This Week in Science

Science  18 Jul 2008:
Vol. 321, Issue 5887, pp. 313
  1. Talking Fish


    Although speech seems a particularly human characteristic, vocalizations that impart social and environmental information are common to a variety of other animals, including birds, frogs, and even fish. Bass et al. (p. 417; see the Perspective by Margoliash and Hale) studied the development of larval Batrachoidid fish, the adults of which use a complex pattern of vocalizations. Analysis of the developing hindbrain, particularly the eighth rhombomere, showed the beginnings of the vocal motor nucleus. The development of this vocal pacemaker circuit in fish reflects similar patterns of development known from other vertebrates. Thus, the brain circuitry driving vocalizations may have its origins far back in the evolution leading to bony vertebrates.

  2. Sleepless in Drosophila

    All animals sleep, and the more they are awake, the stronger the drive to sleep. To better understand the process of sleep, Koh et al. (p. 372; see the news story by Youngsteadt) screened mutagenized Drosophila for genes involved in sleep regulation. They found one—sleepless—that is required for normal sleep; without sleepless, flies sleep much less, about 20% of normal. Sleepless is also required for rebound sleep after prolonged waking. Sleepless is an allele of quiver, a gene that modulates the K+-channel activity encoded by Shaker, which also affects sleep. K+ channel-associated neuronal sensitivity may thus play a role in the control of sleep, and the SLEEPLESS protein may signal the drive to sleep by decreasing membrane excitability.

  3. Afterglow

    Gamma-ray bursts, the most energetic emissions in the universe, are thought to be produced when a black hole consumes a rapidly rotating, high-mass star. Many bursts are followed by an extended x-ray afterglow. Kumar et al. (p. 376, published online 26 June) analyze this afterglow and, assuming that it represents continued emissions from the stars, use it to determine the properties of the consumed stars. The analysis of three stars characterizes their rotation speeds and shows that only a few solar masses are consumed in the outburst, even though the stars may have been several times as large.

  4. Striving for Perfection

    The mechanical properties of a material rarely achieve theoretical or ideal properties, due to defects that are formed during synthesis or processing. For materials with nanoscale dimensions, the gap between the ideal and real cases can close, because it is easier to make materials that are close to being defect-free. Lee et al. (p. 385) measure the elastic properties and breaking strength of graphene membranes, which are one-atom-thick carbon sheets, and find values that agree with recent simulations and calculations. The material can be deformed well beyond the linear regime, and graphene is one of the strongest materials ever measured.

  5. Not Cracking Under the Strain


    Ductile materials will deform before failure, while brittle ones show sudden cracking and rupture and thus give little warning of the impending doom. Most steels will show ductile failure, but if placed under a constant tensile stress and exposed to the right (or wrong) chemical environment, they can suddenly undergo brittle failure through the formation of stress corrosion cracking. King et al. (p. 382; see the Perspective by Stierle) use diffraction contrast tomography to track intergranular stress corrosion cracking. Special grain boundaries could be observed that are resistant to the cracking process due to the formation of bridging ligaments that retain some ductility within the material.

  6. Details from Damage

    Surface-enhanced Raman scattering (SERS) is a well-established phenomenon whereby incident laser fields are locally enhanced a millionfold or more by metallic substrates sharply structured at the nanoscale. The effect has been used for sensitive molecular sensing applications, but approaches toward optimizing substrate geometries for maximal enhancement remain somewhat empirical. A particular challenge has been quantifying the distribution of enhancement magnitudes across multiple sites on a given surface. Fang et al. (p. 388, published online 26 June) explore this distribution by using the field enhancement to induce damage (presumably by ionization) of adsorbed molecules on a widely studied SERS substrate of silver-coated nanoparticles. By steadily ramping up the energy of an incident laser pulse, they progressively damage molecules at sites with diminishing enhancement factors, observing the depletion with a low-intensity probe pulse.

  7. The Invisible Past

    Has the move to electronic publication changed authors' styles of searching and citing the literature? Evans (p. 395) reports that researchers are referencing more narrowly than in the past, citing fewer, more recent references. A database of 34 million articles from journals that became available online between 1998 and 2005 was analyzed for the number of articles (from a given journal) cited by any other articles in a given publication year. The results were consistent over time and were not journal- or subfield-specific. Perhaps because of the lack of hyperlinks and efficient electronic indexing, individuals searching through the print literature may be exposed to a broader set of references and ideas.

  8. Phosphorylation Inside-Out

    A signaling pathway called the Hippo pathway has important roles in the control of tissue organization in development and in the regulation of organ size in the fruit fly. Hippo is a protein kinase that appears to pass signals from atypical cadherin molecules Fat and Dachsous at the cell surface to another intracellular kinase, Warts, which then regulates a transcriptional coactivator. Another protein somewhat distantly related to the protein kinases, Four-jointed, has also been implicated genetically in the pathway. Ishikawa et al. (p. 401) provide evidence that Four-jointed, which is localized to the Golgi complex, is indeed a kinase and that it appears to phosphorylate the cadherin domains of Fat and Dachsous, which will become extracellular domains at the cell surface.

  9. Doubled-Up Decision

    CD8+ T cells are major contributors to cell-mediated immunity to virally infected cells and tumors. Like their helper CD4+ counterparts, these cells rely on the transcriptional regulator T-bet for their correct development. Recently, a second factor called eomesodermin has also been found to control CD8 functions. Intlekofer et al. (p. 408) now find that without both factors, CD8+ T cells fail to develop their normal cell-mediated functions and instead secrete the inflammatory cytokine IL-17, which has been recently characterized in helper T cells. This secretion of IL-17 caused significant pathology in a mouse model of viral infection, suggesting that both transcription factors play a crucial role in maintaining appropriate cell-mediated responses to infection.

  10. Absence of Cooling


    The Younger Dryas was an approximately 1300-year period that interrupted the warming of the last deglaciation, during which markedly colder conditions clearly recurred in many parts of the Northern Hemisphere. Whether or not the Southern Hemisphere experienced concurrent cooling is an open question. Ackert et al. (p. 392; see the Perspective by Lowell and Kelly) measured cosmic-ray exposure ages of a glacial moraine in southern Patagonia in order to determine whether or not the glacial advance that created it occurred during the Younger Dryas chronozone. The moraine was deposited soon after the end of the Younger Dryas, and the glacier grew in response to more precipitation, not because of regional cooling. This suggests that temperatures in the Southern Hemisphere did not drop like those in the North during the Younger Dryas.

  11. Simultaneous Brain Imaging and Microstimulation

    Until now, functional brain-imaging studies have focused on how regions are activated by a particular stimulus or cognitive task. However, how nodes within a functional network causally interact with each other is still poorly understood. Ekstrom et al. (p. 414) used a novel combination of chronic intracortical microstimulation and functional magnetic resonance imaging in awake, behaving monkeys to study the impact of frontal top-down signals on incoming sensory information. Frontal eye fields could modulate early visual areas only in the presence of a visual stimulus, whereas higher-order visual areas could be modulated independent of visual stimulation.

  12. Orbitofrontal Obsessions

    Obsessive-compulsive disorder is a debilitating neuropsychiatric condition characterized by recurrent intrusive thoughts (obsessions) and repetitive rituals (compulsions) often performed according to rigid rules. Abnormal function of the orbitofrontal cortex is central to neurobiological models of this disease. However, it is unclear whether these abnormalities are due to the symptoms of the disorder or represent a vulnerability marker also existing in people at increased genetic risk. In a well-validated brain-imaging study, Chamberlain et al. (p. 421) observed reduced activation of the orbitofrontal cortex during a reversal learning task in patients with obsessive-compulsive disorder and their unaffected first-degree relatives compared to normal controls. This deficit in activation may thus represent an endogenous predisposing factor for obsessive-compulsive disorder.

  13. X-ray Vision

    In a typical diffraction experiment, one is able to capture the amplitude or intensity of the scattered radiation source but not the associated phase information. A number of approaches exist for reconstructing this information, usually through oversampling the diffraction data. Thibault et al. (p. 379; see the Perspective by Chapman) follow earlier work where they scan an object through a beam diffracted from a pinhole. Instead of deconvolving the data, they use a difference map technique to reconstruct the phase information. By using a Pilatus detector, they can rapidly collect data sets free of noise. The technique should allow for the study of buried interfaces in a number of materials-science problems and for characterizing next-generation x-ray sources.

  14. Bigger Is Better

    The species body-size distribution tends to exhibit a heavy right tail within most large taxonomic groups—for example, insects, birds, fish, and mammals. This distribution extends over many orders of magnitude and exhibits a modal size that is significantly larger than the smallest species. Clauset and Erwin (p. 399) show that a model of species body size over evolutionary time, which is limited by physiological constraints and shaped by extinction risks estimated from fossil data, reproduces the empirical distribution of species body size of 4002 terrestrial mammals from the late Quaternary. Additionally, the authors find that the diffusion process in terrestrial mammals is slightly, but universally, biased toward larger sizes.

  15. Golgi-Localization Signals

    Golgi-resident glycosyltransferases lack motifs that would mediate their interaction with the so-called COPI vesicles involved in their recycling. Now, Tu et al. (p. 404) show that a membrane protein, Vps74p, binds to COPI, as well as to a peptide motif present in the cytoplasmically orientated tails of 16 out of 21 yeast Golgi-resident glycosyltransferases. In the absence of Vps74p, a number of these motif-bearing Golgi-resident glycosyltransferases (5 out of 21) are mislocalized to the vacuole. The authors propose that Vps74p functions as a protein-sorting receptor for the sorting of Golgi glycosyltransferases into COPI-coated vesicles.

  16. Nailing a Riboswitch

    In bacteria, the second-messenger cyclic di-GMP regulates a wide range of genes and affects diverse physiological (and disease-causing) processes. It has been suggested that cyclic di-GMP may modulate transcription and translation via specific cyclic di-GMP riboswitches. Sudarsan et al. (p. 411) now show that this is indeed so and that cyclic di-GMP, and not its closely related breakdown products, binds to the highly conserved GEMM RNA domain, which is found upstream of both cyclic di-GMP synthesis and degradation enzymes, as well as likely target genes. The GEMM RNA constitutes the aptamer domain of the cyclic di-GMP riboswitch. The riboswitch is also found in bacteriophages, suggesting viruses monitor and respond to the cyclic di-GMP-driven physiological transformations of their hosts.