This Week in Science

Science  23 Dec 2016:
Vol. 354, Issue 6319, pp. 1546
  1. Brain Research

    Now you feel it, now you don't

    1. Peter Stern

    Mice shed light on mechanisms involved in whisker sensitivity.

    CREDIT: MARQUES/SHUTTERSTOCK

    What determines the detection of a sensory stimulus? To address this question, Takahashi et al. combined in vivo two-photon imaging, electrophysiology, optogenetics, and behavioral analysis in a study of mice. Calcium signals in apical dendrites of pyramidal neurons in the somatosensory cortex controlled the perceptual threshold of the mice's whiskers. Strong reduction of dendritic calcium signaling impaired the perceptual detection threshold so that an identical stimulus could no longer be noticed.

    Science, this issue p. 1587

  2. Cometary Science

    Rosetta observes sublimating surface ices

    1. Keith T. Smith

    Comets are “dirty snowballs” made of ice and dust, but they are dark because the ice sublimates away, leaving some of the dust behind on the surface. The Rosetta spacecraft has provided a close-up view of the comet 67P/Churyumov-Gerasimenko as it passes through its closest point to the Sun (see the Perspective by Dello Russo). Filacchione et al. detected the spectral signature of solid CO2 (dry ice) in small patches on the surface of the nucleus as they emerged from local winter. By modeling how the CO2 sublimates, they constrain the composition of comets and how ices generate the gaseous coma and tail. Fornasier et al. studied images of the comet and discovered bright patches on the surface where ice was exposed, which disappeared as the ice sublimated. They also saw frost emerging from receding shadows. The surface of the comet was noticeably less red just after local dawn, indicating that icy material is removed by sunlight during the local day.

    Science, this issue p. 1563, p. 1566; see also p. 1536

  3. Topological Matter

    Watching Majorana bound states form

    1. Jelena Stajic

    Majorana bound states (MBSs) are peculiar quasiparticles that may one day become the cornerstone of topological quantum computing. To engineer these states, physicists have used semiconductor nanowires in contact with a superconductor. Although many of the observed properties align with theoretical predictions, a closer look into the creation of MBSs is desirable. Deng et al. fabricated nanowires with a quantum dot at one end that served as a spectrometer for the states that formed inside the superconducting gap of the nanowire. Using this setup, topologically trivial bound states were seen to coalesce into MBSs as the magnetic field was varied.

    Nanowires reveal an exotic state of matter.

    CREDIT: DENG ET AL.

    Science, this issue p. 1557

  4. Structural Biology

    Snapshots of bacteriorhodopsin

    1. Valda Vinson

    Bacteriorhodopsin is a membrane protein that harvests the energy content from light to transport protons out of the cell against a transmembrane potential. Nango et al. used timeresolved serial femtosecond crystallography at an x-ray free electron laser to provide 13 structural snapshots of the conformational changes that occur in the nanoseconds to milliseconds after photoactivation. These changes begin at the active site, propagate toward the extracellular side of the protein, and mediate internal protonation exchanges that achieve proton transport.

    Science, this issue p. 1552

  5. Catalysis

    Boron nitride catalysis

    1. Phil Szuromi

    Propene is one of the highest-volume organic chemicals produced. Propene has mainly been made from naphtha, but changes in the global supply chain are creating shortages. Direct conversion from propane, a component of natural gas, via reaction with oxygen is an attractive alternative, but existing approaches produce a large fraction of unwanted CO and CO2. Grant et al. report that boron nitride, normally an unreactive material, has high selectivity to catalyze the production of propene (77%) and ethene (13%).

    Science, this issue p. 1570

  6. Migration

    Mass movement of “invisibles”

    1. Sacha Vignieri

    We know a lot about vertebrate migrations globally. However, the majority of animals that live on this planet are invertebrates, and we know very little about their movements. Hu et al. monitored the migration of large and small insects over the southern United Kingdom for a decade. They found that more than a trillion insects move across this region annually. The movement of such a large biomass has considerable impacts on the ecosystems between which the insects migrate.

    Science, this issue p. 1584

  7. Plant Science

    Prohormone processing by subtilases

    1. Pamela J. Hines

    A flower that has gone to seed will drop its petals in a regulated process called abscission. Schardon et al. analyzed the production of the peptide hormone that regulates floral organ abscission in the model plant Arabidopsis thaliana. They used tissue-specific expression of proteinase inhibitors to identify the subtilisin-like proteinases that act as prohormone convertases required for peptide hormone production in plants.

    Science, this issue p. 1594

  8. Immunology

    A balance between staying and leaving

    1. Wei Wong

    Mobilization of neutrophils from the bone marrow is determined by the balance between two opposing chemokines that either keep neutrophils in the bone marrow or recruit them to tissues. Both chemokines activate the small guanosine triphosphatase Rac. Campa et al. found that the time that it took active Rac to return to baseline determined how long neutrophils stayed in the bone marrow. Mice lacking a Rac inhibitor had more neutrophils in the bone marrow and fewer circulating neutrophils than control mice had.

    Sci. Signal. 9, ra124 (2016).

  9. Cancer

    Combining drugs as the doctor ordered

    1. Yevgeniya Nusinovich

    Cancer immunotherapy is being used for a growing number of cancers. Chemotherapy is still the mainstay of cancer treatment, however, and it can be difficult to find good ways to combine the two approaches. Mathios et al. systematically evaluated the effectiveness of local or systemic chemotherapy before or after immune checkpoint inhibition in mouse models of glioblastoma. Local chemotherapy was particularly effective in combination with checkpoint inhibition, whereas systemic chemotherapy was too damaging to the immune system for the combination to be useful.

    Sci. Transl. Med. 8, 370ra180 (2016).

  10. Human Genetics

    Unleashing the power of precision medicine

    1. Laura M. Zahn

    Precision medicine promises the ability to identify risks and treat patients on the basis of pathogenic genetic variation. Two studies combined exome sequencing results for over 50,000 people with their electronic health records. Dewey et al. found that ∼3.5% of individuals in their cohort had clinically actionable genetic variants. Many of these variants affected blood lipid levels that could influence cardiovascular health. Abul-Husn et al. extended these findings to investigate the genetics and treatment of familial hypercholesterolemia, a risk factor for cardiovascular disease, within their patient pool. Genetic screening helped identify at-risk patients who could benefit from increased treatment.

    Science, this issue p. 10.1126/science.aaf6814, p. 10.1126/science.aaf7000

  11. Cell Fate Decisions

    How to grow hair or sweat glands

    1. Laura M. Zahn

    Unlike other mammals that must pant or seek shade or water when overheated, humans are able to self-cool to tolerate extreme heat. Sweat glands, which enable humans to run in marathons, are instrumental for this remarkable feat. Lu et al. investigated skin appendage diversity during development of the furry backs and sweaty paws of mice (see the Perspective by Lai and Chuong). They also examined human skin, which is capable of making both hairs and sweat glands in the same area of the body. Epithelialmesenchymal interactions, with varied signaling pathways that act at specific times in development, are key to producing different skin appendages for adaptation to the environment.

    Science, this issue p. 10.1126/science.aah6102; see also p. 1533

  12. Quantum Electronics

    Extending qubit lifetime through a shaped environment

    1. Ian S. Osborne

    Qubits are the quantum two-level systems that encode and process information in quantum computing. Kept in isolation, qubits can be stable. In a practical setting, however, qubits must be addressed and interact with each other. Such an environment is typically viewed as a source of decoherence and has a detrimental effect on a qubit's ability to retain encoded information. Gustavsson et al. used a sequence of pulses as a source of “environment shaping” that could substantially increase the coherence time of a superconducting qubit.

    Science, this issue p. 1573

  13. Fisheries

    Marine benefits of the Paris Agreement

    1. Sacha Vignieri

    Keeping recent global agreements to limit temperature increases to 1.5° to 2°C above preindustrial levels will have benefits across terrestrial ecosystems. But what about marine ecosystems? Cheung et al. modeled the influence of temperature increases on two key measures of fishery sustainability, catch and species turnover (see the Perspective by Fulton). Limiting temperature increases to 1.5°C substantially improved catch potential and decreased turnover of harvested species. These results provide further support for meeting this important goal.

    Science, this issue p. 1591; see also p. 1530

  14. Quantum Optics

    A quantum optical circulator

    1. Ian S. Osborne

    A circulator is a passive three- or four-port device that routes signals according to a simple protocol: If the ports are numbered in ascending order, a signal that enters the circulator through port 1, 2, 3, or 4 exits it through port 2, 3, 4, or 1, respectively. Scheucher et al. demonstrate an integrated optical circulator that operates by using the internal quantum state of a single atom (see the Perspective by Munro and Nemoto). Moreover, the routing can be reversed by flipping the atomic spin. Such an integrated optical device may be important for routing and processing quantum information in scalable integrated optical circuits.

    Science, this issue p. 1577; see also p. 1532

  15. Nanomaterials

    Probing packing rules

    1. Phil Szuromi

    The crystals of a well-defined ligand-covered gold nanoparticle can reveal how packing into a lattice happens. Zeng et al. synthesized nanoparticles with a 246-atom gold core surrounded by 80 4-methylbenzenethiol ligands. These nearly spherical nanoparticles did not pack into a cubic arrangement but instead formed a lower-symmetry monoclinic structure. A hierarchy of interparticle ligand interactions controlled the packing, including sets of chiral packing arrangements that reversed between layers.

    Science, this issue p. 1580

  16. Structural Biology

    A closed conformation for Zika virus enzyme

    1. Kristen L. Mueller

    The recent Zika virus epidemic highlights the need for antiviral drugs. One important drug target is the virus's NS2B-NS3 protease, an enzyme that is critical for viral replication. Zhang et al. report high-resolution crystal structures of the protease as a free enzyme and with a peptide bound to the active site in the reverse position. The structures reveal that, unlike in other flaviviruses, the protease adopts a closed conformation, in which NS2B engages NS3 to form the empty substrate-binding site. Moreover, substrate binding did not substantially alter the conformation of the enzyme.

    Science, this issue p. 1597

  17. Oceans

    A precarious balance

    1. Julia Fahrenkamp-Uppenbrink

    All ocean basins have regions with almost no oxygen at depths of a few hundred meters. These oxygen minimum zones are growing in size, and many coastal regions are also devoid of oxygen owing to increased nutrient input from rivers. In a Perspective, Watson explains that in the geologic past, major environmental crises have caused the entire ocean to deoxygenate, with disastrous consequences for ocean life. Modern disturbances would have to continue for a thousand years for the entire ocean to be affected, but locally, today's growing dead zones are already lethal to animals.

    Science, this issue p. 1529