This Week in Science

Science  08 Apr 2011:
Vol. 332, Issue 6026, pp. 145
  1. Asteroseismology Delivers


      Using asteroseismology—the study of stellar oscillations, it is possible to probe the interior of stars and to derive stellar parameters, such as mass and radius (see the Perspective by Montgomery). Based on asteroseismic data from the NASA Kepler mission, Chaplin et al. (p. 213) detected solarlike oscillations in 500 solartype stars in our Galaxy. The distribution of the radii of these stars matches that expected from stellar evolution theory, but the distribution in mass does not, which challenges our knowledge of star formation rates, the mass of forming stars, and the models of the stars themselves. Derekas et al. (p. 216) report the detection of a triple-star system comprising a red giant star and two red dwarfs. The red giant star, instead of the expected solarlike oscillations, shows evidence for tidally induced oscillations driven by the orbital motion of the red dwarf pair. Finally, Beck et al. (p. 205) describe unusual oscillations from a red giant star that may elucidate characteristics of its core.

    1. The Ribozyme World

        In the hypothetical ancient “RNA world,” DNA's chemical sister RNA played the central genetic and catalytic roles in biological processes. Implicit in such a system is the existence of an RNA polymerase ribozyme. Previous in vitro evolution and step-wise engineering created the R18 RNA polymerase ribozyme, which has limited polymerase activity (up to 14 nucleotides). Wochner et al. (p. 209; see the Perspective by Yarus) used the R18 ribozyme as a starting point to engineer and evolve further a new RNA polymerase ribozyme capable of synthesizing templates up to ∼94 nucleotides in length with high fidelity. The improved ribozyme could synthesize a small self-cleaving hammerhead ribozyme.

      1. Capturing 3D on Thin Film

          Holograms store the phase and amplitude information of light bouncing off an object as an interference pattern in a photographic plate. A three-dimensional reconstruction of the object can be achieved by illuminating the hologram with light of the same wavelengths used to store the hologram. Ozaki et al. (p. 218) describe a color holographic technique based on the diffraction of surface plasmons propagating at the surface of a thin metal film. The surface plasmons were excited using white-light–angled illumination and the incident angle of illumination determined the color diffracted to the viewer.

        1. Burn, Baby, Burn

            The summer of 2010 was a real scorcher in large parts of Eastern Europe. Barriopedro et al. (p. 220, published online 17 March) show that the heat wave was the greatest in the last 500 years. In western Russia alone, there were more than 55,000 heat-related deaths, extensive wildfires, an annual crop failure of ∼25%, and a total economic loss of around 1% of Russia's gross domestic product. Models indicate that less extreme heat waves are 5 to 10 times more likely over the next 40 years.

          1. Understanding Intergranular Films


              Intergranular films appear at grain and phase boundaries in polycrystalline materials and at free surfaces. They play an important role in the mechanical and functional properties of many systems. Baram et al. (p. 206; see the Perspective by Harmer) studied the interfaces between gold droplets and a sapphire surface with a partial coating of anorthite glass beads. The anorthite formed the basis of a nanometer-thick intergranular film, which caused a decrease in the gold-sapphire interfacial energy. Unlike other artificially made conventional thin films, these films did not break up during equilibration, which may provide a useful design criterion in thin-film technology.

            1. Probing Suspensions

                Catalysis often takes place in complicated biphasic environments, with molecules in pressurized gas or liquid phase briefly contacting catalyst surfaces and then emerging chemically transformed from the interface. In contrast, studies of catalyst-substrate binding interactions are often restricted to simpler conditions, such as bare catalyst surfaces under near vacuum. Tedsree et al. (p. 224) now show that nuclear magnetic resonance spectroscopy can reveal signatures of binding under realistic conditions—aqueous suspensions of noble metal nanoparticles—that strongly correlate with catalytic activity.

              1. Minor Spliceosome Gains Stature

                  For nearly two decades after the discovery that eukaryotic messenger RNA precursors contain noncoding sequence interruptions called introns, it was assumed that all introns and all spliceosomes (the cellular machinery that excises introns) were alike. Then rare, outlier introns were identified that violated certain sequence rules and were excised by special spliceosomes. Because these so-called “minor” introns account for less than 1% of introns in human cells, their impact on biology has been unclear (see the Perspective by Pessa and Frilander). Now, He et al. (p. 238) and Edery et al. (p. 240) report that mutational disruption of an RNA component specific to the minor spliceosome (U4atac snRNA) causes severe developmental defects in humans. Individuals with homozygous mutations in this RNA are afflicted with a rare inherited disorder called microcephalic osteodysplastic primordial dwarfism type I (MOPD I) or Taybi-Linder syndrome (TALS) and die in the first few years of life.

                1. Eosinophils and Metabolism

                    Alterations in macrophage activation in adipose tissue are associated with metabolic disease. In lean mice and humans, macrophages with an immunoregulatory phenotype (termed alternatively activated macrophages, or AAMs) predominate, whereas AAM numbers decrease and the numbers of proinflammatory macrophages increase when metabolic control is lost. Wu et al. (p. 243, published online 24 March; see the Perspective by Maizels and Allen) now show that eosinophils, an immune cell type classically associated with parasitic infections and allergy, regulate the number of AAMs present in adipose tissue in mice. Eosinophils were detected in adipose tissue where they produced interleukin-4, a cytokine that promotes the AAM phenotype. Eosinophil deficiency in mice was associated with a decrease in AAMs in adipose tissue and increased body fat and blood glucose levels in mice fed a high-fat diet. In contrast, genetic or parasite-induced increases in eosinophil numbers resulted in improved metabolic read-outs in mice fed a high-fat diet.

                  1. Orienting Organic Networks on Graphene

                      Covalent organic frameworks (COFs), like metal organic frameworks, have organic linking groups, but the structure-directing groups in COFs are typically fused aromatic rings rather than metal atoms. Although COF materials are robust, they tend to form as insoluble powders that are difficult to process into films. Colson et al. (p. 228) show that a COF, COF-5, formed from 4-phenylenebis(boronic acid) and 2,3,6,7,10,11-hexahydroxytriphenylene under mild solvothermic conditions, produced crystalline films on different types of single-layer graphene. The layers were vertically aligned, an orientation that may prove useful in organic photovoltaic applications.

                    1. Dynamic Chemistry

                        CREDIT: BHABHA ET AL.

                        Conformational fluctuations can mediate ligand binding and be rate-limiting for enzyme turnover. However, the role of active-site dynamics is debated. Bhabha et al. (p. 234) generated a mutant of Escherichia coli dihydrofolate reductase with significantly impaired hydride transfer but with no significant changes in the structure or electrostatic environment of the active site. Millisecond time-scale fluctuations were abrogated in the active site of the mutant, suggesting that the active site could not sample the higher-energy conformations conducive to transition-state formation efficiently and thus failed to promote the chemical reaction.

                      1. The Real World Is Messy

                          A common theme in recent social psychology research studies is the testing of laboratory-derived theories and mechanisms in so-called ecologically valid settings (that is, in field experiments). Stapel and Lindenberg (p. 251) show that environmental signs of disorder, such as uncollected trash at a train station or cars parked askew on a sidewalk, are sufficient to induce bystanders to desire orderliness. The consequences are that these bystanders elected to sit further from minorities when asked to fill in a survey and donated less of their payments (for participating in the survey) to help immigrants and the homeless. Laboratory-based experiments suggested that the desire for order was fulfilled by an increased propensity toward classification, which includes stereotyping.

                        1. Invasion of the Body Snatchers

                            The whitefly, Bemisia tabaci, ranks in the world's top 15 worst-invasive alien species. Like many other insects, it plays host to several bacteria that affect its physiology in various ways, including enhancing availability of nutrients, viral resistance, and changing sex ratios. The bacterium Rickettsia bellii was first observed in 2000 in a few whitefly specimens collected from the southwestern United States, but in fewer than 80 generations (in just 6 years) it achieved 97% infection rates. Himler et al. (p. 254; see the Perspective by Jiggins and Hurst) found that almost all daughter insects are infected if their mothers are infected and that there is little male-to-female transmission. But, as might be surmised from their spread, infection is not a bad thing for the insects—infected whiteflies double their fecundity, develop faster into adults, and produce more females.

                          1. A Parasite of My Parasite Is My Friend

                              Virophages are parasites of viruses, which in turn parasitize other organisms. Fischer and Suttle (p. 231, published online 3 March) identified Mavirus, a virophage parasite of the giant Cafeteria roenbergensis virus (CroV), that infects a widespread marine zooplankton. Mavirus interfered with the replication of CroV, and, in the process, rescued the zooplankton host from death. The closest genetic relatives of Mavirus are Maverick/Polinton DNA transposons with the Mavirus genome containing homologs of several genes found only in these transposons, which suggests that these transposons originated from an ancient virophage that had integrated into the genome of a eukaryote.

                            1. Energy Requirements for Neuronal Polarization

                                Neuronal polarization lies at the heart of neuronal development, synaptic wiring, and interneuronal communication. Although much progress has been made in understanding axon growth and path finding, the mechanisms that regulate axonal neurite selection and polarity initiation remain poorly understood. Rapid axon growth requires a large quantity of building material and efficient intracellular transport. Coordination between axon initiation and cellular energy homeostasis may thus be important during the early stage of neuronal polarization. Using cultured hippocampal neurons and embryonic brain slices, Amato et al. (p. 247, published online 24 March) investigated the role of adenosine monophosphate–activated protein kinase (AMPK), which is involved in the sensing and regulation of bioenergy homeostasis, in neuronal polarization. Up-regulation of AMPK activity reduced the proportion of neurons possessing a typical axon. The ability of AMPK to inhibit polarization was restricted to early stages of polarization—AMPK activation after axon initiation did not affect polarization or axon growth.