This Week in Science

Science  18 Oct 2019:
Vol. 366, Issue 6463, pp. 320
  1. Exoplanets

    Peering inside extrasolar rocky bodies

    1. Keith T. Smith

    Artist's vision of a white dwarf stripping a planet of its rocky outer layers


    The oxygen fugacity of a rock, fO2, is a measure of how oxidizing or reducing its surroundings were when the rock formed. Different minerals form at different fO2 and have different physical properties, so the internal structure of an exoplanet depends on this value. Doyle et al. exploited the signature left behind when rocky bodies impact a white dwarf—the remnant of a dead star. By examining the rock-forming elements left on the surface of each white dwarf, they determine fO2 in the impacting body. Six systems all had similar fO2 to bodies in the Solar System, consistent with the idea that rocky exoplanets often have internal properties similar to those of Earth and Mars.

    Science, this issue p. 356

  2. Cell Biology

    Origins of collective contraction

    1. Beverly A. Purnell

    In contrast to plants and fungi, animals can deform their bodies by the collective activity of contractile cells. Collective contractility underlies processes such as gastrulation and muscle-based motility. Brunet et al. report that a close relative of animals, a choanoflagellate they name Choanoeca flexa, forms cup-shaped colonies that undergo collective contractility, leading to a rapid change in colony morphology (see the Perspective by Tomancak). C. flexa colonies are each composed of a monolayer of polarized cells. In response to sudden darkness, a light-sensing protein triggers coordinated, polarized contraction of C. flexa cells, which results in colony inversion. The cellular mechanisms underlying this process are conserved between C. flexa and animals, indicating that their last common ancestor was also capable of polarized cell contraction.

    Science, this issue p. 326; see also p. 300

  3. 3D Printing

    Large-scale, continuous 3D printing

    1. Marc S. Lavine

    Many three-dimensional (3D) printing methods build up structures layer by layer, which causes a lamination layer between each discrete step. Continuous printing can be done from a fluid bed if a so-called dead layer is used to buffer between the solidified structure and pool of resin. However, printing speeds are limited by the heat buildup from the exothermic polymerization process, thus limiting the ultimate size of the printed object. Walker et al. use a pumped, nonreactive fluorinated oil to act as the dead layer that removes heat during polymerization. This approach allows for both speedup and scale-up of the printing process.

    Thermal imaging of a 3D-printed lattice


    Science, this issue p. 360

  4. Earthquakes

    Many ruptures across many scales

    1. Brent Grocholski

    The period of seismic quiescence in Southern California was rudely interrupted by the Ridgecrest earthquake sequence in July 2019. Ross et al. mapped the slip sequences during the magnitude 6.4 and 7.1 earthquakes that shook the region. They found that ruptures of a few larger, but many smaller, faults occurred during both earthquakes. The Ridgecrest sequence calls for rethinking seismic hazard, as multifault ruptures are not usually considered when assessing seismic risk.

    Science, this issue p. 346

  5. Quantum Computing

    Generating large-scale cluster states

    1. Ian S. Osborne

    The development of a practical quantum computer requires universality, scalability, and fault tolerance. Although much progress is being made in circuit platforms in which arrays of qubits are addressed and manipulated individually, scale-up of such systems is experimentally challenging. Asavanant et al. and Larsen et al. explore an alternative route: measurement-based quantum computation, which is a platform based on the generation of large-scale cluster states. As these are optically prepared and easier to handle (one simply performs local measurements on each individual component of the cluster state), such a platform is readily scalable and fault tolerant. The topology of the cluster state ensures that the approach meets the requirements for quantum computation.

    Science, this issue p. 373, p. 369

  6. Gene Expression

    A statistical model to find disease genes

    1. Laura M. Zahn

    Genetic variation is high among individuals, which makes it difficult to identify any one specific pathogenetic variant in patients with idiopathic disease, especially those that are in noncoding regions of the genome. Examining tissue-specific and population-level RNA sequencing data, Mohammadi et al. developed a statistical test, analysis of expression variation (ANEVA), that can quantify how one individual's gene expression fits in the context of the variation within the general population. By applying ANEVA to a dosage outlier test, the authors identified pathogenic gene transcripts in patients with Mendelian muscle dystrophy.

    Science, this issue p. 351

  7. Sleep

    Need for sleep

    1. Mattia Maroso

    Sleep is crucial for healthy living and well-being, but individual sleep needs vary greatly. Xing et al. performed whole exome sequencing in a family of short sleepers and identified a point mutation in the neuropeptide S receptor 1 gene (NPSR1) responsible for the short sleep phenotype. The mutation increased receptor sensitivity to the endogenous ligand. Mice carrying the mutation showed increased mobility time, reduced sleep duration, and resistance to sleep deprivation–induced cognitive impairment. NPSR1 may thus play a major role in sleep-related memory consolidation.

    Sci. Transl. Med. 11, eaax2014 (2019).

  8. Fibrosis

    Sequencing in the matrix

    1. Anand Balasubramani

    Biological scaffolds that mimic tissue microenvironments can be used to model wound healing. Using single-cell RNA sequencing in two distinct biomaterial environments, Sommerfeld et al. found that defined populations of macrophages play a role in both fibrosis and regeneration. A subset of CD9+ interleukin-36γ (IL-36γ)–producing macrophages participate in IL-17–driven fibrosis. By evaluating wound healing in IL-17–deficient mice, they report IL-17 to be essential for the generation of CD9+ IL-36γ–producing macrophages during fibrosis. Further studies are needed to understand the functional relationship between IL-17– and IL-36γ–producing cells in fibrosis and in other settings.

    Sci. Immunol. 4, eaax4783 (2019).

  9. Signaling

    Mediating systemic health

    1. Gemma Alderton

    Sphingosine 1-phosphate (S1P) is an important circulating lipid mediator that is derived from the metabolism of cell membranes. Its diverse homeostatic roles, particularly in immunology and vascular biology, can go awry in numerous diseases, including multiple sclerosis, cardiovascular diseases, and fibrosis. The centrality of S1P signaling has led to the development of several drugs, including two approved for treatment of multiple sclerosis. In a Review, Cartier and Hla discuss the current understanding of how one mediator can carry out so many signaling roles in different tissues, how these become dysregulated in disease, and efforts in drug development to target S1P signaling.

    Science, this issue p. eaar5551

  10. Human Evolution

    Adaptive archaic hominin genes

    1. Laura M. Zahn

    As they migrated out of Africa and into Europe and Asia, anatomically modern humans interbred with archaic hominins, such as Neanderthals and Denisovans. The result of this genetic introgression on the recipient populations has been of considerable interest, especially in cases of selection for specific archaic genetic variants. Hsieh et al. characterized adaptive structural variants and copy number variants that are likely targets of positive selection in Melanesians. Focusing on population-specific regions of the genome that carry duplicated genes and show an excess of amino acid replacements provides evidence for one of the mechanisms by which genetic novelty can arise and result in differentiation between human genomes.

    Science, this issue p. eaax2083

  11. Neurodevelopment

    Retinal neurons play musical chairs

    1. Pamela J. Hines

    As the retina develops in fruit flies, subtypes of certain color photoreceptors, the R7 neurons, are stochastically specified even though the downstream neurons they need to connect to, the Dm8 neurons, are not randomly specified. Courgeon and Desplan find that Dm8 neurons are actually specified in subtypes and are produced in excess. Those Dm8 neurons that connect to an R7 input survive; those that fail to find a match die by apoptosis. The matching is facilitated by a pair of cell adhesion molecules. The stochastic results of R7 differentiation are thus propagated downstream even though those downstream elements are not stochastically determined.

    Science, this issue p. eaay6727

  12. Organic Chemistry

    Charging through the looking glass

    1. Jake Yeston

    Asymmetric catalysis is a commonly applied technique to prepare just one of two mirror-image products in a chemical reaction. But what if you already have the compound you want, stuck in a mixture of left- and right-handed enantiomers? Shin et al. now show that light-induced electron transfer can trigger a favorable succession of proton and hydrogen-atom transfer steps, both of which are susceptible to biasing by catalysts, to preferentially convert a mixture of cyclic urea enantiomers into just one (see the Perspective by Wendlandt).

    Science, this issue p. 364; see also p. 304

  13. Biodiversity

    Spatial structure of species change

    1. Andrew M. Sugden

    Biodiversity is undergoing rapid change driven by climate change and other human influences. Blowes et al. analyze the global patterns in temporal change in biodiversity using a large quantity of time-series data from different regions (see the Perspective by Eriksson and Hillebrand). Their findings reveal clear spatial patterns in richness and composition change, where marine taxa exhibit the highest rates of change. The marine tropics, in particular, emerge as hotspots of species richness losses. Given that human activities are affecting biodiversity in magnitudes and directions that differ across the planet, these findings will provide a much needed biogeographic understanding of biodiversity change that can help inform conservation prioritization.

    Science, this issue p. 339; see also p. 308

  14. Neuroscience

    Special moments at cortical quiet states

    1. Peter Stern

    Delta waves are moments of widespread cortical silence that alternate with active states during slow-wave sleep. However, upon closer examination, single neuronal action potentials can be detected during delta waves. Todorova and Zugaro sought to determine whether this neuronal noise could instead be an important signal (see the Perspective by Ikegaya and Matsumoto). They found that persisting action potential firing during delta waves is an overlooked but widespread phenomenon, which could potentially involve all neurons and all delta waves. A critical role of the delta wave may be to insulate specific cortical computations taking place in response to hippocampal replay and involved in memory consolidation.

    Science, this issue p. 377; see also p. 306

  15. Turbulence

    Down and down the energy cascade

    1. Jelena Stajic

    Injecting energy into a turbulent system at large length scales results in the energy cascading down and eventually dissipating at a characteristic small length scale. In conventional fluids, this small scale is set by fluid viscosity. Navon et al. studied the turbulence energy cascade in a quantum gas, a Bose-Einstein condensate of rubidium-87 atoms held in a uniform trap. Dissipation occurred by atoms escaping from the trap at a scale that could be tuned by varying the height of the trapping potential. Thanks to the flexibility of their setup, the researchers were able to study both the steady state, in which energy is injected at the same rate it is dissipated, and the transient regime preceding the steady state.

    Science, this issue p. 382

  16. Water Oxidation

    Inspecting S states in photosynthesis

    1. Michael A. Funk

    Oxygenic photosynthesis uses a Mn4CaO5 cluster in the oxygen-evolving complex to extract electrons from water and produce dioxygen. Visualizing each of the chemical states in this process, S0 to S4, and assigning chemical identities and mechanisms on the basis of structures has been a challenge addressed recently by work at x-ray free-electron lasers. Suga et al. used serial crystallography at cryogenic temperatures to trap and determine the structures of several stable states during photosystem II water oxidation (see the Perspective by Britt and Marchiori). Changes around the water cluster already happen in the S2 state and set the stage for water insertion that occurs during transition to the S3 state. A short 1.9-angstrom distance between the two oxygen atoms in the S3 state is consistent with theoretical studies supporting an oxyl/oxo mechanism for oxygen-oxygen coupling.

    Science, this issue p. 334; see also p. 305

  17. Immunology

    Mobilizing T cells

    1. Gemma Alderton

    Accumulating evidence suggests that a nonclassical antigen presentation pathway, mediated by human leukocyte antigen–E (HLA-E), has an important role in regulating innate and adaptive immune responses to infections and cancer. In a Perspective, Ottenhoff and Joosten discuss the dichotomous role of HLA-E in suppressing immune responses (through an immune checkpoint), as well as in activating unconventional T cells. This nonclassical pathway has the potential to be manipulated to prevent infectious disease through vaccination and to treat cancer through immunotherapy.

    Science, this issue p. 302

  18. Neurodevelopment

    How GABA makes the switch

    1. Leslie K. Ferrarelli

    A high concentration of chloride ions in neurons interferes with signaling mediated by the neurotransmitter γ-aminobutyric acid (GABA). The transporter KCC2 extrudes chloride ions, and Watanabe et al. and Pisella et al. examined mice expressing KCC2 with mutations that mimicked constitutive phosphorylation at two regulatory sites (see the Focus by Zamponi). Dephosphorylation of these sites in KCC2 enables GABA to switch from being an excitatory to being an inhibitory neurotransmitter during neurodevelopment, thus allowing the maturation of the neurocircuitry underlying cognition and respiration.

    Sci. Signal. 12, eaaw9315, eaay0300, eaay8960 (2019).

  19. Neuroscience

    MORE model to fight against addiction

    1. Kevin S. LaBar

    The United States is in the midst of an opioid crisis affecting more than 15 million Americans. Garland et al. provide neurophysiological evidence for a therapeutic approach to help individuals with opioid use disorder (OUD). They conducted a series of randomized experiments using an approach called Mindfulness-Oriented Recovery Enhancement, or MORE. Hedonic dysregulation in brain reward circuitry has been viewed as a core mechanism of addictive behavior; the MORE model aims to restructure reward responsiveness using mindfulness techniques. MORE may remediate hedonic dysregulation by simultaneously increasing responsiveness to natural rewards and decreasing reactivity to drug-related rewards. The use of MORE and other cognitive training interventions may ultimately serve to turn the tide on addiction in the United States.

    Sci. Adv. 10.1126/sciadv.aax1569 (2019).