This Week in Science

Science  10 Aug 2012:
Vol. 337, Issue 6095, pp. 620
  1. Crucial Cerebellar Glial Cells


    The role of glial cells and their interaction with neurons in normal behavior is unclear. To address this question, Saab et al. (p. 749, published online 5 July) studied a special type of glial cell in the cerebellum. Conditional mutant mice were produced in which the two glutamate receptor subunits normally present in Bergmann glial cells were efficiently ablated in a temporally controlled manner. Glutamate signaling of the glial cells contributed to the structural and functional integrity of the cerebellar network. Bergmann glial cells also played a role in the “fine-tuning” of neuronal processing, which is crucial for the fast and precise control of complex motor behavior.

  2. Lattice Trailing the Electrons

    Superconducting order recedes with decreased chemical doping in a typical iron-based superconductor family. Thus, the symmetry of the material is broken by almost simultaneous antiferromagnetic and structural phase transitions. However, some pnictides also exhibit an electronic nematic transition manifested by anisotropy of the electrical resistance. Because this anisotropy occurs at the same time as the structural transition, it is not clear whether it is a consequence of the broken crystal lattice symmetry or its cause. Chu et al. (p. 710) performed constant strain experiments on the series Ba(Fe1−xCox)2As2, which can distinguish between the two scenarios, and confirm that the electrons drive the lattice transition.

  3. UN Coordination

    Uranium is best known for its radioactivity. From the standpoint of lower-energy chemistry, uranium is also intriguing for its bonding motifs, which involve trinodal f orbitals. King et al. (p. 717, published online 28 June; see the Perspective by Sattelberger and Johnson) synthesized and isolated a molecule bearing a uranium-nitrogen triple bond. Theoretical calculations allowed the mapping of the orbital interactions, distinguishing it from similar motifs in compounds of lighter metals. The preparation required use of a rigid, bulky ligand framework to keep the reactive uranium nitride group from binding to another molecule nearby, a pathway that has plagued prior attempts to prepare this class of compounds.

  4. Constraining the Birthplace of Asteroids

    Many primitive meteorites originating from the asteroid belt once contained abundant water that is now stored as OH in hydrated minerals. Alexander et al. (p. 721, published online 12 July) estimated the hydrogen isotopic compositions in 86 samples of primitive meteorites that fell in Antarctica and compared the results to those of comets and Saturn's moon, Enceladus. Water in primitive meteorites was less deuteriumrich than that in comets and Enceladus, implying that, in contradiction to recent models of the dynamical evolution of the solar system, the parent bodies of primitive meteorites cannot have formed in the same region as comets. The results also suggest that comets were not the principal source of Earth's water.

  5. Earthquake in a Maze

    The 11 April 2012 magnitude 8.6 earthquake offshore of Sumatra was the largest measured earthquake along a strike-slip boundary that modern seismological instruments have ever recorded. Despite its size and proximity to a large population, there was no subsequent tsunami and there were no reported fatalities. Meng et al. (p. 724, published online 19 July) used teleseismic data from seismological networks in Japan and Europe to image the source of high-frequency radiation generated by the earthquake to understand the mechanics of this unique event. The resultant back projections showed that the earthquake slowly ruptured along a complex series of faults. The deeper-than-usual rupture path and large stress drop are both features that may not be unique to this earthquake, suggesting that regions in a similar tectonic environment may have the potential for more complex—or larger—intraplate earthquakes than might have been expected.

  6. Cycling Down


    The Mid-Pleistocene Transition, which lasted from approximately 1.25 million to 700 thousand years ago, was a period during which the dominant periodicity of Earth's climate cycles inexplicably changed from 41 thousand to 100 thousand years. This change is clearly apparent in the oxygen isotopic composition of many calcifying marine organisms, but changes in both ice volume and temperature affect the signal, and so exactly what the signal means has remained unclear. Elderfield et al. (p. 704; see the Perspective by Clark) separated these two effects by measuring both the oxygen isotopic makeup and the Mg/Ca (a proxy that reflects changes in temperature only) of certain benthic foraminifera. The findings reveal the contributions of ice volume and temperature to glacial cycles, suggest when and why the Mid-Pleistocene Climate Transition occurred, and clarify how carbon is lost from the ocean-atmosphere during deglaciations but also changes because of ocean circulation.

  7. Phosphoinositide Contributions

    To study the roles of phosphoinositides in the plasma membrane of mammalian cells, Hammond et al. (p. 727, published online 21 June; see the Perspective by Fairn and Grinstein) engineered phosphatase molecules that could be targeted to the membrane on demand, where they would alter the concentrations of the phospholipids phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P2] and phosphatidylinositol 4-phosphate (PI4P). PI4P was thought to provide a major source for the synthesis of PI(4,5)P2, but depletion of PI4P did not have much affect on synthesis of PI(4,5)P2. Instead, PI4P appears to help to establish the negative charge at the membrane and thus promote electrostatic interactions with positively charged amino acids in membrane-associated proteins and influencing function of ion channels.

  8. Cancer Stem Cells in Color


    One of the liveliest debates in contemporary cancer research centers on whether cancer stem cells (CSCs) exist and, if so, how these cells are defined phenotypically. CSCs are hypothesized to be a small population of cells within a tumor that are endowed with the unique capacity to drive tumor growth—a scenario that in principle would offer important therapeutic opportunities. By studying mice expressing multicolor reporter genes, Schepers et al. (p. 730, published online 1 August) were able to visualize and monitor the fate of a candidate stem cell for intestinal adenomas, an early stage of cancer. This “lineage tracing” analysis suggests that tumor cells expressing the intestinal crypt stem cell marker Lgr5 (leucine-rich repeat containing G protein–coupled receptor 5) are the cells that fuel the growth of intestinal adenomas.

  9. Current on Demand

    Deep brain electrical stimulation can be a successful therapy in Parkinson's disease, in depression, and in several other psychiatric diseases, especially in drug-resistant cases. Unfortunately, chronic, continuous stimulation is associated with multiple side effects. This could be alleviated by delivering the electrical perturbation only when it is necessary, using closed-loop stimulation. Such an approach is essential for epilepsy, where seizures occur very rarely but with serious consequences. In a rat model for epilepsy, Berényi et al. (p. 735) prevented seizures by transcranial electrical stimulation using a closed-loop system. Transcranial electrical stimulation was highly effective and reduced seizure duration, on average, by 60 %.

  10. Bio-Inspired Drug Delivery

    Noting that platelets naturally migrate to narrowed blood vessels characterized by high fluid shear stress, Korin et al. (p. 738, published online 5 July; see the Perspective by Lavik and Ustin) developed a nanoparticle-based therapeutic that uses a similar targeting mechanism to deliver a drug to vessels obstructed by blood clots. Aggregates of nanoparticles coated with the clot-dissolving drug tPA (tissue plasminogen activator) were designed to fall apart and release the drug only when encountering high fluid shear stress. In preclinical models, the bio-inspired therapeutic dissolved clots and restored normal blood flow at lower doses than free tPA, suggesting that this localized delivery system may help reduce the risk of side effects such as excessive bleeding.

  11. Promoting the Male X Chromosome

    In mammals and fruit flies, females have a double dose of the X chromosome compared to males, and to compensate for this imbalance, in fruit flies, transcription from across most of the male X chromosome is boosted by twofold. Conrad et al. (p. 742, published online 19 July) measured the binding of RNA polymerase II, responsible for the majority of the transcription on the X chromosome, and found a consistent increase at the promoters of genes on the male X chromosome. Thus, the increase in transcription on the male X chromosome is not driven by increased rates of transcriptional elongation, as has been suggested previously, but must involve up-regulation of transcription initiation.

  12. The Conductor in the Thalamus

    The pulvinar is the largest thalamic nucleus in the brain but its functions remain unclear. The pulvinar is ideally positioned to synchronize activity across the visual cortex. Saalmann et al. (p. 753) combined diffusion tensor imaging with multi-electrode recordings from three different brain areas in monkeys to probe thalamo-cortical interactions during visual attention. The pulvinar was found to play a vital role in attention by routing behaviorally relevant information across the visual cortex.

  13. Addressing a Burning Issue

    Complete combustion of methane is required in order to avoid the unproductive emission of this greenhouse gas into the atmosphere. Palladium catalysts can help to promote complete combustion, but high-temperature operating conditions also promote aggregation of catalyst particles (“sintering”) that lowers their surface area and overall activity. Cargnello et al. (p. 713; see the Perspective by Farrauto) report that cerium oxide–coated Pd catalyst particles could be fully dispersed on an alumina surface prepared with a hydrophobic coating. This treatment resisted Pd sintering up to temperatures of 800°C, and also enabled complete combustion of methane to occur at temperatures as low as 400°C.

  14. Generating the Cortex

    During development of the cerebral cortex, radial glial neural progenitor cells generate layer-specific subtypes of excitatory neurons in a defined temporal sequence, in which deep layers are formed before upper layers. The prevailing model for cortical neurogenesis over the last 20 years has been the common progenitor model, which proposes that the neurogenic potential of the radial glial cell is progressively restricted over time. In contrast to this model, Franco et al. (p. 746) now show that, in mice, two radial glial cell subtypes appear to be specified at the onset of cortical development: one for neurons of the evolutionarily older lower cortical layers and a second for the upper cortical layers that are present in placental mammals and are enlarged in primates, especially humans.

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