This Week in Science

This Week in Science

Science  18 Nov 2016:
Vol. 354, Issue 6314, pp. 843
  1. Geophysics

    A volcanic end to an earthquake

    1. Brent Grocholski

    A small-scale eruption of Mount Aso was also recorded in April 2016.

    CREDIT: KUZNETSOV ET AL.; KYODO KYODO/REUTERS PICTURES

    The dangerous and active Aso volcanic cluster appears to have put an early end to the damaging magnitude 7.1 Kumamoto earthquake that struck Japan in April 2016. Lin et al. found that the fault rupture stopped underneath the Aso caldera. The unzipping of the fault ended where the rocks went from cold and brittle to a more liquid-like magmatic mush. This distinctive example shows how abrupt changes in rock properties can terminate fault rupture and cap the size of an earthquake.

    Science, this issue p. 869

  2. Plant Science

    Faster light adaptation improves productivity

    1. Pamela J. Hines

    Crop plants protect themselves from excess sunlight by dissipating some light energy as heat, readjusting their systems when shadier conditions prevail. But the photosynthetic systems do not adapt to fluctuating light conditions as rapidly as a cloud passes overhead, resulting in suboptimal photosynthetic efficiency. Kromdijk et al. sped up the adaptation process by accelerating interconversion of violaxanthin and zeaxanthin in the xanthophyll cycle and by increasing amounts of a photosystem II subunit. Tobacco plants tested with this system showed about 15% greater plant biomass production in natural field conditions.

    Science, this issue p. 857

  3. Plant Science

    Metabolite channeling by a dynamic metabolon

    1. Pamela J. Hines

    The specialized metabolite dhurrin breaks down into cyanide when plant cell walls have been chewed, deterring insect pests. Laursen et al. found that the enzymes that synthesize dhurrin in sorghum assemble as a metabolon in lipid membranes (see the Perspective by Dsatmaichi and Facchini). The dynamic nature of metabolon assembly and disassembly provides dhurrin on an as-needed basis. Membrane-anchored cytochrome P450s cooperated with a soluble glucosyltransferase to channel intermediates toward efficient dhurrin production.

    Dhurrin synthetic enzyme (green) revealed in plant cells

    CREDIT: LAURSEN ET AL.

    Science, this issue p. 890; see also p. 829

  4. Organic Chemistry

    Pluses and minuses of BTX behavior

    1. Jake Yeston

    Batrachotoxin is a potent neurotoxin produced by the endangered Colombian poison dart frog and is an agonist of voltage-gated sodium ion channels (NaVs). Logan et al. developed a chemical synthesis of this molecule, denoted (−)-BTX, by taking advantage of a tin hydride–mediated radical cyclization to stitch together the polycyclic framework. Using an analogous route, they also prepared the non-natural mirror image, (+)-BTX. Conversely to the natural product, (+)-BTX antagonized NaVs.

    Science, this issue p. 865

  5. Active Matter

    Directing traffic with patterns

    1. Marc S. Lavine

    Biological entities, such as bacteria, may direct their motion in response to their environment, but this usually does not lead to large-scale patterns or collective behavior. Peng et al. found that the orientational ordering of a liquid crystal could direct the flow of self-propelling bacteria, which in turn influenced the patterning of the liquid crystal molecules. Patterns on a substrate caused surface anchoring of the liquid crystals that transmitted to the ordering of the bacteria, thus imparting control on what would otherwise be chaotic out-of-equilibrium behavior.

    Science, this issue p. 882

  6. DNA Methylation

    Combating parasitic DNA by methylation

    1. Guy Riddihough

    DNA methylation plays an important role in repressing the expression of “parasitic” DNAs, such as transposable elements, which have invaded our genomes. Mammals have three DNA methyltransferase enzymes. Barau et al. discovered a fourth DNA methyltransferase enzyme in mice. The enzyme DNMT3C is a duplication of DNMT3B and is found in male germ cells. There it targets evolutionarily young transposons, of which there is a heavy burden in the mouse genome. DNMT3C methylates and silences the young transposons, preserving male fertility.

    Science, this issue p. 909

  7. Neurodegeneration

    Tau phosphorylation—not all bad

    1. Stella M. Hurtley

    Alzheimer's disease presents with amyloid-β (Aβ) plaques and tau tangles. The prevailing idea in the field is that Aβ induces phosphorylation of tau, which in turn mediates neuronal dysfunction. Working in Alzheimer's disease mouse models, Ittner et al. found evidence for a protective role of tau in early Alzheimer's disease. This protection involves specific tau phosphorylation at threonine 205 at the postsynapse. A protective role of phosphorylated tau in disease challenges the dogma that tau phosphorylation only mediates toxic processes.

    Science, this issue p. 904

  8. Drug Delivery

    Toward malaria eradication

    1. Katrina L. Kelner

    Even though we know how to prevent malaria, we have failed to eliminate this damaging disease. Bellinger et al. designed an easy-to-administer device that provides long-lasting delivery of an antimalarial drug. A star-shaped, drug-containing material is packaged into a capsule. When swallowed, the capsule dissolves in the stomach and the star unfolds, assuming a shape that cannot pass further down the intestine. The star delivers the anti-malarial drug for weeks, but eventually falls apart and passes harmlessly out of the body.

    Sci. Transl. Med. 8, 365ra157 (2016).

  9. Type 1 Diabetes

    Exhausting autoimmunity

    1. Angela Colmone

    In the case of autoimmune diseases, such as type 1 diabetes, so-called “exhausted” T cells may be the answer to stopping disease. Long et al. report that the best responses in type 1 diabetics treated with teplizumab, a monoclonal antibody against CD3, were associated with CD8+ T cells with features of exhausted T cells. These cells recognized a broad spectrum of autoantigens but proliferated less than nonexhausted cells ex vivo. However, they were not terminally exhausted: Stimulation with a ligand for the inhibitory receptor TIGIT further down-regulated their activation. Inducing T cell exhaustion may thus represent a potential therapeutic approach in type 1 diabetes.

    Sci. Immunol. 1, eaai7793 (2016).

  10. Applied Optics

    A clear approach to nanophotonics

    1. Ian S. Osborne

    The resonant modes of plasmonic nanoparticle structures made of gold or silver endow them with an ability to manipulate light at the nanoscale. However, owing to the high light losses caused by metals at optical wavelengths, only a small fraction of plasmonics applications have been realized. Kuznetsov et al. review how high-index dielectric nanoparticles can offer a substitute for these metals, providing a highly flexible and low-loss route to the manipulation of light at the nanoscale.

    Science, this issue p. 10.1126/science.aag2472

  11. Quantum Optics

    Integrated quantum nanophotonics

    1. Ian S. Osborne

    Technologies that exploit the rules of quantum mechanics offer a potential advantage over classical devices in terms of sensitivity. Sipahigil et al. combined the quantum optical features of silicon-vacancy color centers with diamond-based photonic cavities to form a platform for integrated quantum nanophotonics (see the Perspective by Hanson). They could thus generate single photons from the color centers, optically switch light in the cavity by addressing the state of the color center, and quantum-mechanically entangle two color centers positioned in the cavity. The work presents a viable route to develop an integrated platform for quantum networks.

    Science, this issue p. 847; see also p. 835

  12. Organic Chemistry

    CO takes the lead to make β-lactam rings

    1. Jake Yeston

    Strained β-lactam rings are a key feature of penicillin and some other drugs. Willcox et al. designed a versatile route to these four-membered ring motifs through the palladiumcatalyzed coupling of carbon monoxide with secondary amines. The bulky carboxylate ligand appears to facilitate preliminary CO incorporation into a Pd anhydride, which is then attacked by the amine to set up ring closure via C–H activation. This approach broadens the substrate scope compared with a previous scheme in which C–H activation preceded CO insertion.

    Science, this issue p. 851

  13. Solar Cells

    Tandem perovskite cells

    1. Phil Szuromi

    The ready processability of organic-inorganic perovskite materials for solar cells should enable the fabrication of tandem solar cells, in which the top layer is tuned to absorb shorter wavelengths and the lower layer to absorb the remaining longer-wavelength light. The difficulty in making an all-perovskite cell is finding a material that absorbs the red end of the spectrum. Eperon et al. developed an infrared-absorbing mixed tin-lead material that can deliver 14.8% efficiency on its own and 20.3% efficiency in a four-terminal tandem cell.

    Science, this issue p. 861

  14. Nanomaterials

    Watching it all fall apart

    1. Marc S. Lavine

    The control of the shape and size of metal nanoparticles can be very sensitive to the growth conditions of the particles. Ye et al. studied the reverse process: They tracked the dissolution of gold nanoparticles in a redox environment inside a liquid cell within an electron microscope, controlling the particle dissolution with the electron beam. Tracking short-lived particle shapes revealed structures of greater or lesser stability. The findings suggest kinetic routes to particle sizes and shapes that would otherwise be difficult to generate.

    Science, this issue p. 874

  15. Geology

    Drilling into Chicxulub's formation

    1. Brent Grocholski

    The Chicxulub impact crater, known for its link to the demise of the dinosaurs, also provides an opportunity to study rocks from a large impact structure. Large impact craters have “peak rings” that define a complex crater morphology. Morgan et al. looked at rocks from a drilling expedition through the peak rings of the Chicxulub impact crater (see the Perspective by Barton). The drill cores have features consistent with a model that postulates that a single over-heightened central peak collapsed into the multiple-peak-ring structure. The validity of this model has implications for far-ranging subjects, from how giant impacts alter the climate on Earth to the morphology of crater-dominated planetary surfaces.

    Science, this issue p. 878; see also p. 836

  16. Neurodevelopment

    Sacral neurons reassigned

    1. Pamela J. Hines

    The autonomic nervous system regulates the function of internal organs such as the gut. The parasympathetic and sympathetic arms of this system tend to operate antagonistically. Espinosa-Medina et al. used anatomical and molecular analyses to reevaluate the assignment of neurons in the sacral autonomic nervous system (see the Perspective by Adameyko). Previously categorized as parasympathetic, these neurons are now identified as sympathetic. The results resolve a persistent confusion about how the two systems developed and open the avenue to more predictable outcomes in developing treatments targeted to the pelvic autonomic nervous system.

    Science, this issue p. 893; see also p. 833

  17. Synthetic Biology

    Optimizing designer metabolisms in vitro

    1. Nicholas S. Wigginton

    Biological carbon fixation requires several enzymes to turn CO2 into biomass. Although this pathway evolved in plants, algae, and microorganisms over billions of years, many reactions and enzymes could aid in the production of desired chemical products instead of biomass. Schwander et al. constructed an optimized synthetic carbon fixation pathway in vitro by using 17 enzymes—including three engineered enzymes—from nine different organisms across all three domains of life (see the Perspective by Gong and Li). The pathway is up to five times more efficient than the in vivo rates of the most common natural carbon fixation pathway. Further optimization of this and other metabolic pathways by using similar approaches may lead to a host of biotechnological applications.

    Science, this issue p. 900; see also p. 830

  18. Pharmacology

    A kinase makes its own inhibitor

    1. Nancy R. Gough

    The kinase GSK-3 is a promising drug target for treating neurodegenerative disorders, including Alzheimer's disease. However, most GSK-3 inhibitors have not reached the clinic because they also inhibit other kinases. Licht-Murava et al. discovered a peptide that was converted by the catalytic site of GSK-3 to an inhibitor of the kinase. This peptide was highly selective for GSK-3, inhibited GSK-3 in cells and animals, and improved cellular symptoms, cognitive function, and social behaviors in a mouse model of Alzheimer's disease. This new mechanism of inhibition may finally enable effective and selective GSK-3 inhibitors to reach the clinic.

    Sci. Signal. 9, ra110 (2016).

  19. Plant Science

    Combining heat and light responses

    1. Pamela J. Hines

    Plants integrate a variety of environmental signals to regulate growth patterns. Legris et al. and Jung et al. analyzed how the quality of light is interpreted through ambient temperature to regulate transcription and growth (see the Perspective by Halliday and Davis). The phytochromes responsible for reading the ratio of red to far-red light were also responsive to the small shifts in temperature that occur when dusk falls or when shade from neighboring plants cools the soil.

    Science, this issue p. 897, p. 886; see also p. 832