Editors' Choice

Science  30 Nov 2012:
Vol. 338, Issue 6111, pp. 1128
  1. Geology

    Toba Timing

    1. Brooks Hanson

    Toba in Sumatra is thought to have been the largest volcanic eruption in the past tens of millions of years—larger than the main eruption at Yellowstone—and it formed a huge lake about 30 km wide and 100 km long. Signals of the eruption are thought to be preserved in both Greenland and Antarctic ice cores. The event has been proposed to have led to a population bottleneck in early Homo sapiens that is recorded in our genetic history. The exact age of the eruption, however, has been uncertain, complicating efforts at global correlation of climatic and environmental events. Storey et al. have now obtained a precise 40Ar/39Ar radiometric age on crystals from Toba deposits in Malaysia. The age, supported by astronomical calibrations, is 73.88 ± 0.32 thousand years ago, close to the presumed age of about 74 ka. The date helps calibrate the signals and thus correlates the age of ice cores in separate hemispheres, and the eruption timing just precedes an abrupt cooling of about 10°C recorded in the Greenland ice.

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1208178109 (2012).

  2. Cell Biology

    STIM1-ulating Phagocytosis

    1. Stella M. Hurtley

    Whether the endoplasmic reticulum (ER) fuses with phagosomes has been hotly debated. What is not in dispute is the juxtaposition of these organelles within cells. However, the mechanism and functional significance of this juxtaposition remain unclear. Nunes et al. found that ER membranes do not fuse with phagosomes but are recruited for signaling purposes by STIM1, which regulates the store-operated calcium entry pathway. A combination of fluorescence and electron microscopy in neutrophils from STIM1-deficient mice and in phagocytic fibroblasts lacking STIM1 revealed that STIM1 recruitment to phagosomes is required for efficient phagocytosis. STIM1 also increased the juxtaposition of thin ER cisternae with phagosomes, promoted the shedding of periphagosomal actin rings, and promoted localized calcium elevations. Furthermore, the effects of STIM1 on phagocytosis, actin shedding, and periphagosomal calcium elevations, but not on ER recruitment, required STIM1 to activate its target channels on phagosomes. Thus, STIM1-mediated ER recruitment to phagosomes, rather than initiating fusion, appears to open phagosomal calcium channels to generate localized calcium elevations that promote phagocytosis.

    Curr. Biol. 22, 1990 (2012).

  3. Physics

    Don't FRET—All Under Control

    1. Ian S. Osborne

    In photosensitive biological or chemical processes involving energy harvesting, such as photosynthesis, photons are absorbed by one molecule and the associated energy is transferred to another (or series of others) through a resonant process called Förster resonance energy transfer, or FRET. With the development of organic electronics, debate has surrounded the question of whether such systems can be designed to control the energy transfer process. Blum et al. conducted a systematic study of the FRET process involving two molecules (an acceptor and donor) bridged by a DNA chain that precisely established the separation distance. They altered the local optical environment by placing the molecules in the vicinity of a mirror and controlling that separation. Their main finding is that although the rate of energy transfer between the molecules is independent of what is done to the optical environment, the efficiency of that energy transfer process is sensitive. Such nanophotonic control might find practical applications in designing better artificial molecular-based electronic energy-harvesting or lighting devices.

    Phys. Rev. Lett. 109, 203601 (2012).

  4. Chemistry

    Better Living Through Chloride

    1. Phil Szuromi

    Conjugated polymers are used as the active element in many flexible optoelectronics devices, including thin-film transistors and light-emitting diodes, and as such, versatile routes to their preparation are in demand. Bonillo and Swager report a distinct method for the synthesis of conjugated polymers with thiophene backbones, a class of materials currently accessed through oxidative and cross-coupling techniques. Their starting point was the previously reported observation that 3-alkoxy-2-bromothiophenes undergo a violent autopolymerization that proceeds through a cationic mechanism with the elimination of HBr. The authors show that the chloro variant of this reaction proceeds in a more controlled manner. They used chlorodibutylpropylenedioxythiophene as a model monomer and studied the promotion of the reaction by different Lewis acids and solvents: Tin tetrachloride in o-dichlorobenzene proved the optimal combination. End-capping by nucleophiles could stop the reaction on account of the chain-growth nature of the mechanism; moreover, the “living” character of the process not only led to products with a low polydispersity index but also enabled the synthesis of block copolymers. In this vein, the authors prepared rod-coil copolymers comprising thiophene and ethyl vinyl ether blocks. They further suggest that the ionic addition/elimination scheme could generalize, offering access to a range of other polyaromatic systems.

    J. Am. Chem. Soc. 134, 10.1021/ja308498h (2012).

  5. Ecology

    Never Too Young to Learn

    1. Sacha Vignieri

    Recognition between parent and offspring is an essential component of reproduction for many species. Its importance is more profound for species that undergo prolonged separations followed by reunions, often facilitated through call recognition by both mothers and offspring, or for species in which there may be competition for parental attention from freeloaders. In most cases, mother and infant imprint on each others' calls shortly after birth or appear to have a genetically based recognition template. Colombelli-Négrel et al. show that superb fairy wrens go one step further by singing a specific incubation song to their in-egg embryos, which helps them to oust parasitizing cuckoo chicks that have not learned the brood's “password.” To ensure that both parents are in the know, females also incorporated their incubation song into begging calls given to their male partners, resulting in males also being more parental to chicks singing the right song. It is not clear why the cuckoo chicks, which are also exposed to the incubation song as eggs, do not produce accurate passwords. Perhaps the early learning ability of the wrens has allowed them to gain ground in the parasitic arms race.

    Curr. Biol. 22, 10.1016/j.cub.2012.09.025 (2012).

  6. Microbiology

    Community Matters

    1. Guy Riddihough

    We often think of bacteria as quintessentially single-celled organisms, finely tuned to survive as rugged individualists. For many prokaryotic species, this would be a mistaken impression. Quorum sensing (QS), a system of communication between cells related to population density, regulates a number of coordinated activities, including biofilm formation, swarming motility, and bioluminescence. Now Goo et al. show that, unlike the wild type, Burkholderia species deficient in QS showed massive die-off in the stationary phase of growth. Bacteria that metabolize amino acids as a carbon source release ammonia and increase the alkalinity of their environment, and this rise in pH killed the QS-deficient bacteria. The wild-type Burkholderia species maintained a lower environmental pH through the production and secretion of oxalate, a small acidic compound, and could thus survive the stationary phase. The production of oxalate—a so-called “public good” of benefit to all in the population—was activated through the QS system, indicating that the bacteria can sense their population density and, just before the stationary phase, cooperate to neutralize a toxic byproduct of their energy metabolism.

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1218092109 (2012).

  7. Neuroscience

    Misplaced Migration

    1. Pamela J. Hines

    Interneurons need to migrate from their birthplace to the cortical layers, where they will build their connections and support the effective function of cortical circuits. Disorders such as autism and schizophrenia that affect cortical circuits may also affect interneuron placement. A microdeletion at chromosome 22q11.2 has been correlated with risk of cortical circuit disorders. Meechan et al. used the Large Deletion 22q11.2DS (LgDel) mouse model to analyze what impact this microdeletion may have on cortical interneurons. In LgDel mice, a subset of the interneurons do not end up in the right place: During development, certain interneurons do not migrate as fast as normal and tend to lose their way. Analysis of transcription profiles identified a regulatory network affecting expression of the cytokine C-X-C chemokine receptor type 4 gene as a key defect in the malfunctioning interneurons. Interneurons carrying reduced amounts of cytokine receptor on their surface could be less responsive to migration signals and could thus easily end up in the wrong place.

    Proc. Natl. Acad. Sci. U.S.A. 109, 18601 (2012).