This Week in Science

Science  24 Jan 2014:
Vol. 343, Issue 6169, pp. 350
  1. A View from the Middle

    The intuitive way to study a bimolecular reaction is to induce a collision between separate reagents and then track the ensuing events. Crossed molecular beam studies have revealed the quantum mechanical details of numerous systems in this fashion. Otto et al. (p. 396, published online 9 January) applied a more recent approach of starting in the middle of the F + H2O → HF + OH reaction trajectory, postcollision, by photodetaching an electron from a stabilized complex of water and a fluoride ion, and then tracking the fate of the neutral fragments.

  2. Copper-Oxide Superconductors

    CREDIT: DA SILVA NETO ET AL.

    Copper-oxide superconductors have a complex electronic structure. A charge density order has been observed in two cuprate families; however, it has been unclear whether such an order exists in Bi-based compounds (see the Perspective by Morr). Comin et al. (p. 390, published online 19 December) and da Silva Neto et al. (p. 393, published online 19 December) address this question in single-layer and double-layer Bibased cuprates, respectively. For both families of materials, surface measurements by scanning tunneling spectroscopy agree with bulk measurements obtained through resonant elastic x-ray scattering, which suggests the formation of short-range correlations that modulate the charge density of the carriers over a range of dopings. Thus, charge ordering may represent a common characteristic of the major cuprate families.

  3. Noise in Motion

    A large earthquake along the southern San Andreas Fault has the potential to cause serious damage to the city of Los Angeles, USA. Earthquake simulations in this region, which lies in a sedimentary basin capable of amplifying shaking, predict strong ground motion but they lack validation with observational data. Denolle et al. (p. 399) developed an independent method to predict ground motion using virtual earthquakes and information gleaned from background seismic noise. This ambient seismic field—generated by sources such as the oceans and atmosphere—produces differences in ground motion in the Los Angeles Basin compared to simulations, but suggests that locally shaking could on average be 3 times larger than the surrounding areas.

  4. Observing the Messenger

    In order to elucidate the dynamics of individual components in the cell, single-molecule technologies are being developed (see the Perspective by Akbalik and Schuman). Park et al. (p. 422) used a mouse expressing fluorescent β-actin messenger RNAs (mRNAs) to visualize mRNA movements in living cells and tissues. Buxbaum et al. (p. 419) showed that neurons contain β-actin mRNAs and ribosomes packaged in a dense structure, impenetrable by oligonucleotide probes. This effectively masks the mRNAs until neuronal stimulation exposes the mRNA and ribosomes briefly, presumably reflecting the local stimulation and translation involved, for example, in the generation of memories.

  5. Sensing HIV

    The depletion of quiescent CD4+ T cells from lymphoid organs is a major event contributing to the development of AIDS. The accumulation of incomplete HIV DNA transcripts in the cytoplasm of these cells, which do not themselves become productively infected, is somehow sensed, which triggers cell death. Monroe et al. (p. 428, published online 19 December; see the Perspective by Gaiha and Brass) now identify the host DNA sensor as interferon-γ–inducible protein 16, which senses viral DNA and activates pyroptosis, an inflammatory cell death pathway.

  6. Dust in the Sea

    The effect of windblown dust on marine productivity in the Southern Ocean is thought to be a key determinant of atmospheric CO2 concentrations. Lamy et al. (p. 403) present a record of dust supply to the Pacific sector of the Southern Ocean for the past one million years, derived from a suite of deep-sea sediment cores. Dust deposition during glacial periods was 3 times greater than during interglacials, and its major source region was probably Australia or New Zealand.

  7. Breaking Tumor Dogma

    Canine transmissible venereal tumor (CTVT) is an unusual form of cancer because the infectious agent is not a virus or bacterium but the tumor cells themselves, which are passed from one dog to another during coitus. To explore the molecular features of the tumor and its possible origins, Murchison et al. (p. 437; see the Perspective by Parker and Ostrander) sequenced the genomes of two CTVTs and their host dogs, one from Australia and one from Brazil. Although CTVT has acquired a massive number of genomic alterations, including hundreds of times more somatic mutations than are normally found in human cancers, the tumor cell genome has remained diploid and stable. Indeed, CTVT may first have arisen in a dog that lived more than 10,000 years ago.

  8. Living Technicolor

    CREDIT: ROY CALDWELL/UNIVERSITY OF CALIFORNIA, BERKELEY

    Color vision is generally carried out through the number of photoreceptor types found in the retina. The mantis shrimps (stomatopods) can have up to 12 photoreceptors, far more than needed for even extreme color acuity. Thoen et al. (p. 411; see the Perspective by Land and Osorio) conducted paired color discrimination tests with stomatopods and found that their ability to discriminate among colors was surprisingly low. Instead, stomatopods appear to use a color identification approach that results from a temporal scan of an object across the 12 photoreceptor sensitivities. This entirely unique form of vision would allow for extremely rapid color recognition without the need to discriminate between wavelengths within a spectrum.

  9. The Present of the Past

    A major goal of evolutionary biology is to understand the process of speciation and the changes that have accompanied and shaped the current distribution of species. Paleogenomics directly addresses these questions through the use of ancient DNA. Shapiro and Hofreiter (10.1126/science.1236573) review the origins and growth of this field and explain how challenges owing to the limited amount of DNA available for analysis and the possibility of contamination by modern material have been overcome.

  10. A Peptide Finds Its Receptor

    CREDIT: MIYOSHI HARUTA

    Because plant cells cannot move around within the plant, developmental changes are orchestrated by changes in cell size and shape. Using quantitative phosphoproteomics, genetics, and chemical analyses, Haruta et al. (p. 408) identified a signaling chain that links a secreted peptide, RALF (rapid alkalinization factor), with its receptor kinase, FERONIA, at the cell surface. FERONIA is involved in reproductive and vegetative development–processes that require the changes in cell size initiated by RALF signaling.

  11. It's Complicated

    Animals have evolved impressive displays used in mate selection. Although intended for the opposite sex of the same species, the potential for eavesdropping is significant. In cases where the sensory signature is the sexual signal itself (such as a bird call), selection from harmful eavesdroppers could result in a reduction in signal intensity that represents a balance between the cost and benefit of the signal. Halfwerk et al. (p. 413), however, show that the physical by-product of a signal can also act as a cue to both intended and eavesdropping recipients. Ripples in the water made by throat sac expansion in calling túngara frogs signal their presence both to rivals and to predatory bats. This physical signature of the call itself cannot be modified; thus, it represents a cost-benefit ratio to calling that cannot be shifted through selection pressure from either side. Thus, physical by-products of sensory signaling create significant complexity in the evolution of sexual signaling.

  12. Vascular Endothelium and Tissue Regeneration

    The vascular endothelium is increasingly being recognized to play a role during organogenesis and tissue regeneration. Hu et al. (p. 416) found that rapid down-regulation of endothelial-derived Angiopoietin-2 following partial hepatectomy releases an endogenous transforming growth factor β1–driven paracrine proliferative brake on hepatocytes. Later, recovery of endothelial Angiopoetin-2 expression facilitates angiogenesis in the regenerating liver in a vascular endothelial growth factor receptor 2–dependent manner. Thus, the vascular endothelium may help to orchestrate tissue regeneration through the control of inhibitory and stimulatory pathways in parenchymal and nonparenchymal cells.

  13. Sourcing CO and Cyanide

    Hydrogenase enzymes derive their activity in part from the coordination of CO and cyanide ligands to metals in their active sites. Recent work elucidated the jettisoning of a tyrosine side chain at the outset of the biosynthetic pathway toward these ligands in the di-iron class of hydrogenase. Kuchenreuther et al. (p. 424; see the Perspective by Pickett) now apply stopped-flow infrared spectroscopy to uncover the next portion of the pathway, during which the residual tyrosine fragment is further broken down into CO and CN ligands at a single iron center in an iron sulfur cluster associated with the HydG enzyme.

  14. An Immune Response to Malnutrition

    Mucosal surfaces, such as those lining the intestine, are in constant contact with potentially pathogenic microbes, including bacteria and parasitic worms. This necessitates so-called barrier immunity, which is mediated in part by innate lymphoid cells, subsets of which combat specific types of infection. Although malnutrition has been associated with immunosuppression, Spencer et al. (p. 432) now show that vitamin A deficiency selectively activates one branch of barrier immunity. Vitamin A deficiency in mice enhanced immunity to chronic worm infections by increasing the levels of one subset of innate lymphoid cells lacking the corresponding retinoic acid receptor. In contrast, another innate lymphoid cell subset that carries the vitamin A receptor and is important for bacterial immunity was depleted. Thus, the immune system can adapt its response to dietary stress, thereby promoting host survival.

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