Editors' Choice

Science  09 Sep 2016:
Vol. 353, Issue 6304, pp. 1110
  1. Microbiology

    Sexual development in schistosomes

    1. Caroline Ash

    Gonad development in female schistosome worms relies on pairing with males.

    PHOTO: DAVID SCHARF/SCIENCE SOURCE

    Schistosomiasis is a severe parasitic disease that affects ~200 million people globally. The flatworms that cause the disease have a complex life cycle in which, unusually, male and female worms must pair to produce eggs. Eggs trapped in host body tissues are the main cause of pathology. Lu et al. used RNA-sequencing analysis to show that gonad development in females requires pairing and occurs when the juvenile worms pass through the host's liver. They also found that neuropeptidergic signaling stimulates female gonad development. At present, there is only one safe treatment for schistosomiasis, and thus elucidating the details of sexual development in schistosomes may offer valuable targets for drugs and vaccines.

    Sci. Rep. 6, 31150 (2016).

  2. Fisheries

    Modeling the distribution of tuna fleets

    1. Pamela J. Hines

    The purse-seine tuna fishery in the eastern Pacific Ocean, off the west coast of the Americas, is fished by vessels with thousand-ton capacities that range over an area the size of Canada. The large size of the fishery means that vessel distribution is patchy. Sun et al. developed a model to predict vessel distribution on the basis of decisions that skippers make before and after going to sea. The model accounts for environmental factors such as chlorophyll content and dissolved oxygen concentration, as well as weather conditions. Modeling the far-flung fishery can inform regulatory decisions aimed at ensuring a sustainable tuna fishery while minimizing dolphin mortality.

    PLOS ONE 10.1371/journal. pone.0159626 (2016).

  3. Superconductivity

    Lightly doping a Mott insulator

    1. Jelena Stajic

    Cuprates usually acquire their superconductivity when charged carriers, typically holes, are chemically introduced into a “parent” state called a Mott insulator. However, this part of the cuprate phase diagram is rich in phases, including a pseudogap and a charge-order phase, whose relationship to each other and to superconductivity is under debate. Cai et al. used scanning tunneling spectroscopy of a very lightly doped Bi2Sr2–x LaxCuO6+δ to unravel the phase conundrum. As the hole dopants were introduced, a pseudogap-like density of states started to emerge, followed by a checker-board pattern characteristic of the charge order. When further doping caused the material to become superconductive, the charge-order pattern became less prominent, indicating a competition between the two phases.

    Nat. Phys. 10.1038/PHYS3840 (2016).

  4. Host Responses

    Inflammation blocks recovery

    1. Kristen L. Mueller

    Although antibiotics can clear the pathogen, doctors typically do not prescribe them to treat nontyphoidal Salmonella infections, which are a major cause of gastroenteritis worldwide. This is because antibiotics actually extend the course of disease. Now, Dolowschiak et al. provide some insight into why. Using a mouse model of Salmonella infection treated with ciprofloxacin, they found that the cytokine interferong-γ(IFNγ) promotes intestinal pathology even after the majority of the bacteria are cleared. T cells and natural killer cells make IFNγ, which drives proinflammatory myeloid cells to accumulate, spewing forth pathology-causing soluble mediators that prevent tissue repair. Targeting this pathway therapeutically may help alleviate the debilitating symptoms that Salmonella can cause.

    Cell Host Microbe 20, 238 (2016).

    Nontyphoidal Salmonella infections are not typically treated with antibiotics.

    PHOTO: MICHAEL ABBEY/SCIENCE SOURCE
  5. Climate Change Impacts

    A sea-route change in the Arctic

    1. H. Jesse Smith

    Shipping routes across the Arctic Ocean will multiply as climate warms.

    PHOTO: MINT IMAGES LIMITED/ALAMY STOCK PHOTO

    Arctic sea ice is rapidly disappearing as climate warms, ushering in an entirely novel era in marine transportation with important economic implications, because more frequent open seas will allow increasing volumes of trans-Arctic shipping. Melia et al. used an ensemble of climate models from the Fifth Coupled Model Intercomparison Project to project how sea ice loss might increase opportunities for ocean-going vessels to cross the Arctic. They find that standard open-water vessels will have twice as many navigable periods by the middle of the 21st century as they do now, including some across the central Arctic. The shipping season length could reach 4 to 8 months by late century, when moderately ice-strengthened vessels could be able to complete Arctic transits during 10 to 12 months of the year.

    Geophys. Res. Lett. 10.1002/2016GL069315 (2016).

  6. Inorganic Chemistry

    A pair of tablemates for aromatic benzene

    1. Jake Yeston

    Chemists do not designate a compound as aromatic because it smells nice. Rather, the term refers to the stability conferred by a particular delocalized arrangement of electrons first characterized in benzene and related carbon rings. Is the concept exclusive to carbon? Over the years, inorganic chemists have extended it to a range of analogs composed of other elements, and now Seitz et al. introduce two more. Specifically, they prepared hexagonal benzene analogs in which three silicon centers alternate with either three phosphorus or three arsenic centers. Structural and computational characterization supported aromaticity. The reactions fortuitously also produced tetragonal cyclobutadiene analogs that were weakly antiaromatic.

    J. Am. Chem. Soc. 10.1021/jacs.6b07389 (2016).

  7. Structural Biology

    Bacteriophage fights back

    1. Valda Vinson

    Bacteria and archaea have CRISPR-Cas systems that target and destroy invading DNA from phages and plasmids. However, invaders can fight back. Wang et al. report a structure that shows how the bacteriophage protein AcrF3 inhibits Pseudomonas aeruginosa Cas3 (PaCas3). The Cascade protein complex recruits Cas3 to target DNA. In addition to binding to a protein in Cascade, Cas3 also binds the nontarget DNA strand. There, Cas3 uses its ATP-driven helicase domain to open up the DNA and its nuclease domain to degrade it. The structure showed an AcrF3 dimer complexed to ADP-bound PaCas3, thus locking it in an inactive conformation. Moreover, AcrF3 blocked both the DNA and the protein binding sites involved in recruiting Cas3 to target DNA.

    Nat. Struct. Mol. Biol. 10.1038/nsmb.3269 (2016).