This Week in Science

Science  30 Sep 2011:
Vol. 333, Issue 6051, pp. 1797
  1. Making the Buzz

    CREDIT: LASSE JAKOBSEN AND COEN ELEMANS

    In both ray-finned fish and songbirds, superfast muscles have been identified in sound-making organs that are integral to acoustic communication in these species. In bats, rapid call rates are known to occur during echolocation, especially during the terminal locating phase or “buzz.” Elemans et al. (p. 1885) show that the extremely high rate of call emission that occurs during the buzz is made possible by superfast muscles, similar to those identified in birds and fish but not previously known in mammals. The presence of these muscles across diverse taxonomic groups suggests that they may be advantageous for species that use acoustic output for communication or predation.

  2. Exploiting Microbial Pathogens

    Microbial pathogens that do their dirty work by co-opting the target cell's genomic controls are now being used by scientists to direct research-driven changes in gene control. Bogdanove and Voytas (p. 1843) review the discovery of the DNA-binding molecules involved in this process, what is known about how they work, and the implications for their future use in biotechnology.

  3. Messages from MESSENGER

    The MESSENGER spacecraft has been in orbit around Mercury, the smallest and innermost planet in the solar system, since 18 March 2011. Based on x-ray spectra obtained during MESSENGER's first 90 days of orbital science operations, Nittler et al. (p. 1847) determined the abundances of the major rock-forming elements in the surface of Mercury. The planet's surface composition is different from those of the other terrestrial planets, which provides clues to what Mercury's precursor materials might have been. Peplowski et al. (p. 1850) analyzed γ-ray emission from the surface of Mercury to determine the abundances of the radioactive elements K, Th, and U, which indicate that the planet formed from relatively volatile-enriched material. High-resolution images obtained from orbit around the planet allow Head et al. (p. 1853) to show that the northern smooth plains of Mercury were made by lava flows, confirming extensive global volcanism; Blewett et al. (p. 1856) describe a previously unknown landform that may have formed by processes involving volatile compounds that could still be active. Anderson et al. (p. 1859) show that the planet's internally generated magnetic field can be represented by a dipole with an axis tilted from the rotation axis by less than 3° and with a magnetic equator displaced northward of the geographical equator by 484 kilometers. Zurbuchen et al. (p. 1862) present analysis of Mercury's ionized exosphere, which reveals that heavy ions are most concentrated near the poles, where the solar wind has access to the planet's surface. Ho et al. (p. 1865) use energetic particle data accumulated during MESSENGER's first Mercury year (88 Earth days) to show that Mercury's magnetosphere is very different from that of Earth's. In particular, its electron population does not seem to circulate around the planet, and thus, Mercury does not sport rings of charged particles like Earth's Van Allen radiation belts.

  4. Too Little Rime on Mars

    The atmosphere of Mars is much thinner and contains a lot less water vapor than that of Earth's. Even so, understanding water vapor's behavior on Mars is important because of its role in the hydrological cycle. Maltagliati et al. (p. 1868; see the Perspective by Heavens) measured the vertical distribution of atmospheric water vapor during portions of the northern spring and summer of one Mars year and compared them with the predictions from global climate models. The amount of water vapor at 20- to 50-kilometer altitude was much higher than expected, in excess of saturation, implying that the water vapor's profile height is not controlled by the saturation vapor pressure. This supersaturation is likely to be the result of inefficient condensation of water vapor into ice because of the presence of clouds.

  5. Predicting Polymer Behavior

    A long-standing goal in polymer science is to connect the molecular architecture of a polymer with its flow properties or viscoelasticity. Through a mixture of experiments and calculations, Read et al. (p. 1871; see the Perspective by Larson) predicted the processing characteristics of a complex branched polymer melt from its synthesis chemistry.

  6. A Well-Behaved Catalyst

    CREDIT: HARPER AND SIGMAN

    The simplest way to design an asymmetric catalyst is to place a bulky group on a single side of the structure, so that molecules will bind on the other side and form just one of two possible mirror-image products. Of course, this strategy doesn't always work; the influence of electronic factors can counteract the steric effect, and there's always a question of just how big the bulky group ought to be. Harper and Sigman (p. 1875; see the Perspective by Wiest and Helquist) took a systematic approach to optimizing steric and electronic factors in devising a catalyst for selective addition of alkyne derivatives to ketones and uncovered an unexpected synergy between sterics and electronics that would not have been obvious in screens of either property alone.

  7. Measuring Zeitgeist?

    It is difficult to acquire data on mood at an individual level for large populations. Golder and Macy (p. 1878) examined more than 509 million Twitter posts by 2.4 million users over a 2-year period in order to study collective mood. Two standard lexicons were used to connect text to mood. The U.S., Canada, the UK, Australia, India, and English-speaking Africa all showed similar mood rhythms—despite very different cultures, geographies, and religions. People tended to be more positive on weekends and early in the morning.

  8. When Is a Demethylase Not a Demethylase?

    A transcriptional negative feedback mechanism is central to the mammalian circadian clock, but the detailed mechanisms that account for precise control of the oscillator, in particular modifications to histones that influence transcription, are not fully understood. DiTacchio et al. (p. 1881; see the Perspective by Brown) show that regulation at the promoter of the Per2 gene, which encodes a clock component that in turn represses transcription of other genes, involves binding of a histone demethylase called JARID1a. The important function of JARID1a at the Per2 promoter, however turned out not to depend on its histone demethylase activity, but rather to be its influence to decrease histone acetylation at the Per promoter. Circadian rhythms were disrupted or altered in flies and mice lacking JARID1a.

  9. Calcium in Color

    Calcium indicators are widely used to detect intracellular signaling activity. A calcium indicator based on green fluorescent protein has been available for a decade. However, despite the success in engineering diverse fluorescent proteins, genetically encoded calcium imaging has remained limited to green. Zhao et al. (p. 1888, published online 8 September) developed a method to screen Escherichia coli colonies for calcium-dependent fluorescent changes and then used directed evolution to develop blue, red, and improved green indicators, as well as an emission ratiometric indicator. The indicators enabled multicolor calcium imaging in single cells, imaging of calcium dynamics, and imaging of neuronal activity in Caenorhabditis elegans.

  10. Yin and Yang Stress Responses

    CREDIT: REFOJO ET AL.

    Corticotropin-releasing hormone and its type 1 high-affinity receptor (CRHR1) are widely distributed throughout the brain. Together, they orchestrate the neuroendocrinological and behavioral adaptation to stress. Using conditional mutant mice, Refojo et al. (p. 1903, published online 1 September) found that CRHR1s on glutamatergic neurons in the amygdala and hippocampus are specifically involved with anxiety. However, CRHR1s on dopamine neurons in the midbrain had an opposing effect on anxiety via the regulation of dopamine release in the prefrontal cortex.

  11. Damaged During Division

    The genomes of cancer cells often show both damage within chromosomes (deletions, insertions, and rearrangements), and loss and gain of whole chromosomes. These types of genetic instabilities are thought to occur independently of each other. Janssen et al. (p. 1895) forced chromosomes to missegregate in human tissue culture cells and saw a proportionate increase in DNA damage foci, which often appeared at the position where the cells divided from one another. Missegregating chromosomes trapped at the point where the cells were about to separate appeared to be broken by the forces dividing the two daughter cells, and the fragments being passed onto the daughters appeared to be inadequately “repaired” by nonhomologous end joining, resulting in chromosomal translocations and fusions.

  12. Go Against the Flow

    Cells of our immune system continuously circulate through the blood and lymphoid tissues, maintaining a constant vigil against infections. Exit and entry between blood and tissues, and cell migration within tissues, is a highly regulated process, controlled by chemokine gradients. However, sometimes lymphocytes move against a chemokine gradient. Arnon et al. (p. 1898) used a genetic approach to show that the G protein–coupled receptor kinase-2 (GRK2) is critical for down-regulating lymphocyte expression of S1P receptor-1 (S1PR1), the receptor for the lipid mediator sphingosine-1-phosphate (S1P). GRK2-mediated down-regulation of S1PR1 expression allows T cells to ignore high concentrations of S1P in the blood and to move into lymph nodes, and it also allows B cells to move between different cellular niches in the spleen to promote optimal access to antigens.

  13. Directing Quality Control

    The unfolded protein response (UPR) is triggered when misfolded secretory and membrane proteins accumulate within the endoplasmic reticulum (ER). It remains unclear how the misfolded state of proteins in the ER is sensed by the transmembrane signal transducing kinase, Ire1. Gardner and Walter (p. 1891, published online 18 August; see the Perspective by Kawaguchi and Ng) now provide evidence that supports the notion that Ire1 directly interacts with misfolded proteins, thereby leading to dimerization and activation of Ire1. Yeast in vitro experiments showed that the luminal domain of Ire1 can bind to peptides enriched in hydrophobic and basic residues typical of misfolded proteins. Furthermore, a misfolded model protein directly interacted with Ire1 in intact yeast cells.

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