This Week in Science

Science  04 Jan 2019:
Vol. 363, Issue 6422, pp. 39
  1. Crowd Dynamics

    A crowd that flows like water

    1. Brent Grocholski

    Runners moving down Columbus Drive at the Chicago Marathon, October 2017

    CREDITS DYLAN BUELL /STRINGER/GETTY IMAGES

    The behavior of large numbers of insects, animals, and other flocks is often based on rules about individual interactions. Bain and Bartolo applied a fluid-like model to the behavior of marathon runners as they walked up to the start line of the Chicago Marathon (see the Perspective by Ouellette). They observed nondamping linear waves with the same speed for different starting corrals of runners and at different races around the world. Their model should apply both to this type of polarized crowd as well as to other groups, which may help guide crowd management.

    Science, this issue p. 46; see also p. 27

  2. Virology

    Mobile detection of Lassa virus

    1. Caroline Ash

    Lassa fever is a hemorrhagic viral disease endemic to West Africa. Usually, each year sees only a smattering of cases reported, but hospitalized patients risk a 15% chance of death. Responding to fears that a 10-fold surge in cases in Nigeria in 2018 signaled an incipient outbreak, Kafetzopoulou et al. performed metagenomic nanopore sequencing directly from samples from 120 patients (see the Perspective by Bhadelia). Results showed no strong evidence of a new strain emerging nor of person-to-person transmission; rather, rodent contamination was the main source. To prevent future escalation of this disease, we need to understand what triggers the irruption of rodents into human dwellings.

    Science, this issue p. 74; see also p. 30

  3. Protein Translocation

    Posttranslational translocon architecture

    1. Stella M. Hurtley

    About a third of proteins are transported into endoplasmic reticulum by the universally conserved Sec61 protein-conducting channel. Itskanov and Park determined a cryo–electron microscopy structure of the Sec complex from yeast, which mediates posttranslational translocation of many secretory proteins across the endoplasmic reticulum membrane. The study reveals how Sec63 activates the Sec61 channel for substrate polypeptide insertion. The structure also explains the mutually exclusive binding of Sec63 and the ribosome to the channel.

    Science, this issue p. 84

  4. Chemical Physics

    C60 at high resolution

    1. Jake Yeston

    It generally takes more energy for molecules to vibrate than to rotate. A vibrational absorption band thus encompasses many distinct concurrent rotational transitions, but these tend to blur together when the molecules have more than a few atoms. Changala et al. succeeded in cooling C60 fullerenes sufficiently to obtain rotational resolution within a C–C stretching band. Success hinged on careful optimization of argon buffer gas flow. Such quantum state–resolved features could aid characterization of fullerene-type compounds in exotic environments such as interstellar space.

    Science, this issue p. 49

  5. Atomic Physics

    Making a strongly coupled plasma

    1. Jelena Stajic

    Plasmas—gases of ionized atoms and electrons—are naturally formed at high temperatures, such as those reached in the interiors of stars. Describing plasmas theoretically is tricky when they are in the strongly coupled regime; reaching that regime in the laboratory would provide a valuable benchmark for theory. To that end, Langin et al. worked with a cold plasma created out of atoms of strontium that were ionized by laser light (see the Perspective by Bergeson). They used lasers to cool the ions down to about 50 millikelvin, reaching the desired strongly coupled regime.

    Science, this issue p. 61; see also p. 33

  6. Paleontology

    A proto-mammalian giant

    1. Sacha Vignieri

    Early terrestrial amniotes evolved into two groups: the sauropsids, which led to the bird and dinosaur lineages, and the synapsids, which led to mammals. Synapsids were diverse during the Permian but were greatly reduced after the end-Permian extinction (about 252 million years ago). The few groups that survived into the Triassic were mostly small and retained a sprawling gait. Sulej and Niedźwiedzki, however, describe a dicynodont from the Late Triassic of Poland that is as large as some coexisting dinosaurs and appears to have had an erect gait—like modern mammals. Thus, megaherbivores in the Triassic were not only dinosaurs.

    Science, this issue p. 78

  7. Social Sciences

    Deadliest 100 days of the Holocaust

    1. Philippa J. Benson

    Transport records have been analyzed to estimate the number of Jews murdered by the Nazis in 1942.

    PHOTO: SHAWSHOTS/ALAMY STOCK PHOTO

    More than 25% of the approximately 6 million Jews murdered during the Holocaust were killed in one 100-day period in 1942. Stone used an unusual dataset of railway transportation records to show that during this period, the Nazis murdered more than 1.47 million Jews, a kill rate that is 10 times higher than previous estimates. Contradicting contemporary analyses of the Holocaust, the author shows that Operation Reinhard was exceptionally violent in its extreme kill rate, number, and proportion of the population murdered, even when compared to other 20th-century genocides.

    Sci. Adv. 10.1126/sciadv.aau7292 (2018).

  8. Prokaryotic Immunity

    Additional, diverse CRISPR systems

    1. Steve Mao

    CRISPR systems have been revolutionizing molecular biology. Mining the metagenomic database, Yan et al. systematically discovered additional subtypes of type V CRISPR-Cas systems. The additional Cas12 effectors displayed a range of activities, including target and collateral cleavage of single-stranded RNA and DNA, as well as double-stranded DNA nicking and cleavage. These diverse nuclease activities suggest how an ancient transposase may have evolved into various type V effectors and expand the nucleic acid detection and genome-editing toolbox.

    Science, this issue p. 88

  9. Drug Development

    A long-lasting poison scavenger

    1. Mattia Maroso

    Nerve agents are neurotoxic compounds found in pesticides and chemical weapons. They act by blocking the transmission of nerve impulses to the muscles, and exposure can be fatal within minutes. Zhang et al. developed a nanoparticle-based bioscavenger that breaks down organophosphate nerve agents into innocuous compounds. Prophylactic treatment of rats and guinea pigs confirmed low immunogenicity and good biodistribution. Treated animals were protected from repeated exposure to the nerve agent sarin over 7 days. This nanoscavenger might thus help prevent nerve-agent poisoning in at-risk subjects.

    Sci. Transl. Med. 11, eaau7091 (2019).

  10. Optics

    Exceptional points in optics

    1. Ian S. Osborne

    Many complex systems operate with loss. Mathematically, these systems can be described as non-Hermitian. A property of such a system is that there can exist certain conditions—exceptional points—where gain and loss can be perfectly balanced and exotic behavior is predicted to occur. Optical systems generally possess gain and loss and so are ideal systems for exploring exceptional point physics. Miri and Alù review the topic of exceptional points in photonics and explore some of the possible exotic behavior that might be expected from engineering such systems.

    Science, this issue p. eaar7709

  11. Neuroscience

    Forgetting and receptor removal

    1. Peter Stern

    The trafficking of AMPA receptors to and from the surface of postsynaptic membranes regulates synaptic strength and underlies learning and memory. Awasthi et al. found that the integral membrane protein synaptotagmin-3 (Syt3) is predominantly found on postsynaptic endocytic zones of neurons, where it promotes AMPA receptor internalization (see the Perspective by Mandelberg and Tsien). In Syt3 overexpressing or knockdown neurons, synaptic transmission and short-term plasticity were unchanged. However, in neurons from Syt3 knockout mice, synaptic long-term depression was abolished and decaying long-term potentiation endured. In Syt3 knockout mice, spatial learning was unaltered; however, these animals showed signs of impaired forgetting and relearning during the water maze spatial memory task.

    Science, this issue p. eaav1483; see also p. 31

  12. Immunology

    Commensal-specific T cells are flexible

    1. Seth Thomas Scanlon

    Barrier tissues, like the skin, are sites where noninvasive commensal microbes constantly interact with resident T cells. These encounters can result in commensal-specific T cell responses that promote, for example, host defense and tissue repair. Harrison et al. show that subsets of skin-resident commensal-specific interleukin-17A–producing CD4+ and CD8+ T cells have a dual nature: They coexpress transcription factors that direct antagonistic antimicrobial (type 17) and antiparasite and pro–tissue repair (type 2) programs. When skin is damaged, epithelial cell alarmins license type 17 T cells to turn on type 2 cytokines. Thus, commensal-specific type 17 T cells can direct antimicrobial activity under homeostatic conditions but rapidly turn on tissue repair in the context of injury.

    Science, this issue p. eaat6280

  13. Plant Science

    Fixing photosynthetic inefficiencies

    1. Pamela J. Hines

    In some of our most useful crops (such as rice and wheat), photosynthesis produces toxic by-products that reduce its efficiency. Photorespiration deals with these by-products, converting them into metabolically useful components, but at the cost of energy lost. South et al. constructed a metabolic pathway in transgenic tobacco plants that more efficiently recaptures the unproductive by-products of photosynthesis with less energy lost (see the Perspective by Eisenhut and Weber). In field trials, these transgenic tobacco plants were ∼40% more productive than wild-type tobacco plants.

    Science, this issue p. eaat9077; see also p. 32

  14. Nanomaterials

    Nanographenes on oxides

    1. Phil Szuromi

    The growth of nanographene islands and ribbons on metal surfaces can be accomplished on single-crystal metal surfaces through carbon-carbon coupling reactions, but the surfaces of oxides do not assist these reactions. Kolmer et al. show that fluorinated aryl groups can be coupled to form nanographenes on the rutile surface of titanium oxide. The fluorine substitution of the aryl groups was selected so that as the carbon-fluorine bonds were thermally activated, a stepwise process sequentially added aromatic rings around a central aryl group until it was completely substituted.

    Science, this issue p. 57

  15. Mesoscopic Physics

    A backward current

    1. Jelena Stajic

    Two-dimensional materials in a magnetic field can exhibit the so-called quantum Hall effect. This regime is characterized by currents running along the edge of the sample in the “downstream” direction determined by the sign of the magnetic field. Lafont et al. studied electrical transport in GaAs-AlGaAs heterostructures, focusing on a previously less-studied spin-unpolarized state in the fractional quantum Hall regime. By considering various experimental configurations, they observed a component of the charge current flowing in the opposite, “upstream” direction.

    Science, this issue p. 54

  16. Neuroscience

    Another primary visual cortex

    1. Peter Stern

    Most functional studies in the visual system have focused on the cortical representation of the geniculo-striate pathway that links the retina to the cortex. The parallel collicular pathway is believed to sparsely project throughout the visual cortex and have a modulatory role on cortical responses to visual stimuli. Beltramo and Scanziani found a visual cortical area that is entirely dedicated to the superior colliculus. This area can discriminate moving visual stimuli that the “classical” primary visual cortex cannot. Thus, the superior colliculus, a phylogenetically ancient structure, has its own projection in neocortex that provides this area with exquisite feature-detection abilities not found in the classical primary visual cortex.

    Science, this issue p. 64

  17. Climate Change

    Deep Pacific cooling

    1. H. Jesse Smith

    Earth's climate cooled considerably across the transition from the Medieval Warm Period to the Little Ice Age about 700 years ago. Theoretically, owing to how the ocean circulates, this cooling should be recorded in Pacific deep-ocean temperatures, where water that was on the surface then is found today. Gebbie and Huybers used an ocean circulation model and observations from both the end of the 19th century and the end of the 20th century to detect and quantify this trend. The ongoing deep Pacific is cooling, which revises Earth's overall heat budget since 1750 downward by 35%.

    Science, this issue p. 70

  18. Evolution

    DNA breakage and adaptation

    1. Sacha Vignieri

    Adaptation to new environments often occurs in similar ways across different colonization events. Stickleback fish represent a classic example of this, in which repeated colonizations of freshwater have resulted in the loss of pelvic hind fins. Previous work has shown that a pelvic enhancer gene is involved. Xie et al. now show that this gene lies within a region of the genome that is prone to double-stranded DNA breakage owing to a high thymine-guanine content. This enhanced region of breakage could lead to enhanced mutation rates that facilitate repeated adaptations to new environments.

    Science, this issue p. 81

  19. Conservation

    The distinctive sound of a biodiverse forest

    1. Julia Fahrenkamp-Uppenbrink

    Assessing the state of biodiversity in a forest is a time-consuming task that typically requires detailed on-the-ground surveys. In a Perspective, Burivalova et al. explain that recordings of soundscapes can provide an easier route to this information. By recording soundscapes from a forest over time and comparing them to a regional baseline, scientists can determine whether a forest's ecosystem is healthy or not. If the soundscape of a forest spared from conversion becomes impoverished and altered, an on-the-ground survey would be warranted. This approach may be particularly useful for companies interested in sustainability certification or zero-deforestation commitments.

    Science, this issue p. 28

  20. Tuberculosis

    Faulty kinase purged by tuberculosis?

    1. Ifor Williams

    Rare mutations in genes involved in interferon-γ–dependent immunity underpin human genetic susceptibility to severe mycobacterial diseases, including primary tuberculosis. Boisson-Dupuis et al. investigated whether two common missense variants of the TYK2 Janus kinase that have impaired catalytic activity conferred an increased risk of tuberculosis. Individuals homozygous for the P1104A (proline to alanine substitution at residue 1104) variant of TYK2 are markedly predisposed to developing primary tuberculosis, defining a common monogenic etiology for the “white plague.” The current frequency of the P1104A allele in European populations is significantly decreased compared with its frequency in ancient European DNA samples. These findings suggest that negative selection against the TYK2 P1104A allele by endemic tuberculosis in Europe may have contributed to a slow genetic purge of this susceptibility allele during recent millennia.

    Sci. Immunol. 3, eaau8714 (2018).

  21. Cancer

    Altering membrane potential for cancer

    1. Wei Wong

    Polymorphisms in the G protein–coupled receptor GPR35 are associated with increased risk for certain inflammatory diseases that can progress to cancer. Schneditz et al. found that GPR35 promoted the activity of Na+- and K+-dependent adenosine triphosphatase (Na+,K+-dependent ATPase), a transmembrane pump that sets the membrane potential in cells. This effect was enhanced by a disease-associated GPR35 variant. Stimulation of Na+,K+-ATPase activity by GPR35 increased glycolysis and proliferation in intestinal epithelial cells. Na+,K+-ATPase deficiency or treatment with a pepducin targeting GPR35 decreased tumor burden in mouse models of intestinal cancer.

    Sci. Signal. 12, eaau9048 (2019).