This Week in Science

Science  04 Nov 2011:
Vol. 334, Issue 6056, pp. 563
  1. The Domineering Brain and Its Synapses


    Social hierarchy is a fundamental organizing principle in many animal societies. The social status of an individual strongly affects its health and quality of life. Yet the underlying mechanisms determining social hierarchical status are unclear. Wang et al. (p. 693, published online 29 September; see the Perspective by Maroteaux and Mameli) determined the social hierarchy within groups of mice by using multiple behavioral tests and discovered that the social hierarchical status of an individual correlated with the synaptic strength in medial prefrontal cortical neurons. Furthermore, the hierarchical status of mice could be changed from dominant to subordinate, or vice versa, by manipulating the strength of synapses in the medial prefrontal cortex.

  2. Seeing Is Believing

    Advances in neuroscience have often relied on advances in microscopy. Lichtman and Denk (p. 618) review how recent advances in microscopy have helped to elucidate the relationship between the structure of the nervous system and its function. Within the brain, synaptic plasticity—the experience-dependent change in connectivity between neurons—is thought to underlie learning and memory. Ho et al. (p. 623) review the cellular and molecular processes that are altered when a neuron responds to external stimuli, and how these alterations lead to an increase or decrease in synaptic connectivity.

  3. Dye-namic Improvement

    In a dye-sensitized solar cell, a molecular dye injects a charge into a semiconductor upon light absorption, and then a charge acceptor on the other side of the circuit shuttles it back around. The most common implementation of the cell has employed a ruthenium complex as a dye and an equilibrating system of iodide and triiodide ions as the charge shuttle. Yella et al. (p. 629; see the Perspective by McGehee) now show that the combination of a zinc porphyrin–derived dye and cobalt ion shuttle substantially boosts efficiency.

  4. Rushing in Fluoride

    Positron emission tomography relies on the rapid decay of radioactive isotopes (most commonly, fluorine-18) embedded in tracer molecules to image biological environments. Increasing the diversity of tracer structures could expand the range of insights afforded by the technique, but it is a substantial synthetic challenge to append the unstable isotope to most molecular frameworks before its activity decays below the necessary threshold. Lee et al. (p. 639) devised a pair of palladium complexes that can rapidly incorporate fluorine substituents into aromatic compounds. A particular advantage of the system is that it uses fluoride anions to provide the unstable isotope: Fluoride anions are available in streams with more concentrated activity than reagents derived from elemental fluorine.

  5. Splitting CO2 and Water

    It is possible to mimic photosynthesis in an electrochemical cell by using an external power source to induce electron transfer from water to CO2, but the instability of the initially formed CO2 anion requires a high applied driving potential. Rosen et al. (p. 643, published online 29 September) found that carrying out the CO2 reduction in an ionic liquid electrolyte substantially lowered the required potential, presumably by stabilizing the anion through complexation. Many solar cell devices can split water to generate hydrogen. However, large-scale implementation of such devices has been precluded by their need for noble metal catalysts and, in some cases, for highly alkaline or acidic electrolytes. Reece et al. (p. 645, published online 29 September) assembled thin films of a cobalt phosphate oxygen reduction catalyst on the indium tin oxide surface of a commercially available amorphous silicon cell. A nickel-molybdenum-zinc alloy was used as a hydrogen-evolving catalyst to produce a device in which more than 60% of the output was able to drive water splitting.

  6. Electrons Staying Hot

    A silicon photovoltatic cell can produce a voltage because once electrons are photoexcited, the voltage bias created by the interface of positive and negative silicon (a p-n junction) draws these electrons in only one direction. Gabor et al. (p. 648, published online 6 October; see the Perspective by Basko) found that single- and double-layer graphene in a p-n junction generated a voltage not through the photovoltaic effect, but through a competing mechanism, whereby the excited electrons in graphene remained hotter than the rest of device, driving a photothermoelectric effect.

  7. Echoes from the Surface


    Vibrational echo spectroscopy can track rapid changes in the distribution of vibrations across a set of tumbling molecules. The technique has been used in solution-phase analysis, and Rosenfeld et al. (p. 634, published online 20 October) now extend it to the study of solid-liquid interfaces, a more complex environment that requires correspondingly higher sensitivity. A layer of metal complexes tethered to a surface—a motif widely applied in catalysis—was probed, which revealed distinctions in conformational dynamics depending on whether the surface was exposed or submerged in solvent.

  8. The Warm and the Cold of It

    In atmospheric blocking, a stationary atmospheric pressure field impedes normal atmospheric circulation over a large region. In Europe, blocking conditions over the North Atlantic Ocean can persist for as long as 2 weeks and cause cold wintertime temperatures, as well as other weather anomalies. Häkkinen et al. (p. 655; see the Perspective by Woollings) reanalyzed 20th-century atmospheric data and found that winters with more frequent blocking in the North Atlantic region tended to persist for decades, mainly during periods in which the North Atlantic Ocean was relatively warm. These periods of warm North Atlantic surface waters were also related to wind and ocean circulation patterns and occurred in phase with the dominant mode of Atlantic multidecadal ocean variability.

  9. Nitrogen in Tropical Forest

    Pollution from nitrogen deposition is well documented in temperate ecosystems and it has been predicted that the globalization of nitrogen deposition will eventually lead to its enrichment in tropical forests. Hietz et al. (p. 664) report a comprehensive data set showing a clear change in the nitrogen cycle in two tropical forests—one in Panama and one in Thailand. The data set provides evidence for nitrogen enrichment from stable isotope analysis of leaves collected for more than 40 years and of tree rings spanning approximately 100 years. Spatial data on nitrogen emissions and tropospheric NO2 suggest that the type of enrichment seen may be widespread in tropical forests.

  10. Common Knowledge

    Cooperative behaviors, such as dancing the tango or singing a duet, require coordination between sensory output and feedback in both participating individuals. Fortune et al. (p. 666) recorded duetting behavior in singing plain-tailed wrens and made extracellular neural recordings from the song centers of their brains. Both singers encoded the combined cooperative duet, but the timing of the singing was established by a single partner, the female. Thus, the entire duet is encoded in each individual's brain, not just by their own contribution.

  11. Fly Guts


    The microorganisms that live within animals' guts are important for regulating many aspects of their host's physiology, including immune responses, energy metabolism, development, and growth. The relatively simple gut microbiota of the fruit fly Drosophila are particularly important in nutrient-poor conditions. Shin et al. (p. 670) identified a single bacterial member of the fruit fly's gut community (Acetobacter pomorum) that could replace the fly's five-member gut flora. The function of one bacterial gene product required for the oxidation of ethanol—pyrroloquinoline quinine–dependent alcohol dehydrogenase—was key to the metabolic generation of acetic acid and for successful development of fly larvae.

  12. More Than a Proton Pump

    When cells are running low of amino acids, they can activate autophagy to digest existing cellular components. But it has been unclear how the depletion of amino acids is sensed. The mTOR complex 1 (mTORC1) is a key regulator of this process and, when amino acids are present, becomes localized to lysosomes and inhibits autophagy. Zoncu et al. (p. 678; see the Perspective by Abrahamsen and Stenmark) used small interfering RNA techniques to search for lysosomal components necessary for mTORC1 signaling. The vacuolar H+–adenosine triphosphatase, which functions to acidify lysosomes, was found also to be necessary for sensing of amino acids within the lysosome. The protein directly interacted in an amino acid–dependent manner with proteins associated with the mTORC1 complex.

  13. Exercise for Life

    An unresolved issue in the field of neurodegenerative diseases is whether exercise would have long-lasting beneficial effects or whether it would have deleterious long-term consequences by increasing the metabolic demands on already susceptible neuronal populations. Fryer et al. (p. 690; see the Perspective by Gitler) now show that exercise significantly extended the life span of a mouse model for the polyglutamine neurodegenerative disorder spinocerebellar ataxia type 1 (SCA1). Exercise up-regulated epidermal growth factor which caused down-regulation of Capicua (Cic), a transcriptional repressor that interacts with Ataxin-1 in vivo. In Cic mutant mice, all SCA1 phenotypes were rescued, including premature lethality, by reducing the level of Cic by 50%.

  14. Assessing Climate Change

    It is well established that climate change influences species distributions, but the way in which past climate fluctuations affect modern species distributions is poorly known (see the Perspective by Ohlemüller). Sandel et al. (p. 660, published online 6 October) used a measure of climate stability, climate-change velocity, to provide a robust test of the effects of climate change at the end of the Last Glacial Maximum on distributions of amphibians, mammals, and birds globally. Higher climate-change velocity suppressed endemism of all groups, but particularly for weakly dispersing species. The rate of climate change is also very relevant to predicting future distributional changes. Burrows et al. (p. 652) performed a global analysis of temperatures over the past 50 years to produce two metrics, the velocity of climate change and the seasonal shift. In both marine and terrestrial environments, these measures relate more directly to changes in distributions of species and the timing of their annual life-cycle events than simple linear trends in temperature.

  15. Getting Connected

    Acetylation of lysine residues in proteins can mediate protein-protein interactions, although few structural mechanisms of acetylation-dependent protein recognition have been elucidated. A common form of protein acetylation is N-terminal acetylation, which occurs cotranslationally for an estimated 30 to 90% of eukaryotic proteins. It is unclear how an N-terminally acetylated amino acid directly mediates protein-protein interactions. Scott et al. (p. 674, published online 22 September) reports that N-terminal acetylation of the E2 enzyme, Ubc12, dictates distinctive E3-mediated Nedd8 ligation to cullins. This mechanism of protein regulation connects protein acetylation with posttranslational modification by ubiquitin-like proteins.

  16. Polymerase Phosphorylation

    The carboxyl-terminal domain (CTD) of the large subunit of RNA polymerase II (RNAP II) has a tandem repeat structure that is conserved from yeast to humans. The CTD links transcription to messenger RNA (mRNA) processing: Phosphorylation of serine (Ser) 2 coordinates RNA 3′-end processing and transcription termination, and that of Ser7 super functions in 3′ processing of small nuclear RNAs. Hsin et al. (p. 683) show that the Thr4 residue of the CTD is also phosphorylated—from yeast to human. In a cell line, Thr4 of the human CTD was essential for viability and was required for the proper 3′ processing of histone mRNAs.

  17. Sufficient Centromere

    Centromeres ensure the correct segregation of chromosomes to daughter cells during cell division, by providing a site for kinetochore assembly and microtubule attachment. In most organisms, DNA sequence does not define a centromere, but instead an epigenetic mechanism is important. Mendiburo et al. (p. 686) found that targeting the Drosophila centromere-specific histone, CID, to a single locus via arrays of Lac Operator sequences resulted in a supernumery CID-containing site able to direct kinetochore assembly and to propagate epigenetically through recruitment of endogenous CID. Plasmids lacking centromeres but containing the CID-containing site segregated and were maintained faithfully. Thus, the Drosophila centromere-specific histone is sufficient for the formation of a functional and heritable centromere.

  18. Monkey See, Monkey Know

    The number of individuals that a single person can keep close track of—known as Dunbar's number—is generally taken to be roughly 150, which would be the size of a tightly knit social grouping. This estimate derives from a comparative analysis of primate neuroanatomy and behavior and has led to the corollary that the magnitude of the number is determined by the size of the neocortex. Sallet et al. (p. 697; see the news story by Miller) asked whether the size of one's social group is causally related to the size of social cognition areas in the brain of the macaque monkey. Structural and functional neuroimaging data was collected from a collection of 23 animals that had been living alone, or in groups of up to 7 animals. The sizes of brain regions known to process social information (such as faces) were indeed relatively larger in animals from larger groups.