This Week in Science

Science  23 Nov 2018:
Vol. 362, Issue 6417, pp. 905
  1. Paleoecology

    Megaherbivore extinctions in Africa

    1. Andrew M. Sugden

    Artist's rendering of a prehistoric African landscape

    IMAGE: MAURICIO ANTON/SCIENCE SOURCE

    Human ancestors have been proposed as drivers of extinctions of Africa's diverse large mammal communities. Faith et al. challenge this view with an analysis of eastern African herbivore communities spanning the past ∼7 million years (see the Perspective by Bobe and Carvalho). Megaherbivores (for example, elephants, rhinos, and hippos) began to decline about 4.6 million years ago, preceding evidence for hominin consumption of animal tissues by more than 1 million years. Instead, megaherbivore decline may have been triggered by declining atmospheric carbon dioxide and expansion of grasslands.

    Science, this issue p. 938; see also p. 892

  2. Genetics

    The mutational burden of aging

    1. Paula A. Kiberstis

    As people age, they accumulate somatic mutations in healthy cells. About 25% of cells in normal, sun-exposed skin harbor cancer driver mutations. What about tissues not exposed to powerful mutagens like ultraviolet light? Martincorena et al. performed targeted gene sequencing of normal esophageal epithelium from nine human donors of varying age (see the Perspective by Chanock). The mutation rate was lower in esophagus than in skin, but there was a strong positive selection of clones carrying mutations in 14 cancer-associated genes. By middle age, more than half of the esophageal epithelium was colonized by mutant clones. Interestingly, mutations in the cancer driver gene NOTCH1 were more common in normal esophageal epithelium than in esophageal cancer.

    Science, this issue p. 911; see also p. 893

  3. Superconductivity

    A monolayer of many talents

    1. Jelena Stajic

    Superconductors with a topologically nontrivial band structure have been predicted to exhibit exotic properties. However, such materials are few and far between. Now, two groups show that the monolayer of the material tungsten ditelluride (WTe2)—already known to be a two-dimensional topological insulator—can also go superconducting. Fatemi et al. and Sajadi et al. varied the carrier density in the monolayer by applying a gate voltage and observed a transition from a topological to a superconducting phase. The findings may lead to the fabrication of devices in which local gating enables topological and superconducting phases to exist in the same material.

    Science, this issue p. 926, p. 922

  4. Metallurgy

    Nanoparticle superalloy

    1. Brent Grocholski

    Improving the strength of a metal alloy is hard to do without sacrificing the ductility. Yang et al. designed an iron-nickel-cobalt (Fe-Ni-Co) alloy laced with aluminum-titanium (Al-Ti) nanoparticles with both high strength and ductility. The key was getting the composition tuned correctly, because the Fe-Ni-Co matrix reacts with the Al-Ti nanoparticles. This was vital for avoiding environmental embrittlement, enhancing work hardening, and improving ductility.

    Science, this issue p. 933

  5. Immunology

    Fine-tuning pyroptosis with ESCRT-III

    1. Seth Thomas Scanlon

    Pyroptosis is an inflammatory form of cell death induced by select caspases downstream of inflammasome complexes. These caspases cleave gasdermin D (GSDMD), whose N-terminal fragments quickly form large permeability pores that induce cell death. However, a large percentage of cells with active inflammasomes are resistant to pyroptosis. Rühl et al. found that the membrane-remodeling ESCRT-III machinery was recruited to the plasma membrane upon GSDMD activation. ESCRT-III–dependent membrane repair limited proinflammatory cytokine secretion and pyroptosis after activation of inflammasomes.

    Science, this issue p. 956

  6. Epidemiology

    Protecting the colony

    1. Sacha Vignieri

    Normally cooperative ants change their behavior toward sick individuals.

    PHOTO: DANI DANIAR/ALAMY STOCK PHOTO

    When we get a cold and then stay home from work, we are not only taking care of ourselves but also protecting others. Such changes in behavior after infection are predicted in social animals but are difficult to quantify. Stroeymeyt et al. looked for such changes in the black garden ant and found that infected workers did alter their behavior—and healthy workers altered their behavior toward the sick. The changed behavior was especially valuable for protecting the most important and vulnerable members of the colony.

    Science, this issue p. 941

  7. Cancer

    Taking aim at a childhood cancer

    1. Leslie K. Ferrarelli

    Rhabdomyosarcoma is a difficult-to-treat soft tissue pediatric tumor. In a particular subtype of this cancer, a fusion protein generated by a chromosomal abnormality drives chemoresistance and aggressive progression. Bharathy et al. investigated why the histone deacetylase inhibitor entinostat shows promise in treating this rhabdomyosarcoma subtype. Entinostat altered epigenetic regulation to inhibit translation of the fusion protein. Without the fusion protein, rhabdomyosarcoma growth in mouse models slowed, and tumors were sensitized to the chemotherapeutic drug vincristine.

    Sci. Signal. 11, eaau7632 (2018).

  8. Robotic Sensing

    A firm, but gentle, touch

    1. Rachel Kline

    Many seemingly simple manual tasks require the ability to detect force direction as well as magnitude. Boutry et al. developed an electronic skin inspired by human skin and nature. Tiny pyramids, similar to hill-like structures in human skin, were arranged in spirals, like the center of a sunflower. These microstructures enabled the sensor array to differentiate pressure applied perpendicularly from pressure applied at an angle—a key feature for dexterity. The pressure information was used to interrupt automatic movement of a robotic arm. The robot was able to touch a fresh raspberry and reverse motion quickly enough to avoid damaging the fruit.

    Sci. Robot. 3, eaau6914 (2018).

  9. Emerging Infections

    Antibodies to abrogate Andes hantavirus

    1. Lindsey Pujanandez

    Andes hantavirus circulates in rodent reservoirs and can cause hantavirus cardiopulmonary syndrome in humans. This results in a potentially lethal disease for which no vaccines or targeted treatments exist. Garrido et al. screened memory B cells from people that had been infected with Andes hantavirus. Antibodies were isolated from one individual with a high viral neutralization capacity. Two of these antibodies were fully protective against disease in a hamster model, even when given several days after infection. These antibodies target distinct epitopes on the viral glycoprotein and could be developed for use alone or as a combination therapy.

    Sci. Transl. Med. 10, eaat6420 (2018).

  10. Agriculture

    The future of farming

    1. Caroline Ash

    In the mid-20th century, food production from agriculture sharply increased worldwide; however, this was achieved through heavy use of agrochemicals. Extensive collateral damage from excessive use of pesticides, herbicides, and fertilizers has occurred to the wider environment. This has led to biodiversity loss, pesticide resistance and the emergence of new pests, pollution and decline of freshwater supplies, and soil degradation and erosion, as well as direct harm to health. In a Review, Pretty examines the alternative approaches that can achieve sustainable intensification of farming systems by integrating pest management with agroecological systems to minimize costs, maximize yields, restore ecosystem services, and ensure environmental enhancement.

    Science, this issue p. eaav0294

  11. Skin Repair

    Myofibroblast diversity with injury and aging

    1. Beverly A. Purnell

    Fibroblasts deposit extracellular matrix (ECM) molecules to regulate tissue strength and function. However, if too much ECM is deposited, fibrosis and scarring results. Shook et al. examined cells during mouse skin wound healing, fibrosis, and aging (see the Perspective by Willenborg and Eming). They identified distinct subpopulations of myofibroblasts, including cells identified as adipocyte precursors (APs). In cellular ablation mouse models, CD301b-expressing macrophages selectively activated proliferation of APs, but not other myofibroblasts. Myofibroblast composition and gene expression changed during aging. Thus, macrophage-fibroblast interactions are important during tissue repair and aging, which may have therapeutic implications for chronic wounds and fibrotic disease.

    Science, this issue p. eaar2971; see also p. 891

  12. Developmental Biology

    Maternal factor sets axis

    1. Beverly A. Purnell

    The vertebrate body form changes from the round shape of the fertilized egg to a cylindrical shape when the body plan is established. However, it is unknown whether a maternal factor controls this body axis formation. Yan et al. identified such a maternal factor and named it Huluwa. Loss of maternal Huluwa, a transmembrane protein, in zebrafish or frog eggs resulted in embryos that lacked the body axis and were missing the head and dorsoanterior tissues. Huluwa promoted Axin degradation, likely independent of Wnt ligand–receptor signaling, to protect β-catenin from degradation and induce body axis development during embryogenesis.

    Science, this issue p. eaat1045

  13. Topological Matter

    A messy topological wire

    1. Jelena Stajic

    Adding irregularity to a system can lead to a transition from a more orderly to a less orderly phase. Meier et al. demonstrated a counterintuitive transition in the opposite direction: Controlled fluctuations in the system's parameters caused it to become topologically nontrivial. The starting point was a one-dimensional lattice of ultracold rubidium atoms in momentum space whose band structure was topologically trivial. The researchers then introduced fluctuations in the tunneling between the lattice sites and monitored the atomic “wires” as the amplitude of the fluctuations increased. The wires first became topologically nontrivial and then went back to trivial for sufficient disorder strengths.

    Science, this issue p. 929

  14. Neuroscience

    Egocentric representation of objects

    1. Peter Stern

    The lateral entorhinal cortex (LEC) and medial entorhinal cortex (MEC) are the two major cortical projections to the hippocampus. The discovery of a variety of functional cell types in MEC has greatly advanced our understanding of the functional anatomy of entorhinal-hippocampal circuits. However, the function of LEC and the behavioral correlates of LEC cells are still not fully understood. Wang et al. analyzed the firing properties of LEC and MEC neurons. They found that LEC and MEC used different reference frames, with LEC encoding objects egocentrically.

    Science, this issue p. 945

  15. Developmental Biology

    A single myosin sets chirality at all scales

    1. Beverly A. Purnell

    When viewed externally, most organisms appear symmetric between the left and right sides. However, many organs are left-right asymmetric. Whether macroscopic asymmetries are directly related to molecular-level chirality remains an open question. Working in Drosophila, Lebreton et al. found that the conserved molecular motor myosin 1D induced stereotyped chirality at all biological scales—from F-actin turning in vitro to the organ level and even organismal behavior. Thus, a single conserved myosin can generate de novo nano-to-macroscopic changes in form and direction through chiral interaction with the actin cytoskeleton.

    Science, this issue p. 949

  16. Immunology

    Visualizing TGF-β1 regulation by GARP

    1. Seth Thomas Scanlon

    Regulatory T cells (Tregs) can suppress immune responses through a variety of mechanisms. One such mechanism involves the activation of a surface-bound latent form of the cytokine transforming growth factor–β1 (TGF-β1). Within the cell, newly synthesized pro-TGF-β1 homodimers form disulfide bonds with the transmembrane protein GARP, which acts to chaperone and orient the cytokine for activation at the cell surface. Liénart et al. reveal how GARP interacts with TGF-β1, using a crystal structure in which the complex was stabilized using a Fab fragment from a monoclonal antibody (MHG-8) that binds to the complex. In so doing, they also demonstrate how MHG-8 prevents membrane-associated TGF-β1 release. These structural and mechanistic insights may inform treatments of diseases with altered TGF-β1 functionality and dysfunctional Treg activity, including cancer immunotherapy.

    Science, this issue p. 952

  17. Behavior

    From behavior change to conservation success

    1. Julia Fahrenkamp-Uppenbrink,
    2. Sacha Vignieri

    Between 1970 and 2014, wild vertebrate populations have declined by 60%, and natural systems worldwide are under increasing pressure from human actions. Changes in human behavior will be key to addressing these conservation challenges. In a Perspective, Cinner discusses a range of cognitive biases and social perceptions that can be leveraged in conservation programs. For example, losses tend to hurt more than gains feel good. Conservation efforts can take account of this loss aversion bias by stressing the potential losses from not pursuing them. However, integration of this and other behavioral insights into conservation is not straightforward. It is crucial that behavior change interventions are not seen as coercive and that they are carefully tailored to the situation to which they are applied.

    Science, this issue p. 889

  18. Stem Cells

    Rethinking stemness

    1. Gemma Alderton

    Stem cells are defined by their ability to produce multiple cell lineages and to self-renew. New technology has allowed the investigation of lineage relationships in hematopoiesis, the process that maintains the cellular constituents of blood. In a Perspective, Yamamoto et al. discuss the recent changes in our definitions of what a stem cell is, as well as in our understanding of the lineage hierarchy in hematopoiesis. They also discuss how this might have consequences for patients receiving stem cell transplants. Such changes in concepts may apply to other systems, such as neurogenesis in the brain, for which stem cell lineages are also being questioned.

    Science, this issue p. 895

  19. Innate Lymphoid Cells

    Fishing for ILCs in zebrafish

    1. Anand Balasubramani

    Most studies on innate lymphoid cells (ILCs) have focused on their functions in mammals. Both lymphoid cells and adaptive immunity are not unique to mammals but are shared by all vertebrates. Hernández et al. studied lymphoid cells in rag1-deficient zebrafish that lack both B and T cells to elucidate the functions of ILC-like cells. They used single-cell RNA sequencing to profile gene expression in gut-resident lymphocytes of rag1-deficient zebrafish after immune challenge. They identified lymphocytes in zebrafish that correspond to mammalian ILC1, ILC2, and ILC3 lineages.

    Sci. Immunol. 3, eaau5265 (2018).

  20. Mass Spectrometry

    Bridging the mass gap

    1. Phil Szuromi

    Viruses and many large biomolecule complexes are in a mass range that is challenging to measure with conventional mass spectrometry methods. Nanomechanical resonators can determine masses of impacting molecules, but separation methods often lose too much of the sample to be efficient. Dominguez-Medina et al. used an aerodynamic lens that improved separation and focusing of nebulized molecules with increasing mass. The mass of both filled and empty viral capsids was determined with an array of 20 nanoresonators.

    Science, this issue p. 918

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