This Week in Science

Science  30 Jan 2015:
Vol. 347, Issue 6221, pp. 515
  1. Supernovae

    Burbling explosions blow metallic bubbles

    1. Margaret M. Moerchen
    PHOTO: NASA/ESA/THE HUBBLE HERITAGE STSCI/AURA, ESA/HUBBLE COLLABORATION

    Stars more than about eight times the mass of the Sun don't go out quietly. Asymmetric explosions are kicked off by the collapse of their iron cores when no more fusion energy can sustain them. Exactly how this stellar catastrophe proceeds is difficult to probe. Milisavljevic et al. have now peered into the supernova remnant Cas A in the near-infrared and present a three-dimensional map of its interior unshocked ejecta. The bubble-like structure points to turbulent mixing, which may help us understand other supernova remnants whose structure cannot be seen in such detail.

    Science, this issue p. 526

  2. Protein Structure

    Structural clues to protein function

    1. Valda Vinson

    Translocator protein (TSPO) is a mitochondrial membrane protein thought to transport cholesterol and porphyrins. Its detailed function remains unclear, but interest in it is high because TSPO is involved in a variety of human diseases. Two papers now present crystal structures of bacterial TSPOs. Li et al. show that a mutant that mimics a human single polymorphism associated with psychiatric disorders has structural changes in a region implicated in cholesterol binding. Guo et al. suggest that TSPO may be more than a transporter. They show how it catalyzes the degradation of porphyrins, a function that could be important in protection against oxidative stress.

    Science, this issue p. 555, p. 551

  3. Optical Imaging

    Overcoming the limits of the microscope

    1. Peter Stern

    3D super-resolution microscopy of mouse hippocampal layers: neurons (green) and synapses (blue and red)

    PHOTO: CHEN ET AL.

    The resolution of a light microscope is limited. Physicists have long since worked out what these limits are and which parameters determine the spatial resolution. Many groups have nevertheless made numerous attempts to overcome these resolution limits. Rather than improving the power and quality of the microscope, Chen et al. instead expanded the biological specimens under study (see the Perspective by Dodt). They introduced a polymer gel into fixed cells and tissues and chemically induced swelling of the polymer by almost two orders of magnitude. They could then produce much higher-resolution images of their samples, which included the mouse hippocampus.

    Science, this issue p. 543; see also p. 474

  4. Reaction Dynamics

    Deuterium fluoride gets born shivering

    1. Jake Yeston

    Modern spectroscopic techniques can analyze collisions between gas phase molecules in exquisite detail, highlighting exactly which vibrations and rotations come into play. However, much chemistry of interest takes place in solution, where it's harder to tease out what happens. Dunning et al. applied infrared spectroscopy to study solution-phase formation of deuterium fluoride (DF) from F atoms, a longstanding test bed of gas phase dynamics. The DF product vibrated for a surprisingly long time before dissipating its energy to the surrounding solvent molecules.

    Science, this issue p. 530

  5. Animal Cognition

    Even chicks may count from left to right

    1. Sacha Vignieri

    For the most part, humans represent numbers across a mental number line, with smaller numbers on the left and larger numbers on the right. Some have argued that this is due to culture rather than being innate. Rugani et al., however, show that 3-day-old chicks share this representation of numbers, consistently seeking lower numbers to the left of a target and larger numbers to the right (see the Perspective by Brugger). These results suggest that there may be an innate spatial representation of numerical values that we share with other animals.

    Science, this issue p. 534; see also p. 477

  6. Identity and Privacy

    Where and when you spend reveals who you are

    1. Barbara R. Jasny

    How do you ensure individual privacy when analyzing bulk information? De Montjoye et al. used 3 months of data on financial traces of 1.1 million people to determine the privacy bounds of credit card metadata. The risk of re-identification from financial data sets was high: Four spatiotemporal observations, (of the shop and the day the transaction took place) were enough to re-identify 90% of the individuals. Knowing the approximate price of a transaction increased the likelihood of re-identification.

    Science, this issue p. 536

  7. Atmospheric Dynamics

    Because the rain falls and the wind blows

    1. H. Jesse Smith

    Global warming is expected to intensify the hydrological cycle, but it might also make the atmosphere less energetic. Laliberté et al. modeled the atmosphere as a classical heat engine in order to evaluate how much energy it contains and how much work it can do (see the Perspective by Pauluis). They then used a global climate model to project how that might change as climate warms. Although the hydrological cycle may increase in intensity, it does so at the expense of its ability to do work, such as powering large-scale atmospheric circulation or fueling more very intense storms.

    Science, this issue p. 540; see also p. 475

  8. Inflammation

    Preventing sepsis in type 1 diabetics

    1. Wei Wong

    Patients with type 1 diabetes have chronic systemic inflammation and are more prone to developing sepsis. Filgueiras et al. found that mice that are a model for type 1 diabetes had higher amounts of leukotriene B4, a proinflammatory lipid, and of 5-lipoxygenase, the enzyme that produces leukotriene B4. Model mice treated with an inhibitor of 5-lipoxygenase survived sepsis and had decreased markers of inflammation. Thus, targeting 5-lipoxygenase to prevent the production of leukotriene B4 could potentially decrease the susceptibility of diabetic patients to sepsis.

    Sci. Signal. 8, ra10 (2015).

  9. Circadian Rhythms

    Defining necessary circadian clock elements

    1. L. Bryan Ray

    The circadian clock in organisms as diverse as fungi and humans have a rather similar structure: Timing depends on daily cycles of transcription in circuits in which feedback loops control the timing of oscillations. A critical role has been ascribed to negative elements, which lead to inhibition of their own transcription, and to degradation of these elements, which is signaled by phosphorylation events. However, Larrando et al. show that in the fungus Neurospora, after manipulations that prevent phosphorylation-signaled degradation of the negative element FREQUENCY (FRQ), rhythms still persist (see the Perspective by Kramer). They suggest a model in which other phosphorylation events on Frq (of which there are over 100) must have critical roles in controlling the clock, independent of negative element degradation.

    Science, this issue 10.1126/science.1257277; see also p. 476

  10. Solar Cells

    Large-crystal perovskite films

    1. Phil Szuromi

    The performance of organic-inorganic hybrid perovskite planar solar cells has steadily improved. One outstanding issue is that grain boundaries and defects in polycrystalline films degrade their output. Now, two studies report the growth of millimeter-scale single crystals. Nie et al. grew continuous, pinhole-free, thin iodochloride films with a hot-casting technique and report device efficiencies of 18%. Shi et al. used antisolvent vapor-assisted crystallization to grow millimeter-scale bromide and iodide cubic crystals with charge-carrier diffusion lengths exceeding 10 mm.

    Science, this issue p. 522, p. 519

  11. Mitochondrial Biology

    Switching transcription and replication

    1. Beverly A. Purnell

    Because mitochondrial DNA is circular, the transcription and replication machinery might be expected to collide. A single mitochondrial RNA polymerase (mtRNAP) transcribes the mitochondrial DNA and also generates primers for replication. Agaronyan et al. now show that transcription and replication are kept separate in human mitochondria, with the mitochondrial transcription elongation factor TEFM serving as a key player in the switch. In the absence of TEFM, mtRNAP terminates downstream from the promoter, forming primers to promote replication. In the presence of TEFM, the primers are not formed, and the overall processivity of mtRNAP elongation complexes is enhanced, promoting genome transcription. These mutually exclusive mechanisms allow the processes to proceed independently as needed by the cell.

    Science, this issue p. 548

  12. Biomaterials

    Location, location, location

    1. Kelly LaMarco

    When buying a house, we research neighborhoods and carefully choose an environment that works for us. So why does a “one-material-fits-all” mentality dominate when choosing a biomaterial for various clinical scenarios? Now, Oliva et al. attempt to shift that mindset by defining the molecular properties of diseased-tissue microenvironments and then tuning a dendrimer:dextran–based material to thrive differentially under selected clinical conditions. The authors measured tissue modifications and material performance in two gut diseases and under varying degrees of severity. The context affected the compatibility between a biomaterial and its neighborhood. A resulting predictive paradigm could match a material with its model home, which may one day translate into improved clinical outcomes.

    Sci. Transl. Med. 7, 272ra11 (2015).

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