This Week in Science

This Week in Science

Science  21 Oct 2016:
Vol. 354, Issue 6310, pp. 297
  1. Evolution

    Expect the unexpected

    1. Sacha Vignieri

    A native of the Andean highlands, the sparkling violetear hummingbird (Colibri coruscans)


    In convergent evolution, similar environmental conditions produce similar sets of adaptations. Does similar convergence exist in the molecular underpinnings of such morphological changes? Natarajan et al. looked across more than 50 species of birds that have adapted to different elevations to identify patterns of similarity in hemoglobin-oxygen binding affinity (see the Perspective by Bridgham). Increases in hemoglobin-oxygen binding affinity occurred in alpine species, but the molecular changes underlying the hemoglobin changes were variable. Thus, even in cases where adaptive phenotypic change is predictable, the molecular pathways to these changes may not be.

    Science, this issue p. 336; see also p. 289

  2. Antigen Presentation

    New players in the repertoire

    1. Kristen L. Mueller

    Antigen-presenting cells, such as macrophages and dendritic cells, activate immunological T cells by presenting them with antigens bound by major histocompatibility complexes (MHCs). The proteasome typically processes these antigens, which include peptides derived from both self and microbial origins. Liepe et al. now report that, surprisingly, a large fraction of peptides bound to class I MHC on multiple human cell types are spliced together by the proteasome from two different fragments of the same protein. Such merged peptides might turn out to be useful in vaccine or cancer immunotherapy development.

    Science, this issue p. 354

  3. Pain

    Social transfer of pain in mice

    1. Philip Yeagle

    Pain experienced by an individual can be modulated by social, cognitive, and emotional factors. In a group setting, can an individual experiencing pain affect other, pain-free individuals' behaviors and responses? Smith et al. explored this question in mice. They examined the responses of “bystander” animals housed in the same room, but not in the same cage, as animals experiencing hyperalgesia—a heightened sensitivity to pain—from tissue damage or withdrawal of opiates. The “bystander” animals also displayed hyperalgesia, which was mediated by olfactory cues.

    Sci. Adv. 10.1126/sciadv.1600855 (2016).

  4. Group Dynamics

    Belief system dynamics

    1. Barbara R. Jasny

    People tend to structure their beliefs in a way that appears consistent to them. But how do some beliefs within groups persist in the face of social pressure, whereas others change and, by changing, influence a cascade of other beliefs? Friedkin et al. developed a model that can describe complexes of attitudes in a group that interact and change (see the Perspective by Butts). Their model revealed how the changing views of the U.S. population on the existence of weapons of mass destruction in Iraq changed their views on whether the invasion by the United States was justified.

    Science, this issue p. 321; see also p. 286

  5. Metallurgy

    A shocking transformation for silver

    1. Brent Grocholski

    Clever processing of metals leads to technologically useful properties such as increased hardness and ductility. Thevamaran et al. fired specially synthesized silver cubes at a hard piece of silica, which produced a shock wave that dramatically changed the microstructure of the silver. The approach produced an extreme range in grain sizes that is useful for creating bendable yet strong metals.

    Silver microcubes deformed by high-velocity impact


    Science, this issue p. 312

  6. Mucosal Immunity

    Sopping up IL-22 drives intestinal disease

    1. Kristen L. Mueller

    The causes of inflammatory bowel disease (IBD) such as Crohn's disease and ulcerative colitis are likely complex and multifactorial, involving loss of epithelial cell integrity, chronic inflammation, and changes to the microbiota. Pelczar et al. investigated potential disease-driving mechanisms by studying IBD patients and mouse models. IBD patients express elevated levels of interleukin-22 binding protein (IL-22BP), which binds to the protein IL-22, preventing its tissue repair–promoting actions. Moreover, IBD development in mouse models requires IL-22BP. Lastly, IBD patients responding to therapy with antibodies against tumor necrosis factor–α exhibited reduced levels of IL-22BP but retained IL-22 expression, suggesting one mechanism by which this therapy may act.

    Illustration of an abnormal growth and inflammation in bowel disease


    Science, this issue p. 358

  7. Force Spectroscopy

    Many tiny force sensors

    1. Phil Szuromi

    Several techniques can measure forces on biomolecules, but the need to connect the molecule to the macroscopic world often limits the rate at which data can be taken. Nickels et al. created large arrays of nanoscale force sensors by using DNA origami structures. Single-stranded DNA molecules of different lengths attached to the molecule of interest acted as entropic springs, with shorter strands exerting more force. The authors used their setup to study the bending of DNA induced by the TATA-binding protein.

    Science, this issue p. 305

  8. Cancer

    Metastasis casts a NET

    1. Yevgeniya Nusinovich

    Neutrophil extracellular traps, or NETs, are DNA structures that are produced by neutrophils in response to infection and can promote the spread of cancer in the presence of infection. Park et al. discovered that even in the absence of infection, metastatic breast cancer cells can stimulate neutrophils to form NETs, which further support the spread of metastasis. The authors also demonstrated an approach to breaking this vicious cycle by using nanoparticles coated with deoxyribonuclease I, an enzyme that breaks down the DNA NETs. This treatment was effective at reducing lung metastases in mice, demonstrating the potential of NETs as a therapeutic target.

    Sci. Transl. Med. 8, 361ra138 (2016).

  9. Biomass Processing

    Formaldehyde protects and serves

    1. Nicholas S. Wigginton

    The lignin found in plants is a desirable renewable feedstock for fuels and other useful compounds. Breaking down such a strong, energy-dense polymer, however, requires pretreatment of plant biomass under harsh conditions. These pretreatment steps often cause side reactions within the polymer itself, which lower the overall yields of lignin monomers. Shuai et al. used formaldehyde during pretreatment to block the reactive groups that lead to carbon-carbon linkages in lignin. This simple step stabilized lignin during pretreatment, resulting in dramatically improved yields.

    Science, this issue p. 329

  10. Organic Chemistry

    How to turn olefins into nucleophiles

    1. Jake Yeston

    The Grignard reaction has a storied place in the development of organic chemistry. Recognized by the Nobel Prize more than a century ago, this coupling of organomagnesium halides with carbonyl compounds remains a widely used route to carbon-carbon bonds. Nguyen et al. review an emerging alternative protocol that replaces the sensitive magnesium reagent with a catalytically activated olefin and a reductant such as hydrogen or an alcohol. In addition to safety and efficiency considerations, this class of reactions benefits from the high abundance and low cost of the olefins.

    Science, this issue p. 300

  11. Structural Biology

    Gating a calcium channel

    1. Valda Vinson

    The type 2 ryanodine receptor (RyR2) controls the release of calcium ions from the sarcoplasmic reticulum in cardiac cells—the initiating step in cardiac muscle contraction. Mutations in RyR2 are associated with cardiac diseases. Peng et al. used single-particle electron cryomicroscopy to determine the structure of RyR2 from porcine heart at 4.4-Å resolution with the calcium channel closed and at 4.2-Å resolution with the calcium channel open. The structures reveal how interdomain motions result in a conformational change in the cytoplasmic region of RyR2 that is transduced by a central domain to cause motions that open or close the channel.

    Science, this issue p. 301

  12. Solid-State Physics

    Relating interactions and nematicity

    1. Jelena Stajic

    The electronic system in a strongly correlated material can sometimes be less symmetrical than the underlying crystal lattice. This loss of symmetry, caused by interactions and dubbed electronic nematicity, has been observed in a number of exotic materials. However, establishing a direct connection between the interactions and nematicity is tricky. Feldman et al. used scanning tunneling microscopy to image the wave functions of electrons on the surface of bismuth placed in an external magnetic field. The exchange interactions in the material caused a loss of symmetry, which was reflected in the orientations of the electrons' elliptical orbits.

    Science, this issue p. 316

  13. Device Technology

    Almost-off transistors

    1. Phil Szuromi

    Wearable devices and environmental sensors ideally should consume very little power to avoid the need for batteries that would have to be replaced. Lee and Nathan developed a thin-film transistor (TFT) from In-Ga-Zn-O thin films. To make the material less conductive, the films were fabricated to avoid oxygen vacancies. The TFT operated at ultralow power (less than 1 nW) and at switching voltages of less than 1 V with very high intrinsic gain. The devices work by changing the height of the so-called Schottky barrier formed between the semiconductor gate material and the metal drain contact.

    Science, this issue p. 302

  14. Chemical Physics

    Acetylene's scission visualized by selfie

    1. Jake Yeston

    Can molecules take pictures of themselves? That is more or less the principle underlying laser-induced electron diffraction (LIED): A laser field strips an electron from a molecule and then sends it back to report on the structure of the remaining ion. Wolter et al. applied this technique to acetylene to track the cleavage of its C–H bond after double ionization (see the Perspective by Ruan). They imaged the full structure of the molecule and also distinguished more rapid dissociative dynamics when it was oriented parallel rather than perpendicular to the LIED field.

    Science, this issue p. 308; see also p. 283

  15. Microbiology

    Conseting mycobacteria

    1. Caroline Ash

    Mycobacteria encompass several slow-growing pathogens, including organisms that cause leprosy and tuberculosis. Mycobacteria use a component of their ESX (or Type VII) secretion system for a distinctive form of genetic exchange called distributive conjugal DNA transfer. Gray et al. investigated a quicker-growing model species, Mycobacterium smegmatis. They found that the secretory apparatus, ESX-4, is essential for DNA transfer into the recipient but is not required for donor cells to pass along their DNA. The ESX-1 secretory apparatus was required in the recipient for ESX-4 induction, but it did not appear to provide the physical channel for DNA. Rather, ESX-1 may secrete cell-surface “mating factor” receptors. More research will be needed to understand the details of this intriguing means of DNA exchange in mycobacteria.

    Science, this issue p. 347

  16. Plankton Dynamics

    Drivers of phytoplankton blooms

    1. Caroline Ash

    Despite decades of study, there is little evidence to link increases in phytoplankton growth in response to springtime warming with the dynamics of phytoplankton blooms. This lack of understanding makes it difficult to make predictions about global biogeochemical cycling in response to climate change. Hunter-Cevera et al. analyzed over a decade of data collected hourly from the New England shelf between 2003 and 2016 (see the Perspective by Worden and Wilken). Blooms now occur 20 days earlier than at the start of observations, because earlier springtime warming stimulates cell division earlier each year. Nevertheless, despite the shift in timing, predatory organisms in the food chain are still ready to consume the superabundance, which brings the blooms to an abrupt end each year.

    Science, this issue p. 326; see also p. 287

  17. Paleontology

    Jaws from the jawless

    1. Sacha Vignieri

    Until a fossil called Entelognathus was found to contain a tripartite jaw a few years ago, it was believed that the skeletons of early osteichthyans (bony fish), the ancestors of all vertebrates, were derived independently of those of the earlier placoderms (so-called jawless fish). Zhu et al. now describe a second Silurian placoderm that more securely bridges the jawless toothlike plates of placoderms to the development of the jawed condition that ultimately led to the three-boned jaw in ancestors of modern vertebrates (see the Perspective by Long). This finding upends the traditional belief that the two types of jaw were nonhomologous and sheds light on the evolution of the complex maxilla, a key component of diversification across many modern taxa, including humans.

    Science, this issue p. 334; see also p. 280

  18. Plant Photobiology

    Turning off the blue-light response

    1. Pamela J. Hines

    In plants, blue light is perceived by cryptochromes, which, once activated, set off signaling events that regulate gene expression, circadian rhythms, and photomorphogenesis. Wang et al. now show that in the model plant Arabidopsis, one of the functions of activated cryptochromes, which are dimers or oligomers when active, is to activate production of the protein BIC1 (blue-light inhibitor of cryptochromes 1) (see the Perspective by Fankhauser and Ulm). BIC1 then favors monomerization and thus inactivation of the cryptochromes. This feedback loop resets the system so that blue-light responses can be turned off as well as turned on.

    Science, this issue p. 343; see also p. 282

  19. Enzymology

    Enzymes for making (or breaking) methane

    1. Nicholas S. Wigginton

    The last enzymatic step of microbial methanogenesis, and the first step of microbial methane oxidation, relies on the nickel-containing tetrapyrrole coenzyme F430. The successful metabolic engineering of any organism to enzymatically consume methane thus also needs the appropriate machinery to synthesize this compound. Using comparative genomics, Zheng et al. identified several candidate genes responsible for coenzyme F430 biosynthesis. Cloning and expression of all the subsequent proteins in Escherichia coli confirmed the complete in vitro conversion of sirohydrochlorin into mature F430.

    Science, this issue p. 339

  20. Ebolaviruses

    Treating Ebola with a Trojan horse

    1. Kristen L. Mueller

    The recent major Ebola virus outbreak in West Africa high-lighted the need for effective therapeutics against this and other filoviruses. Neutralizing ebolaviruses with antibodies is a challenge because the viruses bind their entry receptor, NPC1, inside the cell within endosomes rather than on the cell surface. Furthermore, enzymes in endosomes cleave the Ebola virus surface glycoprotein (GP) to reveal its receptor binding site. Wec et al. now report a bispecific antibody strategy targeting all known ebolaviruses that overcomes this problem (see the Perspective by Labrijn and Parren). They coupled an antibody specific for a conserved, surface-exposed epitope of GP to antibodies that recognize either NPC1 or the NPC1 binding site on GP. Treating mice therapeutically with these antibodies allowed them to survive otherwise lethal ebolavirus infection.

    Science, this issue p. 350; see also p. 284

  21. Microbiology

    Directing the movement of a pathogen

    1. Wei Wong

    The opportunistic pathogen Pseudomonas aeruginosa is particularly resistant to antibiotic treatment when it forms biofilms. Biofilm formation requires both random migration (to enable adjustment to constantly changing conditions) and directed migration (also called chemotaxis). Xu et al. found that binding of the bacterial messenger cyclic diguanylate monophosphate to the adaptor protein MapZ suppressed random migration and biofilm formation by P. aeruginosa (see the Focus by Orr and Lee). Thus, the MapZ-associated pathway could potentially be targeted to prevent the chronic and hard-to-treat infections caused by P. aeruginosa.

    Sci. Signal. 9, ra102 and fs16 (2016).

  22. Infectious Diseases

    Persistent infections “interfere” with B cells

    1. Anand Balasubramani

    Certain pathogens, including HIV, hepatitis virus, and lymphocytic choriomeningitis virus (LCMV), cause persistent infections that are often associated with suboptimal antibody responses. Fallet et al., Moseman et al., and Sammicheli et al. found that up-regulation of type 1 interferon (IFN-1) in the early phase of LCMV infection in mice contributed to premature deletion of virus-specific B cells. Blocking IFN-1 prevented this B cell deletion. Although the studies agree that IFN-1 does not act directly on B cells, they find that distinct immune cells mediate IFN-1–dependent deletion of B cells, depending on the system examined. A related Focus by Laidlaw et al. highlights how targeting the IFN-1 pathway could restore B cell responses during persistent viral infections in humans.

    Sci. Immunol. 10.1126/sciimmunol.aah6817, 10.1126/sciimmunol.aah3565, 10.1126/sciimmunol.aah6789, and 10.1126/sciimmunol.aaj1836 (2016).