Editors' Choice

Science  23 May 2014:
Vol. 344, Issue 6186, pp. 869
  1. Cell Motility

    Cells need to stay in shape, too

    1. Stella M. Hurtley

    Actin visualized in a crawling cell.

    PHOTO: D. BURNETTE ET AL., THE JOURNAL OF CELL BIOLOGY 205, 1 (14 APRIL 2014) © THE ROCKEFELLER UNIVERSITY PRESS

    To move efficiently, people need to stay in shape—and the same is true for cells. Burnette et al. looked at the 3D organization of contractile fibers used by living animal cells as they crawled about on a surface. The cells adopted a wedge-like shape with a wide, flattened front end dragging a slim rear. To keep moving, the cells used a counterbalanced contraction-adhesion system. At the top of the cell, a network of contractile fibers made from actin and myosin (the same proteins used in muscles) coupled to noncontracting stress fibers anchored to the cell's surface. Understanding how cells move is important for understanding normal development, wound healing, and metastasizing tumor cells.

    J. Cell Biol. 205, 83 (2014).

  2. Neuroscience

    How the brain responds to fairness

    1. Peter Stern

    Many people consider freedom of choice and fairness fundamental values, but what are their neural bases? To probe the question, Aoki et al. had pairs of people put their heads in functional magnetic resonance scanners and then play a game. When both players were offered an equal number of choices, they were more likely to report feeling happy, and their brain scans showed increased activity in the area called the ventromedial prefrontal cortex. In contrast, when the combined absolute number of options available to players increased, so did activity in the ventral striatum. Because these regions have been implicated already in value processing, these results may illuminate how a sense of fairness evolved in the human brain.

    J. Neurosci. 34, 6413 (2014).

  3. Host Defense

    Cas proteins help acquire immunity

    1. Valda Vinson

    Crystal structure of the Cas1-Cas2 complex of the CRISPR-Cas system.

    PHOTO: J. K. NUÑEZ ET AL., NATURE STRUCTURAL & MOLECULAR BIOLOGY (4 MAY 2014) © 2014 NATURE PUBLISHING GROUP

    Bacteria and archaea are under constant attack from foreign genetic elements. The CRISPR-Cas immune system affords protection from such invaders. Upon encountering foreign DNA, the CRISPR-Cas system creates DNA fragments that match the sequences of the invading foreign DNA and then inserts these DNA fragments, or “spacers” into the microbe's genome. That way, the next time the organism encounters something similar, it can quickly recognize it and defend against it through an RNA interference–like mechanism. By solving the crystal structures and performing additional biochemical analysis, Nuñez et al. now uncover the specific functions of the enzymes Cas1 and Cas2. Acting as a complex, Cas1 and Cas2 help bacteria and archaea acquire DNA spacers and insert them correctly into the host genome.

    Nat. Struct. Mol. Biol. 10.1038/nsmb.2820 (2014).

  4. RNA Translation

    Yeast's translational hopscotch

    1. Guy Riddihough

    Ribosomes translate mRNA into proteins sequentially, one codon at a time—except when they don't. Lang et al. now report that many of the mitochondrial genes in the yeast Magnusiomyces capitatus are infested with short sequence inserts that should kill the translation of the coded protein and, in theory, the yeast as well, but don't. Why not? The M. capitatus protein-synthesizing machinery was able to ignore the inserts and make functional proteins. The protein-synthesizing ribosomes recognized a special element in the mRNA that warned of the inserts. The ribosome then “hopped” from the upstream codon to an identical or very similar codon downstream, clean over the insert, leaving the insert out of the protein it made.

    Proc. Natl. Acad. Sci. U.S.A. 111, 5926 (2014).

  5. Oceanography

    What goes in does not come out

    1. Julia Fahrenkamp-Uppenbrink

    Vast swaths of floating plastic debris in a northern Pacific Ocean region have earned it a grim nickname: the Great Pacific Garbage Patch. But how much plastic really floats in the Pacific? Different research teams use different methodologies, and coverage is often patchy, making data notoriously difficult to obtain and compare. Using data spanning over 40 years, Law et al. report maps of plastic debris concentrations in the Eastern Pacific and estimate that at least 21,000 metric tons of microplastic are floating in the region. However, despite increased plastic production over the past decade, they could not detect an increase in plastic debris over time. Data coverage may be insufficient for capturing such trends.

    Environ. Sci. Technol. 10.1021 es4053076 (2014).

  6. Applied Physics

    An attractive-sounding proposition

    1. Ian S. Osborne

    Map of the distribution of pressures within the field produced by the ultrasonic tractor beam.

    PHOTO: MIKE MACDONALD AND CHRISTINE DEMORE

    Demore et al. are using sound to build a better tweezer—or at least, to show how it could be done. Today's optical and acoustic tweezers typically use intensity gradients to trap and manipulate the particles. That's because propagating fields such as light and sound are usually associated with positive forces—the radiation pressure they create tends to push objects away. In contrast, Demore et al. have figured out how to use sound not just to push, but to pull. They use an array of ultrasonic resonators to show how the wavefront of a propagating beam of sound can be shaped to apply negative radiation pressure, creating a tractor beam. The new technology could give surgeons and astronauts greater dexterity as they perform operations and repairs from a distance.

    Phys. Rev. Lett. 112, 174302 (2014).

  7. Astrophysics

    A chilly little neighborhood object

    1. Margaret M. Moerchen

    There's a chilly little neighbor lurking near the Sun, just ∼7 light years away. Luhman detected the substellar object, a brown dwarf, by tracking the relative motions of objects in infrared images. Unlike the Sun, such low-mass objects cannot sustain the hydrogen fusion necessary to radiate visible light, so they produce energy primarily at thermal wavelengths. The brown dwarf probably has a mass 3 to 10 times that of Jupiter and a temperature near the freezing point on Earth, making it the coldest brown dwarf detected so far. That means astrophysicists will be able to test atmospheric models at new thermal low values.

    Astrophys. J. 10.1088/2041-8205/786/2/L18 (2014).

  8. Marine Biology

    Why octopuses don't get tied in knots

    1. NA

    An octopus's appendages can form seemingly infinite postures and positions, but somehow they avoid becoming hopelessly entangled. The key appears to be chemicals in the skin, By examining amputated arms from the common octopus (Octopus vulgaris), Nesher et al. found that the animal's suckers would latch on to everything except its own arms. Petri dishes coated with the octopus's skin, whether intact or ground up into a mush, became “immune” to the zombie arms, suggesting that a substance in the skin repels the suckers. As octopuses are known to dine on their comrades, the substance may also prevent them from eating themselves alive.

    Curr. Biol. 10.1016/j.cub.2014.04.024 (2014).

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