This Week in Science

Science  23 Feb 2018:
Vol. 359, Issue 6378, pp. 880
  1. Plant Biology

    Sending a canopy-wide message

    1. Wei Wong

    The closing of leaf stomata can be coordinated from leaf to leaf.

    CREDIT: DENNIS KUNKEL MICROSCOPY/SCIENCE SOURCE

    Although not all leaves in the canopy of a plant may be exposed to light at the same time, it is beneficial to coordinate the closure of the pores (stomata) in the leaves to prevent desiccation. Devireddy et al. showed in Arabidopsis thaliana plants that a wave of reactive oxygen species and Ca2+ enabled leaves experiencing light stress to trigger stomatal closure in leaves not exposed to light. Stomatal closure required abscisic acid in light-stressed leaves and jasmonic acid in nonexposed leaves. This coordinated and dynamic response may enable plants to acclimate to light stress.

    Sci. Signal. 11, eaam9514 (2018).

  2. Imaging

    Improved spy tactics for single cells

    1. Priscilla N. Kelly

    Bioluminescence imaging is a tremendous asset to medical research, providing a way to monitor living cells noninvasively within their natural environments. Advances in imaging methods allow researchers to measure tumor growth, visualize developmental processes, and track cell-cell interactions. Yet technical limitations exist, and it is difficult to image deep tissues or detect low cell numbers in vivo. Iwano et al. designed a bioluminescence imaging system that produces brighter emission by up to a factor of 1000 compared with conventional technology (see the Perspective by Nasu and Campbell). Individual tumor cells were successfully visualized in the lungs of mice. Small numbers of striatal neurons were detected in the brains of naturally behaving marmosets. The ability of the substrate to cross the blood-brain barrier should provide important opportunities for neuroscience research.

    Science, this issue p. 935; see also p. 868

  3. Infectious Diseases

    Memories of exposure

    1. Christiana N. Fogg

    Protective memory B cell responses are shaped through multiple mechanisms, including clonal selection of naïve B cells and affinity maturation. Memory B cell responses are considered critical to the development of a successful malaria vaccine—a goal that has remained remarkably elusive. Murugan et al. characterized memory B cell responses to the Plasmodium falciparum circumsporozoite (PfCSP) protein in human volunteers immunized with sporozoites. Repeated immunization induced potent responses to the immunodominant PfCSP NANP repeat by the clonal selection of naïve and preexisting memory B cell precursors; B cell responses were less influenced by affinity maturation.

    Sci. Immunol. 3, eaap8029 (2018).

  4. Organoids

    Cancer organoids to model therapy response

    1. Priscilla N. Kelly

    Cancer organoids are miniature, three-dimensional cell culture models that can be made from primary patient tumors and studied in the laboratory. Vlachogiannis et al. asked whether such “tumor-in-a-dish” approaches can be used to predict drug responses in the clinic. They generated a live organoid biobank from patients with metastatic gastrointestinal cancer who had previously been enrolled in phase I or II clinical trials. This allowed the authors to compare organoid drug responses with how the patient actually responded in the clinic. Encouragingly, the organoids had similar molecular profiles to those of the patient tumor, reinforcing their value as a platform for drug screening and development.

    Science, this issue p. 920

  5. Ocean Acidification

    Acid reef-flux

    1. H. Jesse Smith

    The uptake of anthropogenic carbon dioxide from the atmosphere is reducing the pH of the oceans. Ocean acidification means that calcium carbonate—the material with which coral reefs are built—will be more difficult for organisms to generate and will dissolve more quickly. Eyre et al. report that some reefs are already experiencing net sediment dissolution. Worryingly, the rates of loss will increase as ocean acidification intensifies.

    Science, this issue p. 908

  6. Paleoanthropology

    Neandertal cave art

    1. Andrew M. Sugden

    It has been suggested that Neandertals, as well as modern humans, may have painted caves. Hoffmann et al. used uranium-thorium dating of carbonate crusts to show that cave paintings from three different sites in Spain must be older than 64,000 years. These paintings are the oldest dated cave paintings in the world. Importantly, they predate the arrival of modern humans in Europe by at least 20,000 years, which suggests that they must be of Neandertal origin. The cave art comprises mainly red and black paintings and includes representations of various animals, linear signs, geometric shapes, hand stencils, and handprints. Thus, Neandertals possessed a much richer symbolic behavior than previously assumed.

    Science, this issue p. 912

  7. Fungal Infections

    Irons in the fire

    1. Orla M. Smith

    Although transplantation is a life-saving therapy, patients receiving new organs are at serious risk for invasive, potentially fatal infections. Aspergillus fumigatus is a particularly common and troublesome fungal pathogen, but its ability to invade transplant tissues is poorly understood. To evaluate this property, Hsu et al. infected transplants in mice. Bleeding, caused by damage to small vessels in grafted airways, led to increased tissue iron, a known growth factor for Aspergillus. Thus, therapies in development that block iron and protect blood vessels may extend the life of organ recipients.

    Sci. Transl. Med. 10, eaag2616 (2018).

  8. Optics

    Miniaturized optical ranging and tracking

    1. Ian S. Osborne

    Light detection and ranging systems are used in many engineering and environmental sensing applications. Their relatively large size and cost, however, tend to be prohibitive for general use in autonomous vehicles and drones. Suh and Vahala and Trocha et al. show that optical frequency combs generated by microresonator devices can be used for precision ranging and the tracking of fast-moving objects. The compact size of the microresonators could broaden the scope for widespread applications, providing a platform for miniaturized laser ranging systems suitable for photonic integration.

    Science, this issue p. 884, p. 887

  9. Cell Biology

    The great escape

    1. Stella M. Hurtley

    Mitochondrial DNA (mtDNA) is a potent damage-associated molecular pattern that, if it reaches the cytoplasm or extracellular milieu, triggers innate immune pathways. mtDNA signaling has been implicated in a wide range of diseases; however, the mechanisms of mtDNA release are unclear, and the process has not been observed in real time thus far. McArthur et al. used live-cell lattice light-sheet microscopy to look at mtDNA release during intrinsic apoptosis. Activation of the pro-death proteins BAK and BAX resulted in the formation of large macro-pores in the mitochondrial outer membrane. These massive holes caused the inner mitochondrial membrane to balloon out into the cytoplasm, resulting in mitochondrial herniation. This process allowed the contents of the mitochondrial matrix, including mtDNA, to escape into the cytoplasm.

    Science, this issue p. eaao6047

  10. Paleoceanography

    CO2 escaped from the deep

    1. H. Jesse Smith

    Why did the concentration of atmospheric carbon dioxide rise so much and so quickly during the last deglaciation? Evidence has begun to accumulate suggesting that old, carbon-rich water accumulated at depth in the Southern Ocean, which then released its charge when Southern Ocean stratification broke down as the climate there warmed. Basak et al. present measurements of neodymium isotopes that clearly show that the deepwater column of the glacial southern South Pacific was stratified, just as would be necessary for the accumulation of old, carbon-rich water. Their data also show that North Atlantic processes were not the dominant control on Southern Ocean water-mass structure during that interval, as has been thought.

    Science, this issue p. 900

  11. Inorganic Chemistry

    Boron learns to give back to nitrogen

    1. Jake Yeston

    Although diatomic nitrogen is famously inert, a variety of transition metals can bind to it through a process termed backbonding. As the nitrogen weakly shares its own electrons, some electrons from the metal reach back out to it. Nonmetals would not seem to have the capacity for this type of bonding, but now Légaré et al. show that conventionally electron-deficient boron can be coaxed into it (see the Perspective by Broere and Holland). The authors treated boron-based precursors with potassium under a nitrogen atmosphere to produce several compounds with sandwiched dinitrogen between two boron centers in reduced motifs reminiscent of metal complexes.

    Science, this issue p. 896; see also p. 871

  12. Metasurfaces

    Patterning a hyperbolic metasurface

    1. Ian S. Osborne

    Structured metasurfaces potentially enable the control of the propagation direction of excitations on the material's surface. However, the high losses associated with the materials used to date has led to relatively short lifetimes for the excitations. Li et al. patterned a subwavelength grating into a layer of hexagonal boron nitride (hBN) and found that the lifetime and propagation length of the excitations could be much longer. Direct imaging of the polariton excitations illustrates that hBN can be a viable platform for nanophotonic circuits.

    Science, this issue p. 892

  13. Fisheries

    More than half the fish in the sea

    1. Sacha Vignieri

    As the human population has grown in recent decades, our dependence on ocean-supplied protein has rapidly increased. Kroodsma et al. took advantage of the automatic identification system installed on all industrial fishing vessels to map and quantify fishing efforts across the world (see the Perspective by Poloczanska). More than half of the world's oceans are subject to industrial-scale harvest, spanning an area four times that covered by terrestrial agriculture. Furthermore, fishing efforts seem not to depend on economic or environmental drivers, but rather social and political schedules. Thus, more active measures will likely be needed to ensure sustainable use of ocean resources.

    Science, this issue p. 904; see also p. 864

  14. Cancer

    SEEK and you may find cancer earlier

    1. Paula A. Kiberstis

    Many cancers can be cured by surgery and/or systemic therapies when detected before they have metastasized. This clinical reality, coupled with the growing appreciation that cancer's rapid genetic evolution limits its response to drugs, have fueled interest in methodologies for earlier detection of the disease. Cohen et al. developed a noninvasive blood test, called CancerSEEK that can detect eight common human cancer types (see the Perspective by Kalinich and Haber). The test assesses eight circulating protein biomarkers and tumor-specific mutations in circulating DNA. In a study of 1000 patients previously diagnosed with cancer and 850 healthy control individuals, CancerSEEK detected cancer with a sensitivity of 69 to 98% (depending on cancer type) and 99% specificity.

    Science, this issue p. 926; see also p. 866

  15. Protein Evolution

    Putting distance between protein relatives

    1. Valda Vinson

    Many proteins form complexes to function. When the gene for a self-assembling protein duplicates, it might be expected that the related proteins (paralogs) would retain interfaces that would allow coassembly. Hochberg et al. show that the majority of paralogs that oligomerize in fact self-assemble. These paralogs have more diverse functions than those that coassemble, implying that maintaining coassembly would constrain evolution of new function. The authors experimentally investigated how two oligomeric small heat-shock protein paralogs avoid coassembly and found that flexibility at regions outside of the interaction interfaces played a key role.

    Science, this issue p. 930

  16. Molecular Biology

    Complete architecture of PRC2

    1. Steve Mao

    Polycomb repressive complex 2 (PRC2) methylates lysine 27 in histone H3 to achieve gene silencing. Kasinath et al. report multiple structures of complete human PRC2 with its four core subunits (EZH2, EED, SUZ12, and RBAP48) and two cofactors (AEBP2 and JARID2) in different active states. These structures describe the molecular mimicry of H3 tails by AEBP2 and JARID2 to regulate PRC2 activity and reveal the organizational role of SUZ12 in maintaining the integrity and stability of the complex.

    Science, this issue p. 940

  17. Structural Biology

    A path to multidrug resistance

    1. Valda Vinson

    Permeability glycoprotein (PgP) uses the energy from adenosine triphosphate (ATP) hydrolysis to transport substrates out of the cell. Many of its substrates are drugs, so it plays an important role in drug resistance. Structures in the inward-facing conformation have been determined for mouse, yeast, and algal PgP. Kim and Chen present the cryo–electron microscopy structure of human PgP in an outward-facing conformation. Two ATP molecules are bound between two nucleotide-binding domains. The substrate-binding site, located in the transmembrane domain, is open to the outside of the cell, but compressed, and no substrate is bound. This suggests that ATP binding, rather than ATP hydrolysis, promotes the transition to the outward-facing conformation and substrate release.

    Science, this issue p. 915

  18. Plant Science

    Can scientists create nitrogen-fixing plants?

    1. Julia Fahrenkamp-Uppenbrink

    Globally, more than $100 billion is spent each year on nitrogen fertilizers, which also cause substantial environmental damage. In a Perspective, Good highlights recent research into creating plants that can directly fix nitrogen from the air. Laboratory studies have shown that genes required for nitrogen fixation can be introduced into plants and that these engineered plants can make a key part of the nitrogen-fixing enzyme nitrogenase. However, no plant has been shown to fix nitrogen directly. Given recent technical advances, a concerted research effort focused on a specific set of suitable model plants could quickly make considerable progress toward this goal. But even once such a plant has been made, substantial hurdles remain in translating this research to the field.

    Science, this issue p. 869