This Week in Science

Science  10 Jan 2020:
Vol. 367, Issue 6474, pp. 158
  1. Natural Hazards

    Limiting sea-level rise sustainably

    1. Kip Hodges

    Future sea-level rise will threaten coastal cities such as Venice, Italy, which experienced a series of severe tidal floods in November 2019.

    PHOTO: BLOOMBERG/GETTY IMAGES

    One of the most devastating effects of anthropogenic global warming will be sea-level rise. Sound climate policy depends on robust predictions of the degree of sea-level rise associated with various emission scenarios. However, over the course of centuries, sea level will respond to atmospheric radiative forcing quite differently than surface temperature, the main focus of current emissions limits. Li et al. developed integrated assessment models that suggest that a more effective way forward involves formally establishing acceptable targets for sea-level rise. According to this work, climate policies designed specifically to limit sea-level rise may be more sustainable and less expensive than policies driven by temperature targets alone.

    Sci. Adv. 10.1126/sciadv.aaw9490 (2019).

  2. Stem Cell Biology

    Niche relocated by muscle contraction

    1. Beverly A. Purnell

    Regulation of adult stem cells by their microenvironment, or niche, is essential for tissue homeostasis and for regeneration after injury and during aging. Normal regression of hair follicles during the hair cycle poses a particular challenge for maintaining a functional proximity of stem cells to their niche, especially the specialized mesenchymal cells of the dermal papilla. Using mice as a model organism, Heitman et al. demonstrate that the follicle dermal sheath is an active smooth muscle that drives tissue remodeling through coordinated cell contraction, enabling renewed contact between the dermal papilla and hair follicle stem cells during hair follicle regression. This biomechanical mechanism of niche relocation may be utilized in other stem cell niche systems.

    Science, this issue p. 161

  3. Paleoanthropology

    Dating the arrival of the first hominins in Java

    1. Andrew M. Sugden

    The World Heritage archaeological site at Sangiran on the island of Java in Indonesia has major importance for the understanding of human arrival and evolution in Asia. However, the timing of the first appearance of Homo erectus at the site has been controversial. Using a combination of dating techniques for hominin-bearing sediments, Matsu'ura et al. resolved the arrival of H. erectus at ∼1.3 million years ago (see the Perspective by Brasseur). This dating suggests that the earliest hominins in Sangiran are at least 200,000 years younger than has been thought and may represent an important step to the resolution of the controversy.

    Science, this issue p. 210; see also p. 147

  4. Quantum Simulation

    Spin and charge go their separate ways

    1. Jelena Stajic

    Strongly interacting chains of fermions are predicted to exhibit two types of collective excitations: spinons, which carry only spin, and holons, which carry only charge. These excitations move at different velocities. Signatures of this so-called spin-charge separation have been observed in solid-state systems, but obtaining direct dynamical evidence is tricky. With this goal in mind, Vijayan et al. perturbed a chain of ultracold interacting fermions housed in a one-dimensional optical lattice by removing one of the atoms. This gave rise to two independent excitations, which the researchers identified as spinons and holons using a quantum gas microscope.

    Science, this issue p. 186

  5. Lightning

    Gamma-ray flash from a lightning leader

    1. Keith T. Smith

    Terrestrial gamma-ray flashes (TGFs) are millisecond pulses of gamma rays produced by thunderstorms. Neubert et al. observed a TGF from above, using instruments on the International Space Station. High-speed photometry in optical, ultraviolet, x-ray, and gamma-ray bands allowed them to determine the sequence of events that produced the TGF. Emission from an intracloud lightning leader was followed within a millisecond by the TGF. The subsequent lightning flash produced an electromagnetic pulse, which induced expanding waves of ultraviolet emission in the ionosphere above the thunderstorm, called an elve. The authors conclude that high electric fields produced within the lightning leader generated the TGF.

    Science, this issue p. 183

  6. Antibiotic Resistance

    Challenges of drug combinations

    1. Caroline Ash

    Combinations of antibiotics are used to treat intractable infections such as methicillin-resistant Staphylococcus aureus. Clinically, however, drugs tend to be used empirically, and results can be contradictory. Liu et al. translated observations made in vitro to patient samples to understand the role of antibiotic tolerance in promoting or suppressing resistance when drug combinations are used (see the Perspective by Berti and Hirsch). Although bacterial populations exposed to multiple antibiotics can develop tolerance to multiple drugs, one drug in a combination may be able counter resistance to a partner drug and provide effective therapy. However, if tolerance has already emerged to one drug, the combination may end up promoting the transmission of resistance to a partner drug.

    Science, this issue p. 200; see also p. 141

  7. GPCR Signaling

    An accessory protein skews signaling

    1. Wei Wong

    Ghrelin is a peptide secreted by the stomach during fasting to promote food intake. The accessory protein MRAP2 interacts with the ghrelin receptor GHSR1a, a G protein–coupled receptor (GPCR), and is important for the appetite-stimulating effects of ghrelin. Rouault et al. found that MRAP2 promoted biased signaling downstream of ghrelin-mediated activation of GHSR1a by inhibiting β-arrestin recruitment to the receptor and potentiating Gαq/11-dependent signaling. Accessory proteins, not just ligands, can thus bias GPCR signaling.

    Sci. Signal. 13, eaax4569 (2020).

  8. Catalysis

    Confining peroxide to make methanol

    1. Jake Yeston

    In principle, hydrogen peroxide would be an efficient oxidant for the conversion of methane to methanol under mild conditions. In practice, however, it is currently too expensive to produce the peroxide ahead of time for this purpose. Jin et al. report a catalyst system that generates and concentrates hydrogen peroxide for immediate reaction with methane. A hydrophobically coated zeolite keeps the peroxide close to the gold and palladium active site, where incoming methane is then selectively oxidized to methanol.

    Science, this issue p. 193

  9. Metallurgy

    An anti-embrittlement roadmap

    1. Brent Grocholski

    Hydrogen is important for energy applications such as fuel cells but tends to diffuse into materials and make them more susceptible to fracture. Chen et al. tackled the challenge of identifying the exact location of hydrogen atoms in two common steels. The light weight and high mobility of hydrogen creates serious problems with conventional techniques. The authors used cryo-transfer atom probe tomography to show that hydrogen is pinned to various interfaces in the steels. This direct look into hydrogen trapping should help with the development of materials that are more resistant to hydrogen embrittlement.

    Science, this issue p. 171

  10. Quantum Chemistry

    Upside-down molecules on a salt surface

    1. Yury Suleymanov

    The quantum states of molecules are usually measured in gas-phase studies to minimize collisions that would blur the spectra. However, for carbon monoxide (CO) molecules adsorbed on a NaCl(100) surface, infrared emission from even high vibrational states can be resolved. In quantum-state resolved spectra, Lau et al. found that infrared-laser excitation of a monolayer of CO adsorbed on NaCl(100) forms an isomer in which CO binds to Na+ through its O atom in an upside-down configuration (see the Perspective by Wu). These results could be understood with a simple vibrationally adiabatic electrostatic theory, making this system convenient for studies of the isomerization chemistry.

    Science, this issue p. 175; see also p. 148

  11. Chemical Physics

    The “hole” story of water ionization

    1. Yury Suleymanov

    The direct observation of the cationic hole H2O+ that is formed in liquid water after ionization has been a long-standing experimental challenge. Previous attempts using optical and ultraviolet techniques have failed to reveal its key spectroscopic signature during ultrafast transformation into a OH radical. Loh et al. address this gap by using intense, ultrafast x-ray pulses from an x-ray free electron laser at ∼530 electron volts. They found compelling evidence for the formation H2O+ and its decay to an OH radical by a proton transfer mechanism and elucidated the other fastest–time scale steps in the early-time dynamics of ionized liquid water.

    Science, this issue p. 179

  12. Topological Matter

    Reaching a conductance plateau

    1. Jelena Stajic

    The surface of the iron-based superconductor FeTe0.55Se0.45 satisfies the necessary conditions to support topological superconductivity. Under the application of a magnetic field, vortices with zero-bias peaks that are consistent with Majorana bound states have been observed. Using scanning tunneling spectroscopy, Zhu et al. studied the conductance of these states as the tip-sample distance was reduced (see the Perspective by Sau). The researchers found that the value of the conductance increased and eventually saturated. For one of the vortices they studied, the conductance reached a quantized value that is characteristic of the Majorana bound states.

    Science, this issue p. 189; see also p. 145

  13. Developmental Biology

    Apoptosis prevents left-right crossing

    1. Beverly A. Purnell

    Animals generally display a bilateral body plan, with symmetry between the left and right sides. Maya-Ramos and Mikawa examined the mechanism that prevents the crossing of cells between sides. Using chick embryos, they show that cellular mixing between sides is prevented by a barrier at the embryonic midline that involves programmed cell death and the extracellular matrix. This work demonstrates the dependence of normal development on programmed cell death during the gastrulation stage.

    Science, this issue p. 197

  14. Signal Transduction

    A tRNA synthase in metabolic control

    1. L. Bryan Ray

    Leucyl-tRNA synthetase 1 (LARS1), which covalently couples leucine to its cognate transfer RNAs (tRNAs), appears to have broader roles in the control of leucine metabolism. The enzyme also serves as a leucine sensor for the mechanistic target of rapamycin complex 1 (mTORC1), which regulates protein synthesis, metabolism, autophagy, and cell growth. Yoon et al. show that in cells deprived of glucose, LARS1 is phosphorylated by Unc-51 like autophagy activating kinase 1 (see the Perspective by Lehman and Abraham). This phosphorylation decreases leucine binding to LARS1 and, in turn, should decrease translation, reduce activation of mTORC1, and perhaps free up leucine for use in the generation of adenosine triphosphate in glucose-starved cells.

    Science, this issue p. 205; see also p. 146

  15. Pancreatitis

    Pancreatic stress management

    1. Catherine A. Charneski

    Pancreatitis results from the premature activation of digestive enzymes in the pancreas and can be life-threatening. Hernandez et al. found pancreatic fibroblast growth factor 21 (FGF21) deficiency in three mouse models and patient biopsies of acute and chronic pancreatitis. This deficiency resulted from the activation of the integrated stress response. Accordingly, both administration of FGF21 and pharmacologic stress-response inhibition restored FGF21 and alleviated symptoms in acute and chronic models of the disease. FGF21 treatment also prevented pancreatitis onset in a model of endoscopic retrograde cholangiopancreatography, a therapeutic procedure that carries pancreatitis risk.

    Sci. Transl. Med. 12, eaay5186 (2020).

  16. Cancer

    Improving cancer screening

    1. Gemma Alderton

    National cancer screening programs, such as mammography for breast cancer, are often variably implemented such that thresholds for positivity, frequency of testing, and the types of tests used are inconsistent. Cancer screening can result in overdiagnosis and other harms. How can the optimal strategy for cancer screening be found? In a Perspective, Kalager and Bretthauer discuss how the harms of cancer screening can be balanced against the benefits by comparing the variables of screening tests in national trials as part of public health programs. These learning screening programs could improve public health by basing screening programs on current clinical data.

    Science, this issue p. 143

  17. Biodiversity

    Finding new species

    1. Sacha Vignieri

    Thousands of species have been described, and, although most may agree that many thousand remain undiscovered, identifying new taxa of charismatic vertebrates, like birds, is rare. Rheindt et al. describe five new songbird species and five new subspecies found on a single small island near Sulawesi, Indonesia, over a single 6-week expedition (see the Perspective by Kennedy and Fjeldså). They targeted the area because of its geological history and complexity and the historical notes of other explorers. They argue that similar approaches in other regions could also lead to the discovery of new species.

    Science, this issue p. 167; see also p. 140

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