This Week in Science

Science  18 Jul 2014:
Vol. 345, Issue 6194, pp. 280
  1. Associative Learning

    How the worm changes its tastes

    1. Peter Stern
    Nematode worm, Caenorhabditis elegansPHOTO: SINCLAIR STAMMERS/SCIENCE SOURCE

    In associative learning, you link potentially unrelated things because you are exposed to them at the same time. Ohno et al. studied a simple associative learning task in the nematode worm Caenorhabditis elegans. They presented the worms with a taste substance while withholding food. After starving in the presence of the taste substance, the animals switched their behavior from being attracted to the taste to finding it aversive. A specific isoform of the insulin receptor is critical for this type of associative learning—at least in worms.

    Science, this issue p. 313

  2. Quantum Mechanics

    Bosons of a feather flit together

    1. Jelena Stajic

    Bosons are a type of particle that likes to congregate. This property has a major effect on the behavior of identical bosons. Kaufman et al. demonstrated quantum interference of two bosonic Rb atoms placed in two neighboring quantum wells (see the Perspective by Thompson and Lukin). They prepared the atoms in exactly the same state so that there would be no way to tell them apart except for which well each atom was in. They then monitored the probability of the two atoms still being in separate wells. At certain times, the probability had a characteristic dip signifying that the bosons preferred to be in the same well.

    Science, this issue p. 306; see also p. 272

  3. Gene Therapy

    Reprogrammed heart cells set the pace

    1. Megan Frisk

    Pacemakers have revolutionized the care of patients with slow or abnormal heart rhythms, but these devices can break or become infected. With these patients in mind, Hu et al. created biological pacemakers to provide temporary, hardware-free support until a damaged electronic device can be replaced. They inserted a gene for a human transcription factor into heart muscle cells. This gene reprogrammed the cells to become pacemakers—cells that emit rhythmic electrical impulses to drive the beating heart. These biological pacemaker cells restored normal heart rate in pigs with complete heart block—a problem with the heart's electrical system.

    Sci. Transl. Med. 6, 245ra94 (2014).

  4. Photovoltaics

    Improved perovskite photovoltaic performance

    1. Phil Szuromi
    Cross section of perovskite solar cellPHOTO: MEI ET AL.

    A recent entry in the solar cell race is perovskite cells, named for the structure adopted by salt made from metal halides and organic cations that absorb the light and generate charges. The charges generated have to be transferred to a metal oxide (typically titanium oxide), and some of these charge carriers are lost in the transfer. Mei et al. made this process more efficient by growing a more crystalline perovskite with fewer defects inside porous versions of titanium and zirconium oxide. They added a second organic cation that stuck to the pore walls and directed the growth of the perovskite crystals. The improved solar cells operated for more than 1000 hours under full sunlight.

    Science, this issue p. 295

  5. Paleoceanography

    Circulating between different cycles

    1. H. Jesse Smith

    Around a million years ago, large-scale ocean circulation changed dramatically during the switch from ∼41,000- to ∼100,000-year long glacial cycles. Pena and Goldstein analyzed the isotopic composition of neodymium in marine sediments from the South Atlantic. The results suggest how the contributions of deep water from northern and southern sources varied across the transition. The boundary between the two glacial states appears to have been marked by a dramatic weakening, perhaps even a shutdown, of deep-water currents.

    Science, this issue p. 318

  6. Food Security

    How to optimize global food production

    1. Andrew M. Sugden

    Keeping societies stable and managing Earth's resources sustainably depend on doing a good, steady job producing and distributing food. West et al. asked what combinations of crops and regions offer the best chance of progress. Their analysis focused on reducing greenhouse gas emissions, nutrient pollution, water use, and food waste. They identify regions that are likely to yield the best balance between applying fertilizer to increase crop yields versus the resulting environmental impact.

    Science, this issue p. 325

  7. Alternative Splicing

    Evolving from an enzyme and into a regulator

    1. Valda Vinson

    Proteins, the work-horses of the cell, are made on a messenger RNA (mRNA) template. An enzyme called aminoacyl tRNA synthetases (AARSs) attaches the correct amino acid to a transfer RNA so that mRNA is accurately translated. Over evolution, additional sequences have been added to AARSs. Lo et al. found a large number of AARS variants in which the domain responsible for enzyme function was deleted. Ninety-four such variants had diverse signaling activities. Thus, AARSs are used both as enzymes and alternately as regulators of signaling pathways.

    Science, this issue p. 328

  8. Mitosis

    Taking a check on chromosome spacing

    1. Stella M. Hurtley

    Animal cells divide by mitosis. Chromosomes become condensed and congregate on the mitotic spindle in the center of the cell—the midzone. The spindle then separates sister chromosomes, pulling them to opposite ends of the cell, ready to form new daughter nuclei. Afonso et al. now show that chromosome separation is monitored by the level of midzone-associated Aurora B kinase activity (see the Perspective by Hadders and Lens). This process ensures that daughter nuclei only reassemble after sister chromosomes have successfully separated.

    Science, this issue p. 332; see also p. 265

  9. Synthetic Biology

    Turning cells into garbage collectors

    1. John F. Foley

    To protect other cells or tissue from injury, professional garbage-collecting cells called phagocytes gobble up dead cells. Sometimes phagocytes become overwhelmed and could use some help. Onuma et al. manipulated nonphagocytic cells to express two proteins: one that recognizes a lipid that marks the surface of dying cells and another that alters the plasma membrane to make the cell phagocytic. The engineered cells bound to and consumed dying cells. Such engineered cells could potentially be used to help the body remove undesirable targets.

    Sci. Signal. 7, rs4 (2014).

  10. Organoid Generation

    The making of bodies part by part

    1. Beverly A. Purnell

    Mention of organoids—organlike structure growing in a Petri dish—might conjure up images of science fiction. However, the generation of organoids is very real, as is the increased understanding of organ form and function that comes from studying them. Lancaster and Knoblich review organoids as structures that include more than one cell type of an organ that exhibit structural and functional features of the natural counterpart. Knowledge of normal organ developmental pathways guides the formation of these structures. Organoids show great promise for modeling human development and disease and for biomedical research and regenerative medicine.

    Science, this issue p. 10.1126/science.1247125

  11. Asymmetric Catalysis

    Iodine blooms as an oxidation catalyst

    1. Jake Yeston

    Most catalysts for organic oxidation chemistry—whether biochemical or artificial—contain a transition metal like iron or palladium. Uyanik et al. now show that iodine can take the place of a metal in catalyzing efficient oxidative ring closures to make chromans—hexagonal rings incorporating oxygen that are perhaps best known as a constituent of the vitamin E structure (see the Perspective by Nachtsheim). The iodine is added as a salt with a chiral cation, which directs the reaction to form just one of two possible mirror-image variants of the product. Key to the success of the system was the addition of a base, which maintained the viability of an unstable, partially oxidized iodine intermediate critical to the reaction cycle. The results bode well for more general use of iodine salts as asymmetric oxidation-reduction catalysts.

    Science, this issue p. 291; see also p. 270

  12. Ultrafast Dynamics

    Tightly tracking charge migration

    1. Jake Yeston

    Electron transfer dynamics underlie many chemical and biochemical reactions. Erk et al. examined the charge migration between individual carbon and iodine atoms during dissociation of iodomethane (ICH3) molecules (see the Perspective by Pratt). After initiating scission of the C-I bond with a relatively low-energy laser pulse, they introduced a higher-energy x-ray pulse to instigate ionization and charge migration. Delaying the arrival time of the x-ray pulse effectively varied the separation distance being probed as the fragments steadily drifted apart. The experimental approach should also prove useful for future studies of charge transfer dynamics in different molecular or solid-state systems.

    Science, this issue p. 288; see also p. 267

  13. Applied Optics

    Extending the range of planar optics

    1. Ian S. Osborne

    To build miniature optical devices, scientists are using silicon to replace bulky three-dimensional devices with flat versions. A patterned surface consisting of dense arrays of nanoscale silicon strips, which act as antennae, can be designed to work as transparent optical devices for the manipulation of light. Lin et al. used their versatile patterning technique to create a suite of planar optical elements. By patterning a 100-nm layer of silicon into a dense arrangement of nano-antennae, they were able to fabricate gratings, lenses, and axicons—a device that can add a shape to a propagating light beam.

    Science, this issue p. 298

  14. Quantum Computing

    Fault-tolerant quantum computing

    1. Ian S. Osborne

    Quantum states can be delicate. Attempts to process and manipulate quantum states can destroy the encoded information. Nigg et al. encoded the quantum state of a single qubit (in this case, a trapped ion) over the global properties of a series of trapped ions. These so-called stabilizers protected the information against noise sources that can degrade the single qubit. The protocol provides a route to fault-tolerant quantum computing.

    Science, this issue p. 302

  15. Optical Metrology

    A more simple route to metrology standards

    1. Ian S. Osborne

    The time standards set by atomic clocks are usually the domain of national metrology laboratories. Li et al. modulated the phase of two closely spaced laser lines to generate a comb of stable and equally spaced frequencies. They then used that comb to generate stable microwaves. Being somewhat simpler than existing optical comb generation techniques and also tunable, the approach may offer a new era of metrology and precision timekeeping.

    Science, this issue p. 309

  16. Oceanography

    Spinning up ocean circulation discretely

    1. H. Jesse Smith

    Ocean eddies with diameters of tens to hundreds of kilometers are an important component of water transport on a global scale. Averaged over periods of many years, ocean circulation is regular and coherent enough to have been described as a conveyor belt. However, over shorter time scales, irregular, discrete events cause significant amounts of water movement—termed mesoscale eddies. Zhang et al. combined data from thousands of autonomous observational devices called ARGO floats with satellite data. The mesoscale eddies moved around as much ocean water as wind or deep-water currents.

    Science, this issue p. 322

  17. Molecular Motors

    How dynein makes the right moves

    1. Stella M. Hurtley

    The molecular motor cytoplasmic dynein moves a wide range of different intracellular cargoes. Dynein's activity in vivo requires another protein, dynactin, but exactly why that should be has been very unclear. Although in vitro experiments have provided some evidence that dynactin increases dynein's processivity, the resulting dynein motility has never come close to matching dynein's cargo-transporting activity in living cells. Now, McKenney et al. show that tripartite complexes of dynein, dynactin, and an adaptor molecule are highly processive in vitro, moving the sort of distances that dynein transports cargo in vivo (see the Perspective by Allan).

    Science, this issue p. 337; see also p. 271