This Week in Science

Science  27 Feb 2015:
Vol. 347, Issue 6225, pp. 960
  1. Pest Control

    Bypassing a plant's defense for pest defense

    1. Pamela J. Hines

    The Colorado potato beetle (Leptinotarsa decemlineata)

    IMAGE: © DANIEL BORZYNSKI/ALAMY

    Colorado potato beetles can skeletonize the leaves on a potato plant, devastating crop yields. Insecticides are increasingly useless as the beetle evolves resistance. Zhang et al. used RNA interference to take down this beetle (see the Perspective by Whyard). Success required shifting production of the double-stranded RNA to the plastids to evade the plant's own RNA management mechanisms. The insect's own RNA interference mechanisms then inactivated two everyday genes that the beetle can't do without.

    Science, this issue p. 991; see also p. 950

  2. Mosquito Biology

    Mating plugs promote malaria parasites

    1. Caroline Ash

    Males of some of the malaria-transmitting mosquitoes “plug” females after copulation to stop interloping males from mating. The mating plug also delivers a steroid hormone into the female uterus. This hormone pulse promotes egg production and stimulates egg laying. It also curbs the mosquitoes' immune responses, which allows parasites such as malaria to develop unhindered. Mitchell et al. discovered that plugs are a recent evolutionary acquisition (see the Perspective by Alonzo). South American anopheline mosquitoes lack these plugs altogether, whereas African and Indian species have complex plugs replete with hormones. It is unlikely to be a coincidence that the most elaborate mosquito plugs are also found in regions where malaria transmission rates are highest.

    Science, this issue p. 985; see also p. 948

  3. Surface Chemistry

    Catching CO oxidation

    1. Phil Szuromi

    X-ray laser probes the transition state during CO oxidation on Ru

    IMAGE: SLAC NATIONAL ACCELERATOR LABORATORY

    Details of the transition state that forms as carbon monoxide (CO) adsorbed on a ruthenium surface is oxidized to CO2 have been revealed by ultrafast excitation and probe methods. Öström et al. initiated the reaction between CO and adsorbed oxygen atoms with laser pulses that rapidly heated the surface and then probed the changes in electronic structure with oxygen x-ray absorption spectroscopy. They observed transition-state configurations that are consistent with density functional theory and a quantum oscillator model.

    Science, this issue p. 978

  4. Optics

    Light with twist and structure

    1. Ian S. Osborne

    Möbius strips are three-dimensional structures consisting of a surface with just a single side. Readily demonstrated by snipping a paper ring, adding a twist, and then joining the ends of paper together again, these structures have intriguing mathematical properties in terms of topology and geometry. Bauer et al. used a liquid crystal to engineer the wavefront of a laser beam to make an optical version of the Möbius strip by effectively “snipping and twisting” the polarization properties of the light beam.

    Science, this issue p. 964

  5. Climate Change

    Is the end of the warming hiatus nigh?

    1. H. Jesse Smith

    Which recent climate changes have been forced by greenhouse gas emissions, and which have been natural fluctuations of the climate system? Steinman et al. combined observational data and a large collection of climate models to assess the Northern Hemisphere climate over the past 150 years (see the Perspective by Booth). At various points in time, the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation have played particularly large roles in producing temperature trends. Their effects have combined to cause the apparent pause in warming at the beginning of the 21st century, known as the warming “hiatus.” This pause is projected to end in the near future as temperatures resume their upward climb.

    Science, this issue p. 988; see also p. 952

  6. Archaeology

    Early wheat movement into Britain

    1. Laura M. Zahn

    The transition into the New Stone Age, or Neolithic period, in Great Britain and Europe was characterized by a change from hunter-gatherers to farmers. However, the early stages of this transition are not well understood. Smith et al. studied archaeological remains at an 8000-year-old site that has been underwater ever since the Neolithic (see the Perspective by Larson). The finds include evidence of wheat (or a relative of wheat) 2000 years before the first documented farmers in Britain. It seems that trade may have preceded the adoption of farming.

    Science, this issue p. 998; see also p. 945

  7. Lung Disease

    Mucus: It's the quality that counts

    1. Angela Colmone

    In patients with cystic fibrosis (CF) or other lung diseases, airway mucus can be highly elastic and very difficult to clear, leading to airflow obstruction and lung infection. Now, Yuan et al. show that the biophysical properties of mucus from CF patients are altered because of neutrophilic oxidative stress. To combat this, they targeted mucin disulfide crosslinks with a thiol-modified carbohydrate and produced fast-acting mucolytic activity toward CF sputum. Their findings support the use of mucolytics as a therapeutic strategy for treating CF and related inflammatory lung diseases.

    Sci. Transl. Med. 7, 276ra27 (2015).

  8. Fuel Cells

    Metal-free catalysts for fuel cell technology

    1. Zakya H. Kafafi

    Metal-free catalysts have recently been designed for use in alkaline fuel cells. Dai et al. have successfully used a metal-free catalyst in an acidic polymer electrolyte membrane fuel cell: the mainstream fuel cell technology. Nitrogen-doped carbon nanotubes and their graphene composites catalyzed oxygen reduction in these practical fuel cells. The carbon-based catalysts showed both excellent activity and durability and offer an inexpensive alternative to metal-based catalysts. Such an approach could potentially reduce the manufacturing cost of fuel cells dramatically and open the door for their commercialization.

    Sci. Adv. 10.1126/sciadv.1400129 (2015).

  9. Ebola Virus

    Channeling Ebola virus entry into the cell

    1. Kristen L. Mueller

    The current outbreak of Ebola virus in West Africa highlights the need for antiviral therapies. One strategy would be to block the Ebola virus's ability to enter host cells. Cells engulf Ebola virus particles, which then traffic into the cell in structures called endosomes. Sakurai et al. now report that the Ebola virus requires calcium channels called two-pore channels (TPCs) in endosomal membranes for successful entry (see the Perspective by Falzarano and Feldmann). The Ebola virus could not enter cells lacking TPCs or cells treated with a TPC inhibitor. Blocking TPCs therapeutically allowed 50% of mice to survive an ordinarily lethal Ebola virus infection.

    Science, this issue p. 995; see also p. 947

  10. Sustainability

    Seeking systems-based solutions

    1. Nicholas S. Wigginton

    Without sustainable solutions, the world's most pressing environmental concerns will continue to persist or worsen. Achieving the goal of sustainability involves so many factors—from economics to ecology—that investigating one or even a handful of variables at a time often overlooks major parts of the problem. Liu et al. review systems-based approaches that are beginning to provide tenable ways to assess sustainability. Further integrating coupled human and natural components of a problem across multiple dimensions, including how one solution can create unintended consequences elsewhere, is essential for developing effective policies that seek global sustainability.

    Science, this issue 10.1126/science.1258832

  11. Plasma Physics

    Shocking! Particle accelerators in space

    1. Margaret M. Moerchen

    The acceleration of charged particles to high energies has been a major mystery, with a number of competing theories based on plasma physics. Many include the concept of turbulence, but with different roles. For example, shock-based theories emphasize the importance of turbulence developed from an unstable shock layer, whereas turbulent reconnection theories emphasize interactions of multiple reconnection sites. Matsumoto et al. present results of a large particle-in-cell simulation and examine how electrons are accelerated in the transition layer of a fast nonrelativistic shock (see the Perspective by Ji and Zweibel). Surprisingly, they find that when the shock is strong enough, charged particles (electrons in this case) are efficiently accelerated by turbulent reconnection within a turbulent shock layer containing multiscale structures.

    Science, this issue p. 974; see also p. 944

  12. Gene Regulation

    Uncaging promoter and enhancer dynamics

    1. Laura M. Zahn

    In order to understand cellular differentiation, it is important to understand the timing of the regulation of gene expression. Arner et al. used cap analysis of gene expression (CAGE) to analyze gene enhancer and promoter activities in a number of human and mouse cell types. The RNA of enhancers was transcribed first, followed by that of transcription factors, and finally by genes that are not transcription factors.

    Science, this issue p. 1010

  13. Actuating Materials

    Making small actuators more effective

    1. Marc S. Lavine

    Liquid-crystal molecules orient locally in response to external fields. When long-chain liquid-crystalline molecules are crosslinked together, changes in local orientation can lead to significant volume changes. Ware et al. made efficient microactuators that can change their shape from flat to three-dimensional structures (see the Perspective by Verduzco). By patterning volume elements so that each has a different preferred alignment for the liquid-crystalline molecules, they could fine-tune the volume changes.

    Science, this issue p. 982; see also p. 949

  14. Stem Cells

    mRNA modification regulates pluripotency

    1. Beverly A. Purnell

    When stem cells progress from an embryonic pluripotent state toward a particular lineage, molecular switches dismantle the transcription factor network that keeps the cell pluripotent. Geula et al. now show that N6-methyladenosine (m6A), a messenger RNA (mRNA) modification present on transcripts of pluripotency factors, drives this transition. Methylation destabilized mRNA transcripts and limited their translation efficiency, which promoted the timely decay of naïve pluripotency. This m6A methylation was also critical for mammalian development.

    Science, this issue p. 1002

  15. Cancer

    The downstream effects of false promotion

    1. Paula A. Kiberstis

    Special DNA sequences at the ends of chromosomes, called telomeres, are replenished by a dedicated enzyme called telomerase. A subset of human tumors harbors mutations in the promoter region of the TERT gene, which codes for a subunit of telomerase. Borah et al. explored the downstream effects of TERT promoter mutations in cells derived from urothelial (urinary tract) cancers. The mutations were associated with aberrantly high levels of TERT mRNA, TERT protein and telomerase activity, and longer telomeres. A small study of clinical samples suggested that high levels of TERT mRNA may be a marker of more aggressive urothelial cancers.

    Science, this issue p. 1006

  16. Transcription

    Keeping repressed genes repressed

    1. Guy Riddihough

    Hox genes confer positional identity to cells and tissues. Maintaining precise spatial patterns of Hox gene expression is vital during metazoan development. The transcriptional repressor CTCF is involved in the regulation of chromatin architecture. Narendra et al. show that a CTCF protein binding site insulates regions of active and repressed Hox gene expression from each other. This protects heterochromatin containing repressed Hox genes from the encroaching spread of active chromatin. The CTCF protein appears to organize the active and repressed chromatin regions into distinct architectural domains.

    Science, this issue p. 1017

  17. Evolution

    Losing and then regaining flagella

    1. Guy Riddihough

    The ability to adapt to changes in the function of gene regulators, as opposed to structural genes, is a crucial aspect of evolutionary change. Taylor et al. mutated a central regulator for the formation of flagella in the bacterium Pseudomonas fluorescens. They then put the mutated flagella-free bacteria under strong selection pressure to regain mobility. The mutated bacteria regained the lost flagella, and motility, within 4 days. Two stereotypical mutations diverted an evolutionarily related regulator that normally controls nitrogen uptake to control flagella biosynthesis. The mutations increased the levels of the co-opted regulator, then altered its specificity for the flagella pathway.

    Science, this issue p. 1014

  18. Inflammation

    Itching to reduce inflammation

    1. John F. Foley

    The kinase p38 is activated in various inflammatory skin disorders, but drugs that block p38 activity can cause toxicity. Mice deficient in the E3 ubiquitin ligase Itch have itchy skin. Theivanthiran et al. studied the α isoform of p38 in these mice. Skin cells from Itch-deficient mice had more active p38α and higher levels of the p38α-binding protein Tab1. In skin cells from normal mice, Tab1 was targeted for degradation by Itch. Skin inflammation in Itch-deficient mice was decreased after injection with a peptide that blocked the Tab1-p38α interaction, suggesting an alternative way to target p38α in inflammatory disorders.

    Sci. Signal. 8, ra22 (2015).

  19. Solar Cells

    Balanced carrier diffusion in perovskites

    1. Phil Szuromi

    The efficient operation of solar cells based on inorganic-organic perovskites requires balanced transport of positive and negative charge carriers over long distances. Dong et al. used a top-seeded solution growth method to obtain millimeter-scale single crystals of the organolead trihalide perovskite CH3NH3PbI3. Under low light illumination, the electron and hole diffusion lengths exceeded 3 mm, and under full sunlight illumination, they exceeded 175 µm.

    Science, this issue p. 967

  20. Water Splitting

    An enduring catalyst built from carbon

    1. Jake Yeston

    Splitting water into its constituent elements, hydrogen and oxygen, generally requires the assistance of metal catalysts. Liu et al. now show that a metal-free hybrid material composed of carbon and nitrogen can promote this reaction all on its own, with the help of some visible light. The photocatalyst combines one material (C3N4) known to split water into hydrogen and peroxide with a second material (CDot) that breaks the peroxide down before it can damage the first. The robust stability of this hybrid bodes well for practical implementation of optimized analogs in solar energy storage schemes.

    Science, this issue p. 970

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