dimensional environment. By studying the self-righting behavior of larval zebrafish immobilized in agar, the authors identified parallel excitatory and inhibitory circuits driving dorsal and ventral hemisegments that could be activated independently.

  10. Preserving Predators


    Large-bodied animals play essential roles in ecosystem structuring and stability through both indirect and direct trophic effects. In recent times, humans have disrupted this trophic structure through both habitat destruction and active extirpation of large predators, resulting in large declines in numbers and vast contractions in their geographic ranges. Ripple et al. (10.1126/science.1241484; see the Perspective by Roberts) review the status, threats, and ecological importance of the 31 largest mammalian carnivores globally. These species are responsible for a suite of direct and indirect stabilizing effects in ecosystems. Current levels of decline are likely to result in ecologically ineffective population densities and can lead to ecosystem instability. The preservation of large carnivores can be challenging because of their need for large ranges and their potential for human conflict. However, the authors demonstrate that the preservation of large carnivores is ecologically important and that the need for conservation action is immediate, given the severity of the threats they face.

  11. Heteroepitaxy Writ Thin

    A common method for creating a thin single-crystal layer of a semiconductor for use in an electronic device is heteroepitaxy—growing the layer on the face of a single crystal of a different material that acts as a template for assembly. Liu et al. (p. 163) now describe a similar process in which the edge of a graphene layer that was grown on a copper surface directs the assembly of a monolayer of hexagonal boron nitride. The boron nitride grew from inside edge of holes created in the graphene layer. The interface and the relative orientation of the two layers were determined by a variety of scanning microscopy and surface diffraction techniques.

  12. Cold Glacier Growth

    Pine Island Glacier in Antarctica has thinned significantly during the last two decades and has provided a measurable contribution to sea-level rise as a result. Both glacier dynamics and climate are thought to be responsible for thinning, but exactly how they influence the glacier are incompletely known. Dutrieux et al. (p. 174, published online 2 January) provide another layer of detail to our understanding of the process through observations of ocean temperatures in the surrounding waters. The thermocline adjacent in the sea adjacent to the glacier calving front (where ice is discharged) lowered by 250 meters in the austral summer of 2012. This change exposed the bottom of the ice shelf to colder surface waters rather than to the warmer, deeper layer, thereby reducing heat transfer from the ocean to the overlying ice and decreasing basal melting of the ice by more than 50% compared to 2010. Those 2012 ocean conditions were partly caused by a strong La Niña event, thus illustrating how important atmospheric variability is for regulating how the Antarctic Ice Sheet responds to climate change.

  13. Carbon Budding in the Ocean

    Bacterial vesicles are gaining increasing attention for their roles in pathogenesis, but the abundance of these structures and their ecological roles in nonpathogenic contexts have received little notice. Biller et al. (p. 183; see the Perspective by Scanlan) provide evidence that membrane vesicles ∼100 nm in diameter are released by marine cyanobacteria and are a major feature of marine ecosystems. Studies of cultures of Prochlorococcus—the most abundant photoautotroph in the oligotrophic oceans—show that vesicles are continually released by this cyanobacterium and are abundant in the marine environment. These vesicles have properties that change the way we think about genetic and biogeochemical exchange among plankton and the dissolved organic carbon pool in marine ecosystems.

  14. Expressing One Allele at a Time

    Although genetic traits are often dominant or recessive, the impact of the same heterozygous genotype can vary quite a bit between individuals. Deng et al. (p. 193), analyzed global gene expression in hundreds of individual mouse cells and found that a substantial fraction of the genes only expressed one of the alleles, chosen randomly, at any given point in time. Such stochasticity in transcription increases the heterogeneity among cells and likely contributes to the phenotypic variance among individuals of identical genotype.

  15. Developing Neurons Make the Cut

    Neurons in the developing central nervous system of vertebrates derive from cells adjacent to the ventricles that then proliferate and differentiate to populate the brain. As one of these cells begins to differentiate, the cell nucleus migrates toward its new residence, away from the ventricle surface, and the cell stretches out. At some point, like any maturing adolescent, the cell has to leave home. Das and Storey (p. 200; see the Perspective by Tozer and Morin) show that instead of letting go and drawing the trailing process up into the migrating cell, the cell cuts off and discards its first roots. The abscission process leaves behind the primary cilium and any signaling systems localized to the cilium.

  16. Persistent Survival

    The role of persister cells—dormant cells that survive multidrug treatment—in the context of bacterial pathogenesis has not been explored in depth. Using a single-cell fluorescent dilution technique, Helaine et al. (p. 204) examined Salmonella Typhimurium persister-cell formation in vitro and in infections in mice. Within 30 min after phagocytosis by macrophages, Salmonella cells follow one of two fates, either to replication and generation of virulence effectors or to remaining viable but become nonreplicating persisters. Salmonella living within a macrophage vacuole are exposed to potentially stressful conditions that induce the expression of 14 Type II toxin-antidote loci in a ppGpp/lon protease-dependent manner, and this system appears to play a role in both virulence factor induction and persister-cell formation. The nonreplicating bacteria represent at least four distinct subpopulations, as defined by their ability to resume growth and their metabolic activity, but different phenotypes are observed in different pathogens and Escherichia coli persisters are distinct from Salmonella persisters.