This Week in Science

Science  22 Apr 2011:
Vol. 332, Issue 6028, pp. 395
  1. Blowing Harder

    CREDIT: YOUNG ET AL.

    Climate change is often discussed in terms of ground surface air temperature, and less often in terms of precipitation, sea surface temperature, or any of the other parameters that constitute climate in its totality. Wind speed and its dependent variable, ocean wave height, are rarely considered. Young et al. (p. 451, published online 24 March) analyzed a 23-year-long database of wind speed and ocean wave heights to investigate how they may have changed. Windiness has been increasing on a global scale. However, the situation for waves is more complex: While wave heights in general show little statistically significant trends globally, the heights of larger waves do seem to be increasing at higher latitudes.

  2. Binary Emissions

    Black hole x-ray binaries consist of a black hole and a normal star that orbit around their common center of mass. Matter moving from the star toward the black hole produces bright x-ray emissions typical of these systems. Laurent et al. (p. 438, published online 24 March; see the Perspective by Hardcastle) report the detection of polarized gamma-ray photons from the black hole, Cygnus X-1. The polarized emission may be related to the jet of relativistic particles that is ejected from the vicinity of the black hole. This detection provides insight into the emission mechanisms in this source, which serves as a prototype for other black hole binaries.

  3. Progranulin Protects

    Rheumatoid arthritis is a systemic autoimmune disease that principally affects synovial joints, including knee, finger, hip, and wrist. The inflammatory cytokine, tumor necrosis factor–α (TNFα), contributes to disease pathogenesis and targeted therapies against TNFα are currently in use. Because the therapeutic efficacy and side effects of anti-TNFα treatments differ among patients, there is interest in discovering new therapies. Tang et al. (p. 478, published online 10 March; see the Perspective by Wu and Siegel) now report that the growth factor progranulin may represent a potential therapeutic target in the treatment of rheumatoid arthritis. Progranulin binds directly to TNF receptors 1 and 2 and competes with TNFα for receptor binding. Progranulin deficiency protected against the development of inflammatory arthritis in multiple mouse models of the disease. Furthermore, an engineered protein composed of peptide fragments of progranulin retained TNF receptor binding, prevented the development of inflammatory arthritis in mouse models, and decreased the mouse disease symptoms when used therapeutically.

  4. A Tight Squeeze

    Cell size and the maximal length of the anaphase spindle vary greatly. How can small cells ensure that their short spindle efficiently separates long chromosomes? Similarly, the size of chromosomes can vary tremendously. Whether and how cells cope with enlarged chromosomes is also unclear. Neurohr et al. (p. 465, published online 10 March) report that a highly elongated chromosome resulting from the fusion of the two longest endogenous chromosomes segregates faithfully and does not affect mitotic progression, spindle size, or cellular viability. It seems that yeast cells detect the presence of long chromosomes and specifically induce their hypercondensation during anaphase. Thus, the spindle midzone may function as an anaphase “ruler,” to promote hypercondensation of long chromosomes and the scaling of their physical length relative to that of the spindle.

  5. Ether Cleaver

    Woody lignins may ultimately prove a useful source of raw material for chemical manufacturing, but producing individual molecular feedstocks from lignin remains a challenge. Lignin contains a network of aromatic hydrocarbons mostly connected through oxygen bonds, and methods to cleave these ether linkages tend to result in undesirable side reactions. Sergeev and Hartwig (p. 439) describe a homogeneous nickel catalyst that directs hydrogen to cleave aryl-oxygen bonds in lignin model compounds with high selectivity, leaving the carbon framework untouched, which provides a promising starting point for improved biomass processing.

  6. Genes in Action

    CREDIT: LARSON ET AL.

    Genes are transcribed in a temporally discontinuous manner in a broad range of organisms (see the Perspective by Nair and Raj). Suter et al. (p. 472, published online 17 March) used a short-lived protein translated from short-lived messenger RNA along with ultrasensitive bioluminescence microscopy to observe transcriptional kinetics of mammalian genes in individual cells. The size of transcriptional bursts, the duration of the silent interval, and the rate of switching transcription on and off all depended on the specific gene. Furthermore, the temporal pattern of transcription was markedly altered by modifications of gene promoter sequences. Larson et al. (p. 475) developed a light-microscopy method for observing transcription of single genes directly, allowing them to separate the different steps in RNA synthesis. Measurement of the in vivo dynamics of a yeast transcription factor indicated that the gene firing rate was directly determined by the search times for the transcription factor to find its target.

  7. Glutamate Receptors in Pollen

    Plant genes that encode proteins similar to mammalian glutamate receptors, which are critical to neuronal function, were identified some time ago, but the function of these proteins in plants has been a mystery. Now, Michard et al. (p. 434, published online 17 March; see the cover) examined two Arabidopsis glutamate receptor–like channels (GLRs) that are expressed in pollen and affect pollen tube growth. The unusual amino acid d-Ser produced by target female tissues activated GLRs in the apical region of pollen tubes, allowing Ca2+ permeation into the cytoplasm and promoted pollen tube growth. This modulation of function by an amino acid signal suggests how pollen tube growth may be coordinated with signals from the tissues that they must grow through.

  8. Shirking Platinum

    A substantial hindrance to the widespread automotive application of fuel cells is the prohibitive cost of their platinum catalysts. Catalysts composed of cheaper materials (often abundant metals in combination with nitrogen-doped carbon) have shown promise, but tend to degrade under the highly acidic conditions in most membrane-based fuel cells. Wu et al. (p. 443) have now discovered that catalysts derived from heating polyaniline with iron and cobalt salts remain stable under these demanding conditions, while approaching the activity of platinum.

  9. Sliding in Nitrogen

    Saturated hydrocarbons, composed exclusively of carbon-carbon and carbon-hydrogen single bonds, are easy to burn into water and CO2, yet are frustratingly hard to convert into a more functional range of organic compounds. Research over the past 30 years has uncovered a number of transition metal–catalyzed processes for inserting oxygen or nitrogen into C–H bonds to yield alcohols or amines, although efficiency and selectivity remain twin, often competing, challenges. Ochiai et al. (p. 448) now show that a highly reactive bromane-based compound can transfer nitrogen to hydrocarbons efficiently at room temperature without the need for a catalyst. The reaction is also reasonably selective, favoring C-H over CH2 centers and bypassing CH3 groups entirely.

  10. Once Upon a Wetter Time

    The Eocene epoch, 56 to 34 million years ago, had a much warmer climate than the present, with global annual temperatures at times as much as 12°C higher than today. Our understanding of the climate system suggests that the Eocene should have had a stronger hydrological cycle than present-day, because its higher temperatures would have caused an increase in the concentration of water vapor in Earth's atmosphere. However, evidence to support this assumption is lacking. Clementz and Sewall (p. 455; see the Perspective by Bowen) now present δ18O measurements of Eocene fossilized tooth enamel from ancient aquatic mammals to show that tropical values were offset from modern ones by more than what was expected from the increased continental ice volume, which may suggest significantly wetter conditions during the Eocene than those of today.

  11. Cardiomyocyte Proliferation Potential

    During cardiac development, progenitor cells give rise to cardiomyocytes that compose the bulk of the mature heart. As development progresses, the proliferative potential of maturing cardiomyocytes is gradually lost. Renewal of cardiomyocytes in adults occurs at extremely low frequency. Heallen et al. (p. 458; see the Perspective by Schneider) now find that Hippo signaling, an organ size–control pathway in Drosophila, underlies the low proliferative potential of cardiomyocytes. The molecular mechanism involves an antagonistic interaction between Hippo and Wnt signaling, which prevents expression of growth-promoting genes. Thus, it may be possible to enhance cardiomyocyte proliferation by interfering with Hippo signaling.

  12. Cell Cycle Fertilization Trigger

    A critical point of cell cycle control, with implications for reproduction, is the exit of oocytes from meiosis II, the stage at which oocytes arrest until they are fertilized. One mechanism that contributes to this process is proteolytic degradation of Cyclin B and consequent inactivation of the cyclin-dependent kinase Cdc2. Another mechanism for inhibiting activity of Cdc2 is phosphorylation by the protein kinase Wee1B. Oh et al. (p. 462, published online 31 March) present evidence that this mechanism is also critical in mouse oocytes. Fertilization causes an increase in the intracellular concentration of free Ca2+, thus activating calcium-calmodulin–dependent protein kinase II, which in turn activates Wee1B.

  13. Understanding Chromosome Fusions

    Telomeres are DNA repeats that cap the ends of linear chromosomes to prevent them from being recognized as DNA damage. Loss of these caps can result in catastrophic end-to-end chromosome fusions, the repair of which frequently shapes the landscape of tumor genomes. Lowden et al. (p. 468) looked at the consequences of end-to-end chromosome fusions in telomerase-deficient mutants of the nematode worm Caenorhabditis elegans, which, unlike humans, has holocentric centromeres that are stable after such fusions. Many of the chromosome aberrations involved complex fusion events—duplications, triplications, and nonduplicated sequences, possibly generated by DNA replication template-switching, as well as breakpoints that were sealed by microhomology—some of which have parallels to events seen in tumor development.

  14. Growth or Retraction

    As axons extend outward, whether in the course of normal development or in regenerating after damage, they encounter an environment that includes proteoglycans. The chondroitin sulfate proteoglycans tend to inhibit axon growth, and the heparan sulfate proteoglycans tend to have the opposite effect. Both proteoglycans can signal through the same receptor, RPTP-σ. Studying neurons from the mouse dorsal root ganglion, Coles et al. (p. 484, published online 31 March) found that both types of proteoglycan used the same binding site on the receptor. However, heparan sulfate binding leads to receptor oligomerization, unlike chondroitin sulfate. Clustering of the receptors thus appears to generate an environment that encourages axonal growth.