This Week in Science

Science  01 May 2015:
Vol. 348, Issue 6234, pp. 536
  1. Quantum Gases

    Making a monopole in an atomic gas

    1. Jelena Stajic

    Artist's impression of a magnetic monopole

    ILLUSTRATION: HEIKKA VALJA

    Some “grand unified theories” of physics predict the existence of the so-called magnetic monopole. No such particles have been seen, but analogs of monopoles may be observable in quantum fluids. Ray et al. created such an analog in a gas of ultracold 87Rb atoms with three spin states at their disposal. The authors used a protocol involving external magnetic fields with particular spatial distributions to create and observe a monopole-like spin texture in the gas.

    Science, this issue p. 544

  2. Three-Body Physics

    Helium caught in the act of triangulating

    1. Jake Yeston

    Helium is the noblest of noble gases, almost completely unattracted to itself or any other chemical element. Of course, when quantum mechanics comes into play, that “almost” is an inevitable caveat. For several decades, researchers have been intrigued by a theoretically predicted Efimov state composed of three helium atoms held loosely together in a triangle. Kunitski et al. now report experimental realization of that state and detection of its acute triangular geometry (see the Perspective by Kornilov). Beyond completing a long quest in helium studies, the results shed light on three-body physics more broadly.

    Science, this issue p. 551; see also p. 498

  3. Ionic Interactions

    Ions' response to hydrophobic surfaces

    1. Phil Szuromi

    The strength of interactions between ions depends on their solvation environment. Schellman postulated in the 1950s that when aqueous solvated ions approached a hydrophobic surface (such as a parts of a protein surface), interactions between ions would be enhanced. Chen et al. experimentally tested this theory by studying the dissociation of organic ions bonded by salt bridges after the addition of acid. The ion pairs were held by tethers at different distances from hydrophobic surfaces. The salt bridge was stronger when it was closer to the hydrophobic surface.

    Science, this issue p. 555

  4. Bacterial Division

    Pop goes the coccus

    1. Stella M. Hurtley

    Daughter cell separation in Staphylococcus aureus proceeds much like the cracking of an egg. So say Zhou et al., who examined dividing cells with millisecond precision using high-speed videomicroscopy. Rather than proceeding gradually, tiny imperfections in the mother cell wall were seen to crack open, leaving two daughter cells linked by a hinge.

    Science, this issue p. 574

  5. Brain Computation

    How the brain sorts and routes messages

    1. Peter Stern

    How do higher brain areas communicate with each other? Do they send out all computations equally to all target areas and leave the recipient to extract the needed and relevant information? Or does the transmitting region package and route computations differentially to distinct target areas, depending on the content? Ciocchi et al. found that the ventral hippocampus routes anxiety-related information preferentially to the prefrontal cortex and goal-related information preferentially to the nucleus accumbens. Hippocampal neurons with multiple projections were more involved in a variety of behavioral tasks and in memory consolidation.

    Science, this issue p. 560

  6. Stress Signaling

    Seeing stress signaling in living mice

    1. Nancy R. Gough

    Stress activates the eIF2α-ATF4 pathway to reduce global protein production while enhancing targeted gene expression, which helps cells adapt and survive. Activation of this pathway is associated with various pathologies, such as tissue fibrosis after injury. Chaveroux et al. developed transgenic mice in which the activation of this pathway could be monitored at the whole-animal level and at the tissue and cellular level. Activation was tissue-specific, depending on the initiating stress. Chemically induced liver fibrosis correlated with activation of the eIF2α-ATF4 pathway by a specific kinase.

    Sci. Signal. 8, rs5 (2015).

  7. Biomechanics

    A beetle's internal bomb

    1. Sacha Vignieri

    Bombardier beetle shoots its enemies

    PHOTO: T. EISNER ET AL. PNAS 96, 17 (17 AUGUST 1999) © 2015 NATIONAL ACADEMY OF SCIENCES

    Bombardier beetles shoot a toxic pulse at potential predators and other harassers. The toxic spray is created by a chemical reaction that occurs inside the beetle's body. Although the details of the reaction are known, how the beetle is able to precisely combine the chemicals at appropriate times and release the pulse at regular intervals has remained a mystery. Arndt et al. used synchrotron x-ray imagery to observe the process as it occurs within live beetles. Expansion and contraction of an internal expansion membrane facilitate the precise cyclic injection of reactants and the subsequent ejection of toxic sprays that keep the beetle's predators at bay.

    Science, this issue p. 563

  8. Retrotransposons

    Keeping jumping genes out of harm's way

    1. Guy Riddihough

    The genomes of most eukaryotes, including our own, are jam-packed with parasitic mobile DNA elements. Most are nonfunctional remnants, but a few are still active, capable of jumping about in our DNA, potentially causing serious damage to our genes. Nevertheless, they avoid landing in and disrupting coding regions. For example, in yeast, the retrotransposon Ty1 is targeted away from protein genes to positions upstream of yeast RNA polymerase III genes. Bridier-Nahmias et al. show that Ty1 is targeted to these “safe havens” through an interaction between a Ty1-encoded protein that controls its genome jumping activity and a subunit of the yeast RNA polymerase III complex.

    Science, this issue p. 585

  9. DNA Repair

    Uncrossing covalently linked DNA strands

    1. Guy Riddihough

    DNA interstrand cross-links (ICLs) covalently link the two strands of the double helix. ICL mutations are difficult to repair, because the two DNA strands cannot be separated and so one strand cannot be used as a template to repair the other. Räschle et al. developed a mass spectrometry–based method to systematically analyze a time series of all the proteins recruited to repair ICLs in Xenopus egg extracts. They found many of the known factors required for ICL repair. They also found a number of new factors, two of which define a new repair pathway for ICL mutations.

    Science, this issue 10.1126/science.1253671

  10. Quantum Simulation

    Simulating magnetism out of equilibrium

    1. Jelena Stajic

    A major goal of quantum simulation is to help us understand problems that are difficult to describe analytically or solve with conventional computers. This goal has been very challenging to reach experimentally, requiring, for example, extremely low temperatures to determine the effects of quantum magnetism in equilibrium. Brown et al. studied a nonequilibrium system of ultracold 87Rb atoms in a two-dimensional optical lattice. They monitored the atoms' dynamics after a sudden change in the lattice parameters and were able to reach a regime where the magnetic interactions dominated the dynamics.

    Science, this issue p. 540

  11. Ferroelectrics

    Getting closure in ferroelectric films

    1. Jelena Stajic

    Ferroelectric materials have a spontaneous electric polarization that can be manipulated for applications. The polarization is usually not uniform throughout the material, and for nanosized ferroelectrics, polarization can be quite complex. Using scanning transmission electron microscopy, Tang et al. found that in thin films of the ferroelectric PbTiO3, the polarization vector rotated in space, forming a closed loop, the so-called flux closure. The flux closure structures formed an array, with the period dependent on the width of the thin film, and caused the buildup of considerable strain within the crystal lattice of the material

    Science, this issue p. 547

  12. Extinctions

    Recognizing the threat of additive risk

    1. Sacha Vignieri

    Humans are accelerating the extinction rates of species in both terrestrial and marine environments. However, species extinctions have occurred across time for a variety of other reasons. Finnegan et al. looked at the extinction rates across marine genera (groups of species) over the past 23 million years to determine intrinsic extinction rates and what traits or regions correspond to the highest rates. Combining patterns of intrinsic extinction with regions of high anthropogenic threat revealed taxa and areas, particularly in the tropics, where the risk of extinction will be especially high.

    Science, this issue p. 567

  13. Climate Change

    Predicting extinction in a changing world

    1. Sacha Vignieri

    There is great interest in understanding how species might respond to our changing climate, but predictions have varied greatly. Urban looked at over 130 studies to identify the level of risk that climate change poses to species and the specific traits and characteristics that contribute to risk (see the Perspective by Hille Ris Lambers). If climate changes proceed as expected, one in six species could face extinction. Several regions, including South America, Australia, and New Zealand, face the greatest risk. Understanding these patterns will help us to prepare for, and hopefully prevent, climate-related loss of biodiversity.

    Science, this issue p. 571; see also p. 501

  14. Structural Biology

    Changing shape to destroy RNA

    1. Guy Riddihough

    Clustered regularly interspaced short palindromic repeats (CRISPRs) together with CRISPR-associated (Cas) proteins form an adaptive immune system that helps bacteria and archaea defend themselves against invading viruses and plasmids. CRISPR RNAs (crRNAs) target CRISPR-Cas protein complexes to the invaders, bringing about their destruction. Taylor et al. used cryo–electron microscopy to determine the structure of a 12-subunit CRISPR-Cas protein complex with crRNA from Thermus thermophilus, in the presence and absence of single-stranded target RNA. Binding to the target RNA causes a change in shape of the CRISPR-Cas complex that results in target recognition and destruction.

    Science, this issue p. 581

  15. Protein Dynamics

    A hierarchy of protein motions

    1. Valda Vinson

    Functioning proteins are not static but explore complex conformational energy landscapes. Lewandowski et al. used multinuclear solid-state nuclear magnetic resonance experiments to measure protein motion over a broad range of temperatures and time scales. Above 160 K there was a strong coupling between solvent and protein motion. The hierarchy of motions as the temperature increased revealed the dynamic modes that relate solvent, sidechain, and backbone motion.

    Science, this issue p. 578

  16. Immune Tolerance

    Early T cells keep autoimmunity at bay

    1. Kristen L. Mueller

    A major challenge faced by the immune system is to react to foreign substances, such as microbes, while simultaneously tolerating the self. Upsetting this balance leads to autoimmunity. Regulatory T cells (Tregs), are a subset of immune cells that help to maintain this balance. Yang et al. found that murine Treg cells generated very early in life are distinct from those generated in older animals and play an especially important role in keeping autoimmunity in check (see the Perspective by Tanaka and Sakaguchi). These changes are due to differences in the way Tregs develop in the thymus in newborn versus adult mice.

    Science, this issue p. 589; see also p. 506

  17. Conservation

    Large herbivore loss threatens biodiversity

    1. Thomas E. Lovejoy

    Large herbivores (100 kg or larger) are suffering dramatic population declines and range contractions worldwide. These losses alter their native ecosystems. Ripple et al. review data on all 76 species of large herbivores. Population declines lead to range contractions, often because of conversion of land to other purposes. Populations of large herbivores should be increased and wildlife trade controlled wherever possible to prevent further range contraction and extinction. These approaches should help to restore normal ecological function and biological diversity.

    Sci. Adv. 10.1126/sciadv.1400103 (2015).

  18. Environment

    How rivers respond to dam removals

    1. Julia Fahrenkamp-Uppenbrink

    Globally, dam building is experiencing a renaissance in the quest for hydropower. However, over the past 40 years, more than 1000 dams have been removed in the United States because they have filled with sediment or have become unsafe or inefficient. Dams are also being taken down in other parts of the world. In a Perspective, O'Connor et al. explore how rivers have responded to these dam removals. Many dam removals have improved ecosystem function and have avoided catastrophic consequences, but most of these dams have been relatively small. As larger dams are increasingly removed, there is a need for longer-term, systematic monitoring.

    Science, this issue p. 496

  19. Conservation Ecology

    Humans and animals vying for space in the air

    1. Julia Fahrenkamp-Uppenbrink

    Human uses of the airspace are increasingly conflicting with wildlife, such as migrating or foraging birds. Flying aircraft are frequently struck by birds, and wind turbines and other human-made structures cause millions of animal deaths each year. In a Perspective, Lambertucci et al. outline such aerial conflicts between human activities and wildlife. Innovative methods aimed at reducing these conflicts include adjusting wind turbine speeds upon radar detection of animal movements and using ultraviolet light to deter birds from windows. These and other measures must be applied at the regional scale to protect migrating species effectively. Judicious management of the airspace should also include airspace reserves in areas with high densities of aerial wildlife.

    Science, this issue p. 502

  20. Bioengineering

    Personalized implants provide a 4D fix

    1. Megan Frisk

    The three-dimensional (3D) printing revolution is in full swing, with printed kidneys, cars, and body armor. Now, 3D is entering into the fourth dimension—time—which renders 4D materials adaptable and enduring. In pediatric medicine, 4D implants are particularly relevant: As the patient grows, so should the material. Morrison et al. used 3D printing to create personalized splints for three pediatric patients with tracheobronchomalacia, a condition in which airways collapse during normal breathing. In all three patients, the 4D devices were stable and functional after 1 month, and one has stayed in place for 30 months. This pilot trial shows that the fourth dimension is becoming a reality for regenerative medicine.

    Sci. Transl. Med. 7, 285ra64 (2015).