This Week in Science

Science  26 Jan 2018:
Vol. 359, Issue 6374, pp. 407
  1. Coral Reefs

    Corals wrapped in plastic

    1. Caroline Ash

    Plastic waste is sickening corals.

    PHOTO: RICHARD WHITCOMBE/SHUTTERSTOCK.COM

    Coral reefs provide vital fisheries and coastal defense, and they urgently need protection from the damaging effects of plastic waste. Lamb et al. surveyed 159 coral reefs in the Asia-Pacific region. Billions of plastic items were entangled in the reefs. The more spikey the coral species, the more likely they were to snag plastic. Disease likelihood increased 20-fold once a coral was draped in plastic. Plastic debris stresses coral through light deprivation, toxin release, and anoxia, giving pathogens a foothold for invasion.

    Science, this issue p. 460

  2. Membrane Targeting

    A new way into the ER

    1. Stella M. Hurtley

    Membrane-embedded proteins are highly diverse in topology, physical characteristics, and location. This diversity necessitates multiple pathways for their effective membrane insertion. Guna et al. found that a widely conserved protein complex is responsible for inserting a subset of membrane proteins into the endoplasmic reticulum (ER) membrane (see the Perspective by Fry and Clemons Jr.). This ER membrane protein complex (EMC) inserts transmembrane domains whose topology and hydrophobicity preclude effective recognition by other insertion factors. This finding helps explain why the loss of EMC causes ER stress and altered protein trafficking.

    Science, this issue p. 470; see also p. 390

  3. Quantum Gases

    Tuning the atomic pairing

    1. Jelena Stajic

    Cold atomic gases are extremely flexible systems; the ability to tune interactions between fermionic atoms can, for example, cause the gas to undergo a crossover from weakly interacting fermions to weakly interacting bosons via a strongly interacting unitary regime. Murthy et al. studied this crossover in a gas of fermions confined to two dimensions. The formation of atomic pairs occurred at much higher temperatures in the unitary regime than previously thought.

    Science, this issue p. 452

  4. Soft Robots

    Bilayer microbot powered by humidity

    1. Rachel Kline

    Many plant seeds, including pine cones, open or close in response to changes in humidity. Inspired by these hygroexpansive seeds, Shin et al. fabricated a “hygrobot.” The hygrobot was composed of a film that was responsive to environmental humidity attached to a film that was not. Aligned nanofibers in the responsive layer swelled when humidity increased, causing the bilayer structure to bend. Decreasing humidity shrunk the moisture-responsive layer, straightening out the robot. Legs with asymmetric friction coefficients converted the bending into directional motion on a moist surface.

    Sci. Robot. 3, eaar2629 (2018).

  5. Atmospheric Physics

    Up with ultrafine aerosol particles

    1. H. Jesse Smith

    Ultrafine aerosol particles (smaller than 50 nanometers in diameter) have been thought to be too small to affect cloud formation. Fan et al. show that this is not the case. They studied the effect of urban pollution transported into the otherwise nearly pristine atmosphere of the Amazon. Condensational growth of water droplets around the tiny particles releases latent heat, thereby intensifying atmospheric convection. Thus, anthropogenic ultrafine aerosol particles may exert a more important influence on cloud formation processes than previously believed.

    Science, this issue p. 411

  6. Human Genomics

    Genetic variants provide a nurturing environment

    1. Laura M. Zahn

    Genetic variants in parents may affect the fitness of their offspring, even if the child does not carry the allele. This indirect effect is referred to as “genetic nurture.” Kong et al. used data from genome-wide association studies of educational attainment to construct polygenic scores for parents that only considered the nontransmitted alleles (see the Perspective by Koellinger and Harden). The findings suggest that genetic nurture is ultimately due to genetic variation in the population and is mediated by the environment that parents create for their children.

    Science, this issue p. 424; see also p. 386

  7. Computer Science

    Libratus versus humans

    1. Jelena Stajic

    Pitting artificial intelligence (AI) against top human players demonstrates just how far AI has come. Brown and Sandholm built a poker-playing AI called Libratus that decisively beat four leading human professionals in the two-player variant of poker called heads-up no-limit Texas hold'em (HUNL). Over nearly 3 weeks, Libratus played 120,000 hands of HUNL against the human professionals, using a three-pronged approach that included precomputing an overall strategy, adapting the strategy to actual gameplay, and learning from its opponent.

    Science, this issue p. 418

  8. Paleontology

    Shaping of human brains and behavior

    1. Mark Aldenderfer

    Brain size and shape changes suggest that modern behaviors developed gradually.

    CREDITS: NEUBAUER ET AL., SCI. ADV. 10.1136/SCIADV.AAO5961 (2018)

    There is little consensus as to when complex cognitive functions and behaviors appeared during human evolution. Traditional explanations propose that these behaviors evolved in tandem with modern human anatomy by 50,000 years ago. Other models postulate a more gradual appearance. Neubauer et al. examined endocasts (the interior of the cranial vault) of a sample of early Homo sapiens skulls. Although brain size at 300,000 years ago falls within the range of that of modern humans, more globular brains only emerged around 40,000 years ago. Combined with evidence from ancient DNA that indicates the fixing of genes critical to early brain development at the origin of the H. sapiens lineage, these findings support models of a more gradual appearance of behavioral modernity.

    Sci. Adv. 10.1126/sciadv.aao5961 (2018).

  9. Human Impacts

    Restrictions on roaming

    1. Sacha Vignieri

    Until the past century or so, the movement of wild animals was relatively unrestricted, and their travels contributed substantially to ecological processes. As humans have increasingly altered natural habitats, natural animal movements have been restricted. Tucker et al. examined GPS locations for more than 50 species. In general, animal movements were shorter in areas with high human impact, likely owing to changed behaviors and physical limitations. Besides affecting the species themselves, such changes could have wider effects by limiting the movement of nutrients and altering ecological interactions.

    Science, this issue p. 466

  10. Aging

    Having your longevity and eating too

    1. L. Bryan Ray

    Although caloric restriction has clear benefits for maximizing health span and life span, it is sufficiently unpleasant that few humans stick to it. Madeo et al. review evidence that increased intake of the polyamine spermidine appears to reproduce many of the healthful effects of caloric restriction, and they explain its cellular actions, which include enhancement of autophagy and protein deacetylation. Spermidine is found in foods such as wheat germ, soybeans, nuts, and some fruits and vegetables and produced by the microbiota. Increased uptake of spermidine has protective effects against cancer, metabolic disease, heart disease, and neurodegeneration.

    Science, this issue p. eaan2788

  11. Organic Chemistry

    How to get two bonds for the price of one

    1. Jake Yeston

    For more than a century, we have known how to couple aryl chlorides at the sites of their C–Cl bonds to form a single C–C bond. Koga et al. found that palladium catalysis can instead activate these C–Cl bonds to attack nearby aromatic C–H bonds in a terphenyl molecular framework. The reaction thereby produces a new ring, fused to the original rings on either side. Polycyclic compounds of this sort are of particular interest in optoelectronics research because of their expansive electron delocalization.

    Science, this issue p. 435

  12. Organic Chemistry

    A reaction screen in flowing solvent

    1. Jake Yeston

    Chemists charged with manufacturing pharmaceuticals have recently been exploring the efficiency advantages of continuous flow techniques. Perera et al. now show that a flow apparatus can also accelerate reaction optimization earlier in the drug discovery process. They modified a high-performance liquid chromatography system to screen a wide variety of solvent, ligand, and base combinations to optimize carbon-carbon bond formation. Injecting stock solution aliquots of the catalyst and reactants into a carrier solvent stream let the authors vary the main solvent efficiently and scale up the optimal conditions for product isolation.

    Science, this issue p. 429

  13. Nanophotonics

    Nanoscale chiral valley-photon interface

    1. Ian S. Osborne

    Occupation of different valleys within the band structure of some materials can be used to encode information. That information is typically encoded in terms of the chirality or polarization of emitted photons. Gong et al. combined a plasmonic silver nanowire with a flake of the transition metal dichalcogenide WS2 to form a nanophotonic platform for the transfer of solid-state spin into optical information over mesoscopic distances. The direction of light emission from the nanowire was strongly dependent on the spin-orbit coupling of light and the WS2 layer. Such a highly efficient interface should prove useful for developing valleytronics into a practical on-chip technology.

    Science, this issue p. 443

  14. Light Metals

    A framework for more ductile magnesium

    1. Brent Grocholski

    Development of ductile magnesium alloys is key to their use in reducing the weight of vehicles and other applications. Wu et al. tackle this issue by determining the underlying mechanisms in unprocessed magnesium alloys. Dilute amounts of solutes enhanced certain ductility-improving mechanisms over ones that cause brittle fracture. From this, the authors developed a theory that may be helpful for screening the large number of potential magnesium alloy compositions.

    Science, this issue p. 447

  15. Quantum Information

    Building an essential quantum component

    1. Jelena Stajic

    To build a universal quantum computer—the kind that can handle any computational task you throw at it—an essential early step is to demonstrate the so-called CNOT gate, which acts on two qubits. Zajac et al. built an efficient CNOT gate by using electron spin qubits in silicon quantum dots, an implementation that is especially appealing because of its compatibility with existing semiconductor-based electronics (see the Perspective by Schreiber and Bluhm). To showcase the potential, the authors used the gate to create an entangled quantum state called the Bell state.

    Science, this issue p. 439; see also p. 393

  16. Paleoanthropology

    Earliest modern humans out of Africa

    1. Andrew M. Sugden

    Recent paleoanthropological studies have suggested that modern humans migrated from Africa as early as the beginning of the Late Pleistocene, 120,000 years ago. Hershkovitz et al. now suggest that early modern humans were already present outside of Africa more than 55,000 years earlier (see the Perspective by Stringer and Galway-Witham). During excavations of sediments at Mount Carmel, Israel, they found a fossil of a mouth part, a left hemimaxilla, with almost complete dentition. The sediments contain a series of well-defined hearths and a rich stone-based industry, as well as abundant animal remains. Analysis of the human remains, and dating of the site and the fossil itself, indicate a likely age of at least 177,000 years for the fossil—making it the oldest member of the Homo sapiens clade found outside Africa.

    Science, this issue p. 456; see also p. 389

  17. Neuroscience

    The neuronal population is the key unit

    1. Peter Stern

    The responses of pairs of neurons to repeated presentations of the same stimulus are typically correlated, and an identical neuronal population can perform many functions. This suggests that the relevant units of computation are not single neurons but subspaces of the complete population activity. To test this idea, Ni et al. measured the relationship between neuronal population activity and performance in monkeys. They investigated attention, which improves perception of attended stimuli, and perceptual learning, which improves perception of well-practiced stimuli. These two processes operate on different time scales and are usually studied using different perceptual tasks. Manipulation of attention and learning in the same behavioral trials and the same neuronal populations revealed the dimensions of population activity that matter most for behavior.

    Science, this issue p. 463

  18. Ecology

    Honey bees put pressure on wild pollinators

    1. Julia Fahrenkamp-Uppenbrink

    Honey bees and other pollinators are essential for agriculture. Declining pollinator populations have thus raised alarm among scientists, policy-makers, and the public. In a Perspective, Geldmann and González-Varo argue that although all pollinators face stressors such as pesticide use, large populations of managed honey bees can themselves put pressure on wild pollinators. It is thus important not to conflate managed honey bees and wild pollinators in conservation efforts. Better honey bee management is particularly crucial during periods when mass-flowering crops are not in bloom, when the bees compete most directly with wild pollinators.

    Science, this issue p. 392

  19. HIV

    Indicative integrins in HIV

    1. Lindsey Pujanandez

    The gut is thought to be a major viral reservoir in HIV infection. Studies in nonhuman primates have suggested that targeting the α4β7 integrin on T cells may be a viable therapy. Sivro et al. now extend these findings to humans by examining HIV acquisition in multiple African cohorts. Higher frequencies of α4β7+ circulating T cells before infection were associated with increased HIV acquisition, higher viral load at set point, and more rapid CD4+ T cell decline. Thus, targeting integrins could help reduce the spread of HIV.

    Sci. Transl. Med. 10, eaam6354 (2018).

  20. Systems Immunology

    Committing to cytotoxicity

    1. Anand Balasubramani

    Cytotoxic CD4+ T cells (CD4-CTLs) were initially identified in patients with chronic viral infections, including dengue virus infection. Patil et al. sequenced the T cell receptors of individual CD4+ T cells from human blood to identify precursors that give rise to CD4-CTL cells. CD4-CTL cells underwent marked clonal expansion, and CD4-CTL precursor cells were characterized by high expression of interleukin-7 receptor. These findings should facilitate improved vaccine design in the context of chronic viral infections.

    Sci. Immunol. 3, eaan8664 (2018).

  21. Immunology

    A drug to fight two lupus symptoms

    1. Wei Wong

    The receptor TLR9 is implicated in autoimmune diseases characterized by erroneous recognition of self DNA, such as lupus. Perego et al. found that guanabenz, an FDA-approved antihypertensive drug with anti-inflammatory effects, altered cholesterol metabolism so that TLR9 did not reach endosomes, where it is fully activated. Guanabenz treatment reduced symptom severity in a mouse model of lupus. Because many lupus patients also suffer from hypertension, guanabenz and related compounds could have dual benefits.

    Sci. Signal. 10, eaam8104 (2018).