This Week in Science

Science  02 Jun 2017:
Vol. 356, Issue 6341, pp. 918
  1. Coral Formation

    Building coral skeletons

    1. H. Jesse Smith

    Coral acid-rich proteins drive stony coral (Stylophora pistillata) skeleton formation.

    Among other things, corals are threatened by ocean acidification and warming. Being able to project the magnitude of these threats requires an understanding of how corals form their carbonate skeletons. Von Euw et al. combined ultrahigh-resolution three-dimensional imaging and two-dimensional solid-state nuclear magnetic resonance spectroscopy to study coral skeletons. They found that mineral precipitation in corals is a biologically controlled process mediated by organic molecules, rather than an abiotic one that depends only on physico-chemical conditions. This has important implications for the health of corals in our warmer, higher-CO2 future.

    Science, this issue p. 933

  2. Structural Biology

    A step on the path to a Lassa vaccine

    1. Valda Vinson

    Lassa fever is a severe, sometimes fatal, hemorrhagic disease. It is caused by the Lassa virus, a single-stranded RNA virus in the arenavirus family. There is no available vaccine. The only antigen on the viral surface is the glycoprotein GPC that engages host cell receptors. Hastie et al. report the high-resolution structure of the trimeric ectodomain of GPC bound to a neutralizing antibody from a human survivor of the disease. The structure gives insight into viral entry mechanisms and antibody neutralization and provides a template for vaccine design.

    Science, this issue p. 923

  3. Molecular Machines

    Coupled motion in a light-activated rotor

    1. Jake Yeston

    Macroscopic motors rely on gears to keep components in synchrony. Štacko et al. demonstrate an analogous type of coupled motion at the molecular scale (see the Perspective by Baroncini and Credi). They constructed a molecular scaffold in which light absorption drives the rotation of upper and lower fragments around a connecting double bond. At the same time, steric constraints modulate the motion of a third component that is tethered to the top of the rotor, so that it continuously exposes the same face to the bottom. The design paves the way toward more complex synchronized motion in an assembly of molecular machines.

    Science, this issue p. 964; see also p. 906

  4. Quantum Optics

    Entangle, swap, purify, repeat

    1. Ian S. Osborne

    The key to a successful quantum internet will be the ability to generate robust entanglement between distant quantum memories. Unavoidable interactions with the environment, however, generally result in the loss of entanglement. Kalb et al. describe an entanglement distillation protocol that could be used to enhance the purity and robustness of entanglement between quantum nodes of a primitive quantum network.

    Science, this issue p. 928

  5. Geophysics

    Methane takes the quick way out

    1. Brent Grocholski

    Accounting for all the sources and sinks of methane is important for determining its concentration in the atmosphere. Andreassen et al. found evidence of large craters embedded within methane-leaking subglacial sediments in the Barents Sea, Norway. They propose that the thinning of the ice sheet at the end of recent glacial cycles decreased the pressure on pockets of hydrates buried in the seafloor, resulting in explosive blow-outs. This created the giant craters and released large quantities of methane into the water above.

    Science, this issue p. 948

  6. Signal Transduction

    Local specificity of growth signals

    1. L. Bryan Ray

    The mechanistic target of rapamycin complex 1 (mTORC1) regulates cell growth in response to nutrients. Marat et al. found that the lipid phosphatidylinositol 3,4-bisphosphate [PI(3,4)P2], which, when generated at the cell surface, is linked to stimulation of mTORC1 and promotion of cell growth, does the opposite when synthesized at the late endosome or lysosome. In cells deprived of nutrients, PI(3,4)P2 was produced at lysosomes, where it recruited an inhibitor of mTORC1. The results elucidate the complex regulation of mTORC1, which is altered in human diseases such as cancer and neurodegeneration.

    Science, this issue p. 968

  7. HIV Clinical Trials

    Vaginal microbiome influences HIV acquisition

    1. Priscilla N. Kelly

    Gardnerella vaginalis can hinder tenofovir's efficacy in HIV prophylaxis.

    PHOTO: STEM JEMS/GETTY IMAGES

    Tenofovir is a preexposure drug used to prevent HIV infection. In clinical trials, tenofovir was effective for men, but not women. Klatt et al. now show that tenofovir efficacy in women depends on the composition of the vaginal microbiome (see the Perspective by Tuddenham and Ghanem). In a clinical trial of 688 women, tenofovir was three times as effective among those with a Lactobacillus-dominant vaginal microbiome as it was among other women. Gardnerella vaginalis tended to predominate in the women for whom tenofovir was less effective, and the authors found that the organism could rapidly metabolize and thereby inactivate the drug.

    Science, this issue p. 938; see also p. 907

  8. Climatology

    Human impacts on rainfall distribution

    1. Kip Hodges

    Changes in precipitation patterns could disrupt agricultural productivity. On the basis of paleoclimatic records, Putnam and Broecker argue that future rainfall patterns will change in response to human-induced global warming. Especially alarming is the suggestion that the effects will differ from one season to the next. During summers, for example, regions that are now wet will become wetter, and regions that are now dry will become drier. During northern winters, rain belts and drylands will expand northward. Thus, climate change projections need to be taken into account when evaluating future freshwater resources on a global scale.

    Sci. Adv. 10.1126/sciadv.1600871 (2017).

  9. Cancer

    No escape for KRAS mutant tumors

    1. Yevgeniya Nusinovich

    RAS mutant tumors are usually resistant to PARP inhibitors, one of the newest classes of anticancer therapeutics. Sun et al. discovered that inhibition of MEK or ERK (proteins in the RAS pathway) reversed PARP inhibitor resistance in KRAS mutant tumors in mouse models of aggressive tumors such as ovarian and pancreatic cancer. Because MEK and PARP inhibitors are clinically approved drugs, they provide a readily translatable therapeutic combination to treat human cancer patients.

    Sci. Transl. Med. 9, eaal5148 (2017).

  10. Evolutionary Genomics

    Loss of flight in the Galapagos cormorant

    1. Laura M. Zahn

    Although rare among existing birds, the loss of flight appears to have occurred multiple times in evolutionary history. However, the genetic changes that ground avian species are not well understood. Burga et al. sequenced genomes from three cormorant species and compared them with that of the flightless Galapagos cormorant (see the Perspective by Cooper). They identified variants in genes involved in primary ciliogenesis. Functional analyses of these variants suggest that the impaired function of the genes may be responsible for skeletal changes associated with the Galapagos cormorant’s loss of flight.

    Science, this issue p. eaal3345; see also p. 904

  11. Martian Geology

    The depths of an ancient lake on Mars

    1. Keith T. Smith

    Gale crater on Mars was once a lake fed by rivers and groundwater. Hurowitz et al. analyzed 3.5 years of data from the Curiosity rover’s exploration of Gale crater to determine the chemical conditions in the ancient lake. Close to the surface, there were plenty of oxidizing agents and rocks formed from large, dense grains, whereas the deeper layers had more reducing agents and were formed from finer material. This redox stratification led to very different environments in different layers, which provides evidence for Martian climate change. The results will aid our understanding of where and when Mars was once habitable.

    Science, this issue p. eaah6849

  12. Quantum Gases

    Detecting unusual oscillations

    1. Jelena Stajic

    Under the influence of a constant force, an electron in the periodic potential of a crystal lattice undergoes so-called Bloch oscillations. The same phenomenon has been seen with ultracold atoms in optical lattices, but it is not expected to occur in a uniform system. Meinert et al. observed Bloch oscillations of an impurity atom in one-dimensional tubes of strongly interacting cesium atoms—a system without built-in periodicity. Owing to the strong interactions, the bosonic atoms stayed away from one another, forming an effective lattice. The researchers observed reflections of the impurity atoms of this effective lattice in momentum space, with the lattice constant corresponding to the interatomic distance of the host gas.

    Science, this issue p. 945

  13. Optics

    Localizing light at the nanometer scale

    1. Ian S. Osborne

    Waves will propagate through a medium until scattering processes result in the excitation gradually dying away. Introducing disorder can affect that propagation by increasing the scattering, potentially reaching a point where transport is stopped. Typically, the length scale of the disorder is larger than the propagating waves. Herzig Sheinfux et al. now show that a stack of several-nanometer-thick layers of alternating high- and low-refractive-index material can result in the localization of light. Such deep-subwavelength structures could provide a route to manipulating light on the nanometer scale.

    Science, this issue p. 953

  14. Magnetospheres

    Probing the structure of the magnetopause

    1. Keith T. Smith

    The magnetopause is the boundary in space that separates the region dominated by Earth’s magnetic field (the magnetosphere) from the surrounding solar wind. The four spacecraft of NASA’s Magnetospheric Multiscale (MMS) mission have repeatedly flown in formation through the magnetopause, measuring the properties of the plasma and magnetic fields in the region. Russell et al. used MMS measurements to study the magnetopause’s structure and force balance. They identified small-scale dynamic features that form a complex topology and evidence for magnetic flux ropes at the boundary. The results aid our understanding of Earth’s space environment and magnetospheres around other planets.

    Science, this issue p. 960

  15. Organic Synthesis

    A versatile synthesis of pleuromutilin

    1. Jake Yeston

    Synthetic flexibility is crucial for antibiotic development, because numerous subtle structural variations can contribute to combating resistant strains. A derivative of the fungal natural product pleuromutilin was approved a decade ago for treatment of Gram-positive bacterial skin infections; recent efforts to tune the structure for activity against Gram-negative bacteria have focused on the stereochemistry at a particular carbon center. Murphy et al. present a synthetic route to pleuromutilin that allows the configurations in that segment of the molecule to be varied, offering a distinct path for structural optimization.

    Science, this issue p. 956

  16. Climate

    Will ice sheets collapse in West Antarctica?

    1. Julia Fahrenkamp-Uppenbrink

    The West Antarctic ice sheet is highly vulnerable to climate warming, raising the specter of substantial sea level rise. In a Perspective, Hulbe examines whether collapse of the ice sheet is inevitable. Models suggest that if the world can rein in fossil fuel emissions and follow a low-emissions pathway, the ice sheet’s retreat may stop. However, the models are incomplete, particularly regarding the ocean cavity under the floating ice. Observational and model studies are under way to further elucidate how warmer water circulating under the ice shelf could destabilize the ice sheet, even under low-emission conditions.

    Science, this issue p. 910

  17. Innate Immunity

    Differentiating myeloid cells

    1. Angela Colmone

    Hematopoietic stem cells are a common progenitor of adaptive and innate immune cells. However, the precise factors that guide differentiation down these disparate pathways remain unclear, in part owing to difficulties in working with small numbers of precursor cells. Lee et al. solve this problem for myeloid lineage cells by immortalizing murine myeloid progenitors with conditionally overexpressed Hoxb8 and labeling these cells with a Ccr2/ Cx3cr1 dual reporter. They found through a small-molecule library screen and confirmatory in vivo validation that the mTORC1-S6K1-Myc pathway regulates myeloid differentiation. Disrupting this pathway in progenitors results in a lack of monocytes and neutrophils. Hence, the mTORC1-S6K1-Myc pathway functions as a checkpoint in terminal myeloid differentiation.

    Sci. Immunol. 2, eaam6641 (2017).