This Week in Science

Science  01 Aug 2008:
Vol. 321, Issue 5889, pp. 608
  1. How Fast Is Fast?

    Ice core records have shown that substantial changes can happen very rapidly. Even with the high temporal resolution that some ice cores provide, it has been difficult to determine exactly how rapidly most shifts occurred, due largely to the amount of interannual variability displayed by most climate indicators and the difficulty of synchronizing the time scales of different records. Steffensen et al. (p. 680, published online 19 June; see the Perspective by Flückiger) employed sophisticated analytical methods to measure multiple climate proxies in a single, high-resolution ice core from Greenland. Measuring several parameters in the same ice obviated problems that arise from trying to intercalibrate data from different sites, and high-resolution measurements tracked changes at subannual time scales. Some attributes of climate were observed to change in as little as a single year during two abrupt warmings within the last deglaciation.

  2. Spotlight on Biodiversity Hotspots

    Certain regions of the globe harbor particularly high numbers of species of organisms. These regions have become known as biodiversity hotspots. However, the history of hotspots is not well charted. Renema et al. (p. 654) review global shifts in marine biodiversity hotspots. By combining evidence from the paleontological and molecular evolutionary literature, they identify multiple Cenozoic hotspots that were mobile and responded to global tectonic events. The authors suggest a mechanistic basis for this mobility and for the formation of modern faunas and explain the dynamic nature of biodiversity.

  3. Nonribosomal Peptide Synthetase Structure

    Nonribosomal peptide synthetases (NRPS) are multimodular megaenzymes that catalyze the biosynthesis of complex peptides, including medically important compounds, such as the antibiotic vancomycin. Each module comprises at least an adenylation domain, a peptidyl carrier protein domain, and a condensation domain. Although structures of all the essential domains are available, how they are organized to achieve peptide elongation has remained unclear. Now Tanovic et al. (p. 659, published online 26 June) have determined the structure of a complete termination module. The organization of the domains suggests how the catalytic steps are coordinated within the NRPS module, which may facilitate efforts to engineer chimeric NRPS proteins to allow biosynthesis of new peptides.

  4. Shaking Out Gold Structures


    Oxidative catalysis by nanoscale gold clusters is exquisitely sensitive to cluster size and geometry, but these parameters can be challenging to determine, particularly in a heterogeneous sample. Gruene et al. (p. 674) take advantage of the structural purity attainable by mass selection in the gas phase to explore the geometries of three neutral clusters: Au7, Au19, and Au20. By measuring vibrational spectra in the far-infrared and comparing them with calculated absorptions of model compounds analyzed by density functional theory, the authors assign a planar structure to the smallest cluster, and a tetrahedral geometry to Au20, which is truncated by loss of a vertex atom in Au19.

  5. Signaling in Time and Place

    Proteins that participate in biological regulatory mechanisms are often assembled into large complexes, within which various signaling molecules interact to propagate a biochemical signal. Matsuzawa et al. (p. 663, published online 17 July; see the Perspective by Eliopoulos) characterize such a complex of proteins assembled at the activated receptor CD40 (a member of the tumor necrosis factor receptor family) on the cell surface. The complex formed at the cell surface within a few minutes after binding of ligand to the receptor, but after 30 minutes had moved to the cytoplasm. Surprisingly, activation of mitogen-activated protein kinases (MAPKs) JNK and p38 and of the MAPK kinase MEKK1 was only detected once the complex left the receptor and moved into the cytosol. Degradation of the adaptor protein TRAF3 was required to initiate release of the complex from CD40. Other receptors may also use such a mechanism to specify the time and place at which signaling proteins are activated in response to receptor stimulation.

  6. A Star Is Born

    Observations of early stars in the universe suggest that even earlier stars that formed after the Big Bang were massive enough to produce some heavy elements. Yoshida et al. (p. 669; see the Perspective by Bromm) now describe computer simulations that begin after the Big Bang and extend to the time of the formation of an early star. The results suggest that a tiny protostar much smaller than the density variations in dust produced by the Big Bang could provide the nucleus for a protostar smaller than the Sun but that can grow to a massive star.

  7. Polymer Electrodes for Oxygen Reduction

    A number of important electrochemical devices, including fuel cells and various air batteries, rely on the fast rate of oxygen reduction over platinum electrodes. The cost and scarcity of Pt has long driven a search for alternatives, which often include Pt as an alloy component or suffer in terms of rate. Conducting polymers could provide an alternative if they could be stabilized as a high-surface-area material. Winther-Jensen et al. (p. 671; see the News story by Service) have grown poly(3,4-ethylenedioxythiophene) (PEDOT) through vapor-phase polymerization onto a Goretex membrane. They report oxygen reduction rates in gas phase and aqueous solution comparable to that of high-area Pt electrodes. Unlike Pt, the PEDOT electrodes are not slowed down by the presence of CO, which can be a contaminant in some applications.

  8. Human Immunity--Naturally

    Animal models continue to influence our understanding of immunity to infection, but how accurately do they predict how our own immune systems respond to different pathogens? Von Bernuth et al. (p. 691) continue a series of studies in which they use rare human immune deficiencies to help unpick the roles played by distinct innate immune pathways. The study focuses on MyD88, a signaling adaptor that is crucial in mice for protection against a wide range of pathogens by connecting key Toll-like receptor (TLR) and interleukin-1 (IL-1) pathways to the activation of immune response genes. In contrast to findings in mice, deficiency of the same protein in the human patients caused susceptibility to only a handful of pyogenic bacteria, despite leaving the subjects with broad deficits in their TLR and IL-1 responses.

  9. Preliminary Purge

    B lymphocytes express somatically rearranged immunoglobulin receptors on their surface containing the same heavy and light chains as the antibodies the cells will produce later. However, only the heavy chain is expressed during early developmental transitions, meaning that a surrogate light chain (SLC) is needed to help the heavy chains arrive at the cell surface to generate a pre-B cell receptor. This strategy “pre-selects” B cells that have successfully completed heavy chain rearrangement before committing them to light chain production. Keenan et al. (p. 696, published online 19 June) provide evidence for a further role of the SLC in weeding out potentially harmful self-reactive B cells. Mice deficient in the SLC showed elevated levels of circulating autoantibodies, resulting directly from the escape of autoreactive cells at the early stages of B cell development.

  10. The Pain Specialists

    In pain research it has been assumed that most nociceptive neurons are polymodal, responding to different damaging stimuli by means of a repertoire of cell surface receptors specialized for the detection of particular types of insult. Attempts to ascribe pain modalities and behavior to individual sensory neuron receptors have been problematic, probably because of the existence of multiple damage-sensing molecules. Now, however, by genetically ablating subsets of nociceptors, followed by behavioral and electrophysiological assays, Abrahamsen et al. (p. 702) have found that sensory neurons expressing a specific type of sodium channel (Nav1.8) have a modality-specific function in pain transmission. Nav1.8-expressing sensory neurons are essential for cold, mechanical, and inflammatory pain behavior. Strikingly, neuropathic and heat pain behavior do not require Nav1.8-expressing neurons.

  11. Pluripotent Reprogramming

    Adult mouse and human fibroblasts can be reprogrammed to a pluripotent state after the viral integration of four transcription factors. However, questions remain as to the origin of the pluripotent cells, whether specific genomic integration sites are needed, and how tumorigenicity might be reduced. Aoi et al. (p. 699, published online 14 February) now reprogram adult mouse hepatocytes and stomach epithelial cells to a pluripotent state, termed iPS cells. These cells show great similarity to embryonic stem cells, are of a differentiated cell origin, do not require a specific viral integration site, and are not tumorigenic to at least 30 weeks. This work provides insight for understanding the mechanism of iPS reprogramming and moves another step toward using these cells to study disease in culture and the hoped-for application in human therapy.

  12. Not Too Hot to Handle

    Solid oxide fuel cells need to operate at high temperatures in order to ensure sufficient ionic conductivity. This results in longer start-up times and can cause additional mechanical or chemical compatibility issues with other parts of the cell. Garcia-Barriocanal et al. (p. 676) show that sandwiching an ultrathin layer of yttria-stabilized zirconia (YSZ) between two thin layers of strontium titanate (STO) or by making multilayers with this arrangement can lead to an eight-orders-of-magnitude increase in lateral ionic conductivity. This increase brings the YSZ-STO combination within the practical operation conditions of solid oxide fuel cells at just above room temperature.

  13. Rotten Nitrogen

    Decomposition of plant litter by microorganisms results in the release of nitrogen in the form of ammonium and nitrate from proteins, which are subsequently immobilized once again into proteins by the decomposers as the organisms assimilate carbon, replicate and grow. Manzoni et al. (p. 684) have amassed data to develop a model of the efficiency of microbial decomposition in relation to the nutritional value of various types of plant litter. Although temperature is important to decomposition rate, the ratio of carbon to nitrogen in the litter has the dominant effect on nitrogen immobilization. Carbon-use efficiency by decomposers adapts to nitrogen levels depending on how much the decomposers need to scavenge nitrogen. At low nitrogen levels, the result is higher respired carbon loss.

  14. Splice Factor

    Alternative splicing of transcripts generates significant functional diversity within genomes. This is particularly well illustrated by the CD45 gene, which undergoes regulated activation-dependent alternative splicing in lymphocytes to generate several functionally distinct isoforms. Oberdoerffer et al. (p. 686, published online 10 July; see the Perspective by Holmes) identify a specific factor, heterogeneous ribonucleoprotein L-like (hnRNPLL), as a principal regulator of CD45 splicing. Evidence for direct interaction of hnRNPLL with its target transcript was uncovered, although further work will be needed to reveal the precise mechanism by which it binds its target sequences and cooperates with spliceosome components to promote exon excision.

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