This Week in Science

Science  13 Apr 2018:
Vol. 360, Issue 6385, pp. 166
  1. Carbon Cycle

    Microbes eat rocks and leave carbon dioxide

    1. H. Jesse Smith

    Microbes oxidize most of the petrogenic organic carbon in Taiwan's fast-eroding Central Range.

    CREDIT: WENILIOU/SHUTTERSTOCK

    The reaction of atmospheric carbon dioxide (CO2) with silicate rocks provides a carbon sink that helps counterbalance the release of CO2 by volcanic degassing. However, some types of rocks contain petrogenic organic carbon, the oxidation of which adds CO2 to the atmosphere, counteracting the drawdown by silicates. Hemingway et al. present evidence from the rapidly eroding Central Range of Taiwan showing that microbes oxidize roughly two-thirds of the petrogenic organic carbon there and that the rate of oxidation increases with the rate of erosion.

    Science, this issue p. 209

  2. Quantum Information

    Scaling up to supremacy

    1. Jelena Stajic

    Quantum information scientists are getting closer to building a quantum computer that can perform calculations that a classical computer cannot. It has been estimated that such a computer would need around 50 qubits, but scaling up existing architectures to this number is tricky. Neill et al. explore how increasing the number of qubits from five to nine affects the quality of the output of their superconducting qubit device. If, as the number of qubits grows further, the error continues to increase at the same rate, a quantum computer with about 60 qubits and reasonable fidelity might be achievable with current technologies.

    Science, this issue p. 195

  3. Organic Chemistry

    A guide for catalyst choice in the forest

    1. Jake Yeston

    Chemists often discover reactions by applying catalysts to a series of simple compounds. Tweaking those reactions to tolerate more structural complexity in pharmaceutical research is time-consuming. Ahneman et al. report that machine learning can help. Using a high-throughput data set, they trained a random forest algorithm to predict which specific palladium catalysts would best tolerate isoxazoles (cyclic structures with an N–O bond) during C–N bond formation. The predictions also helped to guide analysis of the catalyst inhibition mechanism.

    Science, this issue p. 186

  4. Plant Science

    Dormancy by communication shutdown

    1. Pamela J. Hines

    Trees become dormant in winter, with encapsulated buds protected against harsh conditions. Tylewicz et al. found that, as the days get shorter, communication channels between cells in aspen trees shut down. The blocked plasmodesmata sequester the dormant meristems from growth signals. Growth-promoting signals can be turned on and off relatively rapidly, but the closed plasmodesmata are not so nimble. Thus, despite the occasional sunny day, the trees stay dormant until spring.

    Science, this issue p. 212

  5. Norovirus

    Aiding and abetting norovirus disease

    1. Caroline Ash

    Norovirus is highly infectious and usually causes transient, acute disease. In some individuals, norovirus persists and is associated with inflammatory bowel disorders. While investigating the cell tropism for murine norovirus, Wilen et al. discovered that a rare cell type, tuft cells, carrying the CD300lf receptor were the virus's specific target. Tuft cells proliferate in response to the type 2 cytokines interleukin-4 and interleukin-25, which thereby amplify norovirus infection. Moreover, infected tuft cells are resistant to immune clearance. This effect may explain the associated persistent disease symptoms that humans can suffer.

    Science, this issue p. 204

  6. Metrology

    Refining the fine-structure constant

    1. Ian S. Osborne

    The fine-structure constant, α, is a dimensionless constant that characterizes the strength of the electromagnetic interaction between charged elementary particles. Related by four fundamental constants, a precise determination of α allows for a test of the Standard Model of particle physics. Parker et al. used matter-wave interferometry with a cloud of cesium atoms to make the most accurate measurement of α to date. Determining the value of α to an accuracy of better than 1 part per billion provides an independent method for testing the accuracy of quantum electrodynamics and the Standard Model. It may also enable searches of the so-called “dark sector” for explanations of dark matter.

    Science, this issue p. 191

  7. Structural Biology

    The RNA exosome captured in action

    1. Steve Mao

    The RNA exosome, a major RNA degradation machine, processes ribosomal RNA (rRNA) precursors and is directly coupled to the protein synthesis machine, the ribosome. Using cryo–electron microscopy, Schuller et al. investigated the structure of the precursor large ribosomal subunit from yeast with unprocessed rRNA in complex with the RNA exosome. The structure captures a snapshot of two molecular machines transiently interacting and explains how the RNA exosome acts on an authentic physiological substrate and remodels the large subunit during ribosome maturation.

    Science, this issue p. 219

  8. Paleontology

    Early evolution of insect scales

    1. Philippa J. Benson

    Organisms use tiny structures on their surfaces to produce striking optical effects. The wing scales of butterflies and moths exhibit some of the most diverse physical colors produced by insects, but whether they have always been equipped with photonic structures is unknown. Zhang et al. used fossil evidence to establish that these insects possessed color-eliciting structures at least 130 million years earlier than previously thought. They determined the ultrastructure of wing scales from Jurassic Lepidoptera and mid-Cretaceous Tarachoptera. They then used optical modeling to reconstruct the colors that these features would produce.

    Sci. Adv. 10.1126/sciadv.1700988 (2018).

  9. HIV

    Zooming in on human lymph nodes

    1. Anand Balasubramani

    Follicular helper T cells (TFH) play an essential role in shaping B cell–mediated antibody responses. Wendel et al. used mass cytometry and T cell receptor sequencing to examine the TFH response in lymph node tissue collected from HIV+ individuals. HIV infection altered the clonality of TFH cells, with severe infections associating with pronounced oligoclonal TFH responses. TFH cells in the lymph nodes of HIV+ individuals secreted interleukin-21 but were less polyfunctional than TFH cells from healthy individuals. The lack of polyfunctionality correlated with impaired isotype switching of B cells in the lymph nodes.

    Sci. Immunol. 3, eaan8884 (2018).

  10. Synthetic Biology

    Writing a cell's history in its DNA

    1. Steve Mao

    Recording cellular events could advance our understanding of cellular history and responses to stimuli. The construction of intracellular memory devices, however, is challenging. Tang and Liu used Cas9 nucleases and base editors to record amplitude, duration, and order of stimuli as stable changes in both genomic and extrachromosomal DNA content (see the Perspective by Ho and Bennett). The recording of multiple stimuli—including exposure to antibiotics, nutrients, viruses, and light, as well as Wnt signaling—was achieved in living bacterial and human cells. Recorded memories could be erased and re-recorded over multiple cycles.

    Science, this issue p. eaap8992; see also p. 150

  11. Cell Biology

    The mitoCPR unclogs mitochondria

    1. Stella M. Hurtley

    The import of proteins into mitochondria is essential for cell viability. How cells respond when mitochondrial protein import is impaired is poorly understood. Weidberg and Amon showed that upon mitochondrial import stress, yeast cells mounted a response known as the mitoCPR. mitoCPR was activated when mitochondrial protein import was impaired and unimported precursors accumulated on the organelle's surface. mitoCPR restored mitochondrial functions by clearing stalled proteins from the import channels. It did this by inducing expression of Cis1, which recruited the adenosine triphosphatase Msp1 to import channels to remove unimported precursors and target them for degradation by the proteasome.

    Science, this issue p. eaan4146

  12. Population Biology

    Quantitative analysis of millions of relatives

    1. Laura M. Zahn

    Human relationships, as documented by family trees, can elucidate the heritability of a host of medical and biological parameters. Kaplanis et al. collected 86 million publicly available profiles from a crowd-sourced genealogy website and used them to examine the genetic architecture of human longevity and migration patterns (see the Perspective by Lussier and Keinan). Various models of inheritance suggested that life span is predominantly attributable to additive genetic effects, with a smaller component from dominant genetic inheritance. The data also suggested that relatedness between individuals is less attributable to advances in human transportation than to cultural changes.

    Science, this issue p. 171; see also p. 153

  13. Topological Matter

    A topological superconductor

    1. Jelena Stajic

    A promising path toward topological quantum computing involves exotic quasiparticles called the Majorana bound states (MBSs). MBSs have been observed in heterostructures that require careful nanofabrication, but the complexity of such systems makes further progress tricky. Zhang et al. identified a topological superconductor in which MBSs may be observed in a simpler way by looking into the cores of vortices induced by an external magnetic field. Using angle-resolved photoemission, the researchers found that the surface of the iron superconductor FeTe0.55Se0.45 satisfies the required conditions for topological superconductivity.

    Science, this issue p. 182

  14. Single-Cell Genomics

    Identifying single-cell types in the mouse brain

    1. Laura M. Zahn

    The recent development of single-cell genomic techniques allows us to profile gene expression at the single-cell level easily, although many of these methods have limited throughput. Rosenberg et al. describe a strategy called split-pool ligation-based transcriptome sequencing, or SPLiT-seq, which uses combinatorial barcoding to profile single-cell transcriptomes without requiring the physical isolation of each cell. The authors used their method to profile >100,000 single-cell transcriptomes from mouse brains and spinal cords at 2 and 11 days after birth. Comparisons with in situ hybridization data on RNA expression from Allen Institute atlases linked these transcriptomes with spatial mapping, from which developmental lineages could be identified.

    Science, this issue p. 176

  15. Structural Biology

    A close-up view of oligosaccharyltransferase

    1. Stella M. Hurtley

    Many secretory and membrane proteins are modified through the attachment of sugar chains by N-glycosylation. Such modification is required for correct protein folding, targeting, and functionality. In mammalian cells, N-glycosylation is catalyzed by the oligosaccharyltransferase (OST) complex via its STT3 subunit. OST forms a complex with the ribosome and the Sec61 protein translocation channel. Braunger et al. combined cryo–electron microscopy approaches to visualize mammalian ribosome-Sec61-OST complexes in order to build an initial molecular model for mammalian OST.

    Science, this issue p. 215

  16. Immunology

    Autoantibody redemption through rapid mutations

    1. Seth Thomas Scanlon

    Antibodies distinguish foreign epitopes from closely related self-antigens by poorly understood mechanisms. In mice, Burnett et al. found that a proportion of B cells could cross-react with similar foreign and self-antigens (see the Perspective by Kara and Nussenzweig). Challenge with self-antigen resulted in anergy (i.e., a lack of immune response), which was reversed by exposure to high-density foreign antigen. Mutations that decreased self-affinity were rapidly selected for, whereas selection for epistatic mutations that enhanced foreign reactivity took longer. Self-reactivity, rather than being an impediment to immunization, resulted in higher affinities against a foreign immunogen.

    Science, this issue p. 223; see also p. 152

  17. Climate

    Climate effects of aerosol cleanup

    1. Julia Fahrenkamp-Uppenbrink

    Many aerosols emitted by human activities have a cooling effect on the climate and can also change precipitation patterns. In a Perspective, Samset highlights the magnitude of these influences at regional levels. Worldwide, aerosols have reduced the impacts of greenhouse gas emissions on air temperatures. Impacts on precipitation have also been substantial but more variable. Because of the negative impacts of aerosol emissions on health, efforts to reduce them are gathering pace, but this has important implications for future warming and precipitation patterns in many regions of the world.

    Science, this issue p. 148

  18. Cancer

    Can wound healing worsen metastasis?

    1. Lindsey Pujanandez

    Early metastatic recurrence in breast cancer patients could be caused by tumor cells released into the circulation during primary resection or could be the result of existing metastatic outgrowth. To distinguish between these possibilities, Krall et al. used a common wound-healing model in mice harboring breast cancer cells in which the primary tumor bed was not disturbed by surgery. They found that T cells can keep tumor cells in check, but if wound healing is induced, inflammation disrupts this balance. Anti-inflammatory treatment reduced metastasis in the mice. Existing clinical data indicate that perioperative anti-inflammatories reduce early metastatic recurrence in breast cancer patients. By separating surgery from resection, these results may explain this curious clinical occurrence.

    Sci. Transl. Med. 10, eaan3464 (2018).

  19. Structural Biology

    Signaling for nitrogen fixation

    1. Annalisa M. VanHook

    The nitrogen-fixing bacterium Bradyrhizobium japonicum enables high-yield production of soybeans with little use of nitrogen fertilizers, a major source of nutrient pollution. Using structural and modeling techniques, Wright et al. generated a model by which a two-component system of this bacterium, comprising the histidine kinase sensor and response regulator, responds to low oxygen to stimulate the expression of genes required for nitrogen fixation. These results may help in the development of plant growth modulators that are unlikely to affect mammalian species, which do not signal through two-component systems.

    Sci. Signal. 11, eaaq0825 (2018).

  20. Nanomaterials

    Synthesizing graphene nanopores

    1. Phil Szuromi

    Nanosize pores in graphene can make its electronic properties more favorable for transistor applications and may also be useful for molecular separations. Moreno et al. used Ullmann coupling to polymerize a dibromo-substituted diphenylbianthracene on a gold surface (see the Perspective by Sinitskii). Cyclodehydrogenation of the resulting polymer produced graphene nanoribbons, and cross-coupling of these structures created a nanoporous graphene sheet with pores sizes of about 1 nanometer. Scanning tunneling spectroscopy revealed an electronic structure in which semiconductor bands with an energy gap of 1 electron volt coexist with localized states created by the pores.

    Science, this issue p. 199; see also p. 154

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