This Week in Science

Science  11 Jun 2010:
Vol. 328, Issue 5984, pp. 1323
  1. Eye for an I

    Oxidative catalysis is largely the domain of transition metals, whether iron in an enzyme, or rarer palladium in a synthetic system. These metals can efficiently shuttle between oxidation states, easing the transfer of hydrogen and oxygen atoms between hydrocarbons and oxidants. Uyanik et al. (p. 1376; see the Perspective by French) now show that iodine can take the place of the metal to catalytically activate peroxide during the formation of benzofuran derivatives. Pairing iodide anions with chiral ammonium cations allowed the generation of stereoselectivity at levels similar to those seen with metal complexes bearing chiral ligands.

  2. The Inner Life

    CREDIT: HAYES ET AL.

    The influence of intestinal flora on the physiology of the entire host organism has only recently begun to be appreciated. The mammalian gut is not just home to billions of bacteria and archaea, but often harbors much larger creatures such as protozoa, nematodes, and tapeworms. Anticipating a web of interactions among these organisms, Hayes et al. (p. 1391) investigated the relationship between a common nematode parasite of mice, Trichuris muris, and its dependency on the occurrence of enterobacteria, such as Escherichia coli and Salmonella typhimurium. The worms were found to be dependent on the presence of bacteria for hatching, and hatching was triggered by the presence of bacterial surface structures called fimbriae, which bind to proteins at the poles of the worms' eggs.

  3. Warm-Blooded Reptiles?

    Existing reptiles are not thought to be endothermic, but what about extinct species? Three large extinct swimming reptiles, the ichthyosaurs, plesiosaurs, and mosasaurs, were active predators in the Mesozoic oceans. Bernard et al. (p. 1379; see the Perspective by Motani) investigated their metabolism by analyzing the oxygen isotopes in their teeth, compared with fish in deposits from a variety of ocean environments. The data imply that the ichthyosaurs and plesiosaurs, which were both pursuit predators, probably controlled their own temperature. The data for the mosasaurs, which are thought to have hunted by ambush, are more equivocal.

  4. Reconsidering Recurrence

    The very long times between major earthquakes on known susceptible faults make estimating a long-term recurrence interval difficult. Deep, low-frequency earthquakes happen much more frequently and thus provide a natural setting for studying earthquake occurrence. Shelly (p. 1385) examined the timing of over 900 tiny earthquakes along a well-studied portion of the San Andreas Fault during a span of 8.5 years. The recurrence intervals between these microearthquakes, which roughly occurred on 3- and 6-day cycles, were sensitive to larger nearby events. For example, following the Parkfield earthquake in 2004, the 3-day cycle shortened and the 6-day cycle disappeared. If large-earthquake recurrence intervals are similarly variable over time, it will be extremely difficult to predict future damaging earthquakes from a short historical record.

  5. Not GILT-Free Processing

    CD8+ T cells respond to infections by recognizing peptide antigens bound to major histocompatability complex class I (MHC class I) protein expressed on the surface of antigen-presenting cells (APCs). Because MHC class I can only present intracellular antigens, antigen cross-presentation is important for responses to viruses that do not directly infect APCs. Antigen cross-presentation occurs when APCs acquire antigens by phagocytosis of dying virally infected cells and present them to CD8+ T cells. After internalization, antigens must enter the cytosol for processing by the proteasome. Singh and Cresswell (p. 1394) now show that GILT (gamma-interferon–inducible lysosomal thiolreductase) is required for cross-presentation in mice of disulfide-containing viral antigens. In mice lacking GILT, the CD8+ T cell response to antigens derived from disulfide-rich proteins was substantially impaired after influenza A or herpes simplex virus 1 infection. Thus, cross-presentation of some antigens requires an early processing step prior to proteasomal degradation in the cytosol and subsequent MHC class I loading.

  6. Chloride Balancing Act

    The ionic composition of the cytosol and intracellular organelles must be regulated in the face of ongoing membrane traffic into and out of the cell. Now, two papers address the consequences of a change in the transport phenotype of an intracellular Cl transport protein from a coupled exchanger to a passive Cl conductor (see the Perspective by Smith and Schwappach). Novarino et al. (p. 1398, published online 29 April) investigated the consequence of a knock-in of the uncoupled ClC-5 transporter into mouse. The knock-out mouse of this endosomal kidney transporter has a severe endocytic phenotype believed to be due to a defect in vesicular acidification. The current study shows a similarly impaired endocytic phenotype for the uncoupled mutant, but the acidification of endosomes was unaffected. Weinert et al. (p. 1401, published online 29 April) used a similar strategy to investigate the consequence of the equivalent mutation in the lysosomal transporter ClC-7, which is highly expressed in the resorption lacuna of osteoclasts and whose knock-out in mice produces lysosomal storage disease and severe osteopetrosis. A similar (though less severe) phenotype was observed in the knock-in mice containing the uncoupled ClC-7, indicating that coupled transport plays a critical role in lysosomes.

  7. Towering Figures

    CREDIT: A. HAMER

    The Tibetan plateau and adjacent mountain ranges are the source areas of the five major rivers of Asia. Climate change promises to affect both precipitation patterns and glacial melting in the region, which could have marked impacts on river flows and on associated agriculture. Immerzeel et al. (p. 1382) analyzed the relative importance of glacial meltwater and rainfall in the region in order to determine how the rivers depend on different sources of water, and how the river basins may be affected by climate change. Climate change is likely to affect water availability in the river basins in substantial but diverse ways, which may threaten the food security of tens of millions of people.

  8. Writing Conductive Lines with Hot Tips

    CREDIT: WEI ET AL.

    The interface within devices between conductors, semiconductors, and insulators is usually created by stacking patterned layers of different materials. For flexible electronics, it can be advantageous to avoid this architectural constraint. Graphene oxide, formed by chemical exfoliation of graphite, can be reduced to a more conductive form using chemical reductants. Wei et al. (p. 1373) now show that layers of graphene oxide can also be reduced using a hot atomic force microscope tip to create materials comparable to those of organic conductors. This process can create patterned regions (down to 12 nanometers in width) that differ in conductivity by up to four orders of magnitude.

  9. Seeing EPO

    The supply of red blood cells in mammals is controlled by the cytokine erythropoietin (EPO). In physiological situations, the concentration of EPO can change by 1000-fold. Becker et al. (p. 1404, published online 20 May) used a combination of mathematical modeling and experimental analysis to discern how cells can maintain a linear response to such a broad range of EPO concentrations. Critical features included internalization of EPO-bound receptors and subsequent degradation of the EPO ligand. Replenishment of receptors at the cell surface required a large supply of EPO receptors maintained in reserve inside the cell. These mechanisms allow cells to experience large increases in EPO concentration without becoming refractory to further stimulation.

  10. Oxytocin and Intergroup Conflict

    Human society is organized into groups, such as those based on nationality or religion, which can lead to intergroup conflicts, with sometimes devastating consequences. Intergroup conflict engages a human behavior termed parochial altruism: For example, a soldier who fights against the enemy at risk to themselves to protect their country is a parochial altruist. De Dreu et al. (p. 1408; see the cover; see the News story by Miller) have discovered a role for oxytocin, a neuropeptide produced in the hypothalamus, in regulating parochial altruism during human intergroup competition and conflict. Oxytocin is already known to play a role in trusting behavior, and naturally occurring genetic variants of the oxytocin receptor exist within the human population. Administration of oxytocin modulated defense-related aggression toward competing groups, but did not affect unprovoked, hateful behavior. Thus, there may be a neurobiological basis for intergroup conflict in humans.

  11. Lost in a Maze

    In rodents, hippocampal CA1 neurons play a pivotal role in the processing of spatial memory. However, the contribution of CA1 neurons in the human hippocampus to spatial memory has been difficult to establish. Bartsch et al. (p. 1412) studied a group of patients with transient global ischemia, a condition that lasted for at most a few hours and was followed by complete recovery. The patients were tested on a range of complex neuropsychological instruments, including virtual reality, during the ischemic attack. A striking impairment was observed in simple spatial navigation to a hidden target. The performance of the patients was correlated with the duration of the transient global ischemia, as well as with the size of the CA1 lesions.

  12. Mind the Gap

    The symmetry of the pairing gap is one of the most important properties of a superconductor. Whereas conventional superconductors such as lead have a gap that is uniform in momentum space, the enigmatic cuprates have point nodes and a characteristic d-wave symmetry. The heavy fermion compound UPt3 has long been known to exhibit unconventional pairing. Now, Strand et al. (p. 1368) have measured the momentum space dependence of UPt3's superconducting gap as a function of temperature. A real gap with line nodes was observed to develop first; then, at a lower critical temperature, a complex component appeared, with the total gap expected to become fully uniform at absolute zero.

  13. Spin Control Through Molecular Stretching

    Molecules with high symmetry, such as metal complexes with several equivalent ligands, can, in principle, have this symmetry broken by stresses that lengthen bonds in one direction. Parks et al. (p. 1370; see the Perspective by Jarillo-Herrero) placed cobalt complexes in a break-junction contact and then applied a mechanical force to slowly open the contact. Low-temperature measurement of differential conductance revealed a splitting of the Kondo peak at zero-applied voltage into two features, which occurred by breaking the degeneracy of S = 1 triplet states. This assignment of the spin state was confirmed by the evolution of splitting with magnetic field and by comparison to theory for a case where the conduction electrons only partially screen the spin states.

  14. Biodiversity and Productivity

    When data are analyzed at relatively large spatial scales, biodiversity generally increases with productivity, but the pattern at smaller scales is more variable. Chase (p. 1388, published online 27 May) presents results from a 7-year experiment in artificial ponds. β-diversity (the variation in species composition from site to site) in animal species was persistently higher at higher productivity among otherwise homogeneous environments in this controlled experimental venue. This pattern appeared to result from shifts in the relative importance of deterministic versus stochastic community assembly mechanisms along the productivity gradient. Thus, variation in the mechanism of community assembly might be an important process determining the relationship between biodiversity and productivity.

  15. Too Much of a Good Thing

    In peripheral nerves, the insulating myelin sheath speeds up electrical conductivity by allowing impulses to skip down the axon from node to node. Axons signal using neuregulin to get the Schwann cells to begin their wrap-around insulation project. But when is enough myelin too much? Cotter et al. (p. 1415, published online 6 May) have now found the signal that stops further rounds of myelin insulation. In developing mice, the proteins Dlg1 (mammalian disc large 1) and PTEN (phosphatase and tensin homolog) were involved in calling a halt to insulation during early development. The balance between not enough and too much myelin insulation is controlled by opposing signals, which together optimize both the myelination and the velocity of nerve conduction.

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