This Week in Science

Science  13 Dec 2013:
Vol. 342, Issue 6164, pp. 1289
  1. We Are Stardust


    Most of the universe's chemical elements were produced in stars, with the heaviest elements being produced when stars explode. Barlow et al. (p. 1343) used the Herschel Space Observatory to obtain submillimeter spectra of the Crab Nebula, the remains of a stellar explosion that was witnessed on Earth in 1054 AD, and detected the first evidence of a noble gas-containing molecular ion in space—36ArH+. Koo et al. (p. 1346) obtained near-infrared spectroscopic observations of the remains of another stellar explosion, Cassiopeia A, with the Palomar 5-m Hale telescope, and found evidence that a substantial amount of phosphorus was formed in the explosion. Among the six elements essential for life (hydrogen, carbon, nitrogen, oxygen, phosphorus, and sulfur), only the origin of phosphorus remained to be confirmed by observation.

  2. Confusing Colloids in Liquid Crystals

    In a simple fluid, particle diffusion such as the motion of colloidal particles shows a change in the mean squared displacement that is proportional with time. Within a nematic liquid crystal, diffusion of the molecules may show anisotropic behavior. Turiv et al. (p. 1351; see the Perspective by Abbott) asked what happens to colloidal particles in a nematic liquid crystal. At short times, anomalous diffusion was observed with motion both slower and faster than the long-term behavior, indicative of a complex coupling between the diffusive motion of the colloidal particles and the motion of the liquid crystal molecules.

  3. Up and Down

    Climate change is expected to have significant impacts on Earth's hydrological cycle, owing to changes, for example, in air temperature, weather patterns, and land surface evaporation. In the Pacific Northwest of the United States, decreases in stream flow have been attributed to increased temperatures. Luce et al. (p. 1360, published online 29 November) show that these changes in stream flow are not likely to have been caused by temperature change, however, but rather by decreasing precipitation in the mountains where the streams originate.

  4. The Fit Get Fitter

    Advances in modern biology have allowed us to measure evolutionary fitness and estimate the rate of fixation of beneficial mutations. Drawing on the Long-Term Evolution Experiment, studying the evolution of Escherichia coli in a constant environment, Wiser et al. (p. 1364, published online 14 November) demonstrate that even after 50,000 generations over 20 years, gains in fitness show no evidence of leveling off. Instead, fitness is following a power-law relationship that is dependent on epistasis and clonal interference.

  5. Eye to Eyeless

    To what extent does adaptation rely on de novo mutation, as opposed to preexisting variation? It has been proposed that heat shock protein 90 (HSP90) can act to maintain cryptic variation by correcting misfolded proteins, until the system is taxed under stress conditions. Focusing on the cavefish Astyanax mexicanus, Rohner et al. (p. 1372) provide evidence that this mechanism contributed to morphological evolution in a natural setting where cryptic variation in eye size was masked by HSP90 in the ancestral river but revealed when the fish were reared and selected in caves.

  6. Fear Factor

    It has generally been assumed that the most basic aspects of peripheral sensory processing do not change even if they are paired with reward or punishment. A smell should still smell the same, a color should still look the same, and any changes observed would be likely to occur downstream of the primary sensory processing areas. However, using longitudinal in vivo neurophysiology in transgenic mice, Kass et al. (p. 1389) observed that neurotransmitter release from olfactory sensory neurons themselves was selectively enhanced for threat-predictive odors after fear conditioning.

  7. Nondestructive Photon Detection

    The click of a photon detector is the usual method for detecting a photon and can be sufficiently sensitive to detect even a single photon. Such a detection process is, however, destructive—the photon is annihilated. Reiserer et al. (p. 1349, published online 14 November) describe an experimental system capable of detecting a single photon without destroying it.

  8. Blood Fluke Resistance


    The larval stages of the blood fluke Schistosoma mansoni are disseminated via a replicative cycle in freshwater snails. When people come into contact with contaminated water, the larvae attach to and penetrate the skin. The resulting disease, bilharzia or schistosomiasis, afflicts approximately 67 million people in Africa and South America. Unfortunately, the parasite is showing resistance to one of the available therapeutic drugs, oxamniquine, which means that schistosome control relies on a single drug, praziquantel. Valentim et al. (p. 1385, published online 21 November) analyzed the genetic and molecular basis of resistance to oxamniquine through a combination of genetic linkage mapping, genome sequencing, functional genomics analysis, and x-ray crystallography.

  9. Limb Regeneration Mirrors Development

    Salamanders regenerate the right amount of limb after cutting anywhere along its length. A long-discussed explanation suggests that the regenerating tissue first sets the fingertips as a boundary and then regenerates everything in between. However, Roensch et al. (p. 1375) report that the limb regenerates in the opposite order. Similar to the processes followed during development, the regenerating salamander limb first establishes a field of cells with the identity of the cut site, and then cells progressively commit to alternate fates as they grow closer to the tip of the regenerated limb.

  10. The Base of the Animal Tree?


    The identity of the most basal lineages of the animal kingdom evolutionary tree has long been contested. Ryan et al. (p. 10.1126/science.1242592; see the Perspective by Rokas) sequenced the genome of the ctenophore the warty comb jelly or sea walnut, Mnemiopsis leidyi, and conclude that ctenophores alone, not sponges or the clade consisting of both ctenophores and cnidarians, are the most basal extant animals. The results suggest a specific evolutionary process that likely occurred—including repeated gains and loss of mesoderm, expansion of genes associated with the cell cycle, growth signaling, apoptosis, and epithelial and neural cell types. Furthermore, previous hypotheses regarding the evolution of animals may require re-evaluation.

  11. Predicting Disease Dissemination

    In combating the global spread of an emerging infectious disease, answers must be obtained to three crucial questions: Where did the disease emerge? Where will it go next? When will it arrive? Brockmann and Helbing (p. 1337; see the Perspective by McLean) analyzed disease spread via the “effective distance” rather than geographical distance, wherein two locations that are connected by a strong link are effectively close. The approach was successfully applied to predict disease arrival times or disease source using data from the the 2003 SARS viral epidemic, 2009 H1N1 influenza pandemic, and the 2011 foodborne enterohaemorrhagic Escherichia coli outbreak in Germany.

  12. A Glimpse of HOON

    Bonds between two oxygen atoms are relatively weak, as manifested in the sometimes explosive reactivity of O2 and various peroxides. Thus, although nitrous acid (HONO) can be rearranged on paper to an isomer with an O-O rather than N-O bond, nitrosyl-O-hydroxide (HOON) has been considered too unstable to be observed. Crabtree et al. (p. 1354) used microwave spectroscopy to detect HOON formation in a dilute gaseous mixture of NO and OH in neon. Isotopic substitutions enabled determination of its structure, which included an unusually long O-O bond.

  13. EPO via Total Synthesis

    Erythropoietin (EPO) is a hormone involved in the production of red blood cells. Synthetic EPO produced via genetically engineered cell cultures is used to treat anemia and—more controversially—to boost athletic performance. EPO is a glycoprotein, and though its protein component is well-defined, both natural and synthetic EPO exhibit a wide range of attached oligosaccharides. Wang et al. (p. 1357; see the Perspective by Hsieh-Wilson and Griffin) prepared an EPO sample by a chemical synthesis that maintains a uniform pattern of attached sugars throughout, which may prove helpful in the analysis of how variation in the sugar components of EPO impact function.

  14. Transcription Factor Binding Sites

    Transcription factors (TFs) are proteins that bind to DNA to control gene transcription. Stergachis et al. (p. 1367; see the Perspective by Weatheritt and Babu) examined TF binding within the human genome in more than 80 cell types. Nearly 15% of coding regions simultaneously specify both amino acid sequence and TF recognition sites. The distribution of the TF binding sites evolutionarily constrains how codons within these regions can change, independent of encoded protein function. Thus, TF binding may represent a widespread and strong evolutionary force in coding regions.

  15. EMRE Emerges

    Concentrations of calcium within mitochondria are tightly regulated and modulate physiological mitochondrial functions, including control of metabolism and cell death. Sancak et al. (p. 1379, published online 14 November) complete the molecular characterization of the mitochondrial calcium uniporter (MCU), the multicomponent channel that allows concentration of calcium within the organelle. They identified a small protein termed “essential MCU regulator”—or EMRE—which was required for calcium transport activity of the fully assembled uniporter.

  16. Making CO2 Work for You

    Converting carbon dioxide (CO2) to formic acid (HCOOH) is an attractive substrate for the storage and recovery of hydrogen (H2) for use as fuel. Because CO2 is relatively stable, however, its hydrogenation typically requires extreme conditions. Schuchmann and Müller (p. 1382: see the Perspective by Pereira) isolated a hydrogen-dependent carbon dioxide reductase from Acetobacterium woodii that is nearly 2000-fold more effective than the fastest known chemical catalysts. The process, which relies on the formation of formate as a chemical intermediate, also works well in whole-cell systems of A. woodii when certain metabolic pathways are inhibited. The enzyme, whether isolated or present in host bacteria, may lead to the design of more efficient fuel cells capable of functioning under less harsh conditions than fuel cells based on chemical reactions alone.