This Week in Science

Science  15 Jul 2011:
Vol. 333, Issue 6040, pp. 265
  1. Threats to Mountain Runoff


    Snowpack in the mountains of western North America is a major contributor to river runoff in the warmer months. Changes in the size of the snowpack and the timing and degree of warm weather heating could thus have significant impacts on streamflow and water supply in regions within its watershed. Pederson et al. (p. 332, published online 9 June) present an 800-year-long reconstruction of snowpack size in the mountains that feed the Colorado, Columbia, and Missouri rivers in order to compare the decline of the past 50 years to the longer historical record. The severity of the recent decline is nearly unprecedented, owing to a combination of natural variability and anthropogenic warming. Within the context of continued climate warming, the decrease in size of the snowpack over the past half-century may be evidence that the dominant influence on its mass has shifted from the amount of precipitation to temperature, potentially threatening regional water supplies.

  2. Too Much Static

    The rubbing of a balloon on your hair or the accumulation of charge as you walk across a carpet are well-known examples of contact electrification. In the familiar lab experiment of rubbing an ebonite rod with a piece of wool, it is commonly believed that electrons transfer from the wool to the rod, so that the wool becomes positively charged and the rod negatively charged. Using Kelvin force microscopy, Baytekin et al. (p. 308, published online 23 June) examined the local charge state on objects that had been rubbed together. Both objects contained random regions of positive and negative charge, owing to fluctuations on the surfaces of the materials, even though each acquired a different overall net charge.

  3. Sunspots Under the Spotlight

    Sunspots are dark because their strong magnetic fields suppress the convective heat flux from the interior of the Sun. However, convection cannot be fully suppressed; otherwise, sunspots would be a lot darker. The penumbra (the filamentary region that surrounds the sunspot's central dark patch), in particular, has been explained in terms of overturning convection by recent numerical models. Based on observations with the Swedish 1-meter Solar Telescope, Scharmer et al. (p. 316, published online 2 June) present evidence of dark downward flows in the interior penumbra of a sunspot. These downflows are part of a convective flow pattern and their detection validates the model predictions.

  4. Where Is My Reward?


    Efficient reward-seeking requires that environmental stimuli are interpreted in the proper context, to predict when and where reward can be expected. In the brain, the ventral tegmental area and its dopaminergic projections are critical to the regulation of reward-seeking. How the ventral tegmental area system relates to other contextual information, such as where reward can be expected, remains unclear. Luo et al. (p. 353) used a combination of anatomical, physiological, and behavioral techniques to define a polysynaptic pathway from the CA3 region of the hippocampus to the ventral tegmental area. The findings reveal connections between the dorsal hippocampus, a structure implicated in the processing of contextual cues, and the ventral tegmentum, a structure involved in the regulation of motivated behavior.

  5. Pity the Boss Man

    In social hierarchies, life at the top has benefits, including increased access to resources and mates. Thus, it has generally been thought that the advantages of rank dominance outweigh the costs, except in times of social instability, when high-ranking individuals must defend their position or social group. In many primate species, high-ranking individuals in stable groups tend to display less evidence of stress than do lower ranked individuals. Gesquiere et al. (p. 357; see the Perspective by Sapolsky), now show that there is more to the story. A 9-year study of a wild baboon population investigated the role of dominance rank on stress-hormone and testosterone levels. Looking at each rank separately revealed that the alpha males have higher stress-hormone levels than the high-ranked males below them, even in times of stability. Surprisingly, their stress levels are similar to those found in low-ranked males, possibly because of the increased energetic and psychological stress they must endure to fend off rivals for their positions and mates.

  6. Early Years Matter

    Efforts to improve early-childhood education can run the gamut from parenting classes to full-time daycare. Which programs achieve what, and how important are the effects, remain open questions. Reynolds et al. (p. 360, published online 9 June; see the Perspective by Melhuish) studied the lives of children who participated in a full-time preschool program in Chicago. Some 25 years later, individuals who had been in the preschool program were doing better on some, but not all, factors than individuals who had not. Factors considered included income, education, parenting status, personal health care, substance abuse, and criminal involvement. Preschool seems to have made the most difference for children from families with lower education attainment or greater poverty.

  7. Twisting Tubes

    Various animal organs show left-right (LR) asymmetric morphology and need to be able to form tubes (see the Perspective by Horne-Badovinac and Munro). The fly hindgut consists of an epithelial tube that twists to the left during embryogenesis. Before this twist occurs, the epithelial cells of the tube adopt a LR asymmetric (chiral) cell shape within their inner (apical) plane. Taniguchi et al. (p. 339) refer to this novel cell behavior as “planar cell-shape chirality” (PCC). Drosophila E-Cadherin, an adhesion protein, and Myosin ID were asymmetrically distributed and were responsible for generating the PCC. During normal development, lung tubes undergo genetically controlled changes in shape that contribute to the airway architecture that underlies pulmonary function. Tang et al. (p. 342) demonstrate that RAS-regulated ERK1/2 signaling plays a key role in regulating such shape changes by influencing the mitotic spindle angle in embryonic lung epithelial cells: Increasing ERK1/2 activity reduced the fraction of cells that divide parallel to the longitudinal axis of the airway tube.

  8. Trophic Ripple Effects

    Trophic cascades occur when the consumption of one species impacts the abundance and distribution of species at lower trophic levels. Such cascading effects have been documented across both terrestrial and aquatic ecosystems, and often the top, or apex, consumers (such as predators or large herbivores) have been lost due to human activity over the last several thousand years. Estes et al. (p. 301) review the unexpected impact that the loss of these apex consumers has had on disease dynamics, wildfire frequency, and biogeochemical cycles. The loss, or control, of large animals may thus have profound impacts on ecosystem function, resilience, and health, which should be taken into account in conservation and management decisions.

  9. Crystallizing Fanconi Anemia Proteins

    Fanconi anemia (FA) is characterized by hypersensitivity to DNA interstrand cross-linking agents. The resulting genomic instability is thought to underlie early-onset cancer, bone-marrow failure, and other problems seen in the disease. Central to the FA DNA repair pathway is the Fanconi anemia I–Fanconi anemia D2 (ID) complex formed by the FANCD2 and FANCI proteins, which localize to sites of DNA repair. Joo et al. (p. 312) determined the crystal structure of the mouse ID complex and the isolated FANCI protein. The complex has a troughlike shape, with the monoubiquitination sites within the ID interface, at the bottom of the electropositive trough, in two solvent-accessible tunnels that could each accommodate a ubiquitin tail. The trough forms a series of grooves that, in FANCI, are able to bind to a Y-shaped fragment of DNA, suggesting how the complex might bind to a replication fork stalled at a DNA cross-link.

  10. Complex Interactions in Thin Films

    Confinement of a material as a thin film creates a quantum well structure that can alter the spin, charge, and orbital degrees of freedom of conduction electrons and can lead to new properties. Yoshimatsu et al. (p. 319) grew ultrathin layers of SrVO3, which has metallic properties arising from correlated interactions of its electrons, on a Nb:SrTiO3 substrate, and probed its electronic structure with angle-resolved photoemission spectroscopy. A set of subbands corresponding to the different V 3d orbitals near the Fermi level were observed, which changed the properties of these structures with film thickness.

  11. Steady Growth, as a Rule

    Connectedness in a network often shows a threshold behavior. When there are few connections, there are isolated islands of connections, and the largest connected group is a small fraction of total members in the network. However, at some point, the addition of a just a few more connections can cause a substantial fraction of the network to be connected. In the classic Erdös and Rényi growth model and its variants, growth occurs by random sampling of the existing network and applying a connectivity rule in a stepwise fashion. Some recent simulations have argued that these transitions can be discontinuous in nature. Riordan and Warnke (p. 322; see the Perspective by Janson) present a mathematical proof that an explosive growth transition that is discontinuous cannot satisfy all the constraints in many of these models.

  12. Kondo Effects of an Oxygen Lattice

    The Kondo effect, in which electrons scatter from localized spins, is often thought about as a single-site process, such as scattering from a magnetic impurity in a nonmagnetic metal. Jiang et al. (p. 324) examined a Kondo lattice formed by O2 molecules, which have two unpaired spins, on the surface of gold at low temperatures. The O2 molecules adsorb along rows, and scanning tunneling microscopy and spectroscopy reveal signatures of both a delocalized Kondo liquid, as well as a localized Kondo signal between two O2 molecules that probably arises from interactions mediated by antibonding states.

  13. Tuning Zeolites

    Zeolites consist of a family of aluminosilicate minerals whose microporosity has made them valuable for filtration and catalysis. A long-standing goal has been to tailor the structure to add a mesoporous network to the inherent microporosity of the zeolite channel walls. Using specially designed bifunctional templating molecules, Na et al. (p. 328; see the Perspective by Möller and Bein) fabricated a zeolite with both porosity scales. Part of the surfactant directed the crystallization of the walls while a second part guided the formation of the narrow channels. Tuning the chemistry of the surfactant allowed tuning of the porosity and the ordering of the pores and zeolite wall thickness. The mesoporous structure and strong zeolitic framework acidity resulted in significantly improved catalytic activity for various organic reactions involving bulky molecules.

  14. Deadly Oceans

    Large regions of the oceans are hypoxic, meaning that their dissolved oxygen concentrations are so low that most marine organisms cannot survive there. The volume of the oceans that experience hypoxia is growing as climate warms, because oxygen solubility decreases as seawater temperature rises. In order to better understand the genesis and extent of ocean hypoxia, Deutsch et al. (p. 336, published online 9 June) developed model-based reconstructions of historical hypoxia variability in the world's largest suboxic zone in the Pacific Ocean over the past 50 years. The volume of the suboxic zone has varied by a factor of two, primarily in response to changes in the depth of the thermocline. Such changes should have large impacts on the nitrogen cycle and the amount of marine photosynthesis.

  15. Introducing Bacterial Electrophysiology

    Bacterial electrophysiology has been limited by the inability to measure the membrane potential of single cells. Kralj et al. (p. 345) engineered a class of voltage-sensitive fluorescent membrane proteins to perform electrophysiological measurements on individual intact bacteria. These measurements showed that Escherichia coli generate electrical spikes, reminiscent of action potentials in neurons. The response of electrical spiking in bacteria was assessed in response to a wide range of physical and chemical perturbations, and was correlated with efflux activity. In the future, the probe should be useful in determining the roles of membrane potential in a variety of medically, environmentally, and industrially important bacteria.

  16. Synthetic Biology

    The design and construction of synthetic genomes that impart new biological function test the fundamental limits of life and provide technological breakthroughs for biotechnology. However, large-scale de novo synthesis of genomes is laborious, expensive, and prone to failure. Isaacs et al. (p. 348) combined evolution, parallel genome editing, and engineered-conjugation to redesign a 4.6-megabase Escherichia coli genome. The method uses the natural genome as a live template and leverages continuous selection against nonfunctional designs to construct the synthetic genome. This in vivo, template-mediated, genome construction approach was multiplexed to introduce the systematic replacement of all 314 occurrences of the TAG stop codon with the synonymous TAA stop codon into 32 E. coli strains, which were then hierarchically assembled together into a genome with 80 precise changes by engineered conjugation. This strategy allowed for the measurement of the functional impacts of all 314 TAG codon replacements.