This Week in Science

Science  30 Aug 2019:
Vol. 365, Issue 6456, pp. 878
  1. Archaeology

    A synthetic history of human land use

    1. Andrew M. Sugden

    Fields and managed forests, such as these in Eifel, Germany, are common agricultural land uses.

    CREDIT: LOOK/ALAMY STOCK PHOTO

    Humans began to leave lasting impacts on Earth's surface starting 10,000 to 8000 years ago. Through a synthetic collaboration with archaeologists around the globe, Stephens et al. compiled a comprehensive picture of the trajectory of human land use worldwide during the Holocene (see the Perspective by Roberts). Hunter-gatherers, farmers, and pastoralists transformed the face of Earth earlier and to a greater extent than has been widely appreciated, a transformation that was essentially global by 3000 years before the present.

    Science, this issue p. 897; see also p. 865

  2. Computer Science

    AI now masters six-player poker

    1. Jelena Stajic

    Computer programs have shown superiority over humans in two-player games such as chess, Go, and heads-up, no-limit Texas hold'em poker. However, poker games usually include six players—a much trickier challenge for artificial intelligence than the two-player variant. Brown and Sandholm developed a program, dubbed Pluribus, that learned how to play six-player no-limit Texas hold'em by playing against five copies of itself (see the Perspective by Blair and Saffidine). When pitted against five elite professional poker players, or with five copies of Pluribus playing against one professional, the computer performed significantly better than humans over the course of 10,000 hands of poker.

    Science, this issue p. 885; see also p. 864

  3. Organic Chemistry

    Displacing OH groups catalytically

    1. Jake Yeston

    The Mitsunobu reaction is widely used to invert the configuration of alcohols. However, its major drawback is the need to activate the alcohol with a full equivalent of phosphine, thereby generating a phosphine oxide co-product. Beddoe et al. report a phosphine oxide compound that achieves the same result catalytically (see the Perspective by Longwitz and Werner). The key is a phenol substituent that can reversibly bond through its oxygen to phosphorus, forming a ring that the alcohol opens. The phosphorus thus remains in the +5 oxidation state throughout the reaction, and water is the only by-product.

    Science, this issue p. 910; see also p. 866

  4. Mantle Chemistry

    Deep divide in fate of iron

    1. Brent Grocholski

    A large component of Earth's atmosphere comes from the interior, where the gas species are dictated by the redox state of the mantle. After formation of Earth's iron core, the mantle became several orders of magnitude more oxidized. Armstrong et al. conducted a set of experiments looking at the redox state of silicate melt representative of Earth's early magma oceans. They found that at some depth, iron oxide disproportionates into iron(III) oxide and metallic iron. The reduced iron sinks to the core, leaving an oxidized rocky mantle that emits carbon dioxide and water instead of more reduced species.

    Science, this issue p. 903

  5. Astrochronology

    Filling a dating hole

    1. H. Jesse Smith

    The periodic nature of Earth's orbit around the Sun produces cycles of insolation reflected in climate records. Conversely, these climate records can be used to infer changes in the dynamics of the Solar System, which is inherently chaotic and not always similarly periodic. A particular obstacle is the lack of well-defined planetary orbital constraints between 50 and 60 million years ago. Zeebe and Lourens found an astronomical solution for that interval showing that the Solar System experienced a specific resonance transition pattern. These data provide a measure of the duration of the Paleocene-Eocene Thermal Maximum.

    Science, this issue p. 926

  6. Plant Science

    Microbial tRNA pieces regulate nodulation

    1. Pamela J. Hines

    To fix nitrogen, leguminous plants enter into a symbiotic relationship with nodulating bacteria. Ren et al. now reveal the bacteria as active regulators in this process (see the Perspective by Baldrich and Meyers). Small fragments cleaved from rhizobial tRNA molecules tap into the hosts' RNA interference machinery to silence key host genes. Thus, both host and microbe shape the symbiotic environment.

    Science, this issue p. 919; see also p. 868

  7. Immunology

    Empowering NK cells against cancer

    1. John F. Foley

    Natural killer cell (top) and melanoma cell in a scanning electron micrograph

    PHOTO: FERNANDO S. F. GUIMARAES/WEHI, CAROLINA C. CAMARGO/UFPR AND SIMON TAPLIN/WEHI

    Tumors release factors, such as the cytokine transforming growth factor–β (TGF-β), that block antitumor immunity mediated by natural killer (NK) immune cells by promoting their differentiation into a less suppressive cell type. Rautela et al. found that activin-A, another member of the TGF-β family, had similar effects on both mouse and human NK cells but through a pathway independent of TGF-β. Inhibition of activin-A reduced skin cancer growth in a mouse melanoma model, suggesting that targeting this pathway could enhance NK cell function and antitumor immunity.

    Sci. Signal. 12, eaat7527 (2019).

  8. Synthetic Biology

    Programmable genome engineering

    1. Steve Mao

    The model bacterium Escherichia coli has a single circular chromosome. Wang et al. created a method to fragment the E. coli genome into independent chromosomes that can be modified, rearranged, and recombined. The efficient fission of the unmodified E. coli genome into two defined, stable pairs of synthetic chromosomes provides common intermediates for large-scale genome manipulations such as inversion and translocation. Fusion of synthetic chromosomes from distinct cells generated a single genome in a target cell. Precise, rapid, large-scale genome engineering operations are useful tools for creating diverse synthetic genomes.

    Science, this issue p. 922

  9. Microbiota

    Superantigens spur IgA secretion

    1. Lindsey Pujanandez

    Mucosal immunoglobulin A (IgA) is abundant and interacts with the gut microbiome. To examine microbial induction of IgA in humans, Bunker et al. screened microbiota from infants against mouse and human IgA. A subset of samples bound IgA in a way that indicated the presence of superantigens, which bind T cell receptors or B cell receptors outside of the typical antigen-binding region, leading to nonspecific activation. Putative superantigens in commensal members of Lachnospiraceae activated human VH3-positive B cells and induced IgA production in mice. The authors suggest that commensal superantigens may be dominant forces behind IgA production in humans.

    Sci. Transl. Med. 11, eaau9356 (2019).

  10. Neurodevelopment

    Neurons negotiating boundaries

    1. Pamela J. Hines

    Barriers around the brain and spinal cord separate central from peripheral nervous systems, yet the two systems are interlinked. Suter and Jaworski review what is known about how cells, axons, and signals negotiate the boundary zone. Understanding what goes wrong in boundary transgressions reveals the inner workings of multiple, partially redundant mechanisms built during development that separate the two compartments in adulthood.

    Science, this issue p. eaaw8231

  11. Human Genetics

    The genetics of sexual orientation

    1. Laura M. Zahn

    Twin studies and other analyses of inheritance of sexual orientation in humans has indicated that same-sex sexual behavior has a genetic component. Previous searches for the specific genes involved have been underpowered and thus unable to detect genetic signals. Ganna et al. perform a genome-wide association study on 493,001 participants from the United States, the United Kingdom, and Sweden to study genes associated with sexual orientation (see the Perspective by Mills). They find multiple loci implicated in same-sex sexual behavior indicating that, like other behavioral traits, nonheterosexual behavior is polygenic.

    Science, this issue p. eaat7693; see also p. 869

  12. Immunology

    Thirteen is the charm in anaphylaxis

    1. Seth Thomas Scanlon

    Immunoglobulin E (IgE) is a type of antibody associated with allergies and response to parasites such as worms. When high-affinity, allergen-specific IgE binds its target, it can cross-link receptors on mast cells that induce anaphylaxis. It remains unclear, however, how B cells are instructed to generate high-affinity IgE. Gowthaman et al. discovered a subset of T follicular helper cells (TFH13) that direct B cells to do just that. TFH13 cells are induced by allergens but not during parasite infection. Transgenic mice lacking these cells show impaired production of high-affinity, anaphylactic IgE. TFH13 cells, which are elevated in patients with food and aeroallergies, may be targeted in future antianaphylaxis therapies.

    Science, this issue p. eaaw6433

  13. Malaria

    Targeting parasite's protein kinase

    1. Caroline Ash

    Malaria elimination goals are constantly eroded by the challenge of emerging drug and insecticide resistance. Alam et al. have taken established drug targets—CLK protein kinases involved in regulation of RNA splicing—and investigated how inhibition of the parasite's enzymes blocks completion of its complex life cycle. They identified an inhibitor of the parasite's CLK protein kinase that was 100-fold less active against the most closely related human protein kinase and effective at clearing rodent malaria parasites. Not only does this compound halt the development of sexual stages but it also limits transmission to the mosquito vector of the parasite, a key requirement for malaria drugs.

    Science, this issue p. eaau1682

  14. Superconductivity

    Pervasive fluctuations

    1. Jelena Stajic

    Among the many intertwined phases in the cuprate superconductor phase diagram is the charge density wave (CDW) order, which has been detected in all major cuprate families. It is thought that CDW competes with superconductivity, but whether it has bearing on the mechanism of superconductivity remains unclear. Arpaia et al. undertook a comprehensive study of charge density fluctuations in a cuprate family, varying doping and temperature. They found that short-range dynamic charge fluctuations were present in a large portion of the phase diagram, at temperatures considerably higher than those at which the CDW order disappears.

    Science, this issue p. 906

  15. Signal Transduction

    A dynamic signaling scaffold

    1. Valda Vinson

    In neurons, many cellular processes are regulated by receptor tyrosine kinases (RTKs), cell surface receptors whose activation can depend on other signaling pathways. Zhou et al. used super-resolution imaging to visualize colocalization of signaling proteins on the membrane-associated periodic skeleton (MPS) that is formed by actin, spectrin, and related molecules in the axons and dendrites of neurons. The colocalization of signaling proteins in different pathways leads to transactivation of RTK, which initiates intracellular signaling. In a negative feedback loop, the downstream signaling in turn leads to degradation of the MPS. Thus, the MPS is a dynamically regulated platform that coordinates signal transduction in neurons.

    Science, this issue p. 929

  16. Immunology

    Distinct immunology of the placenta

    1. Gemma Alderton

    The placenta is formed when specialized cells from an embryo invade the maternal uterus. The effectiveness of this process can determine whether complications in pregnancy, such as preeclampsia, arise. In a Perspective, Colucci discusses the emerging role of immune cells in the formation of the placenta. Homeostatic immune cell activities facilitate placental implantation without inducing an immune response to foreign antigens expressed on fetal-derived tissues. Understanding this process more fully could help to prevent or treat placenta-associated complications of pregnancy.

    Science, this issue p. 862

  17. Skin Inflammation

    Resurrecting sentinels in the skin

    1. Anand Balasubramani

    Langerhans cells are resident innate immune cells in the skin that play essential roles in promoting local immune responses and maintaining skin homeostasis. Langerhans cells arise from fetal progenitors that seed the skin early in development. In a mouse hematopoietic stem cell transplant model, Ferrer et al. found that monocytes from the blood infiltrate the skin and eventually replenish the Langerhans cell network. These observations are in agreement with previous studies looking at other sites, but the process by which monocytes give rise to Langerhans cells is inefficient, limiting the extent to which they can be renewed in the skin.

    Sci. Immunol. 4, eaax8704 (2019).

  18. Archaeology

    The early occupation of America

    1. Andrew M. Sugden

    The Cooper's Ferry archaeological site in western North America has provided evidence for the pattern and time course of the early peopling of the Americas. Davis et al. describe new evidence of human activity from this site, including stemmed projectile points. Radiocarbon dating and Bayesian analysis indicate an age between 16,560 and 15,280 years before present. Humans therefore arrived in the Americas before an inland ice-free corridor had opened, so a Pacific coastal route was the probable entry route. The stemmed projectile points closely resemble those found in Upper Paleolithic Japan, also supporting the hypothesis of a coastal route.

    Science, this issue p. 891

  19. Magnetism

    Skyrmions in a frustrated magnet

    1. Jelena Stajic

    Skyrmions—tiny, topologically protected whirlpools of spin—have been investigated as potential information carriers in spintronic devices. Usually, skyrmions appear in noncentrosymmetric materials or at interfaces between materials. In contrast to this rule of thumb, Kurumaji et al. observed a skyrmion lattice phase in the centrosymmetric material Gd2PdSi3. The magnetic frustration present in this material helped stabilize the skyrmion phase, which was detected through transport measurements in magnetic field.

    Science, this issue p. 914

Stay Connected to Science