This Week in Science

Science  20 Jul 2018:
Vol. 361, Issue 6399, pp. 240
  1. Collective Behavior

    All together now…fly!

    1. Rachel Kline

    Long-exposure photo of a flight with multiple drones

    CREDIT: ZSOLT BÉZSENYI

    Can the quick, responsive grace of a flock of birds or school of fish be mimicked by robots in real-world environments? Vásárhelyi et al. used a flocking model that balances distance and relative velocity to enable a large group of autonomous robots to fly together in a confined space. They optimized their model with evolution-inspired algorithms, finding the settings most likely to keep robots grouped together without collisions—a challenge when there are communication delays and obstacles in the environment. The authors implemented their model on a flock of 30 real-life quadcopters outdoors, demonstrating fully autonomous, synchronized, and accident-free flight.

    Sci. Robot. 3, eaat3536 (2018).

  2. Topological Matter

    Exotic topology on the surface

    1. Jelena Stajic

    Analyzing the spatial symmetries of three-dimensional (3D) crystal structures has led to the discovery of exotic types of quasiparticles and topologically nontrivial materials. Wieder et al. focus on the symmetry groups of 2D surfaces of 3D materials—the so-called wallpaper groups—and find that some of them allow for an additional topological class. This class hosts a single fourfold-degenerate Dirac fermion on the surface of the material and, on the basis of the authors' calculations, is expected to occur in the compound Sr2Pb3.

    Science, this issue p. 246

  3. Active Matter

    A balance between motion and cooperation

    1. Marc S. Lavine

    In active matter systems, the infusion of energy and motion drives ordering processes. Huber et al. present a combination of experiments and numerical simulations on an active matter system consisting of actin filaments propelled across a surface by surface-attached myosin motor proteins. Adding a depletion agent—polymer chains that weakened interactions between the actin filaments—drove the system between ferromagnetic (polar) and nematic (liquid crystal) ordering.

    Science, this issue p. 255

  4. Red Blood Cells

    A CRISPR screen for RBC regulators

    1. Priscilla N. Kelly

    Hemoglobin in red blood cells (RBCs) carries oxygen to the tissues. Sickle cell disease is an inherited condition that involves abnormal hemoglobin. Current treatments entail modulating the level of fetal hemoglobin expression. Grevet et al. performed a CRISPR-Cas9 screen for regulators of fetal hemoglobin in RBCs and identified heme-regulated eIF2α kinase (HRI). Depleting the kinase in RBCs led to an increase in fetal hemoglobin levels and reduced sickling of cultured human RBCs. Thus, HRI may be a therapeutic target for sickle cell disease and other hemoglobin disorders.

    Science, this issue p. 285

  5. Atmospheric Chemistry

    A puzzle of new particles

    1. H. Jesse Smith

    Atmospheric particulates can be produced by emissions or form de novo. New particle formation usually occurs in relatively clean air. This is because preexisting particles in the atmosphere will scavenge the precursors of new particles and suppress their formation. However, observations in some heavily polluted megacities have revealed substantial rates of new particle formation despite the heavy loads of ambient aerosols. Yao et al. investigated new particle formation in Shanghai and describe the conditions that make this process possible. The findings will help inform policy decisions about how to reduce air pollution in these types of environments.

    Science, this issue p. 278

  6. Cancer

    Mechanistic insights into kidney cancer

    1. L. Bryan Ray

    Many clear cell renal cell carcinomas (ccRCCs) have alterations to the gene encoding the von Hippel-Lindau protein (VHL). VHL is a ubiquitin ligase that degrades target proteins when they are prolyl-hydroxylated. Zhang et al. performed a genome-wide search for VHL target (see the Perspective by Sanchez and Simon). They identified ZHX2, a protein with structural motifs that indicate DNA binding. ZHX2 has been implicated in tumor suppression. Loss of ZHX2 inhibited signaling through the transcription factor NF-κB, and ZHX2 bound to many NF-κB target genes. Depletion of ZHX2 slowed growth of ccRCC cells in vitro and in a mouse model.

    Science, this issue p. 290; see also p. 226

  7. Coral Reefs

    Deep coral reefs are different

    1. Sacha Vignieri

    Mesophotic coral ecosystems are dominated by gorgonians and black coral, not stony corals.

    CREDIT: LUIZ A. ROCHA/CALIFORNIA ACADEMY OF SCIENCES

    Coral reefs are under intense pressure from anthropogenically induced climate warming and habitat destruction. It has been suggested that coral reefs in deeper waters may provide a refuge less affected by human development and climate change. Rocha et al., however, show that shallow and deep reefs are biologically different. Furthermore, deep (or mesophotic) reefs are also suffering from human impacts. Thus, deep reefs do not represent a potential refuge for other reef ecosystems. Indeed, they too are threatened and need protection.

    Science, this issue p. 281

  8. Ice Sheets

    Sliding at the base

    1. H. Jesse Smith

    Predictions of sea level rise caused by dynamic ice sheet loss rely on a good understanding of what controls how fast the sheets slide over the ground below. The standard approach is to model motion on the basis of an assumed frictional stress between the base of the glacier and a hard underlying bed. Now, however, Stearns and van der Veen show that this method is incorrect. Instead, they suggest that net pressure at the glacier bed controls flow.

    Science, this issue p. 273

  9. Paleontology

    Oldest baby snake fossil discovered

    1. Philippa J. Benson

    Two snake specimens preserved in Late Cretaceous amber from Myanmar may represent the oldest known fossilized baby snake. Xing et al. studied the amber samples, which also contain remnants of insects and fragments of plant materials. This suggests, unexpectedly, that these Mesozoic snakes lived in a forested environment. Thus, snakes in this time period were more ecologically diverse than previously thought.

    Sci. Adv. 10.1126/sciadv.aat5042 (2018).

  10. Food Security

    The future of meat

    1. Caroline Ash

    Meat consumption is rising annually as human populations grow and affluence increases. Godfray et al. review this trend, which has major negative consequences for land and water use and environmental change. Although meat is a concentrated source of nutrients for low-income families, it also enhances the risks of chronic ill health, such as from colorectal cancer and cardiovascular disease. Changing meat consumption habits is a challenge that requires identifying the complex social factors associated with meat eating and developing policies for effective interventions.

    Science, this issue p. eaam5324

  11. Climate Change

    'Tis the seasonal

    1. H. Jesse Smith

    Anthropogenic climate change has become clearly observable through many metrics. These include an increase in global annual temperatures, growing heat content of the oceans, and sea level rise owing to the melting of the polar ice sheets and glaciers. Now, Santer et al. report that a human-caused signal in the seasonal cycle of tropospheric temperature can also be measured (see the Perspective by Randel). They use satellite data and the anthropogenic “fingerprint” predicted by climate models to show the extent of the effects and discuss how these changes have been caused.

    Science, this issue p. eaas8806; see also p. 227

  12. Biogeography

    Simulating South American biodiversity

    1. Andrew M. Sugden

    The emergence, distribution, and extinction of species are driven by interacting factors—spatial, temporal, physical, and biotic. Rangel et al. simulated the past 800,000 years of evolution in South America, incorporating these factors into a spatially explicit dynamic model to explore the geographical generation of diversity. Their simulations, based on a paleoclimate model on a 5° latitude-longitude scale, result in shifting maps of speciation, persistence, and extinction (or cradles, museums, and graves). The simulations culminate in a striking resemblance to contemporary distribution patterns across the continent for birds, mammals, and plants—despite having no target patterns and no empirical data parameterizing them.

    Science, this issue p. eaar5452

  13. Surface Chemistry

    Changing emission with charge states

    1. Phil Szuromi

    The fluorescence of electrochromic molecules changes with their charge state. Doppagne et al. studied the optical emission of single zinc-phthalocyanine molecules excited by electron injection from a scanning tunneling microscope tip. The molecules were adsorbed on salt layers grown on a gold surface, so that the cationic and neutral molecules could both be observed. The primary emission shifted to lower energy for the cation, and, in addition, vibrational side bands were observed.

    Science, this issue p. 251

  14. Atomic Physics

    An atom-coupling cavity

    1. Jelena Stajic

    Ensembles of atoms have emerged as powerful simulators of many-body dynamics. Engineering controllable interactions between the atoms is crucial, be it direct or through a mediator. Norcia et al. developed a flexible alternative to existing atomic simulators in a system consisting of strontium atoms placed in an optical cavity. Two atomic states connected by a clock transition each served as an effective spin, with long-range spin-exchange interactions mediated by the cavity photons. With improvements, the setup is expected to be amenable to simulating nonequilibrium quantum dynamics and to have applications in metrology.

    Science, this issue p. 259

  15. Nanomaterials

    Oscillating one-dimensional chains

    1. Marc S. Lavine

    The confinement of materials to nanoscale dimensions often reveals properties not seen in bulk materials. Pham et al. confined NbSe3 within carbon nanotubes (a conductor) or boron nitride nanotubes (an insulator). Transmission electron microscopy revealed an oscillatory motion of the confined chains not observed in bulk crystals. Electronic structure calculations showed that charge transfer drives the torsional wave instability, and the limited covalent bonding between the chains and the nanotube sheath allows unhindered dynamics. Application of an external potential applied to the nanotube should directly affect the torsion and thus lead to different optical and electron transport properties.

    Science, this issue p. 263

  16. Quantum Computing

    Fault-tolerant quantum coding

    1. Ian S. Osborne

    Noise and imperfections in a quantum system can result in the presence and propagation of errors through the system. A reliable quantum processor will need to be able to correct for these errors and error syndromes. Rosenblum et al. used higher quantum states of a superconducting-based quantum circuit to demonstrate a method for the fault-tolerant measurement of an error-correctable logical qubit. Such fault-tolerant measurements will allow more frequent interrogations of the state of the logical qubit, ultimately leading to the implementation of more quantum operations and more complex entangled quantum circuits.

    Science, this issue p. 266

  17. Air Pollution

    South Asian monsoon and pollution

    1. H. Jesse Smith

    Air pollution is growing fastest in monsoon-impacted South Asia. During the dry winter monsoon, the fumes disperse toward the Indian Ocean, creating a vast pollution haze. The fate of these fumes during the wet summer monsoon has been unclear. Lelieveld et al. performed atmospheric chemistry measurements by aircraft in the Oxidation Mechanism Observations campaign, sampling the summer monsoon outflow in the upper troposphere between the Mediterranean and the Indian Ocean. The measurements, supported by model calculations, show that the monsoon sustains a remarkably efficient cleansing mechanism in which contaminants are rapidly oxidized and deposited on Earth's surface. However, some pollutants are lofted above the monsoon clouds and chemically processed in a reactive reservoir before being redistributed globally, including to the stratosphere.

    Science, this issue p. 270

  18. Chemistry

    Rethinking chemical risks

    1. Julia Fahrenkamp-Uppenbrink

    Modern life relies on vast numbers of different chemicals, from pharmaceuticals and cleaning products to pesticides and plastics. Wastewater treatment is widely used to avoid their release into the environment. In a Perspective, Kümmerer et al. explain that such treatments cannot capture all chemicals in wastewaters. Furthermore, even in developed countries, not all wastewater is treated. Preventing harmful chemicals from entering wastewater streams is thus key. This can be achieved through adapting industrial processes, reducing chemical complexity, and prioritizing chemicals that can break down quickly into harmless substances in the environment. In a related Perspective, Kortenkamp and Faust explain that the toxicity of chemical mixtures is typically higher than that of the individual chemicals. Integration of different parts of the regulatory system will be needed to adequately capture the risks from the chemical mixtures to which humans and the environment are routinely exposed.

    Science, this issue p. 222, p. 224

  19. Leukemia

    An alternative treatment for leukemia

    1. Leslie K. Ferrarelli

    In some acute myeloid and juvenile myelomonocytic leukemias (AMLs and JMMLs), tumor growth is driven by activating mutations in the phosphatase PTPN11. Jenkins et al. found that mutant PTPN11 activity is enhanced by the kinase TNK2. The multikinase inhibitor dasatinib decreased TNK2 and mutant PTPN11 activity and downstream proliferative pathways in cultured patient cells. It also extended survival in a JMML patient with mutant PTPN11. Thus, dasatinib, which is clinically approved for the treatment of other leukemias, could potentially slow disease progression in AML and JMML patients.

    Sci. Signal. 11, eaao5617 (2018).

  20. Pain

    Relieving pain with botox

    1. Mattia Maroso

    Chronic pain affects more than 25 million Americans and is associated with reduced life span, anxiety, and depression. Opioid administration is often effective in relieving pain but can cause severe side effects. Maiarù et al. leveraged the inhibitory effects of botulinum toxin on neuronal activity and developed two botulinum-conjugated molecules that silenced pain-related spinal neurons in several mouse models of chronic pain. Intrathecal administration of one dose of either conjugate produced long-term pain relief in the mouse models that was comparable to the effects of opioid treatment. Thus, botulinum-conjugated molecules could potentially provide an opioid-free alternative for treating chronic pain.

    Sci. Transl. Med. 10, eaar7384 (2018).

  21. Microbial Immunity

    A broader repertoire

    1. Christiana N. Fogg

    A subset of T cells can present microbial ligands using MR1, a nonconventional MHC (major histocompatibility complex) molecule. MR1 is known to present metabolites from microbes such as Mycobacterium tuberculosis, but the breadth of the MR1 ligandome is not well understood. Harriff et al. used mass spectrometry and molecular networking to identify MR1-presented ligands from two divergent microbes, Escherichia coli and Mycobacterium smegmatis. MR1 could present a surprisingly broad array of ligands for both microbes, and ligands could be distinguished by different T cell receptors on MR1-restricted T cells exerting inhibitory or activating effects. Thus, MR1 is a critical molecule for presenting microbial ligands to the immune system.

    Sci. Immunol. 3, eaao2556 (2018).