This Week in Science

Science  25 Mar 2016:
Vol. 351, Issue 6280, pp. 1411
  1. Magnetohydrodynamics

    Simulating turbulent solar magnetic fields

    1. Keith T. Smith

    An example of one of the solar magnetic field simulations

    CREDIT: HIDEYUKI HOTTA/CHIBA UNIVERSITY

    An accurate simulation of solar magnetic fields must reproduce both the large-scale dynamo and small-scale turbulence. Simply increasing the computational resolution does not always help, because it can prevent the 11-year solar cycle from emerging. Hotta et al. show how both large- and small-scale phenomena can be reproduced in some of the highest-resolution simulations yet available. This will improve our understanding of both the solar magnetic field and other turbulent magnetohydrodynamic systems.

    Science, this issue p. 1427

  2. C–H Bond Activation

    Methane borylation in a cyclohexane sea

    1. Jake Yeston

    Although methane combusts readily at high temperatures, it is generally the hardest hydrocarbon to transform under gentler conditions, owing to its particularly strong C–H bonds. Cook et al. now show that soluble rhodium, iridium, and ruthenium catalysts can slice through these C–H bonds to add boron substituents to methane at 150°C. Smith et al. report the iridium-catalyzed reaction using phosphine ligands to enhance activity. Both studies were performed in cyclohexane solvent, revealing a remarkable selective preference for the methane reaction over functionalization of the cyclic hydrocarbon.

    Science, this issue pp. 1421 and 1424

  3. Solar Cells

    Perovskite solar cells recycle photons

    1. Phil Szuromi

    Inorganic-organic perovskite solar cells are very efficient in part because the charge carriers exhibit very long path lengths. Pazos-Outón et al. show that photon recycling, as seen previously in highly efficient gallium arsenide solar cells, contributes to this effect (see the Perspective by Yablonovitch). In most solar cells, the recombination of photogenerated charge carriers (electrons and holes) wastes all of the energy. In these lead tri-iodide cells, recombination emits a photon that can be reabsorbed and create more charge carriers.

    Science, this issue p. 1430; see also p. 1401

  4. Structural Biology

    A human spliceosomal subcomplex

    1. Guy Riddihough

    The spliceosome is an RNA and protein molecular machine that cuts out introns from messenger RNAs. Agafonov et al. used cryo-electron microscopy to determine the structure of the largest intermediate subcomplex on the assembly pathway for the human spliceosome (see the Perspective by Cate). The structure shows substantial differences from the equivalent yeast complex. It also reveals how the subcomplex must dock onto the rest of the spliceosome and hints at the structural changes the complex must go through to form the mature spliceosome.

    Science, this issue p. 1416; see also p. 1390

  5. Economics

    Another social science looks at itself

    1. Gilbert Chin

    Experimental economists have joined the reproducibility discussion by replicating selected published experiments from two top-tier journals in economics. Camerer et al. found that two-thirds of the 18 studies examined yielded replicable estimates of effect size and direction. This proportion is somewhat lower than unaffiliated experts were willing to bet in an associated prediction market, but roughly in line with expectations from sample sizes and P values.

    Science, this issue p. 1433

  6. Memory Formation

    Coding what is known and what is new

    1. Peter Stern

    Do neural activity patterns during sleep reflect the replay of a novel experience or an invariant preexisting dynamic? Grosmark and Buzsáki observed that both familiar and novel aspects of learned information are replayed during synchronous bursts of activity in the hippocampus. Familiarity was encoded by fast-firing less-modifiable neurons that showed rate and sequence correlations that persisted into postlearning sleep. The novel features of an experience were represented by a different set of slowly firing and highly plastic cells.

    Science, this issue p. 1440

  7. Cloud Formation

    Organic contributions to cloud theory

    1. H. Jesse Smith

    Current theories about the formation of cloud droplets from aerosol particles containing organic components assume that the organic molecules are distributed throughout the droplet. Ruehl et al. show that this assumption is not always correct (see the Perspective by Noziere). During droplet nucleation, droplet diameters were 50% larger than predicted by the standard model. This suggests that the organic particles reside in a surface layer rather than in the bulk of the droplet. Models that neglect organic surface activity will thus underestimate how well organic-rich particles seed clouds.

    Science, this issue p. 1447; see also p. 1396

  8. Tumor Immunology

    The cellular ancestry of tumor antigens

    1. Paula A. Kiberstis

    Tumors contain cells expressing a variety of novel antigens

    CREDIT: MCGRANAHAN ET AL..

    One contributing factor in antitumor immunity is the repertoire of neoantigens created by genetic mutations within tumor cells. Like the corresponding mutations, these neoantigens show intratumoral heterogeneity. Some are present in all tumor cells (clonal), and others are present in only a fraction of cells (subclonal). In a study of lung cancer and melanoma, McGranahan et al. found that a high burden of clonal tumor neoantigens correlated with improved patient survival, an increased presence of tumor-infiltrating lymphocytes, and a durable response to immunotherapy.

    Science, this issue p. 1463

  9. Cancer

    The spread of bad neighborhoods

    1. Guy Riddihough

    Our genomes have complex three-dimensional (3D) arrangements that partition and regulate gene expression. Cancer cells frequently have their genomes grossly rearranged, disturbing this intricate 3D organization. Hnisz et al. show that the disruption of these 3D neighborhoods can bring oncogenes under the control of regulatory elements normally kept separate from them (see the Perspective by Wala and Beroukim). These novel juxtapositions can result in the inappropriate activation of oncogenes.

    Science, this issue p. 1454; see also p. 1398

  10. Forest Ecosystems

    Forest recovery in China is not so clear cut

    1. Shahid Naeem

    Frequently in developing nations, forests shrink as trees are cut and agriculture expands. This trend does not tend to reverse until significant economic development and urbanization occur. Viña et al. used remote sensing and analytical models to show that heavily deforested regions in China experienced regrowth between 2000 and 2010 in spite of China's status as a developing nation. The key to this success was China's strong conservation policies. Despite this, densely forested regions still shrank, and forest growth may have come at the expense of forests shrinking elsewhere.

    Sci. Adv. 2 10.1126.sciadv.00965 (2016).

  11. Synthetic Biology

    Designing and building a minimal genome

    1. Valda Vinson

    A goal in biology is to understand the molecular and biological function of every gene in a cell. One way to approach this is to build a minimal genome that includes only the genes essential for life. In 2010, a 1079-kb genome based on the genome of Mycoplasma mycoides (JCV-syn1.0) was chemically synthesized and supported cell growth when transplanted into cytoplasm. Hutchison III et al. used a design, build, and test cycle to reduce this genome to 531 kb (473 genes). The resulting JCV-syn3.0 retains genes involved in key processes such as transcription and translation, but also contains 149 genes of unknown function.

    Science, this issue p. 10.1126/science.aad6253

  12. Transporter Function

    A proton pump in action

    1. Valda Vinson

    P-type adenosine triphosphatases (ATPases) use the energy from ATP hydrolysis to pump cations across biological membranes. The electrochemical gradients that are generated control many essential cellular processes. Veshaguri et al. incorporated a plant proton pump into vesicles and monitored the dynamics of single pumps. Pumping was stochastically interrupted by long-lived inactive or leaky states. The work reveals how these proton pumps are regulated by a protein domain and by pH gradients.

    Science, this issue p. 1469

  13. Physiological Ecology

    Variability for a day or a season

    1. Sacha Vignieri

    Species that experience larger seasonal climatic fluctuations are likely to be more physiologically flexible and thus likely to occur across a wider elevational range. Daily changes in temperature are also common but have rarely been considered. Chan et al. used a global data set of vertebrates to look at how these two different sets of variation affect a species' elevational distribution (see the Perspective by Perez et al.). Unexpectedly, larger daily fluctuations were associated with smaller elevational distributions. Thus, specialists are favored where daily fluctuations are dominant, whereas generalists are favored where seasonal fluctuations are the main climate influence.

    Science, this issue p. 1437; see also p. 1392

  14. Protein Evolution

    Variation and transcription factor binding

    1. Laura M. Zahn

    Little is known about the phenotypic and functional effects of genetic variants that result in amino acid changes within functional proteins. Barrera et al. investigated whether amino acid variants changed the DNA binding specificity or affinity of transcription factors. Predictive analyses identified changes in the proteins, and protein-binding microarrays verified changes that affected transcription factor function, including those associated with disease. Thus, within-human protein sequence variation can affect transcriptional regulatory networks, which, depending on the genetic variant, may confer robustness and buffer against amino acid changes and could explain phenotypic variation among individuals.

    Science, this issue p. 1450

  15. DFT Methods

    A comparison of DFT methods

    1. Marc S. Lavine

    Density functional theory (DFT) is now routinely used for simulating material properties. Many software packages are available, which makes it challenging to know which are the best to use for a specific calculation. Lejaeghere et al. compared the calculated values for the equation of states for 71 elemental crystals from 15 different widely used DFT codes employing 40 different potentials (see the Perspective by Skylaris). Although there were variations in the calculated values, most recent codes and methods converged toward a single value, with errors comparable to those of experiment.

    Science, this issue p. 10.1126/science.aad3000; see also p. 1394

  16. HIV-1 Vaccines

    Baby steps toward bNAbs

    1. Kristen L. Mueller

    Some HIV-infected individuals develop heavily mutated, broadly neutralizing antibodies (bNAbs) that target HIV. Scientists aim to design vaccines that would elicit such antibodies. Jardine et al. report an important step toward this goal: They engineered an immunogen that could engage B cells from HIV-uninfected individuals that express the germline versions of the immunoglobulin genes harbored by a particular class of bNAbs. The frequencies of these B cells, their affinities for the immunogen, and structural analysis suggest that the immunogen is a promising candidate. Further shaping of the B cell response with subsequent immunogens may eventually elicit bNAbs in people.

    Science, this issue p. 1458

  17. Neurodevelopment

    Tracking neuronal transcriptional programs

    1. Pamela J. Hines

    Early in brain development, cortical neurons are born near the ventricles, then migrate to their functional destinations. Telley et al. used a fluorescent labeling technique to see what transcripts characterize these earliest stages of neural development. Waves of transcriptional programs are initiated, then passed by as the neuron progresses from proliferative to migratory and finally to connectivity phases.

    Science, this issue p. 1443

  18. Cardiovascular Biology

    A GRK2 peptide prevents heart failure

    1. Wei Wong

    During cardiac hypertrophy, sustained high blood pressure causes the heart walls to thicken to deal with the increased load. If left unchecked, cardiac hypertrophy leads to heart failure. A particular part of the kinase and scaffolding protein GRK2 inhibits a G protein that promotes cardiac hypertrophy. Schumacher et al. generated mice that overexpressed a peptide of this inhibitory region of GRK2 in the heart. Under conditions that cause heart failure, these mice developed less cardiac hypertrophy and retained greater cardiac function.

    Sci. Signal. 9, ra30 (2016).

  19. Autoimmunity

    A glucose balancing act

    1. Angela Colmone

    In autoimmune diseases, T cells engage their hyperdrive, both proliferating and secreting inflammatory cytokines at greater rates than normal. Little is known about the metabolic changes that fuel this process. Yang et al. report that a defect in reactive oxygen species (ROS) could boost proinflammatory T cells in rheumatoid arthritis. A defect in glycolytic flux led to increased ROS consumption, which bypassed a cell cycle checkpoint and contributed to hyperproliferation and proinflammatory cell differentiation. What's more, restoring intracellular ROS reduced proliferation and suppressed inflammation.

    Sci. Transl. Med. 8, 331ra38 (2016).

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