This Week in Science

Science  24 Jun 2011:
Vol. 332, Issue 6037, pp. 1479
  1. Make Your Own Bed

    CREDIT: JOHAN VAN DE KOPPEL

    Animals move through their environments to search for resources, and so movements that provide the greatest efficiency should be advantageous. As animals move and extract resources, however, the search environment is altered by their activity. Thus, search efficiency can be a moving target. De Jager et al. (p. 1551; see the Perspective by Grünbaum) show that individual movements in mussels generate beneficial environmental complexity at the population level. Specifically, individuals move using a type of random walk that consists of both long and short bouts, the cumulative effects of which generate a patchy distribution of mussels within the mussel bed. This patchy distribution confers a fitness advantage to individuals, and it is the walk strategy that allows for the development of this beneficial environment.

  2. Foie Gras: For Birds Only!

    The capacity to store excess fat in liver is beneficial to migrating birds in need of energy, but in humans, fatty liver is maladaptive and can have serious clinical consequences. Accompanying the trend toward unhealthy diets, nonalcoholic fatty liver disease (NAFLD) now affects about one-third of adults in developed countries and is a growing health concern. In the most extreme form of NAFLD, the aberrant accumulation of fat can lead to inflammation, liver cancer, or organ damage so severe that a liver transplant is required. Cohen et al. (p. 1519) review the current understanding of how NAFLD arises in humans, focusing on insights that have emerged from recent genetic and metabolic studies.

  3. A Matter of Understanding

    Quantum chromodynamics theory describes the internal structure of atoms—how quarks are held together to form protons and neutrons. Understanding matter relies on the ability to form a picture of the energy and thermodynamics involved in the interactions. This, in turn, requires the temperature scale to be set to allow the relative energies involved in the processes to be determined accurately. Using data from high-energy ion collisions, Gupta et al. (p. 1525; see the Perspective by Müller) formulate a computational method that allows the phase transition between solid matter and the point where it falls apart—the onset of the quark-gluon plasma—to be determined. The results should provide a clearer understanding of the fundamentals of how matter is put together.

  4. We Are Stardust

    In order to obtain the isotopic and elemental composition of solar matter, the NASA Genesis spacecraft captured samples of the solar wind outside of Earth's magnetosphere and returned them to Earth for laboratory analysis (see the Perspective by Clayton). McKeegan et al. (p. 1528; see the cover) and Marty et al. (p. 1533) describe the measurements of the oxygen and nitrogen isotopic composition of the Sun, based on laboratory analysis of the samples. Compared to the Sun, essentially all solar system materials are systematically enriched in the most heavy oxygen isotopes, 17O and 18O, and in the heavy nitrogen isotope, 15N. Thus, Earth, the Moon, Mars, and the asteroids have oxygen and nitrogen isotopic compositions that are different from the average solar nebula from which they formed.

  5. Fleecing Fluorocarbons

    Synthetic carbon-fluorine bonds pose a conundrum. On one hand, they are turning up in a widening array of effective pharmaceuticals, as well as in a plethora of consumer products that require nonstick interfaces. On the other hand, they are consequently becoming a rising fraction of the waste stream, where they are very hard to break down. Choi et al. (p. 1545) discovered an unusual, indirect mode of activating these bonds, which may ultimately contribute to their more facile manipulation into and out of various compounds. Specifically, hydrofluorocarbons such as CH3F and C2H5F react with an iridium complex through initial scission of a C-H bond, followed by rearrangements that result in metal-mediated cleavage of the C-F bond.

  6. Tiny Capacitors, Big Possibilities

    CREDIT: ZHU ET AL.

    Capacitors work by storing electrical charge in conducting materials separated by a nonconductor. Capacitors charge and discharge more rapidly than batteries but typically hold much less charge, although in some applications supercapacitors can be used instead of rechargeable batteries. Zhu et al. (p. 1537, published online 12 May) fabricated a porous carbon material using microwaves to exfoliate graphite oxide that was then processed with potassium hydroxide to activate the carbon. Once treated, a network of 1- to 5-nanometer-width pores surrounded by single-atom layers of carbon was obtained, which had a low hydrogen and oxygen content and high electrical conductivity. Using acetonitrile as the electrolyte, a high gravimetric capacitance was obtained in a fabrication process that could be readily scaled up.

  7. Bacteria Need Not Apply

    The isotopic variation of some elements (deeply within rocks and sediments) can reflect the conditions at the time the layer was undergoing deposition. Large fractionations of iron isotopes, in particular, have recently emerged as a proxy for understanding which bacterial metabolisms were present and active during ancient Earth history. Guilbaud et al. (p. 1548), however, experimentally demonstrate that similar isotope fractionation values can be obtained abiotically through the formation of the iron-sulfide mineral pyrite. Because these fractionation values are similar to those measured in some of Earth's oldest rocks, iron isotopes may not be a reliable proxy for early bacterial iron-based metabolisms.

  8. The Fountain of Youth?

    Aging results in a slow deterioration of biological structures. Even budding yeast undergo replicative aging, with cells dying after producing a limited number of offspring. However, the effects of aging are not transmitted to offspring: The progeny of old and young organisms have similar life spans. Ünal et al. (p. 1554) find that, in budding yeast, life span is reset during sporulation. The life spans of spores derived from young and aged cells are essentially the same. Indeed, initiation of the sporulation program seems to be the trigger required to reset replicative life span. The transcription factor Ndt80 is associated with the rejuvenation effect, and its ectopic expression extended the life span of vegetatively growing cells.

  9. Sorting Out the Centrosome

    The centrosome is the paired organelle that organizes microtubules to form the mitotic spindle. The yeast centrosome (called the spindle pole body) is composed of 18 proteins. To help better understand how the centrosome is regulated, Keck et al. (p. 1557) made a comprehensive analysis of phosphorylation of the yeast centrosome proteins by mass spectroscopy. Almost 300 sites of phosphorylation were identified, about 100 of which occurred only during mitosis. The results may help point the way for further functional characterization of the more complicated human centrosome, which, with some 100 proteins, is likely to be regulated by a very large set of phosphorylation events.

  10. Sleep on It

    CREDIT: BUSHEY ET AL.
    CREDIT: BUSHEY ET AL.

    Nearly all animals above a certain level of complexity need to sleep. However, we still don't know why we have to sleep at all. By making use of the many genetic tools available in the fruit fly and combining them with sophisticated behavioral and morphological analyses, Bushey et al. (p. 1576) and Donlea et al. (p. 1571) found that the dorsal fan-shaped body, a part of the central complex in the brain of Drosophila, could selectively induce sleep. Induction of sleep was important for long-term memory consolidation, and sleep itself was necessary for synaptic renormalization. Environmental enrichment resulted in a greater need for sleep, enhanced synaptic growth during wakefulness, and increased synaptic renormalization during sleep. Furthermore, the increased need for sleep directly depended on synaptic growth during the awake period.

  11. Light Control

    Melanopsin is a photopigment that triggers an intracellular calcium increase in response to blue light. Ye et al. (p. 1565; see the Perspective by Chow and Boyden) took advantage of calcium regulation of the transcription factor NFAT (nuclear factor of activated T cells) to design a synthetic signaling cascade that achieved light-inducible expression of transgenes under control of the NFAT promoter. Cells designed to display light-induced expression of glucagon-like peptide 1, a hormone involved in glucose homeostasis, were implanted into mice. Blue-light illumination of the implants attenuated glycemic excursions in type II diabetic mice. This approach of using light induction to provide tight regulation has potential applications in therapeutics and protein-expression technology.

  12. Watch Out, Little Monkey

    There has been considerable debate of whether the frontal eye field is associated with selective attention or with programmed eye movements. Performing electrophysiological recordings in monkeys, Schafer and Moore (p. 1568, published online 26 May; see the Perspective by Roelfsema) discovered that selective attention is a natural, untrained consequence of voluntarily driven changes in prefrontal neuronal activity. The activity of neurons in the frontal eye field can be increased and decreased voluntarily by using an operant conditioning, neurofeedback-type paradigm, similar to what has been classically observed in motor cortex. These voluntary changes in neuronal activity automatically resulted in spatially specific changes in visual perception and produced neural correlates of selective attention.

  13. Ordered Disorder

    When electrons or photons propagate through a sample, they are scattered by impurities and defects. The amount of disorder can influence the transport to the extent that the electrons or photons effectively get stuck (or localized) in the sample. Transport through a disordered system has a long history, but in most systems the disorder is fixed, and so the effect of disorder cannot be studied systematically. Levi et al. (p. 1541, published online 12 May) developed an optical system where the amount of disorder could be controlled, producing a quasi-crystal structure. An enhancement of the propagation was observed between the freely propagating regime for zero disorder and the highly disordered localized regimes.

  14. Correcting Mistakes

    The incorporation of ribonucleotides (normally found in RNA) into DNA, instead of deoxyribonucleotides, can result in signature 2 to 5 base pair deletions within short tandem repeats, which destabilized the genome. A similar effect is seen during high levels of transcription and depends on the enzyme topoisomerase 1 (Top1), which is usually involved in removing supercoils from DNA—a process that involves cleaving the DNA. RNase H enzymes normally remove potentially mutagenic ribonucleotides [ribonucleoside monophosphates (rNMPs)] from DNA. Kim et al. (p. 1561; see the Perspective by Cerritelli et al.), working in yeast, show that the ribonucleotide-associated signature 2– to 5–base pair deletions are produced by Top1: The presence of an rNMP at the cleavage site results in an irreversible Top1 cleavage and its subsequent repair results in a deletion. This activity may underlie the mismatch repair-independent microsatellite instability seen in some cancer cells.

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