This Week in Science

Science  15 Dec 2017:
Vol. 358, Issue 6369, pp. 1397
  1. Immunology

    Why aging attenuates antiviral responses

    1. Annalisa M. VanHook

    One of the reasons underlying the elderly's increased susceptibility to flu is elucidated.

    CREDIT: ISTOCK.COM/INSTANTS

    Older adults are more likely to die after influenza A viral infection than younger adults. This is in part because monocytes from older people produce less interferon and show reduced induction of antiviral genes in response to infection. Molony et al. found that monocytes from older human donors showed impaired signaling downstream of the cytosolic RNA sensor RIG-I, which initiates the innate immune response to influenza A virus. Thus, restoring RIG-I signaling in older individuals may reduce age-related mortality from influenza A viral infection.

    Sci. Signal. 10, eaan2392 (2017).

  2. Cancer

    Bacteria go the distance in cancer

    1. Paula A. Kiberstis

    The bacterial species Fusobacterium nucleatum is associated with a subset of human colorectal cancers, but its role in tumorigenesis is unclear. Studying patient samples, Bullman et al. found that F. nucleatum and certain co-occurring bacteria were present not only in primary tumors but also in distant metastases. Preliminary evidence suggests that the bacterium is localized primarily within the metastatic cancer cells rather than in the stroma. Antibiotic treatment of mice carrying xenografts of F. nucleatum–positive human colorectal cancer slowed tumor growth, consistent with a causal role for the bacterium in tumorigenesis.

    Science, this issue p. 1443

  3. Catalysis

    Stable catalysts through steaming

    1. Phil Szuromi

    The lifetime of catalysts that convert automotive exhaust pollutants can be increased by lowering their operating temperature, which helps to prevent deactivation caused by the active metal atoms agglomerating into larger, less active particles. Nie et al. show that a thermally stable catalyst, atomically dispersed Pt2+ on CeO2, can become active for CO oxidation at 150°C after steam treatment at 750°C. In studies with simulated vehicle exhaust, this catalyst treatment also improves its oxidation activity for other exhaust components such as hydrocarbons.

    Science, this issue p. 1419

  4. Phase-Change Memory

    Fast phase change with no preconditions

    1. Brent Grocholski

    Random access memory (RAM) devices that rely on phase changes are primarily limited by the speed of crystallization. Rao et al. combined theory with a simple set of selection criteria to isolate a scandium-doped antimony telluride (SST) with a subnanosecond crystallization speed (see the Perspective by Akola and Jones). They synthesized SST and constructed a RAM device with a 700-picosecond writing speed. This is an order of magnitude faster than previous phase-change memory devices and competitive with consumer dynamic access, static random access, and flash memory.

    Science, this issue p. 1423; see also p. 1386

  5. Nanophotonics

    Tuning the scattering of light

    1. Ian S. Osborne

    The development of nanophotonic technology relies on the ability to control and manipulate light at the nanometer scale. Most devices developed to date have been passive structures or have shown only modest changes in optical properties under an external stimulus. Holsteen et al. tuned the resonant scattering wavelength of silicon nanowires across the entire visible spectrum simply by adjusting the height of the nanowire above a metallic mirror. This nano-electromechanical system illustrates the potential for developing active optical platforms.

    Science, this issue p. 1407

  6. Neurodegeneration

    A structural look at α-synuclein oligomers

    1. Stella M. Hurtley

    Fibrillar aggregates of the protein α-synuclein (αS) are the major constituents of Lewy bodies in Parkinson's disease. However, small oligomers that accumulate during the process of fibril formation are thought to cause the neuronal toxicity associated with the onset and progression of Parkinson's disease. Little is known about the detailed structural properties of αS oligomers and the molecular mechanisms that lead to their toxicity. Fusco et al. report the structural characterization of two forms of αS oligomers, which elucidates the fundamental structural elements giving rise to neuronal toxicity.

    Science, this issue p. 1440

  7. Synthetic Biology

    A CRISPR device to record time

    1. Steve Mao

    The CRISPR adaptation system has been used to record the sequence and ordering of exogenous oligonucleotides that are electroporated into cell populations. Sheth et al. engineered a system bypassing the use of exogenous DNA to directly record temporal signals. An input biological signal is transformed into the ratio of the frequency of incorporating trigger DNA to that of incorporating reference DNA into the genomes of a bacterial population. A multiplexing strategy enables simultaneous recording of three environmental signals with high temporal resolution.

    Science, this issue p. 1457

  8. Paleontology

    How to survive a mass extinction

    1. Shahid Naeem
    Close-up view of Rhaeticosaurus tail vertebraePHOTO: WINTRICH ET AL., SCI. ADV. 10.1126/SCIADV.1701144 (2017)

    The Triassic-Jurassic (T-J) extinction occurred in the midst of the Mesozoic Era (about 65 to 250 million years ago). It provides opportunities to explore why species perish or survive such events. Wintrich et al. describe a previously unknown species of Triassic plesiosaur with characteristics that may explain why this single sauropterygian clade survived the T-J extinction. Its bone histology points to a high metabolic rate, facilitating fast and efficient swimming for living as an open-sea predator. It seems that plesiosaurs survived because they lived in the more buffered open sea, whereas their cousins perished in less buffered coastal habitats.

    Sci. Adv. 10.1126/sciadv.1701144 (2017).

  9. Plant Biology

    An extra sugar protects

    1. Pamela J. Hines

    Many microbial pathogens produce proteins that are toxic to the cells that they are targeting. Broad-leaved plants are susceptible to NLP (necrosis and ethylene-inducing peptide 1–like protein) toxins. Lenarčič et al. identified the receptors for NLP toxins to be GIPC (glycosylinositol phosphorylceramide) sphingolipids (see the Perspective by Van den Ackerveken). Their findings reveal why these toxins only attack broad-leaved plants (so-called eudicots): If the sphingolipid carries just two hexoses, as is the case for eudicots, the toxin binds and causes cell lysis. But in monocots with sphingolipids that have three hexoses, the toxin is ineffective.

    Science, this issue p. 1431; see also p. 1383

  10. 2D Materials

    Finding correlations in a Dirac-cone material

    1. Jelena Stajic

    Researchers have long been on the lookout for signatures of electron-electron interactions in materials whose electrons have linear energy dispersions represented by Dirac cones, such as graphene. However, these effects have remained frustratingly small. Hirata et al. used nuclear magnetic resonance to study the layered organic material α-(BEDT-TTF)2I3, in which a phase featuring Dirac cones is known to be adjacent to one with enhanced electronic correlations. The unusual temperature dependence of spin-related properties in this material indicated strong correlations among the linearly dispersing electrons.

    Science, this issue p. 1403

  11. Batteries

    Wired for success

    1. Marc S. Lavine

    Although overall battery performance is limited by the electrochemistry of the component materials, the actual performance can be limited by a number of factors. Zhu et al. review different electrode architectures for lithium-ion batteries. In particular, they look at the relations between the kinetics and dimensionality of the different electrode constituents. Making things smaller can improve transport of electrons and ions, but at the cost of making the overall architecture more complex. The authors discuss the overall design rules and criteria to guide battery design.

    Science, this issue p. eaao2808

  12. Synthetic Biology

    A rationally designed DNA-based oscillator

    1. L. Bryan Ray

    An important goal of synthetic biology is to create biochemical control systems with the desired characteristics from scratch. Srinivas et al. describe the creation of a biochemical oscillator that requires no enzymes or evolved components, but rather is implemented through DNA molecules designed to function in strand displacement cascades. Furthermore, they created a compiler that could translate a formal chemical reaction network into the necessary DNA sequences that could function together to provide a specified dynamic behavior.

    Science, this issue p. eaal2052

  13. Nucleic Acid Origami

    Large origami from a single strand

    1. Phil Szuromi

    Nanostructures created by origami-like folding of nucleic acids are usually formed by base-pairing interactions between multiple strands. Han et al. show that large origami (up to 10,000 nucleotides for DNA and 6000 nucleotides for RNA) can be created in simple shapes, such as a rhombus or a heart. A single strand can be folded smoothly into structurally complex but knot-free structures by using partially complemented double-stranded DNA and the cohesion of parallel crossovers. The use of single strands also enables in vitro synthesis of these structures.

    Science, this issue p. eaao2648

  14. Quantum Simulation

    Breaking the symmetry in a supersolid

    1. Jelena Stajic

    The concept of broken symmetry has relevance across all branches of physics, including particle and condensed matter physics. In many cases, the shape of the potential energy resembles a Mexican hat, and the symmetry of the system is broken when it chooses a particular spot along the “trough” of the hat. Out of this minimum-energy state, the system can undergo collective excitations either along the trough or perpendicular to it. Léonard et al. detected these so-called Goldstone and Higgs modes in a supersolid Bose-condensed atomic gas held in two crossed optical cavities. By monitoring the dynamics of the light field in each cavity, the oscillations of the order parameter associated with both modes were observed in real time.

    Science, this issue p. 1415

  15. Optics

    Phase transition of scattered light

    1. Ian S. Osborne

    Disordered structures can give rise to intriguing scattering phenomena owing to the unpredictable nature of their interaction with light. Using subwavelength-scale disordered metasurfaces, Maguid et al. observed a phase transition in how the light is scattered as a function of disorder. Weak disorder induced a photonic spin Hall effect, whereas strong disorder led to spin-split modes in momentum space, a random optical-Rashba effect. Thus, designed photonic structure could offer a versatile platform to study similar phenomena in complex solid-state systems.

    Science, this issue p. 1411

  16. Catalysis

    Dispersing small, bimetallic nanoparticles

    1. Phil Szuromi

    For applications of nanoparticles in sensing and catalysis, smaller nanoparticles are often more effective because they expose more active surface sites. The properties of metallic nanoparticles can also be improved by creating bimetallic alloys, but typical synthetic methods yield larger nanoparticles where the metals are poorly mixed. Wong et al. show that well-mixed bimetallic ∼1-nm-diameter nanoparticles can be made on silica supports. To do this, they exploited strong electrostatic adsorption, in which the metal precursors are strongly adsorbed onto the surface by controlling pH relative to the surface point of zero charge. Their method was successful for a wide range of metal alloys.

    Science, this issue p. 1427

  17. Polymer Chemistry

    A little zinc makes the rings all link

    1. Jake Yeston

    Although polymer strands are often informally called chains, molecular topologies that actually resemble extended macroscopic chain links have proven surprisingly challenging to make. Most approaches have settled for tethering pairs of interlocked rings amid spacer segments. Wu et al. now report successful synthesis of polycatenanes in which tens of rings are consecutively interlinked. The key was using zinc ions to template the threading of one macrocycle precursor through flanking preformed macrocycles, after which metathesis catalysis closed up the first ring, and the metal could be flushed out.

    Science, this issue p. 1434

  18. Cytoskeleton

    Tubulin carboxypeptidase identity revealed

    1. Stella M. Hurtley

    Enzymes of the α-tubulin detyrosination/tyrosination cycle create landmarks on microtubules that are essential for their multiple cellular functions and are altered in disease. Tubulin carboxypeptidases (TCPs) responsible for detyrosination have remained elusive for 40 years (see the Perspective by Akhmanova and Maiato). Aillaud et al. identified vasohibins as enzymes that perform the TCP function and found that their small interacting partner SBVP was essential for their activity. Vasohibin/SVBP complexes were involved in neuron polarization and brain cortex development. The authors also developed an inhibitor targeting this family of enzymes. Using a completely different strategy, Nieuwenhuis et al. also showed that vasohibins can remove the C-terminal tyrosine of α-tubulin.

    Science, this issue p. 1448, p. 1453; see also p. 1381

  19. Peptide Design

    Macrocycles by design

    1. Valda Vinson

    Macrocyclic peptides have diverse properties, including antibiotic and anticancer activities. This makes them good therapeutic leads, but screening libraries only cover a fraction of the sequence space available to peptides comprising D and L amino acids. Hosseinzadeh et al. achieved near-complete coverage in sampling the sequence space for 7- to 10-residue cyclic peptides and identified more than 200 designs predicted to fold into stable structures. Of 12 structures determined, nine were close to the computational models. They also sampled and designed 11- to 14-residue macrocycles, but without complete coverage. The designed macrocycles provide a path forward for engineering new therapeutics.

    Science, this issue p. 1461

  20. Conservation

    How to save the African elephant

    1. Julia Fahrenkamp-Uppenbrink

    African elephant populations have been plummeting as a result of poaching. Some states with wild elephant populations have promoted a complete ban on ivory trade, whereas others argue for limited trading to raise funds for conservation efforts. In a Perspective, Biggs et al. propose a route out of this deadlock that explicitly acknowledges the different moral perspectives. Building on successful conflict resolution in other areas such as climate change policy, the authors argue for frequent, iterative interactions among a small group of key parties to foster trust and agreement and develop locally appropriate and workable solutions.

    Science, this issue p. 1378

  21. Mucosal Immunology

    Restraining intestinal lymphocyte migration

    1. Anand Balasubramani

    Migration of intraepithelial lymphocytes (IELs) is controlled by several factors. Sumida et al. report that G protein–coupled receptor 55 (GPR55) negatively regulates IEL migration in the small intestine. Lysophosphatidylinositols, a class of ligands active on GPR55 in vitro, are abundant in the small intestine. In response to indomethacin-induced intestinal leakage, GPR55-deficient mice recruited greater numbers of IELs and were more resistant to intestinal injury.

    Sci. Immunol. 2, eaao1135 (2017).

  22. HIV

    Status is not everything

    1. Lindsey Pujanandez

    Many parameters are examined to try to understand HIV transmission in endemic areas. Tanser et al. used longitudinal data from rural South Africa to argue that a “population viral load” index incorporating geographical location and local prevalence is important to infer transmission. Accounting for HIV-negative individuals in calculations and transmission models is important for appropriate interpretations. Such analyses could be helpful in guiding treatment intervention in these regions.

    Sci. Transl. Med. 9, eaam8012 (2017).