This Week in Science

Science  18 Dec 2015:
Vol. 350, Issue 6267, pp. 1487
  1. Tropical Ecosystems

    Faunal loss reduces tropical forest carbon

    1. Thomas E. Lovejoy

    Large frugivores, like these Seychelles flying foxes, are important for tropical forest carbon storage

    PHOTO: © BLICKWINKEL/ALAMY STOCK PHOTO

    Losing large fruit-eating animals from tropical forests disproportionally affects carbon stocks. Bello et al. modeled the loss of carbon associated with large tropical trees that depend on large vertebrates for seed dispersal and regeneration. As well as reducing deforestation and promoting reforestation, key ecological interactions need to be taken into account to achieve full tropical forest carbon storage.

    Sci. Adv. 10.1126.sciadv.1501105 (2015).

  2. Marine Calcifers

    Passing an acid test

    1. H. Jesse Smith

    Calcifying marine organisms will generally find it harder to make and maintain their carbonate skeletons as increasing concentrations of atmospheric CO2 acidify the oceans. Nevertheless, some types of organisms will be damaged more than others, and some may even benefit from higher CO2 levels. Coccolithophores are a case in point, because their photosynthetic ability is strongly carbon-limited. Rivero-Calle et al. show that the abundance of coccolithophores in the North Atlantic has increased by up to 20% or more in the past 50 years (see the Perspective by Vogt). Thus, this major phytoplankton functional group may be able to adapt to a future with higher CO2 concentrations.

    Science, this issue p. 1533; see also p. 1466

  3. Graft Rejection

    Friendly fire from organ failure

    1. Angela Colmone

    These days organ transplantation may seem like a routine procedure, but rejection of the donated organ still poses a substantial risk. Autoantibodies contribute to rejection, but how these autoantibodies are generated remains unclear. Dieudé et al. found that exosome-like vesicles derived from apoptotic endothelial cells stimulated autoantibody production in mice, which increased graft rejection. These vesicles contained active 20S proteasome core complexes; proteasome inhibition decreased both vesicle immunogenicity and graft rejection in transplanted mice.

    Circulating exosome-like vesicles and increased anti-autoantibody titers were also observed in mouse models of vascular injury, suggesting that the same organ failure that necessitates the transplant might increase the risk of rejection.

    Sci. Transl. Med.7, 318ra200 (2015).

  4. Energy Storage

    Store more energy with a touch of nitrogen

    1. Marc S. Lavine

    In contrast to batteries, capacitors typically can store less power, but they can capture and release that power much more quickly. Lin et al. fabricated a porous carbon material that was then doped with nitrogen. This raised the energy density of the carbon more than threefold—an increase that was retained in full capacitors, without losing their ability to deliver power quickly.

    Science, this issue p. 1508

  5. Ultrafast Dynamics

    The making of a molecular movie

    1. Jelena Stajic

    Phase transitions familiar from everyday life, such as boiling or melting, are caused by changing the temperature. In the laboratory, however, researchers can also change the phase of a material by shining intense light on it. During such transitions, changes occur in both the electronic and lattice structure of the material. Ishikawa et al. used ultrafast optical and electron diffraction probes to monitor both types of change simultaneously during a photo-induced phase transition in a molecular crystal. The resulting molecular movies showed expansion of the intermolecular distance, flattening of the molecules, and tilting of molecular dimers.

    Science, this issue p. 1501

  6. Genomic Evolution

    Cichlids diverge within a crater lake

    1. Laura M. Zahn

    It is not clear how populations diversify and new species form at the genomic level, especially when they coexist in the same location. Malinsky et al. investigated how two ecomorphs of cichlid fish in a small lake in Tanzania are diversifying relative to each other. Although there is gene flow between the two forms, major regions of genetic divergence, known as genomic islands, separate the populations. Within these islands, the authors found genes likely to be associated with mate choice, supporting the idea that genetic changes related to breeding preferences are the first to diverge during speciation.

    Science, this issue p. 1493

  7. Neurodevelopment

    The makings of motor neuron disease

    1. Pamela J. Hines

    Astatotilapia calliptera - a cichlid fish

    PHOTO KEVIN BAUMAN

    Developing motor neurons link the muscles to the central nervous system. Amin et al. found that microRNA-218 (miR-218) was expressed in developing motor neurons and repressed a wide network of genes whose expression typifies other sorts of neurons. Mice lacking miR-218 died at birth with symptoms characteristic of human motor neuron diseases.

    Science, this issue p. 1525

  8. Ecotoxicology

    Red tides make dinner hard to find

    1. Sacha Vignieri

    Domoic acid (DA) is a neurotoxin produced by marine algae. When present in large amounts, it is harmful to marine organisms and to humans. Cook et al. tested California sea lions being treated at a marine mammal rescue facility. Animals that had evidence of exposure to DA had lesions in their hippocampus and displayed reduced performance on spatial memory tasks. Because such tasks are essential to foraging in a marine environment, increasing exposure to DA may be contributing to increasing sea lion strandings.

    Science, this issue p. 1545

  9. Membrane Remodeling

    ESCRTs work in two very different ways

    1. Stella M. Hurtley

    The so-called ESCRT proteins are involved in the budding of vesicles into the lumen of endosomes and in virus budding. These reactions involve the formation of a cytoplasm-filled neck that spirals of the ESCRTs help to seal. McCullough et al. now show that ESCRTs can also promote the scission of membrane tubules with the completely opposite topology. ESCRT-III and IST1 ESCRT subunits form spirals on the outside of membrane tubules and so can mediate the budding of tubules and vesicles into the cytosol. Relatively minor structural rearrangements were required to turn ESCRT function on its head.

    Science, this issue p. 1548

  10. Nanomaterials

    Borophene: Boron in two dimensions

    1. Phil Szuromi

    Although bulk allotropes of carbon and boron differ greatly, small clusters of these elements show remarkable similarities. Boron analogs of two-dimensional carbon allotropes such as graphene have been predicted. Now Mannix et al. report the formation of two-dimensional boron by depositing the elemental boron onto a silver surface under ultrahigh-vacuum conditions (see the Perspective by Sachdev). The graphene-like structure was buckled, weakly bonded to the substrate, and metallic.

    Science, this issue p. 1513; see also p. 1468

  11. Electron Microscopy

    Advances in seeing small things

    1. Marc S. Lavine

    Electron microscopes, particularly those with aberration correction, can view materials at the subnanometer scale. Additional improvements make it possible to obtain images at lower electron doses, thus minimizing the damage to the sample. However, for a number of materials, particularly those of biological origin, samples need to be imaged in solution. Ross reviews recent advances that have made it possible to do liquid cell electron microscopy, which opens up the possibility of studying problems such as the changes inside a battery during operation, the growth of crystals from solution, or biological molecules in their native state.

    Science, this issue p. 10.1126/science.aaa9886

  12. Structural Biology

    A channel involved in pain perception

    1. Valda Vinson

    Voltage-gated sodium (Nav) channels propagate electrical signals in muscle cells and neurons. In humans, Nav1.7 plays a key role in pain perception. It is challenging to target a particular Nav isoform; however, arylsulfonamide antagonists selective for Nav1.7 have been reported recently. Ahuja et al. characterized the binding of these small molecules to human Nav channels. To further investigate the mechanism, they engineered a bacterial Nav channel to contain features of the Nav1.7 voltage-sensing domain that is targeted by the antagonist and determined the crystal structure of the chimera bound to an inhibitor. The structure gives insight into the mechanism of voltage sensing and will enable the design of more-selective Nav channel antagonists.

    Science, this issue p. 10.1126/science.aac5464

  13. Inflammation

    Limiting inflammation in obesity

    1. John F. Foley

    Obese individuals have increased circulating levels of inflammatory cytokines produced by adipose tissue macrophages. Velmurugan et al. found that adipose tissue macrophages from obese mice had decreased levels of the gasotransmitter H2S, increased calcium signaling, and increased production of proinflammatory cytokines. H2S inhibited a calcium channel, which resulted in reduced calcium entry into macrophages. Thus, inflammatory stimuli lead to the depletion of H2S in adipose tissue, which exacerbates inflammatory responses by resident adipose tissue macrophages.

    Sci. Signal. 8, ra128 (2015).

  14. Structural Biology

    A complex channel comes into focus

    1. Valda Vinson

    Voltage-gated calcium (Cav) channels are activated in response to membrane potential to initiate calcium-mediated signaling pathways and are associated with diseases such as cardiac arrhythmia and epilepsy. Cav1.1 couples changes in membrane potential to cardiac muscle contraction. It comprises a core subunit and three auxiliary subunits. Wu et al. isolated the Cav1.1 complex from rabbit skeletal muscle and determined its structure by single-particle electron cryomicroscopy using direct electron detection and advanced image processing. The detailed architecture of the pseudotetrameric eukaryotic Cav channel in complex with its auxiliary subunits provides an important framework for understanding the function and disease mechanisms of related channels.

    Science, this issue p. 10.1126/science.aad2395

  15. Plant Symbioses

    Early stages of a beneficial relationship

    1. Pamela J. Hines

    Plants benefit from widespread symbiosis with arbuscular mycorrhizal fungi. This symbiosis between plant and fungus aids plants in capturing mineral and micronutrients from the soil. Gutjahr et al. have now identified a component of an intracellular receptor, the hydrolase DWARF 14 LIKE, required in rice roots for initiating the symbiosis. A similar receptor detects karrikins in smoke that signal opportunity for fireweed to grow after a forest fire.

    Science, this issue p. 1521

  16. Quantum Simulation

    Simulating electronic transport with atoms

    1. Jelena Stajic

    Two superconductors connected by a bridge made out of nonsuperconducting material form a so-called Josephson junction (see the Perspective by Belzig). Valtolina et al. replaced the superconductors with two reservoirs of a superfluid Fermi gas and connected them by a weak link to allow atoms to move from one side to the other. Then they made one reservoir more populated than the other and studied the ensuing dynamics as a function of interaction strength between the atoms. In a related experiment, Husmann et al. kept the interaction strength at its maximum, but varied the temperature and the properties of the link. As temperature increased, the superfluid disappeared and thermal transport took over.

    Science, this issue p. 1498, p. 1505; see also p. 1470

  17. Batteries

    Peering into cathode layered oxides

    1. Marc S. Lavine

    The quest for better rechargeable batteries means finding ways to pack more energy into a smaller mass or volume. Lithium layered oxides are a promising class of materials that could double storage capacities. However, the design of safe and long-lasting batteries requires an understanding of the physical and chemical changes that occur during redox processes. McCalla et al. used a combination of experiments and calculations to understand the formation of O-O dimers, which are key to improving the properties of these cathode materials.

    Science, this issue p. 1516

  18. Phytoplankton

    Community changes centuries in the making

    1. H. Jesse Smith

    How might climate change affect the base of the marine food chain? Phytoplankton, the foundation of the marine ecosystem, depend on ambient oceanographic conditions such as temperature, salinity, and nutrient availability, which affect ocean chemistry and isotopic distributions. McMahon et al. report carbon isotopic composition changes in the North Pacific Ocean over the past 1000 years, which reflect changes in the community composition of phytoplankton in the region (see the Perspective by Vogt). An ongoing trend toward greater prevalence of nitrogen-fixing cyanobacteria that began 100 years ago might lead to a more efficient carbon pump and remove increasing amounts of CO2 from the atmosphere.

    Science, this issue p. 1530; see also p. 1466

  19. Paleoceanography

    East joins West to complete a picture

    1. H. Jesse Smith

    How have eastern equatorial Pacific sea surface temperatures varied over the past 1000 years? Today, the tropical Pacific Ocean has a large influence on global climate, through processes such as El Niño. Researchers would thus like to know how the ocean varied in the past. Although good records exist from the western ocean, the same has not been true for the eastern side. Rustic et al. analyzed marine sediments recovered from near the Galapagos Islands. They conclude that the tropical Pacific Ocean changed state about 500 years ago, near the transition between the warm Medieval Climate Anomaly and the cold Little Ice Age.

    Science, this issue p. 1537

  20. Microbial Metabolism

    Sulfate reduction via a trisulfide

    1. Nicholas S. Wigginton

    Microorganisms can respire sulfur compounds in the absence of oxygen, eventually leading to the production of hydrogen sulfide. This ancient metabolism is common in modern anoxic environments, but the enzymatic pathways aren't yet fully resolved. Through in vivo and in vitro experiments, Santos et al. clarify the enzymology of the sulfate reduction pathway in both bacteria and archaea (see the Perspective by Fritz and Kroneck). Reduction of the sulfite intermediate results in the linkage of two cysteine residues to a third sulfur atom from sulfite, forming a trisulfide product. Because the reduction of sulfite conveys a strong isotopic signature on sulfur in the environment, isotope fractionation models should account for this additional step.

    Science, this issue p. 1541; see also p. 1476

  21. Evolutionary Genetics

    Essential genes and species incompatibilities

    1. Laura M. Zahn

    Crosses between two fruit fly species, Drosophila melanogaster and D. simulans, result in hybrid progeny that are all female. Although some of the genes responsible for this species barrier are known, the full complement of molecular determinants that lead to inviable males has remained mysterious. Phadnis et al. used mutagenesis and a sequencing-based genomic screen to link hybrid inviability to the cell cycle. The inviable males result from an interaction between three genes, one of which is essential, which precluded its identification with standard genetic screens. This strategy to identify speciation genes can be applied to other model and nonmodel systems.

    Science, this issue p. 1552