This Week in Science

Science  15 Jul 2016:
Vol. 353, Issue 6296, pp. 258
  1. Volcanology

    Driven to collapse

    1. Brent Grocholski

    Iceland, 2 September 2014

    PHOTO: ©F1ONLINE DIGITALE BILDAGENTUR GMBH/ALAMY STOCK PHOTO

    Volcanic eruptions occur frequently, but only rarely are they large enough to cause the top of the mountain to collapse and form a caldera. Gudmundsson et al. used a variety of geophysical tools to monitor the caldera formation that accompanied the 2014 Bárdarbunga volcanic eruption in Iceland. The volcanic edifice became unstable as magma from beneath Bárdarbunga spilled out into the nearby Holuhraun lava field. The timing of the gradual collapse revealed that it is the eruption that drives caldera formation and not the other way around.

    Science, this issue p. 262

  2. Optics

    Making the forbidden allowed

    1. Ian S. Osborne

    Spontaneous emission, in which an excited electron lowers its energy by emitting a photon, is a fundamental process in light-matter interactions. In principle, the electron can relax from the excited state to any unoccupied lower energy level. In practice, however, most of these transitions are too slow and so are effectively forbidden. Rivera et al. show theoretically that the plasmonic excitations associated with two-dimensional materials can be used to enhance and control the light-matter interaction. Transitions that were once considered forbidden can thus be accessed, opening up the entire spectrum of an optical emitter.

    Science, this issue p. 263

  3. Evolutionary Cognition

    The innate wisdom of ducklings

    1. Sacha Vignieri

    Imprinting on an image is one of the first things that a naïve brain learns to do. Such rapid identification of relevant signals allows young animals to recognize their mother and caregiver. Martinho and Kacelnik show that mallard ducks are also capable of higher-level learning of relational concepts and can integrate these into their imprinted image (see the Perspective by Wasserman). Ducklings were imprinted on a set of objects that were either the same or different. The ducklings later preferred to follow other objects that showed the same relationship as that on which they had imprinted. Thus, even this most basic form of learning appears to be shaped by higher-level cognitive reasoning.

    Science, this issue p. 286; see also p. 222

  4. Biochemistry

    Adaptors conduct the EGFR symphony

    1. Leslie K. Ferrarelli

    In signaling networks, there are rate-limiting proteins that direct the signal through specific molecular cascades to dictate the response. Shi et al. sought to identify the proteins in the epidermal growth factor receptor (EGFR) signaling network that serve as the conductors of the EGF signal. The levels of several adaptor proteins were highly variable among cells, and the levels of the adaptor proteins—not the receptor or core pathway proteins—were rate-limiting for the EGFR pathway in normal and malignant cells. Thus, the adaptor proteins are the directors of the signaling script.

    Sci. Signal. 9, rs6 (2016).

  5. Neurodevelopment

    Sending neural stem cells back to the garage

    1. Pamela J. Hines

    In the brain's hippocampus, which modulates memories and emotions, neural stem cells generate new neurons, even during adulthood. How many new neurons are generated, and when, follows from the balance between quiescence and proliferation in the pool of neural stem cells. Urbán et al. asked what signals send proliferating stem cells back into a quiescent state. They found that a key transcription factor that promotes cellular proliferation was degraded through the ubiquitinylation system. This molecular interaction regulated the return to a resting state, but one that was not quite as quiescent as the original state. Stem cells in this resting but primed state sustained the stem cell pool.

    Science, this issue p. 292

  6. Structural Biology

    Transmitting signals across the synapse

    1. Valda Vinson

    Glutamate receptors located on neuronal cells play a role in mediating electrical signals at excitatory synapses. These glutamatergic synapses are extremely important for nearly all cognitive functions. Elegheert et al. analyzed a complex that bridges the synapse, comprising β-neurexin 1, a cell adhesion molecule on the surface of presynaptic axons; cerebellin 1, a synaptic organizer; and the postsynaptic glutamate receptor GluD2. The structural and functional analysis provides insight into the mechanism of synaptic signaling.

    Science, this issue p. 295

  7. Glaciers

    The heat is on

    1. H. Jesse Smith

    Antarctic glacier from the melting Larsen B ice shelf (Antarctic Peninsula)

    PHOTO: ©BLICKWINKEL/ALAMY STOCK PHOTO

    Rising surface air temperatures are understood to cause glacial melting, but it is becoming increasingly clear that the ocean also has a strong impact. Cook et al. studied glaciers that drain the Antarctic Peninsula and found a strong correlation between mid-depth ocean temperatures and glacier-front changes along the peninsula's western coastline. Glaciers in the south, which are exposed to warmer waters, have undergone significant retreat, while those in the northwest, which terminate in cooler waters, have not retreated as much or as uniformly. Thus, ocean-induced melting appears to be the main cause of glacial retreat in the region.

    Science, this issue p. 283

  8. Lithium Ion Batteries

    Carbon nanotubes boost battery storage

    1. Zakya H. Kafafi

    Molybdenum disulfide is a promising anode material for lithium ion batteries. However, it is plagued with low intrinsic electrical conductivity and large strain during cycling, which cause low rate capability and fast capacity decay. Lou et al. designed ultrathin nanosheets of molybdenum disulfide tubular structures wired with carbon nanotubes. These modified electrode structures exhibited lithium battery storage performance with very high specific capacity, exceptional rate capability, and ultralong cycle life.

    Sci. Adv. 10.1126.sciadv.1600021 (2016).

  9. Organic Chemistry

    A light approach to C-N bond formation

    1. Jake Yeston

    The need to form C-N bonds arises frequently in drug discovery research. One versatile approach involves the attachment of the C and N fragments to a Pd catalyst. This approach needs a bulky ligand to “crowd” the fragments together off the metal center. Corcoran et al. present a complementary approach that uses Ni in place of Pd. Instead of the bulky ligand, they used a light-activated cocatalyst that strips an electron from the Ni to accelerate the bond formation. A screen involving elaborately substituted reagents confirmed the utility of this approach in cases that challenge the traditional Pd coupling.

    Science, this issue p. 279

  10. Mitochondria

    How the ER manages mitochondrial division

    1. Stella M. Hurtley

    It has been unclear how mitochondrial DNA (mtDNA) replication is spatially controlled in mammalian cells and how the mitochondrial nucleoid—the protein-DNA structure that is the unit of mtDNA inheritance—is distributed at the cellular level. Lewis et al. now show that homeostatic mtDNA synthesis in mitochondrial nucleoids in mammalian cells is spatially linked to a small subset of endoplasmic reticulum (ER)-mitochondria contact sites that are specifically destined for mitochondrial division. Successive events of mtDNA replication, mitochondrial division, and mitochondrial motility function together to ensure the accurate distribution of mtDNA in cells. Furthermore, ER-mitochondria contacts coordinate the licensing of mtDNA replication with division to distribute newly replicated nucleoids to daughter mitochondria.

    Science, this issue p. 261

  11. Ferroelectricity

    Thinning a ferroelectric makes it better

    1. Jelena Stajic

    As a ferroelectric material becomes thinner, the temperature below which it develops its permanent electrical polarization usually decreases. Chang et al. fabricated high-quality thin films of SnTe that, in contrast to this conventional wisdom, had a considerably higher transition temperature than that of the material in bulk (see the Perspective by Kooi and Noheda). This was true even for single-unit cell films, whereas only slightly thicker films became ferroelectric above room temperature. This finding may enable the miniaturization of ferroelectric devices.

    Science, this issue p. 274; see also p. 221

  12. Biodiversity

    Crossing “safe” limits for biodiversity loss

    1. Andrew M. Sugden

    The planetary boundaries framework attempts to set limits for biodiversity loss within which ecological function is relatively unaffected. Newbold et al. present a quantitative global analysis of the extent to which the proposed planetary boundary has been crossed (see the Perspective by Oliver). Using over 2 million records for nearly 40,000 terrestrial species, they modeled the response of biodiversity to land use and related pressures and then estimated, at a spatial resolution of ∼1 km2, the extent and spatial patterns of changes in local biodiversity. Across 65% of the terrestrial surface, land use and related pressures have caused biotic intactness to decline beyond 10%, the proposed “safe” planetary boundary. Changes have been most pronounced in grassland biomes and biodiversity hotspots.

    Science, this issue p. 288; see also p. 220

  13. Neurobiology

    Epigenetic regulation in the brain

    1. L. Bryan Ray

    The activity of neurons in the brain controls the transcription of genes that influence the pruning of dendritic connections between neurons, and such modifications can influence animal behavior. Yang et al. propose a role for chromatin remodeling by the nucleosome remodeling and deacetylase complex (NuRD) in the inactivation of such activity-dependent transcription in the mouse cerebellum (see the Perspective by Sweatt). Deposition of the histone variant H2A.z at promoters of activity-dependent genes required the NuRD complex. Loss of the NuRD complex function resulted in hypersensitivity of mice to sensory stimuli and excessive neuronal connectivity in animals performing a task on a treadmill.

    Science, this issue p. 300; see also p. 218

  14. Ecology

    This is no time to be a butterfly

    1. Julia Fahrenkamp-Uppenbrink

    Around the world, butterfly communities are declining, with specialists replaced by generalists. In a Perspective, Thomas explains that there are two main drivers of these declines: habitat loss and habitat degradation. Many butterfly species are highly specialized as caterpillars and have small population ranges, making them vulnerable to loss of and changes in habitat resulting from human activities. Although such declines can be reversed with judicious conservation measures, this is much more expensive than protecting butterflies in the first place.

    Science, this issue p. 216

  15. Neurodegeneration

    C9ORF72, a suppressor of autoimmunity?

    1. Orla M. Smith

    Mutations in C9ORF72 are a common contributor to the neurodegenerative disease amyotrophic lateral sclerosis (ALS), yet the function of this gene is still poorly understood. Burberry et al. found that mutations disrupting the normal function of the murine C9ORF72 ortholog caused mice to develop autoimmunity. Furthermore, transplantation of normal mouse bone marrow into mutant animals ameliorated the disease phenotype, whereas transplantation of mutant bone marrow into normal animals caused autoimmunity. Thus, C9ORF72 appears to act through hematopoietic cells to maintain normal immune function. Future investigations should ask whether disruptions in immunity contribute to disease in ALS patients.

    Sci. Transl. Med. 8, 347ra93 (2016).

  16. Ozone Hole

    Turning the corner

    1. H. Jesse Smith

    The Antarctic ozone hole is finally showing signs of disappearing, nearly 30 years after the Montreal Protocol came into effect. The Montreal Protocol, an international treaty that phased out the production of many of the human-made compounds responsible for stratospheric ozone destruction, is widely considered to be the most important and successful international environmental agreement. For years, it has slowed the rate of stratospheric ozone depletion, and now there are signs that the ozone abundance over Antarctica has begun to increase. Solomon et al. present observational data and model results to illustrate the trends and diagnose their causes.

    Science, this issue p. 269

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